A joint is the place where two or more bones come together or articulate, such as in the hip, knee, shoulder, or elbow, the National Institutes of Health notes. The human body is designed to move and this is demonstrated by the complex and varied nature of the many different types of joints throughout the body. Joints are classified and named both structurally and functionally. The three main structural classifications are cartilaginous, which are joined together by cartilage; fibrous, joined by tough fibrous connective tissue; and synovial, which are freely moving. According to Minnesota State University, most of the joints in the body are synovial in nature.
Ball and Socket
One of the most easily recognizable joints in the body is a ball and socket joint. Examples of this type of joint are the shoulder and hip. They are the most easily movable and allow for maximum range of motion in all directions. Because of its high degree of maneuverability, it is also the least structurally sound joint and the most prone to excessive wear and damage. The ball and socket joint is aptly named, as one bone has a rounded ball that fits neatly into a cup-like formation on the other bone. The joint is covered by a joint capsule which gives some stability and contains synovial fluid that lubricates the joint during movement.
Hinge
The hinge joint is movable in only one plane of motion--flexion and extension, according to the University of Michigan Medical School. An example of a hinge joint is the elbow or knee. In this type of joint a convex projection on one bone fits into a concave depression on the other. The joint capsule on this type of joint is thin on the top and bottom where all the motion occurs, but it has strong supporting ligaments on the sides to add stability.
Pivot
The pivot joint is another joint that allows motion in only one plane. These types of joints are referred to as uni-axial joints. In the pivot joint, motion occurs as one bone rotates around the process on another bone. One example of this type of joint is between the first two cervical vertebrae--the atlas and axis. The axis, or the second cervical vertebra, has a projection, called the dens, which stands up into the top vertebra. The first cervical vertebra rotates around the dens and is supported by a strong ligament.
Saddle
The saddle joint is shaped just like it sounds. One bone has a saddle shape to it and the corresponding bone is shaped like a horse's back, according to The University Of Michigan Medical School. One example of this type of joint is where the thumb meets the wrist. Motion in these types of joints can happen in several different planes.
