Severe pincer morphology is associated with incident hip osteoarthritis: Prospective individual participant data from 18 935 hips from the World COACH consortium

Objective To assess the relationship between pincer morphology and incident radiographic hip osteoarthritis (RHOA) and study-specific subgroups. Methods Hips completely free of RHOA at baseline and with follow-up within 4-8 years were drawn from the World COACH consortium. The lateral centre edge angle (LCEA) was calculated uniformly on all baseline radiographs. Moderate pincer morphology was defined as an LCEA ≥40°, and severe pincer morphology as an LCEA ≥45° in sensitivity analyses. The primary outcome was incident RHOA defined by a harmonised OA score. A logistic regression model with generalised mixed effects with three levels (within-cohort, within-person and within-hip side correlation) adjusted for age, biological sex and body mass index (BMI) was employed. Descriptive statistics are reported for age, biological sex and BMI. Results 18 935 hips from nine cohorts were included. 4894 hips (25.8%) had moderate pincer morphology. Within 8 years (mean 6.0±1.7 years), 352 hips (1.9%) developed RHOA. Moderate pincer morphology was not associated with RHOA (OR 1.15 (0.92-1.51)), whereas severe pincer morphology was significantly associated (OR 1.50 95% CI 1.05 to 2.15). Moderate pincer morphology in groups aged 40-50 (RR 2.67, 95% CI 1.43 to 4.95) and BMI ≥25 (RR 1.23 95% CI 0.98 to 1.71) had a higher risk compared with non-pincer hips. Women (RR 1.20 95% CI 0.93 to 1.56) with pincer morphology may be more at risk than men (RR 0.95 95% CI 0.57 to 1.58). Conclusion The odds of developing RHOA within 8 years for hips with severe pincer morphology are 1.5 times higher than pincer-free hips, whereas moderate pincer morphology was not significantly associated with RHOA. Further research is necessary to uncover high risk subgroups of pincer morphology.