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Chapter 5150UHMWPE wear analysisLinear wear, expressed in mm/year, is used in orthopedic surgery to determine the lifecycle of an implant. It does not however determine the total amount of UHWMPE volume that is lost. This is of importance as, along with particle size and shape, the wear volume is a significant determinant for the occurrence of periprosthetic osteolysis (8). Dumbleton et al. (27) concluded that the risk of osteolysis occuring is rare as long as the total amount of linear wear remains under 0.1 mm/year. Similar findings were reported by Oparaugo et al. (28), who found that the risk of osteolysis was rare if the total amount of wear was limited to 80 mm³ per year. Both the coated and non-coated TMJR systems exhibited linear wear equivalent to less than 0.1 mm and volumetric wear equivalent of far less than 80 mm³ per year of human functioning (Tables 1-3). In comparison to the average linear wear of 0.08 to 0.2mm per year and 48-155mm³ volumetric wear per year in total hip implants and 0.05 to 0.23mm linear wear per year for a total knee implant, our results can be considered excellent (29). Important to notice is that, while upon inspection, there was a qualitative difference observed between the fossa articulating with either a coated or non-coated condyle, no statistically significant difference was observed between these samples. A Shapiro-Wilk test confirmed the Gaussian distribution of both the linear and volumetric wear data, supporting the use of a t-test, yet post hoc power calculations indicated that this study would have needed 15 sheep per group to achieve adequate power to detect a significant difference between these two groups of fossa. While the sample size of this study was chosen to minimize the number of animals subjected to the invasive procedures required for this study it is highly likely that the non-statistical difference that was found was due to the small group sizes. Secondly, a displacement of the fossa was found in several ewes. While a 3-month post-operative CT scan revealed a good positioning of the fossa in ewe #7998, during the post-mortem CT scan and dissection a significant caudodorsal displacement of the fossa was seen. This was also reflected by the wear pattern that was found through 3D scanning Nikolas de Meurechy NW.indd 150 05-06-2024 10:14