Partial-thickness tears of the rotator cuff were found exclusively in the tendon of the supraspinatus. Articular side partial tears were more common than bursal side partial tears. Most clinicians agreed that tears involving more than 50% of the thickness influence the surgeon to perform a repair. However, there has been no report demonstrating the thickness of supraspinatus insertion to the greater tuberosity in Japanese. The purpose of this study was to determine the thickness of the supraspinatus insertion to the greater tuberosity in MRI of shoulder joints. There were 32 subjects (mean age; 51 years old, range; 18-82 years old). The mean distance of the supraspinatus insertion at the 10 mm lateral to the bicipital groove was 9.5 ± 1.6 mm; there was no significant difference between male and female or right side and left. Articular side partial supraspinatus tear with more than 5 mm of exposed bone lateral to the articular cartilage edge was considered involving 50% of the tendon substance.
