Baseball pitching biomechanics in relation to pain, injury, and surgery: A systematic review.

OBJECTIVES: To investigate the relationship between baseball pitching biomechanics and pain, injury, or surgery, in pitchers of all ages and competition levels. DESIGN: Systematic review. METHODS: This study was registered on Prospero (CRD42019137462). Four online databases (MEDLINE, SPORTDiscus, CINAHL, and Embase) from inception to June 13, 2019 were systematically searched. Risk of bias was assessed through the modified Downs and Black. RESULTS: 967 titles/abstracts were screened with 11 studies (1376 pitchers) included. Four studies used 3D biomechanical analyses, five studies video analysis, and two studies evaluated EMG activity. Level 1b evidence suggests that injured pitchers had greater elbow valgus torque at late arm cocking (injured: 91.6Nm, non-injured: 74.7Nm, p=0.013) and early trunk rotation was predictive of increased upper extremity surgical risk (Hazard Ratio: 1.69 (95% CI 1.02-2.80)). Level 3b evidence observed pitchers with upper extremity surgical history had greater lateral trunk tilt at release (surgery: 29.3°, controls: 23.4°, p=0.035), and flexor carpi ulnaris EMG activity was decreased (injured: 68% MMT, controls: 103% MMT) in pitchers with elbow injury. CONCLUSIONS: Increased elbow valgus torque and early trunk rotation were injury risk factors, and elbow injured pitchers displayed diminished forearm muscle activity. Due to the low power of many of these studies, and the lack of prospective 3D biomechanical studies, other pitching biomechanical variables cannot be ascertained as injury risk factors. Future studies are needed to prospectively assess pitching injury risk through 3D biomechanical methods.