• Teruhisa Mihata, Rei Morikura, Akihiko Hasegawa, Kunimoto Fukunishi, Takeshi Kawakami, Yukitaka Fujisawa, Mutsumi Ohue, and Masashi Neo.
• Department of Orthopedic Surgery, Osaka Medical College, Takatsuki, Osaka, Japan.
• Am J Sports Med. 2019 Dec 1; 47 (14): 3476-3482.

BackgroundPartial-thickness rotator cuff tears are common shoulder injuries in baseball players. For some tears, the symptoms can be relieved through physical therapy or debridement without rotator cuff repair.PurposeTo assess whether partial-thickness rotator cuff tear by itself causes shoulder pain and muscle weakness in baseball players.Study DesignCross-sectional study; Level of evidence, 3.MethodsWe studied 87 university baseball players (age, 19.5 ± 0.8 years; baseball career, 11.5 ± 1.6 years). All data were obtained during a full-participation annual medical check in 1 team. Rotator cuff tendons were examined ultrasonographically and allocated to 4 groups: (1) no tear, (2) supraspinatus tendon tear, (3) infraspinatus tendon tear, and (4) both supraspinatus and infraspinatus tendon tears. Current shoulder pain and shoulder muscle strength (dominant/nondominant) in abduction, external rotation, and internal rotation were compared by using chi-square and t tests. All players could play baseball with or without shoulder pain in this study.ResultsOf the 87 players, 41 (47%) had articular-sided partial-thickness rotator cuff tears diagnosed on ultrasonography; the remaining 46 athletes were tear-free. Of the 41 affected patients, 19 had tears in the supraspinatus, 13 in the infraspinatus, and 9 in both the supraspinatus and infraspinatus tendons. Tear depth (mean ± SD) was 4.6 ± 2.3 mm in the supraspinatus and 6.2 ± 3.6 mm in the infraspinatus. Neither the rate of shoulder pain nor muscle strength differed significantly among the 4 groups (P = .96 and P = .15-.70, respectively).ConclusionArticular-sided partial-thickness rotator cuff tear-by itself-did not cause shoulder pain and muscle weakness in university baseball players. Most so-called articular-sided partial-thickness rotator cuff tears may not be pathologic tendon tears.

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