There are two types described. In type I,
there is a proximal, smooth fusion of 2 to 6 cm (0.8 to 2.4 inches) between radius and
ulnar, and absent radial head. In type II, there is a fusion just distal to the
proximal radial epiphysis in association with congenital dislocation of the
radial head. Both types result in a limitation of pronation and supination
of the forearm, and in type II, there is also limited extension of the
elbow. Common associated abnormalities are mental retardation, hypotonia,
and abnormal facies.