Reduction in the Occupation Ratio of the Supraspinatus Muscle on CT Following a Simulated Acute Retracted Rotator Cuff Tear

Objective This study was designed to determine the supraspinatus cross-sectional area and occupation ratio in a simulated retracted rotator cuff tear to quantify the reduction of the supraspinatus volume during acute simulated retraction. Methodology Eight CT shoulder scans of patients with normal rotator cuff anatomy were analyzed. CT scans were reoriented to create the Y-view in the oblique sagittal plane. The supraspinatus muscle and fossa cross-sectional areas were measured at the Y-view, and the occupation ratio was calculated. The supraspinatus muscle was also measured at 5, 10, 15, and 20 mm increments toward its insertion, to permit simulation of retraction. The volume of the simulated retracted supraspinatus muscle was extrapolated to the fossa size in the Y-view to create simulated occupation ratios at above mentioned increments. The data set was collected by three different surgeons on two occasions. Results Four-level model analysis showed a decrease in supraspinatus muscle surface area and thus occupation ratio at 5-, 10-, 15-, and 20-mm intervals (<i>P</i> < 0.001). Conclusions Rotator cuff tear is a common presentation in elderly populations. The supraspinatus is a fusiform muscle whose cross-sectional diameter decreases towards its insertion. When determining the reparability of supraspinatus tears, the atrophy and fatty degeneration of the muscle are often used. In a simulated acute supraspinatus tear, muscle retraction led to a significant reduction in cross-sectional area when viewed in the Y-view. This could be misdiagnosed as atrophy, and surgeons should consider this when determining the reparability of acute rotator cuff tears.