Femoral neck shaft angle in relation to the location of femoral stress fracture in young military recruits: femoral head versus femoral neck stress fracture

OBJECTIVE: To evaluate the influences of the femoral neck shaft angle (FNSA) on the location of the femoral stress fracture and to assess the potential differences in FNSA between fractured and normal femurs. MATERIALS AND METHODS: Thirty-seven patients with femoral stress fractures who underwent both plain hip radiographs and MRI, from January 2016 to September 2019, were retrospectively included. Patients were classified as having either femoral head stress fracture (group A, n = 26) or femoral neck stress fracture (group B, n = 11). The FNSA was measured in anteroposterior (AP) hip radiograph. The Mann-Whitney U testing was used to compare the continuous values between the two groups. A receiver operating characteristic (ROC) analysis was used to evaluate the value of FNSA for predicting the risk of femoral stress fracture. RESULTS: The FNSA was significantly higher in group A (median 135.9°, range 129.5–138.6°) than group B (median 124.3°, range 119.5–129.0°) (p < 0.001), but there were no significant differences in other clinical factors. Furthermore, the FNSA was significantly higher at the fractured femurs (median 135.9°, range 129.9–138.6°) than contralateral normal femurs (median 127.9°, range 123.8–132.1°) in the patients with unilateral femoral head stress fracture (n = 22) (p < 0.001). The ROC analysis revealed that the area under curve (AUC), sensitivity, and specificity for predicting the risk of femoral head stress fracture were 0.807, 72.7%, and 68.2%, respectively, at a FNSA cutoff of 131.0°. CONCLUSION: FNSA was associated with the location of the femoral stress fracture. In addition, FNSA could serve as a predictive factor for the risk of femoral head stress fractures.