The four major types of joints in the human body serve various functions. Each has its own capabilities and limitations that determine how we move. There are 206 bones in the human body and a joint occurs at every place where one of these bones intersects with another.
Joint Types
The four major types of joints in the human body are hinge joints, pivot joints, ball and socket joints, and saddle joints. All of these joints allow humans to move freely without knocking their bones together. The joints are distinguished by the way they fit together.
Structure
All four major types of joints are synovial or diathrosis joints. They are surrounded by a collagenous material that lubricates the movements of the bones. A synovial membrane within the collagenous material produces a fluid that acts like oil in a car engine. It lubricates the movements of the joints. Cartilage within the joints cushion the motion and prevents them from bending too far.
Joint Movement
Hinge joints occur where one bone fits inside a concave impression of another bone. This type of joint moves back and forth in one direction. Pivot joints occur where one bone wraps around another bone allowing one bone to pivot on top of the other. Ball and socket joints look exactly like they sound. A ball-like projection of one bone fits inside a socket of another bone allowing for wide, circular motions. Saddle joints are where a bone with a concave surface meets a bone with a convex surface allowing a range of motion.
Joint Locations
Hinge joints are found in the elbows and knees. The skull sitting on top of the spine is a pivot joint. Ball and socket joints are found in the shoulders and hips. The only places where saddle joints exist in the human body are where the thumbs connect to the hands.
Other Joints
In addition to the four main types of joints, several less flexible joints are in the human body. These are places where bones intersect but do not move in a way that is generally visible. These minor joints include condyloid joints and gliding joints in the hands above the fingers and in the feet above the toes. Cartilagenous joints between the bones of the spine move very little as the back twists. Fibrous joints located at the seams of the skull bones do not move at all.
