Pathomechanics of Throwing Injuries of the Shoulder —An Arthroscopic and A Biomechanics Study—

Abstract

Shoulder pain is one of most common complaints among baseball pitchers. This study attempts to clearify the pathomechanics of throwing injuries of the shoulder and compare the findings with arthroscopes and motion analyses. An arthroscopic study : Ten injured baseball players were studied. Nine players had Biceps tendon labrum complex lesions (BLC lesion) and seven players had partial thickness rotator cuff tears. Two cases had insufficient AIGHL with Bennett lesions. A biomechanics study : Five baseball player with shoulder pain and six top athlete baseball players as the control were studied. The subjects were filmed pitching from two directions, and the pictures were syncronized with each other. Velocity, angle and angle velocity the of trunk and the upper arm were calculated using APAS (Ariel Performance Analysis System). The time of maximum velocities of the shoulder, elbow and wrist of the injured players was faster than those of the top athletes, but the intervals of time of maximum velocity between the elbow and the wrist were longer. Comparing stick figures between injured players and top athletes, the upper arm motions of the subjects were larger than those of the top athletes in the acceleration phase. Perhaps these motions induce shoulder stress from the posterior-inferior to anterior-superior on the glenoid according to arthroscopic findings and X-rays. Repeating this stress, the biceps tendon labrum complex is stripped off the glen oid, which induces rotator cuff tears. To prevent the shoulder from disorders and to accelerate the ball smoothly, trunk rotation without shoulder stress is most important in baseball pitc hing. © 2000, The Showa University Society. All rights reserved.