Knee replacement surgery, or knee arthroplasty, offers pain relief and improved movement to those suffering from advanced arthritis of the knee or a weakened knee joint. In most cases, the cartilage is worn away and the surface of the knee becomes pitted, eroded, and uneven. This causes pain, stiffness, instability, and a change in body alignment.
Total knee replacement (TKR) is most common and involves removing the damaged bone and cartilage and replacing the knee joint with implants to restore the natural motion and function of the knee.
You may need surgery if:
To understand TKR, you should be familiar with the structure of the knee, a complex joint consisting of three bones: the femur (thighbone), the tibia (shinbone) and the patella (kneecap).
Strong ligaments also connect the powerful muscles of the thigh and calf to the bones around the knee and power the knee motion and function. Conditioning and strengthening the muscles through physical therapy and dedicated exercise is most important in restoring and maintaining good knee function and comfort. Cartilage (such as the meniscus) and other soft tissues cover and cushion the bones to help them glide together smoothly. When you bend or straighten your knee, the end of the femur rolls against the end of the tibia, and the patella glides in front of the femur.
When the cartilage cushions wears thin or away completely, the knee becomes arthritic. (This is known as osteoarthritis of the knee.) The bones then rub together and become rough. The resulting inflammation and pain cause reduced motion and difficulty in walking.
Treatment for damage and arthritis of the knee joint depends on multiple factors, such as the condition of the knee and the patient’s age and activity level. At first, nonsurgical methods including physical therapy, anti-inflammatory medication, and weight loss are used to manage the condition.
Most patients who need surgical intervention will require total knee replacement (TKR), which involves replacing the entire joint. In this case, surgeons shave down the damaged bone areas and fix implants, or prosthesis, over the ends of the bone so that they glide smoothly against one another. These implants are generally made of metal and plastic and each implant is customized for the individual to provide maximum compatibility.
The weightbearing surfaces of a TKR are smooth, as in a normal knee. A femoral component covers the end of the thighbone, a tibial component covers the top of the shinbone and the patellar component covers the underside of the kneecap.
Most femoral components are metal alloys (cobalt chromium) or metal-ceramic alloys (oxidized zirconium). The patellar component is plastic (polyethylene). The tibial insert component is also plastic (polyethylene). The tibial tray component can be made of the following materials:
On occasion, only a portion of the knee may be involved, so a minimally invasive partial knee replacement or resurfacing (arthroscopy) might be recommended. See the following animations for further details:
Improvements in surgical techniques, technology, and materials have made knee replacement surgery one of the most successful orthopedic procedures, with over 700,000 performed successfully in the US annually. Most people experience less pain, increased movement, and improved quality of life afterwards. However, the implants do not last forever.
Implants are expected to function for at least 15 to 20 years in 85% to 90% of patients. Over time, general wear and tear will loosen the implants and may cause pain, loose particles, infection, and instability. Once this occurs, orthopedic surgeons recommend having knee revision surgery.
While infection after surgery is rare, a knee replacement implant cannot defend itself from infection if bacteria are introduced to the body. Learn more about infection prevention in joint replacement.
Hospital for Special Surgery has been at the forefront of modern knee replacement since the operation's inception in 1968. Each year, HSS leads the field in these ways:
If you have already decided on surgery, there are certain steps that can improve your recovery time and results. It is always important to follow your knee replacement surgeon’s instructions before and after surgery, as well as your rehabilitation therapist’s recommendations.
TKR surgery generally takes 1 to 1.5 hours, but you can expect to be in the operating room for over two hours. Once your surgery is complete, you will recover in the hospital for two to three days and begin your rehabilitation within 24 hours. Your nurse or therapist will help you sit up and stand. Patients begin with a walker and within a few days usually progress to using a straight cane and climbing stairs.
Here is additional material on preparing for knee replacement: