Accuracy of CT-Derived Patient-Specific Instrumentation for Total Ankle Arthroplasty: The Impact of the Severity of Preoperative Varus Ankle Deformity

Background Significant preoperative varus tibiotalar deformity was once believed to be a contraindication for total ankle arthroplasty (TAA). Our primary goal was to evaluate the influence of increasing preoperative varus tibiotalar deformity on the accuracy of final implant positioning using computed tomography (CT)-derived patient-specific guides for TAA. Methods Thirty-two patients with varus ankle arthritis underwent TAA using CT-derived patient-specific guides. Patients were subcategorized into varying degrees of deformity based on preoperative tibiotalar angles (0°-5° neutral, 6°-10° mild, 11°-15° moderate, and >15° severe). Postoperative weightbearing radiographs were used to measure coronal plane alignment of the tibial implant relative to the target axis determined by the preoperative CT template. Average follow-up at the time of data collection was 36.8 months. Results Average preoperative varus deformity was 6.06° (range: 0.66°-16.3°). Postoperatively, 96.9% (30/31) of patients demonstrated neutral implant alignment. Average postoperative tibial implant deviation was 1.54° (range: 0.17°-5.7°). Average coronal deviation relative to the target axis was 1.61° for the neutral group, 1.78° for the mild group, 0.94° for the moderate group, and 1.41° for the severe group (P = .256). Preoperative plans predicted 100% of tibial and talar implant sizes correctly within 1 size of actual implant size. Conclusion. Our study supports the claim that neutral postoperative TAA alignment can be obtained using CT-derived patient-specific instrumentation (PSI). Furthermore, final implant alignment accuracy with PSI does not appear to be impacted by worsening preoperative varus deformity. All but one patient (96.9%) achieved neutral postoperative alignment relative to the predicted target axis. Level of Evidence: Level IV, Clinical Case Series

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

Background: Total ankle arthroplasty (TAA) is a popular and viable option for end-stage ankle arthritis. Posttraumatic arthritis is the most common etiology of ankle arthritis, which creates the additional challenge of osseus deformity. Accuracy and reproducibility in placing the implant on the mechanical axis has been shown to be paramount in all joint arthroplasty including total ankle replacement. Patient-specific preoperative navigation is a relatively new technology for TAA, and up until this past year has been based off of nonweightbearing (NWBCT) or simulated weightbearing computed tomography (WBCT). Our institution has created a protocol to use WBCT in the preoperative patient-specific navigation for TAA using the Prophecy system. The purpose of our study was to compare the accuracy and reproducibility of implant alignment and size using WBCT vs prior studies using NWBCT for the Prophecy reports. Methods: All patients from July 2019 through October 2020 who underwent TAA were evaluated. Inclusion criteria consisted of primary TAA using patient-specific preoperative navigation who had postoperative radiographs in the 4-6-week time frame. Prophecy predictions and measurements were then compared to actual implant placement and size. Results: Ten patients met our inclusion criteria of WBCT Prophecy preoperative planning using 2 different implant systems. Preoperative deformities in this cohort were small. The average postoperative coronal alignment was 0.84 degrees, range 0.19 to 2.4 degrees. Average postoperative sagittal plane deformity was 1.9 degrees, range 0.33 to 5.05 degrees. Tibial component size was properly predicted in all patients, talar component in 9 of 10. Conclusion: This initial report supports accuracy and reproducibility in preoperative patient-specific navigation when using WBCT for TAA with these implants. All TAAs were within the intended target of less than 5 degrees varus or valgus. Level of Evidence: Level III, retrospective comparative analysis.