It can increase surgical risk. It has been used to ‘ration’ NHS knee replacements. Yet now, according to new research, it may not be an appropriate target at all. So what’s going on with weight in relation to knee replacements? Nick London unpicks a complex situation.
Knee replacements and weight have a complicated history. In a recent paper on current best practice authored by Yorkshire Knee Clinic surgeons (which contains graphic imagery of operations), we state that: “It is recommended… that young patients with a high BMI lose weight before surgery, as these patients are at increased risk of early revision.”
Yet a new study by the University of Alberta finds that losing weight before knee replacement surgery doesn’t lead to better outcomes for patients.
If weight loss doesn’t lead to better outcomes why does the NHS use it, at least in part, as a tool for determining who’s next in the queue? And if weight loss doesn’t lead to better outcomes, why have we exhausted a lot of effort explaining that it does?
No single rule
I have a fairly simple philosophy when it comes to the issue of weight and knee replacement surgery, and in essence it involves taking a different approach depending on the group to which the patient belongs:
The extremely obese
Where the BMI is 40-45 or above, the risk to patients in terms of surgical complications and implant failure is high. Generally speaking, weight loss is to be strongly encouraged although this can in itself present issues as we’ll see in a moment.
Older patients who are overweight may be advised to lose weight ahead of surgery, but they may still benefit from partial or total knee replacement whether they lose that weight or not.
There is a trade-off here. A patient with a high BMI (30+) may have to accept a slightly increased risk of infection or of blood clots, and a risk to the longevity of the implant unless they manage to get their weight down.
But I don’t believe that such patients should be excluded from being offered a knee replacement because, as the University of Alberta paper rightly points out, they can do far more damage to the knee when their operation is delayed. A hiatus of several months (or even years) while a patient tries to lose weight can worsen outcomes, not improve them.
The other concern with such patients is that occasionally you will meet someone who commits to a programme of major weight loss and drops four stones in six months. They then arrive ready for surgery in a malnourished state, which in itself can increase the risk of infection.
It is this group of patients who have so often been rather discriminated against by NHS commissioning groups when there is great evidence that knee replacement can be highly beneficial.
I would not, however, apply the same rule to younger patients. It is no longer uncommon for patients in their 40s and 50s to have a knee replacement and with such patients I believe they have a responsibility to lower their weight, preferably before surgery and certainly within a year or two of having it. That’s because the stakes are higher. A 50 year old with a partial knee replacement might live for another 50 years. Many if not most of those years may be highly active ones. That’s a very different situation compared with an 80 year old whose knee replacement simply doesn’t have to cope with the same mileage.
In younger patients it’s critical to manage weight because not only is there a risk of operative complications, there’s also a substantially increased risk of the implant failing prematurely. That then requires the partial knee to be converted to a total replacement, or the total to be revised or even re-revised. The results of such procedures are never as good as the first time around and carry an ever-increasing risk of complication and infection.
Weight loss momentum
Adding further complexity to the relationship between weight and knee replacement is the attitude of the patient. Experience tells us that a patient who starts losing even a small amount of weight before their surgery will be more likely to continue losing weight after it. A patient who doesn’t lose weight before their operation but who says they will afterwards, typically doesn’t.
There are those who take the position that all overweight patients should lose weight before knee replacement surgery. There are those who believe none should. I believe the reality is that we cannot make such blanket statements and that a more nuanced, more tailored approach would lead to better patient outcomes.
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