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.