title: Release of zirconia nanoparticles at the metal stem-bone cement interface in implant loosening of total hip replacements.
abstract: In a previous failure analysis performed on femoral components of cemented total hip replacements, we determined high volumes of abraded bone cement. Here, we describe the topography of the polished surface of polymethyl methacrylate (PMMA) bone cement containing zirconia radiopacifier, analyzed by scanning electron microscopy and vertical scanning interferometry. Zirconia spikes protruded about 300nm from the PMMA matrix, with pits of former crystal deposition measuring about 400nm in depth. We deduced that the characteristically mulberry-shaped agglomerates of zirconia crystals are ground and truncated into flat surfaces and finally torn out of the PMMA matrix. Additionally, evaluation of in vitro PMMA-on-PMMA articulation confirmed that crystal agglomerations of zirconia were exposed to grain pullout, fatigue, and abrasion. In great quantities, micron-sized PMMA wear and zirconia nanoparticles accumulate in the cement-bone interface and capsular tissues, thereby contributing to osteolysis. Dissemination of nanoparticles to distant lymph nodes and organs of storage has been reported. As sufficient information is lacking, foreign body reactions to accumulated nanosized zirconia in places of long-term storage should be investigated.
  
  
  CONCLUSIONS
  The production of wear particles of PMMA bone cement in the interface to joint replacement devices, presents a local challenge. The presence of zirconia particles results in frustrated digestion attempts by macrophages, liberation of inflammatory mediators, and necrosis leading to aseptic inflammation and osteolyses. Attempts to minimize wear of articulating joints reduced the attention to the deterioration of cement cuffs. We therefore investigated polished surfaces of retrieved cuffs to demonstrate their morphology and to measure surface roughness. Industrially admixed agglomerates of the radiopacifier are abraded to micron and nano-meter sized particles. The dissemination of zirconia particles in the reticulo-endothelial system to storage organs is a possible burden. Research to replace the actual contrast media by non-particulate material deserves more attention.
authors.affiliation: University Hospital Göttingen, Department of Orthopedics/Biomaterials Research Laboratory, Robert-Koch-Str. 40, 37075 Göttingen, Germany. Electronic address: a.schunck@hotmail.de.
authors.forename: Antje
authors.initials: A
authors.lastname: Schunck
authors.affiliation: University of Göttingen, Department of Geochemistry, Goldschmidtstr. 1, 37077 Göttingen, Germany. Electronic address: akronz@gwdg.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kronz
authors.affiliation: University of Bremen, MARUM/Department of Geosciences, Klagenfurter Str., 28359 Bremen, Germany. Electronic address: cornelius.fischer@uni-bremen.de.
authors.forename: Cornelius
authors.initials: C
authors.lastname: Fischer
authors.affiliation: University Hospital Göttingen, Department of Orthopedics/Biomaterials Research Laboratory, Robert-Koch-Str. 40, 37075 Göttingen, Germany. Electronic address: gh-buchh@med.uni-goettingen.de.
authors.forename: Gottfried Hans
authors.initials: GH
authors.lastname: Buchhorn
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001843:Bone Cements / Q000737:chemistry*; D003287:Contrast Media / Q000737:chemistry; D003460:Crystallization; D005549:Foreign-Body Reaction; D006622:Hip Prosthesis; D006801:Humans; D007368:Interferometry / Q000379:methods; D008670:Metals / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D053758:Nanoparticles / Q000737:chemistry; D010014:Osteolysis / Q000473:pathology; D010316:Particle Size; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011208:Powders / Q000737:chemistry; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013234:Stem Cells / Q000166:cytology*; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D001843:Bone Cements; D003287:Contrast Media; D008670:Metals; D011208:Powders; D019904:Polymethyl Methacrylate; D015040:Zirconium; C028541:zirconium oxide
keywords: Abrasion; Bone cement; Contrast medium; Polishing; Surface roughness; Zirconia