Accuracy and Precision Evaluation of Image-Based Computer Assisted Surgical System for Total Ankle Arthroplasty

Category: Ankle; Ankle Arthritis Introduction/Purpose: Computer Assisted Surgical (CAS) systems have been used successfully in joint arthroplasty to improve the accuracy of resections. CAS usage leads to reduced outliers and improved targeted alignment of orthopedic implants. Total ankle arthroplasty (TAA) is a surgical treatment for end-stage ankle osteoarthritis, and the latest generation of TAA is associated with favorable clinical outcomes as a modern alternative to ankle arthrodesis. Alignment of the implants during TAA is challenging because of limited surgical exposure and reliance on fluoroscopic alignment. Therefore, a TAA application for CAS system was developed using CT-based alignment alongside required fluoroscopy with the intent of facilitating the procedure and improving accuracy of bone resections. The objective of the study was to evaluate the accuracy and precision of the TAA CAS system. Methods: TAA was performed by a board-certified, fellowship-trained orthopedic surgeon on twelve artificial ankle joint specimens (PN1132-3, Pacific Research) using a CAS system (ExactechGPS, Blue-Ortho) featuring a dedicated ankle application. Scans of each of the twelve specimens were performed before TAA using a structured light industrial scanner. During the simulated surgery, active trackers were fixed to each specimen’s tibia and talus to allow registration of the anatomical landmarks. Bone resections were planned using template software to choose appropriate implant position and size relative to the bony anatomy. Resections on the talus included a flat cut with three degrees of freedom (e.g. varus, slope, and cut height), whereas tibial resections included distal and medial cuts with five degrees of freedom (e.g. varus, slope, axial rotation, medial offset and cut height). Finally, the resected bones were scanned and overlaid with the initial model for assessment of the error relative to the original plan. Results: For all eight angular and positional cut parameters across both the tibia and the talus, the mean signed overall intraobserver error was less than 2mm and 2° relative to the plan, and the 95% confidence interval was less than 2mm and 2°. Both angular and positional overall errors on the tibia were less than 1mm and 1° relative to the plan according to the mean and 95% confidence intervals. One deviation to surgical technique was identified with video tracking: The talar fixator was not tightened on specimen five which leading to tracker movement during talus resection. Therefore, the data from specimen five was removed from the analysis since the operative technique for the TAA navigation system was not followed. Conclusion: The results of the study show that the bone resections using the evaluated TAA application for CAS were associated with satisfactory accuracy level compared to conventional mechanical instruments and PSI blocks. Future work should consider additional surgeon users, cadaver specimens with ankle arthritis and/or deformity, and comparison to patient-specific instrumentation (PSI) and traditional conventional techniques. The results point to resections with errors of less than 2mm and 2° and therefore the system can offer both accurate and precise intraoperative surgical resection measurements during computer-assisted TAA. Total Ankle Arthroplasty with Enabling Technology Example tibial and talar plans and subsequent execution (top), Differences between planned resection and final measured resection, described as overall error (bottom)