Influence of Double Hindfoot Arthrodesis and the Sequence of Joint Fusion on Ankle Kinematics: A Cadaveric Gait Simulation Study

Abstract

Category: Ankle; Basic Sciences/Biologics Introduction/Purpose: Although double hindfoot arthrodesis (subtalar and talonavicular) provides pain relief and deformity correction for patients with end-stage arthritis, altered ankle biomechanics may occur following these procedures. Furthermore, it has been reported that hindfoot fusions may lead to progressive ankle degenerative changes and a higher failure rate in patients undergoing total ankle arthroplasty. Previous biomechanical studies demonstrated that hindfoot fusion altered ankle joint kinematics and contact mechanics during simplified loading scenarios, but the effect during dynamic activity is unknown. Therefore, this study sought to quantify the changes in ankle kinematics after a double hindfoot arthrodesis during the stance phase of simulated gait. In addition, we sought to assess whether the sequence in which joints are fused plays a role in altering ankle kinematics. Methods: Fourteen mid-tibia specimens underwent stance phase simulations of level walking using a validated six-degree of freedom robot. All specimens had neutral hindfoot alignment. An eight-camera motion system tracked reflective markers in the tibia, talus, calcaneus, and navicular bones. Simulated arthrodeses of the subtalar and talonavicular joints were performed using two 7.0mm and two 5.5mm crossing screws, respectively. The subtalar alignment was set at 5º valgus, and the talonavicular at neutral abduction/adduction. Fluoroscopic images confirmed proper screw position and hindfoot alignment. Each specimen was tested in three conditions: pre-arthrodesis(intact), isolated arthrodesis(subtalar or talonavicular joint), and double arthrodesis(double). Specimens were further divided into two groups depending on whether the subtalar(STDouble) or talonavicular(TNDouble) joint was fused first. Ankle kinematics were calculated for each condition for the entire cohort of specimens and each of the two groups. Bias-corrected 95% confidence intervals of the difference in ankle kinematics relative to the intact condition were constructed. Results: Double hindfoot arthrodesis significantly altered ankle kinematics(Figure1A). Ankle plantarflexion decreased during heel strike by up to 2.0° on average and increased during toe-off by 6.5° compared to the intact condition. Ankle eversion increased by 1.5º and 2.5º on average during mid- and late stance, respectively. Internal rotation decreased during midstance by 1.1º on average and increased in late stance by 4.5°. The order in which hindfoot joints were fused significantly influenced ankle kinematics(Figure1B). On average, the TNDouble condition produced 2.3º and 3.5º more ankle eversion during the mid- and late stance, respectively, and 2.10° more ankle internal rotation during the early stance compared to the STDouble condition (not shown). Significant changes were also present after isolated hindfoot arthrodeses and remained consistent after the double arthrodesis. Conclusion: Double hindfoot arthrodesis significantly altered ankle kinematics throughout stance. Ankle kinematics also differed depending on which joint was fused first. Notably, the TNDouble condition produced more ankle internal rotation during early stance and more ankle eversion during mid- and late stance compared to the STDouble condition. This finding suggests that the sequence in which joints are fused affects the resultant ankle kinematics. Finally, the kinematic changes after isolated hindfoot arthrodesis remained consistent after incorporating the second joint into the fusion. It appears that once one joint needs to be fused, avoiding the double arthrodesis may not necessarily protect the ankle.