How critical is body mass index, and who decides?

The impact of obesity on the outcome of hip and knee arthroplasty, as well as other orthopaedic interventions, has generated great debate over the years, and is currently the subject of potential ‘rationing’ in some parts of the United Kingdom.¹

Some surgeons have welcomed this action, notably colleagues who work in countries or regions where obesity is common. Some feel that measures should be taken prior to consideration of arthroplasty in the morbidly obese patient. On the other hand, the situation in the United Kingdom, where body mass index (BMI) thresholds are being used arbitrarily to prevent referral to secondary care, is potentially counterproductive and puts some patients at a disadvantage. At present, almost one third of clinical commissioning groups in the United Kingdom appear to be applying mandatory policies on BMI prior to hip or knee arthroplasty, which suggests that this policy of rationing is on the increase.

There is little doubt that health care faces unprecedented demand and financial pressures. This is particularly prevalent in the United Kingdom. When faced with such challenges in the past, the NHS has looked at restricting access to surgery and other treatments in order to save money. This has come to the fore again recently with plans to deny surgery to patients who smoke and those who are overweight or clinically obese. Many procedures have been subject to these thresholds, including elective hip and knee surgery. In effect, some of these patients are soft targets for savings, as obesity and smoking-related diseases are seen as self-inflicted illnesses.

The cessation of smoking, and weight loss prior to surgery are widely perceived as playing a key role in optimising outcomes, but indiscriminate use of these factors as triage tools has no basis in evidence. Some studies suggest that weight loss is beneficial to surgical outcome, but others do not, and some have shown weight loss pre-surgery as a predictor of adverse outcomes.^2,3

In this issue, Chen et al⁴ show that even patients with high BMI benefit significantly from knee arthroplasty without any major ill effects. Other studies have shown increased surgical difficulty, higher early complication rates and increased length of stay, but good clinical outcomes nevertheless.^5-8

We are aware of increasing levels of obesity in the United Kingdom and worldwide. The NHS classifies a BMI of > 25 kg/m² as overweight, a BMI of between 30 kg/m² and 39 kg/m² as obese, and a BMI > 40 kg/m² as severely obese.⁹

A proportion of severely obese patients benefit from interventions to aid weight loss before surgery, but some are unable or unwilling to entertain such measures or are unsuitable, and yet would nevertheless benefit from orthopaedic surgery. A blanket ban based on BMI alone, to the exclusion of clinical assessment, is difficult to accept. The decision to withhold surgery, or to offer alternative solutions, should always take into account the patient as a whole, and should be based on a full clinical assessment and informed decision making. Delaying or denying surgery can prolong painful symptoms for patients, can cause additional stress, diminish quality of life and permanently disadvantage the ultimate outcome.

Whilst guidelines for clinicians to encourage patients to stop smoking or lose weight before surgery should be encouraged at every stage of the pathway, including primary care and musculoskeletal triage, mandatory policies that deny patients access appear to be excessive and are not evidence-based. The decision to withhold surgery from someone with osteoarthritis must only be taken after an appropriate clinical discussion when the pros and cons of intervention and the alternatives are discussed, and when a qualified and experienced practitioner takes a history, examines the patient, reviews the imaging and discusses all the relevant issues with the patient in order to advise appropriately. BMI is not a surrogate of general health and should not solely influence whether surgery is considered. It is one factor alongside many others that should be considered as part of multidisciplinary assessment and consideration of risks with patients.

As a community, we must undertake to assess the risks of treatment in discussion with our patients and to make decisions based on the individual. We must not indiscriminately offer surgery based on soft indications, but we must also recognise that difficult surgery in obese patients is sometimes inevitable and very successful. We must engage in public health measures to decrease smoking and obesity and optimise our patients’ health prior to surgery, but we must also resist our commissioners withholding treatment based on these metrics without the appropriate clinical review.