Hip morphology in Japanese patients with osteoarthritis: a three-dimensional computed tomography-based analysis

Purpose Restoration of the hip center is a primary goal in total hip arthroplasty (THA). This reconstruction depends on proximal femoral morphology, particularly in Japanese patients, in whom osteoarthritis (OA) is frequently associated with acetabular dysplasia. However, comprehensive three-dimensional information regarding proximal femoral morphology remains limited. This study aimed to clarify proximal femoral morphology in Japanese patients with OA compared with nondysplastic controls to assist THA planning. Methods This morphological study used computed tomography (CT) data from 104 hips of Japanese patients with bilateral Kellgren-Lawrence grade 3–4 OA who underwent THA and 104 propensity score-matched controls who underwent pelvic-to-knee CT in the emergency department. Using three-dimensional software, the femoral head center (FHC) was automatically calculated, and center edge (CE) angle, offset, neck length (NL), neck-shaft angle (NSA), anteversion, anterior femoral offset (AFO), and canal flare index (CFI) were measured. Femoral canal morphology was evaluated using the Noble classification. The three-dimensional location of the FHC relative to the greater trochanter was evaluated. Results Compared with controls, the OA group showed a smaller CE angle, smaller femoral offset, shorter NL, larger NSA, greater femoral anteversion, and greater AFO. Both mediolateral and anteroposterior CFI were greater in the OA group with predominant Noble Type A morphology. The FHC was positioned more inferiorly and anteriorly. Conclusions Japanese patients with OA, primarily those with acetabular dysplasia, exhibit distinctive femoral morphology, a three-dimensionally altered FHC position, and narrow canals. These differences may be clinically relevant for three-dimensional preoperative planning and reconstruction of native hip anatomy in THA.