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May 7, 2026JSES International0 citationsOpen Access

Relation between forearm flexor–pronator muscle elasticity and ulnar collateral ligament laxity of the elbow joint in high school pitchers with and without medial elbow tenderness: evaluation using shear wave elastography

TTTsuyoshi Tajika HSHitoshi Shitara YHYuhei Hatori

Key Points

This study aims to evaluate the relationship between forearm flexor-pronator muscle elasticity and ulnar collateral ligament laxity in high school pitchers with and without elbow tenderness.
115 high school baseball pitchers underwent shear wave ultrasonography to measure muscle elasticity.
Participants were divided into two groups: 25 with medial elbow tenderness and 90 without.
Shear wave velocities of various flexor-pronator muscles were measured under and without valgus stress.
The average shear wave velocities were significantly lower in pitchers with medial elbow tenderness (p<0.05).
A strong correlation was found between decreased muscle elasticity and increased UCL laxity (r=0.76, p<0.01).
Pitchers with medial elbow tenderness exhibited a 30% higher risk of UCL laxity compared to the non-tender group.

Abstract

BackgroundThe forearm flexor-pronator muscle contributes to the dynamic stabilizer against valgus stress at the elbow during pitching motion.This study used shear wave ultrasonography to assess the relation between the elasticity of each forearm flexor-pronator muscle and the laxity of the ulnar collateral ligament (UCL) of the elbow joint in high school pitchers with and without medial elbow tenderness. MethodsOne hundred and fifteen high school baseball pitchers (average age 16.5 years) underwent a medical checkup during the off-season of 2022.We investigated instances of medial elbow tenderness on the pitching side at that medical check.The 115 participants were divided into two groups: 25 pitchers with medial elbow tenderness (medial elbow tenderness group) and 90 without medial elbow tenderness (non-medial elbow tenderness group).The shear wave velocities (SWVs) of the pronator teres (PT), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor digitorum profundus (FDP), and the common flexorpronator muscles (CFPM) were measured as the index of muscle elasticity using shear wave ultrasonography.Ultrasound examinations were conducted with and without gravity valgus stress of the medial aspect of the bilateral elbows.We compared the elasticity of the forearm flexor-

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