Femoroacetabular impingement syndrome in middle-aged individuals is strongly associated with hip OA

Key points

1. 01FAIS was associated with an adjusted OR of 6.85 (95% CI 2.10 to 22.35) for incident radiographic hip OA within 10 years
2. 02Absolute risk of FAIS for developing hip OA was 81%, and 33% for end-stage hip OA requiring joint replacement
3. 03FAIS was diagnosed using three accessible criteria: hip pain, limited internal rotation (25 degrees or less), and cam morphology on X-ray
4. 04Only 21 of 1386 hips met all FAIS criteria, reflecting a low prevalence of 1.5% overall (4.6% in men, 0.8% in women)
5. 05Cam morphology alone carries an absolute OA risk of only 6-25%, far lower than the full FAIS triad

How it was conducted

Design

Nationwide multicentre prospective cohort study (CHECK cohort), 10-year follow-up

Participants

1386 hips from 1002 individuals aged 45-65 years without definite radiographic hip OA at baseline; 80% women, mean age 55.7 years

Exposure

FAIS defined as presence of all three: self-reported hip pain, limited internal hip rotation (25 degrees or less), and cam morphology (alpha angle greater than 60 degrees) on AP pelvic radiograph

Primary outcome

Incident radiographic hip OA defined as Kellgren-Lawrence grade 2 or higher, or total hip replacement at 10-year follow-up

Secondary outcome

Incident end-stage radiographic hip OA defined as Kellgren-Lawrence grade 3 or higher, or total hip replacement

Analysis

Logistic regression with generalised estimating equations, adjusted for age, sex, and BMI

What they found

• 21 of 1386 hips (1.5%) met criteria for FAIS at baseline; 563 hips had no FAIS criteria (reference group)
• Within 10 years, 221 hips (38%) developed incident radiographic hip OA and 15 hips (3%) developed end-stage hip OA including 9 total hip replacements
• FAIS was associated with incident hip OA: adjusted OR 6.85 (95% CI 2.10 to 22.35)
• FAIS was associated with end-stage hip OA: adjusted OR 47.82 (95% CI 12.51 to 182.76)
• Absolute risk of FAIS for incident hip OA: 81.0%; for end-stage hip OA: 33.3%
• FAIS with large cam morphology (alpha angle greater than 78 degrees) showed even higher association with end-stage OA: adjusted OR 88.4 (95% CI 17.7 to 441.4); absolute risk 42.9%
• Unadjusted OR for incident hip OA with FAIS: 7.5 (95% CI 2.4 to 23.4)

Limitations

• Only 21 hips met FAIS criteria, giving wide confidence intervals and limiting precision of effect size estimates
• AP pelvic radiographs only were used to measure cam morphology, likely underestimating true cam prevalence
• The FADIR test was not available in this cohort; only limited internal rotation was used as the clinical sign
• The control group included people with first-onset knee pain, so it may not represent a fully pain-free reference population

Why it matters

For patients

If you have hip pain, stiffness on internal rotation, and a bone shape abnormality on X-ray, your risk of developing hip arthritis within 10 years is very high, and discussing prevention with a clinician is important.

For clinicians

Middle-aged patients presenting with first-onset hip pain who meet all three FAIS criteria (symptoms, limited internal rotation, cam morphology) represent a high-risk subgroup that warrants targeted counselling and investigation of preventive strategies.

For readers

This is the first prospective study linking the full FAIS clinical diagnosis, not just cam morphology alone, to hip OA development, providing a stronger prognostic signal that can guide future prevention trials.