This economic analysis, using routinely collected National Joint Registry data from 2003 to 2012, found that Nexgen was the most cost-effective brand of prosthesis for total knee replacement. The cheapest brand was AGC Biomet, but Nexgen gave greater quality of life improvement, and the additional cost for the benefit - £2,300 per quality-adjusted life-year - was well within usual willingness to pay thresholds. Nexgen also had the lowest rates of revision surgery.
The study is the first to compare commonly-used prostheses for patient outcomes, costs and revision rates (how soon the replacement knee needed replacing). The comparisons relied on non-randomised, routinely collected data, and although the authors made every effort to correct for possible bias, the results should be treated cautiously. Prosthesis design improves over time, and so procurement decisions will need to be periodically re-examined.
Why was this study needed?
Knee replacement surgery (arthroplasty) replaces a damaged or diseased knee with an artificial joint. More than 70,000 knee replacements are carried out in England and Wales each year, and the number is rising. There are two types of surgery: total and partial knee replacement. This study looked at total knee replacement involving both sides of the knee joint (thigh and shin bones).
Most people who have a total knee replacement are over 65 years old. Replacement knees often last 20 years or more before they need replacing (called revision surgery).
There is a lack of evidence on the effectiveness or cost-effectiveness of the more than 60 alternative brands of artificial knee joint (prosthesis) available for knee replacement. This study was an economic evaluation of the five most commonly used brands that together make up about 60% of the market in the UK.
What did this study do?
The authors used modelling techniques to estimate the relative cost-effectiveness of the five prosthesis brands. Quality of life (QALY) data was taken from the Patient Reported Outcome Measures (PROMS) database which collected data immediately before the operation and six months after, for patients who had a knee replacement in the NHS between August 2008 and July 2012. Rates of revision surgery were taken from The National Joint Registry for England, Wales and Northern Ireland for people with osteoarthritis who had surgery between April 2003 and March 2012. Mortality data were estimated from Hospital Episodes Statistics data.
The unit costs for each prosthesis brand were the average price paid by a mid-size NHS provider, taking into account typical negotiated discounts. They were: £1,835 for PFC Sigma, £1,150 for AGC Biomet, £1,676 for Nexgen, £1,294 for Genesis 2, and £1,325 for Triathlon. Total costs in the model included operating theatre and hospital stay costs.
Calculations were adjusted to take into account the age, gender, body mass index and degree of disability of the patient, whether the knee cap (patella) was also being replaced, the use of antibiotic-impregnated cement, the experience of the operating surgeon, and the medical centre in which the operation took place. A number of sensitivity analyses were run to test the assumptions made in the model.
What did it find?
- Nexgen was the most cost-effective brand. AGC Biomet was cheaper, but it gave fewer additional years of quality life. For 70 year old men and women, the incremental cost effectiveness ratio for Nexgen compared to AGC Biomet – how much extra it cost for one QALY - was £2,300. This is well within usual willingness to pay QALY thresholds of £10,000 to £30,000. All other brands were “dominated” by either Nexgen or AGC Biomet – that is they either cost more and/or gave lower QALY benefit.
- Nexgen and PFC Sigma brands had equal lowest revision rates: 2.5% after 10 years in 70 year old women, and 3.1% in 70 year old men. The highest 10 year revision rate was AGC Biomet, at 3.3% for 70 year old women and 4.2% for 70 year old men.
- Quality of life was highest with Nexgen, with a mean post-operative EQ-5D-3L score of 0.74 in 70 year old men and 0.73 in women. Differences between brands were small; the lowest EQ-5D-3L score, with Genesis 2, in 70 year old men was 0.71, 0.70 in women.
- Results were robust to alternative modelling assumptions, and similar results were seen for 60 and 80 year olds.
What does current guidance say on this issue?
NICE do not recommend specific brands of prosthesis.
NICE recommends that surgeons should submit details of all patients undergoing total knee replacement to the National Joint Registry.
What are the implications?
This study cannot guide which prosthesis to use for which patient as different types of knee prosthesis will suit different patients. Nevertheless two thirds of hospitals in England use a single brand for the majority of patients, allowing them to negotiate a discounted price. Therefore, if Nexgen is more cost-effective for most patients, then it should be considered as a first choice prosthesis for total knee replacement unless clinical judgement and patient need suggests otherwise. This is an important contribution to the debate, but other factors may also influence buying decisions.
The data for the analysis was observational studies rather than from randomised controlled trials so confounding is a risk. There were small differences between the different brands in terms of revision rates and quality of life outcomes and although the authors tried to correct for potential bias, by running various sensitivity analyses using alternative assumptions, the results need to be interpreted cautiously.
Citation and Funding
Pennington M, Grieve R, Black N, van der Meulen JH. Cost-Effectiveness of Five Commonly Used Prosthesis Brands for Total Knee Replacement in the UK: A Study Using the NJR Dataset. PLoS One. 2016;11(3):e0150074.
Three of the authors were supported by the Department of Health, United Kingdom (Commissioning Development).
NHS Choices. Knee replacement. London: NHS Choices; 2014.
NICE. Mini-incision surgery for total knee replacement. IPG345. London: National Institute for Health and Care Excellence; 2010.
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