To determine whether intramedullary nail (IMN) size and its relation to the canal diameter [nail-canal (NC) diameter] impacts the union rate or time to union in the treatment of femoral shaft fractures.

Retrospective review.

Two Level 1 and 1 Level 2 trauma centers.

Two hundred eighty-seven patients met the criteria and were included in the study.

Patients were treated with either an antegrade or retrograde IMN. Comparisons were first performed comparing 10- versus 11- versus 13-mm nails. Patients were then divided into 3 groups based on the difference between the size of the femoral canal at the isthmus and the IMN (NC diameter). Group 1: < 1.0 mm, group 2: >1.0 and < 2.0 mm, and group 3: >2.0 mm.

Nonunion rates, mean time to union.

Two hundred eighty-seven patients with a minimum of 12-month follow-up, who were treated with size with IMN for femoral shaft fractures, were assessed for fracture characteristics, time to union, and union rate. When comparing IMN size, no statistical difference was found when comparing time to union or overall union rate. When comparing NC diameter, no significant difference was found in union rate and time to union when comparing between the groups.

Similar rate of union and time to union were exhibited regardless of nail size or NC diameter. This can correlate to the standard utilization of a reamed, titanium 10-mm IMN with 5.0-mm interlocking screws in the treatment of femoral shaft fractures, offering potentially less reaming, shorter operative times, and removing unnecessary stock from inventory.

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.