Abstract
A previous audit of New Zealand Joint Registry data showed that, overall, OXF UKA had over three times the seven–year revision rate (RR) compared with TKA. Where the RR was calculated for surgeons performing one or more OXF UKA per month, however, the RR was comparable to that for all–surgeon TKA (Hartnett et al, NZOA ASM, 2007).
To audit and compare revisions of OXF UKA and TKA performed by one surgeon, as recorded in the New Zealand National Joint Registry, and to highlight a complication of OKF UKA unreported in the literature.
The data from a personal series of 177 consecutive medial Oxford (Phase three) cemented UKAs entered in the Registry from January 2000 to December 2007 was analysed. The number and reasons for revision of the cohort was compared with a similar personal cohort of 229 consecutive cemented TKAs performed over the same period. Comparison was also made between this personal data with that for all surgeons recorded in the Registry.
OXF UKAs were performed at a mean rate of 1.8 procedures per month. The prime indication was antero-medial osteoarthritis: valgus stress x-rays performed routinely had to establish adequate thickness of lateral articular cartilage and ACL had to be competent before the UKA was preferred to TKA. Fifty six (31.6%) of the 177 operations were performed as part of bilateral procedures under the one anaesthetic.
Two OXF UKAs were revised to TKA. In neither was there failure of fixation or integrity of the prosthesis: one case was revised for unexplained pain where OXF UKA was for post–traumatic medial OA. The 2nd revision followed recurrent haemarthrosis and subsequent joint destruction: arteriography found no arterial injury. The RR for personal OXF UKA was therefore 1.1%, which compares with personal TKA RR of 2.2% (difference not significant p=0.42). The RR for all OXF UKAs in NZ was 5.6%, and that for TKA was 1.8%. The difference between personal and national RR for OXF UKA is significant (p=0.010), and that for TKA is not (p=0.63).
Since 2000, two other revisions of OXF UKA outside the studied cohort both followed recurrent haemarthrosis causing joint destruction. The results of OXF UKA reported here confirm that an early revision rate comparable to TKA is achievable when this surgery is performed relatively frequently by the surgeon. Recurrent haemarthrosis occurring later after early successful OXF UKA surgery is not recorded in the English literature. It has been the most frequent reason for revision (three of four revisions).
Correspondence should be addressed to Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
