Kinematic Predictors of Peak Elbow Varus Moments in Adolescent Baseball Pitchers: 2200 Board #352 June 2, 2: 00 PM - 3: 30 PM.

High-magnitude elbow joint moments during overhead throwing may lead to acute or overuse injuries, especially to the medial epicondyle physis and ulnar collateral ligament (UCL). During the pitching motion, the UCL is responsible for 54% of the elbow varus moment that is required to resist valgus motion. The identification of kinematic variables that predict high-magnitude elbow varus moments in adolescent baseball pitchers is needed. PURPOSE:To develop a predictive model for peak elbow varus moments in adolescent male pitchers based on overhead throwing kinematic variables. METHODS:Ten male baseball pitchers (14.9±1.1 years; 175.7±6.7 cm; 80.5±17.9 kg) threw three fastball windup pitches while three-dimensional motion data were recorded using a 10 camera, digital motion analysis system (480 Hz). A total of 24 kinematic variables were analyzed at three temporal events occurring during the pitching motion: 1) Lead footstrike (FS), 2) Peak glenohumeral external rotation (GHER), and 3) Ball release (BR). Elbow varus joint moments were normalized to body weight and height. A multiple linear regression (MLR) using the stepwise procedure was employed to identify a predictive model for peak elbow varus moments. RESULTS:The MLR model identified five significant kinematic variables predictive of peak elbow varus moments (adj. R2=0.90, p<0.001). The model revealed that significant predictors of peak elbow varus moments included contralateral trunk lean (CTL) at FS (β=0.007, p<0.001), sagittal lead knee angle (LKA) at FS (β=-0.030, p<0.001), trunk rotation (TR) at FS (β=-0.011, p<0.001), longitudinal glove distance (LGD) at GHER (β=0.002, p=0.001) and release point distance (RPD) (β=0.011, p=0.04). Standardized β values revealed CTL at FS (β=0.699) as the strongest predictor of peak elbow varus moments, followed by LKA (β=-0.289), TR (β=-0.271), LGD (β=0.232) and RPD (β=0.139). CONCLUSIONS: Greater CTL, less flexed LKA and counter-clockwise TR at FS, greater LGD at GHER and greater RPD at BR are tendencies associated with greater elbow varus moments in adolescent male baseball pitchers. Modifying pitching mechanics may reduce excessive elbow varus moments and decrease risk of elbow injury in adolescent pitchers.