Tibiotalar contact area. Contribution of posterior malleolus and deltoid ligament.

Sixteen fresh ankle specimens were tested under physiologic loads to evaluate the effect on the tibiotalar contact area of increasing-size posterior malleolar fracture fragments and disruption of the deltoid ligament. The tibiotalar joint was maintained in a neutral position, and contact areas were recorded on pressure sensitive film. Posterior malleolar fracture fragments of 25%, 33%, and 50% as visualized on lateral radiographs were created. The deltoid ligament was sectioned after the final fracture fragment was made. There was a corresponding decrease of 4%, 13%, and 22% in tibiotalar contact area with the increasingly larger fracture fragments. The final disruption of the deltoid ligament did not alter the contact area. Statistical analyses using Student's t-test showed a statistically significant decrease in tibiotalar contact area in the samples with a fracture fragment of 33% and 50% involvement of the joint as compared with the control samples. Transection of the deltoid ligament produced no statistically significant further change in contact area. Displaced posterior malleolus fractures produce a significant decrease in contact area with 33% or greater involvement of the joint, which may predispose the tibiotalar joint to degenerative changes that should be lessened by anatomic reduction and internal fixation. Disruption of the deltoid ligament does not appear to alter contact area further, supporting the concept of repair as optional.