Isolated radio-ulnar synostosis

Isolated radio-ulnar synostosis (also known as congenital radioulnar synostosis) is a rare skeletal disorder characterized by an abnormal bony or fibrous fusion (synostosis) between the radius and ulna bones of the forearm. This fusion typically occurs at the proximal (upper) end of the forearm, near the elbow, and results in a fixed position of the forearm, most commonly in pronation (palm facing downward). The condition may be unilateral (affecting one arm) or bilateral (affecting both arms) and is present from birth due to a failure of the normal separation of the radius and ulna during embryonic development. Patients with isolated radio-ulnar synostosis experience limited or absent forearm rotation, meaning they cannot fully turn their palm upward (supination) or downward (pronation). The degree of functional impairment varies depending on the position in which the forearm is fixed. Many individuals develop compensatory movements at the shoulder and wrist joints. In mild cases, the condition may go undiagnosed until childhood when difficulty with activities such as turning doorknobs, receiving change, or using utensils becomes apparent. Pain is generally not a prominent feature in childhood but may develop later. Treatment depends on the severity of functional limitation. Mild cases may require no intervention, while more significantly affected individuals may benefit from surgical correction, typically a derotational osteotomy, which repositions the forearm into a more functional angle of rotation. Complete restoration of rotational movement through surgery is generally not achievable. Occupational therapy can help patients develop compensatory strategies for daily activities. The condition is considered isolated when it occurs without other associated skeletal or systemic anomalies, distinguishing it from syndromic forms of radioulnar synostosis.

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