title: Accuracy of methods for calculating volumetric wear from coordinate measuring machine data of retrieved metal-on-metal hip joint implants.
abstract: This study compared the accuracy and sensitivity of several numerical methods employing spherical or plane triangles for calculating the volumetric wear of retrieved metal-on-metal hip joint implants from coordinate measuring machine measurements. Five methods, one using spherical triangles and four using plane triangles to represent the bearing and the best-fit surfaces, were assessed and compared on a perfect hemisphere model and a hemi-ellipsoid model (i.e. unworn models), computer-generated wear models and wear-tested femoral balls, with point spacings of 0.5, 1, 2 and 3 mm. The results showed that the algorithm (Method 1) employing spherical triangles to represent the bearing surface and to scale the mesh to the best-fit surfaces produced adequate accuracy for the wear volume with point spacings of 0.5, 1, 2 and 3 mm. The algorithms (Methods 2-4) using plane triangles to represent the bearing surface and to scale the mesh to the best-fit surface also produced accuracies that were comparable to that with spherical triangles. In contrast, if the bearing surface was represented with a mesh of plane triangles and the best-fit surface was taken as a smooth surface without discretization (Method 5), the algorithm produced much lower accuracy with a point spacing of 0.5 mm than Methods 1-4 with a point spacing of 3 mm.
authors: J. Vernon Luck Orthopaedic Research Center, UCLA & Orthopaedic Institute for Children Department of Orthopaedic Surgery, Los Angeles, CA, USA.
authors: Zhen
authors: Z
authors: Lu
authors: Harry A
authors: HA
authors: McKellop
mesh_terms: D000465:Algorithms; D001698:Biomedical Engineering; D003198:Computer Simulation; D019544:Equipment Failure Analysis / Q000379:methods*; D006622:Hip Prosthesis; D006801:Humans; D008954:Models, Biological; D011474:Prosthesis Design; D011475:Prosthesis Failure
keywords: Hip prosthesis; coordinate measuring machine measurement; explant; metal on metal; volumetric wear