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Chapter 5140through an indexable PH10M rotary head (Renishaw Benelux B.V., Breda, Netherlands). This LLS system was also used to assess the volumetric wear of the UHMWPE fossa part. To this end, Focus Inspection version 9.4 (Nikon Metrology NV) was used to create an STL file of the point cloud generated through scanning the fossa with the LLS. Prior to scanning the fossa, all of the 21 kinematic error sources (the axes’ translational, rotational and squareness error components) of the MC16 CMM were calibrated, to identify and compensate for any geometrical errors. This calibration was performed by a manufacturer technician, following a standardized method, reaching a micron level of precision for each individual axis. Furthermore, as to eliminate any environmental changes, all measurements were performed in a climate and humidity controlled room with air pressure monitoring. Lastly, prior to performing the CMM, qualification of the combined system of CMM and LLS was performed. This was done by use of a reference sphere, which was measured from all orientations used within the scanning sequence. The margin of error of this entire measurement technique is estimated to range from 0.01 mm to 0.1 mm. This generated STL was then overlapped with the STL of the design of the fossa component by means of a ‘best fit’ iterative closest-point algorithm using GOM Inspect (GOM GmbH). This method does not allow for closed loop information, as would be the case when reference points were marked before implantation ensuring a 100% fit. Instead up to hundreds of matching points are calculated by the program’s algorithm, in order to provide a reliable and reproduceable overlap. For cooperative surfaces, this technique results in the same accuracy and error margin as provided by the scanner. The ‘explanted-STL’ was then subtracted from the ‘design-STL’ to quantify the volume lost due to wear. Next, the articulating areas of the UHWMPE were isolated and evaluated rather than the entire UHMWPE fossa part. This was done to prevent overestimation of the wear volume, due to the scalpel reduction that was performed during implantation. Wear volume was calculated using VGSTUDIO MAX Version 3.3.2 (Volume Graphics GmbH, Heidelberg, Germany). Nikolas de Meurechy NW.indd 140 05-06-2024 10:14