Congenital Dislocation of the Radial Head

Congenital dislocation of the radial head is the most common congenital elbow abnormality and usually occurs in association with other conditions (60% of the time), but can also occur in isolation. The more common associated conditions include lower extremity anomalies, scoliosis, mental retardation, and nail patella and Klippel-Feil syndromes.

The majority of radial head dislocations are posterior (65% of cases), followed by anterior (~15%) and lateral (~15%). Patients are usually asymptomatic in childhood, but may develop pain in adolescence.

The constellation of findings is now believed to be triggered by failure of development of a normal capitulum, which deprives the developing radial head of the contact pressure required for normal development and results in malformation of the radiocapitellar joint. This, in turn, results in altered biomechanics at the proximal radioulnar joint and abnormal development of the ulna.

• Capitulum: Hypoplastic and flattened
• Radius: Domed radial head articular surface.
• Ulna: Severely bowed and relatively short in relation to the radius. Negative ulnar variance at the wrist.
• Humerus: Mechanical erosion distally at pseudoarticulation with the dislocated radial head.

Early radiographic findings are subtle due to the absence of the capitulum and radial head ossification centers. Before radial head ossification (~ 5 years) a line drawn along the shaft of the radius should normally bisect the capitulum ossification center.

References

Hughes T and Chung CB. Chapter 12. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp 487-488.