Effects of imposed hindfoot constraint on ankle contact mechanics for displaced lateral malleolar fractures.

Contact stress distributions on the tibial plafond were mapped in a series of eight fresh-frozen cadaver specimens in which displaced lateral malleolar fractures were studied. These included gripping (a) by snugly lacing the foot in an athletic shoe, (b) by polymethylmethacrylate potting of the calcaneus alone, and (c) by potting of the calcaneus plus talus. Each of these three gripping conditions was tested both for rigid and for nearly frictionless transverse external constraint conditions. Across the series, the grip-dependent changes in contact stress distributions were found to be very minor compared with the wide interspecimen variability that was consistently present. Moreover, although contact stresses generally increased with progressive lateral fibular fragment offsets of up to 5 mm, such an effect was far more modest than that seen in previous cadaver work. The present laboratory cadaver findings suggest that the contact stress elevations occurring clinically for displaced lateral malleolar fractures are probably relatively mild and likely not directly responsible for late secondary degeneration.