Initial Stability of Subtrochanteric Oblique Osteotomy in Uncemented Total Hip Arthroplasty: A Preliminary Finite Element Study

BACKGROUND Subtrochanteric oblique osteotomy (SOO) has been widely used to reconstruct highly dislocated hips in uncemented total hip arthroplasty. The occurrence of complications can be attributed to the instability of the osteotomy region. The aim of this study was to evaluate the initial stability of SOO in uncemented total hip arthroplasty. MATERIAL AND METHODS A 3-dimensional finite element femur-stem model was created, and a virtual SOO was performed at 4 oblique angles: 30°, 45°, 60°, and 90°. The von Mises stress distribution in the femur-stem complex and the displacement under different oblique angles were evaluated in the SOO models, in comparison with that of the intact model. RESULTS The study demonstrated that the distal fragment of the femur bore more stresses than the proximal fragment, and the maximum stress was concentrated in the femoral neck and the cortical bone, which contacted with the distal end of the stem. SOO increased the stress of both the femur and the stem, and fractures may occur in the stress concentration sites. Additionally, comparing the displacement at different oblique angles, the lateral region was larger than that of the medial region on the subtrochanteric osteotomy plane. The minimum micromotion on the osteotomy plane was obtained when the oblique angle was 45°. CONCLUSIONS The fit and fill of the distal fragment of the femur and the stem is essential for the stability of the subtrochanteric osteotomy region. The optimal oblique angle for SOO appears to be 45°.