Development of osteoarthritis in adults with untreated hip dysplasia: a longitudinal observational study.

BACKGROUND AND PURPOSE: Although hip dysplasia is a risk factor for osteoarthritis (OA), its natural progression in adults remains poorly understood. In a longitudinal observational study, we aimed to estimate differences in OA incidence, time to OA, and minimum joint space width (JSW) between dysplastic hips and contralateral non-dysplastic hips. METHODS: Adults aged 20-70 years who underwent pelvic radiographs in Malmö, Sweden, during 2007-2008 were included. Inclusion criteria were unilateral hip dysplasia (lateral center edge angle ≤ 20°), no OA at baseline, and available follow-up imaging of both hips. OA incidence was assessed using last available follow-up imaging, whereas minimum JSW was measured bilaterally on the last available radiograph of native hips. RESULTS: 50 participants (median age 47 years, IQR 39-62, 36 women) were included, with median follow-up 12.5 years (IQR 7.8-14.7). OA developed in 19/50 dysplastic hips and 16/50 non-dysplastic hips, corresponding to a paired risk difference of 6 percentage points (95% confidence interval [CI] -7 to 20). Mean time to OA was 8.2 years (SD 5.2) for dysplastic hips and 9.6 years (SD 5.1) for non-dysplastic hips (mean difference -1.2 years, CI -4.8 to 2.4). Minimum JSW at follow-up was 3.3 mm (SD 1.3) in dysplastic hips and 3.5 mm (SD 0.9) in non-dysplastic hips (mean difference -0.2 mm, CI - 0.6 to 0.2). CONCLUSION: No clear differences were observed in OA incidence, time to OA, or minimum JSW between dysplastic and contralateral non-dysplastic hips.