Hindfoot Alignment after Total Ankle Replacement

CATEGORY: Ankle, Ankle Arthritis INTRODUCTION/PURPOSE: End-stage ankle arthritis can involve misalignment of the ankle in both the coronal and sagittal planes as up to reported 33% to 44% of patients who present for total ankle replacement have greater than 10° of coronal plane deformity. Normalization of the sagittal and coronal alignment is key in improving survivorship and functional outcomes in TAR. In the present study, we analyzed how both the ankle and hindfoot alignment for both a fixed-bearing and mobile bearing TAR system changes over time. Specifically, we measured coronal and sagittal alignment of both the ankle and hindfoot complex. We hypothesize that both significant differences would be seen between all time points and pre-operative radiographs, and that these differences would not change over time. METHODS: A retrospective study performed by a single orthopaedic surgeon was performed on two independent groups of patients undergoing two different systems for total ankle replacement: Zimmer TAR (lateral-approach, fixed-bearing, n=89) and Hintegra (anterior approach, mobile-bearing, n=81). We noted specific demographic data and radiographic data were measured including: Hindfoot alignment view angle (HAV), Hindfoot alignment distance (HAVD), tibiotalar ratio, a angle and ß angle. These were measured pre-operatively, and 6 months, 12 months, and 24 months post-operatively. Within-group comparisons were performed using one-way repeated-measures ANOVA (1-w rANOVA), analyzing temporal course of clinical data (comparisons between different time points, e.g. T0vsT6vsT12vsT24) within the Hintegra and Zimmer groups. To compare the time course of clinical measures between the two groups, 2-w rANOVAs were performed for SA, SD, TT ratio, a and ß angle. Specifically, time*group interaction was tested. RESULTS: At the ankle joint itself, as measured by the a and ß angles (p>.05), the position of the components remains relatively similar in both the fixed and mobile bearing TAR over the course of 24 months. The sagittal alignment, as measured by the TT ratio, demonstrated a posterior shifting of the talus in the mobile bearing group (p=.036). Though the fixed and mobile-bearing TARhad both significant hindfoot alignment improvement between the pre-op radiographs and twenty-four months, over time, the fixed-bearing ankle had a significant increase in both the HAV and HAVD (p<.001), suggesting a dynamism of the hindfoot in the fixed-bearing ankle. CONCLUSION: Correcting coronal and sagittal alignment is important for the long-term survivorship of a TAR. The fixed and mobile-bearing implants had maintained coronal and sagittal alignment in the short term, the temporal course of the fixed-bearing ankle showed an increased in the valgus positioning of the hindfoot. The mobile-bearing implant maintained its hindfoot alignment over the course of the study. More studies are needed to explore the clinical implications of this new data.