title: Polyethylene wear of mobile-bearing unicompartmental knee replacement at 20 years.
abstract: The Oxford unicompartmental knee replacement (UKR) was designed to minimise wear utilising a fully-congruent, mobile, polyethylene bearing. Wear of polyethylene is a significant cause of revision surgery in UKR in the first decade, and the incidence increases in the second decade. Our study used model-based radiostereometric analysis to measure the combined wear of the upper and lower bearing surfaces in 13 medial-compartment Oxford UKRs at a mean of 20.9 years (17.2 to 25.9) post-operatively. The mean linear penetration of the polyethylene bearing was 1.04 mm (0.307 to 2.15), with a mean annual wear rate of 0.045 mm/year (0.016 to 0.099). The annual wear rate of the phase-2 bearings (mean 0.022 mm/year) was significantly less (p = 0.01) than that of phase-1 bearings (mean 0.07 mm/year). The linear wear rate of the Oxford UKR remains very low into the third decade. We believe that phase-2 bearings had lower wear rates than phase-1 implants because of the improved bearing design and surgical technique which decreased the incidence of impingement. We conclude that the design of the Oxford UKR gives low rates of wear in the long term.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, Biomedical Research Unit, Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7LD, UK.
authors.forename: B J L
authors.initials: BJ
authors.lastname: Kendrick
authors.forename: D J
authors.initials: DJ
authors.lastname: Simpson
authors.forename: B L
authors.initials: BL
authors.lastname: Kaptein
authors.forename: E R
authors.initials: ER
authors.lastname: Valstar
authors.forename: H S
authors.initials: HS
authors.lastname: Gill
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
authors.forename: A J
authors.initials: AJ
authors.lastname: Price
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D015992:Body Mass Index; D019544:Equipment Failure Analysis / Q000379:methods*; D005260:Female; D006801:Humans; D007720:Knee Prosthesis / Q000592:standards*; D008297:Male; D008422:Materials Testing / Q000379:methods*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D020959:Polyethylene; D011474:Prosthesis Design / Q000592:standards; D011475:Prosthesis Failure / Q000209:etiology*; D012086:Reoperation; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D020959:Polyethylene