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What is knee replacement surgery?

When a knee is so severely damaged by disease or injury, an artificial knee replacement may be considered. Knee replacement, also called knee arthroplasty, is a surgical procedure to resurface a knee damaged by arthritis. Metal and plastic parts are used to cap the ends of the bones that form the knee joint, along with the kneecap.
Various types of arthritis may affect the knee joint. Osteoarthritis, a degenerative joint disease that affects mostly middle-aged and older adults, may cause the breakdown of joint cartilage and adjacent bone in the knees. Rheumatoid arthritis, which causes inflammation of the synovial membrane and results in an excessive synovial fluid, can lead to pain and stiffness. Traumatic arthritis, arthritis due to injury, may cause damage to the cartilage of the knee.

Sometimes the cartilage wears away in both knees, and there is a need to implant prosthesis in both knees. This is termed a Bilateral Total Knee Replacement. It can be performed in a single instance or in stages. A simultaneous procedure means to replace both knees on the same day, under one anesthesia. This takes place in the same surgical event, within one hospital stay and is followed by a single rehabilitation period. The staged procedure means that both knee replacements take place as two separate surgical events. Surgeries are performed several months apart one from the other, requiring two hospital stays, two anesthesias and two rehabilitation periods. However, the simultaneous procedure is not available to every patient with problems in both knees, because it implies a high stress for the cardiovascular system. Only patients in a good health condition are appropriate candidates, and special emphasis should be made for an adequate patient selection. Also, the initial rehabilitation is slightly more difficult.

The goal of knee replacement surgery is to resurface the parts of the knee joint that have been damaged and to relieve knee pain that cannot be controlled by other treatments. It may also help to restore motion of knees and straighten the limbs.


Anatomy of the knee

Joints are the areas where two or more bones meet. Most joints are mobile, allowing the bones to move. Basically, the knee is two long leg bones held together by muscles, ligaments, and tendons. Each bone end is covered with a layer of cartilage that absorbs shock and protects the knee.
There are two groups of muscles involved in the knee, including the quadriceps muscles (located on the front of the thighs), which straighten the legs, and the hamstring muscles (located on the back of the thighs), which bend the leg at the knee.

Tendons are tough cords of connective tissue that connect muscles to bones. Ligaments are elastic bands of tissue that connect bone to bone. Some ligaments of the knee provide stability and protection of the joints, while other ligaments limit forward and backward movement of the tibia (shin bone).

The knee consists of the following:

  • Tibia. This is the shin bone or larger bone of the lower leg.
  • Femur. This is the thighbone or upper leg bone.
  • Patella. This is the kneecap.
  • Cartilage. A type of tissue that covers the surface of a bone at a joint. Cartilage helps reduce the friction of movement within a joint.
  • Synovial membrane. A tissue that lines the joint and seals it into a joint capsule. The synovial membrane secretes synovial fluid (a clear, sticky fluid) around the joint to lubricate it.
  • Ligament. A type of tough, elastic connective tissue that surrounds the joint to give support and limits the joint’s movement.
  • Tendon. A type of tough connective tissue that connects muscles to bones and helps to control movement of the joint.
  • Meniscus. A curved part of cartilage in the knees and other joints that acts as a shock absorber, increases contact area, and deepens the knee joint.


Reasons for the procedure

Knee replacement surgery is a treatment for pain and disability in the knee(s). The most common condition that results in the need for knee replacement surgery is osteoarthritis.
Osteoarthritis is characterized by the breakdown of joint cartilage. Damage to the cartilage and bones limits movement and may cause pain. People with the severe degenerative joint disease may be unable to do normal activities that involve bending at the knee, such as walking or climbing stairs because they are painful. The knee may swell or “give-way” because the joint is not stable.
Other forms of arthritis, such as rheumatoid arthritis and arthritis resulting from a knee injury, may also lead to degeneration of the knee joint. In addition, fractures, torn cartilage, and/or torn ligaments may lead to irreversible damage to the knee joint.

If medical treatments are not satisfactory, knee replacement surgery may be an effective treatment. Some medical treatments for a degenerative joint disease may include, but are not limited to, the following:

  • Anti-inflammatory medications.
  • Glucosamine and chondroitin sulfate.
  • Pain medications.
  • Limiting painful activities.
  • Assistive devices for walking (such as a cane).
  • Physical therapy.
  • Cortisone injections into the knee joint.
  • Viscosupplementation injections (to add lubrication into the joint to make joint movement less painful).
  • Weight loss (for obese persons).

There may be other reasons for your doctor to recommend a knee replacement surgery.


Risks of the procedure

As with any surgical procedure, complications can occur. Some possible complications may include, but are not limited to, the following:

  • Bleeding.
  • Infection.
  • Blood clots in the legs or lungs.
  • Loosening or wearing out of the prosthesis.
  • Fracture.
  • Continued pain or stiffness.

If there is an infection, although the risk is low, notify your doctor immediately if you notice:

  • Fever greater than 100 F (37.8 C).
  • Shaking chills.
  • Drainage from the surgical site.
  • Increasing redness, tenderness, swelling and pain in the knee.

An infected knee replacement usually requires surgery to remove the artificial parts and antibiotics to kill the bacteria. After the infection is cleared, another surgery is performed to install a new knee. Your chances of a good or excellent outcome that reduces pain and improves function decline with each additional surgery.
The replacement knee joint may become loose, be dislodged, or may not work the way it was intended. Also, subject to daily stress, even the strongest metal, and plastic parts eventually wear out. You’re at a greater risk of joint failure if you put more stress on the joint with high-impact activities or excessive weight. The joint may have to be replaced again in the future. Nerves or blood vessels in the area of surgery may be injured, resulting in weakness or numbness. The joint pain may not be relieved by surgery. There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.


Before the procedure

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
  • You will be asked to sign a consent form that gives your permission to do the test. Read the form carefully and ask questions if something is not clear.
  • In addition to a complete medical history, your doctor may perform a complete physical examination to ensure you are in good health before undergoing the procedure. You may undergo blood tests or other diagnostic tests.
  • You will be asked to fast for eight hours before the procedure, generally after midnight. This is because the procedure is performed using a general anesthetic (you are put to sleep). You may be able to have occasional sips of water until two hours before the operation.
  • If you are pregnant or suspect that you are pregnant, you should notify your doctor.
  • Notify your doctor if you are sensitive or allergic to any medications, iodine, latex, tape, or anesthetic agents (local and general).
  • Notify your doctor of all medications (prescription and over-the-counter) and herbal supplements that you are taking.
  • Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop some of these medications prior to the procedure.
  • Your doctor may request a blood test before the procedure to determine how long it takes your blood to clot.
  • Notify your doctor if you have a pacemaker.
  • Your doctor might want to know about your teeth, for example, notify your doctor if you wear dentures or have caps or a plate.
  • If you smoke, you should stop smoking as soon as possible prior to the procedure. This is because smoking increases your chances of a serious chest infection and slows down the time your wounds will take to heal. Smoking can also increase your risk of blood clots. Quitting smoking may improve your chances for a successful recovery from surgery and benefit your overall health status.
  • Based on your medical condition, your doctor may request other specific preparation.


Preanesthetic assessment

Anesthesia assessment or evaluation refers to the series of interviews, physical examinations, and laboratory tests that are generally used to assess the general fitness of patients scheduled for surgery and to determine the need for special precautions or additional testing.
A mnemonic has been suggested for pre-anesthetic assessment, to ensure that all aspects are covered. It runs alphabetically :

  • A – Affirmative history; Airway
  • B – Blood hemoglobin, blood loss estimation, and blood availability; Breathing
  • C – Clinical examination; Co-morbidities
  • D – Drugs being used by the patient; Details of previous anesthesia and surgeries
  • E – Evaluate investigations; End-point to take up the case for surgery
  • F – Fluid status; Fasting
  • G – Give physical status; Get consent

Patients may have a meeting with their anesthetist a day before the surgery and ask all kinds of questions pertaining to the surgery, and provide all information as mentioned above.


During the procedure

Knee replacement requires a stay in a hospital. Procedures may vary depending on your condition and your doctor’s practices.
Knee replacement surgery is most often performed while you are asleep under general anesthesia. Your anesthesiologist will discuss this with you in advance.

Generally, knee replacement surgery follows this process:

  • You will be asked to remove clothing and will be given a gown to wear.
  • An intravenous (IV) line may be started in your arm or hand.
  • You will be positioned on the operating table.
  • A urinary catheter may be inserted.
  • If there is excessive hair at the surgical site, it may be clipped off.
  • The anesthesiologist will continuously monitor your heart rate, blood pressure, breathing, and blood oxygen level during the surgery.
  • The skin over the surgical site will be cleansed with an antiseptic solution.
  • The doctor will make an incision in the knee area.
  • The doctor will remove the damaged surfaces of the knee joint and resurface the knee joint with the prosthesis. The knee prosthesis is made up of metal and plastic. The most common type of artificial knee prosthesis is a cemented prosthesis. Uncemented prostheses are not commonly used anymore. A cemented prosthesis attaches to the bone with surgical cement. An uncemented prosthesis attaches to the bone with a porous surface onto which the bone grows to attach to the prosthesis. Sometimes, a combination of the two types is used to replace a knee.

The prosthesis is generally comprised of three components:

The tibial component (to resurface the top of the tibia or shin bone); the femoral [thigh bone] component (to resurface the end of the thighbone; and the patellar component (to resurface the bottom of the kneecap that rubs against the thighbone).

  • The incision will be closed with stitches or surgical staples.
  • A drain may be placed in the incision site to remove fluid.
  • A sterile bandage or dressing will be applied.


After the procedure

In the hospital

After the surgery, you will be taken to the recovery room for observation. Once your blood pressure, pulse, and breathing are stable and you are alert, you will be taken to your hospital room. Knee replacement surgery usually requires an in-hospital stay of several days.
It is important to begin moving the new joint after surgery. A physical therapist will meet with you soon after your surgery and plan an exercise program for you. A continuous passive motion (CPM) machine may be used to begin the physical therapy. This machine moves your new knee joint through its range of motion while you are resting in bed. Your pain will be controlled with medication so that you can participate in the exercise. You will be given an exercise plan to follow both in the hospital and after discharge.
You will be discharged home or to a rehabilitation center. In either case, your doctor will arrange for continuation of physical therapy until you regain muscle strength and a good range of motion.


At home

Once you are home, it is important to keep the surgical area clean and dry. Your doctor will give you specific bathing instructions. The stitches or surgical staples will be removed during a follow-up office visit.
To help reduce swelling, you may be asked to elevate your leg or apply ice to the knee.
Take a pain reliever for soreness as recommended by your doctor. Aspirin or certain other pain medications may increase the chance of bleeding. Be sure to take only recommended medications.

Notify your doctor to report any of the following:

  • Fever.
  • Redness, swelling, bleeding, or other drainages from the incision site.
  • Increased pain around the incision site.

You may resume your normal diet unless your doctor advises you differently.
You should not drive until your doctor tells you to. Other activity restrictions may apply. Full recovery from the surgery may take several months.
It is important that you avoid falls after your knee replacement surgery, because a fall can result in damage to the new joint. Your therapist may recommend an assistive device (cane or walker) to help you walk until your strength and balance improve.

Making certain modifications to your home may help you during your recovery. These modifications include, but are not limited to, the following:

  • Proper handrails along all stairs.
  • Safety handrails in the shower or bath.
  • Shower bench or chair.
  • Raised toilet seat.
  • Long-handled sponge and shower hose.
  • Dressing stick.
  • Sock aid.
  • Long-handled shoehorn.
  • Reaching stick to grab objects.
  • Removing loose carpets and electrical cords that may cause you to trip.
  • Avoiding stair-climbing until recommended by your doctor.

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.



Expect to resume everyday activities within four to eight weeks of surgery, such as driving if you can bend your knee far enough to sit in a car and you have enough muscle control to properly operate the brakes and accelerator. Four to six weeks after knee replacement surgery, you generally can resume most normal. It’s important to stay on your exercise and rehab program but also to not overexert yourself. It might take six months to a full year to get back to the activity level you desire. Make sure you avoiding high impact activities. Your goal is to ensure the long-term success of your implant and surgery. People who have both knees replaced at the same time often take longer to recover than those having surgery on just one knee.



Most people who have a knee replacement experience significant pain relief, improved mobility and a better overall quality of life.
After you’ve recovered, you can enjoy a variety of low-impact activities, such as walking, swimming, golfing or biking. But you should avoid higher impact activities — such as jogging, skiing, tennis, and sports that involve contact or jumping. Talk to your doctor about your limitations.
You should expect to have regular follow-up visits with your surgeon to check on how well you’re doing following your knee(s) replacement surgery. After the first year of regular follow-up, your surgeon may recommend that you come in for a check-up visit once a year.