Joints are the areas where 2 or more bones meet. Most joints are mobile, allowing the bones to move. Basically, the knee is 2 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 2 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. 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 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.

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:

1. You will be asked to remove clothing and will be given a gown to wear.

2. An intravenous (IV) line may be started in your arm or hand.

3. You will be positioned on the operating table.

4. A urinary catheter may be inserted.

5. If there is excessive hair at the surgical site, it may be clipped off.

6. The anesthesiologist will continuously monitor your heart rate, blood pressure, breathing, and blood oxygen level during the surgery.

7. The skin over the surgical site will be cleansed with an antiseptic solution.

8. The doctor will make an incision in the knee area.

9. 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 2 types is used to replace a knee.
   
   The prosthesis is generally comprised of 3 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).

10. The incision will be closed with stitches or surgical staples.

11. A drain may be placed in the incision site to remove fluid.

12. 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 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 drainage 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 shoe horn

• 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.