Examination of ten fractured Oxford unicompartmental knee bearings
- E. Pegg, PhD, Post-Doctoral Researcher1;
- H. Pandit, FRCS (Orth), DPhil, Honorary Senior Clinical Lecturer1;
- H. S. Gill, DPhil, Lecturer;
- G. W. Keys, FCS(Orth), FRCS(Orth), Orthopaedic Surgeon2;
- U. G. C. Svard, MD, PhD, Orthopaedic Surgeon3;
- J. J. O’Connor, PhD, Hon DSc, Professor (Emeritus)4; and
- D. W. Murray, MD, FRCS(Orth), Professor1
1Botnar Research Centre, Nuffield Orthopaedic Centre, University of Oxford, Windmill Road, Oxford OX3 7LD, UK.
2East Cheshire NHS Trust, Victoria Road, Macclesfield SK10 3BL, UK.
3Skaraborgs Sjukhus Kärnsjukhuset, Skövde 541 85, Sweden.
4Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
- Correspondence should be sent to Mr H. Pandit; e-mail:firstname.lastname@example.org
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.
The authors would like to thank Dr T. Drobny (Clinic Wilhelm Schulthess, Zurich, Switzerland), Mr P. McLardy-Smith, Mr A. Price (Nuffield Orthopaedic Centre, Oxford, United Kingdom) and Mrs B. Marks (Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, Oxford, United Kingdom) for their assistance with this study. The study was supported by the NIHR Biomedical Research Unit into Musculoskeletal Disease, Nuffield Orthopaedic Centre and the University of Oxford.
The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund, foundation, educational institution, or other non-profit organisation with which one or more of the authors are associated.
- Received April 19, 2011.
- Accepted August 30, 2011.
- ©2011 British Editorial Society of Bone and Joint Surgery