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Journal of Bone and Joint Surgery - British Volume, Vol 91-B, Issue 5, 604-611.
doi: 10.1302/0301-620X.91B5.21525  
Copyright © 2009 by British Editorial Society of Bone and Joint Surgery
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Premature failure of Kinemax Plus total knee replacements

E. Reay, MBBS, MRCSEd, Specialist Registrar1; J. Wu, BEng, MSc, DPhil, Lecturer2; J. Holland, FRCS(Orth), Consultant Orthopaedic Surgeon1; and D. Deehan, MD, FRCS(Orth), Consultant Orthopaedic Surgeon1

1 Department of Orthopaedics Freeman Hospital, Freeman Road, High Heaton, Newcastle upon Tyne NE7 7DN, UK.
2 School of Engineering Durham University, South Road, Durham DH1 3LE, UK.

Correspondence should be sent to Dr E. Reay; e-mail: emsr76{at}aol.com

We describe a cohort of patients with a high rate of mid-term failure following Kinemax Plus total knee replacement inserted between 1998 and 2001. This implant has been recorded as having a survival rate of 96% at ten years. However, in our series the survival rate was 75% at nine years. This was also significantly lower than that of subsequent consecutive series of PFC Sigma knee replacements performed by the same surgeon. No differences were found in the clinical and radiological parameters between the two groups. At revision the most striking finding was polyethylene wear. An independent analysis of the polyethylene components was therefore undertaken. Scanning electron microscopy revealed type 2 fusion defects in the ultra-high molecular weight polyethylene (UHMWPE), which indicated incomplete boundary fusion. Other abnormalities consistent with weak UHMWPE particle interface strength were present in both the explanted inserts and in unused inserts from the same period.

We consider that these type 2 fusion defects are the cause of the early failure of the Kinemax implants. This may represent a manufacturing defect resulting in a form of programmed polyethylene failure.






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Hip, Knee, Trauma, Upper limb, Foot & Ankle, Paediatrics, Oncology, Spine, Arthroplasty, General