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Assessing wear of the acetabular cup using computed tomography: an ex vivo study
Karolinska Institutet, Department of Clinical Science, Intervention and Technology, Division of Radiology.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Karolinska Institutet, Department of Clinical Science, Intervention and Technology, Division of Radiology.
Karolinska Institutet, Dept. Orthoped..
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2005 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 46, no 8, 852-857 p.Article in journal (Refereed) Published
Abstract [en]

Purpose: To validate a clinically useful method for measuring acetabular cup wear using computed tomography (CT). Material and Methods: Eight uncemented acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral component head into the cup and the thickness of the remaining polyethylene liner were measured in the CT volumes using dedicated software. Two independent examiners twice assessed each volume. The CT measurements were compared to direct measurements using a coordinate measuring device and micrometer measurements. Results: Accuracy of wear measurements expressed as penetration depth was +/- 0.6 and +/- 1.0 mm for the two examiners, respectively, with no significant differences between examiners, trials, and CT scans. Accuracy of measurements of remaining polyethylene was +/- 1.3 and +/- 1.0 mm, respectively, for the two examiners. Systematic differences between examiners were found, but no significant differences between trials and CT scans. These differences were due to different interpretations of metal artifacts in the volumes. Conclusion: The proposed CT method for evaluating wear as head penetration depth allows for reliable wear detection at a clinically relevant level. Measurements of remaining polyethylene on CT volumes are not as reliable as wear measurements owing to metal artifacts.

Place, publisher, year, edition, pages
London, UK: Informa Healthcare, 2005. Vol. 46, no 8, 852-857 p.
Keyword [en]
Adults, Computer applications-3D, Hip, CT, Hip, skeletal, Hip, spiral, Technical aspects
National Category
Orthopedics Radiology, Nuclear Medicine and Medical Imaging
Research subject
SRA - ICT
Identifiers
URN: urn:nbn:se:kth:diva-6282DOI: 10.1080/02841850500271074ISI: 000234076700011PubMedID: 16392610OAI: oai:DiVA.org:kth-6282DiVA: diva2:10956
Note
QC 20100729Available from: 2006-10-24 Created: 2006-10-24 Last updated: 2017-12-14Bibliographically approved
In thesis
1. 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
2. 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

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Maguire Jr., Gerald Q.

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