Femoral Neck Shaft Angle Measurement for Differentiating Femoral Head Stress Fracture from Avascular Necrosis

Abstract

Objective: The study aimed to evaluate whether the measurement of Femoral Neck Shaft Angle (FNSA) can be helpful in differentiating femoral head Stress Fracture (SF) from Avascular Necrosis (AVN). Methods: From September 2019 to April 2022, sixty-four patients [median age 32.0 years, interquartile range (IQR) 23.0-39.0 years] who underwent both hip radiograph and Magnetic Resonance Imaging (MRI) and diagnosed as femoral head SF or AVN were included in our retrospective study. Patients were divided into as having either femoral head SF (n = 34) or AVN (n = 30). The FNSA was measured in anteroposterior hip radiography. Continuous values were compared using the Mann-Whitney U test. The assessment of the predictive value of FNSA for femoral head SF was performed by Receiver Operating Characteristic (ROC) analysis. Results: The FNSA was significantly higher in patients with SF (median 133.5 degrees, IQR 128.0-136.7 degrees) than those with AVN (median 127.5 degrees, IQR 124.0-132.0 degrees) (p = 0.001). In addition, the FNSA was significantly higher in SF femurs (median 134.8 degrees, IQR 129.2-137.4 degrees) than in contralateral normal femurs (median 127.1 degrees, IQR 124.3-132.5 degrees) in patients with unilateral femoral head SF (n = 30) (p < 0.001). In ROC analysis, the sensitivity, specificity, and Area Under the Curve (AUC) for predicting the femoral head SF were 77.3%, 63.3%, and 0.785 (95% confidence interval: 0.666-0.905), respectively, at a cutoff of 130.2 degrees. Conclusion: Increased FNSA was associated with femoral head SF; thus, measurement of FNSA could be helpful for differentiating femoral head SF from AVN.