Forearm Rotation Moments are Associated with Elbow Varus Moments

OBJECTIVES: The incidence of upper extremity injury in baseball has increased over the past decade, and much of the research into the biomechanics of pitching has focused on the shoulder and elbow. However little attention has been placed on how forearm rotation and the forearm rotation moment could affect a pitcher’s risk of injury. Therefore this study sought to determine the association between forearm moments and the elbow varus moment in collegiate baseball pitchers. METHODS: Collegiate level baseball pitchers that were recruited for this study were actively pitching for an NCAA team and had no history of surgery to their pitching arms. All pitchers underwent a pitching analysis using computerized motion analysis techniques. The forearm’s position, rotational velocity, and supination and pronation moments were analyzed using a random intercept mixed-effects regression model to determine if there were significant associations between the variables of interest and the elbow varus moment. All moments are presented as internal moments. RESULTS: A total of 78 collegiate level pitchers with a mean age of 19.9 ± 1.3 years, were include in this study. The average fastball velocity was 32.1 ± 2.5m/s. The results indicated that there was no association with the forearm’s position or rotational velocity and the elbow varus moment. However, there were statistically significant associations between the forearm supination moment and the elbow varus moment (p=0.002). The results showed that for every 1Nm increase in the supination moment there was a corresponding 1 Nm increase in the elbow varus moment. Whereas a pronation moment was associated with a decrease in the elbow varus moment (p=0.013). CONCLUSION: The forearm’s absolute position was not associated with an increased elbow varus moment, indicating that the position of the forearm does not play a role in injury mechanisms for baseball pitchers. However the regression analysis indicated a significant association with the forearm moments and the elbow varus moment. Specifically that an increased supination moment increased the elbow varus moment. Therefore as the body resists the pronation motion associated with pitching this increases the stresses on the medial side of the elbow. Suggesting that an increased need to resist pronation in pitchers that over supinate their arms during a pitch could be placing additional stresses on their elbows and therefore increasing their risk for injury. This finding also provides evidence that a potential injury prevention strategy for pitchers could be to increase their forearm supination and reduce the speed at which they pronate especially during the deceleration of the pitch cycle.