Knee

The knee is the joint connecting the bone of the upper leg to the bones of the lower leg.

Description

The structures that help provide stability to the knee are the bones of the leg and thigh, cartilage, muscles, ligaments, and tendons.

Role of Knee in the Body

It allows a hinge-like motion between the upper and lower leg, and it also provides stability and strength to help support the weight of the body. Flexibility, strength, and stability are essential for proper posture, standing, and motions like walking, running, jumping, turning, and bending down.

How It Works

The Parts of the Knee

Like any joint, the knee is composed of bones and cartilage, ligaments, tendons, and muscles. See the diagram, and take a closer look at the different parts of the knee.

Bones and cartilage

The knee joint is made up of 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 (knee cap). The patella is 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 knee 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 (men-NISS-sky). The menisci are two crescent-shaped discs (each called a meniscus (men-NISS-kus) 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 several muscles involved in moving the knee. The four quadriceps muscles on the front of the thigh work to straighten the knee from a bent position. The hamstring muscles, which run along the back of the thigh from the hip to just below the knee, help to bend the knee. Several muscles of the hip help to bring the leg towards the body or away and provide added support. The large muscle of the calf (the gastrocnemius) attaches above the knee and helps to control the knee especially while walking or running.

Tendons and ligaments

The quadriceps tendon connects the quadriceps muscle to the patella and provides the power to straighten the knee. From the patella there is a tendon called the patellar tendon. It is considered an extension of the quadriceps muscles as it works to convey the pulling force to extend the lower leg.

The following four ligaments connect the femur and tibia and give the joint strength and stability:

• The medial collateral ligament (MCL), which runs along the inside of the knee joint, provides stability to the inner (medial) part of the knee.
• The lateral collateral ligament (LCL), which runs along the outside of the knee joint, provides stability to the outer (lateral) part 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.

Knee Capsule

The knee capsule 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.

Diseases of the Knee

Injuries

Each of these structures may be the source of potential knee problems. Injuries to the knee and other problems can have a significant impact on a person's life. They may limit participation in sports or reduce mobility in doing simple tasks such as walking or rising from a chair.

Conditions

Multiple diseases may have as a symptom pain, swelling or fluid in the joint of the knee. Lupus, Rheumatoid Arthritis, Gout and other inflammatory and autoimmune disease. The physician should rule out all of these if the history and symptoms are pertinent.

Related Professions

Inflammatory diseases of the join are usually seen by a Rheumatologyst and physical damage can be seen either by a Orthopedic Surgeon or a Sports Medicine physician.