CONTACT AREAS AND PRESSURE DISTRIBUTIONS IN THE SUBTALAR JOINT

We investigated how foot position and ankle arthrodesis affect the con tact characteristics of the subtalar joint. Nine fresh-frozen specimen s of amputated lower legs were used. Pressure-sensitive films were ins erted into the anterior and posterior articulation of the subtalar joi nt. The contact areas and pressure for various foot positions and unde r axial loads of 600, 1200, and 1800 N were determined based on the gr ay level of the digitized film. In neutral position and under a 600 N load, the maximum contact pressure in the subtalar joint was 5.13 +/- 1.16 MPa. The contact area (1.18 +/- 0.35 cm(2)) was only 12.7% of the whole subtalar articulation area (9.31 +/- 0.66 cm(2)), and the total force (348.5 +/- 41.7 N) transmitted via this contact area was about 58% of the applied load (600 N). Dorsiflexion of the foot increased th e contact area and the force transmitted, but decreased the average co ntact pressure in the subtalar joint, while the reverse occurred in pl antar flexion. Eversion increased the subtalar contact stress, whereas inversion up to 10 degrees decreased it. Ankle joint arthrodesis shif ted the contact areas in the subtalar joint posteriorly in all inversi on/eversion positions. Moreover, total force transmitted through the s ubtalar joint as well as the contact pressure increased.