2 of 12 Top Hip Papers – The clinical relevance of FAI

PAPER 2: The Prevalence of Cam and Pincer Morphology and its Association with Development of Hip Osteoarthritis

With the explosion of research into femoroacetabular impingement (FAI), its prevalence and relationship to symptoms and development of osteoarthritis, this clinical commentary paper was timely, bringing together the evidence and commenting on the clinical relevance. There had been a dramatic increase in arthroscopic osteotomies being performed not just for symptoms, but also and sometimes only with the aim of joint preservation.

While osteoplasty aims to ‘correct’ cam (aspherical femoral head) and pincer (acetabular overcoverage of the femoral head) morphologies, the developing evidence suggests that although FAI was believed to result in hip symptoms and osteoarthritis (OA), that is not a consistent finding. Researchers demonstrated that cam and pincer morphology is highly prevalent in the general population and most people with such morphologies do not develop hip OA. Cam morphology appears to be most relevant, with odds of developing hip OA increasing with size of the cam (alpha angle). However, the relevance of pincer morphology is less clear, with no increased risk found for the development of hip OA.

Key learnings on the relevance of FAI:

Cam morphology

• develops during adolescence from 12 years, increasing until completion of growth
• athletic load is associated with development of cam morphology, with higher exercise loads in adolescence linked with higher alpha angles
• more common in males: 13 -72% of asymptomatic males compared to 0-11% of asymptomatic females
• increases the risk of OA with risk increasing with size of the cam (alpha angle)
• only 6% - 25% of those with cam morphology will develop hip OA within 5 to 19 years

Pincer morphology

• related to global overcoverage (coxa profunda – deep socket) or focal overcoverage (acetabular retroversion – acetabulum facing relatively more posteriorly)
• wide range of prevalence rates reported
• similar prevalence in males & females
• does not appear to play a role in the development of hip OA, with some evidence suggesting a protective effect (less likely to develop hip OA)

Further research is required to identify characteristics that may differentiate those with cam or pincer morphology who are more likely to develop symptoms and/or hip OA, helping clarify the relevance of FAI and bony shape. Risk is likely to be multifactorial, including both non-modifiable and modifiable risk factors. The authors suggest that identification of modifiable risk factors such as hip muscle strength, gait-pattern characteristics, and the type and amount of physical activities performed, will allow us to target these characteristics in the management and perhaps even prevention of joint disease.

There is some evidence growing currently with respect to impairments in those with FAIS, but much further high-quality research is needed to establish which factors when modified with rehabilitative approaches can alter symptoms and/or disease progression.