Investigation reveals rationing of knee replacement is unjustified
CHICAGO — As knee replacement is so cost-effective based on a recent cost analysis, rationing these procedures in the United Kingdom is unjustified, according to a presenter at the Knee Society Specialty Day.
“If a threshold for rationing knee replacement based on cost-effectiveness was to be introduced, it would be so high that virtually no patient would be excluded, so there is no justification for rationing,”
“As far as the design is concerned, patellar resurfacing is cost-effective. Mobile bearings do not affect cost-effectiveness. All polyethylene tibias are not cost-effective, even in the elderly. Unicompartmental replacements are cost-effective,” he said.
The U.K. National Health Service (NHS) has limited funds and considers knee replacement to be a procedure of “limited value.” In some parts of the NHS, thresholds are being used to restrict knee replacement. These thresholds are usually based on the Oxford Knee Score (OKS), but body mass index (BMI) is also used. The most commonly used threshold above which a knee replacement is not offered is an OKS of 26. The decision whether to introduce a new procedure into the NHS is based in part on whether it is considered to be cost-effective. Procedures costing less than £20,000 to £30,000 per QALY (quality adjusted life years) are deemed to be cost-effective.
If a threshold is to be used to ration knee replacement, then the only fair way to determine the level for the threshold would be to base it on cost-effectiveness, Murray noted. He used data from a large, multicenter study to identify thresholds above which knee replacement was not cost-effective. This study included 2,131 knee replacements from 34 centers with a 10-year follow-up. A detailed analysis of cost and effectiveness was undertaken and, based on conservative assumptions cost-effectiveness was determined
The investigators found the cost of the knee replacement and 5 years subsequent care was £7,458 per patient with 1.33 QALYs gained. Overall, the knee replacement cost £5,623 per QALY gained, which is considered to be highly cost-effective. The factor that influenced cost-effectiveness most was preoperative OKS, other influential factors were age, gender and ASA grades. BMI did not influence cost-effectiveness. Therefore, Murray noted, the best threshold would be based on pre-operative OKS. As BMI did not influence cost-effectiveness, there is no justification to restrict knee replacement in patients with high BMI. “[Even] with a BMI of 40 or higher,” Murray noted.
Knee replacements in patients with a preoperative OKS of <38 were cost-effective using a £20,000/QALY threshold. Therefore, Murray noted, if knee replacement is to be rationed, an appropriate threshold would be a preoperative OKS of 38. This threshold would exclude about 3% of patients having knee replacement. As so few patients would be excluded, he noted that rationing would not be justified due to the costs and bureaucracy involved.
A further analysis based on implant design was undertaken which found that patellar resurfacing was found to be cost-effective compared with not resurfacing. There was no difference in cost-effectiveness between mobile and fixed-bearing prostheses. Metal-backed tibial components were more cost-effective than all polyethylene tibial components particularly in patients older than 70 years. Unicompartmental replacements were more cost-effective than total knee replacements, Murray noted, citing data relating to the poor cost-effectiveness of the all-polyethylene tibial components in a large multicenter randomized controlled trial using implants from many different manufactures. – by Renee Blisard Buddle
Murray D. Rationing of total knee replacement: a cost-effectiveness analysis. Presented at: Knee Society Specialty Day; March 23, 2013; Chicago.
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Disclosure: Murray receives royalties from Biomet and research support from Biomet, DePuy, Stryker and Zimmer.