Depends on your MD. We don't do surgery on patients with a bmi above 38, primarily because the implant companies are not going to stand behind their implants when they are put in the morbidly obese. At 6'3" the limit is 304 lbs in our practice.
? There is no specific # but bmi over 40 or certainly over 50 makes it a great deal harder to do also risk tends to go up with increased weight.
It is good to be fit. For your height, your weight should be between 80 to 85kg (175 to185 pounds). This is healthy weight but it is not an absolute figure that determines your fitness for surgery. Ask your orthopedic doctor's advice too.