Knee Replacement

Definition

Total knee replacement is a surgical procedure in which injured or damaged parts of the knee joint are replaced with artificial parts, called prostheses.

Description

The knee is the largest joint in the body. It is commonly known as the "hinge" joint, because it allows the knee to flex (bend) and extend (straighten), similar to the hinge on a door. The knee also has the ability to rotate (turn) and translate (glide).

The knee joint is composed of the tibia (shin bone), the femur (thigh bone) and the patella (kneecap). Each bone is covered with a layer of cartilage that cushions, protects and keeps the bones from rubbing together. Ligaments (bands of tissues) connect the femur and tibia, while muscles and tendons stabilize the knee and enable it to move. The patella helps protect the knee joint and anchor the tendons while allowing movement.

Reasons for Knee Replacement

The most common causes of knee joint damage are:

Osteoarthritis: a disease in which there is a gradual deterioration, caused by time and usage of the cartilage between the femur and the tibia. Osteoarthritis occurs in most people over the age of 60, but it can occur in younger people, too, due to injury to the knee or a congenital joint deformity. Osteoarthritis causes pain, swelling, creaking and stiffness in the knee joint.

Rheumatoid arthritis: an autoimmune disorder (the immune system attacks the tissues of the body) in which the tissues surrounding the knee joint become inflamed, causing deterioration of cartilage and other parts of the knee. Rheumatoid arthritis usually starts in early adulthood or middle age, but in the case of juvenile rheumatoid arthritis, it can begin in childhood. Rheumatoid arthritis causes pain, swelling and stiffness in the knee joint.

Post-traumatic arthritis: a type of arthritis that results from a knee injury.

Who Is A Candidate For Knee Replacement?

A person would be considered for total knee replacement if there is:

• Daily pain

• The pain is severe enough to restrict work, recreation and ordinary activities of daily living

• Significant stiffness in the knee

• Significant instability (constant giving way) of the knee

• Significant deformity (knock-knees or bow-legs) that hinders normal function of the knee

• Damage from arthritic conditions, such as osteoarthritis, rheumatoid arthritis or post-traumatic arthritis

Evaluation

After understanding the symptoms, limitations and progression of the knee problem, the doctor will perform a variety of tests that may include measuring the knee's range of motion, analyzing muscle strength and evaluating the legs for variances, such as bow-legs or knock-knees. Additionally, an x-ray of the knee will be done to assess the damage. From the medical history, physical examination and test results, the doctor will determine if total knee replacement is necessary.

Preoperative Evaluation

Before surgery, joints adjacent to the damaged knee (such as the hip and ankle) are evaluated. Replacing a knee joint adjacent to a severely damaged joint may not yield significant improvement in knee function. All medications that the patient is taking prior to surgery are reviewed. Routine blood tests for liver and kidney function, as well as urine tests for signs of anemia, infection, or abnormal metabolism are given. A chest x-ray and an EKG are performed to exclude significant heart and lung disease which may preclude surgery or anesthesia.

Procedure

Total knee replacement is performed by an orthopedic surgeon (a doctor specializing in the muscle and skeletal systems). The operation lasts about an hour and a half to three hours, and is performed under spinal or general anesthesia. The surgeon begins the procedure by making an incision (cut) that runs 3 to 4 inches above the knee and down along the inside of the patella to several inches below the knee. The surgeon will then move aside the muscles, patella and connective tissues and remove the diseased bone.

The prostheses (artificial parts) that will replace the damaged bone consist of three components - the femoral component, the tibial component and the patellar component. The femoral (thigh) component is made of metal and covers the end of the thigh bone. This part may be cemented to the bone using bone cement (methyl methacrylate), or for some prostheses, inserted without cement for tissues to grow into the porous coating of the device. (This method is called biological fixation.)

The tibial (or shin bone) component is made of metal and polyethylene (plastic) and covers the top of the tibia. The metal forms the base of this component, while the plastic is attached to the top of the metal to serve as a cushion and smooth gliding surface between the metal of femorial and tibial components. The tibial component can be secured to the bone with bone cement or fixed biological as well. The patellar component is made of plastic or a combination of plastic and metal, and affixed with or without bone cement. The muscles and connective tissues are put back into place and repaired, and the incision is closed.

Complications

Complications of total knee replacement include:

• Blood clots in the legs and lungs

• Urinary tract infection

• Chronic knee pain and stiffness

• Bleeding into the knee joint

• Nerve damage

• Blood vessel injury

• Loosening of the prosthesis

Rehabilitation

After surgery, the patient will stay in the hospital three to five days. During this period, they will undergo physical therapy to adjust to the new knee. At home, the person will use crutches or a walker for about six weeks and then a cane for another three to six weeks.

An exercise program and physical therapy are a must if the patient is to regain movement of the knee. When muscles are not used, they become weak and do not perform well in supporting and moving the body. The leg muscles are probably weak because they have not been used much, due to the knee problems. After surgery, an exercise program will be outlined by the doctor and physical therapist to include quadriceps setting, terminal knee extension, knee flexion, straight leg raising and use of heat and ice. Note: the physical therapist will demonstrate how to do all exercises properly.

Prognosis

An artificial knee is not a normal knee, nor is it as good as a normal knee. The operation will provide pain relief for at least 10 years. If the patient does not have other health problems that inhibit their activity, they can resume any active sports or heavy labor which was enjoyed before the knee problem.

About 85 to 90 percent of all total knee replacements are successful for up to 10 years. A second operation is necessary if there is loosening of the prosthesis due to cement problems, fractures, weight gain and activity. The cement used to adhere the prosthesis to the bone may start to crumble, or the bone may melt away from the cement. Excessive weight and activity will put undue stress and strain on the joints.

Questions to Ask Your Doctor

Am I a candidate for total knee replacement?

How long after the surgery can normal activities resume?

What can and cannot be done with the new knee?

Will the new knee need to be replaced in the future?