A simple linear alternative to necrotic volume for predicting collapse in osteonecrosis of the femoral head.

Objective: The clinical use of magnetic resonance imaging-based volumetric measurement for osteonecrosis of the femoral head (ONFH) is restricted by its complexity. This study aimed to identify a practical computed tomography-based imaging parameter as a reliable alternative to necrotic volume and to evaluate its ability to predict femoral head collapse.

Materials and methods: This retrospective study included 125 hips from 90 patients with ONFH and initial collapse of < 3 mm. Four-dimensional ratios were examined for their association with necrotic volume using generalized estimating equation models. The parameter showing the strongest association was determined by comparing models with the Quasi-likelihood Information Criterion (QIC). Receiver operating characteristic curve analysis was then used to establish a cutoff value for predicting a necrotic volume of ≥ 30%, the threshold defined as severe in the Steinberg classification. This prognostic value of this cutoff for collapse (> 3 mm) was tested with a robust Cox proportional hazards model.

Results: The coronal vertical diameter ratio (CVDR) showed the strongest association with necrotic volume, yielding the lowest QIC. A CVDR cutoff of 51% predicted a large necrotic volume (AUC 0.931). Hips with a CVDR ≥ 51% had a significantly higher risk of collapse compared with those with a CVDR < 51% (HR, 6.07; 95% CI, 3.25-11.34; P < 0.001). This predictive value was consistent across all Japanese Investigation Committee type subgroups.

Conclusion: The CVDR represents a simple and reliable alternative to volumetric assessment. A cutoff of approximately 51% provides clinically useful risk stratification, and incorporating lesion location may further enhance predictive accuracy.