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Anatomy of the knee

These sophisticated joints include bones, tendons, cartilage, muscles and ligaments.

The knee joint is the junction of three major bones—the femur (the thigh bone or upper leg bone), tibia (shin bone) and patella (knee cap).

The patella, 3 to 4 inches long and 2 to 3 inches wide, sits over the other bones at the front of the knee to provide protection.

Other parts of the knee include:

Menisci—pads of connective tissue between the tibia and femur that provide cushioning and absorb shock.

Articular cartilage—tough, elastic tissue that covers the ends of all three bones in the knee joint. Cartilage absorbs shock and allows smooth motion.

Muscles—including the quadriceps at the front of the thighs, which help straighten the leg from a bent position, and the hamstrings on the back of the thighs, which bend the leg at the knee.

Ligaments—strong bands of tissue that connect the bones in the knee joint, provide stability and prevent the knee from moving in the wrong direction. They include the:

  • MCL (medial collateral ligament) on the inner side of the knee.
  • LCL (lateral collateral ligament) on the outer side of the knee.
  • ACL (anterior cruciate ligament) in the center of the knee.
  • PCL (posterior cruciate ligament) in the back center of the knee.

Tendons—soft tissue that connects muscles to bones.

Sources: National Institute of Arthritis and Musculoskeletal and Skin Diseases; American Academy of Orthopaedic Surgeons

reviewed 9/30/2019

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