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prosthesis component have been calculated in three steps. First, the surface models of all threecomponents as well as their position and orientation were extracted from the data files producedby the fluoroscopic kinematic analysis. Next, a set of 12 points were located on the post of eachtibial insert (fig2.). Finally, for each point, the distance to the femoral component wasquantified. For each step in this process, custom MATLAB ® (The MathWorks Inc., Natick,MA, USA) programs were used.For each of the 12 points on the post, a line was constructed through the point and parallel tothe outward-facing local surface normal of the post. The resulting set of lines was thenintersected with the femoral component model. Intersection points where lines ran “out of” thefemoral component, detected by a positive dot product of the femoral component surfacenormal with the post surface normal (used to define the line), were discarded.Finally, the distances between the 12 points on the post and the intersection points on each linewere calculated. For each line, the smallest distance was retained as a measure of the separationbetween insert and femoral component. Where a line did not intersect the femoral component,the corresponding separation distance was set to infinity.In each position, distances are measured at 6 pairs of points. Two indices of asymmetry areanalysed:1) The absolute difference between both measurements within a pair. Perfect symmetry ispresent when this absolute difference equals zero.2) The proportion of pairs where one of both measurements equals infinity. Indeed, thissituation refers to the presence of ‘extreme’ asymmetry.A linear model for repeated measures is used to analyse the absolute differences as a functionof the between-subjects factor condition (mobile bearing or fixed bearing) and the withinsubjectfactors position (4 levels) and pair (6 levels). More specifically, a direct likelihoodapproach is adopted using a compound symmetric covariance matrix.Results :There is a significant difference in absolute difference between the fixed and mobile bearingcondition (p=0.046). On average, the absolute difference is higher in the fixed bearingcondition, 1.75 (95%CI: 1.39;2.11) vs 1.20 (95%CI:0.78;1.62). (fig2.).Conclusion:The separation distances between post and cam show less asymmetry in the Rotating platformTKA,meaning less or no contact between the post and cam surfaces which are possible sourcesof wear.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]