Posttraumatic radioulnar synostosis (RUS) is a rare event following forearm fractures. Consequences are disabling for patients who suffer from functional limitation in forearm pronosupination. Distal RUS are even more rare and more difficult to treat because of high recurrence rates. The patient we describe in this paper came to our attention with a double distal RUS recurrence and a Darrach procedure already performed. We performed a radical excision of RUS and interposition with a vascularized dorsoulnar artery (DUA) adipofascial perforator flap. Four years after surgery, the patient shows the same complete range of motion in pronosupination, and MRI confirms that the flap is still in place with signs of vascularization. Simple synostosis excision has been proven ineffective in many cases. Interposition is recommended after excision, and biological material interposition seems to be more effective than foreign material. Surgeons are increasingly performing vascularized interposition, and the results are very encouraging.