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