Background: Increased external rotation (ER) and decreased internal rotation (IR) of the dominant shoulder (DS) compared to the nondominant shoulder (NDS) are frequently observed in throwing athletes. However, few studies demonstrated when the changes in shoulder rotation occurred and how it developed.
Purpose: The purpose of this study was to determine when the side-to-side difference in shoulder rotation was present in baseball players, and to clarify the relationship between the degrees in rotation, and physical findings.
Materials and Methods: One thousand eighty-nine baseball players and 423 soccer players were investigated. The ages of baseball players ranged from 10 to 15, and those of soccer players from 10 to 14. ER and IR, the crank test, the sulcus sign, and the general joint laxity were examined. ER and IR were measured at 90 degrees abduction in both shoulders. The questionare including age, position played, shoulder pain on throwing during prior 6 months, and the progression of shoulder pain used for the baseball players.
Results: In the baseball players, ER in DS and NDS were 120 and 117 degrees in 10 years old players, 117 and 114 degrees in 11, 115 and 110 degrees in 12, 120 and 113 degrees in 13, 115 and 110 degrees in 14, and 112 and 105 degrees in 15. In the soccer players, ER in DS and NDS were 119 and 118 degrees in 10 years old players, 118 and 114 degrees in 11, 114 and 111 degrees in 12, 119 and 117 degrees in 13, and 111 and 109 degrees in 14. ER of DS was significantly greater than NDS from 10 to 15 years old baseball players, and in 11 and 12 years old soccer players. In the baseball players, IR in DS and NDS were 55 and 64 degrees in 10 years old players, 56 and 63 degrees in 11, 54 and 63 degrees in 12, 59 and 68 degrees in 13, 57 and 67 degrees in 14, and 57 and 68 degrees in 15. In the soccer players, IR in DS and NDS were 56 and 63 degrees in 10 years old players, 56 and 63 degrees in 11, 56 and 64 degrees in 12, 61 and 64 degrees in 13, and 63 and 66 degrees in 14. IR of DS was significantly less than NDS from 10 to 15 years old baseball players, and from 10 to 12 years old soccer players. IR of DS and NDS in the baseball players with positive crank test were 53 and 62 degrees, and those with negative crank test were 57 and 66 degrees. IR of both the shoulders was significantly decreased in the baseball players with positive crank test. ER of DS and NDS in baseball players with general joint laxity were 120 and 116 degrees, and those without general joint laxity were 116 and 111 degrees. ER of both shoulders was significantly increased in the baseball players with general joint laxity.
Conclusion: There was side-to-side difference in shoulder motion from 10 to 15 years old baseball players, but there was not side-to-side difference in over than 12 years old soccer players. In baseball players, the results of crank test and general joint laxity related the changes in IR and ER, respectively.
