Morphological abnormalities of the femur in the dysplastic hip. Relation between femur en acetabulum.

AIMS: To apply cutting edge geometry processing techniques and statistical shape modelling to perform a quali-tative and quantitive evaluation of femoral deformity in developmental hip dysplasia and to describe its relation to the amount of acetabular coverage in full 3D. An observational case-control study consisting of 40 right dysplastic cases compared to 43 normal hips, was designed. All subjects were Asian females with an average age of 53.9 years. The right femurs were scanned using computed tomography, followed by 3D reconstruction for statistical shape modelling. Inter- shape correspondences of the femoral shape were used to portray changes in femoral morphology to the amount of acetabular coverage. Partial least-squares regression was applied to establish a direct connection between acetabular coverage and the geometry of the femoral shape. Acetabular coverage accounted for 7.1% of variation in the overal femur shape (p<0.05). Significant changes in femoral morphology (p<0.05) were observed with decreasing acetabular coverage. The regression model demonstrated progressive shortening of the femur neck, as well as increasing attening of the femur head. Further, analysis of curvature and normal displacement demonstrated significant (p<0.05) flat- tening of the femur head especially in the area of the head-neck junction with increasing severity of acetabular dysplasia. Anatomic abnormalities inherent to the dysplastic hip are limited to the very proximal part of the femur and significantly increase when the acetabular coverage decreases. Flattening of the femur head is most pronounced at the peripheral part of the head, in specific the femoral head-neck region.