The human body contains more than 200 joints -- sites where 2 or more bones come together. Joints not only allow for movement but can also provide stability. The human body has 3 different types of joints, based on their structure: fibrous, cartilaginous and synovial. Each type serves a different function and is found at specific locations within the body.
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Fibrous joints are held together by strong connective tissue with only a slight capacity to stretch. This tough connection allows very little movement between the joined bones, thus providing great stability. Fibrous joints are found in the skull, which is made up of several bone plates held tightly together to protect the fragile brain. A dense band of tissue connects the radius and ulna bones in the lower arm forming a fibrous joint that keeps these bones stable as the forearm rotates. The lower leg bones, called the tibia and fibula, are also joined by a fibrous joint that limits movement between these bones. Fibrous joints also hold the teeth firmly within their sockets in the jaw bones.
Cartilaginous joints allow for slight movement and occur where bone ends are covered by a somewhat flexible, compressible connective tissue called cartilage. Some cartilaginous joints are temporary, such as those present during the growth of the long bones of the arms and legs in children. Other cartilaginous joints allow limited flexibility and provide shock absorption. These joints are found where the ribs attach to the breastbone and between some of the pelvic bones. They also occur between the bones of the spine, where they provide strength, flexibility and cushioning.
Synovial joints allow the greatest degree of movement due to their structure. These joints consist of a capsule of connective tissue that encloses a space or cavity between the bones. The cavity contains fluid that lubricates the joint and reduces friction. Most joints of the body are synovial joints, which are found in the elbow, shoulder, knee, wrist, hand, ankle and foot. There are several different types of synovial joints that are classified by their shape and the range of movement they allow.
Types of Synovial Joints
The many synovial joints of the human body enable movement of various types, largely based on their shape. For example, the elbow and knees joints are classified as hinge joints and act like the hinges of a door, with one bone remaining stationary and the other bone moving along a single axis. The highly movable ball-and-socket joints of the shoulder and hip allow movement in all directions. Another common type of synovial joint is the condyloid joint, which is found in places like the knuckles and wrist. These joints allow up-and-down movement like a hinge joint but also permit some side-to-side movement.