The knee is one of the largest and most complex joints in the body. The knee is made up of bones, cartilage, ligaments, and tendons. The knee joins the thigh bone (femur), the shin bone (tibia), the smaller bone that runs alongside the tibia (fibula) and the kneecap (patella) altogether to make up the knee joint. The knee is a synovial joint, meaning it contains a fluid-filled capsule.

Tendons connect the knee bones to the leg muscles that move the knee joint, and ligaments join the knee bones and provide stability to the knee.