Knee replacement surgery restores the weight-bearing façade of a damaged, worn, or diseased knee joint. The aim is to remove pain and restore mobility.

It is also known as knee arthroplasty, or "knee resurfacing."

The surgeon caps the ends of the bones that form the knee joint with metal or plastic components, or implants a prosthetic, shaped as a joint. This enables the knee to move properly.

Replacement knee surgery can help patients whose knee or knees have degenerated due to osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis, when an injury has damaged the knee.

It is considered a routine procedure. Every year, over 600,000 knee replacement surgeries are carried out in the United States. Most patients are aged between 50 and 80 years. Over 90 percent of patients experience a dramatic improvement in pain levels and mobility.

As long as the patient follows the surgeon's instructions for knee care, in 90 percent of cases, a replacement knee still functions well after 15 years, and 80 to 85 percent of replacements last 20 years.

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As the covering of the knee bones wear out and the ends of the bones rub together, damage can occur.

Knee replacement is a kind of arthroplasty. Arthroplasty literally means "the surgical repair of a joint," and it involves the surgical reconstruction and replacement of degenerated joints, using artificial body parts, or prosthetics.

When the articular cartilage of the knee becomes damaged or worn, it becomes painful and the knee is hard to move. Instead of sliding over each other, the bones rub and crush together.

With a prosthesis, the patient will feel less pain, and the knee will move properly.

Why have knee replacement surgery?

There are three common reasons for the procedure:

Osteoarthritis: this type of arthritis is age related, caused by the normal wear and tear of the knee joint. It mostly affects patients aged over 50 years, but younger people may have it.

Osteoarthritis is caused by inflammation, breakdown, and the gradual and eventual loss of cartilage in the joints. Over time, the cartilage wears down and the bones rub together. To compensate, the bones often grow thicker, but this results in more friction and more pain.

Rheumatoid arthritis: also called inflammatory arthritis, the membrane around the knee joint to become thick and inflamed. Chronic inflammation damages the cartilage, causing soreness and stiffness.

Post-traumatic arthritis: this type of arthritis is due to a severe knee injury. When the bones around the knee break or the ligaments tear, this will affect the knee cartilage.

Who might need a knee replacement?

Knee surgery may be suitable for patients who experience:

  • Severe knee pain or stiffness that prevents them from carrying out everyday tasks and activities, such as walking, going upstairs, getting in and out of cars, getting up from a chair
  • Moderate but continuous knee pain that continues while sleeping or resting
  • Chronic knee inflammation and swelling that does not improve after taking medications or resting
  • Knee deformity, where there is a noticeable arch on the inside or outside of the knee
  • Depression, resulting from an inability to carry out daily or social activities

If the other available treatment options have not worked, surgery may be the best option.

Types of knee replacement surgery

Knee replacement can be total or partial.

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If a knee is damaged by arthritis, replacing part of the joint may bring relief.

Total knee replacement (TKR): Surgery involves the replacement of both sides of the knee joint. It is the most common procedure.

Surgery lasts between 1 and 3 hours. The individual will have less pain and better mobility, but there will be scar tissue, which can make it difficult to move and bend the knees.

Partial knee replacement (PKR): Partial replacement replaces only one side of the knee joint. Less bone is removed, so the incision is smaller, but it does not last as long as a total replacement.

PKR is suitable for people with damage to only one part of the knee. Post-operative rehabilitation is more straightforward, there is less blood loss and a lower risk of infection and blood clots.

The hospital stay and recovery period are normally shorter, and there is a higher chance of more natural movement.

Knee arthroplasty involves major surgery, so pre-operative preparation, medical consultations, and physical evaluations usually begin a month before the set date of the operation.

Preparatory and diagnostic tests will include checking blood count, seeing how the blood clots, carrying out electrocardiograms (ECGs), and urine tests.

Surgery is usually performed either under general, spinal, or epidural anesthetic.

During the procedure, the orthopedic surgeon will remove the damaged cartilage and bone, and then position the new implant, made of metal, plastic, or both, to restore the alignment and function of the knee.

A patient who has knee replacement surgery will be hospitalized for 1 to 3 days, depending on how well they follow and respond to rehabilitation.

There will be pain, but a day after the procedure medical staff will encourage patients to get up and try to walk about, usually with some kind of walking aid. It is important to follow the instructions for rehabilitation.

Physical therapy sessions aim to strengthen the knee. These may be painful, but they significantly reduce the risk of future complications.

Patients who do not have help at home may need to stay in the hospital for longer.

Recovering at home

According to the American Association of Hip and Knee Surgeons (AAHKS), it can take up to 3 months to recover completely from a knee replacement surgical procedure.

Patients can normally drive again after 4 to 6 weeks, and return to work after 6 to 8 weeks. Physical therapy may be provided for 3 months.

Patients must comply with the instructions given by doctors, nurses and the physical therapist.

The patient may be asked:

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Crutches may be needed during recovery.
  • To take iron supplements to aid wound healing and muscle strength
  • Not to bend down and lift heavy things, at least for the first few weeks
  • Not to stay standing still for long periods, as the ankles might swell
  • To use crutches, a walking stick, or a walker until the knee is strong enough to take your body weight
  • To use all medications according to the instructions
  • To carry out the recommended exercises to encourage proper mobility
  • To keep the affected leg raised on a footstool when sitting
  • To avoid soaking the wound until the scar is completely healed, because of the risk of infection
  • To monitor for any signs and symptoms of infections, blood clots or pulmonary embolism

Precautions should be taken to avoid a fall, as this might mean further surgery.

Useful measures include:

  • Ensuring there is a secure handrail and using a stable, nonslip bench or chair in the shower
  • Where possible, sleeping downstairs
  • Securing any loose carpets and removing wrinkly mats around the house
  • Removing or securing any trip hazards, such as loose wires

Most people can resume normal activities 6 weeks after the operation, but there may be some pain and swelling for up to 3 months, and scar tissue and muscles will still be healing for the next 2 years.

Items that may help at home include:

  • A raised toilet seat
  • A reaching stick for picking up items from the floor
  • A long-handled shoe horn

Patients who have undergone knee replacement surgery can expect to participate in moderate and low-impact exercise activities, such as walking, swimming, and biking, but they should avoid extreme sports.

Total knee replacements have low complication rates.

Possible complications include:

  • Infection, which affects fewer than 2 percent of patients
  • A blood clot in the legs, known as deep vein thrombosis (DVT)
  • A blood clot in the lungs, or pulmonary embolism
  • A fracture during or after surgery
  • Nerve damage, leading to numbness or weakness
  • Continued pain or stiffness

Medical help should be sought at once if the patient has signs of an infection or a blood clot.

Signs of infection include a fever, redness, swelling, bleeding, draining, or an increase in pain around the area of the operation.

If there is redness, tenderness, or swelling below the knee, or in the calf, ankle, or foot, this may indicate a blood clot in the leg. Shortness of breath or chest pain may suggest a blood clot in the lung.

Other common complications include:

  • Allergic reaction to the bone cement
  • Excess bone forming around the artificial knee joint, leading to restricted movement in the knee
  • Excess scar tissue restricts movement of the knee
  • Instability of the kneecap, resulting in painful dislocation to the outer side of the knee
  • Ligament, artery, or nerve damage around the knee joint
  • Dislocated kneecap
  • Bleeding in the knee joint
  • Wearing down of implant surfaces, causing components to loosen

Further surgery may be necessary if the replacement becomes loose or wears out, if there is a serious infection, or if the person has a fall.

Depending on how severe the damage is, a number of alternative procedures may be possible. However, knee replacement surgery tends to have better long-term results.

Kneecap replacement can be done when only the kneecap is damaged. It is a short surgical procedure with a fast recovery time.

Mini-incision surgery (MIS) involves a small cut in front of the knee, through which specialized instruments are inserted to maneuver around the tissue. The procedure is less harmful to the joint, and the recovery time is quicker and less painful.

Image-guided surgery uses computerized images and infrared beacons to perform the surgery while the surgeon works from another, the operating theater.

Arthroscopic washout and debridement involves the insertion of an arthroscope, a tiny telescope, through small incisions in the knee. The surgeon washes out the knee with saline solution clears away small fragments of bone. This is not advisable for patients with severe arthritis.

Osteotomy is an open operation in which the shin bone is cut and re-aligned. After this, the patient will no longer bear their body weight on one part of the knee. It may be used for younger patients with limited arthritis, to postpone a knee replacement.

Autologous chondrocyte implantation (ACI) introduces new cartilage from the patient´s own cells into the damaged area. The cells are matured artificially in a test tube. This procedure is more common in cases of accidental injury.

Learn more about the causes of severe knee pain here.