CONGENITAL DISLOCATION OF RADIAL HEAD
Congenital dislocation of the radial head is typically not diagnosed until 2 to 5 years of age, when parents notice a mild limitation of elbow extension and an abnormal lateral prominence of the elbow in their child. The abnormality can be unilateral or bilateral, and the most common direction of dislocation is posterior or pos-terolateral, although anterior or lateral dislocations can occur. Approximately half of all cases are bilateral, and in approximately 60% of patients the deformity occurs in association with a specific syndrome or a connective tissue disorder. Therefore, a search for other anomalies should be made whenever this abnormality is diagnosed. Most congenital dislocations of the radial head are asymptomatic and cause no functional disability, because the limitation of elbow motion is mild. Congenital subluxations of the radial head are less common than congenital dislocations but are more likely to be associated with pain. Anterior dislocations cause a slight decrease in flexion and supination, whereas posterior dislocations result in a slight limitation of extension and pronation.
Plain radiographs reveal the abnormality, and the radiographic features considered to be characteristic of a congenital dislocation are (1) a dislocated or subluxated radial head, (2) an underdeveloped radial head, (3) a flat or dome-shaped radial head (rather than the normal concave cup shape), (4) a more slender radius than normal, (5) a longer radius than normal, (6) an underdeveloped capitellum, and (7) a lack of anterior angulation of the distal humerus. A shortened ulna may also commonly occur with a congenital dislocation of the radial head. These associated findings may help to distinguish a congenital dislocation from an acquired postnatal or traumatic dislocation, as will the presence of bilaterality and other musculoskeletal anomalies. However, a traumatic dislocation occurring in an infant and left untreated may result in deformities over time that appear similar to a congenital dislocation.
The lack of symptoms and functional limitations make treatment of congenital dislocation of the radial head largely unnecessary. Attempts at open reduction have been reported, but often with recurrence. If an unacceptable appearance or pain can be attributed to the dislocation, or painful arthritic changes develop, the radial head can be excised when growth is complete. This procedure relieves pain but does not usually improve range of motion because long-standing soft tissue contractures persist.