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Assessment of acetabular cup wear with computed tomography and influence of surface roughness on wear of materials for hip prostheses
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
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 [en]
Hip prostheses, Computed Tomography, Surface roughness, UHMWPE, Wear, Coating, γ-irradiation, pin-on-disc, hip simulator
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4157ISBN: 91-7178-448-9 (print)OAI: oai:DiVA.org:kth-4157DiVA: diva2:10959
Note
QC 20101117Available from: 2006-10-24 Created: 2006-10-24 Last updated: 2010-11-17Bibliographically 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

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