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Since the Oxford knee was first used unicompartmentally in 1982, a small number of bearings have fractured. Of 14 retrieved bearings, we examined ten samples with known durations in situ (four Phase 1, four Phase 2 and two Phase 3). Evidence of impingement and associated abnormally high wear (> 0.05 mm per year) as well as oxidation was observed in all bearings. In four samples the fracture was associated with the posterior radio-opaque wire. Fracture surfaces indicated fatigue failure, and scanning electron microscopy suggested that the crack initiated in the thinnest region. The estimated incidence of fracture was 3.20% for Phase 1, 0.74% for Phase 2, 0.35% for Phase 3, and 0% for Phase 3 without the posterior marker wire. The important aetiological factors for bearing fracture are impingement leading to high wear, oxidation, and the posterior marker wire. With improved surgical technique, impingement and high wear should be prevented and modern polyethylene may reduce the oxidation risk. A posterior marker wire is no longer used in the polyethylene meniscus. Therefore, the rate of fracture, which is now very low, should be reduced to a negligible level.

Original publication

DOI

10.1302/0301-620x.93b12.27408

Type

Journal article

Journal

The Journal of bone and joint surgery. British volume

Publication Date

12/2011

Volume

93

Pages

1610 - 1616

Addresses

Botnar Research Centre, Nuffield Orthopaedic Centre, University of Oxford, Windmill Road, Oxford OX3 7LD, UK.

Keywords

Humans, Prosthesis Failure, Treatment Failure, Arthroplasty, Replacement, Knee, Prosthesis Design, Equipment Failure Analysis, Knee Prosthesis, Aged, Middle Aged, Female, Male