In 5 cadavers, type C malleolar fractures of the pronation-eversion rotation type, were produced. The stability of the ankle mortice under stress was tested before and after rigid internal fixation of the fracture in the fibula. The intact interosseous membrane above the fracture in combination with the internal fixation of the fibula was sufficient to keep the lateral malleolus in place. A clinical series of 8 equivalent fractures treated with rigid internal fixation without suture of the syndesmodesis was collected and evaluated clinically and radiologically 3 years after the injury. None of the patients had significant complaints and all ankle joints were stable.