Influence of infraspinatus and subscapularis pathologies on supraspinatus muscle atrophy-a retrospective cohort study

Introduction: Many factors could affect the supraspinatus (SSP) muscle after tendon rupture. We aimed to determine how infraspinatus and subscapularis tendon problems affect supraspinatus muscle atrophy associated with tears, in a retrospective cohort study conducted in a tertiary-level centre. Materials and Methods: Fifty-eight patients with a full-thickness SSP tendon tear who fulfilled the inclusion criteria were enrolled in the study. They were evaluated for tear retraction, fatty degeneration, and other rotator cuff tendon pathologies. Supraspinatus muscle was assessed using the Goutallier classification, and its average area was also measured. Accompanying lesions of the subscapularis and infraspinatus tendons and degree of supraspinatus muscle atrophy were evaluated using magnetic resonance imaging. Results: Our results showed that supraspinatus tendon tears ranged between 3mm and 41mm, and the estimated average cross-sectional area of the SSP muscle was 247.6mm2. Any degree of infraspinatus tendon pathology, ranging from tendinosis to full-thickness tears, was significantly correlated with the SSP muscle area (P < 0.05). The subscapularis tendon pathologies did not show a similar correlation. The interobserver and intraobserver reliabilities of the measurements were graded as excellent. Conclusion: Impairment of any of the rotator cuff muscles may affect the other muscles inversely. Our study showed that all infraspinatus tendon pathologies and partial subscapularis tears affect and alter the SSP muscle belly. We suggest early intervention for supraspinatus tears to avoid further fatty degeneration, as muscle atrophy and fatty degeneration progress in combination with the accompanying lesions.