Posted by Informant on June 07, 19105 at 20:04:37:
Background: The ulnar collateral ligament (UCL) of the elbow is critical for valgus stability of the elbow and is the primary elbow stabilizer. As such, the UCL plays an important role in most throwing sports, including baseball and javelin, as well as racquet sports and ice hockey.
Elbow injuries in young athletes generally are chronic, with persistent pain and instability from repetitive overhead activities. In the athlete, ligamentous injury can also be heralded by an acute traumatic event such as an elbow dislocation. This can lead to chronic pain and valgus instability. An understanding of the anatomy and biomechanics of the elbow in throwing sports is essential to the correct diagnosis and treatment of this potentially disabling injury.
Functional Anatomy: The UCL originates at the posterior distal aspect of the medial epicondyle and inserts into the base of the coronoid process. At 90° of flexion, it provides 55% of the resistance to valgus stress at the elbow. In full extension, the UCL, bony architecture, and the anterior capsule maintain valgus stability equally.
The UCL is composed of 3 bands: the anterior, posterior, and transverse. The anterior band, arising from the anteroinferior surface of the medial epicondyle and inserting on the sublime tubercle of the ulna, provides the major contribution to valgus stability.
Sport Specific Biomechanics: The acceleration phase of the overhead throw causes the greatest amount of valgus stress to the elbow. Extension occurs at a rate of up to 2500° per second and continues to 20° of flexion. During this phase, the forearm lags behind the upper arm and generates valgus stress while the elbow is primarily dependent on the anterior band of the UCL for stability. During the acceleration phase, valgus stress can exceed 60 Newton meter (Nm), which is significantly higher than the measured strength of the UCL in cadavers. The valgus force can, therefore, overcome the tensile strength of the UCL and cause either chronic microscopic tears or acute rupture.
History:
Medial elbow pain in athletes who throw is the most common symptom. Pain may be especially prominent during the acceleration phase of the overhead throw.
Pain is often chronic or recurrent and may lead to a slow erosion of throwing ability.
Athletes may report similar pain in previous seasons.
Rest generally helps relieve pain.
Occasionally, athletes may experience acute pain over the medial elbow, sometimes associated with a popping sensation, during a single throw that causes them to stop throwing immediately.
Physical:
Medial elbow tenderness and swelling are the most notable findings. UCL tenderness may occasionally be difficult to differentiate from flexor pronator tendonitis, but the pain of flexor pronator tendinitis is aggravated by resisting forearm pronation.
Loss of elbow range of motion (ROM) is occasionally observed.
With acute rupture, ecchymosis may be observed over the medial elbow.
Pain may be reproduced on making a clenched fist.
Valgus stress with the elbow in 25° of flexion (elbow abduction stress test) reproduces pain and may cause joint opening. The affected side should be compared with the contralateral elbow as a reference for baseline laxity.
Preseason documentation of baseline elbow laxity in elite athletes, especially pitchers, may be helpful for comparison if an injury occurs during the season because some throwing athletes have a baseline asymmetry.
Causes:
Repetitive throwing motions are the most common cause of UCL injury in the athlete.
Traumatic valgus stress to the elbow during a fall or with the arm outstretched may lead to UCL rupture in association with elbow dislocation.