Osteotomy angle to the femoral neck axis affects the postoperative intact ratio in curved varus osteotomy for osteonecrosis of the femoral head

Curved varus osteotomy (CVO) is a surgical option to preserve a hip joint affected by osteonecrosis of the femoral head (ONFH). Femoral anteversion varies among patients; however, the osteotomy design on the axial plane in CVO has not been well investigated. This study evaluated the variation in the osteotomy angle on the axial plane in a CVO and its effect on the postoperative intact ratio, which determines the postoperative outcome. This study included 10 patients with Type C1 ONFH who underwent CVO according to the Japanese Investigation Committee classification. The osteotomy angles relative to the posterior condylar and femoral neck axes on the axial plane were measured on postoperative computed tomography images. The progression of collapse and osteoarthritic change were reviewed on serial radiographs. The mean osteotomy angles to the posterior condylar axis and the femoral neck axis were 0.2° and 15.3°, respectively. The mean postoperative intact ratio was 45.6% (range: 28.0-62.8%). The osteotomy angle to the femoral neck axis was significantly and negatively correlated with the postoperative intact ratio (<i>ρ</i> = -0.782, <i>P</i> = .008). In three cases, the osteotomy line was directed >25° anteromedial to the femoral neck axis, and the postoperative intact ratio was less than the target (34%); one showed progression of the collapse of the femoral head, and another an osteoarthritic change. We observed wide variations in the osteotomy angle on the axial plane during manually performed CVO. The osteotomy angle to the femoral neck axis on the axial plane affected the postoperative intact ratio.