The Influence Of Rotator Cuff Muscles And Lateralization On Internal And External Rotation In Reverse Shoulder Arthroplasty

Background: The subscapularis and its antagonist muscles, the infraspinatus-teres minor, affect functional rotational movements in daily life. A deficiency in either of these muscles leads to a strength imbalance. In patients undergoing reverse shoulder arthroplasty (RSA), the repair of the subscapularis muscle is a debated topic. This study aimed to determine the relationship between the isokinetic and endurance values of internal and external rotation in patients post-RSA, and the presence of this muscle pair and lateralization. Methods: Thirty-one patients who underwent RSA between 2020-2023 were retrospectively included in the study. Isokinetic and endurance values were measured using a dynamometer device. Lateralization was calculated from postoperative X-ray images by determining the global offset . Patients’ Visual Analogue Scale (VAS), American Shoulder and Elbow Surgeons Score (ASES), and Constant scores were measured, and range of motion (ROM) was evaluated. Based on the presence of the subscapularis and infraspinatus-teres minor muscles, patients were divided into four groups (Group A, B, C, D). Results: Isokinetic and endurance values for both internal and external rotation were significantly higher in Group A. There was a significant and strongly negative correlation between the presence of these muscles for isokinetic and endurance values of internal and external rotation from Group A to Group D. A significant positive correlation was found between component lateralization and isokinetic and endurance values of external rotation. A significant negative correlation was identified between lateralization and internal rotation ROM difference. Conclusions: The presence of the force couple in the post-RSA period positively impacts the isokinetic and endurance values of shoulder rotational movements.