Femoral Neck Stress Fractures: MRI Risk Factors for Progression.

Background: Femoral neck stress fractures are overuse injuries with devastating consequences if not diagnosed and treated appropriately. The aim of this study was to retrospectively review femoral neck stress fractures using a magnetic resonance imaging (MRI)-based protocol and to identify imaging risk factors that could predict fracture progression requiring surgical intervention.

Methods: We identified all femoral neck stress fractures treated at our institution from 2002 to 2015. Inclusion criteria for the study were unilateral pathology involving either an incomplete femoral neck stress fracture with a visualized fracture line or edema without a distinct fracture line. MRI data were evaluated for edema, fracture line percentage, and hip effusion. A surgical procedure was offered to patients with fractures with interval progression on serial MRI after 6 weeks of nonoperative treatment.

Results: We identified 305 patients who met inclusion criteria. Initial MRI showed edema with a fracture line in 54.4% of patients and isolated edema in 45.6% of patients. Interval MRI was performed in 194 patients at a mean time of 6 weeks, and it revealed fracture progression in 13.9% of patients. There were no significant differences in the size of the fracture line on initial MRI between the group who progressed to a surgical procedure and those who resolved with nonoperative treatment (mean [and standard deviation], 24.6% ± 8.1% [95% confidence interval (CI), 21.4% to 27.8%] and 25.5% ± 11.1% [95% CI, 22.9% to 28.1%]; p = 0.287). Of the patients who required a surgical procedure, 85.2% had an effusion on the initial MRI compared with only 26.3% of those who showed interval resolution with nonoperative treatment. Those who had a hip effusion on the initial MRI had 8 times (relative risk, 8.02 [95% CI, 2.99 to 21.5]; p < 0.0001) the risk of fracture progression to surgical fixation compared with those without a hip effusion.

Conclusions: In patients with a femoral neck stress fracture and fracture line, the presence of a hip effusion on the initial MRI screening is an independent risk factor for fracture progression and early prophylactic surgical intervention should be considered. All patients with isolated edema in the femoral neck without a fracture line on the initial MRI had resolution with nonoperative treatment and did not have fracture progression toward surgical fixation.

Level Of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.