Effect of Interlocking Mode on the Outcomes of Exchange Nailing for the Treatment of Aseptic Femoral Shaft Nonunion

BACKGROUND: Exchange nailing is a standard treatment for femoral shaft nonunion after intramedullary nailing. However, substantial uncertainty and controversy remain regarding the mode of interlocking fixation. This study aimed to compare the success rate and time to union of exchange nailing based on interlocking modes. METHODS: We retrospectively analyzed all consecutive patients who underwent exchange nailing for aseptic femoral shaft nonunion between February 2000 and February 2021. Patients who underwent exchange nailing using the dynamically locked mode and statically locked mode constituted the dynamic group and static group, respectively. We compared the success rates of the index surgery and the time to union between the groups and measured the extent of interlocking screw migration on the dynamic oblong hole in the dynamic group. RESULTS: The dynamic group and static group comprised 17 patients and 18 patients, respectively. All patients in the dynamic group achieved bone union, whereas 5 patients in the static group did not and underwent additional intervention. The success rate of the index surgery was significantly higher in the dynamic group than in the static group (100% vs. 72.2%, p = 0.045). Four of the 5 failed unions in the static group achieved bone union after dynamization. The median time to union was significantly shorter in the dynamic group than in the static group (6.0 months [range, 4.0–6.0] vs. 12.0 months [range, 3.7–21.7], p = 0.035). In the dynamic group, 3 of 17 patients exhibited interlocking screw migration ranging from 1.1 to 4.1 mm. CONCLUSIONS: Exchange nailing with dynamic mode yields a higher success rate and shorter time to union in aseptic femoral shaft nonunion than that with static mode, without the risk of excessive shortening.