Repetitive Pitching Decreases the Elbow Valgus Stability Provided by the Flexor-Pronator Mass: The Effects of Repetitive Pitching on Elbow Valgus Stability.

Abstract

Baseball pitching induces a large elbow valgus load, stressing the ulnar collateral ligament. Flexor-pronator mass contraction contributes to valgus stability; however, repetitive baseball pitching may weaken the flexor-pronator mass contractile function. The present study investigated the effects of repetitive baseball pitching on the medial valgus stability measured using ultrasonography. We hypothesized that repetitive pitching would decrease elbow valgus stability. This was a controlled laboratory study. Fifteen young male baseball players at the collegiate level (age: 23.0 ± 1.4 years) were enrolled. The medial elbow joint space was measured using ultrasonography (B-mode, 12-MHz linear array transducer) in the following three conditions: at rest (unloaded), under 3 kg valgus load (loaded), and under valgus load with maximal grip contraction to activate flexor-pronator mass (loaded-contracted). All measurements were performed before and after the pitching tasks, which comprised five sets of 20 pitches. Two-way repeated-measures analysis of variance was applied to determine changes in the medial elbow joint space. The post-hoc test with Bonferroni adjustment was applied to assess the changes within the time and condition. The medial elbow joint space was significantly greater under the loaded than the unloaded and loaded-contracted conditions both before- and after- pitching (p < 0.001). In the loaded-contracted condition, the medial elbow joint space significantly increased after repetitive baseball pitching (p < 0.001). The results of the present study indicated that repetitive baseball pitching reduced the elbow valgus stability. This reduction could be attributed to the decreased flexor-pronator mass contractile function. Insufficient contraction may increase the tensile load on the ulnar collateral ligament with pitching. Flexor-pronator mass contraction plays a role in narrowing the medial elbow joint space; however, repetitive baseball pitching reduced the elbow valgus stability. It has been suggested that sufficient rest and recovery of the flexor-pronator mass function are required to reduce the ulnar collateral ligament injury risk.