While there are many different types of joints in the skeletal system, each type fits within one of three categories. The first of these categories includes joints that do not move, known technically as fibrous joints. A second category, called cartilaginous joints, includes joints that have a limited range of movement. The final category, synovial joints, is made up of joints that have a wide range of motion. It is the synovial joints of the skeletal system which facilitate many bodily movements.
Fibrous joints occur where two pieces of bone are connected to one another in such a way that the connection point does not move. The joint which connects these bones is made up of a tough ligament, providing a rigidity that can help protect the fragile organs that lie beneath them. Examples of fibrous joints in the skeletal system include the joints which connect the bones of the skull and the joints that join the teeth to the jaw.
Those joints in the skeletal system which offer limited movement are known as cartilaginous joints. As their name suggests, these joints are made out of cartilage, a type of tissue which is more flexible than that which comprises fibrous joints. Cartilaginous joints can be found in between the vertebrae of the spine. It is these joints which allow the spine to twist and bend.
The joints in the skeletal system responsible for many crucial bodily movements are the synovial joints. This category of highly movable joints is made up of a combination of cartilage and a structure known as a synovial capsule. The synovial capsule secretes a liquid called synovial fluid which acts as a kind of “grease” for the joints, allowing them to move easily.
Six individual joint types fall within the category of the synovial joints: ball-and-socket joints, hinge joints, pivot joints, saddle joints, gliding joints, and condyloid joints. Found in the hips and shoulders, ball-and-socket joints can rotate in many directions, and consist of a “cup” which surrounds a round-ended bone. The knees and elbows are hinge joints, which can be extended or bent, and the neck is a pivot joint, which allows for a rotating movement around a central axis. Saddle joints, gliding joints, and condyloid joints are primarily found at the conjunctions of the small bones of the hands, wrists, feet, and ankles, and allow for the up and down or back and forth movement of these body parts.
