Biomechanical Evaluation of Humerus Fracture After Subpectoral Biceps Tenodesis With Interference Screw Versus Unicortical Button

Abstract

To compare the torsional failure strength of the humerus after subpectoral biceps tenodesis with an interference screw versus a unicortical button in a human cadaveric model. Thirteen matched pairs of fresh-frozen human cadaveric upper extremities were randomized to receive either 2.6× 12 mm unicortical button or 6.25-mm interference screw subpectoral biceps tenodesis. After the procedure, the humeri were loaded into a materials testing machine. The humeri were loaded in external rotation with respect to the elbow at 1.0°/s until failure. Rotation angle to failure, failure torque, energy absorbed, and stiffness were compared by paired t-tests with alpha set at 0.05. Humeri that were fixed with unicortical buttons showed statistically significant higher rotation to failure (26.87 ± 5.83 vs 19.04 ± 3.86°, P < .001), failure torque (54.11 ± 22.01 vs 44.95 ± 17.47 Nm, P < .001), and energy absorbed (883.93 ± 582.28 vs 451.40 ± 216.19 Nm-Deg, P= .002) than humeri fixed with interference screws. In a cadaveric biomechanical model, at time 0, the use of a 2.7× 12-mm unicortical button fixation in biceps tenodesis resulted in higher loads required to fracture the humerus when compared with a 6.25-mm interference screw fixation in a torsion model. This study demonstrates a significant biomechanical difference with regards to fracture of the humerus, between 2 commonly used fixations methods and implant sizes, interference screw, and unicortical button. The results of this study can aid surgeons in implant selection as well as help to improve patient education prior to surgery.