Cam morphology and the risk of developing radiographic hip osteoarthritis within 8 years: an individual participant data meta-analysis of 23 886 hips from the world COACH consortium.

OBJECTIVE: To assess the relationship between cam morphology and the development of radiographic hip osteoarthritis (RHOA), overall and in subgroups based on age, biological sex and body mass index (BMI). METHODS: Hips with no RHOA at baseline and with available follow-up during 4-8 years were selected from the Worldwide Collaboration on Osteoarthritis PrediCtion for the Hip (World COACH) consortium. Alpha angles were uniformly measured on anteroposterior radiographs, with a threshold of 60° used to define cam morphology. Incident RHOA was defined as the transition from an RHOA-free state at baseline to definite diagnosis of RHOA at follow-up. The association between baseline cam morphology and the development of RHOA was assessed using a three-level mixed-effects logistic regression model, accounting for hip side, individual and cohort-level variation. RESULTS: A total of 23 886 hips were included (mean age: 62.2±8.4 years; 70.6% female; BMI: 27.4±4.5; mean time to follow-up: 6.1±3.0 years). Cam morphology was associated with RHOA (OR: 1.87, 95% CI 1.36 to 2.59), as was a greater alpha angle (OR 1.02, 95% CI 1.01 to 1.03 for every degree increase). The overall relative risk of developing RHOA in hips with cam morphology was 1.62 (95%CI 1.26 to 2.07), greatest for those aged 51-60 years (2.15, 95% CI 1.55 to 2.98) and higher in males (2.50, 95% CI 1.67 to 3.73), compared with females (1.75,95% CI 1.24 to 2.48). CONCLUSION: Hips with cam morphology have higher odds of developing RHOA within 4-8 years compared with hips without cam morphology. The relative risk was highest in subgroups of participants aged 51-60 years and in males, making cam morphology a potential target for primary or secondary prevention of RHOA.