Dislocation of the Radial Head

GENESIS

Dislocation of the radial head is the most common congenital anomaly of the elbow, but it is relatively rare, accounting for 0.15–0.2% of outpatient orthopedic visits. It can occur as an isolated abnormality or as part of several different syndromes. The presence of associated anomalies and bilateral involvement suggests a congenital joint dislocation syndrome. Some authors believe that many unilateral cases might be attributed to low-energy greenstick fractures of the ulna, which may result in radial head dislocation as the forearm shortens (eponym Monteggia fracture). These can be relatively benign in appearance with transient mild symptoms that are initially unnoticed by parents and clinicians. Acutely, the traumatically dislocated radial head will still look like a cup (concave) while the chronically dislocated radial head will look round (convex). Over time, however, the acute radial head will round the longer it is dislocated, and eventually it becomes more difficult to distinguish radiographically between congenital dislocation and late post-traumatic cases, so the genesis of many isolated cases is seldom understood.

Radial head dislocation can be associated with radioulnar synostosis, antecubital pterygia, distal hand and limb anomalies, congenital hip dislocation, extra X chromosomes, syndromes resulting from collagen abnormalities, abnormal endochondral ossification of the developing growth plate, abnormalities of forearm ossification outside the growth plate, disproportionate growth of the radius and ulna, and altered HOXD expression or activity, as well as arthrogryposis, Larsen syndrome, Ehlers-Danlos syndrome, occipital horn syndrome (X-linked cutis laxa), multiple exostosis, nail-patella syndrome, cleidocranial dysplasia, surviving camptomelic dysplasia, atelosteogenesis, small patella syndrome, and craniofacial dysostosis.

Bilateral congenital posterior dislocation of the radial heads without other anomalies can also be inherited as an autosomal dominant trait. Vertical transmission within a consanguineous family could be caused by autosomal recessive inheritance, but most isolated hereditary cases appear to manifest autosomal dominant inheritance. Acromesomelic dysplasia type Maroteaux is an autosomal recessive disorder characterized by severe short stature, shortened middle and distal segments of the limbs, redundant skin of fingers, radial head subluxation or dislocation, large great toes and cranium, and normal intelligence. This condition is caused by autosomal loss-of-function variants in the natriuretic peptide receptor B ( NPRB or NPR2 ), which is involved in endochondral ossification and longitudinal growth of limbs and vertebrae. The combination of short stature, congenital dislocation of the hip, carpal coalition, dislocation of the radial head, cavus deformity, scoliosis, hearing loss, eye defects, and vertebral anomalies was first described in 1993 by Steel in 23 children from Puerto Rico. Steel syndrome is caused by autosomal recessive mutations in COL27A1 . Posterolateral dislocation of the proximal head of the radius results in the inability to fully supinate at the elbow and some limitation in extension ( Fig. 13.1 ). It generally gives rise to little disability and is seldom treated. Anterior and lateral dislocations are less frequent forms of presentation than posterior dislocation; however, this form is the most frequent congenital pathology of the elbow in children.