Sabick Michelle B, Torry Michael R, Kim Young-Kyu, Hawkins Richard J
Steadman-Hawkins Sports Medicine Foundation, 181 West Meadow Drive, Vail, CO 81657, USA.
Am J Sports Med. 2004 Jun;32(4):892-8. doi: 10.1177/0363546503259354.
Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion.
The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations.
Peak humeral axial torque reached a mean value of 92 +/- 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures.
Fractures are most likely to occur near the time of maximum shoulder external rotation when humeral torque peaks. Pitchers whose elbows were more extended at stride foot contact tended to have lower peak humeral torques.
投掷运动员肱骨干自发性骨折是一种罕见但广为人知的现象。尽管有人推测投掷的生物力学导致了此类骨折，但尚不清楚在投球动作中骨折是如何发生以及何时发生的。
对25名在比赛中投掷的职业棒球投手，计算作用于肱骨干长轴的扭矩。
在投球准备阶段结束时，当肩部外旋达到最大值时，肱骨干轴向扭矩峰值平均达到92±16牛米。该扭矩倾向于使肱骨远端相对于近端发生外旋。扭矩方向与投掷运动员中出现的肱骨外旋螺旋骨折一致。肱骨干扭矩峰值大小平均为肱骨理论抗扭强度的48%，这表明反复应力在肱骨干骨折中起作用。
当肱骨干扭矩达到峰值且肩部外旋接近最大值时，骨折最有可能发生。在跨步脚着地时肘部伸展程度更大的投手，其肱骨干扭矩峰值往往较低。
