Understanding Joints: Types and Structures of the Human Skeleton's Connecting Components

A joint, also known as an articulation, is a point where bones and cartilage come together. These joints are important for holding the skeleton together and allowing for movement.

Synovial joints

Joints are classified based on their movement and structure. There are three types of bones based on the amount of movement they allow, including immovable, slightly movable, and freely movable joints. In immovable and slightly movable joints, there is no space between the bones.

On the basis of structure, joints are classified into three types: fibrous joints, cartilaginous joints, and synovial joints.

Fibrous joints are immovable and held together by short fibers embedded in dense connective tissue. Examples include sutures in the skull and the articulation of teeth with the mandible and maxilla.

Cartilaginous joints are slightly movable and are connected by hyaline or fibrocartilage, such as the costal cartilages that connect the ribs to the sternum or intervertebral discs.

Synovial joints are freely movable and contain synovial fluid. These joints have a cavity separating the bones, which is lined by a synovial membrane that produces synovial fluid. Ligaments hold the bones in place, and menisci and bursae help reduce friction. Examples of synovial joints include the knee and shoulder joints.

There are six types of synovial joints: hinge, ball and socket, gliding, ellipsoid, pivot, and saddle joints. Hinge joints, like the elbow and knee joints, allow movement in one plane or direction only. Ball and socket joints, like the hip and shoulder joints, allow movement in various directions. Gliding joints only allow a sliding movement, while ellipsoid joints are modified ball and socket joints that allow movement in two directions. Pivot joints, like the articulation between the axis and atlas, allow rotation around a single axis. Finally, saddle joints allow movement in two directions and consist of two saddle-shaped articulating surfaces, like the carpometacarpal joint of the thumb.