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.