The Fate of Subtalar Arthrodesis Performed with Total Talus Replacement
Authors: Massaglia Joseph , Allam Koushikreddy , McGarvey William , Greaser Michael C. , Beaver Richard , Gauvain Taggart 
Published: December 2024

Category: Hindfoot; Other Introduction/Purpose: Avascular necrosis (AVN) of the talus is a potentially debilitating condition. Total talus replacement (TTR) is a motion sparing surgical option for those patients with AVN of the talus. TTR is commonly performed as a spacer, but can be combined with resurfacing of the distal tibia, or arthrodesis of the adjacent subtalar and talonavicular joints. Subtalar arthrodesis is typically performed at the same time as TTR for those patients with associated subtalar joint arthritis. The purpose of this study is to evaluate the TTR implant-bone interface at the subtalar joint with and without concomitant arthrodesis utilizing advanced imaging techniques. We hypothesize that patients who underwent TTR with subtalar arthrodesis will have greater bone density at the implant-bone interface signifying bony ingrowth and successful fusion. Methods: This was a retrospective case series of patients who underwent primary TTR with or without concomitant procedures by one of four surgeons at a single, academic institution. Patients were excluded if they underwent explant of the TTR, failing to maintain the implant. Chart reviews were performed to obtain information on patient demographics, comorbidities, nicotine use, operative details, and post-surgical complications. Based on the procedures performed, patients were divided into three cohorts: 1) TTR alone, 2) TTR with total ankle replacement (TAR), and 3) TTR with subtalar arthrodesis (Figure). Patients at least 6 months from surgery were asked to obtain a dual energy CT scan of the operative ankle. Bone density, reported in Hounsfield units (Hu), was measured in 4 different quadrants (anterolateral, anteromedial, posterolateral, and posteromedial) of the posterior facet immediately inferior to the implant-bone interface (Figure). Student's t-test was performed to evaluate differences in bone densities among the cohorts. Results: There were 22 patients included. The three cohorts were comprised of 4 patients who underwent TTR alone, 8 patients who underwent TTR with TAR, and 10 patients who underwent TTR with subtalar arthrodesis. Overall, 10/22 patients obtained a postop CT scan. None of the patients who underwent TTR alone obtained a CT scan; therefore, this cohort was excluded from statistical analysis. One author measured bone densities. The mean total bone density in patients who underwent TTR with subtalar arthrodesis (538.8 Hu) was greater than that in patients who underwent TTR with TAR (393.1 Hu) (p=0.046). The mean bone density of the posterolateral and posteromedial quadrants combined was greater in those who underwent TTR with subtalar arthrodesis (522.4 Hu) versus TTR with TAR (299.5 Hu) (p=0.005). Conclusion: TTR is gaining popularity as a motion sparing alternative for surgical management of AVN of the talus. TTR can be performed as a spacer alone, with resurfacing of the distal tibia, or with arthrodesis of the adjacent subtalar and talonavicular joints. To our knowledge, this is the first study evaluating the TTR implant-bone interface at the subtalar joint with and without concomitant arthrodesis. The bone density of the posterior facet of the subtalar joint under the TTR implant was significantly greater in patients who underwent arthrodesis, signifying bony ingrowth onto the undersurface of the implant and successful fusion.