The Obesity Factor

Obesity, my friends, is on the rise and we are going to see more and more such patients in the near future. Obesity means arthritis, especially of the knee, is going to happen at an earlier age. 

 ‘A morbidly obese patient posted for a TKR’ – just the idea causes anxiety. It doesn’t require a genius to figure out that such a surgical exercise is hugely difficult. But as I was going through literature I realised that there are so many more issues with obesity than just technical hardship. It is imperative that we as surgeons are aware of these issues and it is our duty to warn our patients of these concerns before we take on this humongous challenge.

I always thought that obese patients with bad knees would have a tough time losing weight. Once the knee had been replaced then they would be able to lose it. But Pritchett JW et al have shown that TKR does not facilitate weight reduction.

Though an improvement in knee score does occur after TKR in morbidly obese, it is less than in non obese patients. In short even though morbidly obese patients benefit from TKR, we cannot expect the fantastic results that we see in thinner patients. Foran JR et al reported in 2004 that any degree of obesity (defined as BMI > or = 30) compromised the result of TKR. 

Obesity results in more technical errors during knee replacement surgery. I found some technical tips while reviewing literature. I invite comments on more technical tips from my readers. There is little place for MIS in the morbidly obese. One should use large incisions. Patella eversion is often not possible. It is better to just subluxate the patella. A tourniquet may be difficult to apply and may fail to work. One should be prepared to do the surgery without tourniquet. Fractures occur more commonly while operating on these patients. One should keep a set of screws and stemmed implants ready to deal with such an eventuality. Similarly ligament injuries are more common especially to the medial collateral ligament. One should be ready with a semiconstrained option.

An excellent review by Samson et al from Australia opened my eyes on the complications faced by this patient population. These patients are at a higher risk for wound complications. This has been attributed to poor oxygenation of adipose tissue, increased wound tension and underlying endocrine disorders like diabetes. These patients also have a 3 to 9 times greater risk of deep prosthetic infection.  And we all know what that means. To add to this is the increased risk of damage to MCL and introp fractures as already mentioned.  

And last but not the least, TKR in the morbidly obese results in reduced survival of the prosthesis and earlier revision (not conclusively proven)

In view of so many problems, some centres advocate bariatric surgery before undergoing knee replacement. Even though there is no conclusive data, early results are very encouraging for this approach.    

To conclude, TKR in obese and definitely in morbidly obese is a different ball game. Functional results and prosthesis survival are poorer and complications are higher. We need to discuss these issues in detail with the patient. We also need to better prepared for controlling co morbidities preoperatively, for handling intraoperative complications and for anticipating and managing postoperative issues. We may be forced to think of bariatric surgery before TKR in this patient group in the near future.