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What is radioulnar synostosis?

Radioulnar synostosis is a rare condition in which the two bones of the forearm the radius and the ulna are abnormally connected. This limits rotation of the arm. Radioulnar synostosis is usually congenital (something your child was born with). It can also occur as the result of a forearm fracture or trauma.

The information on this page focuses on congenital radioulnar synostosis.

What are the symptoms of congenital radioulnar synostosis?

Congenital radioulnar synostosis can be mild to severe. The telltale symptom is a limitation in your child’s ability to rotate their forearm from a palms-down (pronated) position to a palms-up (supinated) position. A child with radioulnar synostosis may also carry their elbow at an abnormal angle and their forearm may be short or bowed.

In severe cases, the bones are connected and the forearm is fixed in one position, usually with the palm facing down to some degree. Depending on the position of the forearm and the flexibility of your child’s wrist, their activity may be limited in ways that are either subtle or noticeable.

What causes congenital radioulnar synostosis in babies?

A baby’s arms develop between the fifth and eighth week of pregnancy. In the early stages, the radius and ulna bones are connected. These bones later separate and become individual bones. If the radius and ulna do not fully separate, the baby will be born with radioulnar synostosis.

Most cases of congenital radioulnar synostosis happen for no known reason. About one in five children born with the condition have a family history of radioulnar synostosis. It can also be part of an underlying syndrome or developmental abnormality.