TOTAL KNEE REPLACEMENT

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CONTENTS:

Introduction

The purpose of this booklet is to provide basic information about the diagnosis and treatment of knee disorders. There are many structures about the knee, and problems can occur in any one of them.

Normal Anatomy

The normal anatomy of the knee includes bone, cartilage, ligaments, meniscus, muscles and tendons. The bones involved in the knee joint include the lower end of the thigh bone (femur), the top end of the leg bones (tibia and fibula), and the knee cap (patella). These bones are separated by cartilage, which is normally a low friction surface that allows smooth motion of the joint.

The knee joint consists of three distinct compartments: one is the joint between the femur and the tibia on the inner half of the knee; the second is between the femur and the tibia on the outer half of the knee; and the third compartment is between the patella and the femur. In addition to the cartilage covering the bones, two menisci lie between the femur and tibia (one in each compartment), which function as shock absorbers. Ligaments hold the bones together in the same way that a hinge holds a door to the door frame. There are four main ligaments in the knee: collateral ligaments on each side of the knee, and the posterior and anterior cruciate ligaments which are inside the joint. There are two main groups of muscles about the knee. The muscles on the front part of the thigh are the quadriceps muscle; they extend or straighten the knee. They are attached into the top of the kneecap, and the bottom of the kneecap is attached to the tibia by the patellar tendon. The muscles on the back side of the thigh are called the hamstring muscles and function to flex or bend the knee.

Knee Abnormalities 

Disease can involve any of the normal anatomic structures discussed in the previous section.

Bone

Many problems occur in bones, but the two most frequent in the knee are fractures and avascular necrosis. Avascular necrosis, which results from a reduction in the blood supply to the bone, is death of the bone, which may lead to painful collapse of the dead segment and overlying cartilage. When this process occurs, arthritis usually follows.

Cartilage And Arthritis

Arthritis occurs when there is loss of cartilage lining the knee joint. There are two main categories. The first is osteoarthritis, which is also known as "wear-and-tear" arthritis and degenerative arthritis. When the cartilage is worn away, the knee is painful. (See X-ray.) There is no effective way to stimulate regeneration of cartilage.
Another type of knee arthritis is caused by rheumatoid arthritis, which is a systemic disease with an inflammatory arthritis. The basic problem is that the body's immune system for some reason goes awry and begins to attack normal joints, which causes inflammation and eventually destruction of the joint.

Meniscus

Meniscal problems usually involve tears of this piece of cartilage that can displace and become wedged between the joint surfaces causing the knee to lock. Treatment of this condition involves removing the torn portion of the meniscus, which often can be done by arthroscopy.

Ligaments

As mentioned earlier, ligaments provide stability to the knee; if ligaments are torn, the knee may become unstable. Ligament injuries often require operative treatment in the form of repair or replacement.

Muscles

Injury can occur to either the muscles or tendons around the knee. Muscle tears (strains) are treated with rest and medication for pain. Incomplete tears of the tendon are treated as muscle strains. Complete tearing of a tendon may require surgical repair.


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For questions or comments,
please contact
msmiller@med.unc.edu
January 2006