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Computed Tomography of Acetabular Cup Wear and Effect of Surface Roughness on Wear and Oxidation of UHMWPE Hip Prostheses
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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 [en]
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: urn:nbn:se:kth:diva-4522ISBN: 978-91-7178-786-6 (print)OAI: oai:DiVA.org:kth-4522DiVA: diva2:12664
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
List of papers
1. Tribological investigation of coatings for artificial joints
Open this publication in new window or tab >>Tribological investigation of coatings for artificial joints
2008 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, 958-966 p.Article in journal (Refereed) Published
Abstract [en]

A modified pin-on-disc machine was used for the tribological investigation of ultrahigh molecular weight polyethylene (UHMWPE) sliding on stainless steel or stainless steel coated with diamond-like carbon, titanium nitride or Micronite. Micronite is a new type of coating applied by a physical vapour deposition technique combined with a very low friction coating material giving improved tribological properties. The tribological parameters used were chosen to mimic the conditions prevailing in the human body. The wear debris and the counter-surfaces were analysed. The surface analysis showed that the coating changed the roughness of the counter-surfaces. The diamond-like carbon and Micronite coatings had a much higher surface roughness than the titanium nitride coating. The results indicated that the enhanced tribological behaviour of the Micronite/UHMWPE sliding pair might be used as a material combination in artificial joints. Further studies are however required in order to support this.

Keyword
Artificial joints; Coating; Surface engineering; Tribology; UHMWPE; Wear debris; Coatings; Debris; Friction; Molecular weight; Polyethylenes; Stainless steel; Titanium nitride; Wear resistance;
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-6281 (URN)10.1016/j.wear.2007.07.003 (DOI)000254766900008 ()2-s2.0-40049105508 (Scopus ID)
Note
QC 20100729. Uppdaterad från Submitted till Published 20100729.Available from: 2006-10-24 Created: 2006-10-24 Last updated: 2017-12-14Bibliographically approved
2. Assessing wear of the acetabular cup using computed tomography: an ex vivo study
Open this publication in new window or tab >>Assessing wear of the acetabular cup using computed tomography: an ex vivo study
Show others...
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
Keyword
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:nbn:se:kth:diva-6282 (URN)10.1080/02841850500271074 (DOI)000234076700011 ()16392610 (PubMedID)
Note
QC 20100729Available from: 2006-10-24 Created: 2006-10-24 Last updated: 2017-12-14Bibliographically approved
3. Effect of head surface roughness and sterilization method on wear of UHMWPE acetabular cups: preliminary hip joint simulator results
Open this publication in new window or tab >>Effect of head surface roughness and sterilization method on wear of UHMWPE acetabular cups: preliminary hip joint simulator results
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.

Keyword
Hip prostheses; Hip simulator; Roughened femoral heads; Surface roughness; UHMWPE; Wear
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-14266 (URN)000249558200108 ()2-s2.0-33845808362 (Scopus ID)978-079183779-5 (ISBN)
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
4. A new approach for assessment of wear in metal-backed acetabular cups using computed tomography: a phantom study with retrievals
Open this publication in new window or tab >>A new approach for assessment of wear in metal-backed acetabular cups using computed tomography: a phantom study with retrievals
Show others...
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.

Keyword
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:nbn:se:kth:diva-14270 (URN)10.1080/17453670710015003 (DOI)000256188900009 ()2-s2.0-44249083239 (Scopus ID)
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
5. Effect of head surface roughness and sterilization on wear of UHMWPE acetabular cups
Open this publication in new window or tab >>Effect of head surface roughness and sterilization on wear of UHMWPE acetabular cups
Show others...
2009 (English)In: Journal of Biomedical Materials Research, ISSN 0021-9304, E-ISSN 1097-4636, Vol. 90, no 4, 1032-1042 p.Article in journal (Refereed) Published
Abstract [en]

The impact of femoral head surface roughness on wear of gamma-irradiation sterilized (3 MRad in nitrogen, crosslinked) and nonsterilized (not crosshnked) UHMWPE acetabular cups has been evaluated. Gravimetric wear testing was performed in a hip joint simulator for 2 x 10(6) cycles. CoCrMo heads were used with different surface roughness (R-a = 15 nm and R-a = 400 rim). The surface roughness after wear test was unchanged for the roughened heads, whereas the initially smooth heads showed a few scratches. The roughened heads increased the wear of the acetabular cups 2-fold. The gamma-irradiated cups tested against rough heads underwent the highest wear. The absorption of water was highest for the gamma-irradiated cups (0.0204% compared to 0.0031% after 85 days). Raman spectroscopy showed small but significant crystallinity changes in the wear zone, where the gamma-irradiated cups with the most extensive abrasion increased in crystallinity, whereas the nonsterilized cups underwent a crystallinity decrease.

Keyword
Crystallinity; Gamma-irradiation; Raman spectroscopy; Roughness; UHMWPE acetabular cups
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-14275 (URN)10.1002/jbm.a.32161 (DOI)000268940100009 ()2-s2.0-68249152033 (Scopus ID)
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
6. Effect of γ-irradiation sterilization in nitrogen on oxidation of hip-simulated UHMWPE cups
Open this publication in new window or tab >>Effect of γ-irradiation sterilization in nitrogen on oxidation of hip-simulated UHMWPE cups
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A hip simulator study with roughened heads revealed unexpected high wear rates for the γ-irradiated UHMWPE cups (sterilization performed in nitrogen) and also higher fluid absorbtion than that of the non-sterilized cups. Infrared spectroscopy and high-resolution scanning of samples stained with HCl and SO2 showed that the outer parts of cross-sections of the sterilized cups were oxidized after the wear testing. The non-sterilized cups showed essentially no polymer oxidation with only minor surface oxidation due to roughened head. The higher wear rate and the more extensive fluid absorption of the sterilized cups is thus attributed to oxidation of the polymer; the latter presumably being facilitated by the presence of long-living radicals generated during γ-irradiation sterilization.

Keyword
UHMWPE; gamma irriadiation; sterilization; oxidation
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-14278 (URN)
Note
QC 20100729Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2010-07-29Bibliographically approved

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  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
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  • Other locale
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Output format
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