Accuracy and Reproducibility of a Patient-Specific Instrumentation in Total Ankle Arthroplasty

CATEGORY: Ankle Arthritis INTRODUCTION/PURPOSE: Ankle arthritis (OA) is a frequent and debilitating disease with the two primary surgical options being ankle arthrodesis or total ankle arthroplasty (TAA). TAA has the advantages maintenance of range of motion (ROM), a more normalized gait and potentially improved functional outcome over arthrodesis. Malaligned protheses have been demonstrated to have increased peak component pressures, potentially leading to component loosening, failure and overall worse outcomes. One TAA system uses pre-op CT to build patient-specific surgical instrumentation, with purported benefit of more reliable and accurate component positioning. The goal of this study is to evaluate reproducibility and accuracy of this system by surgeons without affiliation with the prosthesis design team. METHODS: A retrospective radiological study was performed including two centers with four fellowship-trained foot and ankle surgeons using the patient-specific TAA system. All patients operated on between 2015-2018 were included. The primary outcome was alignment of the tibial implant in coronal and sagittal orientation relative to the tibia anatomic axis. All measurements were performed in duplicate an orthopaedic foot and ankle fellow and a musculoskeletal fellowship-trained radiologist. Secondary outcomes included accuracy of prediction of tibial and talar component size implanted compared to the engineered pre-operative plan, rate of prosthesis revision (at least one component) and overall re-operation rate. RESULTS: 79 patients were included in the final review. The mean absolute deviation of the tibial component from tibial anatomical axis was 1.31° +/- 1.14in the coronal plane and 2.68°+/- 1.74 in sagittal alignment. 94.7 % of the implants were implanted within 3°of varus or valgus and 73.7% within 3°of dorsiflexion or plantiflexion. 86 % of the implanted tibial component were of the size predicted by the pre-op plan whereas it was found to be the case in 63 % of the talar component.At a mean follow-up of 22 months(3-52), two TAA (2.5%) have been revised due to aseptic tibial implant loosening. CONCLUSION: The patient-specific guide has been found to be a reliable system for coronal tibial implant alignment but less in the sagittal plane in the hand of surgeons not involved in the design of any TAA system. Accuracy of prediction of the tibial component size is high, moderate on the talar side. In this series there was a low rate of early component revision (2.5 %).