High stress conditions do not increase wear of thin highly crosslinked UHMWPE.
Introduction of highly crosslinked polyethylene has increased interest in large femoral heads, because thin acetabular liners can be used while maintaining low wear rates and larger heads decrease the incidence of instability. However, crosslinking and subsequent thermal treatments can cause decreased mechanical properties that might obviate the reduced wear under extreme conditions. To examine whether increased contact pressures would adversely affect wear in thin liners, we tested thin and thick highly crosslinked liners (3.8 mm thickness/44-mm head and 7.9 mm thickness/36-mm head, respectively) to 5 million cycles on a hip simulator under near impingement conditions. Conventional polyethylene liners (7.9 mm thickness/36-mm head) served as controls. Large femoral heads with highly crosslinked polyethylene liners as thin as 3.8 mm in thickness do not wear at a higher rate than a thicker liner of the same material, even when subjected to large contact pressures such as occur under near-impingement conditions. Crosslinked polyethylene may allow for liners that are thinner than has been traditionally accepted. This conclusion, however, is based solely on wear test results with idealized cup position, no intentional edge loading, no head subluxation, and no artificial aging. Continued monitoring will be necessary to elucidate the clinical efficacy of these devices.
Kelly
Natalie H
NH
Department of Biomechanics, Hospital for Special Surgery, 535 E 70th Street, New York, NY 10021, USA. kellyn@hss.edu
Rajadhyaksha
Amar D
AD
Wright
Timothy M
TM
Maher
Suzanne A
SA
Westrich
Geoffrey H
GH
D002858:Chromium Alloys / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry* / Q000528:radiation effects; D019544:Equipment Failure Analysis; D020342:Finite Element Analysis; D005720:Gamma Rays; D006622:Hip Prosthesis; D008422:Materials Testing; D011095:Polyethylenes / Q000737:chemistry* / Q000528:radiation effects; D011312:Pressure; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D013499:Surface Properties; D044366:Transition Temperature
D002858:Chromium Alloys; D003432:Cross-Linking Reagents; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene