Ethnic differences in femoral and acetabular version in developmental dysplasia of the hip: a 3D CT-based comparative study of Japanese and Caucasian American cohorts

Abstract Developmental dysplasia of the hip (DDH) is associated with altered acetabular and femoral morphology that can influence hip joint mechanics and surgical planning. Although ethnic differences in hip morphology have been reported, no study has directly compared femoral version (FV), acetabular version (AV), combined version (CV), or FV–AV distribution patterns among DDH patients of different ethnic backgrounds. This retrospective study compared FV, AV, and their combined distribution between 55 hips from Japanese patients and 55 hips from Caucasian American patients with symptomatic DDH who underwent periacetabular osteotomy. Age and sex were matched using propensity score methods. FV and AV were classified as increased (>25°), normal (10–25°), or decreased (<10°). Between-group differences were assessed for FV, AV, CV, and FV–AV combinations. Japanese patients showed significantly greater FV (mean difference + 5.5°, P < .05) and CV (mean difference + 5.5°, P < .05) compared with Caucasian American patients. FV–AV distribution patterns differed significantly between groups (P = .0031). The most frequent pattern in Japanese patients was increased FV with normal AV (45.5%), whereas Caucasian American patients most commonly demonstrated normal FV with normal AV (36.4%). Decreased FV was more common in the Caucasian American cohort (10.9% vs. 5.5%). Ethnic differences were observed in the distribution patterns of FV and AV, suggesting morphological diversity in DDH that may influence its natural history. At the same time, these findings underscore the need for individualized assessment of hip morphology—rather than reliance on ethnic averages—when planning surgery and evaluating outcomes.