Revision rates following unicompartmental knee arthroplasty may be surgeon-dependent

Russell Tregonning

GLASGOW — Analysis of the New Zealand National Joint Registry revealed that the 10-year revision rates for unicompartmental knee prostheses were 2.6 times higher than those of total knee arthroplasty; however, patients reported better results with the unicompartmental prostheses up to 5 years.

Russell Tregonning, MBChB, FRACS, FNZOA, and colleagues analyzed the registry’s 10-year data to identify causes of failure and revision rates of the medial Oxford phase 3 cemented prosthesis (Biomet) as compared with other unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) prostheses.

“[The New Zealand National Joint Registry] is one of the few to record the results of patient-derived data, and the only to use the Oxford score for patients to give their views as to the success of the operation at 6 months and 5 years after surgery,” Tregonning said at the 2010 Meeting of the Combined Orthopaedic Associations, here.

Revision rates

Tregonning and colleagues assessed the data from 3,624 patients who received a medial Oxford phase 3 cemented prosthesis. They found 216 revisions were performed in that subgroup.

“This gives a revision rate of 1.39 per 100 component years, compared with 1.42 for all unicompartmentals combined,” Tregonning said.

As a means of comparison, he reported the following 10-year revision rates according to UKA prosthesis type: 0.98 per 100 component years for the Miller-Galante (Zimmer), 1.66 for the Genesis (Smith & Nephew) and 1.87 for the Preservation (DePuy).

Additionally, Tregonning reported a “highly significant difference” between the Oxford revision rate of 1.39 per 100 component years and the TKA revision rate of 0.54.

The most common cause for revision among Oxford patients was unexplained pain: 38% of all Oxford revisions were performed for unexplained pain, compared with 28% of all TKA revisions, representing another significant difference. “This raises the possibility that surgeons have a lower threshold for revising unicompartmental than total knees,” Tregonning said.

Surgeon factor

High-use surgeons — those who perform 10 or more Oxford UKAs per year — and medium-use surgeons — those who perform between two and nine Oxford UKAs per year — both had a revision rate of 1.3 per 100 component years.

“This is the first time I’ve seen this. Over the years there have been significant differences between these two groups, but not at 10 years,” Tregonning said, adding that significant differences were seen when comparing the revision rates of these two groups with those of surgeons who perform less than two Oxford UKAs per year.

Reference:
Tregonning R, et al. Revisions of the Oxford phase 3 cemented medial unicompartmental knee joint arthroplasty: an audit of the New Zealand Joint Registry over 10 years. Presented at the 2010 Meeting of the Combined Orthopaedic Associations. Sept. 13-17, 2010. Glasgow.

David W. Murray

This is a very important paper from the New Zealand Joint Registry, presenting data up to 10 years on the Oxford knee. It is important because it includes both patient-reported outcome measures, the Oxford knee score as well as the survival.

It showed that the functional outcome of the Oxford was better than that of the totals, whereas the survival was worse. Part of the explanation for this difference [was] ease of revision of the unicompartmental replacement.

It was also interesting to note that the revision rate of the cementless Oxford was substantially better than that of the cemented Oxford and other unicompartmental replacements. Further study is needed to see if this is a real improvement.

— David W. Murray, MD, FRCS(C)
Nuffield Orthopaedic Center, University of Oxford
Oxford, UK

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