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Effect of head surface roughness and sterilization method on wear of UHMWPE acetabular cups: preliminary hip joint simulator results
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Laboratorio di Tecnologia Medica, Istititi Ortppedci Rizzoli, Bologna.
Laboratorio di Tecnologia Medica, Istititi Ortppedci Rizzoli, Bologna.
Laboratorio di Tecnologia Medica, Istititi Ortppedci Rizzoli, Bologna.
2006 (English)In: Proceedings of 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Vol. 3, 2006Conference paper, Published paper (Refereed)
Abstract [en]

More than one million hip joint replacements are performed each year in the world. However, the implants do not last forever due to material limitations, even though the operation is successful. The most common material combination used today is a CoCr head articulating against an UHMWPE (Ultra High Molecular Weight Polyethylene) acetabular cup. Several investigations have shown that the metal head is roughened inside the body and thus accelerating wear of the polymer cup. The sterilization method is also known to have effect on the wear properties. In vitro wear tests are however usually performed with as new implants. This investigation aimed at study the impact of head surface roughness on wear of both sterilized and non-sterilized acetabular cups. A total of nine acetabular cup and head pairs were wear tested in a hip joint simulator for 2Million cycles (Mc) with bovine calf serum as lubricant. Wear was determined by weighing of all cups. The heads were of CoCrMo and the average initial head surface roughness was 15nm (R-a), measured with a white light interference profilometer. The roughening was produced with a SiC paper producing circular multidirectional wear tracks to a surface roughness of about 400nm (R-a). The cups were of UHMWPE and the sterilized cups were 3Mrad gamma-radiated in nitrogen. The surface roughness after wear test was unchanged for the roughened heads, while the initially smooth heads were slightly roughened. Preliminary results show that the rough heads increase the wear of the cups 2-fold. The gamma-irradiation affected both wear- and soak rate.

Place, publisher, year, edition, pages
2006.
Keyword [en]
Hip prostheses; Hip simulator; Roughened femoral heads; Surface roughness; UHMWPE; Wear
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-14266ISI: 000249558200108Scopus ID: 2-s2.0-33845808362ISBN: 978-079183779-5 (print)OAI: oai:DiVA.org:kth-14266DiVA: diva2:331978
Conference
8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2010-11-19Bibliographically 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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