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Once considered high-tech, joint replacements are now a common operation. Surgeons replace more than a million hips and knees each year in the U.S. Studies show joint replacements can significantly relieve pain and increase mobility in about 90% of people who get them.

"Joint replacement can be a life-changing procedure for the right patients," says Tariq Nayfeh, MD, PhD, assistant professor of orthopaedic surgery at Johns Hopkins Bayview Medical Center in Baltimore, MD, "but it won't help everyone with hip or knee pain."

If you're suffering, how do you know if joint replacement is right for you? How can you weigh the potential benefits -- less pain and a more active life -- with the risks that always come with surgery? WebMD talked to some experts to find out when joint replacement makes sense -- and when it may not.

Reasons for Hip or Knee Replacement

Who needs a hip or knee replacement? Surgeons look at a few basic criteria. They include:

  • Pain and stiffness. Most people who need joint replacement have severe pain that makes it difficult to walk, climb stairs, get up from a chair, or carry on with other normal activities. The pain is also chronic, lasting at least six months, says Matthew Austin, MD, an orthopaedic surgeon and spokesman for the American Academy of Orthopaedic Surgeons.
  • Poor quality of life. It's not only pain itself that matters, but how the pain affects your daily life, Austin says. Do your joint problems limit what you can do? Do they affect your mood?
  • Bone damage. X-rays and other imaging may show severe joint damage from osteoarthritis or other conditions.
  • Non-surgical treatment failure. Medication, injections, devices -- like walkers -- and other treatments aren't helping enough.
  • Deformity. Your knee is severely swollen or your leg is bowed.

When Joint Replacement May Not Help

Joint replacement may not be a good idea if you have these problems.

  • Infection. "The number one reason to avoid a joint replacement is recent infection anywhere in the body," says Nayfeh. That infection could spread to the area of the joint immediately after surgery or months later, causing serious problems -- including joint problems and further surgery.
  • Other health problems. Anyone with a history of heart attacks or strokes or with currently uncontrolled diabetes may be at increased risk for complications. People who are very obese may need to lose weight before getting a joint replacement.
  • Uncertain cause of pain. Your surgeon must be certain that the pain you feel is really caused by joint damage and that replacing the joint will help. "People can have pain that feels like joint pain, but the scans don't seem to show damage in the joint," says Nayfeh. There are lots of reasons for severe pain in the knee or hip -- such as nerve damage -- but a joint replacement won't help with them.
  • Pain when at rest but not when walking. "Joint replacements are well established for treating pain that gets worse when walking," says Nayfeh. "But people who only have pain while at rest seem less likely to benefit."