Weakening and factors of medial elbow dynamic stabilizers against elbow valgus laxity after repetitive pitching in high school baseball players

Abstract

BackgroundOverhead throwing activity induces elbow valgus loading. Medial elbow dynamic stabilizers are thought important for medial elbow joint protection, but the effects of repetitive pitching on stabilizing function are largely unknown. This study aimed to investigate changes in the dynamic stabilizers during repetitive pitching as well as factors related to dynamic stabilizing ability. Our hypothesis was that repetitive pitching reduces dynamic stabilizer function, hence reducing the ability to minimize elbow valgus load. MethodsThirty high school baseball pitchers participated (age, 16.6 ± 0.5 years). Each participant pitched 100 times (5 blocks of 20 pitches). Prior to and after 100 pitches, medial elbow joint width and strain ratios, indicating the hardness of the ulnar collateral ligament (UCL) and forearm flexor-pronator muscles (FPMs), were measured using ultrasound at rest (non-contraction) and during gripping (contraction). Pre- and post-pitching data were compared using Paired t-tests. Multiple regression analysis was used to investigate factors related to the change rate in the medial elbow joint width during gripping. ResultsMedial elbow joint width during gripping significantly increased comparing pre- to post-pitching (P < 0.001). Both UCL and FPMs strain ratios after pitching significantly decreased (i.e., softer) compared to those before pitching (UCL, P = 0.001; FPMs, P = 0.006). The ratio of strain ratio in the UCL and FPMs (UCL/FPMs) during gripping prior to pitching was significantly and independently correlated with the change rate in medial elbow joint width during gripping (β = 0.44, P = 0.016). ConclusionPitching 100 balls induces a significant reduction in dynamic stabilizing ability against elbow valgus laxity. High school baseball pitchers should limit themselves to less than 100 pitches per game, or rest after 100 pitches before resuming. Furthermore, the ratio of hardness (UCL/FPMs) during dynamic stabilizing associated with gripping prior to pitching was significantly related to the change rate of elbow valgus laxity during the dynamic stabilization. Maintaining FPMs harder relative to UCL during gripping prevent elbow valgus laxity associated with repetitive pitching and may protect the medial elbow joint during repetitive pitching.