This most common form of arthritis mainly affects joints in your hands, knees, hips and spine. Meniscus Tear, Patellar Instability Septic Arthritis (Infectious Arthritis) The knee joint is one of the biggest joints in the body and its located in the middle of the leg, where the thigh bone (femur) meets the shin bone (tibia). The knee joints play a crucial role in leg movment, supporting the body and keeping the body balanced.