In a modern knee replacement, what we’re doing is replacing the surfaces of the knee joint, not the joint itself. The tendons, ligaments and all the other structures around the knee are left in place. I sometimes compare it to a dentist capping a tooth: We are adding new caps to the bones.
Knee replacement surgery usually takes an hour or two. It’s almost always done under regional anesthetic, like an epidural block. This means that only the surgical area is numb. Most patients are able to go home within 24 hours.
We will encourage you to get up and start walking right after your surgery. That’s because there will be a lot of swelling and inflammation, and moving the joint is important to prevent it from getting stiff.
Physical therapy after knee replacement surgery is vital, and we have a program that allows you to do your PT at home via telehealth. You’re guided by a therapist who monitors you on a computer screen. We were offering this option even before the COVID-19 pandemic, but now we’ve ramped it up and it’s great. If you prefer to meet with a physical therapist in person, you can do that.
Your recovery time will vary, depending on whether you have a partial or full knee replacement. You’ll need to walk with a cane for at least a few weeks, and you won’t be able to go back to work right away.
For the first four to six weeks after surgery, therapy will focus on improving your range of motion. Many people start with muscles that are atrophied, or weakened, especially if they were limiting their activities for a long time before surgery. For them, it may take longer to recover, making it important to continue an exercise program focused on building strength. After three months, most people are close to fully recovered, although you may still have small aches and pains for a while longer.
There are very few long-term limitations after knee replacement surgery. The main thing I tell my patients to avoid is long-distance running. It’s high impact and repetitive, and it puts a lot of force on your knee. Most other physical activities and sports are fine. What’s more important is that you not do anything that makes you feel uncomfortable. Some people are bothered by kneeling, because it compresses the joint and puts direct pressure on it. There’s no harm in kneeling, but if it bothers you, you should put a cushion underneath your knee, especially if you’re kneeling on a hard surface.
The main reason we put limitations on your activities is that we want your implants to last a lifetime. If you are younger—in your 40’s & 50’s, for example—it’s more important for you to follow these restrictions. We don’t have a set lifespan for these implants and past experience has shown that the vast majority of knee implants last at least 20 to 30 years. Our goal however is to last a lifetime.
Dr. Steven B. Haas is Chief of the Knee Service at HSS and holds the John N. Insall Chair in Knee Surgery. He is a leader in advancing surgical techniques and pain control, which allows for more rapid recovery from knee replacement.