Three-Dimensional Kinematics of an Unconstrained Ankle Arthroplasty: A Preliminary In Vivo Videofluoroscopic Feasibility Study

Background: Understanding the functionality of total ankle arthroplasties (TAA) requires thorough knowledge of the kinematics during activities of daily life. Videofluoroscopy enables the in vivo measurement of the 3D kinematics of implant components more accurately than by means of skin marker tracking. The aim of the present preliminary study was to quantify the 3D kinematics of a TAA during the stance phase of level and slope walking using single plane videofluoroscopy. Methods: The experimental set up consisted of a videofluoroscopy system (BV Pulsera, Philips Medical Systems, Switzerland, 25 Hz, 1 ms shutter time) integrated in a walkway, allowing the assessment of free level gait, uphill, downhill and cross-slope walking. 2D/3D registration was performed using the CAD models of the TAA. In a preliminary feasibility study, the presented method was applied on four patients with successful unilateral TAA (Mobility™ Total Ankle, DePuy) with good outcomes. Results: Isolated 3D TAA kinematics was quantified with a rotational and translational error of 0.2 degrees and 0.4 mm in plane and 1.3 degrees and 2.1 mm out of plane. In the feasibility study it was found that only minor limitations occurred in sagittal plane motion. Any restrictions were caused by a limitation in dorsiflexion, whereas plantarflexion was for all gait conditions sufficiently provided. Transverse and frontal plane rotation was marginal, the main rotation occurred around the talar construction axis itself. Conclusion: The presented method enabled accurate estimation of the 3D TAA kinematics in vivo, without being limited by skin movement artifacts and isolated from subtalar motion. Since the available amount of dorsiflexion is the crucial factor to allow unrestrictive gait, walking uphill is an appropriate motion task to challenge and evaluate the performance of the TAA. Clinical Relevance: The presented method has the potential to identify specific kinematic patterns and thereby help clinicians and implant developers to evaluate current designs and future design modifications.