Medical information
A starting point for understanding radioulnar synostosis, with the original site’s resources gathered into one clearer guide.
This information is educational. A clinician who can review your history and imaging is the right person to interpret symptoms or discuss treatment.
Radioulnar synostosis symptoms can include being unable to fully turn the palm up or down, sometimes with pain or strain from compensating movements. There are two broad forms of RUS.
Research libraryArticles and plain-language summaries organized by topicCongenital RUS
Congenital radioulnar synostosis (CRUS) is present from birth. It occurs when the radius and ulna do not fully separate during early fetal development, most often near the elbow. The original guide described normal separation as happening between weeks five and eight of gestation; an older duplicate page described it as around week seven.
The original site summarized older clinical references as suggesting that RUS occurs in families in roughly 20–25% of cases and alongside another genetic syndrome about 30% of the time. Published estimates and definitions vary.
It also reported a male-to-female diagnosis ratio around 3:2 and bilateral involvement in roughly 60–80% of people. These figures come from small rare-condition samples and vary between references.
The original guide gave an average diagnosis age of about six. People with one affected arm may be identified later or go undiagnosed because they compensate with shoulder and wrist movements.
Compare types of RUS →Post-traumatic RUS
Radioulnar synostosis can also develop after physical trauma, commonly following a forearm fracture. The original guide cited a 3–9% figure in its trauma section; clinical references generally frame this as incidence after surgically treated forearm fractures rather than among all people with RUS.
The legacy guide named a forearm fracture, delayed treatment, and forearm surgery as possible contexts in which post-traumatic RUS can develop.
Post-traumatic RUS can look different from congenital RUS on an X-ray, and treatment decisions depend on the location of the fusion, symptoms, function, and the person’s goals.
Read about treatment →