TIBIOTALAR CONTACT AREA - CONTRIBUTION OF POSTERIOR MALLEOLUS AND DELTOID LIGAMENT

Sixteen fresh ankle specimens were tested under physiologic loads to e valuate the effect on the tibiotalar contact area of increasing-size p osterior malleolar fracture fragments and disruption of the deltoid li gament, The tibiotalar joint was maintained in a neutral position, and contact areas were recorded on pressure sensitive film, Posterior mal leolar fracture fragments of 25%, 33%, and 50% as visualized on latera l radiographs were created, The deltoid ligament was sectioned after t he final fracture fragment was made, There was a corresponding decreas e of 4%, 13%, and 22% in tibiotalar contact area with the increasingly larger fracture fragments. The final disruption of the deltoid ligame nt did not alter the contact area, Statistical analyses using Student' s t-test showed a statistically significant decrease in tibiotalar con tact area in the samples with a fracture fragment of 33% and 50% invol vement 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 produc e a significant decrease in contact area with 33% or greater involveme nt of the joint, which may predispose the tibiotalar joint to degenera tive changes that should be lessened by anatomic reduction and interna l fixation, Disruption of the deltoid ligament does not appear to alte r contact area further, supporting the concept of repair as optional.