Joints with caps is a term used to describe the knee joints, which are the largest and most complex joints in the human body. They are formed by the lower end of the femur (thigh bone) and the upper end of the tibia (shin bone), and are held together by a fibrous capsule and ligaments. The knee joint is also protected by two crescent-shaped pieces of cartilage called menisci, which act as shock absorbers and help to distribute the weight evenly across the joint.