Pitching or otherwise throwing a baseball involves a coordinated body movement culminating in straightening the elbow joint as the baseball is released from the hand. More specifically, pitching involves four general phases: wind-up, cocking, acceleration, and follow-through. The wind-up and cocking phases involve bending the elbow joint and rotating the shoulder backward in preparation for propelling the baseball in a forward direction. During acceleration, the shoulder rotates forward while simultaneously straightening the elbow joint in order to accelerate the baseball. Once the baseball has achieved sufficient velocity, the baseball is released from the hand and flies in the forward direction. The pitcher then follows-through on the pitch, which may involve further extension of the elbow joint.
During both the acceleration and follow-through phases, a relatively large extension and valgus load may be placed on the elbow joint. More particularly, valgus stress may be placed on the elbow joint during the acceleration phase. Tensile forces that result from the valgus stress may cause injury to the flexor musculature, injury to the medial collateral ligaments, avulsion fractures of the medial epicondyles, and traction spurs of the ulnar coronoid, for example. Compressive forces associated with the acceleration phase may also result in osteochondral fracture of the capitellum, osteochondritis dissecans, deformity of the radial head, lateral epicondylitiss, and lateral collateral ligament sprain, for example. During the follow-through phase of the throwing motion, the triceps muscle forcefully extends the elbow, which may develop tensile forces along the length of the muscle-tendon unit. These forces may result, for example, in olecranon avulsion fractures, triceps strains, olecranon spurs, and joint degeneration.
Although the specific motions necessary to properly throw a fastball, curveball, and knuckleball, for example, may vary significantly, repeatedly pitching a baseball during practice or competition induces stresses in the elbow joint. As the number of pitches increases during a particular game, practice session, or over the course of a season, the repeated application of stresses to the elbow joint may lead to overuse syndromes of the elbow joint.