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  • 51. von Schewelov, T.
    et al.
    Sanzen, L.
    Borlin, Niclas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Markusson, P.
    Onsten, I.
    Accuracy of radiographic and radiostereometric wear measurement of different hip prostheses - An experimental study2004In: Acta Orthopaedica Scandinavica, Vol. 75, no 6, p. 691-700Article in journal (Refereed)
    Abstract [en]

    Background In vivo measurement of wear in the ball and socket articulation of total hip arthroplasties is of interest in the evaluation of both existing and new implants. Controversy reigns regarding the accuracy of different radiological measurement techniques and in particular how accuracy has been assessed. Material and methods We assessed the accuracy of 2 radiostereometric (RSA) techniques for wear measurement and 3 standard radiographic techniques, namely Imagika (image analyzing software), Imagika corrected for head center displacement, and the Charnley Duo method. 5 custom-made adjustable phantoms with different prosthetic components were used. Results In 20 measurements of all 5 phantoms at 3 levels of simulated wear (0.2 mm, 1.0 mm and 1.5 mm), the mean measurement error of the digital RSA examinations was 0.010 mm (accuracy 0.42). The corresponding error values for the three radiographic techniques were 0.19 (accuracy 1.3) for Charnley Duo, 0.13 (accuracy 1.3) for Imagika corrected, and 1.021 (accuracy 2.99) for Imagika. Measurement error decreased from 0.011 mm with ordinary RSA to 0.004 with RSA digital measurement. Head size, direction of wear in relation to the cup or type of prosthetic component did not influence the measurement error. The results of Charnley Duo and Imagika corrected were similar but the latter had an inexplicable systematic error in measuring one of the phantoms. Imagika had the worst results due to its inability to compensate for the out-of-head center effect. Alumina heads were difficult to analyze with all methods. Interpretation By using the ISO standard for assessing accuracy, RSA can be expected to measure wear with an accuracy of about 0.4 mm irrespective of prosthetic component studied or direction of wear, whereas the best technique, in our study, based on standard radiographs can be accurate to about 1.3 mm.

  • 52.
    Zhou, Zong-ke
    et al.
    University of Western Australia.
    Li, Ming G.
    University of Western Australia.
    Börlin, Niclas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wood, David J.
    University of Western Australia.
    Nivbrant, Bo
    University of Western Australia.
    No Increased Migration in Cups with Ceramic-on-Ceramic Bearing: An RSA Study2006In: Clinical Orthopaedics and Related Research, ISSN 0009-921X, E-ISSN 1528-1132, no 448, p. 39-45Article in journal (Refereed)
    Abstract [en]

    Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migrationwas followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07–0.40 mm vs. 0.05–0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31–0.92° vs. 0.57–1.40°). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender. Levels of Evidence: Therapeutic Level I. See the Guidelinesfor Authors for a complete description of levels of evidence.

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