DECELERATION PHASE MOMENTS: A POTENTIAL CAUSE FOR ELBOW INJURY IN COLLEGIATE LEVEL BASEBALL PITCHERS

Matthew J. Solomito; Erin J. Garibay; Carl W. Nissen

摘要

Background: Over the past three decades there has been an increase in the incidence of elbow and shoulder pain experienced by baseball pitchers, which can limit or lead to an end of pitching activities. Although there are a number of theories that suggest poor pitching mechanics or throwing breaking pitches prior to skeletal maturity may be the cause, biomechanical investigations have yet to elucidate a single cause for this rise in injuries. It is also well established that the highest stresses and fastest angular velocities experienced by pitchers occurs during the acceleration phase of the pitch cycle, which has led to extensive biomechanical investigations of this portion of the pitching cycle. However, the deceleration phase of the pitch, although 150% longer than the acceleration phase, still requires an abrupt reversal of motion to allow pitchers to get into a fielding position after they have delivered the pitch. Therefore, the purpose of this study was to determine if the elbow joint was subjected to an additional varus stress during the deceleration phase of the pitch cycle. Methods: NCAA Division I and Division III baseball pitchers were recruited for this study and underwent a comprehensive biomechanical pitching evaluation. All pitchers were injury free at the time of data collection and reported no history of an upper extremity injury within the previous six months of the analysis date. Additionally, all pitchers had at least two years of pitching experience. All participants pitched from a 10” mound towards a target with a designated strike zone set 60’6” away. Kinematic data was collected using a 12-camera motion capture system, and kinetic data was calculated using standard inverse dynamic techniques. The typical pitching cycle, starting with lead foot contact and ending with maximum internal rotation of the glenohumeral joint (MIR), was expanded to end when the pedestal foot reached its maximum height; allowing for the analysis of deceleration phase moments at the elbow joint. The deceleration phase elbow varus (EV) moment was compared across multiple pitch types (i.e. fastball, curveball, slider, and change-up) using the type III effects from a random intercept mixed effects model. Additionally, the deceleration phase EV moment was compared to the peak EV moment occurring during the acceleration phase of the pitch cycle. Results: The results of this study are based on 87 baseball pitchers with a mean age of 19.9 ± 1.4 years. All participants pitched a fastball, 78 pitched a curveball, 31 pitched a slider, and 60 pitched a change-up. The results indicated that there was the presence of an elbow varus moment for all pitch types that occurred during the deceleration phase of the pitching cycle after MIR that was on average about half of the peak acceleration phase moment (Table 1). Overall 26% of pitchers pitching a fastball, 33% of pitchers throwing a curveball and change-up, and 55% of pitchers throwing a slider had deceleration EV moments greater than 50% of their peak acceleration phase EV moment. There was a statistically significant difference in the number of pitchers with a deceleration phase EV moment greater than half of the acceleration phase EV moment when pitching the slider when compared to the other pitch types (p=0.029). Conclusion/Significance: The majority of pitching biomechanics research focuses on the acceleration phase of the pitching cycle because the highest speeds and moments are achieved during this portion of the pitch. However, the pitcher’s need to rapidly decelerate during the pitch does expose them to an additional elbow varus moment. This additional moment could be a potential source of injury as it is a second stress exposure for the UCL. Additionally, given that the highest deceleration EV moments were noted in the slider this may potentially explain why pitchers and coaches believe that sliders are more harmful than other pitch types. Table 1: Comparison of Acceleration and Deceleration phase elbow varus moments among different pitch types. EV Moment Acceleration Phase (Nm) EV Moment Deceleration Phase (Nm) Deceleration phase EV moment (percentage of the acceleration EV moment (%)) Fastball 75.9±15.8 32.8±10.9 ~(?a) 44±14 Curveball 70.6±15.7 ~(??) 29.7±11.5 ~(?) 42±15 Slider 71.9±15.6 34.4±11.7 ~(a) 48±13 Change-up 69.4±15.1 ~(??) 31.8±8.5 ~(a) 47±13 ~(?)Statistically different than the fastball (acceleration)?? ~(?)Statistically different than the slider (deceleration) ~(?)Statistically different than the slider(acceleration)?? ~(a) Statistically different than the change-up (deceleration)

机译：背景：在过去的三十年中，棒球投手所经历的肘部和肩部疼痛的发生率有所增加，这可能会限制或导致投球活动的结束。尽管有许多理论表明，俯仰机械性能不佳或在骨骼成熟之前扔断球可能是原因，但生物力学研究尚未阐明造成这种伤害增加的单一原因。众所周知，投手所经历的最高应力和最快角速度是在俯仰周期的加速阶段发生的，这导致了对俯仰周期这一部分的广泛生物力学研究。但是，俯仰的减速阶段虽然比加速阶段长150％，但仍然需要突然反转，以允许投手在交付俯仰之后进入调准位置。因此，本研究的目的是确定在俯仰周期的减速阶段肘关节是否承受了额外的内翻应力。方法：本研究招募了NCAA I级和III级棒球投手，并对其进行了全面的生物力学投球评估。收集数据时，所有投手均未受伤，并且在分析日期的前六个月内均未报告有上肢受伤史。此外，所有投手都有至少两年的投球经验。所有参与者都从10英吋的土墩向标有60乘6英吋的指定打击区的目标投球。运动数据是使用12相机运动捕捉系统收集的，动力学数据是使用标准逆动态技术计算的。典型的俯仰周期从前脚接触开始，到盂肱关节（MIR）的最大内部旋转结束，然后扩展到基座脚达到最大高度时结束。可以分析肘关节的减速相力矩。使用随机拦截混合效果模型中的III型效果，比较了多种俯仰类型（即快球，弯球，滑杆和换挡）的减速相肘内翻（EV）力矩。此外，将减速阶段EV力矩与在俯仰周期的加速阶段发生的峰值EV力矩进行了比较。结果：这项研究的结果基于平均年龄为19.9±1.4岁的87个棒球投手。所有参与者都投了快球，78投了曲线球，31投了滑杆，60投了零钱。结果表明，在MIR之后的俯仰周期的减速阶段，所有俯仰类型均存在弯头内翻矩，平均大约为峰值加速阶段矩的一半（表1）。总共26％的投手向快速球投球，33％的投手向曲线球投掷和换球，以及55％的投手向滑块投掷，其减速EV力矩大于其峰值加速阶段EV力矩的50％。与其他俯仰类型相比，在使滑块俯仰时，减速阶段EV力矩大于加速阶段EV力矩的一半的投手数量在统计上有显着差异（p = 0.029）。结论/意义：大多数的俯仰生物力学研究都集中在俯仰周期的加速阶段，因为在俯仰的这一部分可以实现最高的速度和力矩。但是，投手在投球过程中需要迅速减速，这会使他们遭受额外的肘内翻力矩。此额外的时刻可能是潜在的伤害来源，因为这是UCL的第二次压力暴露。此外，鉴于在滑块中记录了最高的减速度EV力矩，这可能可以解释为什么投手和教练认为滑块比其他类型的桨头更具危害性。表1：不同俯仰类型之间的加速和减速相位肘内翻力矩比较。 EV力矩加速阶段（Nm）EV力矩减速阶段（Nm）减速阶段EV力矩（加速度EV力矩的百分比（％））快速球75.9±15.8 32.8±10.9〜（Δa）44±14曲线球70.6±15.7〜（ ??）29.7±11.5〜（？）42±15滑块71.9±15.6 34.4±11.7〜（a）48±13变化69.4±15.1〜（??）31.8±8.5〜（a）47±13〜（？）与快球（加速度）的统计差异?? 〜（？）与滑块（减速度）在统计上不同〜（？）与滑块（加速度）在统计上不同〜（a）统计上与变化（减速度）不同

DECELERATION PHASE MOMENTS: A POTENTIAL CAUSE FOR ELBOW INJURY IN COLLEGIATE LEVEL BASEBALL PITCHERS

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