The team used routinely collected data from the National Joint Registry (NJR) and found that partial replacements, also known as unicompartmental replacements (UKR), are better for patients who have only part of their knee affected by arthritis and could therefore have either a partial or a total replacement.
The procedure is less invasive, allows for a faster recovery, carries less post-operative risks and provides better function. It is also a cheaper intervention for the NHS, in both the short and long term.
"The main strength of this study is that we were able to use real data, from very large numbers of people, about their actual operations, their GP visits, and their own reported quality-of-life outcomes in a way that is not always possible," says co-lead researcher and NDORMS Senior Health Economist Dr Rafael Pinedo-Villanueva, who is funded by the National Institute of Health Research (NIHR) Oxford Biomedical Research Centre (BRC) and the Medical Research Council.
"This has allowed us to provide strong proof that partial knee replacements are both better for patients and cheaper for the NHS," he added.
The research, published on Monday 30 April in BMJ Open, compared people who had a partial knee replacement with those who had a total knee replacement, but could have had a partial replacement.
The main reason for knee replacement surgery is osteoarthritis, and about half of the patients needing knee replacement could be suitable for a partial replacement, a procedure where only the affected part of the knee joint is replaced. However, according to data from the NJR, of the 98,147 knee replacements undertaken in 2016, only 9% were partial.
The use of partial replacement varies greatly between different surgeons. Partial replacements done by surgeons using them for a small proportion of knee replacements provide worse outcomes than total replacements. Whereas partial replacements done by surgeons using them for a high proportion of knee replacements provide better outcomes and are cheaper for the NHS than total replacements.
"This is an important finding," co-lead researcher Prof David Murray explains. "If surgeons aim to use partial knees in a quarter or more of their knee replacements, this will substantially improve the results of knee replacement and will save money. In addition more partial knee replacements will be done and more patients will benefit from this procedure."
The new study provides clear evidence of the lifetime benefits for patients over 60, for whom partial knee replacements are better and cheaper. Whilst partial replacements are still cheaper for patients under 60, the long-term health benefits of this intervention are less clear, compared to those of total knee replacements. However, for surgeons using partials in a high proportion of their knee replacements, partials should provide better long-term health benefits than totals even in these younger patients.
"For patients and the NHS to see the benefits of partial replacements, we need the buy-in of surgeons, who would need to feel comfortable performing a greater proportion of their knee replacements as partials," the paper's first author, Ed Burn, explains.
"If we see surgeons carrying out this procedure more often, the proportion of knee replacements that are partials would increase from the current figure of 9% and we would see an increase in future economic and population health gains".