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A new study by researchers at NDORMS, University of Oxford now published in Osteoarthritis and Cartilage found that the average lifetime risk of needing further surgery following knee and hip replacement – revision surgery – was around 5% after knee replacement and 8% after hip replacement, with neither body mass index (BMI, combining an individual's height and weight) or smoking having any meaningful effect on these risks.

Mounting evidence that bmi and smoking should not be used for rationing knee and hip replacement

The team, which included senior researchers in epidemiology, health economics and orthopaedic surgery, used routinely-collected hospital and primary care data from patients who had a knee replacement or a hip replacement in England, assessing over 10,000 patients for each procedure.

With healthcare budgets stretched, the provision of knee and hip replacements has come under increased pressure in the NHS. One result is that access to these surgeries has been restricted, and a number of clinical commissioning groups (CCGs) are currently limiting access based on patient's BMI and smoking status. In 2015, 22% of CCGs had a mandatory policy for knee and replacement regarding BMI, varying their cut-offs from a BMI of 30 to 40, and 4% of CCGs had mandatory policies requiring smoking cessation.

"Our findings, along with those from previous research, suggest that there is little evidence to support the rationing of knee and hip replacement based on individuals' BMI or smoking" said Ed Burn, DPhil student at the University of Oxford. "While there are many benefits from losing weight if overweight and stopping smoking, there seems to be little justification in limiting access to knee and hip replacement until such changes are made".

Previous research had already shown that BMI and smoking have little effect on patient reported outcomes after knee and hip replacement, but may be associated with a slight increase in the risk of post-operative complications.

Revision procedures are where implant components are removed, added, or exchanged. Revisions are an enduring risk, are more costly than primary procedures, and are associated with reductions in patient quality of life.

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