Maximum shoulder external rotation during throwing motion on the elbow in injured baseball players.

The purpose of this study was to identify risk factors for medial elbow pain in high school baseball players by comparing the passive range of motion (ROM) of shoulder external rotation and maximum external rotation angle (MER) during throwing. Twenty high school baseball players who had recent episodes of medial elbow pain (elbow-injured group) and another twenty baseball players who had never experienced medial elbow pain (control group) participated in this experiment. Throwing motion data was collected by two high-speed video cameras, and three-dimensional (3D) coordinates of the shoulder complex were established by the direct leaner translation method for the MER calculation. Passive ROM of the shoulder external rotation was also bilaterally measured. Finally, the ratio of the MER to the ROM of the shoulder external rotation, which is the proposed index that shows the magnitude of valgus force on the elbow, was computed. A Mann-Whitney U test was performed for comparison. Although the difference was not statistically significant, the greater MER were found in the elbow-injured group than in the control group. In addition, the ratio of the MER to the ROM was significantly greater in the elbow-injured group. Our findings indicate that relatively large MER when compared with ROM could be one of the risk factors for medial elbow pain in high school baseball players. The greater ratio of the MER to the ROM may be responsible for increasing elbow valgus stress during throwing. [ABSTRACT FROM AUTHOR]