Why is this study important?
Hip osteoarthritis (OA) is a highly prevalent and debilitating condition with significant socioeconomic costs, and current management is largely reactive due to a lack of curative treatments (1). A potential causal risk factor is cam morphology, an extra bone growth at the femoral head-neck junction (2). While previous studies have linked cam morphology to an increased risk of radiographic hip osteoarthritis (RHOA), the reported strength of this association varies widely, limiting its generalizability and clinical utility. This large-scale individual participant data (IPD) meta-analysis was conducted to provide a more robust and generalizable estimate of this relationship using standardized measurements and a strict definition of disease onset.

How did the study go about this?
We performed an IPD meta-analysis using data from the Worldwide Collaboration on Osteoarthritis Prediction for the Hip (World COACH) consortium, which included 23,886 hips from nine prospective cohort studies (3). All hips were free of RHOA at baseline. Cam morphology was uniformly and automatically measured on anteroposterior pelvic radiographs, defined by an alpha angle ≥60°. The primary outcome was the development of incident RHOA over a 4- to 8-year follow-up period. The association was assessed using a three-level mixed-effects logistic regression model to account for clustering of hips within individuals and across different cohorts.

What did the study find?
Our analysis yielded several key findings. First, cam morphology was significantly associated with the development of RHOA. Hips with cam morphology had nearly twice the risk of developing RHOA compared with those without (odds ratio 1.87, 95% CI 1.36–2.59). Similarly, every degree increase in the continuous alpha angle was associated with higher odds of RHOA (Odds Ratio: 1.02, 95% CI: 1.01-1.03). Second, subgroup analyses revealed that this association was not uniform across all groups. The risk was particularly strong in males (Relative Risk: 2.50, 95% CI: 1.67-3.73) compared to females, and among individuals aged 51-60 years (Relative Risk: 2.15, 95% CI: 1.55-2.98).

What are the key take-home points?
This study provides robust evidence that cam morphology, as identified on standard AP pelvic radiographs, is a significant and independent risk factor for developing hip osteoarthritis within 4-8 years. These findings highlight cam morphology as a key target for primary prevention strategies—aimed at preventing its development during adolescence—and for secondary prevention—aimed at preventing the progression to RHOA in adulthood. Early identification of this morphological trait could enable targeted interventions, such as load management and education, to mitigate the future burden of hip OA.

Authors information

1. Jinchi Tang (j.tang2025@outlook.com)
2. Rintje Agricola (r.agricola@erasmusmc.nl)

Department of Orthopaedics and Sports Medicine, Erasmus MC, University Medical Center, Rotterdam, The Netherlands

References

1. Collaborators GBDO. Global, regional, and national burden of osteoarthritis, 1990-2020 and projections to 2050: a systematic analysis for the Global Burden of Disease Study 2021. Lancet Rheumatol 2023;5(9):e508-e22. doi: 10.1016/S2665-9913(23)00163-7 [published Online First: 20230821]
2. Agricola R, Waarsing JH, Arden NK, et al. Cam impingement of the hip: a risk factor for hip osteoarthritis. Nat Rev Rheumatol 2013;9(10):630-4. doi: 10.1038/nrrheum.2013.114 [published Online First: 20130723]
3. van Buuren MMA, Riedstra NS, van den Berg MA, et al. Cohort profile: Worldwide Collaboration on OsteoArthritis prediCtion for the Hip (World COACH) – an international consortium of prospective cohort studies with individual participant data on hip osteoarthritis. BMJ Open 2024;14(4):e077907. doi: 10.1136/bmjopen-2023-077907 [published Online First: 20240418]