Comparison of elbow valgus laxity and medial elbow stabilizer parameters during repetitive pitching between high school baseball players with and without a history of medial elbow injury

Adolescent baseball players with a history of medial elbow injury are often reinjured during demanding practice sessions or games. The physical characteristics of baseball players with a history of medial elbow injury have been reported in several previous studies, but the nature of their medial elbow stabilizers is unknown. This study investigated the difference in characteristics of elbow valgus laxity and medial elbow stabilizer parameters between baseball players with and without a history of medial elbow injury, prior to and during repetitive pitching.Sixteen high school baseball players with no history of medial elbow injury (No-Injury group) and 14 high school baseball players with a history of medial elbow injury (Injury History group) participated. The participants pitched 100 fastballs. Medial elbow joint-space gapping and strain ratio indicating tissue elasticity of ulnar collateral ligament (UCL) and forearm flexor-pronator muscles (FPMs) were measured by ultrasound before pitching and following each of five 20-pitch blocks. Student t tests and Mann-Whitney U tests were used to compare each parameter between groups.Medial elbow joint-space gapping and UCL elasticity were not significantly different between the 2 groups in each pitching block (P > .05). The strain ratio of FPMs before pitching and after 100 pitches in the Injury History group were significantly greater than that in the No-Injury group (No-Injury vs. Injury History group: before pitching, 0.47 ± 0.19 vs. 0.68 ± 0.26, P = .016; 100 pitches, 0.35 ± 0.12 vs. 0.53 ± 0.20, P = .007). In the other pitching blocks, there was no significant difference between groups, but the effect size was medium and showed a similar tendency (20 pitches, P = .069, Cohen d = 0.69; 40 pitches, P = .116, Cohen d = 0.59; 60 pitches, P = .102, Cohen d = 0.62; 80 pitches, P = .058, Cohen d = 0.72).The results of this study indicate that FPM elasticity at baseline and during repetitive pitching in players with a history of medial elbow injury was harder than in players without injury history. This may suggest that baseball players with a history of medial elbow injury increase support of their previously injured medial elbow by hardening FPM elasticity to counteract elbow valgus stress generated during pitching, which may lead to long-term change in the FPMs. Therefore, physical management for this change may be important to prevent reinjury in baseball players with a history of medial elbow injury.