The capitellum (capitulum) is the rounded lateral articular surface of the distal humerus that articulates with the radial head, forming the radiohumeral joint. It faces anteriorly and inferiorly, and the radial fossa above it receives the radial head in full flexion. Unlike the trochlea which articulates with the ulna in a hinge arrangement, the capitellum-radial head joint allows both flexion-extension and forearm rotation. Its blood supply enters mainly from posterior end arteries, which helps explain why osteochondritis dissecans of the capitellum is a common injury in young throwers and gymnasts.
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| Ossification | The capitellum ossification centre (C in CRITOE) appears first at approximately age 1, making it the first elbow secondary centre to ossify and a reference for assessing other elbow ossification centres. |
Osteochondritis dissecans of the capitellum affects young overhead athletes (gymnasts, baseball pitchers) aged 11 to 17 from repetitive compression of the radial head against the capitellum. It produces lateral elbow pain and clicking from unstable osteochondral fragments. MRI with or without arthrography identifies the lesion and fragment stability. Stable lesions are treated with rest; unstable fragments require arthroscopic removal, drilling or fixation, or osteochondral grafting. Panner disease is a similar, self-limiting condition in younger children (about 7 to 12) affecting the entire capitellum epiphysis rather than a focal fragment. Shear fractures of the capitellum in adults are classified by the Dubberley system.
A shearing fracture of the capitellum from a fall onto an outstretched hand, which can block elbow flexion.
Repetitive compression in young throwers and gymnasts damages the capitellar cartilage and bone, which may form loose bodies.
Osteochondrosis of the whole capitellum ossific nucleus in children under about 10, which usually heals with rest.
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