title: Wear, debris, and biologic activity of cross-linked polyethylene in the knee: benefits and potential concerns.
abstract: Cross-linked polyethylene currently is being introduced in knee prostheses. The wear rates, wear debris, and biologic reactivity of non cross-linked, moderately cross-linked, and highly cross-linked polyethylene have been compared in multidirectional wear tests and knee simulators. Multidirectional pin-on-plate wear studies of noncross-linked, moderately cross-linked (5 Mrad), and highly cross-linked (10 Mrad) polyethylene showed a 75% reduction in wear with the highly cross-linked material under kinematics found in the hip, but only a 33% reduction under wear in kinematics representative of the knee. In knee simulator studies, with the fixed-bearing press-fit, condylar Sigma cruciate-retaining knee under high kinematic input conditions, the wear of 5 Mrad moderately cross-linked polyethylene was 13 +/- 4 mm per 1 million cycles, which was lower (p < 0.05) than the wear of clinically used, gamma vacuum foil GUR 1020 polyethylene (23 +/- 6 mm/1 million cycles). For the low-contact stress mobile-bearing knee, the wear of moderately cross-linked polyethylene was 2 +/- 1 mm per 1 million cycles, which was lower (p < 0.05) than GVF GUR 1020 polyethylene (5 +/- 2 mm/1 million cycles). The wear debris isolated from the fixed-bearing knees showed the moderately cross-linked material had a larger percentage volume of particles smaller than 1 mum in size, compared with GVF GUR 1020 polyethylene. Direct cell culture studies of wear debris generated in sterile wear simulators using multidirectional motion showed a increase (p < 0.05) in tumor necrosis factor-alpha levels and reactivity for GUR 1050 cross-linked polyethylene debris compared with an equivalent volume of noncross-linked GUR 1050 polyethylene. The use of cross-linked polyethylene in the knee reduces the volumetric wear rate. However, the clinical significance of reduced fracture toughness, elevated wear in abrasive conditions, and the elevated tumor necrosis factor-alpha release from smaller more reactive particles warrant further investigation.
authors.affiliation: Institute for Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, UK. j.fisher@leeds.ac.uk
authors.forename: John
authors.initials: J
authors.lastname: Fisher
authors.forename: Hannah M J
authors.initials: HM
authors.lastname: McEwen
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Tipper
authors.forename: Alison L
authors.initials: AL
authors.lastname: Galvin
authors.forename: Jo
authors.initials: J
authors.lastname: Ingram
authors.forename: Amir
authors.initials: A
authors.lastname: Kamali
authors.forename: Martin H
authors.initials: MH
authors.lastname: Stone
authors.forename: Eileen
authors.initials: E
authors.lastname: Ingham
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D003432:Cross-Linking Reagents; D019544:Equipment Failure Analysis; D006801:Humans; D007720:Knee Prosthesis; D008422:Materials Testing; D011095:Polyethylenes / Q000737:chemistry* / Q000592:standards*; D011475:Prosthesis Failure; D013499:Surface Properties; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; D011095:Polyethylenes; D014409:Tumor Necrosis Factor-alpha; C111601:ultra-high molecular weight polyethylene