The medial compartment of the elbow joint encompasses the medial part of the humeroulnar articulation, including the medial trochlea and the medial ulnohumeral articulation. It is stabilised medially by the anterior bundle of the ulnar collateral ligament (UCL), and distally the elbow medial compartment is the site of compressive forces during the follow-through phase of throwing. Valgus stress at the medial elbow is the dominant loading pattern in overhead athletes.
The medial elbow compartment is the focus of overuse pathology in throwing athletes. Valgus extension overload produces both medial tension stress (UCL attenuation and tearing) and posteromedial compression stress (olecranon osteophyte and chondromalacia). UCL reconstruction (Tommy John surgery) using a palmaris longus or gracilis tendon graft is the standard treatment for complete UCL tears in overhead athletes. Medial elbow compartment assessment includes provocative valgus stress testing, milking manoeuvre, and moving valgus stress test.
Cumulative valgus stress tears the anterior bundle of the UCL at the medial elbow, producing medial pain during late cocking and acceleration with an audible pop in acute complete tears; managed conservatively in partial tears or by UCL reconstruction (Tommy John procedure) for complete tears in professional throwing athletes.
Combined valgus stress and hyperextension in throwing produces posteromedial olecranon impingement with the medial trochlea, causing chondromalacia and osteophyte formation in the posteromedial olecranon tip and medial trochlear groove, managed arthroscopically by osteophyte debridement.
