LAUSR

BACKGROUND One of the leading challenges for surgeons shifting to stemless anatomic total shoulder arthroplasty (TSA) is subscapularis repair. In the available literature reporting outcomes after stemless TSA, subscapularis tenotomy with side-to-side repair is the most common technique despite some concerns in biomechanical and clinical literature with this technique. Accordingly, the present study investigated repair of subscapularis tenotomy with stemless TSA with two primary objectives: (1) to evaluate the subscapularis tendon dimensions with reference to subscapularis tenotomy to determine the amount of tendon remaining for side-to-side repair after shoulder arthroplasty and (2) biomechanically compare two methods of repair of subscapularis tenotomy after stemless TSA: side-to-side repair and anchor-based repair. METHODS 12 male shoulder specimens were utilized for the study. In the first objective, measurements were made to determine the dimensions of the subscapularis tendon at the superior, middle and inferior levels to determine the amount of tendon remaining after tenotomy. These specimens were then divided into two groups (n = 6 each group) to biomechanically compare subscapularis tenotomy repair with (1) traditional side-to-side repair and (2) anchor-based repair. The shoulders then underwent biomechanical testing with primary outcomes including load to failure and cyclic displacement evaluation. RESULTS The mean subscapularis tendon width measured from the medial insertion at the lesser tuberosity to the muscle tendon junction varied depending on level: 19.5 mm [95% CI 16.2mm - 22.8mm] superiorly; 18.3 mm at midportion [95% CI 13.6mm - 23.0mm]; and 13.1 mm [95% CI 9.1mm - 17.1mm] inferiorly. With a tenotomy made 1 cm medial to the lesser tuberosity insertion, a mean of 3.1 mm of tendon remained medially at the inferior subscapularis, with 1/3 of specimens having no tendon left medially at that level. When comparing tenotomy repair techniques, the anchor-based technique had a 57% higher ultimate load to failure compared to side-to-side repair (448N vs 249N, p < 0.001). There were no significant differences in cyclic displacement (6.1mm vs 7.1mm, p = 0.751) and construct stiffness (38.1 N/mm vs 42.9 N/mm, p = 0.461) between techniques. CONCLUSIONS With traditional techniques for subscapularis tenotomy for anatomic TSA, there is very little tendon remaining inferiorly for side-to-side repair. When subscapularis tenotomy is performed for stemless TSA, a double-row anchor-based repair has better time-zero ultimate load to failure compared to side-to-side repair.