Postoperative computed tomography-based intact ratio predicts femoral head collapse after curved intertrochanteric varus osteotomy for osteonecrosis of the femoral head.

purposeCurved intertrochanteric varus osteotomy (CVO) is a joint-preserving procedure for osteonecrosis of the femoral head (ONFH); however, postoperative femoral head collapse remains a concern. Although the intact ratio has traditionally been assessed using plain radiography, the clinical relevance of computed tomography (CT)-based intact ratios remains unclear. This study aimed to evaluate the usefulness of the postoperative CT-based intact ratio in predicting the progression of collapse after CVO.

methodsWe retrospectively reviewed data from 54 patients (58 hips) with non-traumatic ONFH who underwent CVO. Collapse progression was defined as an increase in collapse depth ≥ 3 mm compared with the immediate postoperative state. The patients were categorized into collapse and non-collapse groups. The intact ratio was measured on central coronal CT images of the femoral head. Receiver operating characteristic (ROC) curve analysis and Kaplan-Meier survival analysis were performed.

resultsWith a mean follow-up of 47.4 months, collapse progression occurred in 12 hips (21.1%). The postoperative CT-based intact ratio was significantly higher in the non-collapse than in the collapse group (48.4 ± 14.3% vs. 31.8 ± 13.4%, P = 0.001). ROC analysis showed an optimal cutoff value of 39.2% (area under the curve = 0.809). Kaplan-Meier analysis revealed significantly lower three year survivorship with postoperative CT-based intact ratios < 39.2% versus ≥ 39.2% (50.6% vs. 92.1%, P < 0.001).

conclusionsThe postoperative CT-based intact ratio was a strong predictor of femoral head collapse progression, with an optimal cutoff value of 39.2%. Applying conventional radiograph-based thresholds directly to CT evaluations may lead to an underestimation of the risk of collapse.