Cam morphology is strongly and consistently associated with development of radiographic hip OA

Key points

1. 01Cam morphology (alpha angle over 60 degrees) roughly tripled the odds of developing incident radiographic hip OA at every follow-up.
2. 02Large cam morphology (alpha angle over 78 degrees) carried an even higher risk, especially for end-stage osteoarthritis.
3. 03The strength of the association stayed consistent across the 2-, 5-, 8-, and 10-year visits.
4. 04Absolute risk of developing radiographic OA in a cam hip climbed from 14.4% at 2 years to 69.2% at 10 years.
5. 05Because cam shape can be seen before any OA appears, it may be a useful target for early prevention.

How it was conducted

Design

Nationwide multicenter prospective cohort study (CHECK) with 2-, 5-, 8-, and 10-year follow-up

Participants

1002 individuals aged 45 to 65 with first-onset hip or knee pain or stiffness; 1514 baseline hips free of OA (KL grade under 2) analyzed

Exposure

Cam morphology defined as alpha angle over 60 degrees; large cam morphology as alpha angle over 78 degrees, measured on weight-bearing AP radiographs

Outcomes

Incident radiographic hip OA (KL grade 2 or higher, or total hip replacement) and end-stage OA (KL grade 3 or higher, or replacement)

Analysis

Logistic regression with generalized estimating equations at each visit plus Cox regression over 10 years, adjusted for age, sex, and BMI

What they found

• For incident radiographic OA, cam morphology gave adjusted odds ratios from 2.7 (95% CI 1.8 to 4.1) to 2.9 (95% CI 2.0 to 4.4) across follow-ups.
• For incident radiographic OA, large cam morphology gave adjusted odds ratios from 2.5 (95% CI 1.5 to 4.3) at 10 years to 4.2 (95% CI 2.2 to 8.3) at 2 years.
• For end-stage radiographic OA, cam morphology gave adjusted odds ratios from 4.9 (95% CI 1.8 to 13.2) to 8.5 (95% CI 1.1 to 64.4).
• For end-stage radiographic OA, large cam morphology gave adjusted odds ratios from 6.7 (95% CI 3.1 to 14.7) to 12.7 (95% CI 1.9 to 84.4).
• Cox regression over 10 years gave adjusted hazard ratios of 2.1 (95% CI 1.7 to 2.6) for incident OA and 4.1 (95% CI 2.5 to 6.8) for end-stage OA with cam morphology, and 2.1 (95% CI 1.5 to 2.8) and 5.8 (95% CI 3.4 to 9.9) respectively for large cam morphology.
• Baseline prevalence was 8.9% (134 hips) for cam morphology and 4.7% (71 hips) for large cam morphology; incident OA rose from 5.9% of hips at 2 years to 43.4% at 10 years.

Limitations

• Cam morphology was measured only on AP radiographs, which capture the femoral head-neck junction in a single coronal plane and may miss cam shapes in other planes.
• This is an observational cohort, so it shows association but cannot prove that cam morphology directly causes osteoarthritis.
• Some end-stage outcome estimates had very wide confidence intervals (for example an upper bound of 84.4), reflecting few events and imprecise effect sizes.
• Findings are radiographic and may not fully reflect symptoms, pain, or function experienced by patients.

Why it matters

For patients

If imaging shows a cam-shaped hip, you have a meaningfully higher chance of developing hip osteoarthritis over the coming decade, which is worth discussing with your clinician.

For clinicians

Measuring the alpha angle on a hip radiograph can flag patients at substantially elevated risk of radiographic OA, especially when the cam is large.

For readers

This decade-long cohort strengthens the case that hip bone shape is a durable, sizeable risk factor for osteoarthritis and a candidate target for prevention.