Pathomechanics

Biomechanics of Elbow Injuries During Throwing

Elbow injuries in pitchers can be divided into three types, based upon their location within the joint. All three types of elbow injuries are related to the large rotational force – called “torque” – needed to slow down the cocking of the arm and accelerate the forearm, hand, and ball forward. Elbow torque is greatest when the arm is in its maximum cocked position.

Medial Elbow Injuries – The Ulnar Collateral Ligament

From the cocked position, the ulnar collateral ligament (UCL) pulls the forearm forward with the rotating upper arm. The tremendous tension produced in the relatively small UCL is close to its limit. When improper mechanics are used or arm muscles become fatigued, the load placed on the UCL may be increased to more than it can withstand, causing small “micro”-tears in the UCL. Microtears in muscles or ligaments can heal when given enough recovery time. In fact, microtears during exercise followed by healing is how muscles become bigger and stronger. However, when a pitcher continues to tear his UCL without allowing enough time for it to heal, the microtears add up to be one large tear in the ligament. Pitchers with UCL injuries often describe feeling or hearing a “pop” in the elbow on one particular pitch. These types of stories lead many people to believe that a pitcher blows out his UCL on one bad pitch – such as the first pitch on a cold day or a poorly thrown breaking pitch. Really, this is usually not the case. Quite frequently the one bad pitch was really just “the straw that broke the camel’s back” and was the final microtear that led a series of microtears to become a large tear.

Lateral Elbow Injuries

At the same time the medial elbow is under tension, the lateral side of the elbow is compressed. The compression between the forearm’s bone (the radius) and the upper arm’s bone (the humerus) helps the forearm stop cocking back and start rotating forward. This large crushing force on tiny bone surfaces sometimes results in small bone chips breaking off. These bone chips float in the elbow joint and may result in pain, loss of elbow motion, and diminished pitching performance.

Posterior Elbow Injuries – “Valgus Extension Overload”

From the arm-cocked position, the arm rapidly rotates forward at the shoulder and straightens out at the elbow. The elbow straightens out so fast that it takes less than a tenth of a second (0.1 sec) to go from the 90-degree bent position to the nearly straight position at ball release. The combination of this rapid elbow extension and the large torque generated to rotate the arm forward can cause a grinding injury in the posterior-medial elbow (the “funny bone” area of the elbow). Small bone chips can break off and float in the elbow joint, which may result in pain, loss of motion, and diminished pitching performance.

Copyright © 2000, American Sports Medicine Institute
October 05, 2004