Knee[nee] – Anatomy. The joint of the leg that allows for movement between the femur (thighbone) and tibia (shinbone) and has a sesamoid bone called the patella (kneecap) that offers protection and increases the power of the muscles surrounding the knee.

Your knees are the largest and the most commonly injured joints in your body. Unlike your shoulder that moves in all directions, your knees appear only to bend and straighten, but actually their movements are much more complex and involve rotation, translation, sliding and rolling.

Ligaments

There are four main ligaments connecting the bones at the knee joint and provide stability when you walk, run and jump. They are the:

• Anterior cruciate (ACL)
• Posterior cruciate (PCL)
• Medial collateral (MCL)
• Posterolateral corner ligaments including the lateral collateral ligament (LCL)

Cartilage and Meniscus

The joint surface of the knee is covered with a thin, but robust, layer of cartilage over the ends of the femur, tibia and patella, and, along with the meniscus, allow the knee surfaces to articulate, move smoothly–almost frictionless and painlessly along each other. The cartilage and meniscus lack a blood supply and get their nutrition from the joint fluid. Without a blood supply, and because of their relatively less active cellular makeup, they cannot maintain or repair themselves. The cartilage and meniscus are extremely durable, but in time with “wear and tear” or following injury, they break down, fail and lead to meniscus tears, cartilage damage and eventually symptomatic (pain, stiffness, swelling) arthritis (failure of this protective joint surface).

Tendon and Muscle

Tendons also help provide knee joint stability and movement. They act like strong cables connecting your muscles to your bones. These muscle-tendon units cross joints from different directions to move or hold the joint in different directions or positions. Like other parts of your knee, they are susceptible to injury and tendonitis. The two knee tendons most commonly injured are the quadriceps and patellar tendons.