No abstract

It is a well known entity that fractures of the tibia heal with some component of angular deformity. Ankle and subtalar joints may compensate for small degrees of angular deformities, but the exact amount of malunion that can be accepted without development of late sequalae has yet to be determined. Two recent studies from this institution have concluded that contact changes at the tibiotalar joint tend to be greater with distal third tibial fracture deformities compared to proximal and middle with the ankle in neutral, 5 degrees dorsiflexion, and 20 degrees of plantar flexion. Anterior and posterior bow deformities produced a greater change in contact area of the tibiotalar joint than with valgus or varus deformities. This phenomena may be possibly explained by the subtalar motion in the horizontal plane which averages 23 degrees. Thus, it was the primary purpose of this paper to determine the exact role, if any, in subtalar motion on tibiotalar contact in angular deformities of the tibia. To achieve this objective the subtalar joint was transfixed thereby eliminating its perceived compensatory movement. Six cadaveric lower extremities were disarticulated at the knee joint and stripped of soft tissue preserving capsular and ligamentous structures. A custom universal joint was used to create various angulatory deformities at proximal, middle, and distal third levels of the tibia.(ABSTRACT TRUNCATED AT 250 WORDS)

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.