Evaluation of Hindfoot Alignment After Fixed- and Mobile-Bearing Total Ankle Prostheses

Background: End-stage ankle arthritis can involve malalignment of the ankle in both the coronal and sagittal planes. Up to 33% to 44% of patients who present for total ankle replacement (TAR) have greater than 10 degrees 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 changed over time. Specifically, we measured coronal and sagittal alignment of both the ankle and hindfoot complex. Methods: A retrospective study was performed on 2 independent groups of patients undergoing 2 different systems for total ankle replacement: Zimmer (lateral approach, fixed-bearing) and Hintegra (anterior approach, mobile bearing). Specific demographic data and radiographic data were measured. Within-group comparisons were performed using 1-way repeated measures ANOVA, analyzing the temporal course of clinical data within the Hintegra and Zimmer groups. Results: At the ankle joint, as measured by the alpha and beta angles (P > .05), the position of the components remained relatively similar in both the fixed- and mobile-bearing TAR at 24-month follow-up. The sagittal alignment, as measured by the TT (tibiotalar) ratio, demonstrated a posterior shifting of the talus in the mobile bearing group (P = .036). Although the fixed- and mobile-bearing TAR had both significant hindfoot alignment improvement between the preoperative radiographs and at 24 months, over time, the fixed-bearing ankle had a significant increase in both the hindfoot alignment view angle and hindfoot alignment distance (P < .001), suggesting a possible dynamism of the hindfoot in the fixed-bearing TAR. Conclusion: The lateral-approach fixed and anterior approach mobile-bearing implants maintained coronal and sagittal alignment in the short term; the temporal course of the lateral approach fixed-bearing ankle showed an increase in the valgus positioning of the hindfoot. The anterior approach mobile-bearing implant maintained its hindfoot alignment over the course of the study.