Tibiotalocalcaneal Arthrodesis Utilizing a Titanium Intramedullary Nail With an Internal Pseudoelastic Nitinol Compression Element: A Retrospective Case Series of 33 Patients.

Abstract

Nitinol has been shown to generate durable compression under loading via pseudoelastic shape memory. The purpose of this study was to evaluate the effectiveness of a hindfoot arthrodesis nail with an internal pseudoelastic nitinol compression element. Patients who had undergone tibiotalocalcaneal arthrodesis from 2013 to 2016 were identified at 2 tertiary referral centers (12-week follow-up minimum). Patients managed with a tibiotalocalcaneal nail with an internal nitinol compression element were identified for review. Sagittal computed tomographic scan reformats were reviewed to calculate a percentage of joint surface bony union. Intraoperative and postoperative radiographs were compared to calculate postoperative screw position change generated by the nitinol element, a surrogate for postoperative unloading of compressive forces. Thirty-three patients were included in analysis and 81% of patients had successful union of both tibiotalar and subtalar joints. Overall, 90% of all arthrodesis surfaces united. The union rate of arthrodesis surfaces among patients without Charcot osteoarthropathy was 94%. A history of Charcot was identified as a risk factor for subtalar nonunion (p = .04) and was associated with less complete computed tomography-based tibiotalar union: 94% versus 71% (p < .01). The posterior-to-anterior screw translated an average of 3.9 mm proximally relative to the rigid portion of the nail from intraoperative to initial postoperative radiographs (p < .0001). High rates of computed tomography-confirmed union were demonstrated in the face of challenging clinical scenarios. Shortening of the pseudoelastic nitinol element occurs early in the postoperative period, indicating continued unloading of the nitinol compression element through the arthrodesis sites after initial implantation.