Humeral retrotorsion in collegiate baseball pitchers with throwing-related upper extremity injury history.

Bilateral difference in the glenohumeral rotation range of motion is a common characteristic among competitive baseball players. Specifically, a typical baseball player would present with greater external rotation and less internal rotation on the dominant limb.4,5,12,17,35,39 While this bilateral difference is considered a healthy adaptation in baseball players, studies demonstrate that these limb differences in humeral rotation are more pronounced in those individuals diagnosed with a throwing-related shoulder or elbow injury, which indicates that changes in soft tissue characteristics (ie, passive joint rotation range of motion) beyond what is considered a normal adaptation may be associated with injuries.7,14,26,27,36 The bilateral limb difference in humeral rotation is often attributed to soft tissue tightness in the posterior shoulder. However, the limb difference is also influenced by the amount of humeral retrotorsion present within the upper extremity.28,35,40 For example, Myers et al28 demonstrated that the almost 15° of limb difference in humeral internal rotation found in baseball players became negligible once the amount of retrotorsion was accounted for. As such, the range of motion differences that are seen clinically with throwing-related upper extremity pain/injury may be partially explained by the amount of retrotorsion present and not soft tissue tightness alone. Research studies that examine the role that retrotorsion plays in throwing-related upper extremity injury are limited. It has been suggested that overhead athletes with increased humeral retrotorsion may be at less risk of shoulder injury.12,31,33 For example, Pieper et al33 demonstrated that competitive handball players with chronic shoulder pain had less retrotorsion in the dominant limb compared with the players with no shoulder pain. The authors hypothesized that the increased humeral retrotorsion may be an adaptation to repetitive external rotation from throwing during growth and that the athletes who failed to acquire the retrotorsion adaptations may experience the shoulder pain and anterior glenohumeral instability because they place more strain on their anterior capsules as the arm moves into external rotation during throwing. Whiteley et al43 conducted the only study to date specific to baseball players and throwing-related injury and demonstrated that the amount of retrotorsion present in the nondominant arm was predictive of whether upper extremity injury occurred in adolescent baseball players. In adolescent baseball players, having less retrotorsion in the nondominant limb was found to be predictive of throwing arm injury incidence. The retrotorsion on the nondominant limb is considered to represent the amount of retrotorsion the individual was born with (congenital retrotorsion). Yet the amount of humeral retrotorsion in the dominant limb represents the amount of retrotorsion gained from throwing adaptation superimposed on the congenital retrotorsion. Thus, the limb difference in humeral retrotorsion represents the amount of retrotorsion acquired on the dominant limb. It is thought that the less congenital retrotorsion an athlete has, the more retrotorsion the athlete has to acquire to place one’s limb in a cocking position. The authors speculated that the greater need/room for osseous adaptation makes the athlete susceptible to a throwing-related injury. However, due to the limited number of studies conducted in this area, it is still unclear what role retrotorsion plays in injury in the overhead athlete. Baseball pitchers are especially prone to throwing-related shoulder and elbow injuries, with higher incidences of injury reported at the high school,20 collegiate,13,24 and professional levels11 when compared with their position player counterparts. Thus, understanding the role that retrotorsion plays in the injuries that occur in a pitching population will be beneficial given the high incidence of pitching injuries reported. The purpose of this study was to compare dominant-limb retrotorsion, nondominant-limb retrotorsion, and bilateral limb difference retrotorsion in collegiate pitchers with and without a history of throwing-related shoulder or elbow injury.