Posterior Talar Shifting in Mobile-Bearing and Fix-Bearing Total Ankle Replacement

Abstract

Category: Ankle Arthritis Introduction/Purpose: Sagittal implant malalignment after total ankle replacement (TAR) has been considered to be a possible cause for premature implant failure. In a prior study, the change of the tibiotalar ratio (T-T ratio) over time in TARs was assessed in an unconstrained, three component implant. A significant increase in the T-T ratio between 2 and 6 months after surgery (from 34.6% to 37.2%) was documented. This variation of the talar position in the sagittal plane may be due to the presence of an inlay between the tibial and the talar components. Aim: The aim of this study was to compare the translation of the talus in TARs performed with an unconstrained, three-component design (Hintegra, Newdeal, Lyon, France; Integra, Plainsboro, NJ), and those performed with a semi-constrained, two- component design (Zimmer Trabecular Total Ankle, Zimmer, Warsaw, IN). Methods: The study included 71 consecutive patients (71 ankles) who underwent TAR with the Hintegra implant and 24 consecutive patients (24 ankles) who received the Zimmer implant between May 2011 and December 2014. The most common indication for TAR was post-traumatic arthritis (80.3% and 75.0% in the Hintegra group and in the Zimmer group, respectively). Patients were assessed clinically and radiologically preoperatively (T0), at 6 months (T2) and 12 months (T3) post-surgery. There was also a radiological assessment 2 months after surgery (T1). Results: The comparison of the T-T ratio between the two groups and over time indicated an interaction between time and group, therefore the changes of the T-T ratio with time were affected by the implant type factor (p < 0.0001). The changes of the post-operative T-T ratio over time were not significant in the Zimmer group (35.7%±6.7% at T1, T2, and T3; p=1.0 for each pairwise comparison). In the Hintegra group, the T-T ratio at 2 months (34.4%±5.5%) was significantly different to the T-T ratio at 6 months (37.0% ± 5.8%; p < 0.0001). The American Orthopaedic Foot & Ankle Society (AOFAS) score significantly increased from pre-op to 6 months post-surgery in both the Hintegra group (53.3±16.0 at 6 mos; p < 0.0001) and the Zimmer group (76.8±7.0 at 6 mos; p < 0.0001). There was no statistical difference in the preoperative scores (Hintegra: 32.7 ± 12.8; Zimmer: 34.6 ± 11.9; p=0.5347). Conclusion: The significant antero-posterior translation of the talus documented only in the cohort receiving the unconstrained, three-component implant may have associated with, and produced by the presence of the mobile bearing interface between the polyethylene insert and the tibial prosthesis.