Effects of repeated pitching on the elbow joint: Investigating changes in magnetic resonance images of elbow joints before and after 100 pitches

Overuse caused by repeated pitching is a crucial factor in pitching disorders. However, only a few studies have investigated changes in magnetic resonance （MR） images of elbow joints before and after pitching. This study examined MR images of elbow joints of 11 healthy baseball players before and after 100 pitches. Echography was used to measure the medial elbow joint space gapping, whereas a hand-held dynamometer was used to measure the upper-limb muscle strength. Kinematic and kinetic data during the pitching motion were measured using wearable sensors. MR images taken before and after pitching were used to investigate abnormalities in the medial collateral ligament （MCL）. Mean values were compared using paired Student t-test or the Wilcoxson test. MR images showed no abnormalities in the MCL before and after pitching. However, we observed a significant increase in the medial elbow joint space gapping and a significant decrease in the shoulder external rotation muscle strength in the zero position （Zero ER） after pitching. After throwing 100 pitches, the MCL showed no brightness or morphological changes on MR imaging. However, we noted an increase in the medial elbow joint space gapping and a decrease in Zero ER. The significant enlargement in the medial interspace distance before and after pitching suggests the development of MCL loosening. No brightness or morphological changes were observed on MR images, and none of the patients developed pain.