Treatment of infra-isthmal femoral fracture with an intramedullary nail: Is retrograde nailing a better option than antegrade nailing?

Introduction: Antegrade intramedullary (IM) nailing is ideal for femoral shaft fractures, but fixing the fracture distal to the isthmal level may be difficult because of medullary canal widening and the proximity of fracture location from the distal femoral joint line. This study aimed to compare treatment results between antegrade and retrograde nailing for infra-isthmal femoral shaft fracture, and to identify influencing factors of nonunion and malalignment. Materials and methods: Sixty patients with infra-isthmal femoral shaft fractures treated with IM nailing and followed-up for > 1 year were enrolled in this retrospective study, 38 in the antegrade nailing group, and 22 in the retrograde nailing group. The two groups had no significant differences in age, sex, and fracture location (p = 0.297, Mann–Whitney test). Radiological evaluation was performed, and functional result was assessed using the Knee Society scoring system. Complications were analyzed in accordance with fracture location, fracture type, and operative method. Results: According to the AO/OTA classification, 35, 16, and 9 cases were type A (A1: 1, A2: 11, A3: 23), B (B1: 2, B2: 7, B3: 7), and C fractures (C2: 4, C3: 5), respectively. The mean follow-up duration was 29.5 months. In the antegrade and retrograde nailing groups, the primary bony union rates were 73.7% in 20.7 weeks (range 12–41) and 86.4% in 17.4 weeks (range 12–30), respectively. The two groups showed no significant differences in union rate (p = 0.251, Pearson’s Chi-square test) and union time (p = 0.897, Mann–Whitney test). No cases of malalignment of > 10° in any plane were found in both groups. The mean Knee Society scores were 92 (range 84–100) and 91 (range 83–95) in the antegrade and retrograde nailing groups, respectively, showing no significant difference (p = 0.297, Pearson’s Chi-square test). Although fracture location was not significantly related to union rate (p = 0.584, Mann–Whitney test), patients with an effective working length of the distal segment of < 0.75 were prone to nonunion (p = 0.003, Pearson’s Chi-square test). Conclusions: Although no significant difference was found in IM nail type, the IM nail with a shorter working length distal to the fracture showed a strong relationship with nonunion.