We have written before about how obesity is a risk factor for knee conditions, and in this article we cover an associated topic – how obesity affects joint replacement surgery.
Research has shown a clear link between obesity and a higher risk of complications after any type of surgery. After surgery, compared to normal weight patients, obese patients have anything up to five times the risk of heart attack, four times the risk of peripheral nerve damage, nearly twice the risk of wound infection and a 50% increased risk of urinary tract infection. This risk is especially significant in joint replacement surgery as wound problems and infection have devastating consequences including the need for multiple surgeries, revision procedures and in the worst case scenario, amputation.
But two questions beg further consideration.
First is the debate regarding threshold weight or level of obesity that could be considered unsafe for joint replacement surgery. This is measured in terms of BMI or Body Mass Index. It is generally agreed now that BMI greater than 40 kg/m2 increases the risk of complications significantly compared to a BMI threshold of 30 or 35 kg/m2.
Second is an ethical issue, pitting patients' willingness to assume risks against surgeons' reasonable desire to limit high-risk elective surgeries. A recent study(1) concluded that six months after total joint replacement (TJR), severely or morbidly obese patients reported excellent pain relief and substantial functional gain that was similar to the findings in other patients. While obesity is associated with a greater risk of early complications, obesity in itself should not be a deterrent to undergoing TJR to relieve symptoms.
Another recent study(2) on the risks and benefits of joint replacement among the obese sheds new — and positive — light on an issue that affects many thousands of people. With a BMI criterion of ≥40 kg/m2, the number of patients denied a complication-free surgical procedure is about 14 times larger than those spared a complication. On a population level, such a policy would reduce the overall number of complications, but would also result in denying total joint arthroplasty access to a much larger number of patients who would not have had a complication.
In spite of contradictory evidence in medical literature regarding the importance of BMI and effect of obesity in patient selection for joint replacement surgery, it is prudent and relevant to consider the effects and complications of obesity in this patient group.
If we divide the process of joint replacement into two – the surgery itself and the recovery period – we can examine the effect obesity has at each stage.
1) The Surgery Itself
Working with an obese patient presents a number of challenges not present in normal weight patients. These challenges are…
These are related to large amounts of fatty tissue in the body…
- Exposure - large fat accumulations can in some circumstances make it hard for the surgeon and his team to achieve what is called 'exposure', which is the ability to properly view the tissue and area being operated on. Where fatty tissue needs to be moved, or where it is pressing on the area being operated on, this can also present a physical challenge as these large fat tissue accumulations can be heavy
- Injury risk – there is an increased risk of damage to other tissue and organs in the body with an obese patient, partially due to the physical and exposure issues, but also due to the colour of fatty tissue; fatty tissue is white and can make differentiating between different tissue and organs challenging for the surgeon
An obese patient will require special consideration relating to anaesthesia, for example…
- Making sure the anaesthesia dose is correct for the weight and body makeup of the patient
- Placement of intravenous anaesthetic supply and of breathing tubes (which can be more difficult in obese patients)
- Increased risk of breathing issues under anaesthesia
Obese patients are also more likely to take longer to regain consciousness after the procedure. Overall, the impact of these extra considerations means that surgery involving obese patients on average takes longer, involves greater blood loss during surgery and longer recovery periods for the patient.
2) The Recovery Period
For obese patients the recovery period could be longer than for normal weight patients. This is due to a number of factors which can hinder the healing process, for example…
- Increased risk of wound problems, infection and deep vein thrombosis
- Obese patients are often also diabetic, and diabetes slows wound healing
- Fatty tissue is more vulnerable to bacterial infection than other tissue
(1) Functional Gain and Pain Relief After Total Joint Replacement According to Obesity Status Li W et al. J Bone Joint Surg Am. 2017 Jul 19
(2) Risk reduction compared with access to care: Quantifying the trade-off of enforcing a body mass index eligibility criterion for joint replacement Giori NJ et al. J Bone Joint Surg Am 2018 Apr 4