Biomechanical Evaluation of Unicortical Stress Risers of the Proximal Humerus Associated With Pectoralis Major Repair

Abstract

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. [Orthopedics. 2017; 40(5):e801-e805.].

Outcomes and Return to Sport After Pectoralis Major Tendon Repair: A Systematic Review

“…12,37 Other studies have found varying results when comparing bone trough repairs with suture anchor repairs, with 1 reporting that bone trough repairs were stronger and another reporting that bone trough techniques may increase postoperative fracture risk. 34,39 Wilson et al 39 found that unicortical button fixation with larger caliber suture and suture tape may provide superior construct strength compared with transosseous suture repairs. 39 The interval between injury and surgery may have an impact on the outcome after pectoralis major tendon repair.…”

“…34,39 Wilson et al 39 found that unicortical button fixation with larger caliber suture and suture tape may provide superior construct strength compared with transosseous suture repairs. 39 The interval between injury and surgery may have an impact on the outcome after pectoralis major tendon repair. 5 While several included studies have noted marginally better functional outcomes after acute repairs compared with chronic repairs, 1,2,26,35 none of the included studies indicated statistically significantly improved outcomes in acute repairs, although the majority of studies were not sufficiently powered to show differences between the 2 groups.…”

Anatomic Pectoralis Major Repair With Intramedullary Anchor Fixation

“… 15 Wilson et al. 16 performed a biomechanical study testing the effects of cortical defects on the humeral diaphysis. Their study compared the effect of a 5-mm × 40-mm bone trough, two 7-mm × 15-mm biocomposite interference screws, and three 2.9-mm unicortical suture anchors.…”

“…Proximal humeral shaft fractures may occur at the site of bone troughs and cortical drill holes after a pectoralis tendon rupture repair. 15 Wilson et al 16 performed a biomechanical study testing the effects of cortical defects on the humeral diaphysis. Their study compared the effect of a 5-mm  40-mm bone trough, two 7mm  15-mm biocomposite interference screws, and three 2.9-mm unicortical suture anchors.…”

“…In addition, the unicortical suture anchors were the most resistant to fracture. 16 When repairing the pectoralis major, we believe it is important to re-create the anatomic pectoralis major footprint. The clavicular head commonly remains intact; therefore, it helps to define the distal-most insertion of the tendon.…”