Purpose: The purpose of this study was to evaluate and compare the accuracy of three different techniques of measuring the extent of osteonecrosis involvement of the femoral head on MRI to determine the best predictor of collapse and to identify the size of the lesion volume which best predicts collapse.
Methods: We prospectively enrolled 48 hips of osteonecrosis femoral head (ONFH) with stage 1 or 2 osteonecrosis and the enrolled patients were followed up for 1 year. Angular measurements (modified Kerboul Angle and modified index of necrotic extent) were compared with the 3D volumetric measurement of necrotic lesion based on MRI in predicting the collapse of the head. ROC analysis was done to evaluate the diagnostic performance of the 3 indices in predicting collapse. Survival analysis of all the hips in the collapsed and non-collapsed group were interpreted using Kaplan Meir survival analysis.
Results: In lesion sizes larger than 25% of femoral head volume - 90.6% (29/32) of hips collapsed within 1 year as compared to 31.3% (5/16) hips collapsed in lesion volume <25% of femoral head (Log-rank test p = 0.001). There was good inter-observer (ICC, 0.94; 95% CI, 0.89-0.97) and intra-observer reliability (ICC, 0.93; 95% CI, 0.88-0.96).
Conclusions: The Volumetric method assessed the severity of lesion size with the future collapse better and more predictably than angular measurements. Necrotic lesion volume of 25% is a potential cut off beyond which future collapse of early ONFH can be predicted and aid in the further management. This study can help in solving the mystery behind prediction of collapse in ONFH.
Keywords: Collapse of femoral head; modified Kerboul angle; modified index of necrotic extent; osteonecrosis of femoral head; volumetric assessment.