How Common Are Knee Problems? What Causes Them?

According to the American Academy of Orthopaedic Surgeons, more than 4.1 million people seek medical care each year for a knee problem.

Some knee problems result from wear of parts of the knee, such as occurs in osteoarthritis. Other problems result from injury, such as a blow to the knee or sudden movements that strain the knee beyond its normal range of movement.

How Can People Prevent Knee Problems?

• Some knee problems, such as those resulting from an accident, cannot be foreseen or prevented. However, a person can prevent many knee problems by following these suggestions:
• First warm up by walking or riding a stationary bicycle, then do stretches before exercising or participating in sports. Stretching the muscles in the front of the thigh (quadriceps) and back of the thigh (hamstrings) reduces tension on the tendons and relieves pressure on the knee during activity.
• Strengthen the leg muscles by doing specific exercises (for example, by walking up stairs or hills, or by riding a stationary bicycle). A supervised workout with weights is another pathway to strengthening leg muscles that benefit the knee.
• Avoid sudden changes in the intensity of exercise. Increase the force or duration of activity gradually.
• Wear shoes that both fit properly and are in good condition to help maintain balance and leg alignment when walking or running. Knee problems may be caused by flat feet or overpronated feet (feet that roll inward). People can often reduce some these problems by wearing special shoe inserts (orthotics). Maintain appropriate weight to reduce stress on the knee. Obesity increases the risk of degenerative (wearing) conditions such as osteoarthritis of the knee.

What Kinds of Doctors Treat Knee Problems?

Extensive injuries and diseases of the knees are usually treated by an orthopaedic surgeon, a doctor who has been trained in the nonsurgical and surgical treatment of bones, joints, and soft tissues (for example, ligaments, tendons, and muscles). Patients seeking nonsurgical treatment of arthritis of the knee may also consult a rheumatologist (a doctor specializing in the diagnosis and treatment of arthritis and related disorders).

What Are the Major Structures of the Knee? What Do They Do?

The knee joint works like a hinge to bend and straighten the lower leg. It permits a person to sit, stand, and pivot. The knee is composed of the following parts (see diagram):

Bones and Cartilage

The knee joint is the junction of three bones—the femur (thigh bone or upper leg bone), the tibia (shin bone or larger bone of the lower leg), and the patella (kneecap). The patella is about 2 to 3 inches wide and 3 to 4 inches long. It sits over the other bones at the front of the knee joint and slides when the leg moves. It protects the knee and gives leverage to muscles.

The ends of the three bones in the knee joint are covered with articular cartilage, a tough, elastic material that helps absorb shock and allows the knee joint to move smoothly. Separating the bones of the knee are pads of connective tissue called menisci, which are divided into two crescent-shaped discs positioned between the tibia and femur on the outer and inner sides of each knee. The two menisci in each knee act as shock absorbers, cushioning the lower part of the leg from the weight of the rest of the body, as well as enhancing stability.

Muscles

There are two groups of muscles at the knee. The quadriceps muscle comprises four muscles on the front of the thigh that work to straighten the leg from a bent position. The hamstring muscles, which bend the leg at the knee, run along the back of the thigh from the hip to just below the knee.

Ligaments

Ligaments are strong, elastic bands of tissue that connect bone to bone. They provide strength and stability to the joint. Four ligaments connect the femur and tibia:

• The medial collateral ligament (MCL) provides stability to the inner (medial) aspect of the knee.
• The lateral collateral ligament (LCL) provides stability to the outer (lateral) aspect of the knee.
• The anterior cruciate ligament (ACL), in the center of the knee, limits rotation and the forward movement of the tibia.
• The posterior cruciate ligament (PCL), also in the center of the knee, limits backward movement of the tibia.

Other ligaments are part of the knee capsule, which is a protective, fiber-like structure that wraps around the knee joint. Inside the capsule, the joint is lined with a thin, soft tissue, called synovium.

Tendons

Tendons are tough cords of tissue that connect muscle to bone. In the knee, the quadriceps tendon connects the quadriceps muscle to the patella and provides power to extend the leg. The patellar tendon connects the patella to the tibia. Technically, it is a ligament, but it is commonly called a tendon.

How Are Knee Problems Diagnosed?

Doctors use several methods to diagnose knee problems.

• Medical history—the patient tells the doctor details about symptoms and about any injury, condition, or general health problem that might be causing the pain.
• Physical examination—the doctor bends, straightens, rotates (turns), or presses on the knee to feel for injury and discover the limits of movement and location of pain.
• Diagnostic tests—the doctor uses one or more tests to determine the nature of a knee problem.
• X ray (radiography)—an x-ray beam is passed through the knee to produce a two-dimensional picture of the bones.
• Computerized axial tomography (CAT) scan—x rays lasting a fraction of a second are passed through the knee at different angles, detected by a scanner, and analyzed by a computer. This produces a series of clear cross-sectional images ( slices”) of the knee tissues on a computer screen. CAT scan images show soft tissues more clearly than normal x rays. Individual images can be combined by computer to give a three-dimensional view of the knee.
• Bone scan (radionuclide scanning)—a very small amount of radioactive material is injected into the patient's bloodstream and detected by a scanner. This test detects blood flow to the bone and cell activity within the bone, and can show abnormalities in these processes that may aid diagnosis..
• Magnetic resonance imaging (MRI)—energy from a powerful magnet (rather than x rays) stimulates tissues of the knee to produce signals that are detected by a scanner and analyzed by computer. This creates a series of cross-sectional images of a specific part of the knee. An MRI is particularly sensitive for detecting damage or disease of soft tissues, such as ligaments and muscles. As with a CAT scan, a computer can be used to produce three-dimensional views of the knee during MRI.
• Arthroscopy—the doctor manipulates a small, lighted optic tube (arthroscope) that has been inserted into the joint through a small incision in the knee. Images of the inside of the knee joint are projected onto a television screen.