Biomechanical evaluation of subscapularis repair used during shoulder arthroplasty.

Dysfunction of the subscapularis after total shoulder replacement has become concerning and may represent poor tendon healing after surgical repair. The objectives of this study were to evaluate the restoration of subscapularis footprint anatomy and failure strength for subscapularis repair via transosseous tunnels and a second anatomic repair via combined transosseous tunnels and direct tendon-to-tendon repair. Six matched pairs of fresh-frozen human cadaveric shoulders were used, with one shoulder from each pair randomly assigned to a transosseous repair and the contralateral shoulder assigned to a combined transosseous tunnel and direct tendon-to-tendon repair. The repair footprint was digitized. Cyclic loading to the tendon repair was performed followed by a constant ramp displacement to complete failure. The transosseous tunnel repair insertional footprint area (228.6 mm2) was significantly less than that of the native footprint (697.3 mm2), and the footprint centroid moved 9.1 mm medially (P = .0001) and 5.5 mm superiorly (P = .003). The combined repair required a statistically significantly greater number of cycles (P = .028) to reach a 5-mm gap (205.7 +/- 65.1) than did the isolated transosseous tunnel technique (76.4 +/- 34.2). A similar greater number of cycles was observed for the 10-mm gap (P = .01) for combined repair (307.5 +/- 82.4) compared with isolated transosseous repair (166.2 +/- 85.8). This study has shown that transosseous tunnel repair alters subscapularis insertional anatomy, resulting in weaker strength of fixation and less contact area when compared with combined transosseous tunnel and direct tendon-to-tendon repair.