Referencing the pectoralis major tendon for humeral stem height placement in reverse shoulder arthroplasty for fracture

Background: Proximal humerus fractures remain a challenging problem, and reverse total shoulder arthroplasty (RSA) has demonstrated reliable outcomes in fracture applications. Despite this, guidelines for placement of the humeral component are lacking. Methods: Twelve cadaveric shoulders (6 cadaveric torsos) were utilized. An onlay RSA stem was placed with the lateral potion of the humeral cup positioned at the level of the greater tuberosity. Measurements were taken from the top of the pectoralis major tendon to the top of the humeral stem. A separate computer-aided analysis was conducted analyzing the height of an RSA humeral stem and an RSA humeral stem with a cup using values extrapolated from prior data. Results: The average distance from the top of the pectoralis to the top of the humeral stem was 4.0 cm (3.4 cm to 4.8 cm) with a standard deviation of 4.1. The humeral cup added an average of 9.1 mm. Computer-aided design data demonstrated the average height of the humeral stem was 3.9 cm above the superior aspect of the pectoralis tendon, and the average height with the humeral cup added was 4.8 cm. Conclusion: Both the cadaveric and computer-aided design data demonstrated a similar height for both the distances from the superior portion of the pectoralis to the superior aspect of an onlay RSA stem and the humeral cup. The measurement from the humeral cup may allow for translational use with inlay RSA humeral stems. This study demonstrates the superior border of the pectoralis major tendon to be a reliable landmark in RSA humeral stem placement.