Distance Mapping of Subtalar Joint after Total Ankle Arthroplasty - A Pilot Study

Category: Hindfoot; Ankle Arthritis Introduction/Purpose: Patients with ankle arthritis often present with concomitant subtalar joint deformity, as the subtalar joint may compensate for ankle malalignment. This compensation in the subtalar joint may manifest as joint space narrowing and sinus tarsi impingement. The objective of this study was to use 3D distance maps (DMs) from weightbearing computed tomography (WBCT) images to see if altering alignment of the tibiotalar joint with total ankle arthroplasty alters alignment of the subtalar joint. We hypothesized that, in patients with ankle arthritis, improving alignment of the tibiotalar joint from total ankle arthroplasty would increase the mean distances across the subtalar joint, indicative of improved alignment. Methods: A retrospective review of WBCT data of randomly selected patients who underwent total ankle arthroplasty between February 2022-July 2023 was performed as a pilot study. Using principal components analysis, the calcaneus was divided into 9 regions on the posterior facet, 4 regions in the sinus tarsi, 1 region in the middle facet, and 1 region in the anterior facet of the subtalar joint, as shown in Figure 1. 3D distance technique was used to objectively measure joint space across the subtalar joint. DMs were measured in millimeters, and DMs of the posterior facet and sinus tarsi were also averaged. Descriptive analysis was performed. Results: A total of 15 patients were included – 10 patients with preoperative and 5 patients with postoperative WBCT scans. The mean DMs in all regions increased postoperatively, showing a trend toward improved alignment. The greatest change in mean DM was seen in the middle facet articulation, from 1.78 mm preoperatively to 2.44mm postoperatively. The sinus tarsi was the second highest change, from a mean DM of 2.45 mm preoperatively to 2.80 postoperatively. Conclusion: This pilot study demonstrates that improved tibiotalar alignment through total ankle arthroplasty results in changes in the subtalar joint. Further study with adequate power is warranted to quantify the effect that improved tibiotalar alignment has on subtalar alignment.