Changes in the Medial Elbow Joint During Repetitive Pitching and Related Factors in High School Baseball Players: An...

The medial elbow joint undergoes changes after repeated pitching; however, the relationship with elbow valgus torque remains unclear. This study aimed to investigate the relationship between the rate of change in medial elbow conditions and the factors related to physical characteristics, including the maximum elbow valgus torque (MEVT) after 100 repetitive pitches.

Descriptive laboratory study.

This controlled laboratory study included 26 male high school baseball players from a baseball team. Participants were instructed to throw 100 pitches (20 pitches × five sets). After pitching, the rate of change in the medial elbow joint width, ulnar collateral ligament (UCL), and stiffness of the forearm flexor pronator muscles (FPMs) were examined using ultrasound imaging. The primary outcome was the post-to-pre pitching change ratio of medial elbow tissue; associated factors were evaluated using stepwise multiple regression analysis.

Immediately after pitching, the medial elbow joint width significantly increased, whereas the UCL and FPMs stiffness significantly decreased. The change rate in the medial elbow joint width was associated with the pre-pitch medial elbow joint width. The change rate in UCL stiffness correlated with the nMEVT and shoulder abduction strength. In addition, the change rate in FPM stiffness was associated with the thoracic kyphosis angle at maximum shoulder flexion and change in thoracic kyphosis angle.

Completion of 100 pitches resulted in changes in the medial elbow. Only the rate of change in UCL stiffness after repetitive pitching was related to nMEVT. These findings support monitoring ultrasound-based medial elbow changes after pitching and warrant prospective evaluation of whether their magnitude and the IMU-derived metric relate to later symptoms or injury.

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