The different subtypes of cam morphology as defined by statistical shape modeling and their relationship with the development of hip osteoarthritis: A nationwide prospective cohort study (CHECK) with 10 years follow-up

Objective: 

To determine if subtypes of cam morphology on anteroposterior radiographs exist using statistical shape modeling (SSM), and to assess their association with incident radiographic hip osteoarthritis (RHOA) within 10 years. 

Design: 

The nationwide prospective Cohort Hip and Cohort Knee (CHECK) study included 1002 participants aged 45–65 years with 10-year follow-up. Subtypes of cam morphology were defined as SSM-based shape variations of femoral head-neck junction that are associated with baseline cam morphology (alpha angle ≥60°). The association between each subtype in hips free of osteoarthritis at baseline (Kellgren & Lawrence (KL) grade <2) and incident RHOA (KL grade≥2, or a total hip replacement) was estimated using logistic regression at 10-year follow-up and stratified by sex. 

Results: 

In sex-combined group, but also for males and females separately, cam morphology subtypes were captured in modes 1, 3, 4, and 5 with odds ratios (ORs) ranging from 0.39 (0.27–0.58) to 2.25 (1.64–3.10). For sex-combined group, only mode 3, a flattened head-neck junction, was associated with incident RHOA (OR:1.14, 1.02–1.27). Males’ modes 1 and 3 and females’ modes 3 and 4 were associated with RHOA. Notably, the female mode 4, a slightly flattened neck but with subtle curvature, was significantly protective for RHOA (OR:0.88, 0.80–0.98). 

Conclusions: 

We identified four distinct morphological subtypes of cam morphology defined by alpha angle. Only some subtypes were found acting as risk factors for RHOA at 10-year follow-up, which differed between males and females. This highlights the need to study cam morphology beyond the alpha angle alone.