Evaluation of Error Sources for an Image-Based Computer Assisted Surgical System for Total Ankle Arthroplasty
Authors: Rueff Matthew C. , Tupper Zach , Hamilton Matthew , Chinimilli Prudhvi , Gulbransen Scott , Prouvost Laureline , Haupt Edward T. , Angibaud Laurent , Ing. Dipl 
Published: December 2024

Category: Ankle; Ankle Arthritis Introduction/Purpose: Computer Assisted Surgical (CAS) systems have been used successfully in joint arthroplasty to improve the accuracy of bony resections. CAS usage leads to reduced outliers and improved targeted alignment of orthopedic implants. The whole procedure is a suite of numerous surgical steps, and even using CAS systems, each of these steps may be associated with error such as mispositioning of the cutting block, play between the sawblade and the cutting slot due to the length and width of slot, or saw bending and skiving of the blade during the resection. However, the incidence of these errors may not be all equal. For this reason, the error sources of the individual surgical steps were evaluated for a novel image-based CAS system for total ankle arthroplasty (TAA). 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 individually virtually planned and performed by the surgeon using template software to choose appropriate implant position and size relative to the bony anatomy. Finally, the resected bones were scanned and overlaid with the initial model for assessment of the error relative to the original plan. The abstract figure shows the flow of the procedure from plan to final cut as well as the outlay of the error measurements during slot positioning cut execution and cut verification. Results: Opportunities for error were identified during positioning, execution, and verification. Error from each step was also summated for an overall error value. Mean and 95 % confidence intervals for positioning, execution and verification errors were less than 2mm and 2° . Average absolute errors for the tibia were: 0.30°/.26mm for positioning, 0.87°/.53mm for execution, 0.89°/.56mm for verification, and 0.74°/.59mm overall. Average absolute errors for the talus were: 0.82°/.52mm for positioning, 0.41°/.51mm for execution, 0.64°/.62mm for verification, and 1.13°/.67mm overall. One deviation to surgical technique was identified with video tracking: The talar fixator was not tightened on specimen five per the operative technique, therefore, the data from specimen five was removed from the analysis. Conclusion: TAA performed with a CAS system resulted in overall error less than 2mm and less than 2° on all specimens. Design elements of the CAS system likely contribute to the low observed error. The surgeon receives visual confirmation of the plan and resection confirmation throughout the procedure which allows for real-time adjustments. The plan and the resection are confirmed during the procedure, and the cut itself can be refined. As a result, there is potential to remove the need for other checks for positioning guides which could reduce the burden on the user and reduce radiation exposure of the patient.