Kinematics of a Pyrocarbon Ankle Spacer for the Treatment of Arthritic Disease

CATEGORY: Ankle, Ankle Arthritis INTRODUCTION/PURPOSE: Treatment options for ankle arthritis in younger patients are currently limited. Since the longevity of modern total ankle replacements is not sufficient for this patient population, ankle arthrodesis is typically utilized when joint preserving treatment is not a viable option. A new procedure using a pyrocarbon ankle spacer has been developed as a potential alternative, allowing for talar articular resurfacing for pain relief with minimal bone resection. The objective of this study was to assess whether this pyrocarbon ankle spacer could provide normal ankle kinematics as the native ankle joint using cadaveric gait simulation. METHODS: Five mid-tibia cadaveric specimens without deformity and no history of lower limb injury or surgery were utilized. The stance phase of gait was simulated for each specimen using a six degree-of-freedom robotic device. A force plate was moved relative to stationary specimen through an inverse tibial kinematic path calculated from in vivo data while extrinsic tendons were actuated using physiologic loads (Figure 1A). Magnitudes of load were scaled to that of 25% bodyweight. Ankle kinematics were measured from reflective markers attached to the tibia and talus via surgical pins. The pyrocarbon ankle spacer (Exactech, Gainesville, FL, USA) was implanted in a nest formed 3-4 mm in depth on the talar articular surface using a custom burring technique (Figure 1B). Ankle spacer kinematics were compared to 95% confidence intervals of native, intact ankle joint kinematics to assess agreement. RESULTS: Outcomes revealed no significant difference in ankle joint kinematics between the native, intact condition and post- pyrocarbon spacer implantation (Figure 1C). This result was consistent for the sagittal, coronal and axial planes of motion. CONCLUSION: The results of this study demonstrate that a pyrocarbon spacer permits normal ankle kinematics. Further, the device was observed to be stable in the joint throughout simulations. While the testing was performed at 25% bodyweight for analyses on all specimens, load magnitudes were also increased up to 75% on a subset of specimens and the structural integrity of the device remained pristine. With these findings, we concluded that the pyrocarbon spacer device offers promising potential as a treatment option for ankle arthritis.