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A new approach for assessment of wear in metal-backed acetabular cups using computed tomography: a phantom study with retrievals
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
Department of Radiology, New York University School of Medicine, New York.
Department of Hand Surgery, Södersjukhuset, Stockholm.
Department of Radiology, Karolinska University Hospital Solna, Stockholm.
Show others and affiliations
2008 (English)In: Acta Orthopaedica, ISSN 1745-3674, E-ISSN 1745-3682, Vol. 79, no 2, 218-224 p.Article in journal (Refereed) Published
Abstract [en]

Background and purpose Polyethylene wear is an important cause of aseptic loosening in hip arthroplasty. Detection of significant wear usually happens late on, since available diagnostic techniques are either not sensitive enough or too complicated and expensive for routine use. This study evaluates a new approach for measurement of linear wear of metal-backed acetabular cups using CT as the intended clinically feasible method.

Material and methods 8 retrieved uncemented metal-backed acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral head into the cup was measured in the CT volumes using dedicated software. Landmark points were placed on the CT images of cup and head, and also on a reference plane in order to calculate the wear vector magnitude and angle to one of the axes. A coordinate-measuring machine was used to test the accuracy of the proposed CT method. For this purpose, the head diameters were also measured by both methods.

Results Accuracy of the CT method for linear wear measurements was 0.6 nm and wear vector angle was 27 degrees. No systematic difference was found between CT scans.

Interpretation This study on explanted acetabular cups shows that CT is capable of reliable measurement of linear wear in acetabular cups at a clinically relevant level of accuracy. It was also possible to use the method for assessment of direction of wear.

Place, publisher, year, edition, pages
2008. Vol. 79, no 2, 218-224 p.
Keyword [en]
bone cement; polyethylene; acetabuloplasty; article; computer assisted tomography; computer program; diagnostic accuracy; diagnostic approach route; endoprosthesis loosening; ex vivo study; femur head; functional assessment; human; image analysis; metal backed acetabular cup; orthopedic equipment; phantom; reliability; acetabulum; computer simulation; hip arthroplasty; hip prosthesis; prosthesis; prosthesis failure; reproducibility; sensitivity and specificity; Acetabulum; Arthroplasty, Replacement, Hip; Computer Simulation; Hip Prosthesis; Humans; Polyethylene; Prosthesis Design; Prosthesis Failure; Reproducibility of Results; Sensitivity and Specificity; Tomography, X-Ray Computed
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-14270DOI: 10.1080/17453670710015003ISI: 000256188900009Scopus ID: 2-s2.0-44249083239OAI: oai:DiVA.org:kth-14270DiVA: diva2:331987
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Computed Tomography of Acetabular Cup Wear and Effect of Surface Roughness on Wear and Oxidation of UHMWPE Hip Prostheses
Open this publication in new window or tab >>Computed Tomography of Acetabular Cup Wear and Effect of Surface Roughness on Wear and Oxidation of UHMWPE Hip Prostheses
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Aseptic loosening is the most common complication in total hip replacement (5- 10% at 10 years follow up). The magnitude of the problem is illustrated by the fact that about one million hip prostheses are implanted worldwide each year. Many parameters affect the longevity of the implant where aseptic loosening caused by wear debris and raised intraarticular pressure are the most common reasons for revisions. To monitor wear in vivo and also to predict the longevity of new materials for hip prostheses are therefore important issues.

The main aims of this thesis are to validate a new non-invasive method for assessment of in vivo wear of acetabular cups in 3 dimensions using computed tomography (CT), and to investigate the influence of counterface surface roughness and γ-irradiation sterilisation in wear testing of ultra high molecular weight polyethylene (UHMWPE) for hip prostheses. A new low friction coating, Micronite was also investigated using a multidirectional pin-on-disk machine.

The 3D-CT method was found to be easy to use and showed an accuracy and repeatability at a clinical relevant level for assessment of acetabular cup wear. The method should lend itself well to semi-automation. The Micronite coating showed potential for use in artificial joints due to its low friction and intact surface after wear testing compared to a stainless steel disk that showed wear tracks. However, the surface roughness of the stainless steel disks was increased by the coating. Therefore further investigations are needed. In the hip simulator study, it was found that a rougher counter surface increased the wear 2-fold. It was also found that sterilisation by γ-irradiation (in nitrogen) increased both fluid absorption and wear of the UHMWPE cups compared to the non-sterilised cups. A study with infrared spectroscopy and derivatisation techniques using NO, HCl, and SO2 showed that the increased wear and absorption were due to oxidation induced by γ-irradiation. The oxidation was found to be inhomogeneous with higher oxidation near the surfaces. The contribution of the roughened heads to the increased oxidation was only minor. Crystallinity changes upon wear testing of the sterilised cups were detected with Raman spectroscopy and differential scanning calorimetry. However, the changes were small and the influence on wear properties is therefore questionable.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 70 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:69
Keyword
Hip prostheses, Computed Tomography, Surface roughness, UHMWPE, Wear, Coating, Gamma-irradiation, pin-on-disc, hip simulator
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-4522 (URN)978-91-7178-786-6 (ISBN)
Public defence
2007-11-23, F3, F, Lindstedtsväg 26, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100716Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2010-11-19Bibliographically approved
2. Assessment of acetabular cup wear with computed tomography and influence of surface roughness on wear of materials for hip prostheses
Open this publication in new window or tab >>Assessment of acetabular cup wear with computed tomography and influence of surface roughness on wear of materials for hip prostheses
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Over one million hip prostheses are implanted in patients worldwide each year and the need is increasing as the patient group of younger and more active patients is increasing. Many parameters affect the longevity of the implant, where aseptic loosening caused by wear debris is the most common reason for revision. To be able to monitor wear in vivo and also to predict the longevity of new materials for hip prostheses are therefore important issues in this interdisciplinary research area. This thesis comprise a true non-invasive 3D method for determination of acetabular cup wear using Computed Tomography (CT) intended for clinical routine use in order to plan for a revision. It also comprises investigations of the influence of surface roughness and sterilization method in wear testing of materials for hip prostheses. Mainly wear of ultra high molecular weight polyethylene (UHMWPE) was investigated since it is the most common soft bearing in hip prostheses. The 3D-CT method was found to be easy to use and showed an accuracy and repeatability at a clinical relevant level for acetabular cup wear. It should lend itself well to semi-automation. The influence of surface roughness was investigated with both a multidirectional pin-on-disk machine and with a hip simulator. A new low friction coating, Micronite, was also evaluated with the pin-on-disk machine. This coating showed potential for use in artificial joints, but further investigations are needed. In the hip simulator test, it was found that not only a rougher counter surface increased wear, but also sterilization by γ-irradiation increased wear of UHMWPE cups.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 59 p.
Keyword
Hip prostheses, Computed Tomography, Surface roughness, UHMWPE, Wear, Coating, γ-irradiation, pin-on-disc, hip simulator
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4157 (URN)91-7178-448-9 (ISBN)
Note
QC 20101117Available from: 2006-10-24 Created: 2006-10-24 Last updated: 2010-11-17Bibliographically approved

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