The trochlea is the spool-shaped medial articular surface of the distal humerus that articulates with the trochlear notch of the ulna, forming the humeroulnar hinge joint. The central groove of the trochlea fits precisely into the ridge of the ulna's trochlear notch, providing the inherent bony stability of the elbow that makes it one of the most congruous joints in the body. Its medial lip projects further distally than the lateral, contributing to the carrying angle of the elbow. The medial epicondyle, origin of the UCL, lies just above and medial to it.
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| Ossification | The trochlea ossification centre appears at age 9 to 10 (T in CRITOE), late in the sequence, and its multiple appearance centres can look irregular until fusion in the mid-teens. |
Lateral condyle fractures in children involving the capitellum and lateral portion of the trochlea (Milch classification) are the most common paediatric elbow fracture requiring surgical fixation. Unlike supracondylar fractures they are intra-articular and produce a Salter-Harris IV growth plate injury with risk of physeal damage and malunion if inadequately reduced. The trochlea develops from multiple ossification centres, one of the later centres in the CRITOE sequence, which can appear fragmented and be confused with fractures. In adults, the trochlea may be involved in capitellar shear fractures (Dubberley classification). Hegemann disease is a rare osteochondrosis of the trochlea in children.
Fractures extending into the trochlea disrupt the ulnohumeral joint and usually need open fixation.
Avascular necrosis of part of the trochlea after a childhood distal humerus fracture leaves a central notch and later elbow arthritis.
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