Does Sagittal Tibiotalar Alignment of TAR Predict Failure?

CATEGORY: Ankle Arthritis INTRODUCTION/PURPOSE: The long term outcome of total ankle replacement is contingent on restoring the anatomic tibiotalar alignment of the ankle joint. Prior studies have mainly looked at the effect of coronal and hindfoot alignment of TAR on outcome and failure with few studies focusing on the effect of sagittal tibiotalar alignment. From these, we know that sagittal alignment has a greater impact on joint mechanics and that proper positioning of the talar component in the sagittal plane results in greater postoperative pain relief and better functional outcome, especially ankle range of motion. The goal of this study was to define a sagittal radiographic value that predicts failure in TAR. METHODS: We analyzed the data of a retrospective patient cohort of consecutive TAR patients, which were treated from 2004 and 2011. Patients with two types of prosthesis were included, Salto Talaris (fixed bearing) and STAR (mobile bearing). All measurements were completed by two blinded observers, including the sagittal distal tibial articular angle (sDTAA), the lateral talar station (LTS) and the talar component inclination angle (γ angle). A total of 90 patients were included, 51 were male and 39 female patients. Seventy-seven patients received a Salto and 13 patients a STAR prosthesis. The average age was 63.7 years. RESULTS: The mean sDTAA was 83.9 degrees and the mean γ angle was 21 degrees, both without significant difference in the two different prosthesis designs. A significant association (p=0.03) between post-op LTS as a continuous variable per unit increase and clinical failure was demonstrated, which included all the revision cases, with an odds ratio of 1.25. In addition a significant association (p=0.03) between increased LTS and sDTAA change of >5°, which is indicative of anterior subsidence, was shown. This was associated with an odds ratio of clinical TAR failure of 1.27. CONCLUSION: The abnormal radiographic post-op lateral talar station appears to predict clinical TAR failure and correlates with the abnormal sDTAA; the anterior translated talus loads the anterior tibia leading to anterior subsidence of the prosthesis. Limitation of this study is the inclusion of two different types of prosthesis designs.