When a knee is so severely damaged by disease or injury, an artificial knee replacement may be considered. During knee replacement surgery, joint surfaces are substituted or replaced by prosthesis.
Who might be a candidate for knee replacement?
The most common condition that results in the need for knee replacement surgery is osteoarthritis, a degenerative joint disease, which affects mostly middle-aged and older adults. Osteoarthritis is characterized by the breakdown of joint cartilage and adjacent bones in the knee. There are other forms of arthritis, such as rheumatoid arthritis and arthritis that results from a knee injury, that can lead to degeneration of the knee joint.
The decision to replace the painful knee with an artificial one is a joint decision between the patient and surgeon. Other alternative treatments may first be used, including but not limited to assistive walking devices and anti-inflammatory medications.
What happens before surgery?
In addition to a complete medical history, the surgeon may perform a complete physical examination, including x-rays, to ensure that the patient is in good health before undergoing surgery. In additions, the patient may also meet with a physical therapist to discuss rehabilitation after the surgery and undergo blood tests (or any other ordered test). It is a good idea that the patient attends our pre-operative total joint replacement class to understand what to expect in the hospital and ideas to prepare for discharge.
How will the worn out knee be replaced with an artificial knee?
Although each procedure varies, generally the surgery to replace a knee will last up to two hours. In knee replacement surgery, the ends of the damaged thigh and lower leg (shin) bones and usually the kneecap are capped with artificial surfaces lined with metal and plastic. Usually, orthopedic surgeons replace the entire surface at the ends of the thigh and lower leg bones. However, it is becoming increasingly popular to replace just the inner knee surfaces or the outer knee surfaces, depending on the location of the damage. This is called a partial replacement, or unicompartmental replacement. The orthopedic surgeon usually secures knee joint components to the bone with cement.
The prosthesis (artificial knee) is comprised of the following three components:
- Tibial component (to replace the top of the tibia, or shin bone)
- Femoral component (to replace the two femoral [thighbone] condyles and the patella groove)
- Patellar component (to replace the bottom surface of the kneecap that rubs against the thigh bone)
Orthopedic surgeons sometimes use general anesthesia for joint replacement surgeries, which means the patient will be unconscious during surgery. However, usually they will use regional anesthesia, which means the patient can't feel the area of the surgery and is sedated. The choice of anesthesia depends on the surgeon, anesthesiologist, the patient's overall health and, to some degree, the patient's preference.
When the patient wakes up from surgery, there will be a bandage on the knee and possibly a drain to collect fluid from the joint. A compression pump (SCDs), which squeezes the patient's legs to keep the blood circulating, preventing blood clots, will be in place while the patient is in bed. Some surgeons recommend that the patient spends time in the continuous passive motion machine (CPM) to help keep the new knee flexible. The CPM has a cradle for the operative leg and is fitted to the leg length and joint position. The amount it bends the knee is adjustable.
The patient will be taught to do simple breathing exercises with an incentive spirometer to help prevent congestion in the lungs while the activity level is decreased. The patient will also learn to move their feet up and down (ankle pumps) to flex the muscles and keep blood circulating.
Knee replacement surgeries usually require an in-hospital stay of one to two night or more. Pain medication will be administered to keep the patient comfortable. Anticoagulants (blood thinners) will also be administered to help prevent blood clots. At any time, if the patient becomes nauseated or uncomfortable, medications will be administered by the nurse.
Rehabilitation (rehab) after a knee replacement can be very intense. The main goal of rehab is to allow the patient to bend the new knee at least to 90 degrees — enough to do daily activities such as walking, climbing stairs, sitting in a chair and getting up from it, as well as getting in and out of a car. Most patients can get considerably more bending than 90 degrees after surgery. One factor, however, that affects how much bend the patient gets after surgery depends on how much bend the patient had before surgery. In order for the patient to get the most benefit from knee replacement surgery, it is important to take part in physical therapy while in the hospital and after going home from the hospital.
During the hospital stay, a case manager will assess the patient and their goals for discharge. The case manager will help with equipment that may be needed at home, set up with a home health agency and inpatient rehabilitation if needed.