The effect of simulated tibial deformities on the ankle joint during the gait cycle.

The effect of angular deformities of the tibial shaft on the area, location, and shape of the ankle joint contact during the normal extremes in the gait cycle was studied with the use of a cadaveric model. Six lower limbs were first examined radiographically and found to be free of pathology. These specimens were then stripped of soft tissues proximal to the ankle joint and had a custom-designed universal joint-plate inserted into the tibia at the proximal, middle, or distal third level. An anterior ankle arthrotomy was performed, and pressure sensitive film was inserted into the tibiotalar joint. Load was then applied with the ankle set in dorsiflexion or plantarflexion via metal wedges, and tibial deformities of 5, 10, and 15 degrees were simulated in varus, valgus, anterior bow, and posterior bow. Contact area and location changes were noted to be of greater magnitude with proximal and distal third tibial deformities than with middle third deformities. Varus and valgus deformities showed smaller contact area changes than anterior or posterior bow deformities. Contact area changes tended to be larger in dorsiflexion compared to plantarflexion for each level and degree of tibial angulation. Posterior bow deformities at all levels resulted in greater changes in contact area and shape than other deformities. The role of subtalar compensation, stiffness of the foot-ankle complex, and geometric factors are all thought to influence the changes noted. On the basis of this experimental study it would appear that angular deformity of the tibia less than 10 degrees would not significantly alter ankle joint contact.