Native-hip survival after modified Chiari osteotomy and the outcome of conversion to total hip arthroplasty: a retrospective cohort study with a matched comparison

Joint preservation in the young dysplastic hip aims to defer an arthroplasty that would otherwise carry a high lifetime revision burden. Whether the preceding osteotomy affects that arthroplasty is unclear, because the two have usually been reported in separate cohorts. We assessed both in one cohort. We reviewed 50 hips treated with a modified Chiari osteotomy for dysplasia or other childhood hip disease. The primary outcome was native-hip survival, estimated by Kaplan-Meier analysis with conversion to total hip arthroplasty (THA) as the endpoint. In an exploratory secondary analysis, conversion THAs were matched 1:2 with primary THAs by diagnosis, sex and operative year and compared by the post-THA modified Harris Hip Score (mHHS); operative details were compared between 18 conversion and 30 primary hips. Native-hip survival was 84.5% at 10 years and 55.5% at 20 years (95% confidence interval [CI] 37.1–74.0), and did not differ between dysplastic hips and those with Legg-Calvé-Perthes disease sequelae (log-rank p = 0.552). In preserved hips the mean mHHS improved from 55 to 72 (p < 0.001). Eighteen hips (36%) were converted at a median of 12.4 years. No significant difference in post-THA mHHS was detected between the conversion and primary groups (83.1 vs 84.7; difference − 1.5, 95% CI − 5.8 to 2.8), also after age adjustment. Operative time (110 vs 108 min) and blood loss (300 vs 300 mL) did not differ. More than half of the hips were still preserved 20 years after the osteotomy. When preservation failed, no significant difference in function was detected versus matched primary THA, and operative time, blood loss and the use of acetabular bone graft did not differ significantly, although this small exploratory comparison was not powered to establish equivalence. Native-hip survival after a Chiari osteotomy and the outcome of the arthroplasty that follows have almost always been reported in separate cohorts. This study follows one consecutive series through both phases, quantifying how long the native hip is retained and how the eventual arthroplasty performs early in the same patients.