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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.