Is acetabular dysplasia and pelvic deformity properly interpreted in patients with congenital femoral deficiency? A 3D analysis of pelvic computed tomography.

Purpose: The aim of this study is to assess the pelvis's morphology and spatial orientation of the acetabulum, and their relation to the severity of Congenital Femoral Deficiency (CFD) using 3D imaging. Defining these pathologies is crucial for adequate surgical correction.

Methods: The shape and structure of the acetabulum and pelvis were evaluated in 14 children with unilateral CFD via 3D computed tomography (CT) scans, and then analysed with geometric morphometrics (Procrustes ANOVA). The association between pelvic directional asymmetry and CFD classifications (Aitken, Paley) was assessed. The affected acetabulum's orientation was compared to the non-affected side, and the variability of orientation in different CFD types was evaluated (bivariate correlation).

Results: The hemipelvis with CFD is characterized by a smaller acetabulum, a laterally curved ischium and a less upright ilium (p < 0.001). Multivariate regressions revealed a greater level of pelvis asymmetry in more severe types of CFD (p < 0.001). The acetabulum orientation assessment showed a significant decrease in mean anteversion (1.3°) and inclination (9.6°) angle, when compared to the non-affected side (26°and 17.1° respectively; p < 0.001).

Conclusions: The affected side of the pelvis is considerably smaller and more deformed, and this should be considered during limb lengthening. The acetabulum presents with significant dysplasia due to its severe retroversion and steepness (superoposterior distortion). This should not be interpreted as a simple wall deficit, but as a complete acetabular misalignment (often misinterpreted in 2D imagery). Using transiliac osteotomies (e.g. Dega, Salter) is debatable due to abnormal acetabular orientation (superoposterior malalignment). Therefore, alternative options, e.g. San Diego or triple pelvic osteotomy, should be considered.