Biomechanical evaluation of unicortical stress risers of the proximal humerus associated with pectoralis major repair

Proximal humerus fracture after pectoralis major tendon repair has been recently reported. Although this complication is rare, it may be possible to decrease such risk using newer techniques for myotenodesis. This study was designed to evaluate various unicortical stress risers created at the proximal humeral metadiaphysis during myotenodesis for repair of pectoralis major ruptures. A simulated pectoralis major myotenodesis was performed using fourth-generation Sawbones (N=30). Using previously described anatomic landmarks for the tendinous insertion, 3 repair techniques were compared: bone trough, tenodesis screws, and suture anchors (N=10 each). Combined compression and torsional load was sequentially increased until failure. Linear and rotational displacement data were collected. The average number of cycles before reaching terminal failure was 383 for the bone trough group, 658 for the tenodesis group, and 832 for the suture anchor group. Both the tenodesis and the suture anchor groups were significantly more resistant to fracture than the bone trough group (P<.001). The suture anchor group was significantly more resistant to fracture than the tenodesis group (P<.001). All test constructs failed in rotational stability, producing spiral fractures, which incorporated the unicortical defects in all cases. When tested under physiologic parameters of axial compression and torsion, failure occurred from rotational force, producing spiral fractures, which incorporated the unicortical stress risers in all cases. The intramedullary suture anchor configuration proved to be the most stable construct under combined axial and torsional loading. Using a bone trough technique for proximal humerus myotenodesis may increase postoperative fracture risk.