Outcomes debated for partial versus total knee arthroplasty

A major study shows partial knee replacements offer similar clinical outcomes and improved cost effectiveness compared to total knee replacements in patients with late-stage isolated medial compartment osteoarthritis.

But an Australian knee surgeon says revision rates may be different in real world practice compared to the highly selected trial participants recruited into the TOPKAT study.

The randomised controlled trial of 528 patients across 27 sites in the UK, included similar Oxford Knee Scores (38.0 v 37.0) in both patient groups five years post surgery.

The procedures were conducted by 68 surgeons including those with sufficient expertise in either one or both types of arthroplasty. Surgeons were free to use the implant of their choice.

Other secondary outcome measures, including the EQ-5D-3L score, the High Activity Arthroplasty Score, the University of California, Los Angeles Activity Score and American Knee Society scores, were similar in both groups at five years.

Only the EQ-5D visual analogue scores were different between the two groups – favouring the patients who underwent a partial arthroplasty.

Patient satisfaction was similar in both groups although self-reported answers to other specific questions were variable.

Partial procedures resulted in fewer complications including unexplained pain and knee stiffness than total knee replacements (20% v 27%) and shorter length of hospital stay (3.2 v 4.3 days).

The number of re-operations (9% v 10%) and revisions (4% v 4%) were also comparable between both groups.

A cost-effectiveness analysis showed partial knee replacements resulted in additional quality-adjusted life years (QALYs) and were about £910 ($1600) less expensive than total knee replacements.

“The probability that PKR was the most cost-effective option was more than 99·9% for all reasonable threshold values. This finding was a result of better outcome, as measured by QALYs derived from EQ-5D scores and survival, lower costs of PKR surgery, and lower follow-up health-care costs with PKR than TKR,” the study said.

“Even assuming equal costs of the implant device, PKR was less costly and more effective than TKR.”

However Australian Knee Society president Dr Bruce Caldwell said their revision rates were likely biased by very strict selection criteria reflected in the study’s slow rate of patient recruitment.

“This paper is true – it’s just that you’ve got to pick really selected patients.”

“And if you have pure medial compartment osteoarthritis, with nothing in the lateral side and nothing in the patellofemoral joint then it’s true that partials do better than totals.”

Dr Caldwell said the reality was that only a small proportion of knee surgery patients fit that profile.

According to the Australian Orthopaedic Association’s National Joint Replacement Registry, partial knee replacements represent only about 6% of all knee replacements.

“In the Australian registry, the failure rate of partials is three times higher than totals,” he said. “And that’s usually because the knee cap has got arthritis as well.”

He added that the outcomes following the conversion of a partial to a total knee replacement were worse than having a total replacement in the first instance.

An accompanying Comment article in The Lancet said the findings were “a welcome addition to our knowledge base”.

“In view of the results of the TOPKAT study, we agree that the potential benefits and drawbacks associated with PKR versus TKR should be discussed as part of the informed consent process with patients meeting the inclusion criteria for this trial.”

“Further studies that use methods such as discrete choice experiments and qualitative methods to explore the lived experience of patients undergoing PKR and TKR could help patients and surgeons in the difficult choice between PKR and TKR in those patients who are suitable to receive either option.”

A 10-year follow-up on TOPKAT which is underway will deliver more long-term data on revision rates.

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