Abstract
Category:
Ankle; Ankle Arthritis; Basic Sciences/Biologics
Introduction/Purpose:
Clinical and functional improvement after total ankle arthroplasty (TAA) in end-stage ankle arthritis has been well documented. However, despite the implantation of TAA devices designed to restore normal walking kinematics, patients with end-stage arthritis develop compensatory walking patterns which do not return to normal, postoperatively. This discrepancy between the normative and adaptive gait patterns could influence implant loading and intended function; however, the independent influence of implant constraints and adaptive gait on joint function is unknown. Therefore, this study aimed to isolate the individual and combined effects of TAA implantation and gait adaption from ankle arthritis on foot and ankle kinematics during simulated level walking. We hypothesized that foot and ankle kinematics would primarily be altered through adaptations in gait resulting from ankle arthritis.
Methods:
Twelve mid-tibia cadaveric specimens were utilized. A validated six-degree of freedom robotic gait simulator was used to simulate the stance phase [3]. The specimen was first placed on the simulator in the intact condition, simulated with both healthy and adaptive gait inputs collected from healthy and post-surgical TAA subjects (average follow-up: 46 months), respectively. The TAA (Salto Talaris; Integra LifeSciences) was then implanted, and adaptive and healthy gait trials were conducted in the implanted condition. Four conditions were collected on each specimen: intact with a healthy walking trajectory (intact- healthy), intact with an adaptive walking trajectory (intact-adaptive), implanted with TAA with a healthy walking trajectory (TAA- healthy), and implanted with TAA with an adaptive gait trajectory (TAA-adaptive). Ankle, subtalar, and talonavicular joint kinematics in each condition were compared to intact-healthy to isolate the effects of implantation and adaptive gait on kinematics. Bias-corrected 95% confidence intervals were calculated for the difference between conditions.
Results:
Significant differences were observed in the ankle, subtalar, and talonavicular joints across all comparisons. In the comparison between the intact-healthy and intact-adaptive conditions, to isolate the effect of adaptive gait (Figure 1A), ankle dorsiflexion and subtalar eversion increased late in stance, while talonavicular abduction increased in early and late stance. In the comparison between intact-healthy and TAA-healthy conditions, to isolate the effect of implant constraints (Figure 1B), ankle plantarflexion, subtalar eversion, and talonavicular abduction significantly increased in mid-stance after implantation. In the comparison between the intact healthy and the TAA-adaptive conditions, to evaluate the combined effect of adaptive gait and implantation (Figure 1C), ankle plantarflexion was increased during early stance and decreased in late stance, subtalar eversion increased during mid-to-late stance, and talonavicular abduction increased throughout most of the stance phase.
Conclusion:
The results from this study indicate that both gait adaption and implant constraint contributed to changes in ankle and adjacent joint kinematics. The two factors appear to influence different aspects of the stance phase, where gait adaption appeared to influence early, and late stance and implantation influenced kinematics in mid-stance. The synergistic influence of both factors seemed to exaggerate deviations away from normal kinematics in the subtalar and talonavicular joints while negating deviations from normal in the ankle joint. This suggests that ankle implants designed to restore normative walking patterns may not account for the loading environment seen in patients.
