Procedures guide

Knee Replacement

Knee replacement is surgery that replaces damaged parts of the knee joint with artificial parts. It is most often done for severe arthritis.

Last updated 3 sources

At a Glance

  • Knee replacement replaces worn joint surfaces with metal and plastic parts called a prosthesis.
  • The most common reason is osteoarthritis that causes ongoing pain and limits daily activities.
  • It can be a total replacement or a partial replacement of one part of the knee.
  • Physical therapy is a major part of recovery.
  • Full recovery commonly takes several months.

What It Is

The knee joint is where the thigh bone (femur), shin bone (tibia), and kneecap (patella) meet. These surfaces are normally covered with smooth cartilage. When cartilage wears away, as in arthritis, bones can rub together and cause pain, stiffness, and swelling.

In knee replacement, the surgeon removes damaged bone and cartilage and covers the ends of the bones with artificial parts. A plastic spacer is placed between the metal parts to allow smooth movement.

Knee replacement is usually considered after other treatments, such as exercise, physical therapy, weight management, medicines, and injections, no longer control symptoms well enough.

Common Terminology

Arthroplasty
Surgery to replace or rebuild a joint.
Total knee replacement (TKR or TKA)
Replacement of all the main joint surfaces of the knee.
Partial (unicompartmental) knee replacement
Replacement of only one damaged part (compartment) of the knee.
Prosthesis
The artificial joint parts, typically made of metal alloys and medical-grade plastic.
Osteoarthritis
Wear-and-tear arthritis in which the cartilage cushioning the joint breaks down over time.
Range of motion
How far a joint can bend and straighten.
Deep vein thrombosis (DVT)
A blood clot in a deep vein, usually in the leg, which is a known risk after joint surgery.
Revision surgery
A later operation to repair or replace a knee implant.

Why It Is Done

Knee replacement is generally considered for:

  • Severe osteoarthritis causing ongoing knee pain and stiffness.
  • Rheumatoid arthritis or other inflammatory arthritis that has damaged the joint.
  • Arthritis that develops after a knee injury (post-traumatic arthritis).
  • Knee deformity, such as bowing in or out, related to joint damage.
  • Pain that limits walking, sleeping, or daily activities despite other treatments.

How It Is Performed

This is a general description; details vary by surgeon and implant.

  • The surgery is done under general anesthesia or spinal anesthesia, often with a nerve block for pain control.
  • The surgeon makes a cut over the front of the knee to reach the joint.
  • Damaged cartilage and a small amount of bone are removed from the ends of the thigh and shin bones.
  • Metal parts are attached to the bone ends, often with bone cement, and a plastic spacer is placed between them.
  • The underside of the kneecap may also be resurfaced with a plastic piece.
  • The surgery commonly takes about one to two hours.

Before the Procedure

Before surgery, in general:

  • X-rays of the knee and a physical exam help the surgeon plan the procedure.
  • A pre-surgery checkup may include blood tests, an ECG, and a review of other health conditions.
  • The care team typically reviews all medicines and supplements, including blood thinners, and gives specific instructions.
  • Some programs offer pre-surgery classes or exercises to prepare for recovery.
  • Preparing the home, such as removing tripping hazards and arranging help, is commonly suggested.

Recovery Overview

Recovery varies, but generally includes:

  • Getting up and walking with help, often on the day of surgery or the next day.
  • Some people go home the same day or after a short hospital stay; others go to a rehabilitation facility.
  • Physical therapy to rebuild strength and range of motion, which continues for weeks to months.
  • Measures to help prevent blood clots, such as moving the legs, compression devices, or medicines chosen by the care team.
  • Pain, swelling, and stiffness that gradually improve over several weeks; full recovery can take several months or longer.
  • Many modern knee implants last many years, though they can wear out over time.

Risks and When Complications May Be Discussed

Possible risks of knee replacement, which are generally discussed before surgery, include:

  • Blood clots in the legs that can travel to the lungs.
  • Infection of the wound or the joint implant.
  • Ongoing pain or stiffness.
  • Loosening or wear of the implant over time, which may lead to revision surgery.
  • Nerve or blood vessel injury, which is uncommon.
  • Calf pain or leg swelling, fever, or wound redness or drainage are signs surgical teams generally ask to be told about; sudden shortness of breath or chest pain is generally treated as a medical emergency, and in the US people are advised to call 911.

Questions to Ask a Healthcare Professional

General questions people often find useful to bring to an appointment:

  • Have other treatments been fully considered, and when is surgery generally recommended?
  • Is a total or partial knee replacement being considered, and why?
  • What kind of anesthesia and pain control are typically used?
  • What does physical therapy involve, and how long does it last?
  • How are blood clots and infections generally prevented?
  • How long do knee implants usually last?

Sources

This guide was written in plain language from the following authoritative references.

  1. Knee Replacement — MedlinePlus (U.S. National Library of Medicine)
  2. Total Knee Replacement — American Academy of Orthopaedic Surgeons (OrthoInfo)
  3. Knee replacement — NHS

Last updated October 8, 2026. FreeDoc guides are general educational information and are not a substitute for care from a qualified professional.