Assessing Lateral Stability of the Hip and Pelvis

Alison Grimaldi, PhD1

Adequate function of the hip abductor mechanism has been shown to be integral to ideal lower limb function and musculoskeletal health. Clinical assessment of hip abductor muscle function may include observational assessment of postural habits, muscle bulk, and of the ability to control optimal frontal plane femoropelvic alignment during a variety of single leg tasks. Strength testing using a hand held dynamometer is perhaps our most robust clinical assessment tool but should not be considered a ‘gold standard’ in the assessment of abductor muscle function. Evidence from magnetic resonance imaging (MRI), and electromyography (EMG) studies provides a deeper understanding of specific deficits that occur within the abductor synergy. The assessment of abductor function should not be based on a single test, but a battery of tests. The findings should be interpreted together rather than independently, and in the context of a thorough understanding of function of the lateral stability mechanism. Manner and comprehensiveness of abductor assessment will have important implications for management and particularly therapeutic exercise. Read more

Can local muscles augment stability in the hip? A narrative literature review

This paper was published in
Journal of Musculoskeletal and Neuronal Interactions 2013; 13(1):1-12

T.H. Retchford1,2, K.M. Crossley3, A. Grimaldi4, J.L. Kemp3, S.M. Cowan1

1Melbourne Physiotherapy School, University of Melbourne, Melbourne, Victoria, Australia; 2School of Community Health, Charles Sturt University, Albury, New South Wales, Australia; 3Division of Physiotherapy, School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Australia; 4Physiotec Physiotherapy, Brisbane, Queensland, Australia

ABSTRACT

Hip pain and dysfunction are increasingly recognised as important causes of morbidity in younger and older adults. Pathology compromising the passive stability of the hip joint, including acetabular labral injury, may lead to increased femoral head translation, greater joint contact pressures and ultimately degenerative hip disease. Activation of hip muscles may play an important role in augmenting the stability in the normal and the passively unstable hip. Research at other joints suggests that the local, rather than global, muscles are well suited to provide subtle joint compression, limiting translation, with minimal metabolic cost. Based on the known characteristics of local muscles and the limited research available on hip muscles, it is proposed that the local hip muscles; quadratus femoris, gluteus minimus, gemelli, obturator internus and externus, iliocapsularis and the deep fibres of iliopsoas, may be primary stabilisers of the hip joint. Interventions aimed at restoring isolated neuromuscular function of the primary hip stabilisers may be considered when treating people with passive hip instability prior to commencing global muscle rehabilitation. Finally, further research is needed to investigate the potential association between function of the hip muscles (including muscles likely to have a role in stabilising the hip) and hip pathology affecting hip stability such as acetabular labral lesions.

Keywords: Hip Joint, Hip Instability, Hip Muscle Control, Deep Hip External Rotator Muscles, Rehabilitation

INTRODUCTION

Our understanding of hip pathology, particularly degenerative hip pathology, is increasing1. There is growing evidence that pathology affecting the hip joint’s passive stability, such as acetabular labral tears, can progress to degenerative hip pathology2-5. Improving the active control of hip muscles in people with hip pathology and compromised joint stability may be the key to optimising joint loads and function, alleviating pain, and potentially even slowing the progression of hip disease.

Joint stability refers to the resistance that musculoskeletal tissues provide at a joint and is the product of contributions from passive, active and neural subsystems. Joint instability may result from a deficit of one or more of these subsystems and lead to excessive joint translation and subsequent joint overload if the other subsystems cannot compensate6-11. Hip joint instability was previously thought to be rare and usually associated with trauma12-14, or developmental bony abnormalities such as acetabular dysplasia. Whilst the hip joint is considered to be stable due to its bony architecture and strong capsuloligametous restraints, evidence suggests that deficits in the acetabular labrum and iliofemoral ligaments may lead to increased femoral head translation16-18 and possibly to early degenerative hip pathology3. Although surgical techniques can be used to help improve symptoms and joint function19, there is currently little evidence that surgery in people with hip joint instability alters the progression to degenerative hip disease.

Capsuloligamentous laxity may be generalised or focal. Generalised laxity is associated with connective tissue disorders whilst focal laxity may result from an acute injury or from repetitive weight bearing rotational forces overloading specific parts of the capusuloligamentous system. Sporting activities involving repeated axial loading and rotation, such as gymnastics, football, tennis, ballet, martial arts, and golf may influence the development of focal laxity. Active stability of the hip joint from tension in hip muscles may augment passive stability in the normal and structurally abnormal hip10. Despite this likely important role, little is known about what muscle or muscle synergies are involved or if hip pathology has an influence on hip muscle function.

It is theorised that in the human body two muscular systems exist; local and global8. Local muscles are thought to be important in joint stability by acting close to the joint axis, thereby providing predominantly joint compression rather than torque, and having the ability to stiffen the joint by virtue of their extensive attachments to key passive elements of the joint. In contrast, global muscles are more superficial muscles that can generate greater torque at joints as a result of their larger physiological cross sectional area (PCSA) and greater moment arm. There is considerable research investigating muscle function and pathological muscle dysfunction at the lumbar spine, cervical spine38, knee and pelvis41. This research has identified local muscle dysfunction in people with pain and pathology and that specific muscular retraining can restore muscle function at these joints. Currently, there is a paucity of literature investigating individual hip muscle function, or the association between hip pathology and dysfunction of the active hip stabilisers. Furthermore, with the exception of one study42, all research investigating links between hip pathology and muscle function has studied older populations suffering from osteoarthritis (OA) of the hip43-47.

A greater understanding of the relationship between hip muscle function and hip joint stability may enhance the specificity of exercise therapy interventions with potential to improve treatment outcomes. Therefore the aim of this study was to review the available literature relating to the role the hip muscles may play in the active stability of the hip.

Methodology

Literature examining hip musculature and active stability and the possible association between hip pathology and muscle dysfunction was retrieved. In addition, literature pertaining to neuromuscular function at other joints was also retrieved to provide a broad understanding of the relationship with joint pathology. The literature search was conducted in MEDLINE (PubMed) using search terms hip, joint, muscle, joint protection, stability, instability, quadratus femoris, gluteus medius, gemelli, obturator externus, obturator internus, piriformis, gluteus medius, gluteus maximus, pectineus, adductors, hamstrings, hip rotator cuff, lumbar spine, shoulder, knee, cervical spine, feed-forward mechanism, postural adjustments, motor control, muscle control, Real Time Ultrasound (RTUS), electromyography (EMG), Computer tomography (CT) and Magnetic Resonance Imaging (MRI). The reference lists of the articles were then hand searched to retrieve articles that were not identified with the computer search.

Contributors to passive hip stability and instability

The hip comprises a multiaxial ball and socket joint with six degrees of freedom48, and is important in load transference during functional activities involving both the lower and upper limbs4. During weight bearing activities (e.g. running), the hip is subjected to loads many times greater than body weight49. To maintain passive stability, the hip relies on ideal bony structure, normally formed labrum and intact and ideal capsuloligamentous support. Based on modelling studies, deficits in these passive structures may lead to increased femoral head translation, or shearing forces16-18. It is proposed that increased shearing force of the hip joint may be associated with pathology of passive soft tissue joint restraints and subsequent pathology of joint cartilage (Figure 3).

Bony structure

The hip joint is formed by the articulation between the femoral head and the acetabulum14. The acetabulum is formed by the union of the ischium, ilium, and pubis. Only the periphery of the acetabulum articulates with the femoral head48. Although the hip joint is considered congruent, the large femoral head has considerably more articular area compared to the acetabulum. As a result, during stance, parts of the anterior and superior articular cartilage of the femoral head remain exposed48. This allows for greater mobility into hip flexion but also increases the reliance on anterior soft tissues for stability13.

Bony abnormalities resulting in reduced congruence between the femoral head and acetabulum (e.g. Developmental dysplasia of the hip (DDH)) may lead to passive hip instability and increased reliance on surrounding soft tissue structures, particularly the anterior capsulolabral structures. Over time this increased stress may lead to fatigue failure of the acetabular labrum and subsequent chondropathy. Although this theory has not been directly studied, there is evidence suggesting increased severity53 and high frequencies of labral lesions with DDH and a strong association between DDH and the development of early OA.

Other bony abnormalities such as those seen in FAI (Femoro-Acetabular Impingement – abnormal morphology of the acetabulum, femoral head or neck), have been shown to be associated with an increased risk of acetabular labral pathology and hip OA59. This in itself may result in the development of hip instability50. In addition, a link between posterior hip instability and FAI has recently been made, the authors proposing that as the hip reaches end range prematurely in flexion and internal rotation, the femoral head is levered against the posterior joint structures, and may result in subluxation with only low velocity force62.

Capsule and ligaments

The hip capsule attaches to the periphery of the acetabulum and acetabular labrum and extends down to the femoral neck48 (Figure 1). Its fibres are aligned in a circumferential manner and are considered to provide significant passive stability to the hip joint. The capsule is further reinforced by strong extra-capsular ligaments; the iliofemoral, pubofemoral and ishiofemoral ligaments. In addition to the extra-capsular ligaments, passive hip stability may also be augmented by the intra-articular ligamentum teres. The ligamentum teres is taut in external rotation of the hip and may undergo compensatory hypertrophy in passively unstable dysplastic or labral deficient hips. In addition ligamentum teres contains free nerve endings64 and attaches to the transverse acetabular ligament and thus the acetabular labrum63, suggesting a proprioceptive role.

Capsuloligamentous laxity may be generalised or focal. Generalised laxity is associated with hypermobility syndromes and often has an underlying connective tissue disorder. It is speculated that focal laxity may arise from acute high-force trauma or repetitive overload of specific areas of the capsuloligamentous complex. People who compete in sports that require repetitive weight bearing combined with hip rotation towards, or at, the limit of normal physiological movement, such as golf, tennis and football, are reported to be more likely than inactive people to develop laxity in the capsuloligamentous system of the hip, particularly in the iliofemoral ligament. In addition, evidence of focal ligamentous instability when passive instability exists is provided by a cadaveric study of fifteen male hips. The authors noted a significant increase in hip external rotation and femoral head translation after sectioning the iliofemoral ligament, suggesting the ligament may have a significant stabilising role in the hip17. Furthermore, the proposed relationship between capsuloligamentous laxity, generalised or focal, capsular redundancy and labral lesions, particularly in active people has been highlighted in a number of review papers.

Acetabular Labrum

The acetabular labrum is a fibrocartilagenous extension to the rim of the acetabulum (Figure 2). While its function is not fully understood, it is considered important in improving joint congruity (increasing joint contact area by 25-28%), helping contain the femoral head in extremes of range and enhancing joint proprioception. In addition, the acetabular labrum and the inferiorly placed transverse acetabular ligament are thought to have an important role acting as a seal, limiting fluid movement in and out of the intra-articular space67. This sealing mechanism could potentially help hydraulically distribute load evenly across the articular surfaces of the hip, thereby reducing direct hyaline cartilage contact. This sealing mechanism may also help maintain a partial vacuum in the joint, further contributing to passive stability48. Biomechanical modelling studies suggest that in hip flexion, atmospheric pressure plays a greater joint stability role than the capsuloligamentous structures68.

Disruption of the acetabular labrum is thought to “break the seal” of the hip joint and lead to increased femoral head translation16-18, greater contact pressure of the femoral head against the acetabulum, and subsequent pathology of joint cartilage3. However, due to the difficulties associated with measuring intra-articular pressure in vivo, this theory has not been proven. Key risk factors for labral pathology are capsuloligamentous laxity and bony abnormalities, particularly DDH and FAI. Based on review papers, it is proposed that hip joint laxity can compromise the ability of the labrum to provide adequate joint protection and may allow excessive femoral head translation, potentially leading to abnormal labral loading and subsequent pathology51. The link between bony abnormalities and labral pathology has been previously discussed.

Overview of muscle function, joint function and pathology

Studies on muscle function, joint function and pathology have primarily focussed on the lumbar spine, pelvis, knee and cervical spine. To date little is known of the role of the muscles acting at the hip joint and even less is known of their association with hip pathology. Knowledge of muscle function at other joints, and its association with pain or pathology may help inform understanding of hip stability and appropriate rehabilitative strategies.

Panjabi6 proposed a model of joint stability for the lumbar spine involving the coordinated interaction between the passive, neural and active subsystems. He suggested that joint instability could occur with deficits in one or more of these subsystems, resulting in excessive motion and overload to joint structures if the other subsystems cannot compensate9. Particular muscles which form part of the active subsystem are biomechanically and physiologically well placed to provide joint protection with limited metabolic cost72. Although controversy exists, the weight of evidence suggests that local muscles rather than global muscles are preferentially suited to joint protection at the lumbar37 and cervical spines73, shoulder joint74 and pelvis36. The properties of these local muscles are discussed below.

Local muscles, such as lumbar and cervical multifidus, are predominantly composed of Type I slow twitch muscle fibres making them fatigue resistant and well suited to tonic muscle contraction; thus being ideal for postural control75-77. Fibre type gradients exist with type I fibres typically occupying deep and type II occupying more superficial regions. In vivo studies have demonstrated differential activity of deep and superficial fibres of lumbar multifidus in response to functional movement and provided evidence that deep fibres have a significant stabilising role, possibly through exertion of compressive forces with minimal associated torque, whilst superficial fibres contribute primarily to joint orientation72. Moseley et al.72 theorised that the deeper fibres are anatomically and biomechanically more suited to metabolically efficient stability by virtue of their proximity to the joint’s centre of rotation whilst more superficial fibres, owing to their larger CSA and moment arms, have greater torque generating capacity. At the shoulder, the rotator cuff muscles are thought to be ideally aligned to provide a net compressive force on the glenohumeral joint irrespective of shoulder position79, whilst the transverses abdominis, owing to its transversely oriented muscle fibres, is reported to significantly increase joint compression in the sacroiliac joints36.

It is rare that individual muscles act in isolation. In most instances muscle synergies exist23. Co-contraction of muscle groups, particularly agonists and antagonists, is thought to enhance joint stiffness80. Local muscle synergies have been described at the lumbar spine35, cervical spine73 and shoulder joint74. Contractions of the local muscles are considered a feed-forward strategy by the nervous system, preparing, and thus stabilizing and protecting the joint or joints for the perturbation caused by limb movement. This hypothesis is formed on the basis that these postural adjustments occur before feedback is available81 and in advance of a limb movement40.

Induced pain studies in the lumbar spine30, and cross-sectional studies of the sacroiliac joint41, the cervical spine38, and knee joint39suggest that pain alters normal feed-forward postural adjustments. Pain can also cause selective and rapid atrophy of the local muscles in the lumbar spine in response to lower back pain (LBP)27 and experimental disc or nerve root injury29. The underlying mechanism is unclear. The rapid onset may be more suggestive of pain inhibition rather than disuse atrophy27. Global muscles are also affected by joint pain, with evidence of increased activation, which may be a compensation for local muscle dysfunction.

Studies have shown that exercise therapy targeted specifically at the local stabilising muscles can improve function, reduce pain, restore the normal feed-forward response and reduce recurrence of pain in the knee40, cervical spine84, and the lumbar spine24,81,85,86 in symptomatic individuals. Specific isolated local muscle retraining is suggested to be more effective in stabilising joints than global muscle bracing36, and may lead to immediate alterations in feed-forward postural adjustments in symptomatic people81. Interventions targeting isolated tonic activation of the local muscles were found to be associated with earlier feed-forward postural activations, whereas non-specific training involving contraction of local and global muscles resulted in delayed local muscle activation. Once selective local muscle function has been restored, the use of exercises that simultaneously challenge the local and global muscles has been advocated.

Review of muscle function at the hip joint

Currently, it is unclear which muscle synergies have potential to stabilise the femoral head within the acetabulum. This is largely due to the inherent difficulties with measuring joint stability and muscle forces in vivo. The following review discusses what is known about individual muscles acting at the hip and explores their potential role in active joint stability. It is based on electromyography, modelling, cadaveric studies, MRI and RTUS studies and strongly guided by recent studies investigating the line of force87 and muscle morphology of the hip muscles88. The primary role of muscles, local or global, is considered to be influenced by multiple factors. It is speculated, however, that muscle architecture (PCSA relative to fibre length) and lines of action are perhaps the most important features in determining primary muscle roles. Muscles that can generate large forces over small changes in muscle length and muscles that have lines of forces predominately creating joint compression could be considered to be primary active stabilisers. A number of muscles impact on the hip. However, the focus of the review is on the deeper muscles of the hip due to their potential stability role and the abductors of the hip due to information available that suggests this muscle group is closely associated with joint loading patterns.

Quadratus femoris, obturator internus and externus and gemelli

The deep external rotators (quadratus femoris, obturator internus and externus and the gemelli) have been proposed as key active stabilisers of the hip and, along with the internally rotating gluteus minimis, are often described as the “rotator cuff” of the hip. Previous research on these muscles has been limited to anatomical modelling studies and descriptive cadaver studies90-93. The quadratus femoris, gemelli and obturator externus and internus are described as external rotators of the hip48, however their rotational force producing capacity, particularly in the weight bearing leg, is likely to be minimal given their small PCSA and moment arms22. These muscles do however have a favourable ratio between PSCA and fibre length, potentially making them suited to stabilising the femoral head in the acetabulum. Ward88 speculates that the deep external rotators may play a role in modulating hip joint stiffness and providing subtle positional adjustments to the hip joint. Modelling studies suggest that the deep external rotators, with the exception of piriformis, have a nearly horizontal line of force, which is advantageous for producing external rotation, but perhaps more importantly, compression of the joint surfaces87. As such, their morphology and proposed role is very much analogous to the rotator cuff muscles of the shoulder, particularly infraspinatus and teres minor87.

Indirect evidence of the stabilising role of these muscles comes from studies showing increased rate of prosthetic dislocation and functional deficits following resection of the external rotator muscles with posterior surgical approach94. When the external rotators and capsule were spared on a posterior approach using a capsular-enhanced repair, dislocation rates dropped dramatically.

Further indirect evidence of the dynamic stabilising role of quadratus femoris comes from a bed rest study by Miokovic et al.97 who demonstrated significant preferential atrophy of the quadratus femoris muscle when investigating the effects of unloading on the postero-lateral hip muscles in 24 male subjects. Interestingly, the other deep external rotators studied (obturator internus and externus) did not demonstrate significant changes in muscle size after sixty days of bed rest. Previous bed rest studies have demonstrated preferential atrophy of the local stabilising muscles when investigating the muscles of the trunk with preservation of global muscle size25.

To date, no human studies have investigated the fibre types of the hip cuff muscles. However, several animal studies have reported high proportions of slow twitch fibres in hip cuff muscles (up to 69.9% in quadratus femoris of mice). It is surmised that this high percentage of slow twitch fibres may imply a high spindle density and therefore an important proprioceptive role at the hip98.

The lack of information on the deep hip external rotator muscles, particularly EMG data, may be explained by the depth of the muscles and their proximity to the sciatic nerve22. While RTUS and MRI studies may provide a pathway to greater understanding of deeper muscles, no studies have investigated these muscles in symptomatic and asymptomatic individuals.

Iliocapsularis

Iliocapsularis is a muscle not well described in anataomical texts. Ward et al.100 described the muscle as originating from the anteromedial hip capsule as well as the inferior border of the anterior inferior iliac spine, inserting just distal to the lesser trochanter, based on observations of 20 human cadavers. Iliocapsularis’ extensive attachments to the hip capsule may provide potential to tighten the anterior aspect of the capsule, enhancing joint stability. An MRI study by Babst et al.101 reported greater cross sectional area, greater partial volume and less fatty infiltrate of iliocapsularis muscles of subjects with hip dysplasia compared to subjects with excessive acetabular coverage. The findings suggest that hypertrophy of iliocapsularis may represent a compensatory strategy to improve active hip joint stability in the presence of passive hip instability100.

Piriformis

The piriformis may be important in stability of the hip with evidence of lower dislocation rates when the piriformis is preserved following insertion of a prosthetic hip via a posterior approach. This may imply an important role in stabilising the hip, however it should be noted that these studies looked at piriformis in conjunction with quadratus femoris94, and obturator internus89. Piriformis is most active in resisted external rotation of the hip102. Like the other deep external rotators, the piriformis muscle has a high ratio of PSCA: fibre length suggesting a potential stability role, however unlike the other external rotators of the hip, the line of force of the piriformis muscle is not as favourable to enhance joint compression87.

Gluteus minimus

Gluteus minimus, the deepest part of the abductor synergy, is an abductor, rotator and flexor of the hip103. However, its primary function is considered to be as a stabiliser of the hip and pelvis103-105. Its fibres run parallel to the neck of the femur104, and it has attachments to the superior aspect of the capsule106, supporting the contention that gluteus minimis is an important stabiliser of the femoral head in the acetabulum. A cadaveric study by Beck et al.103 of 16 hips found the gluteus minimus had extensive attachments to the hip joint capsule. Gluteus minimus may therefore be important in stabilising the hip by being able to modulate joint capsule stiffness; it may also help prevent anterior dislocation and superomedial migration of the femoral head, as well as providing a proprioceptive role. A recent fine wire EMG study has provided support for the role of the gluteus minimus as a stabiliser in their demonstration that the anterior portion of gluteus minimus is active in both prone hip extension and in late stance phase, acting presumably to provide anterior support to the joint, rather than as a hip extensor for which is has no moment arm107.

Gluteus medius

Gluteus medius is the primary abductor of the hip and important stabiliser of the pelvis and hip, preventing the pelvis from dropping in single leg stance. It is has three segments; anterior, posterior, middle or superficial. Each segment is separately innervated and has unique fibre orientation. Electromyographic analysis suggests that the amplitude of activity in any of the segments is highly dependent upon the task and gluteus medius activation is not always consistent across the segments109. Based on anatomical and surface electromyographic studies, Gottschalk et al.104 propose that during gait the posterior portion of gluteus medius is an important stabiliser of the femoral head in the acetabulum whilst the middle subdivision helps initiate hip abduction and the anterior subdivision contracts to cause pelvic rotation. Other gait studies suggest that the gluteus medius plays an important stabilising role of the pelvis on the hip by contracting prior to and after foot contact to prevent adduction of the hip. This activity does not seem to change with increased speed. In contrast to Gottschalk et al.104 these studies did not individually test the three subdivisions of gluteus medius. A fine wire EMG study investigating the activation of the three segments of gluteus medius during non weight bearing hip movements, found the anterior portion of the muscle to be highly active during hip extension, perhaps suggesting a stability role in this position to minimise anterior femoral head translation110. Anatomical modelling studies indicate that gluteus medius may act as a hip stabiliser on the basis of a high ratio of PSCA: fibre length, however its large moment arm for abduction makes it better suited to produce force, advantageous for stabilising the pelvis in weight bearing, rather than optimal positioning of the femoral head in the acetabulum during functional activities.

Iliopsoas

Iliopsoas has two main portions, psoas major and iliacus, which are separately innervated. Both are active throughout hip flexion. Psoas major has been found to have a greater percentage of fast twitch than slow twitch muscle fibres, particularly in its caudal portion based on muscle biopsies of 15 male subjects78, whereas an animal histology study suggested iliacus may contain a large proportion of slow twitch fibres98. A fine wire EMG study by Andersson et al.114 investigating 11 subjects, supports the role of iliacus as a stabiliser of the hip, particularly in late stance phase of gait. Lewis et al.115 surmised that the iliacus and psoas muscles may play a role similar to that of the rotator cuff muscles at the shoulder by being able to influence joint stability not only by its insertion but also by tension in musculotendinous units as they pass over the anterior aspect of the hip joint.

A prolonged bed rest study by Mendis et al.116 investigated the effect on the anterior hip muscles of 8 weeks of bed rest, with results showing reduced CSA of the deep fibres of iliopsoas at the level of the head of femur, suggesting preferential atrophy.

Discussion

Active hip stability is likely to be primarily modulated by the deep local muscles

If the passive stability mechanisms of the hip are inadequate, due to local pathology or insufficiency, the muscular system will be needed to augment stability. The local muscles of the hip including gluteus mimimis, quadratus femoris, gemelli, obturator internus and externus, iliocapsularis and possibly the deep fibres of iliopsoas are anatomically, biomechanically and physiologically well suited to provide dynamic stabilisation of the femoral head in the acetabulum, helping reduce shearing forces on the joint. These muscles share many of the characteristics of other local muscles of the lumbar spine, pelvis, shoulder and knee. Although most have relatively small PCSA, they have short muscle fibre lengths and are therefore able to produce significant forces over small changes in muscle length. They also have advantageous lines of force to provide compression of the head of the femur in the acetabulum. They may also contain predominantly slow twitch muscle fibres, making them suited to tonic contractions and providing fatigue resistance and have direct capsular attachments, suggesting a significant proprioceptive role.

Co-contraction of local muscles is theorised to occur in the lumbar spine, shoulder and knee. It is plausible that local muscles act with synergy to provide hip joint stability, perhaps with the coordinated contraction of the deep internal and external rotators.

More research is needed to elucidate the effect of pathology on these local muscles. Many of the seminal articles investigating the function and dysfunction of muscles such as trans-versus abdominis, lumbar multifidus72, and gluteus medius117 have used fine wire EMG to demonstrate changes in the timing of the muscle contractions. Unfortunately the inaccessibility of the deeper stabilising muscles, particularly those lying posterior to the hip joint, makes them difficult to assess. Although fine wire EMG studies are likely to give the most definitive data, new technologies such as RTUS and dynamic MRI, may provide a less invasive method of collecting data.

Future directions in hip rehabilitation

Hip muscle strengthening exercises, particularly hip abductor strengthening, are the most commonly prescribed intervention by physiotherapists in patients with hip pain but current evidence suggests that joint stability may be enhanced via retraining of deep hip stabilisers. Although most clinicians advocate for the use of functional rehabilitation exercises, there is some evidence to suggest that this alone is inadequate for the effective retraining of normal feed-forward postural activity81. Much akin to the current rationale of strengthening the local muscles at the lumbar spine and pelvis, cervical spine, and shoulder joint prior to addressing the more superficial global muscles, it could be argued that effective therapeutic exercise programs for the pathological hip should initially target local stabilising muscles using low load tonic exercises. Specific exercises for retraining the local muscles of the hip are commonly started in positions of low postural load such as prone or sidelying. The patient can be taught to monitor their motor performance by careful palpation. In the case of a patient presenting with concurrent aberrant lumbopelvic motor control, co-contraction of the deep hip stabilisers and lumbopelvic stabilisers can be taught. Clinically such an approach appears to be effective however there is currently no evidence to support its use as it has not been evaluated. One difficulty facing clinicians is reliably measuring the function of the local muscles of the hip. RTUS is now commonly used by physiotherapists to assess and retrain muscles of the abdominal wall and lumbar spine. This technology may prove to be a reliable and valid tool for measuring local hip muscle function and for providing feedback on motor performance whilst performing rehabilitation exercises. To date there has only been one study validating the use of RTUS for measuring the size of anterior hip muscles, with findings that this clinical tool is reliable compared to MRI119. More research is needed to validate the use of RTUS as a measuring tool in other active stabilising muscles. Hand held dynamometry has been utilized to reliably determine muscle function in previous studies examining hip OA120, FAI42, and groin pain121. This may provide some insight, but further research is required to elucidate tests that are more specific for assessing deep muscle function. Testing the ability to actively move into inner range, for which the deep musculature has a better lever arm, and to tonically hold an inner range contraction have previously been suggested as important motor control assessments and retraining strategies for lumbopelvic stabilisation34 but these have not been well tested around the hip.

Once isolated contraction of the deep external rotator muscles is successfully achieved, progression can be made to the rehabilitation of secondary stabilisers and prime movers of the hip, particularly the gluteus maximus, initially using non-weight bearing exercises and progressing to weight bearing exercises once motor control and strength allows. Pre-activation of the deep external rotators may make these exercises more effective. Deficits in flexibility and proprioception should also be addressed at this stage. Once adequate hip muscle strength and endurance is achieved, functional and sports specific exercises can then be implemented.

Furthering our understanding of the role of muscles and muscle synergies at the hip may provide insight into the development of more specific assessment and treatment protocols, ensuring adequate hip joint stability in people with hip pain or pathology.

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EXERCISE AND LOAD MODIFICATION VERSUS CORTICOSTEROID INJECTION VERSUS ‘WAIT AND SEE’ FOR PERSISTENT GLUTEUS MEDIUS/MINIMUS TENDINOPATHY (THE LEAP TRIAL): A PROTOCOL FOR A RANDOMISED CLINICAL TRIAL

Rebecca Mellor1 Alison Grimaldi1,2, Henry Wajswelner3 Paul Hodges4, Haxby Abbott5, Kim Bennell6, Bill Vicenzino1

1 School of Health and Rehabilitation Sciences, The University of Queensland, St Lucia, QLD 4072, Australia. 2 Physiotec, 23 Weller Road, Tarragindi, QLD 4121, Australia. 3 Department of Physiotherapy and Lifecare Physiotherapy, LaTrobe University, Bundoora, VIC 3086, Australia. 4 NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, St Lucia, QLD 4072, Australia. 5 Centre for Musculoskeletal Outcomes Research, Dunedin School of Medicine, University of Otago, Dunedin, NZ 9054. 6 Department of Physiotherapy, Centre for Health, Exercise and Sports Medicine, University of Melbourne, Carlton, VIC 3053, Australia.

 

ABSTRACT:

Background

Lateral hip pain is common, particularly in females aged 40–60 years. The pain can affect sleep and daily activities, and is frequently recalcitrant. The condition is often diagnosed as trochanteric bursitis, however radiological and surgical studies have revealed that the most common pathology is gluteus medius/minimus tendinopathy. Patients are usually offered three treatment options: (a) corticosteroid injection (CSI), (b) physiotherapy, or (c) reassurance and observation. Research on Achilles and patellar tendons has shown that load modification and exercise appears to be more effective than other treatments for managing tendinopathy, however, it is unclear whether a CSI, or a load modification and exercise-based physiotherapy approach is more effective in gluteal tendinopathy. This randomised controlled trial aims to compare the efficacy on pain and function of a load modification and exercise-based programme with a CSI and a ‘wait and see’ approach for gluteal tendinopathy.

Methods

Two hundred one people with gluteal tendinopathy will be randomly allocated into one of three groups: (i) CSI; (ii) physiotherapist-administered load modification and exercise intervention; and (iii) wait and see approach. The CSI therapy will consist of one ultrasound (US) guided CSI around the affected tendons and advice on tendon care. Education about load modification will be delivered in physiotherapy clinics and the exercise programme will be both home-based and supervised. The group allocated the wait and see approach will receive basic tendon care advice and reassurance in a single session by a trial physiotherapist. Outcomes will be evaluated at baseline, 4, 8, 12, 26 and 52 weeks using validated global rating of change, pain and physical function scales, psychological measures, quality of life and physical activity levels. Hip abductor muscle strength will be measured at baseline and 8 weeks. Economic evaluation will be performed to investigate the cost-effectiveness of the active interventions compared with the wait and see approach. Analyses will be conducted on an intention-to-treat basis using logistic and linear mixed regression models and the economic evaluation will report incremental cost-utility ratios. The trial reporting will comply with CONSORT guidelines.

Discussion

This study will provide clinicians with directly applicable evidence of the relative efficacy of three common approaches to the management of gluteal tendinopathy.

Trial registration

Australia New Zealand Clinical Trials Registry ACTRN12612001126​808. Date Registered: 22/10/2012.

Published by BioMed Central Musculoskeletal Disorders, Open Access Publisher, 30 April 2016, 17:196 DOI 10.1186/s12891-016-1043-6

Link:  http://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/s12891-016-1043-6

Gluteal Tendinopathy: A Review Of Mechanisms, Assessment and Management

Alison Grimaldi1, Rebecca Mellor2, Paul Hodges3, Kim Bennell4, Henry Wajswelner5, Bill Vicenzino2

1 Physiotec, 23 Weller Road, Tarragindi, QLD 4121, Australia. 2 School of Health and Rehabilitation Sciences, The University of Queensland, St Lucia, QLD 4072, Australia. 3 NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, St Lucia, QLD 4072, Australia. 4 Department of Physiotherapy, Centre for Health, Exercise and Sports Medicine, University of Melbourne, Carlton, VIC 3053, Australia. 5 Department of Physiotherapy and Lifecare Physiotherapy, LaTrobe University, Bundoora, VIC 3086, Australia.

ABSTRACT

Tendinopathy of the gluteus medius and gluteus minimus tendons is now recognized as a primary local source of lateral hip pain. The condition mostly occurs in mid-life both in athletes and in subjects who do not regularly exercise. Females are afflicted more than males. This condition interferes with sleep (side lying) and common weight-bearing tasks, which makes it a debilitating musculoskeletal condition with a significant impact. Mechanical loading drives the biological processes within a tendon and determines its structural form and load-bearing capacity. The combination of excessive compression and high tensile loads within tendons are thought to be most damaging. The available evidence suggests that joint position (particularly excessive hip adduction), together with muscle and bone elements, are key factors in gluteal tendinopathy. These factors provide a basis for a clinical reasoning process in the assessment and management of a patient presenting with localized lateral hip pain from gluteal tendinopathy. Currently, there is a lack of consensus as to which clinical examination tests provide best diagnostic utility. On the basis of the few diagnostic utility studies and the current understanding of the pathomechanics of gluteal tendinopathy, we propose that a battery of clinical tests utilizing a combination of provocative compressive and tensile loads is currently best practice in its assessment. Management of this condition commonly involves corticosteroid injection, exercise or shock wave therapy, with surgery reserved for recalcitrant cases. There is a dearth of evidence for any treatments, so the approach we recommend involves managing the load on the tendons through exercise and education on the underlying pathomechanics.

Published in Sports Medicine August 2015, Volume 45, Issue 8, pp 1107-1119.

Link: http://link.springer.com/article/10.1007%2Fs40279-015-0336-5

Published in Sports Medicine August 2015, Volume 45, Issue 8, pp 1107-1119.

Gluteal Tendinopathy: Integrating Pathomechanics And Clinical Features In Its Management

JOSPT coverAlison Grimaldi, PhD1,2  ,  Angela Fearon, PhD3-5

1Physiotec Physiotherapy, Tarragindi, Australia. 2School of Health and Rehabilitation Sciences, The University of Queensland, St Lucia, Australia. 3Hip Physio, Watson, Australia. 4Trauma and Orthopaedic Research Unit, Australian National University, Canberra City, Australia. 5School of Physiotherapy, University of Canberra, Bruce, Australia.

 

SYNOPSIS

Gluteal tendinopathy is now believed to be the primary local source of lateral hip pain, or greater trochanteric pain syndrome, previously referred to as trochanteric bursitis. This condition is prevalent, particularly among post-menopausal women, and has a considerable negative influence on quality of life. Improved prognosis and outcomes in the future for those with gluteal tendinopathy will be underpinned by advances in diagnostic testing, a clearer understanding of risk factors and comorbidities, and evidence-based management programs. High-quality studies that meet these requirements are still lacking. This clinical commentary provides direction to assist the clinician with assessment and management of the patient with gluteal tendinopathy, based on currently limited available evidence on this condition and the wider tendon literature and on the combined clinical experience of the authors.

Published in Journal of Orthopaedic & Sports Physical Therapy November 2015, Volume 45, Issue 11, pp 910-922.

Link:  http://www.jospt.org/doi/abs/10.2519/jospt.2015.5829?journalCode=jospt

Hip Abductor Muscle Weakness In Individuals With Gluteal Tendinopathy

Medicine & Science in Sports & Exercise CoverKim Allison1, Bill Vicenzino2, Tim V Wrigley1, Alison Grimaldi3, Paul W Hodges2, and Kim L Bennell1

1Centre for Health and Exercise Science, University of Melbourne, Parkville, VIC, Australia. 2School of Health & Rehabilitation Sciences St Lucia, The University of Queensland QLD, Australia. 3Physiotec Physiotherapy, Tarragindi, QLD, Australia.

 

 

ABSTRACT

Purpose. To compare hip abductor muscle strength between individuals with symptomatic, unilateral gluteal tendinopathy (GT) and asymptomatic controls.

Methods. Fifty individuals with GT aged between 35 and 70 years, and 50 sex- and age-comparable controls were recruited from the community. Maximal isometric strength (torque normalized to body mass) of the hip abductors was recorded in supine using an instrumented manual muscle tester. A two-way mixed analysis of covariance (ANCOVA), with covariates of self-reported pain during testing and pain limiting maximum effort, was used to compare hip abductor strength of the symptomatic and asymptomatic hip between GT and control individuals. Data were expressed as mean and standard deviation, with the pairwise comparisons expressed as mean differences and 95% confidence intervals.

Results. Individuals with GT demonstrated significantly lower hip abductor torque of both their symptomatic and asymptomatic hip than healthy controls (both p<0.05) with mean strength deficits of 0.35 Nm/kg (32%) on the symptomatic hip and 0.25 Nm/kg (23%) on the asymptomatic hip. In individuals with GT, the symptomatic hip was significantly weaker than the asymptomatic hip with a mean strength deficit of 0.09 Nm/kg (11%) (p<0.05).

Conclusion. People with unilateral GT demonstrate significant weakness of the hip abductor muscles bilaterally when compared with healthy controls. Although it is not clear whether hip weakness precedes GT or is a consequence of the condition, the findings provide a basis to consider hip abductor muscle weakness in the treatment plan for management of GT.

Published in Medicine & Science in Sports & Exercise March 2016, Volume 48, Issue 3, pp 337-579.

Link: http://journals.lww.com/acsm-msse/Abstract/2016/03000/Hip_Abductor_Muscle_Weakness_in_Individuals_with.2.aspx

Lateral Hip Pain: Mechanisms and Management

 

This article was published in In Touch magazine, a resource exclusive to members of Musculoskeletal Physiotherapy Australia, a National Group of the Australian Physiotherapy Association. For more information on the exercise apparatus pictured in this article, Physiotec's TWS Slider, click here

This article was published in In Touch magazine,
a resource exclusive to members of
Musculoskeletal Physiotherapy Australia,
a National Group of the Australian Physiotherapy Association.

For more information on the exercise apparatus pictured in this article,
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History and prevalence

Lateral hip pain (LHP) has traditionally been referred to as trochanteric bursitis. More recent evidence has demonstrated that bursal distension is an inconsistent feature of lateral hip pain (Connell et al. 2003—15%; Bird et al. 2001—8%). Furthermore, histological studies of the bursa in such cases have found no signs of acute or chronic inflammation (silva et al. 2008). radiological and surgical studies have now shown that bursal distension is almost always a secondary finding associated with a primary pathology of gluteus medius or minimus tendinopathy (Bird et al. 2001, Cvitanic et al. 2002, Connell et al. 2003, dwek et al. 2005, Kingzett-taylor 1999, Kong et al. 2007, Pfirrmann et al. 2005, Woodley et al. 2008).

Prevalence studies suggest that degenerative tears of the gluteus medius or minimus tendons occur in 20% of patients with osteoarthritis of the hip (Howell et al. 2001). Prevalence of tendinopathy that has not yet progressed to a tear is therefore likely to be much higher. Gluteus medius tendinopathy (GMt) also occurs in 20–35% of patients with low back pain (Collee et al. 1991, tortolani et al. 2002). due to the pseudoradicular referral pattern from the greater trochanter down the lateral thigh, it is often misdiagnosed as lumbar pathology. this may lead to years of inappropriate and ineffective treatment, including laminectomy (tortolani et al. 2002). GMt is much more common in females than males, with a ratio of 3–4:1, peaking in the perimenopausal period. However, this condition may also occur in young athletes, particularly runners or those involved in step training.

Mechanisms

While aetiological mechanisms for tendinopathy continue to be explored, compression is thought to be a key factor in the development of insertional tendinopathies (Cook & Purdam 2009; almekinders et al, 2003). Consideration of this mechanism in exercise prescription has been shown to be integral to positive program outcomes in insertional achilles tendinopathy (Jonsson et al. 2008). similarly, identification and control of compressive mechanisms in normal daily life, and in exercise prescription, are central to optimal short and long-term outcomes for the management of GMt.

Compression of the insertions of the gluteus medius and minimus tendons into the lateral and anterior facets of the greater trochanter occurs beneath the iliotibial band (itB). any increases in tension in the itB will increase compressive loading. tightness and overactivity of muscles of the superficial lateral stability system—tFL, upper gluteus maximus, and vastus lateralis—will directly impact on this tension, and therefore tendon compression. those who stand and sit in abduction, which is more common in males, may develop functional tightness over time. the use of saddle chairs tends to promote excessive static abduction and subsequent soft tissue tightness of the lateral structures. this will be particularly so for those working in seated occupations over many years.

On rising from static abduction, the hips will be brought into relatively more adduction for dynamic function, resulting in significant increases in compressive loading of the gluteus medius and minimus tendons.
Birnbaum et al. (2004) demonstrated that rapid increases in compressive loading occur

Beneath the ITB at the level of the greater trochanter as the hip is moved into adduction. While in neutral hip adduction, the ITB exerts only four newtons (N) of pressure over the greater trochanter. this has risen to 36N by 10 degrees adduction and continues to rise to 106n by 40 degrees adduction. if the lateral structures are tighter than normal, these loads are likely to be reached even more rapidly. it is more common, however, that those suffering from LHP have normal or even excessive length in the lateral soft tissues. in this situation it is the frequency and degree of functional adduction that has the most important role to play in aetiological mechanisms.

Increases in functional adduction, and therefore compression, appear to be linked to poor postural and movement habits. standing ‘hanging on one hip’ in hip adduction is a common postural habit as it requires less energy to hang passively on the itB. sitting with the legs crossed in adduction, and sleeping in sidelying with the uppermost hip positioned in flexion/adduction will also add significantly to time spent in a position of compression. it is also known that prolonged positioning of a muscle in a lengthened position results in structural change by which there is a shift in the optimal position of function to the new, lengthened position (Goldspink 1977, Kendall & McCreary 1983, Williams & Goldspink 1978). subsequent to this shift in the length–tension relationship, dynamic function such as walking and stairclimbing will also occur in relatively greater degrees of hip adduction. Furthermore, functioning in hip adduction will favour greater recruitment of the superficial over the deeper members of the hip abductor synergy (Kumagai et al. 1997), adding to compressive loading of the deepest and most commonly affected portions of the trochanteric tendons.

fig1Other factors that may impact on degree of functional adduction include leg length differences, pelvic obliquity such as that associated with scoliosis, hip flexor dysfunction resulting in midline or cross-midline striking (foot placement in a position of greater hip adduction), inadequate distal shock absorption at foot strike, and training errors such as running on the camber of a road, the camber of the beach, or the same direction around a track. Bony factors may also contribute to pathoaetiological mechanisms due to impacts on the relative association between the greater trochanter and the itB. For example, femoral offset will affect prominence of the greater trochanter, while genu valgum, and femoral anteversion will affect orientation of the itB. other factors such as abdominal girth, systemic disease, and hormonal profile may also play a role, but they are beyond the scope of this short report.

There are little other than anecdotal descriptions of physical therapy approaches for lateral hip pain in the literature. treatments that have been mentioned for trochanteric bursitis or ‘greater trochanteric pain syndrome’ have been ice, ultrasound for the anti-inflammatory effects and stretching of the itB, which involves placing the hip frequently and often forcefully into end-range hip adduction. With current knowledge of the pathoanatomy and proposed pathomechanics of the situation, there is little sound rationale for this approach. the contemporary approach to management of GMt is based on a clearer under•standing of mechanisms and contributing factors. education, tendon decompression strategies and therapeutic exercises aimed at reducing excessive functional hip adduction are the core elements of contemporary management. the identification and management of predisposing factors is extremely important for the long-term control of symptoms.

Education on the condition, its mechanisms, and the natural time course of tendon recovery can empower the patient and reduce fear and catastrophisation. Better understanding will also improve compliance with decompression and exercise programs, and reduce frustration associated with unrealistic expectations of time to full recovery.

Tendon decompression strategies aim to minimise the amount of compressive loading that may occur over a 24-hour period. this is the key to early symptom control. increasing awareness of negative postural habits and controlling them are critical. Positions to avoid include standing hanging on one hip in adduction, sitting with legs crossed, or sitting with the feet wide and knees together, which is a common female trait. due to the connection of the fascia lata into the gluteal and thoracodorsal fascia, sitting in more than 90-degree hip flexion for prolonged periods can also be a problem. sitting in low lounges and car seats, which generally slope backwards, often results in ‘start up’ pain on rising to stand. avoiding low chairs and using a wedge cushion to bring the hips higher than the knees can be very beneficial.

Night time is the other major issue, as it represents a significant portion of the 24-hour period. eight hours of either lying on the symptomatic side (direct compression against bed), or lying with the symptomatic hip in flexion/ adduction will significantly add to the cumulative compressive load. Patients may be most painful at night, particularly lying on their side, or when initiating a rolling manoeuvre, similar to the sit-to•stand ‘start up’ pain. sleeping in supine with a pillow under the knees to offload the hips and lumbar spine minimises compressive loading. Many patients, however, find it difficult to sleep in this position. to reduce compression for the side-sleeper, an appropriate recommendation would be to add an eggshell mattress overlay to the bed, and sleep with a pillow, or pillows, between the knees and ankles that preferably approximates a horizontal position of the uppermost lower limb.

For the patient who has tightness and overactivity of the superficial soft tissues, stretching, while a common strategy, will only aggravate the situation due to the associated compressive loading. Massage, self-trigger point releases, acupuncture, dry needling and heat will all be more appropriate. But this should never be an isolated management approach. Long-term positive outcomes will only be achieved by addressing poor postural and movement habits, and active correction of muscle dysfunction.

Therapeutic exercise should be directed towards techniques that aim to recruit the muscles of the abductor synergy in a way in which:

  • there is adequate recruitment of the deep abductors, gluteus minimus and the deep fibres of gluteus medius;
  • there is consistency with the natural function of these muscles; and
  • compressive loading is minimised by avoidance of repetitive or loaded hip adduction.

Real-time ultrasound presents the best opportunity in a clinical situation to assess and retrain the deeper hip abductors. once appropriate recruitment strategies have been elicited, graduated strengthening should occur wherever possible in a weightbearing environment. sidelying ‘clams’ (abduction/ external rotation to adduction/ internal rotation) and sidelying leg lifts are often provocative due to repetitive compressive loading on return to adducted start positions. these exercises should therefore be avoided.

Furthermore, open chain exercise is unlikely to replicate closely enough the natural proprioceptive stimulus and balanced abductor activation of weightbearing function. sliding platforms (e.g. Pilates reformers) that allow resisted abduction in standing provide both a low compression exercise alternative and a situation more consistent with natural functioning in these antigravity muscles. Further bias for the deeper abductors can also be achieved via targeted inner range abductor strengthening on these sliding platforms. the primary focus during other functional weightbearing tasks such as single leg stance, lunges and step work should be on minimising hip adduction, which may require hand support (stick, back of chair, wall) in the early phases. Higher level exercises should be progressed as appropriate for the patient’s needs. a graduated return to activity should also be instituted to avoid rapid changes in tendon loading which may be provocative.

The Association Between Degenerative Hip Joint Pathology and Size of the Gluteus Maximus and Tensor Fascia Lata Muscles

1 Alison Grimaldi PhD, MPhtySt, BPhty
1
 Carolyn Richardson PhD, BPhty(Hons) 
Gail Durbridge MAppSci, Grad Dip Ultrasound, DipAppSci Medical Radiography
2
 William Donnelly MBBS, FRACS
1
 Ross Darnell PhD
1,4 
Julie Hides PhD, MPhtySt, BPhty.

 

  1. Division of Physiotherapy,
    School of Health and Rehabilitation Sciences,
    The University of Queensland,
    Brisbane, 4072, Australia
  2. Brisbane Orthopaedic Specialist Services, Brisbane, Australia
  3. Centre for Magnetic Resonance Imaging, Brisbane, Australia
  4. The UQ/ Mater Back Stability Clinic
    Mater Health Services,
    Raymond Terrace, South Brisbane, Queensland, 4101, Australia

PUBLISHED IN MANUAL THERAPY 14 (2009) 611-617     doi:10.1016/j.math.2008.11.002

 

ABSTRACT

The aim of this study was to obtain, using Magnetic Resonance Imaging (MRI), muscle volume measurements for the gluteus maximus (upper:UGM and lower:LGM portions) and tensor fascia lata (TFL) muscles in both healthy subjects (n=12) and those with unilateral osteoarthritis of the hip ( mild: n=6, and advanced: n =6). While control group subjects were symmetrical between sides for the muscles measured, subjects with hip joint pathology showed asymmetry in GM muscle volume dependent on stage of pathology. The LGM demonstrated atrophy around the affected hip in subjects with advanced pathology (p< 0.05), however asymmetry of the UGM (p<0.01) could be attributed largely to hypertrophy on the unaffected side, based on between group comparisons of muscle volume. TFL showed no significant asymmetry, or difference compared to the normal control group. This study highlights the functional separation of UGM and LGM, and the similarities of the UGM and TFL, both superficial abductors appearing to maintain their size around the affected hip. Further research is required to determine the specific changes occurring in the deeper abductor muscles. This information may assist in the development of more targeted and effective exercise programmes in the management of OA of the hip.

INTRODUCTION

Therapeutic exercise has been cited as an important approach used in management of osteoarthritis (OA) of the hip (Altman et al 2000, Hochberg et al 1995, National Collaborating Centre for Chronic Conditions 2008, Smidt et al 2005, Zhang et al 2008). There is however, a distinct scarcity of literature investigating the effectiveness of therapeutic exercise of the hip. Programmes have often been quite generalised with small to moderate short term effects and poorer long term effects (Tak et al 2005, van Baar et al 2001). Outcomes may be improved through the development of more specific programmes based on a greater understanding of muscle function and dysfunction around the hip joint. One of the most consistent findings in subjects with hip dysfunction is an inability to maintain adequate lateral control of the hip and pelvis in single leg stance (Hardcastle & Nade 1985). Studies assessing hip abductor muscle strength in subjects with OA of the hip have found deficits of up to 31% (Arokoski et al 2002, Jandric 1997, Murray & Sepic 1968), while others have found no significant losses in abductor strength (Sims et al 2002, Teshima 1994). These apparent inconsistencies may be associated with specific changes occurring within muscles of the abductor synergy, and the association of these changes with stage of pathology.

While strength testing provides information on global abductor muscle function, a resultant effect of all synergists, specific changes within the synergy will only become evident by addressing each muscle individually. Muscles of the abductor synergy providing lateral stability of the hip and pelvis could be divided into superficial muscles that provide their effect via insertion into the iliotibial band, and deeper muscles that act via insertion into the greater trochanter. Muscles of the superficial system include the tensor fascia lata (TFL) muscle and the gluteus maximus muscle (GM) muscle. The deep system would include the gluteus medius (GMED), piriformis (PIRI) and gluteus minimus (GMIN) muscles. This paper will focus on the study of muscles of the superficial system, while the deep muscle system will be addressed in a further publication (Grimaldi et al, unpublished at this time).

In clinical rehabilitation settings, the gluteus maximus (GM) muscle has been targeted for strengthening exercises, due to its reported tendency to weaken and atrophy (Sims 1999, Janda 1983, Sahrmann 2002). In contrast, the tensor fascia lata (TFL) muscle has been targeted for lengthening techniques, due to its reported tendency to become excessively active (Sims 1999, Janda 1983, Sahrmann 2002). There has been little attention paid in either research or clinical settings, to the impact of the functional differentiation of the GM muscle on joint mechanics and the prescription of therapeutic exercise. The upper portion of the GM muscle (UGM) arises from the posterior iliac crest, while the lower portion of the GM muscle (LGM) arises from the inferior sacrum and upper lateral coccyx (Williams et al 1989). Despite a lack of fascial separation in adult humans, studies on morphogenesis of the GM muscle have revealed that it arises from two muscle primordia with a loose connective tissue separation between cranial and caudal portions in the foetus followed by fusion in the prenatal period (Tichy & Grim 1985). The UGM, acting above the centre of rotation of the hip, has a primary function of hip abduction, and does not have a role in hip extension. While both portions may externally rotate the femur, the lower portion of the gluteus maximus muscle (LGM), acting below the centre of rotation of the hip, is the primary hip extensor (Jaegers et al 1992, Stern 1972, Stern et al 1980, Lyons et al 1983) playing an important protective role in absorbing ground reaction forces at heel strike during gait.

The role of the hip abductor synergy in joint protection is less clear. While hip abductor strengthening is generally considered as a priority in patients with hip pain, an in vivo study on joint loads during gait revealed that peak joint loads were associated with peaks in hip abductor muscle activity during stance phase rather than solely loads applied from body weight (Krebs et al 1998). Contrary to common clinical belief, the authors from this study recommended that clinicians aiming to reduce joint load should reduce hip abductor activity.

Another important aspect that should be considered in the prescription of therapeutic exercise for patients with OA of the hip is the stage of pathology. While global atrophy of hip muscles may be present in end stage pathology, in the earlier stages of the condition, more specific changes in the muscles of the hip abductor synergy may occur. It has been proposed that these changes can result in alteration of the orientation of the resultant hip joint vector, and ultimately result in joint damage over time (Kummer 1993, Sims 1999). Further information pertaining to hip muscle dysfunction at different stages of pathology would be useful as it could be used in the development of more specific and possibly more effective conservative intervention or prevention programmes for those with degenerative hip joint pathology.

Table 1
Subject characteristics for each group

Group No Sex M:F Age
Mean (SD)
Weight(kg)
Mean (SD)
Height(cm)
Mean (SD)
AMI
Mean (SD)
MHHS(P)
Mean (SD)
MHHS(F)
Mean (SD)
MHHS(Total)
Mean (SD)
Mild 6 3:3 46.5 (9.5) 80.4 (15.1) 171.3(9.7) 63,667 (23,884) 25 (10.5) 41.5 *3.0) 73.2 *(11.3)
Adv 6 3:3 57.7 (6.7) 78.3 (8.5) 172.0 (7.4) 82,890 (75,410) 16.7 (5.2) 36.2 (5.5) 58.1 *(58.7)
Con 12 3:3 51.8 (9.7) 73.5 (13.3) 168.2 (10.2) 123,175 (68,766) —- —- —-

No = Number. BMI =Body Mass Index. AMI =Activity Metabolic Index
MHHS = Modified Harris Hip Score. P = Pain. F = Function
M:F = Male:Female. SD = Standard deviation. Adv = Advanced Pathology. Con = Control.
*Significant difference between pathology groups (p<0.05)

 

Imaging studies provide an excellent opportunity to analyse individual muscles of the hip. Only one study has measured muscle size in subjects with OA of the hip. Arokoski et al (2002) used magnetic resonance imaging (MRI) to measure hip muscle cross sectional area (CSA) in men with and without hip OA. Two axial slices through the pelvis provided a single CSA for LGM and a combined CSA of all hip abductors, including the UGM. This measure unfortunately failed to provide specific information of individual muscles of the abductor synergy. Furthermore, volume measurements rather than single slice CSA measurements, may be more representative of the complex pelvic musculature. One study has reported muscle volume measurements of the hip muscles for three healthy subjects (Jaegers et al 1992), but no volume measurements have been reported in subjects with hip OA.

The main aim of this study was to investigate size of the muscles of the superficial lateral stability mechanism of the hip, TFL and GM muscles, in subjects with either mild or advanced degenerative pathology of the hip. Subjects with unilateral pathology were selected in order to provide both within and between subject comparisons. The specific aims were to examine i) if there was significant side asymmetry in the superficial muscles across 3 groups (mild degenerative change, advanced degenerative change, matched controls), ii) if there were significant differences in actual muscle size among the pathology and control groups, and iii) if the functionally separate portions of the GM muscle, UGM, and LGM, display similar patterns of change in subjects with hip pathology. This study also examined the association of both stage of pathology, and muscle size, with the factors of age, height, weight, pain, function and activity levels.

The hypotheses of the study were that

  1. ia) there would be significant asymmetry in size of the UGM, LGM, and TFL in subjects with hip joint pathology, but not in controls,
  2. ib) asymmetry would be greater in subjects with advanced pathology,
  3. ii) the affected side LGM muscle would be smaller that the comparable side in control subjects, based on clinical expectation (Sahrmann 2002, Sims 1999), and

iii) changes in the UGM would more closely reflect changes in the TFL muscle based on their close functional relationship.

METHODS

Subjects 

Twenty-four subjects (12 subjects with hip joint pathology and 12 control subjects) were recruited for this study via community advertisement and via contact with medical practitioners. Control subjects were recruited to match each subject with pathology by sex and age. The age of the control subject was required to be within 5 years of the age of the matched subject with hip pathology. There was an equal distribution of males and females in each group. Subject details are listed in Table 1.

Subjects with hip joint pathology were included in the study if they had both a medical diagnosis and radiographic evidence of unilateral degenerative hip joint pathology. Radiographic evidence included XRay or MRI demonstrating OA or atraumatic, degenerative labral pathology. OA of the hip joint was classified by an experienced radiologist using the Kellgren/Lawrence (K/L) global scoring system (Hirsch et al., 1998; Kellgren & Lawrence, 1957). Six subjects with early joint space narrowing and osteophytes (K/L grades 1-2) were recruited for the ‘Mild Group’ and 6 subjects with moderate to severe joint space narrowing and osteophytes (K/L grades 3-4) were recruited for the ‘Advanced Group’. Seven subjects had left sided pathology and five subjects had right sided pathology.

Exclusion criteria for all subjects included any systemic disease affecting the muscular or nervous system, history of congenital or adolescent hip disease, hip trauma or previous surgery, inflammatory joint disease, presence of tumour, any lower limb injuries in the previous 2 years, participation in unilateral sports, use of a walking aid, and factors that would preclude them from MRI scanning procedures (eg. pacemaker, metal implants, pregnancy, claustrophobia). Subjects in both groups were also excluded if that had experienced any lower back pain in the previous 2 years or if there had been any significant lifetime history of lower back pain that resulted in a period of immobility, or required further investigation or treatment. Subjects in the control group were excluded if they had any history of hip pain.

Information on the study was sent to the subjects prior to admission to the study. Ethical approval was obtained from the institutional review boards and informed consent was obtained from all subjects.

Procedure

Table 2
Side to side differences in muscle volume (cm3), and percentage differences within groups for upper gluteus maximus, lower gluteus maximus, and tensor fascia lata muscles

Group Side UGM
Mean (SD)
LGM
Mean (SD)
TFL
Mean (SD)
Mild Affected
Unaffected
% Difference
405
421
3.8%
(70)
(60)
508
539
5.8%
(118)
(120)
82.5
73.8
10.05%
(20)
(19)
Advanced Affected
Unaffected
% Difference
378
479
21.0%
(96)
(118)
457
569
19.7%
(158)
(144)
86.2
89.5
3.8%
(38)
(27)
Control Affected
Unaffected
% Difference
352 (106)
359 (125)
(106)
(125)
453
495
8.6%
(130)
(158)
74.3
80.6
7.8%
(24)
(29)

SD = Standard Deviation. UGM = Upper gluteus maximus muscle
LGM = Lower gluteus maximus muscle. TFL = Tensor fascia lata muscl
p<0.01 * p<0.05

Self-Report Questionnaires.

Information on subject activity levels was gathered using a 12 month Leisure Time Physical Activity questionnaire providing an activity metabolic index (AMI) (Taylor et al 1978, Arokoski et al 2002). Activities were coded using the intensity code provided (Taylor et al 1978).The AMI for each activity the subject participated in was calculated with the formula: AMI = Intensity code (mean metabolic units) x average number of times per month x the number of months per year (frequency) x the time the activity was performed per occasion (duration). Total AMI reflects the addition of AMI for all activities (Taylor et al 1978) and provides a measure of metabolic units used/year.

The Modified Harris Hip Score (MHHS) was used to assess pain and function in the subjects with OA of the hip (Byrd & Jones 2000). The pain section consisted of 44 points, where a score of 44 represents a pain-free state. The function section consisted of 47 points, where a score of 47 points represents full, normal function. The multiplier 1.1 was used to achieve a total score out of a possible 100 (pain-free normal function).

Fig.1. Diagramatic representation of the portions of the GMmuscle. UGM; LGM; ITB.

Fig.1. Diagramatic representation of the portions of the GMmuscle.
 UGM       LGM      an_ther_green_bar ITB

Testing of Leg Domnance.

Subjects were also tested for leg dominanceKicking was used as the test function (Herneth et al 2004). The weight-bearing leg was recorded as “stance dominant” and the kicking leg as the “skill dominant” leg.

MRI Assessment.

Subjects were first screened for contraindications to MRI by a medical practitioner. Subjects were positioned in supine lying with legs extended to a neutral position. Leg rotation was controlled with the use of sand bags. A 1.5 Tesla Siemens Sonata MR system was used. A T2 True FISP sequence using 2 series of 28 x 6 mm contiguous slices from the iliac crest to the most distal extent of the gluteus maximus muscle was employed (TR: 3.78ms/TE:1.89ms/FOV:390mm).

Measurement Procedure.

An MRI measurement software package (Osiris) was used to measure CSA (cm2) of UGM, LGM and TFL muscles on each image in which the muscle appeared. Muscle volume (cm3) was calculated by multiplying CSA by slice width and then adding the volumes from each slice to determine the total muscle volume (Fukunaga et al 1992, Alkner & Tesch 2004) (Figure 2).The two functionally separate parts of GM were measured (UGM and LGM). The UGM includes that part of the muscle acting above the centre of rotation of the femoral head. These fibres insert almost exclusively into the iliotibial band (ITB) via a thick laminar tendon (Lieberman et al 2006). The LGM inserts below the centre of rotation, superficial fibres into the ITB, deep fibres into the gluteal ridge of the femur (Lieberman et al 2006). This anatomy is depicted in Figure 1. In this study the largest CSA of the femoral head was used as an anatomical landmark to functionally separate the UGM from the LGM muscle, to approximate the centre of rotation of the femoral head (Stern 1972).

Reliability of the assessor’s measurement technique was tested by retracing all slices of one subject (44slices) with an interim period of 6 weeks. Intra-tester reliability was tested for each separate measurement on each slice using a two sided bootstrapped interval of intraclass correlation coefficient (ICC2,1). Intra-rater reliability was found to be good, with correlation coefficients ranging from 0.87 to 0.99. Standard error of measurement (SEM) was calculated using the formula SEM= pooled SD x (1-ICC) ½ (Wallwork et al 2007). Standard deviation of the difference (SDD) was also calculated as the standard deviation of the differences between measurement 1 and 2. SEM for the GM muscle was 0.495cm2 and the SDD was 3.87cm2, while for the TFL muscle the SEM was 0.536cm2 and the SDD was 2.44cm2. These values represent good measurement stability with low error.

Statistical Analysis

The comparison of muscle volumes among groups and between sides was performed using a mixed linear model describing muscle volume with group as a between-subject factor, and side as a within-subject factor (Dependent variable=muscle volume, Independent variables=sides & groups). Each muscle was analysed separately. Contrasts of means were performed to compare sides within groups. Muscle volumes around the affected and unaffected hips of the subjects with hip joint pathology were compared with muscle volumes of the corresponding sides of their matched control subjects. That is, if the pathological side was left, the left side muscle volume of the matched control subject was used for comparison, and the right compared with the unaffected side value of the pathology group counterpart. Percent differences were calculated using the formula: % Difference= [ (larger value-smaller value)/larger value] * 100 (Hides et al 1996).

Analyses were also conducted to assess participant characteristics in relation to

  1. a) the similarity of the groups and
  2. b) the extent of association with muscle size.

One way analysis of variance was used to assess group equivalence across each of the dependent measures of age, height, weight, pain, function, and metabolic activity. The association between these patient characteristics and UGM, LGM, or TFL muscle size was assessed using analysis of covariance.

 

2A. Through ilia showing UGM in the proximal pelvis Control Subject

2A. Through ilia showing UGM in the proximal pelvis
Control Subject

2B. showing LGM and TFL just below the hip joint Control Subject
2B. showing LGM and TFL just below the hip joint
Control Subject
2C. Through ilia showing UGM in the proximal pelvis Subject with mild left hip OA (right side as viewed in image)
2C. Through ilia showing UGM in the proximal pelvis
Subject with mild left hip OA (right side as viewed in image)
2D. showing LGM and TFL just below the hip joint Subject with mild left hip OA (right side as viewed in image)
2D. showing LGM and TFL just below the hip joint
Subject with mild left hip OA (right side as viewed in image)
2E. Through ilia showing UGM in the proximal pelvis Subject with advanced left hip OA
2E. Through ilia showing UGM in the proximal pelvis
Subject with advanced left hip OA
2F. showing LGM and TFL just below the hip joint Subject with advanced left hip OA 
2F. showing LGM and TFL just below the hip joint
Subject with advanced left hip OA

Figure 2: Axial MRIs through the pelvis
an_ther_pink_bar GF      an_ther_green_barTFL

RESULTS

Side to side differences in muscle volumes within groups

There were no significant side to side differences in the control or mild pathology groups. While LGM size was smaller on the affected side in all but one subject in the group with mild joint changes, the asymmetry was not great enough to be statistically significant. In the group with advanced pathology there were significant between side differences in the GM but not the TFL muscle. The asymmetry was greater in the UGM muscle (mean difference 21%, p<0.01) than the LGM muscle (mean difference 19.7%, p<0.05). Means, standard deviations, and percentage difference in muscle volumes are reported for each group in Table 2. Examples of side to side differences are illustrated for each group in Figure 2.

Differences in muscle volumes between groups

No significant differences in muscle volumes were found between the mild and advanced pathology groups. The UGM muscles were significantly larger on the unaffected side (Mean difference 30.5%) of the subjects in the advanced pathology group when compared with matched controls (p<0.05, Table 3). No other comparisons reached statistical significance Although LGM volumes were on average 15.2% larger (p=0.12) on the unaffected side in the group with advanced pathology, compared with controls, statistical analysis did not reveal a significant difference in this relatively small sample size. Means, standard deviations, and percentage difference in muscle volumes around matched hips of the pathology and control groups are reported in Table 3.

Self-Report Questionnaires

Results of the AMI for all subjects and the MHHS for subjects with OA of the hip are shown in Table 1. Pain and function scores were lower for the group with more advanced radiological changes, reflecting higher pain levels and more functional disability, as measured by the MHHS. These scores considered alone were not significantly different statistically, however when the total score was calculated there was a significant difference between scores in the mild and advanced pathology groups (p<0.05). There was no statistically significant difference between groups for the AMI.

Leg Dominance

All subjects were left stance dominant/right skill dominant.

Effect of subject characteristics on muscle size

Results of the analyses indicated the groups were comparable in terms of age, height, weight, and metabolic activity (all p>0.05). In addition there was no significant relationship between these patient characteristics, or pain and function, and UGM, LGM or TFL muscle volume (p>0.05).

Table 3
Between group differences in muscle volume (cm3) for upper gluteus maximus, lower gluteus maximus, and tensor fascia lata muscles

Group Side UGM
Mean (SD)
LGM
Mean (SD)
TFL
Mean (SD)
Mild Affected
Unaffected
Control
405
378
354
(70)
(96)
(103)
508
457
460
(118)
(158)
(128)
82.5
86.2
74.9
(20)
(38)
(24)
Advanced Affected
Unaffected
Control
421
479
361
(60)
(118)*
(119)
539
569
489
(539)
(569)
(489)
73.8
89.5
75.4
(19)
(27)
(26)

UGM =Upper gluteus maximus muscle. LGM =Lower gluteus maximus muscle. TFL=Tensor fascia lata muscle. SD=Standard Deviation. Side refers to the named side in the pathology group, and for the control group side is aligned by matched pair dependent on side of pathology; 1Reference group for significance values; * p <0.05

DISCUSSION

This study investigated the influence of degenerative hip joint pathology on size of the GM and TFL muscles.

Side to side differences in muscle volumes within groups

The results of this study showed that subjects with demonstrated unilateral hip joint pathology exhibited marked side to side differences in the size of the GM muscle, specific to stage of pathology. While asymmetry in LGM size in subjects with mild joint pathology was not great enough to be statistically significant, in those with advanced joint changes the mean volume of the LGM muscle was on average 19.7% smaller on the affected side (p<0.05). The only previous study to investigate muscle size in those with OA of the hip/s reported that the mean CSA of the LGM muscle was 9% smaller on the side of the worse hip in those with either unilateral or bilateral OA (Arokoski et al 2002). The most likely explanations for the smaller percent difference are the inclusion of subjects with bilateral pathology in the latter study which would be expected to reduce the degree of side to side difference demonstrated, and the inclusion of subjects with both mild and advanced joint pathology in the analysis. Some explanation may also be provided by the different measurement techniques. A single CSA measurement may not provide a true reflection of change in total muscle volume.

The UGM muscle similarly showed no significant side to side difference in those with mild joint pathology. In the presence of advanced pathology, the UGM was on average 21% smaller on the affected side, representing a significant side to side difference in muscle size (p<0.01).

The TFL muscle was not significantly different between sides in either pathology group, although the mild group was on average 10.5% larger on the affected side. In contrast Arokoski et al (2002) reported that the CSA of the TFL muscle was 13% smaller on the more affected side in men with OA. This difference is again most likely due to differences in subject selection and/or measurement technique.

Another important consideration when interpreting side to side differences in muscle size is that in the absence of longitudinal data, the determination of side to side differences as atrophy or hypertrophy around weight-bearing joints must be approached with caution. Side to side differences could reflect either atrophy or hypertrophy. Decreases in muscle size on the affected side could occur in response to pain (Lund et al 1991) or reflex inhibition (Stokes & Young 1984). However, as pain causes an instinctive shift in weight-bearing towards the unaffected side, side to side volume differences may occur due to disuse atrophy around the affected hip and/or overuse hypertrophy of the unaffected side. For this reason, a control group was included for comparison of actual muscle volumes between groups, thereby assisting in the interpretation of side to side differences.

Differences in muscle volumes between groups

As with the Arokoski et al study (2002), the current study was unable to demonstrate any between group difference in LGM size. This may be due simply to the inherent variability within the population and the relatively small sample size. Another consideration is the fact that the measurement of muscle size by tracing around the perimeter of a muscle in the subjects with pathology of the hip joint may underestimate the loss of contractile muscle tissue. Replacement of normal viable muscle tissue with intramuscular fatty or connective tissue has been reported as ‘fatty atrophy’ at the hip in the gluteus medius muscle (Pfirrmann et al 2005). Differences in tissue quality of the LGM muscle are observable as increased black markings within the muscle on the side of the affected hip in Fig 1D and 1F. This assists in the support of the assumption that side to side differences in the LGM muscle in those with hip pathology are at least in part due to atrophy around the affected hip. It is most likely however that together with atrophy around the affected hip, there may be concurrent hypertrophy of the unaffected side LGM secondary to patterns of antalgic weight shift. The finding that advanced group subjects LGM volumes were 15.2% larger on the unaffected side than matched control subjects (p=0.12), provides some support for this effect although not reaching statistical significance.

Between group differences for the UGM muscle showed that the mean muscle volume of the UGM muscle on the unaffected side in those with advanced pathology was significantly (Mean difference 30.5%) larger than the corresponding muscles in the control group subjects. This finding suggests that the significant asymmetry (Mean difference 21%) observed in subjects with advanced joint pathology may be largely attributable to hypertrophy on the unaffected side. Some degree of atrophy on the affected side however cannot be discounted although fatty atrophy was not commonly observed in the UGM muscle. Around the affected hip neither the UGM muscle, or the other superficial hip abductor, the TFL muscle, were significantly different in size to a normal population.

The other information that was assessed with regard to the subjects of this study was gathered through self report questionnaires and leg dominance testing. While pain, function and leg dominance had no significant effect on GM or TFL muscle size, the information collected provided 2 important pieces of information.

Pain, function & radiological change

The first of these relate to the association between pain, function, and radiological change.

It has been previously noted that there is often no clear relationship between severity of radiological change in an osteoarthritic joint and severity of pain or degree of disability (Hurley 1999). In studies of subjects with OA of the knee, advanced radiological change may in some people be accompanied by very little pain, while others with only mild degenerative change may experience severe disabling pain (Claessens et al 1990; McAlindon et al 1993). Arokoski et al (2002) in their study of men with OA of the hip were unable to demonstrate a correlation between grade of severity of OA and pain measured on a visual analogue scale. There was however significantly more pain within individuals on the side with the highest radiographic OA score. Similarly the findings of the current study reflect the difficulty in linking a pain score alone to degree of radiographic change. By combining measures of pain and function, the Modified Harris Hip Score was able to demonstrate significant differences between subjects with early radiographic change and those with advanced radiographic change. This may suggest that this particular combination of questions may be more sensitive to degree of radiographic change than those available for OA of the knee.

The influence of leg dominance

The second finding of importance relates to the potentially confounding variable of leg dominance. Although there is evidence that dominance has an effect on muscle strength (Balogen & Onigbinde 1992), particularly in upper limb strength in those involved in unilateral sports (Ducher et al 2005; Ellenbecker et al 2006), there is a much weaker link between leg dominance and muscle strength (Hunter et al 2000; Zakas 2006), and little evidence to link leg dominance to asymmetry in muscle size. Greater muscle strength of the dominant limb may be associated with improved neuromuscular functioning, rather than muscle size alone. In the current study the exclusion of all subjects involved in unilateral sports sought to avoid the effect of this potentially confounding variable on muscle symmetry. The results of this study were able to demonstrate that for the normal control subjects tested there was no significant asymmetry in muscle size for the muscles measured. All subjects were left stance dominant which, if this factor were imparting an effect, would favour a larger muscle volume on the left side particularly for the weightbearing LGM muscle. This was not the case, allowing greater clarity in interpretation of results for the pathology groups.

Possible Clinical Implications

The balance of muscle activity around a joint may either protect a joint from injury or accelerate destructive joint forces. Both the UGM and LGM muscles are known to be active at heel strike in gait to help absorb ground reaction forces causing lateral pelvic drop and flexion moments at the hip and knee (Stern et al 1980, Lyons et al 1983). While reduced activation of the GM muscle may fail to absorb these ground reaction forces, excessive activation in the abductor muscles, may lead to an increase in joint loading (Krebs et al 1998). So both atrophy of the LGM muscle around the affected hip, and hypertrophy of the UGM muscle around the unaffected hip may have negative effects on their respective underlying joints. Hurley (1999) has suggested that the presence of bilateral muscle dysfunction may help explain why unilateral OA years later often becomes bilateral OA. The findings of this study imply that the LGM and UGM muscles should be assessed individually, and on both sides, with clinical management directed towards restoring normal symmetrical weight-bearing patterns and muscle bulk.

Further, the finding that neither of the superficial hip abductor muscles appear to be affected on the side of pathology, and recommendations to reduce recruitment of the hip abductor muscles in order to reduce peak acetabular pressures during gait (Krebs et al 1998), the current clinical rationale for generalised hip abductor muscle strengthening could be questioned. While some authors have reported hip abductor muscle strength deficits of up to 31% (Arokoski et al 2002, Jandric 1997, Murray & Sepic 1968), others have reported no significant difference (Sims 2002, Teshima 1994). These variable findings may be a reflection of the relative degrees of atrophy of individual muscles of the abductor synergy. If both superficial abductor muscles are not significantly affected by pathology, strength changes may possibly reflect weakness in the deeper abductor muscles. Together with the information provided by this study, further information on the response of the deep muscle system to degenerative change of the hip may provide further insight into specific changes within the abductor synergy. Greater specificity in exercise prescription around the hip may allow development of interventions that achieve more significant and longer lasting changes in pain and function scores in patients with OA of the hip.

Limitations and Future Directions

The main limitation of this study was low subject numbers. Valuable additional information may be gained by subsequent studies with larger subject numbers and the inclusion of a method to measure quality of muscle tissue. Furthermore, this study assessed only two of many hip muscles which may be associated with hip pathology. Further investigation of other muscles, such as the deeper abductor muscles, is required to provide a more complete picture of muscle dysfunction.

Conclusion

This study has demonstrated that the gluteus maximus muscle should be considered as 2 functionally separate entities, the UGM a hip abductor and the LGM, a hip extensor, these muscles having differing responses to the presence of joint pathology. The UGM muscle like its functional counterpart, the TFL, is unaffected by the presence of joint pathology, while the LGM muscle demonstrates local atrophy. The lack of affect on the superficial hip abductors suggests that muscle weakness demonstrated in subjects with OA of the hip may be related to changes in the deeper hip abductors (GMED, GMIN and PIRI) and require more specific therapeutic exercise intervention.

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The Association Between Degenerative Hip Joint Pathology and Size of the Gluteus Medius, Gluteus Minimus, and Piriformis Muscles

1 Alison Grimaldi PhD, MPhtySt, BPhty
1
 Carolyn Richardson PhD, BPhty(Hons)
2 Warren Stanton PhD, BPsych
Gail Durbridge MAppSci, Grad Dip Ultrasound, DipAppSci Medical Radiography
2
 William Donnelly MBBS, FRACS
1,2 Julie Hides PhD, MPhtySt, BPhty.

 

  1. Division of Physiotherapy,
    School of Health and Rehabilitation Sciences,
    The University of Queensland,
    Brisbane, 4072, Australia
  2. The UQ/ Mater Back Stability Clinic
    Mater Health Services,
    Raymond Terrace, South Brisbane, Queensland, 4101, Australia
  3. Centre for Magnetic Resonance Imaging, Brisbane, Australia
  4. Brisbane Orthopaedic Specialist Services, Brisbane, Australia

PUBLISHED IN MANUAL THERAPY 14 (2009) 605-610    doi:10.1016/j.math.2009.07.004

 

ABSTRACT

This study aimed to investigate changes in the deep abductor muscles, gluteus medius(GMED), piriformis (PIRI), and gluteus minimus (GMIN), occurring in association with differing stages of unilateral degenerative hip joint pathology (mild: n=6, and advanced: n =6). Muscle volume assessed via magnetic resonance imaging was compared for each muscle between sides, and between groups (mild, advanced, control (n=12)). GMED and PIRI muscle volume was smaller around the affected hip in subjects with advanced pathology (p<0.01, p<0.05) while no significant asymmetry was present in the mild and control groups. GMIN showed a trend towards asymmetry in the advanced group (p=0.1) and the control group (p=0.076) which appears to have been associated with leg dominance. Between group differences revealed a significant difference for the GMED muscle reflecting larger muscle volumes on the affected side in subjects with mild pathology, compared to matched control hips. This information suggests that while GMED appears to atrophy in subjects with advanced hip joint pathology, it may be predisposed to hypertrophy in early stages of pathology. Assessment and exercise prescription methods should consider that the response of muscles of the abductor synergy to joint pathology is not homogenous between muscles or across stages of pathology.

INTRODUCTION

Osteoarthritis (OA) of the hip poses a considerable problem for modern society. As the incidence of OA of the hip increases with the aging population it has been declared by March and Bagga (2004) that ‘primary and secondary programs aimed at…improving rehabilitation and physical activity are urgently required’ in the management of OA. Therapeutic exercise programmes designed to improve muscle function around the affected hip will only be maximally effective when we have further information available on both normal muscle function, and changes occurring in association with joint disease.

Hip abductor muscle function has been a primary focus of research due to the importance of these muscles in performing single leg function, the basis of human locomotion. Patients with OA of the hip have demonstrated a change in pelvic-femur alignment during gait depending on stage of pathology. Those with mild OA demonstrate increased hip adduction during stance (Watelain et al., 2001), while those with more advanced changes reduce adduction by increasing frontal plane trunk movement (Krebs et al., 1998). The specific changes in abductor muscle function occurring in association with OA are however unclear at this point. While some authors have demonstrated reduced electromyographic (EMG) activity in the gluteus medius (GMED) muscle in subjects with OA of the hip (Long et al., 1993), others have shown increased EMG activity during dynamic function (Angielczyk and Bronarski 1982, Sims et al., 2002). EMG testing of the tensor fascia lata (TFL) muscle has shown similar inconsistency (Long et al., 1993, Sims et al., 2002). No EMG investigations of the other hip abductor muscles, upper gluteus maximus (UGM), gluteus minimus (GMIN) or piriformis (PIRI) muscles, in patients with OA of the hip, have been reported in the literature. Studies that have involved strength testing as a measure of hip abductor muscle function in subjects with OA of the hip, have used dynamometry to measure open chain isometric or isokinetic abduction strength, providing a global assessment of the abductor synergy (UGM, TFL, GMED, GMIN, PIRI). These studies have, like EMG studies, displayed considerable variability (Murray & Sepic 1968, Teshima 1994, Jandric 1997, Arokoski et al., 2002, Sims et al., 2002). The body of literature to date thus provides an incomplete and unclear picture of hip abductor muscle dysfunction. More specific information on patterns of change within the abductor synergy is required.

The use of magnetic resonance imaging (MRI) provides an opportunity to assess each individual member of the abductor synergy simultaneously. One previous MRI study assessed cross sectional area (CSA) of the abductor muscles in subjects with OA of the hip, however most of the muscles were grouped together providing a global measure of abductor muscle size (Arokoski et al., 2002). In addition, single CSA measurements are unlikely to be as reflective of a muscle’s morphology as a measurement of muscle volume. The research undertaken by the current authors used MRI to assess muscle volume of each individual member of the abductor synergy in subjects with OA of the hip. This has been presented as two papers with muscles divided on an anatomical basis. An initial study (Grimaldi et al., In Press) investigated changes present in the superficial lateral musculature (UGM and TFL) that insert into the iliotibial band (Williams et al., 1989). The TFL was unaffected by the presence of joint pathology, while the UGM demonstrated asymmetry in subjects with advanced unilateral OA that appeared to be more closely related to hypertrophy of the unaffected side, than atrophy around the affected hip (Grimaldi et al., In Press).

The main aim of the current study was to investigate in these same subjects, size of the muscles of the deep lateral stability mechanism of the hip, the GMED, GMIN, and PIRI muscles, that assert their effect via direct insertion into the greater trochanter. Subjects with either mild or advanced unilateral degenerative pathology of the hip were chosen for maximum clarity of effect. The specific aims were to examine i) if there was significant asymmetry in the deep abductor muscles across 3 groups (mild degenerative change, advanced degenerative change, control) and ii) if there were significant differences in actual muscle size among the pathology and control groups. This study also examined the association of both stage of pathology, and muscle size, with the factors of age, height, weight, pain, function and activity levels. Leg dominance was also tested as all of these factors were considered to have the potential to impact upon muscle size and symmetry.

The hypotheses of the study were that ia) there would be significant asymmetry in size of the GMED, GMIN, and PIRI in subjects with hip joint pathology, but not in controls, ib) asymmetry would be greater in subjects with advanced pathology, and ii) the GMED, GMIN and PIRI muscles would be smaller around the affected hip in those with advanced pathology compared to the matched hip of control subjects.

METHODS

Subjects

Twelve subjects with degenerative hip joint pathology, and twelve age and sex matched control subjects were recruited for this study via medical practitioners and community advertisement. Control group subjects were required to be within 5 years of the age of their matched subject with joint pathology. Each group had equal numbers of males and females and all participants gave their informed consent to participate in this study after receiving detailed information on the study. Ethical approval was provided by the institutional review boards.

Inclusion criteria required subjects with pathology to have a medical diagnosis of unilateral degenerative joint pathology, and radiographic evidence of their pathology. Subjects with OA were recruited for either a ‘Mild’ or an ‘Advanced’ group. Those determined by an experienced radiologist to have early joint space narrowing and osteophytes (Kellgren/Lawrence (K/L) global scoring system grades 1-2 (Kellgren & Lawrence, 1957, Hirsch et al., 1998) were included in the mild group. Subjects with moderate to severe joint space narrowing and osteophytes (K/L grades 3-4) were recruited for the advanced group. Pathology was right sided for 5 subjects and left for 7 subjects. An analysis of variance (ANOVA) reported previously for these subjects determined that there was comparability between the mild, advanced and control group subjects for the factors of age, height and weight (Grimaldi et al., In Press). Details of subject characteristics are listed in Table 1.

Table 1
Subject characteristics for each group

Group No Sex M:F Age
Mean (SD)
Weight(kg)
Mean (SD)
Height(cm)
Mean (SD)
BMI
Mean (SD)
Mild 6 3:3 46.5 (9.5) 80.4 (15.1) 171.3 (9.7) 27.3 (3.5)
Adv 6 3:3 57.7 (6.7) 78.3 (8.5) 172.0 (7.4) 26.6 (4.4)
Con 12 3:3 51.8 (9.7) 73.5 (13.3) 168.2 (10.2) 25.9 (3.3)

Exclusion criteria included any factors that may represent confounding variables for muscle size or asymmetry such as systemic diseases of the muscular of nervous systems, congenital or childhood hip disease, any history of hip trauma, surgery, inflammatory joint disease, tumours, or lower limb or lower back injury within 2 years of testing. In addition subjects were excluded if they reported any significant lifetime history of lower back pain that resulted in a period of immobility, investigation, or treatment. Subjects were also excluded in both groups if they reported participation in unilateral sports, use of a walking aid, or any problems that would preclude them from MRI scanning procedures (eg. pacemaker, metal implants, pregnancy, claustrophobia). Control group subjects must have had no history of pain in the hip region.

Procedure

Self-Report Questionnaires. Subjects activity levels were rated using a 12 month Leisure Time Physical Activity questionnaire providing an activity metabolic index (AMI) calculated with the formula: AMI = Intensity code (mean metabolic units) x average number of times the activity is performed per month x the number of months per year (frequency) x the time the activity was performed per occasion (duration). AMI for each activity is added so total AMI is compared across individuals (Taylor et al., 1978, Arokoski et al., 2002). A previously reported ANOVA for these subjects found no significant differences between groups for metabolic activity (Grimaldi et al., In Press). Pain and function were also assessed for pathology groups using the Modified Harris Hip Score (MHHS) (Byrd & Jones 2000). This analysis has been reported in a prior paper revealing a significantly lower score for the advanced group (p<0.05), reflecting higher pain and lower function (Grimaldi et al., In Press). The relationship between pain, function, and radiographic change has been discussed in detail in the same paper.

Testing of Leg Dominance. Leg dominance during kicking function was tested with the weight-bearing leg recorded as “stance dominant” and the kicking leg as the “skill dominant” leg (Herneth et al., 2004). All subjects in this study were left stance dominant.

Table 2
Intra-rater reliability across repeated measurement for the same image sequence for gluteus medius (GMED), glutteus miimus (GMIN) and pirpformis (PIRI) muscles.

 

Muscle ICC2,1 (95% CI) Weight(kg)
Mean (SD)
Height(cm)
Mean (SD)
GMED 0.998 (0.997 – 0.999) 0.506 7.86
GMIN 0.997 (0.994 – 0.998) 0.379 3.72
PIRI 0.985 (0.955 – 0.995) 0.675 6.74

Intraclass correlation coefficient (ICC), (95% confidence interval at p<0.05); Standard error of measurement (SEM); Standard deviation of the difference (SDD).

 

MRI Assessment. After medical screening for suitability for MRI procedures subjects were positioned in supine with their legs extended to a neutral position. A 1.5 Tesla Siemens Sonata MR system was employed to collect a T2 True FISP sequence using 2 series of 28 x 6 mm contiguous slices throughout the pelvis (TR: 3.78ms/TE:1.89ms/FOV:390mm).

Measurement Procedure. CSA (cm2) of GMED, GMIN and PIRI muscles was measured by tracing each muscle on each slice using an MRI measurement software package (Osiris Version 4.19, University Hospitals of Geneva, Switzerland). Muscle volume (cm3) was determined as the sum of the muscles CSA on each slice in which the muscle appeared, multiplied by the slice width (Fukunaga et al., 1992, Alkner & Tesch 2004).

Reliability of the assessor’s measurement technique was tested by retracing all slices of one subject with an interim period of 6 weeks. Intra-tester reliability was tested for each separate measurement on each slice using a two sided bootstrapped interval of intraclass correlation coefficient (ICC2,1). Intra-rater reliability was found to be very good, with correlation coefficients ranging from 0.985 to 0.989. Standard error of measurement (SEM) was calculated using the formula SEM= pooled SD x (1-ICC)½ (Wallwork et al., 2007). Standard deviation of the difference (SDD) was also calculated as the standard deviation of the differences between measurement 1 and 2. ICC, SDD and SEM values are presented in Table 2.

Statistical Analysis

Analysis was performed using the Statistical Package for the Social Sciences (version 14; www.spss.com). The first analysis addressed the issue of symmetry in muscle size between sides across the 3 groups. A comparison of muscle volumes among groups and between sides was performed using a mixed linear model describing muscle volume with group as a between-subjects factor (control, mild, advanced), and side (affected/unaffected for the pathology groups; left/right for the control group) as a within-subjects factor (Dependant variable: muscle volume; Independent variables: side, group). Each muscle (GMED, GMIN, PIRI) was analysed separately. Contrasts of means were performed to compare sides within groups.

Further analysis was conducted to assess whether control group subjects had larger hip abductor muscles than subjects with hip pathology. Separate ANOVAs were conducted for each side to compare muscle volumes across groups. Side comparisons were determined via the following method: if the pathological side was left, the left side muscle volume of the matched control subject was used for comparison, and the right compared with the unaffected side value of the pathology group counterpart. The dependant variable was muscle volume and the independent variable was group. Each muscle (GMED, GMIN, PIRI) was analysed separately, and contrasts of means were performed to compare size across groups.

For ease of presentation of results, percent differences were calculated using the formula: % Difference= [ (larger value-smaller value)/larger value] * 100 (Hides et al., 1996).

Analyses were also conducted to assess participant characteristics in relation to the extent of association with muscle size. The association between the patient characteristics of age, height, weight, pain, function, and AMI and GMED, GMIN, or PIRI muscle size was assessed using analysis of covariance.

RESULTS

Side to side differences in muscle volumes within groups

There was no significant asymmetry in the control group for GMED, GMIN or PIRI muscle volume, although there was a trend for the GMIN muscle to be larger on the left side (p=0.076, 9 of 12 control subjects larger on the left). No significant differences were observed for any of the muscles studied for the mild group. GMED and PIRI were both significantly smaller on the affected side for subjects with advanced pathology (t=2.951, p=0.008; t=2.195, p=0.03 respectively). Although comparisons of GMIN muscle volume did not reach statistical significance, there was a trend for asymmetry in the advanced group (p=0.1) with smaller GMIN size around the affected hip (mean 8.3% smaller). Five of the 6 subjects in this group were on average 21.5% smaller on the affected side, with one subject demonstrating a 48% larger GMIN muscle volume on the affected side.

Means, standard deviations, and percentage difference in muscle volumes are reported for each group in Table 3. Examples of side to side differences are illustrated for each group in Figure 1.

Differences in muscle volumes between groups

Comparisons between groups revealed that the GMED muscle was significantly larger (mean 15%) around the affected hip in the mild group, compared with the same hip of the matched control subjects (p=0.026). No differences were evident between groups for the GMIN or PIRI muscles.

Effect of subject characteristics on muscle size

There was no significant relationship between the patient characteristics of age, height, weight, and metabolic activity, or pain and function, and GMED, GMIN or PIRI muscle volume (p>0.05).

DISCUSSION

This study investigated the influence of degenerative hip joint pathology on size of the deep abductor muscles, GMED, GMIN and PIRI.

Group Side GMED
Mean (SD)
GMIN
Mean (SD)
PIRP
Mean (SD)
Mild
(n = 6)
Affected
Unaffected
% Difference
369
367
0.4%
(63)
(62)
87
95
7.9%
(23)
(32)
28
29
2.6%
(10)
(14)
Advanced
(n = 6)
Affected
Unaffected
% Difference
317
361
12% **
(94)
(71)
84
91
8.2%
(34)
(33)
28
33
14.4% *
(8)
(8)
Control
(n = 12)
Affected
Unaffected
% Difference
317
305
3.7%
(75)
(88)
86
79
8.3%
(21)
(21)
28
28
0.4%
(8)
(8)

Gluteus medius muscle (GMED); Gluteus minimus muscle (GMIN); Piriformis muscle (PIRI); Standarddeviation (SD); * p<0.05; ** p<0.01.

Table 3
Muscle volumes (cm3) for gluteus medius, gluteus minimus, and piriformis muscles, and percentage difference between sides

 

Figure 1: The gluteus medius muscle (), gluteus minimus muscle (), and piriformis muscle () in axial images above the hip joint in control group subject (A), and subjects with mild left osteoarthritis (B), and advanced left osteoarthritis (C). White dot indicates left ilium.
Figure 1:The gluteus medius muscle orange_bar, gluteus minimus muscle blue_bar, and piriformis muscle purple_bar in axial images above the hip joint in control group subject (A), and subjects with mild left osteoarthritis (B), and advanced left osteoarthritis (C).White dot indicates left ilium.
Side to side differences in muscle volumes within groups
Side to side differences in muscle volumes within groups

Although subjects with mild degenerative hip joint pathology were not significantly asymmetrical, those with advanced pathology demonstrated significant asymmetry for the GMED and PIRI muscles with smaller muscle volumes around the affected hip (mean 12%, p<0.01 & mean 14.4%, p<0.05 respectively). This is consistent with the changes in gait pattern at this stage of pathology (Krebs et al., 1998). Peak acetabular pressures have been shown to coincide with peak GMED activity rather than peak ground reaction forces (Krebs et al., 1998). The associated increases in lateral trunk flexion over the weight-bearing leg during stance phase of gait was proposed to be a strategy to reduce abductor muscle activity, thereby reducing compressive forces across painful degenerated joint surfaces. This functional disuse would be in line with the muscle atrophy illustrated in the current study. Part of the asymmetry revealed may also be accounted for by hypertrophy of these muscles on the unaffected side as this side becomes favoured for weight-bearing function.

Despite a lack of statistically significant asymmetry in the deepest abductor muscle, GMIN, there was a trend towards asymmetry in the advanced group (mean 8.3% smaller on affected side, p=0.1). The importance of this trend is further highlighted when the removal of a single subject results in an asymmetry reflecting an average 21.5% smaller GMIN muscle volume on the affected side. The reason for the lack of atrophy around the affected hip in the remaining subject is unclear. This subject did remain very active with an AMI just below the average for normal control subjects, which may provide some explanation for this variation. Without this subject there is a clear pattern of asymmetry, smaller on the affected side, in the majority of the advanced pathology group. Atrophy in this deepest hip abductor muscle would be consistent with atrophy evident in other local muscles involved in joint protection, such as the multifidus muscle in the lumbar spine (Hides et al., 1994), although some concurrent hypertrophy on the unaffected side cannot be excluded.

The other consideration in the interpretation of results for the GMIN muscle is the trend towards GMIN asymmetry, larger on the left side, in control subjects (p=0.076). This asymmetry may be related to leg dominance as all subjects were left stance dominant. The GMIN muscle may be particularly important in weight-bearing function to assist in joint protection and stabilisation of the femoral head in the acetabulum (Beck et al., 2000, Walters et al., 2001). The relevance of this trend towards asymmetry in control group subjects is that for subjects with left sided hip joint pathology, the loss of muscle size may be underestimated.

The only other study to date to investigate symmetry of hip abductor muscle size in subjects with OA of the hip showed a 6% smaller CSA of the ‘gluteal muscles’ around the most affected hip in those with unilateral or bilateral OA (Arokoski et al., 2002). Although the general picture is consistent with our findings the combined measure of all hip abductor muscles is difficult to directly compare to that of the present study.

Differences in muscle volumes between groups

Differences in muscle volumes between groups were not significant for PIRI and GMIN muscles, consistent with the lack of between group difference (OA & control) reported by Arokoski et al (2002). A significant difference between control and mild pathology groups for the GMED muscle however, provides some important information for understanding changes occurring in this muscle, and inconsistencies in previous EMG research. For subjects with mild joint pathology, GMED muscle volume of the affected side was on average 16% larger than those of normal control subjects (p<0.05). This information may indicate that the GMED muscle could be more predisposed to hypertrophy rather than atrophy in the early stages of joint pathology. This could help explain why subjects with early OA of the hip exhibit higher levels of EMG for this muscle (Sims et al., 2002), while patients just prior to arthroplasty exhibit reduced GMED EMG activity (Long et al., 1993).

Differing gait patterns may provide some further explanation for the apparent disparity in GMED response across stages of joint pathology. As GMED muscle atrophy appears inherently linked to offloading strategies used in gait during late stage joint pathology (Krebs et al., 1998), GMED muscle hypertrophy may occur in early joint pathology associated with increases in relative hip adduction (Watelain et al., 2001). Kumagai et al (1997) determined that the GMED muscle provides maximal contribution to abduction force from a position of 20° hip adduction and more specifically, the most superficial, ‘middle’ portion of the GMED muscle is more active in a position of hip adduction than the deeper anterior and posterior portions (Figure 2), and the GMIN muscle, which are favoured in a more neutral hip position. Increasing pelvic tilt or lateral shift to a position of increased adduction may be an inherent compensatory strategy to increase the contribution from the more superficial abductors to lateral pelvic support. This alignment not only creates preferential recruitment in the superficial portion of the GMED muscle, but also pretensions the iliotibial band potentially increasing the effect of the TFL and UGM muscles.

Figure 2: The three separate portions of the gluteus medius muscle. Anterior (A), Middle (M), Posterior (P).
Figure 2: The three separate portions of the gluteus medius muscle. Anterior (A), Middle (M), Posterior (P).

As the GMED muscle is composed of 3 fascially distinct portions, anterior and posterior portions sitting deep to the middle portion (Jaegers et al., 1992) (Figure 2), all with independent nerve supply (Gottschalk et al., 1989), it is possible that while the overall volume of the GMED muscle increased, the deeper anterior and posterior portions may be responding differently to their superficial counterpart.

Possible Clinical Implications

Information from this and our previous study (Grimaldi et al., In Press) together demonstrate that the abductor synergy does not respond homogenously to joint pathology. While the deeper abductor muscles GMED, PIRI and GMIN demonstrate atrophy in subjects with advanced OA, superficial abductor muscles UGM and TFL appear less affected by underlying pathology. Another finding of important clinical significance is that the GMED muscle may hypertrophy in patients with mild joint pathology. In light of the fact that peak acetabular pressures during gait are associated with peaks in GMED muscle activity (Krebs et al., 1998), non specific exercise programmes focusing on generalised abductor strengthening may need to be reassessed. Programmes assessing and retraining specific portions of the abductor synergy, with particular attention to pelvic-femur alignment, may be most effective in both rehabilitation and prevention strategies. Real time ultrasound has been used successfully for assessment and specific rehabilitation of deep trunk musculature (Stokes et al., 1997, Painter et al., 2007). This tool also holds great potential for use in assessment and retraining of deeper members of the hip abductor synergy.

Limitations and Future Directions

This study provides information from only a small subject population. This may have impacted on our ability to demonstrate significant differences in muscle size in subjects with mild pathology. The other factor that may have resulted in underestimation of muscle loss is the technique of measuring around the circumference of a muscle. This technique does not account for replacement of viable muscle tissue with intramuscular fatty or connective tissue. As fatty atrophy has been shown to be unevenly distributed within the GMED and GMIN muscles (Pfirrmann et al., 2005) however, the use of a volume measurement should provide the most valid estimation of muscle size in comparison to a single CSA.

Furthermore in the early stages of pathology motor control changes are likely to preempt changes in muscle size. Future research aimed at quantifying not only size, but ideally concurrent dynamic EMG activity of each member of the abductor synergy, including the functionally separate portions within the GMED muscle, may be able to elucidate the specific functions and exercise requirements for muscles of the abductor synergy.

CONCLUSION

This study has shown that the deeper members of the hip abductor synergy, the GMED, GMIN, and PIRI muscles are smaller around the affected hip in subjects with advanced unilateral hip joint pathology. This atrophy was not measurable in subjects with mild pathology, however differing processes are likely in place associated with differing functional weight-bearing patterns. In subjects with mild pathology GMED muscle size was significantly larger on the affected side than control group subjects suggesting the GMED muscle may hypertrophy at this stage of pathology. Assessment and rehabilitation strategies should carefully consider stage of pathology and specific changes occurring within the abductor synergy. This more specific approach may improve long term outcomes of conservative intervention in the management of OA of the hip, and may provide a direction for future prevention programmes.

 

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Utility of clinical tests to diagnose MRI-confirmed gluteal tendinopathy in patients presenting with lateral hip pain

bmjbjsmpubcoverAlison Grimaldi1,2, Rebecca Mellor2, Phillipa Nicolson3, Paul Hodges4, Kim Bennell3, Bill Vicenzino2,4

1Physiotec Physiotherapy, Tarragindi, QLD, Australia,2School of Health & Rehabilitation Sciences St Lucia, The University of Queensland QLD, Australia, 3Centre for Health and Exercise Science, University of Melbourne, Parkville, VIC, Australia,4NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, Brisbane, Queensland, Australia.

ABSTRACT

Purpose. Gluteal tendinopathy (GT) is a source of lateral hip pain, yet common clinical diagnostic tests have limited validity. Patients with GT are often misdiagnosed, resulting in inappropriate management, including surgery. This study determined the diagnostic utility of clinical tests for GT, using MRI as the reference standard

Methods. 65 participants with lateral hip pain were examined to evaluate the ability of clinical tests to detect MRI-determined GT (an increase in intratendinous signal intensity on T2-weighted images). Palpation of the greater trochanter and several clinical pain provocation tests applying compressive and tensile loads on the gluteal tendons were investigated. MRI of the painful hip was examined by a radiologist, blind to clinical findings.

Results. Pain reported within 30 s of standing on the affected limb conclusively moves a (nominal) 50%pretest probability of GT presence on MRI to a post-test probability of 98% (specificity 100%, positive likelihood ratio ∼12), whereas no pain on palpation (80%sensitivity) would rule out its presence. 20 participants (31%) had GT on MRI but clinically negative (ie, not positive on palpation and another test).

Conclusion. Keeping in mind that the sample size was small (ie, possibly underpowered for indices of diagnostic utility with low precision), the results of this study indicate that a patient who reports lateral hip pain within 30 s of single-leg-standing is very likely to have GT. Patients with lateral hip pain who are not palpably tender over the greater trochanter are unlikely to have MRI-detected GT.

Conclusion. Keeping in mind that the sample size was small (ie, possibly underpowered for indices of diagnostic utility with low precision), the results of this study indicate that a patient who reports lateral hip pain within 30 s of single-leg-standing is very likely to have GT. Patients with lateral hip pain who are not palpably tender over the greater trochanter are unlikely to have MRI-detected GT.

Published in BJSM Online First on September 15, 2016 as 10.1136/bjsports-2016-096175

Link: http://bjsm.bmj.com/content/early/2016/09/15/bjsports-2016-096175.abstract

Listen to the BJSM Podcast with Dr Alison Grimaldi that discusses assessment and management of gluteal tendinopathy

Link: https://soundcloud.com/bmjpodcasts/dr-alison-grimaldi-with-practical-physiotherapy-tips-on-treating-lateral-hip-pain?in=bmjpodcasts/sets/bjsm-1#t=0:00