A biomechanical comparison of subscapularis tenotomy repair techniques for stemless shoulder arthroplasty.

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 regarding this technique in the biomechanical and clinical literature. Accordingly, this study investigated subscapularis tenotomy repair with stemless TSA with 2 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) to biomechanically compare 2 methods of subscapularis tenotomy repair after stemless TSA-side-to-side repair and anchor-based repair.

METHODS

We used 12 male shoulder specimens for this study. To address our first objective, measurements were made to calculate 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 2 groups (n = 6 in 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.

RESULTS

The mean subscapularis tendon width measured from the medial insertion at the lesser tuberosity to the muscle-tendon junction varied depending on the level: 19.5 mm superiorly (95% confidence interval [CI], 16.2-22.8 mm); 18.3 mm at the midportion (95% CI, 13.6-23.0 mm); and 13.1 mm inferiorly (95% CI, 9.1-17.1 mm). 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 one-third of specimens having no tendon left medially at this level. On comparison of tenotomy repair techniques, the anchor-based technique had a 57% higher ultimate load to failure compared with the side-to-side repair (448 N vs. 249 N, P < .001). There were no significant differences in cyclic displacement (6.1 mm vs. 7.1 mm, P = .751) and construct stiffness (38.1 N/mm vs. 42.9 N/mm, P = .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 a better time-zero ultimate load to failure compared with side-to-side repair.