Femoral Neck Stress Injuries: Analysis of 156 Cases in a U.S. Military Population and Proposal of a New MRI Classification System.

OBJECTIVE: The objective of this study is to formulate a new MRI classification system for fatigue-type femoral neck stress injuries (FNSIs) that is based on patient management and return-to-duty (RTD) time.

MATERIALS AND METHODS: A retrospective review of 156 consecutive FNSIs in 127 U.S. Army soldiers over a 24-month period was performed. The width of marrow edema for low-grade FNSIs and the measurement of macroscopic fracture as a percentage of femoral neck width for high-grade FNSIs were recorded. RTD time was available for 90 soldiers. Nonparametric testing, univariate linear regression, and survival analysis on RTD time were used in conjunction with patient management criteria to develop a new FNSI MRI classification system.

RESULTS: The FNSI incidence was 0.09%, and all FNSIs were compressive-sided injuries. RTD time was significantly longer for high-grade FNSIs versus low-grade FNSIs (p < 0.001). Our FNSI MRI classification system showed a significant difference in RTD time between grades 1 and 2 (p = 0.001-0.029), 1 and 3 (p < 0.001), and 1 and 4 (p = 0.001-0.01). There was no significant RTD time difference between the remaining grades. The rates of completing basic training (BT) and requiring medical discharge were significantly associated with the FNSI MRI grades (p = 0.038 and p = 0.001, respectively).

CONCLUSION: The proposed FNSI MRI classification system provides a robust framework for patient management optimization by permitting differentiation between operative and nonoperative candidates, by allowing accurate prediction of RTD time, and by estimating the risk of not completing BT and requiring medical discharge from the military.