Congenital radioulnar synostosis

Alternate names

Radio-ulnar synostosis; Radioulnar synostosis; Radial-ulnar synostosis

Definition

Congenital radioulnar synostosis is a rare condition in which there is an abnormal connection (synostosis) of the radius and ulna (bones in the forearm) at birth.

Types

There are 2 types of radioulnar synostosis: type 1 and type 2.

• In type 1, the fusion involves 2-6 cm of the area between the radius and ulna bones which is closer to the elbow and the knobby end of the radius that meets the elbow is absent (radial head).
• In type 2, the fusion is farther from the elbow and there is dislocation of the radial head.
• Both types result in a limitation of inward roll (pronation) and outward roll (supination) of the forearm, and in type 2 there is also a restriction of extension at the elbow.

Cause

• Congenital radioulnar synostosis is caused by abnormal development of the forearm bones during the fetal period, although the underlying cause of the developmental abnormality is not always known.
• The condition may be isolated (occur without other abnormalities) or it may be associated with various other skeletal, heart (cardiac), neurologic, or gastrointestinal abnormalities.
• When other abnormalities are present, the condition may be due to an underlying genetic cause, including a variety of syndromes or chromosome abnormalities.
• Some chromosome abnormalities that may include radioulnar synostosis are Klinefelter syndrome and XXXY syndrome.
• Examples of genetic syndromes that may include radioulnar synostosis are Apert syndrome, Crouzon syndrome, Carpenter syndrome, arthrogryposis, Treacher Collins syndrome, Williams syndrome, amegakaryocytic thrombocytopenia, and Holt-Oram syndrome.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

• Congenital radioulnar synostosis appears to be inherited in an autosomal dominant manner in some cases.
• This means that one mutated copy of the disease-causing gene in each cell is sufficient to cause the condition. The mutated gene may occur for the first time in an affected individual, or it may be inherited from an affected parent. Each child of an individual with an autosomal dominant condition has a 50% (1 in 2) risk to inherit the mutated copy of the gene.
• Congenital radioulnar synostosis may also occur with a variety of other abnormalities and may be associated with a chromosome abnormality or with a genetic syndrome. In these cases, the inheritance pattern may depend upon that of the underlying genetic abnormality.
• Congenital radioulnar synostosis may also occur sporadically as an isolated abnormality, in which case the cause may be unknown.

Signs and symptoms

• Signs and symptoms depend on the severity of the abnormality and whether it is bilateral; people with the condition often have limited rotational movement of the forearm.
• Pain is usually not present until the teenage years.
• In type 1, the fusion involves 2-6 cm of the area between the radius and ulna bones which is closer to the elbow and the knobby end of the radius that meets the elbow is absent (radial head).
• In type 2, the fusion is farther from the elbow and there is dislocation of the radial head. Both types result in a limitation of inward roll (pronation) and outward roll (supination) of the forearm, and in type 2 there is also a restriction of extension at the elbow.

Diagnosis

X-ray and computed tomography confirms the diagnosis of bilateral radioulnar synostosis.

Treatment

• Congenital radioulnar synostosis may be treated with surgery.
• Surgery is more commonly performed in patients who have bilateral radioulnar synostosis and/or patients who have very limited movement due to the radioulnar synostosis.
• In some cases, surgery is best performed in early childhood, usually before school starts, and in some cases it may need to be done in several stages.
• Surgery is not generally recommended for older patients with milder deformities who have learned to compensate for the limited range of movement caused by the synostosis, by using their shoulders and/or wrists.
• Complications of the surgery may include nerve damage or recurrence of the fusion.

NIH genetic and rare disease info

• NIH info on Congenital radioulnar synostosis

Congenital radioulnar synostosis is a rare disease.

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