To identify frequency and patterns of Oxford Phase 3 Unicompartmental Knee Arthroplasty (UKA) failure in New Zealand through analysis of national primary and revision data. Compare the results of this data with that of total knee arthroplasty and other international joint registers.

Retrospective audit examining all Oxford Phase 3 UKAs recorded in the New Zealand National Joint Register from January 2000 to December 2007 were analysed and then statistic al analysis performed to identify patterns of failure and reasons for revision.

Two thousand six hundred and twenty Oxford UKAs were performed by 99 Orthopædic Surgeons. The average age was 66.1 years (range 35–94).

Osteoarthritis was the primary diagnosis. Mean time to revision 839 days (2.3 years). Revision rate was 5.6% (n=148). The most common reasons for revision were pain (n=61, 41%), aseptic loosening (n=53, 36%), and bearing dislocation (n=16, 11%). Deep infection rate was 0.26% (7/2620) compared with 1.76% of total knee arthroplasties (564/32029). Six surgeons (high use & #8805;10 UKAs/year) performed 699 (26.7%) operations, revision rate 2.6%. Fifty-five surgeons (low use & #8804; two UKA/year) performed 283 (10.8%) operations, revision rate 10.6%. There was a statistically significant difference seen with an inverse relationship between surgeon experience and revision. The revision rate for the Oxford is three, two times greater than TKA.

UKA is now decreasing in New Zealand whilst Total Knee Arthroplasty (TKA) continues to increase. The number of is now decreasing in New Zealand whilst Total Knee Arthroplasty (TKA) continues to increase. The number of surgeons using Oxford UKA has increased by 19% but the number of Oxfords being done has fallen by 13%. High use surgeons’ revision rate is now higher than TKA. An inverse relationship between failure and surgeon experience exists which confirms Swedish Knee Arthroplasty register reports. The deep infection rate is less than TKA. Revisions were performed early for unexplained pain in the absence of obvious mechanical failure. This is against generally held wisdom for TKA and may reflect the perception that UKA is easily revised to TKA.