THE INFLUENCE OF A DIASTASIS SCREW ON THE OUTCOME OF WEBER TYPE-C ANKLE FRACTURES

We performed a retrospective study of the factors affecting the outcom e of Weber type-C ankle fractures in 43 patients reviewed at two to ni ne years after injury, We determined the functional result in relation to the use of a diastasis screw the accuracy of reduction, the presen ce of tibiotalar dislocation, and of injury to the medial side of the ankle by medial malleolar fracture or deltoid ligament rupture. We ass essed the use of a diastasis screw as appropriate or inappropriate on the basis of an anatomical study performed by Boden et al (1989). The diastasis screw was used unnecessarily in 19 of the 31 patients so tre ated, but this did not appear to affect the final functional result, T he worse functional results were in ankles dislocated at the initial i njury, and in those with medial malleolar fractures as opposed to thos e with deltoid ligament ruptures. The best results were after accurate reduction of the fibula and the syndesmosis, and greater increase in the width of the syndesmosis was associated with a worse result. Our r esults suggest that an increase of more than 1.5 mm in syndesmosis wid th is unacceptable. We recommend that when the deltoid ligament is rup tured, a diastasis screw should be used if the fibular fracture is mor e than 3.5 cm above the top of the syndesmosis. When a medial malleola r fracture has been rigidly repaired a diastasis screw is required if the fibular fracture is more than 15 cm above the syndesmosis.