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transformation associated with the increased roughness of Y-TZP would influence skewnessand thus the wear potential of the heads.Materials and Methods: Y-TZP (n = 18) and Mg-PSZ (n = 17) femoral heads were retrievedfrom revision THA. Heads were cleaned and scanned by optical profilometry (magnification =10x) at three locations per specimen. After subtracting the curvature of the heads, roughnessstatistics (Sa, Ssk) were calculated and averaged for each specimen and then correlated to agein vivo, with p < 0.05 for significance.Results and Discussion: As expected, the roughness Sa of Y-TZP heads increasedexponentially with age in vivo (p < 0.001, r 2 = 0.766), while Mg-PSZ heads did not roughenwith age (r 2 = 0.007; Figure 1). The skewness data of Y-TZP retrievals were noisy with a weakpositive correlation to age in vivo (r 2 = 0.016), but were consistently positive (average Ssk ofall Y-TZP specimens = 0.770), indicating its roughness was caused by positive features.Positive features such as raised edges have been reported to adversely affect wear rates in thelab, and combined with the increased average roughness suggests an accelerated wear potentialwith age in vivo. In contrast, the skewness data for the Mg-PSZ retrievals were negative(average Ssk = -1.00), indicating its roughness was caused by small negative features, with norelationship to age in vivo (r 2 < 0.001). A surface best described by negative features wouldtend to entrap lubricant for better wear characteristics. Recent hip wear simulator tests reportedMg-PSZ femoral heads to exhibit significantly less wear compared with CoCr femoral heads.These in vitro data suggest that the low average roughness and negative polarity of Mg-PSZfemoral heads should provide superior wear characteristics in vivo.Conclusions: This study illustrated that Mg-PSZ zirconia ceramics remained stable and did notroughen or develop raised edges in vivo, in contrast to Y-TZP ceramic femoral heads. Webelieve that clinical studies with Mg-PSZ femoral heads would illustrate a significant reductionin wear of cross-linked UHMWPE liners. Future work will expand this study with additionalspecimens, and attempt to reduce the noise of the skewness data to more clearly discern anytrends between Ssk and age in vivo.FiguresSaturday, October 9, 2010, 11:15-11:50Session B19: Hip MechanicsThe Effect on Radiographic Osseointegration of Geometric Variations inAcetabular Component Design*James Waddell - University of Toronto - Toronto, CanadaMax Edwards - University of Toronto - Toronto, CamadaMichael Lutz - University of Toronto - Toronto, CanadaOliver Keast-Butler - University of Toronto - Toronto, CanadaBenjamin Escott - University of Toronto - Toronto, CanadaEmil Schemitsch - University of Toronto - Toronto, Canadafile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]