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Anatomy of the Knee

The knee is the joint where the bones of the upper leg meet the bones of the lower leg, allowing hinge-like movement while providing stability and strength to support the weight of the body. Flexibility, strength, and stability are needed for standing and for motions like walking, running, crouching, jumping, and turning.

Several kinds of supporting and moving parts, including bones, cartilage, muscles, ligaments, and tendons, help the knees do their job. Each of these structures is subject to disease and injury. When a knee problem affects your ability to do things, it can have a big impact on your life. Knee problems can interfere with many things, from participation in sports to simply getting up from a chair and walking. Take a closer look at the different parts of the knee in the diagrams below.

anatomy of the knee joint

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 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. The menisci are two crescent-shaped discs, each called a meniscus, 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 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.

Tendons and Ligaments

The quadriceps tendon connects the quadriceps muscle to the patella and provides the power to straighten the knee. The following four ligaments connect the femur and tibia and give the joint strength and stability:

  • The medial collateral ligament, which runs along the inside of the knee joint, provides stability to the inner (medial) part of the knee.
  • The lateral collateral ligament, which runs along the outside of the knee joint, provides stability to the outer (lateral) part of the knee.
  • The anterior cruciate ligament, in the center of the knee, limits rotation and the forward movement of the tibia.
  • The posterior cruciate ligament, also in the center of the knee, limits backward movement of the tibia.

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.

Above content provided by National Institute of Arthritis and Musculoskeletal and Skin Diseases in partnership with Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.

March 2011

Contact Information

Carl J. Shapiro Department of Orthopaedics
Beth Israel Deaconess Medical Center
330 Brookline Avenue
Boston, MA 02215
617-667-3940

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