This is a very topical subject with more and more primary care organisations restricting joint replacements to obese patients with a BMI of 35 and greater. Is this based on evidence or is this a measure to reduce access to joint replacements for some?
An interesting publication looking at a number of papers on obesity and hip replacements was published recently (Barrett et al, https://doi.org/10.1302/2058-5241.3.180011). I have analysed this information and my experience of treating overweight patients to highlight the issues below.
Total hip replacement is one of the most successful in common surgical procedures with over 1,191,000 operations recorded in the National Joint Registry 2020 annual report. The prevalence of obesity in the population is increasing. Obesity is a known risk factor for the development of osteoarthritis. This is because of increased joint contact forces and altered biomechanics resulting in wear and tear of the joint. This in time increases the likelihood of needing a joint replacement.
The BMI or body mass index is used to categorise peoples weight Into underweight, overweight, and obese. Obesity is defined as a BMI greater than 30, morbid obesity is a BMI of greater than 35.
One of the most important outcomes of a hip replacement is how long it lasts. Overall this paper showed that there was evidence of a higher failure rate of hip replacements in the obese patient. However this was not uniformly seen in all the reported studies. Some papers showed no difference between the obese and non obese groups.
Another important outcome of a hip replacement is how patients function after the surgery. The studies clearly demonstrated an improved functional outcome following hip replacement in obese patients. This means most patients improved in terms of pain and their ability to function after hip replacement irrespective of their weight. It is likely that the hip replacement may fail sooner in the group of patients who are obese or morbidly obese. The counter argument is that patients who are in that group tend to be more sedentary and put less demand on the joint replacement.
There is also evidence that morbidly obese patients have higher complications after surgery, wound problems and longer hospital stay.
In my practice I advise obese patients to lose weight before surgery as a general rule. I do not have a BMI cut off and do not believe this should be used as a tool to determine who should have and not have a hip replacement. Sometimes weight loss is achievable but at times it is impossible due to the severity of pain and inability to exercise. It is useful to ask your GP if you could be referred to a dietician. Procedures such as hip injections can be used to manage the pain enabling a period to attempt loosing weight. At the end of the day after a period of counselling and understanding the risks involved, a hip replacement can be undertaken to achieve the goal of pain relief.