_STP_1445-2004.pdf

STP 1445 Crosslinked and Thermally Treated Ultra-High Molecular Weight Polyethylene for Joint Replacements Steven M.Kurtz,Ray A.Gsell,and John Martell,editors ASTM Stock Number:STPt445 INTERNATIONAL ASTM International 100 Barr Harbor Drive PO Box C700 West Conshohocken,PA 19428-2959 Printed in the U.S.A.Library of Congress Cataloging-in-Publication Data Crosslinked and thermally treated ultra-high molecular weight polyethylene for joint replacements/Steven M.Kurtz,Ray A.Gsell,and John Martell,editors.p.cm.-(STP;1445)ASTM Stock number:STP 1445.Includes bibliographical references and index.ISBN 0-8031-3474-6 1.Orthopedic implants-Materials-Congress.2.Polyethylene-Therapeutic use-Congresses.3.Artificial joints-Congresses.4.Biomedical materials-Congresses.5.Implants,Artificial-Congresses.I.Kurtz,Steven M.,1968-II.Gsell,Ray A.,1944-II1.Martell,John,1957-IV.ASTM special technical publication;1445.RD755.5.C768 2004 617.580592-dc22 200359 Copyright?9 2004 ASTM Intemational,West Conshohocken,PA.All rights reserved.This material may not be reproduced or copied,in whole or in part,in any printed,mechanical,electronic,film,or other distribution and storage media,without the written consent of the publisher.Photocopy Rights Authorization to photocopy items for internal,personal,or educational classroom use,or the internal,personal,or educational classroom use of specific clients,is granted by ASTM International(ASTM)provided that the appropriate fee is paid to the Copyright Clearance Center,222 Rosewood Drive,Danvers,MA 01923;Tel:978-750-8400;online:http:/ Review Policy Each paper published in this volume was evaluated by two peer reviewers and at least one editor.The authors addressed all of the reviewers comments to the satisfaction of both the technical editor(s)and the ASTM International Committee on Publications.To make technical information available as quickly as possible,the peer-reviewed papers in this publication were prepared camera-ready as submitted by the authors.The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s),but also the work of the peer reviewers.In keeping with long-standing publication practices,ASTM International maintains the anonymity of the peer reviewers.The ASTM International Committee on Publications acknowledges with appreciation their dedication and contribution of time and effort on behalf of ASTM Intemational.Printed in Saline,MI Foreword The Symposium on Crosslinked and Thermally Treated Ultra-High Molecular Weight Polyethylene(UHMWPE)for Joint Replacements was held in Miami Beach,Florida on 5-6 November,2002.ASTM International Committee F04 on Medical and Surgical Materials and Devices served as the sponsor.Symposium co-chairmen and co-editors of this publication were Steven Kurtz,Exponent,Inc.,Philadelphia,PA;Ray Gsell,Zimmer,Inc.,Warsaw,IN;and John Martell,University of Chicago,Chicago,IL.iii Contents FOREWORD QUANTIFYING CLINICAL RESPONSE Generalized Size and Shape Description of UHMWPE Wear Debris-A Comparison of Cross-Linked,Enhanced Fused,and Standard Polyethylene Particles-C.M.SPRECHER,E.SCHNEIDER,AND M.A.WIMMER iii SHORT-TERM RETRIEVALS Microscopy of Highly Cross-Linked UHMWPE Wear Surfaces-w(and w 0),w and l are w=P/7r-(P/Tr)-(4 A/70)(4)l=(P-w Tr)/2+w(5)Finally,the Equivalent Shape Ratio(ESR)is defined by ESR=w/l(6)Similarly to other shape factors,the ESR ranges from 0(needle shape)to 1(perfectly round).The three-dimensional model of the particle,which is based on the assumption that its height equals its width,is shown in Figure ld.It has a cigar-like shape with half-spherical caps connected by a cylinder with the diameter w.Its volume and surface are VeSR=w e 7r/4(l-w)+w 3 rr/6(7)SESR=w 7r lo+w 2 7r(8)The Equivalent Circle Diameter(ECD),a measure of particle size,is defined ac-cording to ASTM F1877-98 ECD=(4 A/70/(9)Scott et al.18 developed a particle volume model based on ECD,which will be used for comparison.In his model,particle volume and surface are defined by Vc=ECD r/6(10)SeCD=ECD 2 rr(11)If the wear volume Wv is known,the total number of particles can be calculated ac-cording to NESR-Wv/VESR(12)NECO=Wv/Veco(13)with VESR and VECD as the mean particle volume determined by the ESR and ECD-approach,respectively.Once the particle number is known,the free surface of all parti-SPRECHER ET AL.ON UHMWPE WEAR DEBRIS 7 cles can be determined SEss-T=SESR NES8 SECD-T=SECD NECD where again the subscripts ESR and ECD refer to the approach taken.(15)(16)Materials and Methods Three different types of polyethylene were used:(1)Ref-PE:ram extruded GUR 4150 UHMWPE(so-called HSS reference polyethylene),(2)Cross-PE:electron beam irra-diated,melt annealed,highly crosslinked UHMWPE(commercially available under the rk|tradema DURASUL,),and(3)Hex-PE:via the meta-stable hexagonal phase proc-essed UHMWPE.According to Rastogi et al.20,the latter produces a completely fused polyethylene without grain boundaries.From each