Sabick Michelle B, Kim Young-Kyu, Torry Michael R, Keirns Michael A, Hawkins Richard J
Steadman-Hawkins Sports Medicine Foundation, 181 West Meadow Drive, Suite 1000, Vail, Colorado 81657, USA.
Am J Sports Med. 2005 Nov;33(11):1716-22. doi: 10.1177/0363546505275347. Epub 2005 Aug 10.
The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton.
The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retro-torsion.
Descriptive laboratory study.
A total of 14 elite youth baseball pitchers (mean age, 12.1 +/- 0.4 years) were filmed from the front and dominant side while throwing fastballs in a simulated game. The net force and torque acting on the humerus throughout the throwing motion were calculated using standard biomechanical techniques.
The external rotation torque about the long axis of the humerus reached a peak value of 17.7 +/- 3.5 N.m (2.7% +/- 0.3% body weight x height) just before maximum shoulder external rotation. A shoulder distraction force of 214.7 +/- 47.2 N (49.8% +/- 8.3% body weight) occurred at, or just after, ball release.
Shear stress arising from the high torque late in the arm-cocking phase is large enough to lead to deformation of the weak proximal humeral epiphyseal cartilage, causing either humeral retrotorsion or proximal humeral epiphysiolysis over time. The stresses generated by the external rotation torque are much greater than those caused by distraction forces generated during the pitching motion of youth baseball pitchers.
The motion of throwing fastballs by youth baseball pitchers results in force components consistent with proposed mechanisms for 2 clinical entities.
由于描述青少年投手生物力学的数据匮乏以及发育中骨骼的可塑性，重复性投球对发育中运动员肩部的影响尚未得到充分理解。
在快速投球动作中，肱骨近端骨骺处存在的应力方向和大小与肱骨近端骨骺溶解（小联盟肩部）和/或肱骨后扭转的发展一致。
描述性实验室研究。
在模拟比赛中，从正面和优势侧对14名精英青少年棒球投手（平均年龄12.1±0.4岁）投快速球时进行拍摄。使用标准生物力学技术计算整个投球动作中作用于肱骨的净力和扭矩。
在肩部最大外旋之前，围绕肱骨长轴的外旋扭矩达到峰值17.7±3.5N·m（2.7%±0.3%体重×身高）。在球释放时或之后，出现了214.7±47.2N（49.8%±8.3%体重）的肩部牵张力量。
手臂上举阶段后期高扭矩产生的剪切应力足够大，足以导致薄弱的肱骨近端骨骺软骨变形，随着时间的推移导致肱骨后扭转或肱骨近端骨骺溶解。青少年棒球投手投球动作中外旋扭矩产生的应力远大于牵张力量产生的应力。
青少年棒球投手投快速球的动作所产生的力成分与两种临床病症的推测机制一致。
