Rotational deformity following intramedullary nailing of femoral shaft fractures is a clinically significant and underdiagnosed problem. Intraoperative determination of rotation is difficult and may be caused by several factors. The insertion of interlocking screws at a slightly oblique angle may cause a substantial degree of rotational deformity, and this factor has not been evaluated as a cause of malrotation.

In eight paired cadaveric femurs, a midshaft transverse fracture was created and an antegrade nail was placed. The specimens were placed in a custom jig which allowed free rotation of the distal segment. Distal interlocking was performed using either a freehand technique or with navigation, and femoral anteversion was measured before and after interlocking to determine the change caused by the interlocking screw.

Freehand placement led to rotational shift up to 7 degrees (mean, 5.8 degrees ; range, 4-7 degrees ), and navigated insertion led to a change of 2.0 degrees (range, 1-3 degrees ; p< 0.05). In addition, drill-nail contact and a visible shift of the fracture site occurred in all freehand trials, whereas in the navigation group, contact occurred in only one trial without fracture movement.

Freehand distal interlocking may be a substantial cause of rotational deformity, and the assistance of computer navigation systems may improve this malrotation.