What Is Knee Replacement?
The knee joint is a connection of the femur, or thigh bone, and the tibia (shinbone), and is capped with the patella. The ends of the femur and tibia are coated with articular cartilage, which allows them to glide together and prevents bone-on-bone contact. Other pieces of cartilage called menisci sit between the tibia and femur and act as shock absorbers.
Knee replacement surgery, or knee arthroplasty, aims to remove damaged bone and cartilage and replace them with metal and plastic parts. More than 600,000 total knee replacements are performed each year in the United States, and by 2030 that number is estimated to jump to 3.48 million knee replacements annually.
Common Reasons for Knee Replacement
Most chronic knee pain is caused by one of three types of arthritis:
- Osteoarthritis—This is a degenerative disease that causes wear-and-tear. The articular cartilage capping the femur and tibia wears away, causing bone-on-bone contact, pain and often bone spurs.
- Rheumatoid arthritis—This is an autoimmune disease that causes the body’s immune system to attack the synovium, a thin fluid-filled membrane that surrounds the knee joint. Rheumatoid arthritis causes synovial inflammation that damages cartilage.
- Post-traumatic arthritis—This form of arthritis occurs after a knee injury. A fracture to the femur or tibia may cause articular cartilage tears.
Candidates for Knee Replacement
Not everyone with one of these arthritic conditions is a candidate for knee replacement surgery. Those for whom knee replacement is the best option may:
- Have a deformity of the knee due to their condition
- Have chronic inflammation that does not respond to rest or conservative treatments
- Have moderate pain at rest
- Have severe pain that limits daily activities
- Have tried more conservative treatments such as anti-inflammatory medications, physical therapy, cortisone injections, weight loss or other, less extensive surgeries
Most people who have their knee or knees replaced are between the ages of 50 and 80.
There are a number of considerations on both the surgeon side and the patient side. The surgeon will usually begin with a medical history and physical examination, which can include X-rays, to determine if the patient is a good candidate for knee replacement surgery. Occasionally dental and urinary exams may be ordered, as a healthy mouth and urinary tract may reduce the risk of post-surgical infection.
Patients must manage their expectations regarding outcomes of knee replacement. According to the American Academy of Orthopaedic Surgeons, more than 90 percent of people undergoing knee replacement surgery will have a reduction in pain and an increase in quality of life.
However, patients should be aware that a knee replacement will not allow them to do more than they could when their knees were healthy. The surgeon may also recommend against taking part in certain high-impact activities such as running, jumping or contact sports–permanently.
How the Procedure Is Performed
The procedure is usually broken down into four steps. First, the surgeon removes damaged articular cartilage and usually a small amount of bone from the ends of the femur and tibia. Next, the cartilage and bone is replaced with metal that is cemented or anchored into the bones. Then, the surgeon implants a piece of plastic on the underside of the kneecap. Finally, plastic spacers are inserted between the prostheses. The patient will be sedated with spinal anesthesia during the operation.
Surgeons use a number of pain management techniques to control pain immediately after the surgery. Some patients can go home the day of the surgery, while others may need a brief (one to two day) hospital stay.
Physical therapy will begin almost immediately, sometimes even the same day of the surgery. It is important to get moving as soon as possible, both to speed recovery time and to prevent blood clots, which can form when blood pools due to lack of movement. Infection, pneumonia and stiffness are other potential complications of the surgery.
Exercise at home is a critical component of recovery after a knee replacement surgery. Walking, performing specific exercises prescribed by a physical therapist and resuming normal activities will all help minimize complications.
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