Diagnostic value of necrotic lesion boundary in bone collapse of femoral head osteonecrosis

Our research developed a novel approach to quantitatively evaluate the boundary of necrotic lesions in osteonecrosis of the femoral head (ONFH) and to explore its diagnostic value in predicting bone collapse of the femoral head. A retrospective cross-sectional study was conducted in our institution, and 146 hips (121 cases) identified as ONFH were recruited. The anterior and lateral boundaries of each enrolled subject were measured in standard anteroposterior (AP) view and frog-leg (FL) view of plain radiographic images, the intact rate of which was then calculated and presented as the anteroposterior view intact ratio (APIR) and frog-leg view intact ratio (FLIR), respectively. Univariate and multivariate logistic regression analyses were performed to identify risk factors for collapse. A receiver operating characteristic (ROC) curve analysis was performed to determine the sensitivity, specificity and cutoff value of the APIR and FLIR. A Kaplan–Meier (K-M) analysis was applied to calculate the survival rate of the femoral head, and bone collapse of the femoral head was regarded as the endpoint. Femoral head collapse was observed in 61 hips during the follow-up period. Patients with or without femoral head collapse were categorized into the collapse group and non-collapse group, respectively. The mean follow-up time was 3.7 years (2–9) for the collapse group and 7.7 years (5–20) for the non-collapse group. Univariate and multivariate logistic regression analysis and ROC analysis showed that APIR (< 25.61%) and FLIR (< 24.43%) were significantly associated with femoral head collapse. The K-M survival curves indicated that the overall survival rate of APIR (≥ 25.61%) was 94.8% at 7.5 years and 76.6% at 10 years, while that of FLIR (≥ 24.43%) was 87.3% at 7.5 years and ten years. The present study demonstrates that APIR and FLIR are of high diagnostic value in the early and middle stages of ONFH. APIR and FLIR can be used to predict the occurrence of femoral head collapse in patients with JIC classification types B and C1. The measurement of these two parameters in plain radiography images may contribute to the selection of a proper hip preservation strategy.