Small Femoral Nails and the Development of a Nonunion: A Case-Control Study

Background and Objective: Locked intramedullary (IM) nails are the primary treatment modality for femoral shaft fractures. This study aimed to determine the risk of developing a femur nonunion as a function of nail-to-bone diameter mismatch. Materials and Methods: A retrospective case-control study was performed at a Level I trauma center. Adult patients with femoral shaft fractures (AO/OTA 32 classification) treated with IM nail fixation from 2016 to 2022 were identified from the institutional database. Cases required nonunion surgery. Controls were randomly selected in a 3:1 ratio and included only if fractures healed at final follow-up based on the modified Radiographic Union Score of the femur (mRUSF). The primary outcome was nonunion. The study compared the association of nonunion with nail diameter (range, 9 mm to 13 mm) relative to femur width (range, 12 mm to 36 mm) and adjusted for smoking status, open fracture, and the degree of comminution. Results: In total, 203 patients were included: 50 cases and 153 controls. Patients with a femur anterior-to-posterior diameter >22 mm at the level of the lesser trochanter (11% of this sample) were at increased odds for nonunion when treated with a small diameter IM nail (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.2–3.7; P = .01). In patients with narrower femur diameters, the nail diameter was not associated with increased odds of nonunion surgery. Conclusion: Larger IM nails (≥11 mm) might have protected against nonunion in patients with wide femoral canals (≥22 mm) but likely conferred no significant benefit in patients with narrower femoral canals.