Congenital Radioulnar Synostosis
Congenital Radioulnar Synostosis usually involves the proximal ends of the radius and ulna.
Most often forearm is fixed in a pronated position.
In this condition, a bony union exists proximally between the radius and ulna.
The precise cause of the synostosis of the forearm is unknown.
Synostosis represents a failure of differentiation of the parts.
It may occur sporadically or inherited as an autosomal dominant trait.
At approximately 5 weeks of post-conception, the elbow forms from the three cartilaginous condensations representing the humerus, radius, and ulna.
For a short period, these cartilage analogs share a common perichondrium.
A cavitation process ensues, forming the three distinct bones in the late first trimester.
If this process fails, enchondral ossification results in the bony synostosis.
Fetal forearm bones separated when the forearm is in pronation, so all forearm synostosis is fixed in pronation.
Congenital radioulnar synostosis is seen in conjunction with other syndromes such as Apert’s syndrome, Carpenter’s syndrome, Arthrogryposis, Mandibulofacial dysostosis, Klinefelter syndrome, and Poland’s anomaly.
It is also associated with tetralogy of Fallot, ventricular septal defect, absence of first rib or pectoral muscle, microcephaly, hydrocephalus, mental retardation, genitourinary and gastrointestinal anomalies.
Boys are slightly more often affected than girls.
Children usually present between 2 and 6 years of age with a painless absence of forearm rotation and a slight elbow flexion contracture.
Congenital radioulnar synostosis is bilateral in 80% of cases.
On examination, the forearm is usually fixed in pronation and forearm rotations are absent.
Radiographs of the forearm with elbow and wrist show the proximal radioulnar coalescence with an absence of the radial head.
However, extensive synostosis extending into the forearm is occasionally seen in Holt-Oram Syndrome.
Other imaging studies are done to rule out the associated anomalies.
No treatment is indicated until the children or parents express concern or complaints.
It is difficult to treat.
Surgical intervention is recommended only when there is a significant amount of pronation deformity of more than 60 degrees and it is associated with functional limitation and complaints.
The long term consequences are minimal as the child gets accustomed to restriction of movement and will lead a near-normal life.