Objective
This study aims to develop hip morphology-based radiographic hip osteoarthritis (RHOA) risk prediction models and investigates the added predictive value of hip morphology measurements and the generalizability to different populations.

Methods
We combined data from nine prospective cohort studies participating in the Worldwide Collaboration on OsteoArthritis prediCtion for the Hip (World COACH) consortium. RHOA grades were harmonized, and incident RHOA was defined as hips without definite RHOA at baseline that developed definite RHOA within four to eight years. Baseline hip morphology was quantified with automatically and uniformly determined lateral center edge angle and alpha angle measurements on anteroposterior radiographs. Discriminative performance of generalized linear mixed model (GLMM) definitions with and without hip morphology measurements was determined with stratified cross-validation. With leave-one-cohort-out cross-validation, the generalizability to unseen populations of hip morphology–based GLMMs and random forest (RF) models was evaluated.

Results
From the included 35,984 hips without definite RHOA at baseline, 4.7% developed incident RHOA within four to eight years. The GLMM with cohort-specific intercept, considering baseline demographics, RHOA grade, and hip morphology measurements, showed a mean area under the receiver operating characteristic curve (AUC) of 0.80 (±0.01) in stratified cross-validation. Using a marginal intercept decreased performance by 0.1 in AUC. Similar results were found for a GLMM without hip morphology measurements. Leave-one-cohort-out cross-validation showed comparable discrimination (AUC between 0.56–0.88) and calibration performance for hip morphology-based GLMMs and RF models.

Conclusion
In hips free of definite RHOA, our AUCs for the incident RHOA models showed good predictive performance in similar populations. However, the added predictive value of the morphology measurements was small, and model performance was heterogeneous in leave-one-cohort-out cross-validation.

Objective
To study the association between various radiographic definitions of acetabular dysplasia (AD) and incident radiographic hip osteoarthritis (RHOA), and to analyze in subgroups.

Methods
Hips free of RHOA at baseline and with follow-up within 4–8 years were drawn from the World COACH consortium. The Wiberg center edge angle (WCEA), acetabular depth width ratio (ADR), and the modified acetabular index (mAI) were calculated. AD was defined as WCEA≤25°, and for secondary analyses as WCEA≤20°, ADR ≤250, mAI ≥ 13°, and a combination. A logistic regression model with generalized mixed effects with 3 levels adjusted for age, biological sex, and body mass index (BMI) was used. Descriptive statistics stratified by age, biological sex and BMI were reported.

Results
A total of 18,807 hips from 9 studies were included. Baseline characteristics: age 61.84 (± 8.32) years, BMI 27.40 (± 4.49) kg/m², 70.1% women. 4766 hips (25.3%) had WCEA≤25°. Within 4–8 years (mean 5.8 ±1.6) follow-up, 378 hips (2.0%) developed incident RHOA. We found an association between AD and RHOA (adjusted OR [aOR] 1.80 95% confidence interval [CI] 1.40–2.34). In secondary analyses, all other definitions of AD were also associated with incident RHOA (aOR ranging from 1.52 95% CI 1.19–1.94 to 1.96 95% CI 1.26–3.02). Descriptive statistics showed that the relative risk (RR) in AD hips to develop RHOA was higher compared to non-AD hips in age group 61–70 (RR 1.70), BMI<25 (RR 1.66), and in female hips (RR 1.73).

Conclusion
AD was consistently associated with incident RHOA. Explorative analyses show that AD hips in women and age group 61–70 years seem to be more at risk of developing RHOA compared to non-AD hips.

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.

Purpose Hip osteoarthritis (OA) is a major cause of pain and disability worldwide. Lack of effective therapies may reflect poor knowledge on its aetiology and risk factors, and result in the management of end-stage hip OA with costly joint replacement. The Worldwide Collaboration on OsteoArthritis prediCtion for the Hip (World COACH) consortium was established to pool and harmonise individual participant data from prospective cohort studies. The consortium aims to better understand determinants and risk factors for the development and progression of hip OA, to optimise and automate methods for (imaging) analysis, and to develop a personalised prediction model for hip OA. Participants World COACH aimed to include participants of prospective cohort studies with ≥200 participants, that have hip imaging data available from at least 2 time points at least 4 years apart. All individual participant data, including clinical data, imaging (data), biochemical markers, questionnaires and genetic data, were collected and pooled into a single, individual-level database. Findings to date World COACH currently consists of 9 cohorts, with 38 021 participants aged 18–80 years at baseline. Overall, 71% of the participants were women and mean baseline age was 65.3±8.6 years. Over 34 000 participants had baseline pelvic radiographs available, and over 22 000 had an additional pelvic radiograph after 8–12 years of follow-up. Even longer radiographic follow-up (15–25 years) is available for over 6000 of these participants.