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.
Keywords: Cam morphology; Radiographic hip osteoarthritis; Subtype.
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