Computer assisted total knee arthroplasty using patient specific templates

Current techniques used for total knee arthroplasty (TKA) rely on conventional instrumentation (CI) systems that violate the intramedullary canals. The accuracy of these systems is questionable, and set up and assembly of their numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. The aim of this study was to prove a new concept of computer assisted preoperative planning to provide patient-specific templates (PST) that can replace conventional instruments. Computed tomography based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. Forty five TKA procedures were performed on 16 cadaveric and 29 plastic knees using the PST technique. Six out of 29 TKA procedures were included in a comparative trial against 6 procedures performed using CI systems. Computer assisted analysis of 6 random postoperative CT scans was performed to evaluate the accuracy of this technique. A reliability test was performed, in which five observers positioned the templates on a plastic knee model and a navigation system was used to measure alignment and the level of bone cutting for the planned tibial and femoral cuts. Each observer repeated the test 5 times. Errors in placement of the templates as well as intraobserver and interobserver variations were measured. The study showed that it was possible to perform all 45 TKA procedures without CI systems. There was no need for intramedullary perforation, tracking or registration. The mean time for bone cutting was 9 minutes (15 minutes for CI systems), when the surgeon had an assistant and 11 minutes (30 minutes for CI systems), when the surgeon was unassisted. Postoperative CT scans showed mean errors of 1.70 and 0.8 mm (maximum 2.30 and 1.2 mm) for alignment and bone resection respectively. The reliability test had a mean alignment error of 0.670(maximum 2.50). The mean error for bone resection was 0.32 mm (maximum 1 mm). The positioning of the templates was reliable, as there was no significant intraobserver and interobserver variation. This study proved the concept of patient-specific templating for TKA. It also showed a satisfactory level of accuracy and reliability of this technique. In conclusion, the PST technique has several advantages over conventional instrumentation and it is a simple alternative to navigation and robotic techniques for TKA. Further clinical validation is required before recommending this technique for new users.