SUPPORT OF THE TALUS - A BIOMECHANICAL INVESTIGATION OF THE CONTRIBUTIONS OF THE TALONAVICULAR AND TALOCALCANEAL JOINTS, AND THE SUPEROMEDIAL CALCANEONAVICULAR LIGAMENT

The goal of this study was to determine the magnitude of force transmi ssion to the talus by its inferior articulations to provide insight in to mechanisms involving acquired deformities of the hindfoot. Cadaver feel were mounted in a loading apparatus that applied axial force thro ugh the tibia and fibula as well as tensile loading of the tendons of extrinsic musculature. This also permitted positioning of the tibia in the sagittal plane. Eighteen specimens were tested in three selected positions of the gait cycle. In one series, pressure-sensitive film wa s inserted into the posterior and anteromedial facets of the talocalca neal joint as well as into the talonavicular joint. In a second series , film was inserted between the talar head and the superomedial calcan eonavicular ligament. In stance position, the specimens were also test ed without posterior tibial tendon (PTT) tension. Contact areas and fo rce transmitted across the articulations were greatest in near toe-off position, in the posterior facet of the talocalcaneal joint. The talo navicular joint, the anteromedial facet of the talocalcaneal joint, an d the calcaneonavicular ligament articulation showed sequentially decr easing amounts of contact area and force transmission. Mean pressures were similar across all articulations, except in the posterior facet i n near toe-off position. From heel-strike to stance, to near toe-off, a trend to increasing contact area and force was noted. No difference in contact characteristics was found in the calcaneonavicular ligament articulation after PTT release. The contact force of the calcaneonavi cular ligament against the talus was found to be much smaller than tho se of other talar articulations; however, its medially oriented direct ion must contribute to stabilization of the head of the talus against medial displacement. Loss of PTT tension was not found to alter the co ntact forces acting at the talar head in this model, which might indic ate that it shares its talar stabilizing function with other structure s.