title: A new method to make 2-D wear measurements less sensitive to projection differences of cemented THAs.
abstract: Wear curves from individual patients often show unexplained irregular wear curves or impossible values (negative wear). We postulated errors of two-dimensional wear measurements are mainly the result of radiographic projection differences. We tested a new method that makes two-dimensional wear measurements less sensitive for radiograph projection differences of cemented THAs. The measurement errors that occur when radiographically projecting a three-dimensional THA were modeled. Based on the model, we developed a method to reduce the errors, thus approximating three-dimensional linear wear values, which are less sensitive for projection differences. An error analysis was performed by virtually simulating 144 wear measurements under varying conditions with and without application of the correction: the mean absolute error was reduced from 1.8 mm (range, 0-4.51 mm) to 0.11 mm (range, 0-0.27 mm). For clinical validation, radiostereometric analysis was performed on 47 patients to determine the true wear at 1, 2, and 5 years. Subsequently, wear was measured on conventional radiographs with and without the correction: the overall occurrence of errors greater than 0.2 mm was reduced from 35% to 15%. Wear measurements are less sensitive to differences in two-dimensional projection of the THA when using the correction method.
authors.affiliation: Department of Orthopaedic Surgery, University Medical Center Groningen, Hanzeplein 1, Groningen, The Netherlands. b.the@orth.umcg.nl
authors.forename: Bertram
authors.initials: B
authors.lastname: The
authors.forename: Gunnar
authors.initials: G
authors.lastname: Flivik
authors.forename: Ron L
authors.initials: RL
authors.lastname: Diercks
authors.forename: Nico
authors.initials: N
authors.lastname: Verdonschot
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D001843:Bone Cements; D003198:Computer Simulation; D005260:Female; D005500:Follow-Up Studies; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D008954:Models, Biological; D011095:Polyethylenes; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D001843:Bone Cements; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene