[Tridimensional gait analysis after unilateral subtalar arthrodesis].

Purpose Of The Study: Subtalar arthrodesis can be useful in various conditions. Initially used for the treatment of congenital or acquired foot deformities, it was later applied to surgical repair of traumatic injury. The subtalar joint does however play an important role in gait, particularly for transmitting rotational movement of the leg to the foot. The functional outcome after subtalar arthrodesis has been the object of many studies. These studies examined clinical and radiological results and raised the problem of determining the appropriate extent of the fusion. None of these studies has however provided a three-dimensional analysis of gait after subtalar arthrodesis, performed in the present work.

Material And Methods: We used the Vicon VX3D system with 2 integrated force platforms. Acquisition was made at 50 Hz. The Vicon recording was coupled with EMG recordings of the gastrocnemius, the rectus, the anterior tibialis, and the glutius medius. Gait was analyzed in 8 patients who had undergone unilateral subtalar arthrodesis at least 18 months earlier. Several recordings were made for each patient but only one complete gait cycle was retained for analysis of kinematic, kinetic and electromyographic curves and ground reaction forces. Wilcoxon's test for paired series was used to compare the operated side to the healthy side (excepting EMG recordings).

Results: The operated and healthy side were significantly different. Total amplitude of joint movement was lower for the operated side: 16.5 degrees versus 21.5 degrees for the healthy side. Peak power generated at the ankle for plantar flexion was lower at the end of the stance phase. Electromyography recordings showed a shift in muscle activity between the healthy and fused foot.

Discussion: Few statistical differences were found between the tested values. It can thus be concluded that gait pattern is globally symmetrical after subtalar arthrodesis and that this fusion has little functional impact on the knee or the hip. The difference in amplitude between the healthy and operated side showed a wider variability than observed by Winter in the healthy subject that was also greater than the measurement error reported by Laasel. We did not perform a statistical analysis of the EMG data since the values recorded were arbitrary and the observed shift in activities had no general impact.

Conclusion: Despite the reduction in flexion-extension amplitude of the ankle, subtalar arthrodesis allows a globally symmetrical gait in the experimental conditions described.