Infraspinatus muscle atrophy in professional baseball players.

BACKGROUND: Infraspinatus muscle atrophy has been observed in athletes who stress their upper extremities in an overhead fashion. The majority of such case reports have been in volleyball players, with far fewer cases reported in baseball players.

HYPOTHESIS: Infraspinatus muscle atrophy occurs to a notable degree in professional baseball players.

STUDY DESIGN: Retrospective cohort study.

METHODS: At the end of the 1999 baseball season, data were collected from all Major League Baseball teams in regards to players affected with infraspinatus muscle atrophy.

RESULTS: Twelve of the 1491 major league professional baseball players were identified as having appreciable infraspinatus muscle atrophy. There was an increased prevalence of the muscle atrophy in professional pitchers (10 of 494, 4%) compared to position players (2 of 997, 0.2%) (P <0.001). Among affected pitchers, the atrophy was identified more frequently in starting pitchers (8 of 10) compared to relief pitchers (2 of 10) (P = 0.036), pitchers who had played for more years at the major league level (8.7 +/- 4.9 versus 5.2 +/- 4.0) (P = 0.017), and pitchers who had thrown for more innings at the major league level (971.4 +/- 784.4 versus 485.0 +/- 594.6) (P <0.001).

CONCLUSION: Infraspinatus atrophy was identified in 4.4% of major league starting pitchers and occurred in those pitchers who pitched for more years and innings during their major league career.