Ulnar Collateral Ligament Injury
- Author: Robert F Kacprowicz, MD, FAAEM; Chief Editor: Sherwin SW Ho, MD more...
The ulnar collateral ligament (UCL) of the elbow is critical for valgus stability of the elbow and is the primary elbow stabilizer.[1, 2] 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 are generally 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 then 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.
The UCL originates at the posterior distal aspect of the medial epicondyle and inserts into the base of the coronoid process. At 90 º of flexion, it provides 55% of the resistance to valgus stress at the elbow. In full extension, the UCL, bony architecture, and anterior capsule equally maintain valgus stability.
The UCL is composed of 3 bands: anterior, posterior, and transverse. The anterior band, which arises from the anteroinferior surface of the medial epicondyle and inserts on the sublime tubercle of the ulna, provides the major contribution to valgus stability.
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 º per second and continues to 20 º 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 meters (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.
Bushnell et al examined maximum pitch velocity and elbow injury in 23 professional baseball pitchers over a period of 4 seasons and found a statistically significant association (P = .0354). Of 9 pitchers who had elbow injuries, 4 had an elbow muscle strain and/or joint inflammation, and 5 had an ulnar collateral ligament sprain or tear. Surgery was required for 3 of the 5 players with ulnar collateral ligament injuries; these pitchers also had the highest maximum ball velocity.
A study by DeFroda et al found that there is a statistically significant difference in the mean fastball velocity of pitchers who injure their UCL. Players who injured the UCL tended to have higher fastball velocities. The study also added that there has been an increased incidence of injury in the first 3 months of the season and that early tears are more likely to occur in relief pitchers than starters.
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