Morphological features and long-term outcomes after periacetabular osteotomy for borderline hip dysplasia

The role of periacetabular osteotomy (PAO) in symptomatic borderline hip dysplasia (borderline HD) remains controversial because the lateral centre-edge angle may not reflect global dysplastic morphology. We examined whether selected borderline dysplastic hips showed additional dysplastic features and compared mid- to long-term outcomes with frank hip dysplasia (frank HD).

This retrospective comparative cohort study included 33 patients (35 hips) with borderline HD (18° ≤ lateral centre-edge angle < 25°) and 319 patients (357 hips) with frank HD (lateral centre-edge angle < 18°) treated with PAO from 1996 to 2009. Radiographic morphology, Kaplan-Meier total hip arthroplasty-free survival, and patient-reported outcome measures (PROMs) after 1:3 propensity score matching were analysed.

In the borderline HD cohort, 33 hips (94.3%) met at least one frank HD criterion other than lateral centre-edge angle and 12 hips (34.3%) met three or more. Mean follow-up was 14.0 years in the borderline HD cohort and 13.9 years in the frank HD cohort. One borderline dysplastic hip and 50 frank dysplastic hips underwent total hip arthroplasty. The 20-year survival rate was 90.0% in borderline HD and 78.8% in frank HD (log-rank p = 0.101). Matched PROMs did not differ significantly between groups.

Borderline dysplastic hips selected for PAO usually showed multidirectional dysplastic morphology resembling frank HD. In carefully selected symptomatic borderline HD, PAO was associated with favourable long-term survival and PROMs comparable with frank HD.