Effects of Contralateral Trunk Tilt on Shoulder and Elbow Injury Risk and Pitching Biomechanics in Professional Baseball Pitchers

Abstract

Background: Baseball pitchers employ various contralateral trunk tilt (CTT) positions when pitching depending on if they have an overhand, three-quarter, or sidearm delivery. There are no known studies that have examined how pitching biomechanics are significantly different in professional pitchers with varying amounts of CTT, which may provide insight into shoulder and elbow injury risk among pitchers with different CTT. Purpose: To assess differences in shoulder and elbow forces and torques and baseball pitching biomechanics in professional pitchers with maximum 30° to 40° CTT (MaxCTT), moderate 15° to 25° CTT (ModCTT), and minimum 0° to 10° CTT (MinCTT). Study Design: Controlled laboratory study. Methods: In total, 215 pitchers were examined, including 46 pitchers with MaxCTT, 126 pitchers with ModCTT, and 43 pitchers with MinCTT. All pitchers were tested using a 240-Hz, 10-camera motion analysis system, and 37 kinematic and kinetic parameters were calculated. Differences in kinematic and kinetic variables among the 3 CTT groups were assessed with a 1-way analysis of variance (P < .01). Results: Maximum shoulder anterior force and maximum elbow proximal force were significantly greater in ModCTT (403 ± 79 N) than MaxCTT (369 ± 75 N) and MinCTT (364 ± 70 N), while maximum elbow flexion torque and shoulder proximal force, respectively, were significantly greater in ModCTT (69 ± 11 N·m and 1176 ± 152 N, respectively) than MaxCTT (62 ± 12 N·m and 1085 ± 119 N, respectively). During arm cocking, maximum pelvis angular velocity was greater in MinCTT than MaxCTT and ModCTT, and maximum upper trunk angular velocity was greater in MaxCTT and ModCTT than MinCTT. At ball release, trunk forward tilt was greater in MaxCTT and ModCTT than MinCTT and greater in MaxCTT than ModCTT, while arm slot angle was less in MaxCTT and ModCTT than MinCTT and less in MaxCTT than ModCTT. Conclusion: The greatest shoulder and elbow peak forces occurred in ModCTT, which occurs in pitchers who throw with a three-quarter arm slot. More research is needed to assess if pitchers with ModCTT are at a higher risk of shoulder and elbow injury compared with pitchers with MaxCTT (overhand arm slot) and MinCTT (sidearm arm slot), although in the pitching literature, excessive elbow and shoulder forces and torques have been shown to correlate with elbow and shoulder injuries. Clinical Relevance: The results from the current study will help clinicians better understand if differences in kinematic and kinetic measures differ with pitching, or if differences in force, torque, and arm position occur at different arm slots.