What you might casually refer to as a “fake knee” is known as an artificial knee or a knee replacement. It’s a structure that replaces a knee severely damaged by arthritis.

An orthopedic surgeon may recommend a total knee replacement if your knee joint is badly damaged from arthritis and the pain is seriously affecting your daily life.

Knee replacements come in different designs, but the overall goal is to cover the worn-out joint surface with an artificial material such as metal, plastic, or ceramic.

In a healthy knee joint, the cartilage that lines the ends of the bones protects the bones from rubbing together and allows them to move freely against one another.

Arthritis affects this cartilage, and over time, it can become worn away, allowing the bones to rub against one another. This often results in pain, swelling, and stiffness.

During knee replacement surgery, the damaged cartilage and a small amount of underlying bone are removed and replaced with metal and a special type of plastic. The plastic acts to replace the function of the cartilage and allows the joint to move freely.

Every knee replacement procedure is different. However, for 90% of people who have the surgery, it provides significant pain relief.

Research also suggests that more than 60-80% of people are satisfied with their artificial knee after their procedure.

That said, your outlook depends on your specific case and the type of implant you and your surgeon will choose to use.

Learn more: Is there a ‘best’ knee replacement implant? What to know when choosing.

Research from 2019 showed that approximately 82% of total knee replacements were still functioning and doing well at 25 years.

The American Association of Hip and Knee Surgeons (AAHKS) reports that only 0.5-1% of all knee replacement surgeries result in failure each year.

Learn more: Clinical outcomes and statistics of knee replacement

Your new knee doesn’t come with an owner’s manual, but recognizing potential issues and preparing for them can help maximize your quality of life after surgery.

It can take some time to get used to the new knee, so it’s important to understand what is normal during recovery and how having an artificial knee can affect your day-to-day life after surgery. Consider the following:

Clicking and sounds from your knee

It’s not unusual for your artificial knee to make some popping, clicking, or clunking sounds, particularly when you bend and extend it. This is most often normal, so you shouldn’t be alarmed.

Several factors can affect the likelihood of these noises or sensations after surgery, including the specific artificial knee (prosthesis) used.

If you’re concerned about the sounds the device is making, check with your doctor.

New sensations

After knee replacement, it’s common to experience new sensations and feelings around your knee. You may have skin numbness on the outer part of your knee and have a sensation of “pins and needles” around the incision.

In some cases, bumps may also appear on the skin surrounding the incision. This is common and, most of the time doesn’t indicate a problem.

If you’re concerned about new sensations, don’t hesitate to talk with your healthcare team for more information.

Warmth around the knee

It’s typical to experience some swelling and warmth in your new knee. Some describe this as a feeling of “hotness.” This usually subsides over a period of several months.

Some people report feeling mild warmth years later, particularly after they exercise. Icing may help reduce this sensation.

Weak or sore leg muscles

Many people experience soreness and weakness in their legs following surgery. Remember, your muscles and joints need time to strengthen!

A 2018 study reported that the quadriceps and hamstring muscles may not regain their full strength with usual rehabilitation exercises, so talk with your physical therapist about ways to strengthen these muscles.

Sticking with an exercise program can make your new joint as strong as that of an adult of the same age with their original knee.

Bruising

Some bruising after surgery is expected. It normally disappears within a couple of weeks.

Your surgeon may prescribe a blood thinner after surgery to prevent blood clots in the lower leg. These medications can increase the risk of bruising and bleeding.

Monitor any persistent bruising and talk with your doctor if it doesn’t go away.

Learn more: What to expect from bruising, pain, and swelling after a total knee replacement.

Stiffness

Mild to moderate stiffness isn’t unusual after knee replacement surgery. Keeping active and closely following your physical therapist’s recommendations will help you achieve the best possible result following your operation.

If you experience extreme or worsening stiffness and soreness that significantly limits the motion in your knee, you should let your doctor know.

Weight gain

A study from 2017 found that among people who had a total knee replacement, 54% reported weight gain after their procedure.

According to another 2018 study, about 22-33% of people gain more than 2.5% of their body weight and have a lower chance of losing weight in the 1-2 years after the procedure.

It’s important to try to avoid putting on weight after joint replacement surgery, as the extra pounds place unnecessary strain on your new knee.

You can minimize the chance of weight gain by staying active and adhering to a healthy diet. Some sports and activities are better than others following total knee replacement.

If you’re concerned about the way your knee is functioning, speak to your surgeon. It’s critical to the health and longevity of your knee replacement.

Getting the answers to your questions will increase your comfort level and your overall satisfaction.