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.