Supraspinatus muscle occupation ratio predicts rotator cuff reparability

Background We wished to determine the correlation between supraspinatus muscle occupation ratio and reparability of rotator cuff muscles and that of each occupation ratio with 1-muscle, 2-muscle, and 3-muscle rotator cuff injury. Methods We evaluated 170 patients (average age, 62.3 [40-83] years) with complete (type II) or incomplete (type III) rotator cuff repair by arthroscopy. Type II repair was defined as complete repair but less optimal coverage of the entire medial-lateral footprint. Type III repair was defined as incomplete repair; a small portion (<10 mm) of the humeral head is exposed. Patients were divided into 2 groups: 96 and 74 patients who underwent type II and type III repair, respectively. Patients were also categorized into 4 groups: isolated supraspinatus tears, supraspinatus and infraspinatus tears, supraspinatus and subscapularis tears, and tears in all 3 muscles. Supraspinatus muscle atrophy was evaluated by the occupation ratio on the most lateral T1-weighted sagittal oblique view in which the scapular spine contacted the scapular body. The supraspinatus muscle occupation ratio was measured by 2 independent observers. Results On magnetic resonance imaging, the supraspinatus muscle occupation ratio was significantly different between the completely repaired and incompletely repaired groups. The mean occupation ratio of the completely repaired group (42.39 ± 10.1) was significantly higher than that of the incompletely repaired group (36.64 ± 6.94). The cutoff value of the supraspinatus muscle occupation ratio (complete to incomplete repair) was 41. The supraspinatus muscle occupation ratio significantly decreased as the tear increased (P < .001). Conclusion A supraspinatus muscle occupation ratio of <41 can be the cutoff value for greater tuberosity coverage vs. incomplete coverage. There was a significant correlation between tear pattern and supraspinatus muscle atrophy ratio. The supraspinatus tear group had the lowest degree of muscle atrophy.