Congenital radioulnar synostosis is the most common congenital functional disorder of the elbow. It demonstrates an autosomal dominant pattern of inheritance with no sex predilection, and is bilateral in 60-80% of cases. Approximately 400 cases of congenital radioulnar synostosis have been documented in the worldwide literature, and the average age at diagnosis is 6 years.
Four types of congenital synostosis are described, as follows:
- type I - fibrous synostosis, does not involve bone, and is associated with a normal, articulating radial head.
- type II - osseous synostosis, associated with a normal, articulating radial head.
- type III - osseous synostosis, with a hypoplastic and posteriorly dislocated radial head.
- type IV - short osseous synostosis with an anteriorly dislocated, mushroom shaped radial head.