Small Residual Fracture Gaps Delay Time to Union in Length Stable Femur Fractures Treated with Intrameduallary Fixation.

Objectives: The purpose of this study was to investigate whether residual fracture gapping and translation at time of intramedullary nail (IMN) fixation for diaphyseal femur fractures were associated with delayed healing or nonunion. Design: Retrospective cohort study Setting: Level 1 trauma hospital, quaternary referral center Patients/Participants/Intervention: Length stable Winquist type 1 and 2 diaphyseal femur fractures treated with IMN at a single Level I trauma center were retrospectively reviewed. Main Outcome Measure: The largest fracture gap and translation were evaluated on immediate anteropos-terior (AP) and lateral postoperative radiographs. Radiographic healing was assessed using Radiographic Union Score in Femur (RUSF) scores at each follow-up. Radiographic union was defined as a RUSF score >= 8 and consolidation of at least 3 cortices. ANOVA and student's t-tests were used to evaluate the in-fluence of fracture gap parameters on time to union (TTU) and nonunion rate. Patients were stratified to measured average gap and translation distances < 1mm, 1-3mm and > 3mm for portions of the analysis. Results: Sixty-six patients who underwent IMN with adequate follow-up were identified. A total of 93.9% of patients achieved union at an average of 2.8 months. Fractures with average AP/lateral gaps of < 1mm, 1-2.9 mm, and > 3mm had an average TTU of 70.1, 91.7, and 111.9 days respectively; fractures with larger residual gap sizes had a significantly longer TTU (p = 0.009). Fractures with an average gap of 1-2.9mm and > 3 mm had a significantly higher nonunion rate (1.5% and 4.5% respectively) compared to 0% nonunion in the < 1 mm group (p = 0.003). Conclusion: Residual gapping following intramedullary fixation of length stable diaphyseal femur frac-tures is associated with a significant increase in likelihood of nonunion. Summary: Residual displacement of length stable femoral shaft fractures following intramedullary nailing can have a significantly negative impact on fracture healing. An average 3 mm AP/lateral residual fracture gap or a total of 6 mm of the AP + lateral fracture gap appeared to be a critical gap size with increased rates of nonunion and time to union. Therefore, we suggest minimizing the sum of the residual AP and lateral fracture gap to less than a total of 6 mm. (c) 2022 Elsevier Ltd. All rights reserved.