Effect of tibiotalar joint arthrodesis on adjacent tarsal joint pressure in a cadaver model.

BACKGROUND: Tibiotalar arthrodesis is the most common treatment of end-stage symptomatic ankle arthritis, but concerns exist about late findings of adjacent tarsal joint osteoarthritis. The purpose of this study was to evaluate the changes of pressure in the talonavicular, subtalar, and calcaneocuboid joints before and after rigid tibiotalar joint immobilization and at different levels of tibiopedal dorsiflexion.

METHODS: Twelve cadaver foot specimens were cyclically loaded on a servohydraulic test frame to 700 N. Joint contact pressure, peak pressure, and contact area in the three tarsal joints were measured before and after tibiotalar joint immobilization with three 6.5-mm screws to simulate ankle arthrodesis. Measurements were obtained at tibiopedal dorsiflexion angles of 0, 10, 20, and 30 degrees in normal ankle joints and at dorsiflexion angles of 0, 10, and 20 degrees in fixed tibiotalar joints. Paired Student's t-tests and one-way ANOVA with repeated measures were used to analyze the data.

RESULTS: Joint contact pressures did not show any statistically significant difference for the talonavicular and calcaneocuboid joints in the intact ankle. Contact pressures in the talonavicular and calcaneocuboid joints showed significant differences between 0 and 10 degrees and between 0 and 20 degrees of dorsiflexion (p<0.05) in the fused ankle specimens. Comparison of the contact pressure of the talonavicular and the calcaneocuboid joints between the intact and the fused ankle specimens showed a significant difference at 10 and 20 degrees of dorsiflexion (p<0.05). Subtalar joint contact pressure in the intact ankle showed a significant difference between 0 and 30 degrees of dorsiflexion (p<0.05).

CONCLUSIONS: These changes in joint pressures and contact area are consistent with findings of transverse tarsal joint arthritis seen in clinical studies. The current findings suggest that a substantial pressure increase in the talonavicular and calcaneocuboid joints at tibiopedal dorsiflexion levels simulating a late stance phase of the gait cycle may be responsible for the secondary tarsal joint degeneration occurring in late ankle arthrodesis.