Skeletal Modeling Parameters and Clinical Factors Related to Injury Risk in Baseball Pitchers

ABSTRACT Baseball pitching is a well-studied area of biomechanics partially due to high injury rates in the upper extremity. While current known injury risk factors for pitchers include limited shoulder range of motion (ROM), increased ball velocity, and limited shoulder strength, there has been a lack of scientific evidence linking increased joint kinetics to injury risk. The aims of this research were to (1) explore relationships between known risk factors for injury and joint kinetics, (2) establish more specific biomechanical models of pitchers to calculate joint kinetics with greater precision, and (3) deploy these models prospectively to determine how model sensitivity influenced injury risk findings. The first study was cross-sectional where pitchers were examined clinically for shoulder ROM and rotator cuff strength. Pitchers then returned for biomechanics data collection where their throwing mechanics were recorded. Results from the study indicated that passive shoulder ROM, fastball velocity, and rotator cuff strength are linked to elbow and shoulder joint loads in pitchers. This study demonstrated how known risk factors for injury may be related to internal joint stresses pitchers experience when pitching. A model sensitivity study was conducted using dual-energy X-ray absorptiometry (DXA) scans to obtain individual-specific body segment inertial parameters (BSIPs) in pitchers. Compared to individualized models, using traditional models to compute upper extremity joint kinetics introduced a measurement error of approximately ±17%. This study demonstrated the importance of model specificity for accurate joint kinetic calculations. Lastly, a prospective injury study in which pitchers were followed for the duration of their respective seasons was conducted. Elbow joint kinetics, using both modeling methods described above, were used to determine the relationship between elbow varus torque and medial elbow injury risk. Results from the study indicate that elbow varus torque is likely a risk factor for throwing-related injury; however, risk may be overestimated using traditional biomechanical models. Joint kinetics, shoulder ROM, rotator cuff strength, and fastball velocity all may play a significant role in injury risk for pitchers. While joint kinetics may be related to injury risk, caution should be taken when using traditional modeling methods as these may exaggerate true injury risk