We report the results of a prospective randomised controlled clinical trial assessing the radiosterophotogrametric analysis (RSA), clinical and radiological performance of a metal backed and an all-polyethylene tibial cruciate retaining, condylar design, PFC-TKA up to twenty four months.

65 patients were recruited, of which 41 patients were randomised. There were 20 metal backed and 21 all-polyethylene. None were lost to follow-up. There were no significant inter-group demographic differences. We found a significant increase in SF-12 and Oxford knee scores after surgery in both groups. No significant difference was found between the groups in the RSA, SF-12, Oxford Knee score, radiological alignment and range of movement at 6, 12 or 24 months. At 2 years one metal backed implant showed translational migration > 1mm. No all polyethylene implant migrated > 1mm. Further analysis identified possible progressive subsidence of the metal backed implants compared to all-polyethylene implants, although the magnitude of this difference was very small.

We conclude that in the uncomplicated primary total knee arthroplasty, all polyethylene PFC-_ tibial prostheses had equivalent performance to the metal backed counterpart, using RSA as the primary assessment instrument at 24 months. We found no differences between the two designs as assessed by the secondary instruments: SF-12, Oxford knee score, alignment and range of movement at 24 months. Should half of all primary total knee replacements performed in the UK receive an all-polyethylene tibial implant, the estimated annual cost saving would be 21 million pounds per annum.