Comparison of torsional strength of humeral intramedullary nailing: a cadaveric study.

Control of rotation after intramedullary fixation of the humeral shaft has been observed to vary clinically. Two of the newer intramedullary nails specifically designed for the humerus were tested. Transverse and spiral fractures were created in 35 fresh-frozen cadaveric humeri. The constructs were tested in a materials testing system to evaluate in vitro the torsional strength of the nailed humeral fractures. Intact bones showed a mean peak torque of 53 +/- 17 Nm. The humeri fixed with the Russell-Taylor nail (n = 18) using one interlocking screw proximally and one distally showed a mean torsional strength of 10.4 +/- 3.6 Nm. The specimens fixed with the Seidel nail (n = 17), interlocked proximally with two screws and distally by the friction of three expanded flanges against the inner cortex, had a significantly lower mean torsional strength of 1.5 +/- 0.6 Nm (p < 0.0005). When compared with intact bones, constructs using the Russell-Taylor nail achieved 20% of mean peak torque. This improved rotational strength should permit an earlier return to full functional use of the extremity.