Location and initiation of degenerative rotator cuff tears: an analysis of three hundred and sixty shoulders.

BACKGROUND It has been theorized that degenerative rotator cuff tears most commonly involve the supraspinatus tendon, initiating at the anterior portion of the supraspinatus insertion and propagating posteriorly. The purposes of this study were to determine the most common location of degenerative rotator cuff tears and to examine tear location patterns associated with various tear sizes. METHODS Ultrasonograms of 360 shoulders with either a full-thickness rotator cuff tear (272) or a partial-thickness rotator cuff tear (eighty-eight) were obtained to measure the width and length of the tear and the distance from the biceps tendon to the anterior margin of the tear. Tears were grouped on the basis of their size (anteroposterior width) and extent (partial or full-thickness). Each tear was represented numerically as a column of consecutive numbers representing the tear width and distance posterior to the biceps tendon. All tears were pooled to graphically represent the width and location of the tears within groups. Frequency histograms of the pooled data were generated, and the mode was determined for each histogram representing various tear groups. RESULTS The mean age (and standard deviation) of the 233 subjects (360 shoulders) was 64.7 +/- 10.2 years. The mean width and length of the tears were 16.3 +/- 12.1 mm and 17.0 +/- 13.0 mm, respectively. The mean distance from the biceps tendon to the anterior tear margin was 7.8 +/- 5.7 mm (range, 0 to 26 mm). Histograms of the various tear groups invariably showed the location of 15 to 16 mm posterior to the biceps tendon to be the most commonly torn location within the posterior cuff tendons. The histograms of small tears (a width of <10 mm) and partial-thickness tears showed similar distributions of tear locations, indicating that the region approximately 15 mm posterior to the biceps tendon may be where rotator cuff tears most commonly initiate. CONCLUSIONS Degenerative rotator cuff tears most commonly involve a posterior location, near the junction of the supraspinatus and infraspinatus. The patterns of tear location across multiple tear sizes suggest that degenerative cuff tears may initiate in a region 13 to 17 mm posterior to the biceps tendon.