Migration of Wear Debris of Polyethylene Depends on Bone Microarchitecture He ´ le ` ne Libouban, 1 Philippe Massin, 1,2 Christine Gaudin, 1 Philippe Mercier, 1,3 Michel F. Basle ´, 1 Daniel Chappard 1 1 INSERM, U922, LHEA, Faculte ´ de Me ´ decine, 49045 Angers Cedex, France 2 Service d’Orthope ´ die, CHU d’Angers, 49933 Angers Cedex, France 3 Laboratoire d’Anatomie, Faculte ´ de Me ´ decine, 49045 Angers Cedex, France Received 21 July 2008; revised 31 October 2008; accepted 12 December 2008 Published online 20 February 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31341 Abstract: The mechanism of hip arthroplasties loosening is related to the migration of wear debris throughout the implant environment. In vivo, polyethylene particles (PE) were shown to infiltrate the bone implant interface and the medullary spaces of the cancellous bone. Our test hypothesis was that polyethylene particle migration is correlated to bone porosity. Bone samples with a high or low trabecular volume and microarchitecture were harvested in 20 calves and 20 human cadavers. They were extensively washed to remove marrow cells. Bone cylinders were filled with a light-curing monomer having the same viscosity as bone marrow. PE particles (7 and 33 lm) were deposited at the surface of the polymer. The bone cylinders were agitated during 7 days on an orbital shaker and the gel was left to polymerize at day light. X-ray microtomography was performed to characterize bone volume and microarchitecture. Cylinders were sectioned and observed under polarized light. The migration distance and rate were determined. Migration of PE particles strongly depended on trabecular bone volume and microarchitecture. We found a linear relationship (r 5 0.61) between speed migration and bone volume and an exponential relationship between speed migration and bone architecture. The present in vitro model confirmed our hypothesis about the key role of bone microarchitecture in the migration of large PE wear particles. This is an explanation for the development of inflammatory reaction at distance from a prosthesis although our study did not include submicron particles. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 730–737, 2009 Keywords: polyethylene; wear debris; microCT; bone architecture; photopolymerization INTRODUCTION Wear debris are generated in great quantity in the joint cavity of patients with a hip prosthesis. 1 When polyethyl- ene (PE) acetabular liners are involved, the PE wear debris have variable forms and sizes according to the mechanism of wear formation (abrasion, friction...). 2 Because PE par- ticles cannot be degraded by any enzymatic system, they induce an inflammatory reaction in the receiver site, lead- ing to the release of osteolytic substances, 3,4 bone loss and finally implant loosening. 5–7 The bioactive range for PE particles has been reported to be 0.1 to 10 lm 8 with submi- cron particles being the most reactive. 9 Submicron particles are typically generated under both adhesive and abrasive process. 10,11 In the fibrous membranes that are removed at revision of failed arthroplasties, birefringent wear debris are observed either in the cytoplasm of macrophages (when they are less than 5–10 lm in length) or surrounded by giant cells when their size exceeds the phagocytic capacity of a single cell. 12–19 Some particles can be several tens of microns to 1–2 millimeters in length. Small and large par- ticles can reach the lymphatic system and accumulate in lymph nodes, spleen or liver. 20,21 However, the migration route of PE particles is not fully understood from the prosthetic site. In particular, it is not clear how, in some cases, particles induce an osteolytic reaction at locations remote of the joint space, although no mechanical phenomenon has previously loosened the bone implant interface. In fact, localized osteolysis has been observed in well-fixed implants far from the joint. 22–24 According to the concept of the effective joint space, the fixation interfaces may be considered as extensions of the joint space into which articular fluids, propelled by high Correspondence to: Daniel Chappard (e-mail: daniel.chappard@univ-angers.fr) Contract grant sponsors: ‘‘Pays de la Loire’’–Axe Biomate ´riaux Bioregos and INSERM ' 2009 Wiley Periodicals, Inc. 730