Your Medical e-Magazine

Your knees. Over a lifetime, these hard-working joints have helped you walk, jump, dance–maybe even climb a mountain. But years of wear, tear, injury and perhaps arthritis have taken their toll. At first, one or both of your knees ached a bit after a long walk or lively tennis match. Now, simple, everyday activities are painful. Rest and medication are no longer effective. Once, painful knees would have sidelined you permanently. That may not be true today. Knee replacement surgery now helps more than 137,000 Americans get back on their feet each year. It may be the treatment you need to resume an active, pain-free lifestyle.

Cartilage cushion

Your knee is an engineering marvel. More than a simple hinge, it has one of the widest ranges of motion of any joint in your body. Not only does it bend, but it also slides, glides and swivels. In addition, it absorbs the force of up to seven times your body’s weight when you use it.

To do all this requires a symphony of bones, muscles, tendons, ligaments and other tissues working together. The bottom end of your thighbone (femur) rests atop your shinbone (tibia). When you bend your knee, the ends of these two bones move against each other, much like a hinge. In between is a cushion of cartilage–tough, shiny-white tissue that keeps the bones from rubbing together. Ligaments connect the thigh and shin bones, while muscles and tendons stabilize the joint and enable it to move. Your kneecap (patella) helps protect the joint and anchors important tendons.

Replacing diseased tissue

Time, injury and disease can affect all of these parts. Pain, swelling and stiffness can result. But since the 1970s, knee replacement surgery has offered people with chronic, debilitating knee pain a chance to resume an active lifestyle. Also known as total knee arthroplasty (ARTH-ro-plas-tee), the procedure has become as successful as hip replacement surgery–one of the century’s best-known medical advances. Knee replacement surgery involves removing or resurfacing parts of your thighbone, shinbone or kneecap, and putting in prosthesis made of metal alloy and high-density plastic. Pain relief comes from replacing the diseased bone or tissue with the new knee parts.

 While most who undergo knee replacement are age 60 or older, surgeons occasionally replace knees in people who are younger. However, the active lifestyles of younger people may cause greater wear and stress on the artificial knee, requiring it to be replaced in the future.  

Common causes

The most common reason for surgery is osteoarthritis, which causes a gradual deterioration of the cartilage between the thigh and shin bones. Without the shock-absorbing cartilage, the bones begin to rub together, causing pain.

Less common reasons for knee replacement include:

Rheumatoid arthritis–An inflammation of the tissue surrounding your joints, rheumatoid arthritis can cause deterioration of cartilage and other parts of the joint.

Post-traumatic arthritis–This type of arthritis results from a knee injury and can cause debilitating pain even years later.

Realignment and replacement

Before recommending surgery, your doctor may advise you to first try pain medication, physical therapy, anti-inflammatory medication, avoiding activities that cause pain and, if necessary, losing weight. If these aren’t effective, surgery may be an option. The procedure is performed by an orthopedic surgeon, a doctor who specializes in the muscle and skeletal systems. The operation lasts about two hours and is done under spinal or general anesthesia. Much of the operation focuses on getting your joint ready for the new knee. After making an incision, your surgeon moves aside your muscles, kneecap and connective tissues. Before the area is ready for the prosthesis, diseased bone must be removed.

 Your existing connective tissues are realigned and will continue to hold the joint together after the prosthesis is in place. Leg bones damaged by arthritis may also need to be realigned. The prosthesis usually consists of several parts not directly connected to each another. One of the largest is made of metal alloy and attaches to the end of your femur Anchoring your new knee joint in place“) where diseased bone has been removed. Another major component, also of metal alloy, resembles a tray on a pedestal. The surgeon anchors the pedestal of the tray into the shaft of your shinbone. The platform of the tray has a surface of high-density plastic. It provides a resting place for the metal component attached to your femur. The plastic acts as the new joint’s cartilage. The replacement may also include another small component–a circular piece of plastic that attaches to your kneecap to replace cartilage or diseased bone.  

Leave a Reply