The most common cause of chronic knee pain and disability is arthritis. Although there are many types of arthritis, most knee pain is caused by just three types: osteoarthritis, rheumatoid arthritis, and posttraumatic arthritis.

• Osteoarthritis. This is an age-related wear-and-tear type of arthritis. It usually occurs in people 50 years of age and older, but may occur in younger people, too. The cartilage that cushions the bones of the knee softens and wears away. The bones then rub against one another, causing knee pain and stiffness.

Osteoarthritis often results in bone rubbing on bone. Bone spurs are a common feature of this form of arthritis.

• Rheumatoid arthritis. This is a disease in which the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain, and stiffness. Rheumatoid arthritisis the most common form of a group of disorders termed "inflammatory arthritis."

• Posttraumatic arthritis. This can follow a serious knee injury. Fractures of the bones surrounding the knee or tears of the knee ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

A total knee replacement (also called total knee arthroplasty) might be more accurately termed a knee "resurfacing" because only the surfaces of the bones are replaced.
There are four basic steps to a knee replacement procedure:

• Prepare the bone. The surgeon removes the damaged cartilage surfaces at the ends of the femur and tibia, along with a small amount of underlying bone.
• Position the metal implants. The surgeon replaces the removed cartilage and bone with metal components that re-create the surface of the joint. These metal parts may be cemented or "press-fit" into the bone.
• Resurface the patella.The surgeon cuts the undersurface of the patella (kneecap) and resurfaces it with a plastic button. Some surgeons do not resurface the patella, depending upon the case.
• Insert a spacer. The surgeon inserts a medical-grade plastic spacer between the metal components to create a smooth gliding surface.

(Left) Severe osteoarthritis. (Right) The arthritic cartilage and underlying bone has been removed and resurfaced with metal implants on the femur and tibia. A plastic spacer has been placed in between the implants..

The decision to have total knee replacement surgery should be a cooperative one between you, your family, your primary care doctor, and your orthopaedic surgeon. Your primary care doctor may refer you to an orthopaedic surgeon for a thorough evaluation to determine if you might benefit from this surgery.

When Surgery Is Recommended

There are several reasons why your orthopaedic surgeon may recommend total knee replacement surgery. People who benefit from total knee replacement often have:
• Severe knee pain or stiffness that limits everyday activities, including walking, climbing stairs, and getting in and out of chairs. It may be hard to walk more than a few blocks without significant pain, and it may be necessary to use a cane or walker.
• Moderate or severe knee pain while resting, either day or night.
• Chronic knee inflammation and swelling that does not improve with rest or medications.
• Knee deformity — bowing in or out of the knee.
• Failure to substantially improve with other treatments, such as anti-inflammatory medications, cortisone injections, lubricating injections, physical therapy, or other surgeries.

Total knee replacement may be recommended for patients with bowed knee deformity, like that shown in this clinical photo.

Candidates for Surgery
There are no absolute age or weight restrictions for total knee replacement surgery. Recommendations for surgery are based on a patient's pain and disability, not age. Most patients who undergo total knee replacement are aged 50 to 80, but orthopaedic surgeons evaluate patients individually. Total knee replacements have been performed successfully at all ages, from the young teenager with juvenile arthritis to the elderly patient with degenerative arthritis.

(Left) In this X-ray of a normal knee, the space between the bones indicates healthy cartilage (arrows). (Right) This X-ray of a knee that has become bowed from arthritis shows severe loss of joint space (arrows).

Your orthopaedic surgeon will review the results of your evaluation with you and discuss whether total knee replacement is the best method to relieve your pain and improve your function. Other treatment options — including medications, injections, physical therapy, or other types of surgery — will also be considered and discussed.

Realistic Expectations An important factor in deciding whether to have total knee replacement surgery is understanding what the procedure can and cannot do.

Most people who have total knee replacement surgery experience a dramatic reduction of knee pain and a significant improvement in the ability to perform common activities of daily living. But total knee replacement will not allow you to do more than you could before you developed arthritis.

With normal use and activity, every total knee replacement implant begins to wear in its plastic spacer. Excessive activity or weight may speed up this normal wear and may cause the knee replacement to loosen and become painful. Therefore, most surgeons advise against high-impact activities such as running, jogging, jumping, or other high-impact sports for the rest of your life after surgery.

Realistic activities following total knee replacement include unlimited walking, swimming, golf, driving, light hiking, biking, ballroom dancing, and other low-impact sports.

Medical Evaluation
If you decide to have total knee replacement surgery, your orthopaedic surgeon may ask you to schedule a complete physical examination with your primary care doctor several weeks before the operation. This is needed to make sure you are healthy enough to have the surgery and complete the recovery process.

Patients with chronic medical conditions, like heart disease or kidney disease, may also be evaluated by a specialist, such as a cardiologist or nephrologist, before the surgery.

Tests
Several tests, such as blood and urine samples, and an electrocardiogram, may be needed to help your orthopaedic surgeon plan your surgery.

Medications
Tell your orthopaedic surgeon about the medications you are taking. They will tell you which medications you should stop taking and which you should continue to take before surgery.

Dental Evaluation
Although the incidence of infection after total knee replacement is very low, an infection can occur if bacteria enter your bloodstream. To reduce the risk of infection, major dental procedures (such as tooth extractions and periodontal work) should be completed before your total knee replacement surgery.

Urinary Evaluations
People with a history of recent or frequent urinary infections should have a urological evaluation before surgery. Older men with prostate disease should consider completing required treatment before undertaking knee replacement surgery. Social Planning Although you will be able to walk with a cane, crutches, or a walker soon after surgery, you will need help for several weeks with such tasks as cooking, shopping, bathing, and doing laundry.

Home Planning
Several modifications can make your home easier to navigate during your recovery. The following items may help with daily activities:
• Safety bars or a secure handrail in your shower or bath
• Secure handrails along your stairways
• A stable chair for your early recovery with a firm seat cushion (and a height of 18 to 20 inches), a firm back, two arms, and a footstool for intermittent leg elevation
• A toilet seat riser with arms, if you have a low toilet
• A stable shower bench or chair for bathing
• Removing all loose carpets and cords
• A temporary living space on the same floor, if possible, because walking up or down stairs will be more difficult during your early recovery

You will either be admitted to the hospital on the day of your surgery day.

Anesthesia
Upon arrival at the hospital or surgery center, you will be evaluated by a member of the anesthesia team. The most common types of anesthesia are:
• General anesthesia (you are put to sleep)
• Spinal, epidural, or regional nerve block anesthesia (you are awake, but your body is numb from the waist down)
The anesthesia team, with your input, will determine which type of anesthesia will be best for you.


Procedure The surgical procedure usually takes 1 to 2 hours. Your orthopaedic surgeon will remove the damaged cartilage and bone, then position the new metal and plastic implants to restore the alignment and function of your knee.

Different types of knee implants are used to meet each patient's individual needs.


(Left) An X-ray of a severely arthritic knee. (Right) The X-ray appearance of a total knee replacement. Note that the plastic spacer inserted between the components does not show up in an X-ray.