Category: Ankle Arthritis Introduction/Purpose: It has been shown that total ankle replacement (TAR) is effective in reducing pain and maintaining function in posttraumatic ankle osteoarthritis (OA). Compared to ankle fusion, TAR restores hindfoot kinematics more physiological. However, the assumption that the maintenance of ankle motion has a protective effect on the subtalar joint is still a matter of debate. Only a scarce number of long-term studies exist to support this statement.The purpose of this study was (1) to evaluate to which extent the integrity of the subtalar joint can be preserved by treating patients with a TAR, (2) to determine the rate of subtalar fusion following TAR, and (3) to determine whether the need of subsequent subtalar fusion was predictable at time of TAR. Methods: A consecutive series of 1140 primary TAR (508 female, 632 male, median age 63.5 years), performed between May 2000 and December 2015, were prospectively documented. The indication for TAR was posttraumatic OA in 78%, primary and systemic OA in 10% each, and other secondary OA in 3% of the cases. 199 subtalar joints were either fused before (n=73) or during TAR surgery (n=126), leaving 941 subtalar joints available for analysis. Radiographs before implantation and at latest follow-up were classified using the Kellgren and Lawrence Grading Score (KLS). In case of a subtalar fusion, the radiograph prior to the fusion was classified. Results: After a median radiographic follow-up of 6.1 years, the KLS remained unchanged in 66% of all cases. While it was increased by one stage in 30%, it was increased by two stages in 3%; whereas, signs of OA decreased by one stage in 1%. Cases with an increase of two stages on the KLS had a longer follow-up compared to cases without increase (p=0.047).37 cases (3.9%) underwent a subtalar joint fusion, of which the indication was progressive OA in 19 cases (51%), instability in 10 cases (27%) and others in 8 cases (22%). Subtalar joints that required a fusion after TAR did not show higher preoperative KLS than the group which did not need a subtalar joint fusion. Conclusion: Apparently, TAR protects the subtalar joint from secondary degeneration, as found in 67% with no increase in KLS. Although 33% showed an increase in the KLS, only 2% required a subtalar fusion due to progressive OA. Overall, the rate of subtalar joint fusion after TAR was low and comparable to the rates reported in the literature. Subtalar joints requiring fusion after TAR did not show higher preoperative rates of OA. Therefore, the KLS classification of subtalar OA on conventional radiographs provides only limited information about the need for postoperative subtalar fusion, and thus need to be interpreted with caution.
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