The purpose of this study was to clarify the mechanism of rotator cuff tears seen in baseball players.
Forty baseball players who injured their shoulders through repetitive throwing and underwent shoulder arthroscopy were studied retrospectively using a videotaped arthroscopic tour. They ranged in age from 13 to 48 years (average: 24 years) and were classified into 3 groups according to the rotator cuff findings: articular-side partial rotator cuff tear (APRCT)in Group 1 (29 patients), cuff inflammation only in Group 2 (5 patients), and intact cuff in Group 3 (6 patients). The existence and the site of rotator cuff tears, labral tears and notches of the greater tuberosity were examined in each group.
All APRCTs were located around the posterior aspect of the supraspinatus tendon (SSP) and the anterior aspect of the infraspinatus tendon (ISP). Localized splits of the posterior rotator interval were recognized in 5 patients. In most of the other patients in Group 1, the deepest APRCT was also located in the posterior rotator interval. Posterior-superior labral fraying was seen in 22 patients (17/29 in Group 1,0/5 in Group 2, and 5/6 in Group 3). However, posterior labral lesions localized to the superior portion were only recognized in 4 patients in Group 1 and SLAP lesions were combined with this posterior lesion in 5 patients. The remaining 8 patients in Group 1 had labral fraying of the whole posterior portion. A notch of the greater tuberosity around the insertion of the ISP was recognized in 23 players, which showed it had a significant relationship to cuff lesions (21/29 in Group 1,2/5 in Group 2, and 0/6 in Group3).
The most significant APRCTs were located around the posterior rotator interval between the SSP and ISP. APRCTs caused by repetitive throwing activity may be initiated by tearing between the SSP and ISP due to an eccentric or shearing force. They were not always associated with posterior-superior labral lesions as predicted by the internal impingement theory.
