[Fracture of the two forearm bones and congenital radioulnar synostosis: a case report].

We report a case of shaft fracture involving both forearm bones in an 18-year-old male presenting congenital radioulnar synostosis. The mechanism of fracture involved both direct blunt trauma and forced supination on forearm frame blocked in 30 degrees pronation. Emergency osteosynthesis was performed using a standard procedure without any attempt to modify the ankylosis position. Congenital radioulnar synostosis appears to produce a rather vulnerable forearm due to restrained torsion. This notion must be taken into account in such subjects participating in contact sports which solicit pronation-supination.