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The outcome of TKA is dependent on surgical techniques 7,8,36 that require a high degree ofaccuracy and reproducibility. Component malalignment may lead to early failure and revisionsurgery. 15,17,33,44 As little as 3º of varus/valgus angulation can significantly change the pressuredistribution of the total load, and hence the pressure distribution in the medial and lateralcompartments of the tibial component. 44 The accuracy of plane radiographs in planning andevaluation is limited. 14,19,22,26 The accuracy of conventional instrumentation has beenquestioned by many authors. 3,4,16,20,40 Malalignment errors of > 3º may occur as a result ofusing intramedullary or extramedullary alignment guides. 33,40,41 The accuracy of usingconventional instrumentation for selecting the size of the prosthetic components is alsoquestionable. 13 Moreover, conventional instrumentation is based on average bone geometry,which may vary widely between patients. 29Several authors have reported the superior accuracy of computer assisted techniques, such asnavigation and robotics. 3,4,6,30,37,40 However, the broad clinical applications of such techniquesare limited by cost, complexity, set up time, and a long learning curve. 31 Recently, a newtechnique 10,11 was reported where computer assisted preoperative planning was used to providepatient-specific templates (cutting blocks) for TKA. Surgery can then be performed withoutconventional instruments or medullary guides. The most critical step of this technique is theintraoperative positioning of the femoral and tibial templates (cutting blocks) on the distalfemur and the proximal tibia. The templates are patient specific and their positioning is basedon surface matching with their respective bones. Malpositioning would most likely result inerrors in bone cutting. No reports have been published to test the reliability of positioning thetemplates, particularly by new users.The purpose of this study was to validate the accuracy and reliability of positioning the femoraland tibial templates of the patient specific templating technique for total knee arthroplasty.MATERIALS AND METHODSThis laboratory experiment was performed by 5 observers; a surgeon (MAH) who is familiarwith the PST technique, and 4 engineers who were experienced in using computer assistedsystems such as robotics and navigation, but not familiar with the templating technique. Thesenew users were initially sceptical about the accuracy of PST. The experiment was conductedusing only one plastic knee specimen (Foam Cortical Shell, Model # 1151). The planning forTKA was based on the PFC prosthesis (DePuy/Johnson and Johnson, Leeds, UK). The typicalsteps for the PST technique are illustrated in Figure 1), were applied to this knee model. Thisincludes CT scanning, reconstruction of 3-D images, sizing and alignment of prostheticcomponents, surgical simulation, template designing and finally production of patient specifictemplates using rapid prototyping technology. The knee specimen was held rigidly in a specificleg holder. The primary outcome measure was alignment and level of bone cutting, asdetermined by the position of the templates. A navigation system was used as a tool to measurealignment and level of bone cutting for reference cuts, while placing the femoral and then thetibial templates by each observer.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]