Open subpectoral biceps tenodesis is one of the most common shoulder procedures and is performed in response to injury of the long head of the biceps tendon (LHB) or surrounding soft tissue. Excellent results and very low complication rates have been reported for biceps tenodesis with interference screws. Although the hole is drilled through an open approach, overlying soft tissue often prevents direct visualization of the bicipital groove and the drill placement if the medial and lateral borders of the humeral cortices are not fully exposed. This may lead to eccentric malpositioning of the screw and potential iatrogenic breaching of the humeral cortex. Biomechanically, cortical defects caused by screws or drill holes have been shown to significantly reduce bone strength when compared with an intact control.

Recently, Rios and Dein reported cases of proximal humeral fractures at the site of the tenodesis, presumably due to weakening of the cortex. Although only described in case reports so far, instances of proximal humeral fracture after biceps tenodesis or other procedures, which create significant holes, keyholes, or troughs in the humeral shaft, have been reported. Most of the fractures were associated with a malpositioned screw or drill hole. The most frequent mechanism of injury for proximal humeral fractures is direct compression load in abduction, typically described as a fall onto the outstretched hand. However, strength reduction of the humeral diaphysis after biceps tenodesis has never been quantified. Furthermore, the biomechanical consequences of concentric and malpositioned (eccentric) biceps tenodesis in response to compressive forces with the arm abducted, similar to a fall on the outstretched hand, have yet to be investigated.

The purpose of this study was to determine whether malpositioned (laterally eccentric) tenodesis screw placement affects humerus strength compared with central placement. We hypothesized that (1) laterally eccentric tenodesis screw placement would cause significant strength reduction compared with intact humeri and (2) concentric placement would not cause significant reduction in the strength of the humerus compared with the intact controls.

Full Article: Biomechanical Analysis of Subpectoral Biceps Tenodesis