Do type B malleolar fractures need a positioning screw?

Type B malleolar fractures (AO/ASIF classification) are usually stable ankle joint fractures. Nonetheless, some show a residual instability after internal fixation requiring further stabilization. How often does such a situation occur and can these unstable fractures be recognized beforehand?From 1995 to 1997, 111 malleolar fractures (three type A, 90 type B, 18 type C) were operated on. Seventeen out of 90 patients (19%) with a type B fracture showed residual instability after internal fixation (one unilateral, four bimalleolar and 12 trimalleolar fractures). Five of these patients showed a dislocation in the sagittal plane (anteroposterior) clinically or on the radiographs, five a dislocation in the coronal plane with dislocation of the tibia on the medial aspect of the ankle joint, and four an incongruency on the medial aspect of the joint. In three cases, no preoperative abnormality indicating instability was found. The fractures were all fixed using an additional positioning screw. In 11 patients, the positioning screw was removed after 8-12 weeks, in six patients removal was performed after 1 year along with removal of the plate. All 17 patients were reviewed 1 year after internal fixation, 16/17 showed a good or excellent result with identical or only minor impairment of range of motion of the ankle joint.

Unstable ankle joints after internal fixation of type B malleolar fractures exist. Residual instability most often occurs after trimalleolar fractures with initial joint dislocation. Treatment with an additional positioning screw generally produced a satisfactory result.