Femoral shaft fracture with a third fragment treated with an intramedullary nail: Is the displacement of the third fragment predictive of nonunion?

Purpose: Femoral shaft fractures with third fragments are difficult to reduce anatomically, affecting bone healing chances. The goal of this study is to determine the impact of the third fragment's radiological characteristics assessed on post-operative radiographs, as well as other factors, on the healing of type 32B femur shaft fractures treated with intramedullary nail.

Methods: We conducted a retrospective study of 93 patients treated for femoral shaft fractures type 32 B. On post-operative X-rays, two radiologic parameters were evaluated: the third fragment size and the mean third fragment displacement. Patients had radiologic follow-up at 2, 4, 6, 9, and 12-months and were separated into 3 groups based on their fracture healing time: within 6 months (group 1), between 6 and 12 months (group 2), or nonunion after 12 months (group 3).

Results: Among the 93 patients, 72 (77.4%) showed fracture healing at 6 months, 13 (14%) at 12 months, and 8 (8.6%) demonstrated nonunion at 12 months. The mean third fragment displacement was notably different between groups (p < 0.001) and was considerably greater in group 3 than in groups 1 and 2. The influence of third fragment displacement on outcomes under 6 months was determined by ROC analysis, using a cut-off value of 14 mm. Displacement under 14 mm predicted healing within 6 months with a sensitivity of 90.3% and a specificity of 61.9%. The statistical analysis demonstrated that the odds of experiencing non-union or delayed healing were approximately 15 times higher for patients with a third fragment displacement of 14 mm or greater.

Conclusion: The third fragment displacement is the most important factor influencing healing within twelve months in femur shaft fractures type 32B managed with an intramedullary nail. Inversely, the third fragment size had no effect on the healing of the fractures in our series.