Radioulnar synostosis

Radioulnar synostosis describes a congenital fusion of the radius and ulna in the forearm. It is a failure of skeletal differentiation in the IFSSH/Swanson classification scheme of congenital upper limb anomalies.

It is a rare condition and usually presents with bilateral involvement. There is an equal gender distribution. Most cases are sporadic, but environmental exposures have been implicated including fetal alcohol syndrome. Of the genetic associations, it has been linked with:

• an autosomal dominant inheritance pattern with variable penetrance and expressivity
• trisomy 13 and 21
• a range of syndromes including:
  • mandibulofacial dysostosis
  • acrocephalopolysyndactyly

Clinically, the forearm tends to be fixed in pronation. There may be compensatory supination at the radiocarpal joint with most patients adapting very well from a functional perspective. Deformities less than 45 degrees are well tolerated.

Pathologically, the synostosis may be fibrous or bony. It may be associated with a hypoplastic, dislocated radial head. Dislocation may be in an anterior or posterior direction.

Most patients adapt well to the deformity but if pronation is greater than 45 degrees or causing great functional impairment, a derotational osteotomy can be undertaken. This can be undertaken in one of two ways, either division through the site of fusion proximally, or separate derotation of each bone distally. Complications of surgery can include compartment syndrome, nerve injury (particularly the posterior interosseous nerve), vascular injury and stiffness.