Healed Subscapularis and Its Clinical Implications for Internal Rotation in Humeral Lateralized Reverse Shoulder Arthroplasty

Abstract

The efficacy of subscapularis (SSC) repair in reverse shoulder arthroplasty (RSA) remains controversial. Few studies have evaluated the postoperative integrity and effect on clinical outcomes of repaired SSC; however, conflicting results regarding whether the healing of the repaired SSC influences outcomes have also been reported. Therefore, this study aimed to address the controversy by evaluating clinical outcomes in SSC repair compared to non-repair after humeral lateralized RSA, and to evaluate the significance of the integrity of the repaired SSC. This study included patients who underwent humeral lateralized RSA between 2015 and 2019 and categorized them into two groups: repaired (n=66) and non-repaired (n=36) SSCs. The clinical outcomes, such as the visual analog scale score, constant score, American Shoulder and Elbow Surgeons (ASES) score, active range of motion (aROM), activities of daily living scores consisting of active internal rotation and forward flexion (ADL score), and rotational strength, were compared. Ultrasonography was used to assess the integrity of the repaired SSC following the modified Sugaya classification and to evaluate the acromial fracture. Subgroup analysis was performed on patients with healed SSC versus non-healed SSC, versus non-repaired SSC. Overall, 102 patients were included, with a mean age of 73 ± 5 years. Both groups exhibited substantial postoperative improvements in clinical scores, active ROM, and rotational strength without significant differences. At the 2-year follow-up, 52% of patients showed healed tendons, while 44% exhibited retears in the repaired SSC group. Significant clinical improvements were noted in both groups, regardless of the SSC integrity. However, the healed SSC group exhibited significantly improved outcomes in ADL score, IR aROM, and IR strength compared to the non-healed SSC group (p=0.002, p=0.011, p<0.001). Meanwhile, compared to the non-repaired SSC group, the healed SSC group also showed significant improvements in IR aROM and IR strength (p=0.016, p=0.002), but the difference in ADL score was not statistically significant (p=0.133). Furthermore, while the SSC repair group showed a marginally higher rate of acromial fractures (9% vs. 6%, p=0.709) as evaluated through both radiography and ultrasonography, the overall rates of complications remained statistically comparable across the groups (13% vs. 11%, p=0.854). Healed SSC groups showed significantly better IR aROM, and IR strength than both non-healed and non-repaired SSC groups, highlighting SSC healing's crucial role in enhancing IR functional outcomes even with humeral lateralized RSA; hence, SSC repair should be advocated whenever possible during RSA, though further research is needed to improve its low healing rate.