Sagittal Tibiotalar Alignment May Not Affect Functional Outcomes in Fixed-Bearing Total Ankle Replacement: A Retrospective Cohort Study

Background In total ankle replacement (TAR), correct positioning of the implant is crucial. Malposition of the components may increase contact pressures and diminish prosthesis survival. The effect of sagittal tibiotalar alignment on functional outcomes after fixed-bearing TAR remains unclear, however, and no studies have compared fixed-bearing implants with respect to the anteroposterior (AP) position of the talar component. Questions/Purpose The purposes of this study were (1) to evaluate the effect of sagittal tibiotalar alignment on functional outcomes in fixed-bearing TAR and (2) to compare post-operative sagittal tibiotalar alignment in two types of fixed-bearing implants. Methods In a retrospective analysis of 71 primary TARs performed at a single center, we studied the INBONE (TM) II Total Ankle System and the Salto Talaris(R) Ankle. Radiographic measurements of the tibial axis-talus (T-T) ratio and the AP offset ratio were performed before and after surgery, respectively, and we evaluated Foot and Ankle Outcome Scores (FAOSs) and the 12-item Short Form Health Survey (SF-12) mental component summary (MCS) and physical component summary (PCS) scales pre-operatively and at 2 years after surgery. The Pearson correlation and independent-samples t test were used to evaluate differences in FAOSs, SF-12 MCS scores, and SF-12 PCS scores regarding post-operative sagittal alignment. Results Post-operative sagittal tibiotalar alignment was neutral in 39 ankles and anterior in 32 ankles. We observed no significant between-group differences in clinical outcome scores. Patients with a Salto Talaris Ankle prosthesis had a greater AP offset ratio (0.12) than patients with an INBONE II implant (0.05). However, the greater translation did not correlate with outcome scores. Conclusion At the 2-year follow-up, no correlation between the post-operative AP offset ratio and functional outcome scores was observed between the two fixed-bearing-implant groups. Further studies with longer follow-up are needed to determine whether the difference in sagittal alignment has an effect on functional outcomes in the long term.