Background This study retrospectively evaluated the clinical outcomes of intramedullary nailing of femoral shaft fractures with third fragments and analyzed the risk factors for delayed union.

Methods Retrospective analyses involving 51 patients who underwent intramedullary nailing of femoral shaft fractures with third fragments (AO classification type B, 35 cases; type C, 16 cases) were conducted. Delayed union was defined as either more than 10 months required for callus formation in more than three of the four cortical bone surfaces observed in the frontal and lateral radiographic views or the requirement for additional surgery such as nail conversion or bone transplantation. Seventeen patients developed delayed union (D group). Thirty-four patients achieved bony union within 9 months (U group). The following background variables were compared between groups: age at the time of the injury; AO classification; ratio of open fracture; waiting period before surgery; rate of the infraisthmal fracture; diameter of the intramedullary nail; ratio of the intramedullary nail to the femur; length and displacement of the third fragment; and use of open reduction, poller screws, or dynamization.

Results Significant differences were found between the D and U groups for age (32.2±14.1 vs. 25.3±9.6 years), open fracture ratio (35.3% vs. 11.8%), and displacement of the third fragment (13.7±6.4 vs. 9±6.3 mm). Multiple logistic regression analysis only identified displacement of the third fragment as a risk factor for delayed union (p=0.03; OR 1.13; 95% CI 1.01 to 1.26).

Discussion Delayed union was observed in 17 cases (33.3%) after intramedullary nailing of femoral shaft fractures with third fragments. Displacement of the third fragment influenced delayed union.

Level of evidence Level III.