Tibiotalar contact area and pressure distribution: the effect of mortise widening and syndesmosis fixation.
An unconstrained cadaver ankle model was designed to reevaluate the effect of ankle mortise widening and syndesmotic fixation on the load-bearing characteristics of the tibiotalar joint. Tibiotalar contact area, centroid shift, and mean contact pressure were quantified using a pressure-sensitive film technique. Six fresh-frozen below-knee amputation specimens were axially loaded with 500 N in three positions: neutral, 10 degrees of dorsiflexion, and 20 degrees of plantarflexion. The tibiotalar contact area and centroid position for each specimen in its intact state were first determined and then compared with values obtained after syndesmotic fixation, mortise widening of 2 and 4 mm, and deep deltoid ligament transection. Syndesmotic fixation significantly decreased joint contact area but did not consistently affect centroid position. However, unlike earlier studies, which used more constrained ankle fracture models, mortise widening with or without deltoid rupture was not found to significantly affect contact area, centroid position, or joint contact pressure. When statically loaded, the talus moved to its position of maximal congruence in the mortise, rather than displacing laterally along with the lateral malleolus.