Accuracy of Weightbearing CT vs Non-Weightbearing CT Scans for Patient-Specific Instrumentation in Total Ankle Arthroplasty

Abstract

Category: Ankle Introduction/Purpose: Total ankle arthroplasty (TAA) is a popular and viable option for end stage ankle arthritis. Accuracy and reproducibility in placing the implant on the mechanical axis has been shown to be paramount in total ankle replacement. Patient specific pre-operative navigation up until this past year has been based off of non-weightbearing computerized tomography (CT). Our institution has created a protocol to use weightbearing CT in the pre-operative patient specific navigation for TAA using the Prophecy TM system. The purpose of our study was to compare the accuracy and reproducibility of implant alignment and size using WBCT versus prior studies using NWBCT for the Prophecy reports. Methods: Patients who underwent TAA using our WBCT protocol for their Prophecy scans had their charts reviewed to see if they met the proper inclusion criteria. Inclusion criteria was a primary TAA with proper follow-up to have first post-operative weightbearing radiographs. The first post-operative weightbearing radiographs were used to measure alignment of the axis of the implant in frontal and sagittal planes comparative to the tibial axis. These results were then compared to the pre-operative prophecy scans to determine reproducibility. The size of the implants components were also recorded for each patient and compared to the pre-operative predicted implant sizes from the patient specific reports. Our results were also compared to previous studies on reproducibility of patient specific navigation when using non-weightbearing CT. Results: Ten patients met our inclusion criteria of WBCT Prophecy TM preoperative planning. 100% of the TAA were within the intended target of less than 50 varus or valgus. The average post-operative coronal alignment was an average of 0.844 degrees. Average sagittal plane deformity was 1.88 degrees post-operative. Tibial component size was properly predicted 100% of the time and talar component in all but one patient. Conclusion: This data supports superior accuracy and reproducibility in pre-operative patient specific navigation when utilizing WBCT for TAA vs published controls with non-weightbearing CT.