A recent study that has pooled data from multiple smaller studies, found that patients having knee replacement surgery had more problems when they were overweight.
The study found that obese patients had more short-term complications including infection, a potentially devastating problem with knee replacement surgery. In addition, obese patients had less successful long-term results after knee replacement surgery.
Unfortunately, many overweight patients are in a very difficult situation. Unable to lose weight because of painful knees, many of these patients end up having knee replacement despite being at higher risk for potentially serious problems. Certainly, attempts should be made to lose weight prior to knee replacement, but for many this may not be realistic.
Related: Weight Loss and Joint Replacement
Sources: The Influence of Obesity on the Complication Rate and Outcome of Total Knee Arthroplasty
It makes sense since the amount of stress on the leg is greater stands to reason that it might not be as successful with this kind of surgery