Let’s start off with the good news about being overweight and having knee replacement.

The very good news for people with a body mass index (BMI) of 30+ having knee replacement surgery, is that in terms of pain-relief and implant survival (how long the implant lasts), the results are equal to patients with a normal BMI. This is shown in our research. Read abstract at PubMed.

Patient satisfaction levels with the outcome of knee replacement surgery for large people, is equal to patients with normal BMI. We have found this in our own research and it is also supported by other studies done around the world. Knee replacement can also give patients an opportunity to begin with an exercise program to lose weight, which may not have been an option for them prior to surgery because of their pain.

In some parts of the world, there’s talk of withholding this surgery from people with a 30+ BMI, presumably because of the additional cost on the health care system. It is undoubtedly true that large people are on average more expensive to treat. I was recently interviewed by Channel 9 for a news story and was asked my opinion about this. My view is that patients should do everything to get weight off prior to surgery, but knee replacement for patients with a high BMI, may be the event which allows them to make a difference to their weight in the future, and that is an excellent reason to do it.

Of course, for patients with a BMI over 30, any surgical episode itself has increased risks. For large people, the anaesthetist is perhaps the most important person in the team, as this is the person who really manages all aspects of the patient’s physiology during and immediately after surgery. Our studies, which are supported by other studies done around the world, have shown that patients with BMI 30+ who have a knee replacement do indeed take longer to recover after surgery, tend to stay in hospital longer and have higher risk of wound complications than those with normal BMI. With regard to the performance of the joint itself, the results are equal to patients with normal BMI, although there is less flexion in the joint, which is simply due to the fatty tissue preventing the full range of motion.

For anyone who needs a bit of encouragement to get some weight off before they get close to needing a knee replacement, here are some facts worthy of attention:

• Patients with a BMI between 30 and 35 are 8.5 times more likely to need a knee replacement compared to someone with normal BMI.
• Patients with a BMI between 35 and 40 are 18.7 times more likely to need a knee replacement compared to someone with normal BMI.
• Obese patients are on average younger than patients within a healthy weight range.