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It was planned to collect 175 observations; 25 sets of observations (5 observers X 5 times) foreach of these 7 measurements: tibial coronal alignment, tibial sagittal alignment, level of tibialcutting, femoral coronal alignment, femoral sagittal alignment, femoral rotation and level offemoral cutting. However, it was only possible to collect 163 observations, representingcomplete (25) sets of observations for all measured parameters, except for femoral rotation,which had only 13 sets of observations from 3 observers. Tibial rotation was not measured inthis experiment, because it is difficult to accurately quantify the angle of rotation, based on illdefinedlandmarks, such as the medial third of tibial tuberosity.These recorded measurements were compared to the recommended figures for alignment,rotation and level of bone cutting that have also been followed during preoperative planning ofPST. Femoral and tibial coronal cut were zeroº to mechanical axis, femoral sagittal was in 3ºflexion, tibial sagittal was 5º in posterior slope, level of bone cutting was 10 mm from thehealthy component in both femur and tibia. These recommended figures were used as controlmeasurements (ground truth) to determine the deviation of recorded measurement in degreesand mm. The difference between the recorded and the control measurements was considered asan error. When the recorded measurement was equal to the control measurement, the error wasconsidered zero. These errors were analysed to calculate the mean, standard deviation andmaximum (outliers). To assess the reliability of the PST technique, both qualitative andquantative data were used to measure interobserver and intraobserver agreement. Kappastatistics was used to analyse qualitative data and determine whether the recorded measurementwas within 3º or 3 mm (agreement) or more than 3º or 3 mm (no agreement). The use of 3º as alimit was based on clinical studies that showed 3º to be the maximum error that could beclinically accepted 15,17,33 .Quantative analysis was performed using Fredman's repeated measure non- parametric analysisof variance (ANOVA) and Kruskal Wallis analysis of variance (ANOVA). The recordedmeasurements from all observers (would be 175) were compared to a control measurement ofzeroº or zero mm. This control represents the ideal measurement (i.e. no error). Interobserverand Intraobserver concordance was tested using Kundall coefficient of concordance. Correlationbetween the results of the study observers was done using Pearson moment correlation test (r).A probability value (p value) less than 0.05 was considered significant. All statisticalcalculations were done using computer programs Microsoft Excel version 7 (MicrosoftCorporation, NY, USA) and SPSS (Statistical Package for the Social Science; SPSS Inc.,Chicago, IL, USA) statistical program.RESULTSThe positioning of the templates and the alignment of the subsequent femoral and tibial bonecuts had a mean error of 0.67º. The maximum error was 2.5º, which was recorded for theposterior sloping of one of the tibial cuts for one observer. The mean error in positioning thetemplates for the level of bone cutting was 0.32 mm (maximum 1 mm). The mean, standarddeviation and maximum errors were calculated separately for each alignment measurements(tibial coronal, tibial post slope, femoral coronal, and femoral sagittal) and for each bone cuttingmeasurements (femoral distal cut and tibial cut) (Table 1).Table 1: The reliability test: Errors & interobserver agreementfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]