Morphological differences between residual childhood hip dysplasia with previous osteotomy and adolescent-onset hip dysplasia.

Background: Hip dysplasia (HD) at skeletal maturity can result from residual developmental dysplasia of the hip (DDH) treated in childhood or from primary adolescent-onset HD (AOHD). This study aims to compare the pathomorphology of these two HD subtypes with that of a normal control group.

Methods: This retrospective study reviewed patients who underwent periacetabular osteotomy for symptomatic HD between 2013 and 2020. The study included 27 residual HD patients (32 hips) following a previous pelvic osteotomy and 39 AOHD patients (68 hips), compared to 29 age- and sex-matched healthy individuals. Acetabular morphology was assessed using plain radiographs, measuring the lateral and anterior center-edge angle (LCEA/ACEA), Sharp angle, Tönnis angle (TA), acetabular depth ratio (ADR), acetabular head index (AHI), and head lateralization index (HLI). On 2D axial and frontal CT scans, we measured acetabular version (AV), anterior and posterior acetabular sector angle (AASA/PASA), femoral neck shaft angle (NSA) and femoral anteversion (FAV).

Results: Both HD groups presented frontal and sagittal acetabular dysplasia with lower LCEA (p < 0.001), lower ACEA (p < 0.001), and lateral subluxation, indicated by lower AHI (p < 0.001) and higher HLI (p < 0.001). Compared to AOHD, residual HD demonstrated greater lateralization, with a higher HLI (p = 0.028). In the axial plane, both HD groups had similar deficient anterior coverage, with lower AASA (p < 0.001). However, residual HD exhibited poorer posterior coverage, with a lower PASA (p < 0.001) and a lower AV (p = 0.006). NSA did not differ between groups, but residual HD had excessive FAV compared to the other groups (p < 0.001).

Conclusions: Although both residual HD and AOHD demonstrated anterior and lateral acetabular deficiencies, residual HD was further characterized by reduced acetabular version, more femoral head lateralization, poorer posterior acetabular support, and excessive FAV.