MRI Predictive Model's Utility in a Recruit Training Environment for Tibia Stress Fractures

The purpose of the study was to assess the utility of Fredricson Magnetic Resonance Imaging Grading model in predicting return to duty in Marine recruits who sustain tibia stress fractures at Marine Corps Recruit Depot San Diego (MCRDSD).

A retrospective review of 106 tibia stress fractures in 82 Marine recruits was performed. A baseline Fredricson grade was assigned, based on magnetic resonance imaging (MRI) evaluation. The electronic health record was reviewed for return to full duty. Non-parametric testing and descriptive statistics were used to evaluate the study population, varying subgroups, and the utility of this model in predicting the return to full duty in the recruit population and any differences based on stress fracture location or training platoon.

The mean return to full duty (RTFD) was 11.8 weeks. The study participants sustained a greater percentage of middle tibia stress fractures (51.2%) and grade IV stress fractures (37.8 %) than other tibia sites and severities. There was a difference in RTFD amongst the Fredricson grades (p is equal to 0.001). The median RTFD for grade I stress fracture was 8.5 weeks, the median RTFD for grade II stress fracture was 10.00 weeks, the median RTFD for Grade III stress fracture was 10.00 weeks, and the median RTFD for grade IV stress fractures was 13.00 weeks. As Fredricson grade increased, RTFD increased (p is equal to 0.00) although no median RTFD met the Bonferroni correction for statistical significance.

The analysis suggested the Fredricson MRI grade was associated with RTFD in the recruit population. As Fredricson grade increased, median RTFD increased; however, mid-grade stress fractures (i.e., II-III) had similar median RTFD.