The ulnar collateral ligament of the elbow has three bundles with the anterior bundle being the primary stabiliser against the valgus stress of overhead throwing. In baseball pitchers it sustains cyclic valgus overload exceeding its tensile strength with every pitch, making UCL reconstruction (Tommy John surgery) one of the most common procedures in professional baseball. Its anterior bundle integrity is essential for the acceleration phase of throwing when valgus stress peaks.
| Origin | Medial epicondyle of the humerus |
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| Insertion | Coronoid process (anterior bundle) and olecranon (posterior bundle) of the ulna |
| Actions | Primary stabiliser of the medial elbow against valgus stress; critical for the valgus load of overhead throwing |
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UCL insufficiency in overhead athletes produces medial elbow pain during the late cocking and acceleration phases of throwing, reduced velocity, and the milking manoeuvre and moving valgus stress test are the clinical provocations. MRI arthrography is the most sensitive imaging study for partial tears. UCL reconstruction with a palmaris longus or gracilis tendon graft restores valgus stability and allows return to throwing at 12 to 18 months post-operatively.
Valgus overload injury from overhead throwing producing medial elbow pain at late cocking and acceleration, confirmed by positive moving valgus stress test and MRI arthrography, with surgical reconstruction for athletes wishing to continue overhead sport.
