Rotational stability of femoral osteosynthesis in femoral fractures - navigated measurements.

Rotational malalignment after intramedullary nailing of femoral fractures is common, and symptoms occur when malrotation reaches 15 degrees . Intraoperative measurement of rotation remains difficult, and multiple techniques have been described to address this. Regardless of the method used, rotational toggling may occur between the interlocking screws and the screw holes. We hypothesized that a clinically significant amount of rotation may occur with standard statically locked intramedullary nails. Mid-shaft diaphyseal fractures were created in 24 cadaveric femurs. Specimens were divided into 4 groups, and were stabilized with a statically locked intramedullary nail, a dynamically locked intramedullary nail, a compression plate, and a locking plate. Six additional femurs were kept intact as a control group. Specimens were mounted in a custom holding jig, which stabilized the constructs proximally and allowed free rotation distally. A computer navigation system was applied, and the femoral anteversion was measured. 4 N-m of internal and external torque was applied, and the change in version was measured. The statically locked nails rotated 14.2 degrees , and the dynamically locked group rotated 15.7 degrees . Both intramedullary nail groups showed significantly greater rotation than the plated groups. The compression plate specimens rotated 6.5 degrees on average, and the locked plate group rotated 3.8 degrees . Intramedullary femoral nailing with static or dynamic interlocking allows 15 degrees of rotation of the femur around the nail under physiologic load. This may exacerbate intraoperative errors in determining and setting rotation. Angular stable plates or nails may minimize this problem.