What is Bicompartmental Knee Replacement?

If your knee is severely damaged by arthritis or injury, it may be hard for you to perform simple activities such as walking or climbing stairs. You may even begin to feel pain while you're sitting or lying down.

If medications, changing your activity level, and using walking supports are no longer helpful, you may want to consider knee replacement. By resurfacing your knee's damaged and worn surfaces, knee replacement can relieve your pain, correct your leg deformity, and help you resume relatively normal activities. A partial knee replacement is a less invasive procedure than total knee replacement – done if only part of your knee is damaged by arthritis.

How the Normal Knee Works

The knee is the largest joint in the body. Nearly normal knee function is needed to perform routine everyday activities. The knee is made up of the lower end of the thighbone (femur), which rotates on the upper end of the shinbone (tibia), and the kneecap (patella), which slides in a groove on the end of the femur. Large ligaments attach to the femur and tibia to provide stability. The long thigh muscles give the knee strength.

Normally, the joint surfaces where these three bones touch are covered with articular cartilage, a smooth substance that cushions the bones and enables them to move easily.

All remaining surfaces of the knee are covered by a thin, smooth tissue liner called the synovial membrane. This membrane releases a special fluid that lubricates the knee which reduces friction to nearly zero in a healthy knee.

Normally, all of these components work in harmony. But disease or injury can disrupt this harmony, resulting in pain, muscle weakness, and less function.

Common causes of knee pain and loss of knee function

The most common cause of chronic knee pain and disability is arthritis. Osteoarthritis, rheumatoid arthritis, and traumatic arthritis are the most common forms.

Osteoarthritis usually occurs after the age of 50 and often in an individual with a family history of arthritis. 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.

Rheumatoid Arthritis is a disease in which the synovial membrane becomes thickened and inflamed, producing too much synovial fluid which over-fills the joint space. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain and stiffness.

Osteonecrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones.

Traumatic Arthritis can follow a serious knee injury. A knee fracture or severe tears of the knee's ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

How the partially replaced knee works

The diseased cartilage and irritated nerve endings have been replaced by highly durable materials, both at the femur and at the tibia (knee cap not shown). Full, free painless range of motion has been restored. (Oblique view of a left knee replacement, view image).

Realistic Expectations About Knee Replacement

An important factor in deciding whether or not to have knee replacement surgery is understanding what the procedure can and can't do.

More than 90 percent of individuals who undergo unicondylar knee replacement experience a dramatic reduction of knee pain and a significant improvement in the ability to perform common activities of daily living. However, unicondylar knee replacement won't make you a super-athlete or allow you to do more than you could before you developed arthritis.

Following surgery, you will be advised to avoid some types of activity for the rest of your life, including jogging and high impact sports.

With normal use and activity, every knee replacement develops some wear in its plastic cushion. Excessive activity or weight may accelerate this normal wear and cause the knee replacement to loosen and become painful. With appropriate activity modification, knee replacements can last for many years.

About the Surgery

The procedure itself takes about one to two hours. Your orthopedic surgeon will remove the damaged cartilage and bone and then position the new metal and plastic joint surfaces to restore the alignment and function of your knee.

Many different types of designs and materials are currently used in partial knee replacement surgery. Nearly all of them consist of two components: the femoral component (made of a highly polished strong metal), the tibial component (made of a durable plastic often held in a metal tray).

After the Surgery

Bruising on the side of the operated leg is not uncommon after joint replacement – this sometimes lasts 1-2 weeks post-operatively.

You also may experience some swelling and stiffness in the operated leg after the surgery – this may last weeks to months after the surgery and is entirely normal. You may feel some numbness in the skin around your incision.

 These symptoms often diminish with time and most patients find these are minor compared to the pain and limited function they experienced prior to surgery.

Improvement of knee motion is a goal of partial knee replacement. The motion of your knee replacement after surgery is predicted by the motion of your knee prior to surgery. Many people with arthritis have limited knee motion before surgery and it is important to note that their final motion may improve somewhat, but will often never be as full as it was prior to the onset of arthritis.

Most patients can expect to bend and straighten the replaced knee and to bend the knee sufficiently to go up and down stairs and get in and out of a car. Kneeling is usually uncomfortable, but it is not harmful. Occasionally, you may feel some soft clicking of the metal and plastic with knee bending or walking – this is entirely normal. These differences often diminish with time and most patients find these are minor, compared to the pain and limited function they experienced prior to surgery.

Your new knee may activate metal detectors required for security in airports and some buildings. Tell the security agent about your knee replacement if the alarm is activated.

 

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