Time to union in ballistic trauma lower extremity diaphyseal fractures treated with intramedullary nailing

Background: Time to union in civilian firearm injuries is variable and not well described in the literature. This study measures the time to union for femoral and tibial shaft fractures treated with an intramedullary nail (IMN). Time to union is compared across open, closed, or ballistic trauma (BT) fractures. The goal of the study is to answer the questions: (1) Do tibial shaft fractures heal in specific temporal patterns based on mechanism of injury and (2) Do these temporal healing patterns apply to both the tibia and femur? Patients and methods: Included patients had tibial or femoral shaft fractures (OTA/AO 32 and 42) treated at an urban level 1 trauma center between 2015 and 2020 with IMN. Patients were eligible if radiographic imaging was available for any four of five follow-up timepoints, absence of preexisting hardware, and BT was from low velocity handgun injuries. Radiographic union scale (RUS) was compared amongst six groups (Open, Closed or BT for Femur and Tibia fractures), at 60-90 days, 91-180 days, 181- 270 days, and 271-365 days and greater than 365 days. Statistical comparison was performed using a two-way ANOVA and Tukey's multiple comparisons. Results: Included in the study were 114 patients, with 20 patients in each group except the OPEN femur fracture group with 14. Tibia: At the 91-180 day time point, CLOSED tibia RUS was significantly higher than for BT and OPEN tibia RUS. At 181-270 days, CLOSED tibia RUS was significantly higher than OPEN tibia. At 271-365 days and >365, CLOSED and BT RUS were significantly higher than OPEN RUS.Femur: At the 91-180 day time point, OPEN femur RUS was significantly lower than CLOSED and BT femur RUS. At later timepoints, all three groups achieved union with mean RUS>10. Discussion: This study demonstrates that healing of tibial shaft fractures from BT is not significantly different from closed fractures after 180 days post-operatively. Additionally, femoral shaft fractures from a BT healed similarly to closed and open fractures after 180 days post-operatively. Level of evidence: Prognostic Level III