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.
