A large pooled analysis links a higher alpha angle on X-ray to later radiographic hip osteoarthritis, especially in men and people aged 51–60.
Cam morphology on baseline hip radiographs was linked to higher odds of developing radiographic hip osteoarthritis within 4–8 years. Risk rose as the alpha angle increased, even beyond a single cut-off. The association was strongest in males and in adults aged 51–60.
Quick summary
- What the study found: Cam morphology (alpha angle ≥60° on anteroposterior radiographs) and higher alpha angles were associated with incident radiographic hip osteoarthritis over 4–8 years.
- Why it matters: A simple radiograph-based measure may help flag higher-risk hips before osteoarthritis is visible, supporting earlier prevention planning.
- What to be careful about: Radiographs can underestimate cam morphology, the sample skewed older, and unmeasured factors (and other hip shapes) could also influence risk.
What was found
In the journal article Cam morphology and the risk of developing radiographic hip osteoarthritis within 8 years: an individual participant data meta-analysis of 23 886 hips from the world COACH consortium, researchers tested whether cam morphology predicted later radiographic hip osteoarthritis (RHOA).
They selected hips that had no RHOA at baseline and had follow-up radiographs 4–8 years later. Cam morphology was defined as an alpha angle of 60° or more on anteroposterior (AP) radiographs.
Across 23,886 hips, cam morphology at baseline was associated with incident RHOA at follow-up (odds ratio 1.87, 95% CI 1.36 to 2.59). A greater alpha angle also predicted higher odds of developing RHOA (odds ratio 1.02 per degree, 95% CI 1.01 to 1.03).
Absolute incidence was low but meaningfully different: 3.2% in hips with cam morphology versus 2.0% in hips without. The overall relative risk of developing RHOA in hips with cam morphology was 1.62 (95% CI 1.26 to 2.07).
Subgroup analyses showed higher relative risk in participants aged 51–60 (2.15, 95% CI 1.55 to 2.98). Risk was also higher in males (2.50, 95% CI 1.67 to 3.73) than females (1.75, 95% CI 1.24 to 2.48), with evidence that sex modified the association.
What it means
Cam morphology is a bony shape variant at the femoral head–neck junction. The alpha angle is a radiographic measure used to estimate how “non-spherical” that junction is; higher angles indicate more cam-like shape.
RHOA refers to osteoarthritis changes visible on radiographs, such as joint space narrowing and osteophytes. This study focused on new, definite RHOA developing after an initially RHOA-free baseline.
Practically, the signal is not that most people with cam morphology will develop hip osteoarthritis soon. It is that cam morphology shifts risk upward over the next several years, and risk appears more pronounced in some groups.
Where it fits
A key design choice here was excluding hips with definite or doubtful signs of RHOA at baseline. That matters because early osteoarthritis changes can blur cause and effect, and may distort alpha angle readings.
The authors also argue that AP radiographs are not a “gold standard” for characterising cam morphology, since cam shape is three-dimensional and CT or MRI can capture it better. But radiographs are far more feasible for large-scale screening and follow-up.
The findings position cam morphology as a plausible prevention target, both for identifying higher-risk adults and for studying how cam morphology forms earlier in life. The paper notes that primary cam morphology is stable after skeletal maturity, yet formation may be influenced during growth.
How to use it
For clinicians, the immediate use is risk stratification: if an AP pelvic radiograph already exists, the alpha angle can help identify hips that may merit closer monitoring over time. This is especially relevant when other risk factors for joint degeneration are present.
For patients, the actionable takeaway is planning, not panic. If you’ve been told you have cam morphology, consider a prevention mindset: targeted physical activity, load management, and avoiding rapid spikes in hip-intensive training are common-sense strategies consistent with injury-prevention principles (not proven by this study).
For coaches and trainers working with adolescents, the implication is upstream. The study supports further work on training design—periodised training, education, and load management—aimed at reducing harmful hip loading during growth, without assuming that sport alone “causes” cam morphology.
Limits & what we still don’t know
Generalisation is constrained by the sample’s age profile (mean age 62; range started at 40). The results may not apply well to people under 40, where symptoms and activity exposure can differ.
Measurement limitations matter: AP radiographs can underestimate the alpha angle and the prevalence of cam morphology, and reliability of alpha angle measurement was reported as low to moderate. Sex differences in typical cam location may also affect detection.
The analysis adjusted for age, biological sex, and body mass index, but unmeasured confounders could still influence results. The study also did not account for other hip morphologies such as hip dysplasia or pincer morphology, which may contribute to RHOA risk.
Closing takeaway
This large meta-analysis shows that cam morphology, defined by an alpha angle of at least 60° on AP radiographs, is linked to higher odds of developing radiographic hip osteoarthritis over 4–8 years. Risk increases with higher alpha angles and appears strongest in males and those aged 51–60. The practical value is early identification: a simple radiographic measure can help target prevention efforts before osteoarthritis is visible.
Data in this article is provided by PMC OAI-PMH.