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Biological response to wear debris after total hip arthroplasty using different bearing materials.
A clinical prospective and randomised study


Marianne Nygaard  


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Accepted by: The Faculty of Health Sciences Copenhagen
Defended on: June 24, 2005
Official opponents: Professor, Dr. Med. Mogens Spang-Thomsen , Professor, PhD, Lars Nordsletten , PhD Ole Rahbek
Tutors: Professor, Dr. Med, PhD Kjeld Søballe , Arne Borgwardt

Published in the PhD Database: November 9, 2005


English abstract
SUMMARY
World wide, approximately 1 million hip arthroplasties are implanted every year. The cumulated rate of revision is annually about 1 % (approximately 10% of these prostheses will be revised after 10 years) and is most often a result of implant loosening. The loosening is often aseptic and the condition is a well-known limit for a long-term survival of the implant. Wear particles derived from the articulating materials of the implant are an accepted cause of aseptic loosening.
The accumulated wear particles attract white blood cells, especially monocytes/macrophages that can phagocytize the non-digestible wear particles. In some occasions, the macrophages with intracellular non-digestible wear particles accumulate into foreign body granulomas or giant cells. The giant cells can be found in revision tissue of failed implants and have common morphological and biological features with osteoclasts, cells that are specialised in bone resorption.
The number of macrophages is positively correlated to the number of polyethylene particles in the periprosthetic tissue and the degree of bone resorption is correlated to the degree of granulomatous inflammation.
This correlation between wear particles and implant loosening has contributed to the wish for more wear resistant alternatives to the conventional polyethylene-metal bearings. These bearings are most often ceramic-ceramic (alumina) or metal-metal (CoCr) or polyethylene-ceramic (zirconia).
A reduced wear rate or a different biological response of these bearing materials may influence the formerly described cellular response and thus the bone resorption around the implant. The goal is to reduce the rate of revision in the future.


The aim of the present phd thesis was to investigate if there was a difference in the biological response between three groups with identical hip implants except from the bearing materials: polyethylene-ceramics (zirconia), metal-metal (CoCr), or ceramic-ceramic (alumina).
A total two hundred and twenty five patients were included. Prior to the operation, the patients were randomised into one of the three groups.

After the operation, the periprosthetic bone mineral density was measured by DEXA (bone mineral density). The procedure was repeated after one year, and the change in bone mineral density was calculated and compared within the groups.
After one year, biopsies were taken from the pseudosynovial membrane in 37 volunteers (of the 225 patients) and examined as follows.
1. Biopsies were evaluated in which the volume fraction of macrophages, granulomas, and endothelial cells was quantified by light microscopy.
2. Biopsies were evaluated by the transmission electron microscope to describe the ultrastructural morphology of the cells and the localisation of the particles in pseudosynovial membrane.
3. Biopsies were used for quantification of cytokines in the pseudosynovial membrane by flow cytometry and ELISA.

The results showed no significant differences in mean change of BMD, volume fraction of macrophages, granulomas, and endothelial cells or the ultrastructural localisation of wear particles between the three groups with the three different bearing combinations. The cytokine study is not yet finished.



Danish abstract
RESUMÉ PÅ DANSK
På verdensplan indsættes årligt omkring 1 million primære hoftealloplastikker. Den kumulerede udskiftningsrate for disse proteser er omkring 1 % årligt (omkring 10 % af disse proteser vil blive udskiftet i løbet af 10 år). Årsagen er oftest en aseptisk betinget og tilstanden er en velkendt begrænsning til hofteprotesers langtidsoverlevelse. Slidpartikler fra protesens egne slidflader er en accepteret årsag til den aseptiske proteseløsning.
De akkumulerede slidpartikler tildrager hvide blodlegemer, specielt monocyt/makrofager, der fagocyterer (optager) disse ikke nedbrydelige partikler. I nogle tilfælde danner makrofager med intracellulære slidpartikler granulomer (en hob af makrofager) eller kæmpeceller. Kæmpeceller kan findes i vævet omkring løse proteser og har morfologiske og biologiske egenskaber der minder om osteoklaster, celler specialiseret i knoglenedbrydning. Antallet af makrofager er positivt korreleret til antallet af polyethylenpartikler i vævet omkring protesen og knoglenedbrydningen er korreleret til graden af den granulomatøse inflammation.
Denne sammenhæng mellem slidpartikler og proteseløsning har medført et ønske om stærkere slidfladematerialer som alternativ til den konventionelle polyethylen ¿ metal kombination. Disse slidmaterialer er oftest keramik-keramik (alumina), metal-metal (CoCr) eller polyethylen-keramik (alumina eller zirconia).
En reduceret slidrate eller varierende biologisk respons for disse materialer kan have betydning for den tidligere beskrevne cellulære respons og hermed knoglenedbrydningen omkring protesen. Målet er at reducerer antallet af revisioner i fremtiden.


Formålet med phd studiet var at undersøge, hvorvidt der efter et år var forskel på vævsreaktionen hos tre grupper af patienter med identiske hofteimplantater undtaget slidfladematerialerne: polyethylen ¿ keramik (zirconia), metal - metal (CoCr) eller keramik ¿ keramik (alumina).
I alt tohundrede og femogtyve 225 patienter indgik i studiet. Forud for operationen blev patienterne randomiseret til en af de tre gruppe.
Efter operationen blev knoglemineraltætheden omkring protesen målt ved DEXA (knogletæthedsmåling). Proceduren blev gentaget efter et år og ændringer i knoglemineraltætheden blev beregnet og sammenlignet for de respektive grupper.
Efter et år blev der udtaget vævsprøver fra pseudosynovial membranen på 37 frivillige (af de 225 patienter) og undersøgt for følgende:
1. Biopsierne blev evalueret og volumenfraktion af makrofager, granulomer og endotelceller blev kvantiteret i lysmikroskop.
2. Biopsierne blev evalueret ved transmission elektron mikroskop og den ultrastrukturelle morfologi og partikellokalisation i pseudosynovial membranen blev beskrevet.
3. Biopsier blev benyttet til kvatitering af cytokiner i pseudosynovial membranen ved flow cytometri og ELISA.

Resultaterne ikke nogen signifikant forskel på knogletætheden omkring protesen, volumenfraktion af makrofager, granulomer og endotelceller eller den ultrastrukturelle morfologi for de tre grupper med forskellige slidflader. Cytokinstudiet er ikke færdigt.