Tibiotalar Contact Area and Pressure Distribution: The Effect of Mortise Widening and Syndesmosis Fixation

Abstract

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.

Ankle Syndesmosis Injuries: Anatomy, Biomechanics, Mechanism of Injury, and Clinical Guidelines for Diagnosis and Intervention

“…Chronic instability of the syndesmosis may then result in increased shear stress and altered contact pressure patterns that might predispose the individual to degenerative articular cartilage changes in the ankle joint. 40 Ankle diastasis, with many subtypes, including lateral subluxation of the talus, posterior rotatory displacement of the fibula and talus, and complete diastasis with superior subluxation of the talus, could result from more severe injury to the syndesmosis. 16 Individuals who participate in skiing, football, soccer, and other turf sports that involve planting of the foot and cutting may have the greatest risk for ankle syndesmotic sprains.…”

“…Ogilvie-Harris et al 40 investigated the relative contribution of the 4 syndesmotic ligaments to the stability of the ankle mortise by imposing up to 2 mm of lateral displacement of the fibula on the tibia. The investigators varied the order of sectioning of the syndesmotic ligaments.…”

“…Pereira et al 40 investigated tibiotalar contact area, mean pressure distribution, and central shift of the ankle mortise by examining the effects of syndesmosis fixation, mortise widening of 2 mm and 4 mm, and transection of the deep deltoid ligament in an unconstrained cadaveric ankle model. Central shift was defined as medial-lateral displacement of the center of contact area on the articular surface of the talus.…”

“…Their data also indicated significant decreases in tibiofibular contact area after syndesmosis fixation with the ankle joint in 10°d orsiflexion and 20°plantar flexion, when compared with the control condition. Pereira et al 40 concluded, therefore, that syndesmotic fixation may have an adverse effect on contact area of the ankle joint and may increase contact stress during weight bearing and walking.…”

“…The resulting incongruent joint motion can lead to degenerative changes in the ankle joint. 40 Screw fixation 2 cm proximal to the ankle joint can increase stability of the ankle joint and decrease widening of the syndesmosis. The potential adverse effects of screw application are to produce an abnormal constraint of the mortise, perhaps resulting in secondary problems such as insufficient range of motion and incongruent joint motion during walking and weight bearing.…”