Polyethylene wear of the Oxford Knee replacement

• Research type

  Research Study

• Full title

  In vivo wear of Oxford Unicompartmental knee replacement Phase 3 bearings made of three different polyethylene resins

• IRAS ID

  201795

• Contact name

  David Murray

• Contact email

  david

• Sponsor organisation

  Clinical Trials and Research Governance

• Duration of Study in the UK

  0 years, 8 months, 31 days

• Research summary

  The Oxford Unicompartmental knee replacement (UKR) was designed with mobile bearings to have extremely low wear rates and excellent long term survival. Retrieval studies have shown that the very low wear rates predicted from the design are achievable in practice with linear wear rates (LPR) as low as 0.01 mm/year.
  We have developed a Radiostereometric Analysis (RSA) system that can measure the wear of the polyethylene bearing in the Oxford UKR.
  There have been three main iterations of the OUKR with some design changes between each iteration. The Phase 1 was used from 1976 to 1987, the Phase 2 from 1987 to 1998 and we are currently using the Phase 3. Using the RSA system we have measured the wear rate of Phase 2 bearings at both ten and twenty years. In both cases the mean wear rate was about 0.02 mm/year.
  We have recently analysed the five year wear from a randomised controlled trial comparing migration of cemented and cementless Phase 3 OUKR components with RSA. In both groups, the wear rate was significantly higher than we had measured with Phase 2 bearings. This is a concern as it may cause problems in the long term.
  The differences between the design of the phase 2 and 3 components are small. Around 10 years ago the polyethylene resin used to manufacture the mobile bearings changed from a 1900 to a 1050 resin, and these were supplied by different companies. The primary difference between the two resins is their molecular weight, which affects their mechanical properties. In addition, for a limited period of time the 1050 bearings were produced by a machining process instead of direct compression moulding (DCM), producing a third variant. The differences in the manufacturing process could explain the discrepancy between the expected and measured wear rates.
  We plan to measure the wear of the Phase 3 OUKR at a minimum follow-up of about 5 years and to compare the wear rates of DCM 1900 and machined and DCM 1050 polyethylene resins.

• REC name

  South Central - Oxford B Research Ethics Committee

• REC reference

  16/SC/0456

• Date of REC Opinion

  19 Sep 2016

• REC opinion

  Favourable Opinion