Hello, this is Dr. Christopher Gross, talking to you from the Medical University of South Carolina in Charleston, and today we're going to be discussing an evaluation of hindfoot alignment after a fixed and multiple bearing total ankle prosthesis. And I'd like to thank my co-authors in Italy right now, who helped me with this presentation as well as the data collection. We do not have any relevant financial disclosures to this presentation. End-stage ankle arthritis can involve malalignment of the ankle in both the coronal and sagittal planes, as up to 33 to 44% of patients who present for a total ankle replacement have greater than 10% of coronal plane deformity. And normalization of the sagittal-coronal alignment is key in improving survivorship of the tibial and talar component. We must re-establish the original center of rotation of the tibial-talar joint to prevent aseptic loosening, premature wear, and instability of the ankle. Specifically, we hypothesize that the coronal and sagittal alignment of the ankle and hindfoot complex would both improve from pre-op to post-operatively from a total ankle replacement, and more importantly, remain stable over time for either the mobile bearing or fixed bearing device. So the study included a data analysis of 126 total ankle patients. It's a retrospective study performed on two independent groups of patients undergoing two different systems of total ankle replacement. One is the trabecular metal ankle from Zimmer, which is a transfibular lateral approach, and it's fixed bearing. The other is the Integra anterior-based approach, and it's a mobile bearing system. So this included consecutive patients who underwent total ankle replacement with a mobile bearing prosthesis from May 2011 through April 2014 when the primary surgeon switched to the lateral-based approach. The minimum follow-up was 24 months. We looked at demographic data, and radiographic data was more importantly measured. We looked at the hindfoot alignment, the coronal and sagittal angles as well, and we'll go over those in a second. These were measured preoperatively at 6 months postoperatively, 12 months postoperatively, and 24 months postoperatively. So in the A picture here, we have the alpha angle, which is the angle between the tibial axis and tibial component in the coronal plane. In the B portion of this picture, we have the beta angle, which is the angle between the tibial axis and the tibial component in the sagittal plane. C represents the tibiotalar ratio, which is the ratio of the length of the posterior segment of the talus to the longitudinal talar length expressed as a percentage. So in A, we have the hindfoot alignment distance, which is the distance between the tibial axis and the calcaneal axis, and in B, we have the hindfoot alignment view angle, which is the angle between the tibial axis and the calcaneal axis. And again, we measured this preoperatively and 6, 12, and 24 months postoperatively, and we had some pretty interesting results. So in the lateral approach and fixed bearing trabecular metal angle, we had an increase in both the hindfoot alignment angle and distance at 24 months compared to preoperatively. In the anterior approach and mobile bearing device, we saw improvements in the hindfoot alignment angle, the distance, the tibiotalar ratio, and alpha and beta angles, and no post-vertical differences were seen over time. So the coronal and sagittal alignment remained constant in the short term as measured by the alpha and beta angles, and the sagittal alignment as measured by the TT ratio demonstrates a posterior shifting of the talus in the mobile bearing group, and that was demonstrated in a previous paper. But interestingly, over time, the lateral approach and fixed bearing angle has significant increase in both the hindfoot alignment angle and distance, which suggests perhaps a dynamism of the hindfoot. So in a fixed bearing implant, the hindfoot may end up compensating for the lack of movement between the implant and the polyethylene component, whereas in a mobile bearing implant, the hindfoot may not need to accommodate its position because there's some motion of the implant-poly interface. So we did have some pretty significant limitations. Again, we compared it thinking that it was a fixed versus mobile bearing total ankle. However, it may also be a function of an anterior approach versus a lateral approach. So no patient-reported outcomes were also measured, and there's no correlation with alignment. And we also have long-term outcomes and complications. Again, this is a short follow-up study at 24 months, and we do not know what happens at 5 or 10 years out. Perhaps it gets to a stable position at 24 months and stays relatively the same for the remaining years. So in conclusion, while the fixed and mobile bearing implants have maintained chronosaggeral alignment in the short term, in the fixed bearing ankle, there is an increase in the valgus positioning of the hindfoot, whereas in the mobile bearing implant, it maintained its hindfoot alignment over the course of the study. Thank you.

Dr. Christopher Gross

hindfoot alignment

total ankle prosthesis

fixed bearing

mobile bearing