Types of Joints of the Human Skeleton

The human body consists of 206 bones, consisting of four types: short, long, irregular and flat. The bones connect to each other in various places through joints that, in most cases, allow movement. Tendons, ligaments and muscles involved in these connections hold the bones and joints in place as the body moves.

Immovable or Suture

• The skeletal plates in the upper part of the skull -- called suture or immovable joints -- don't move. At birth, a baby's skull contains soft and flexible bones joined together like the bones in a adult's skull. This softness allows the baby's head to fit through the birth canal easily. As they grow older, the bones become harder.

Hinge

• Like the hinges on a door, hinge joints in the human body only move in one direction. The elbow serves as a good example, as well as the fingers, toes and knees. The knee ranks as the most flexible of the hinge joints -- it swivels slightly due the number of ligaments and muscles holding it in place. Another distinction of the knee: The kneecap, which covers the area where the thigh and lower leg bones meet, isn't connected to any other bone. It simply floats in place.

Ball and Socket

• The hip, where the leg bone meets the pelvis, is a ball-and-socket joint. These joints allow you the most flexibility, moving in a circular motion, as well as a hinge-like motion. The shoulder also provides a good example of this type of joint. In fact, the shoulder socket, where the arm meets the top of the torso, ranks as the most flexible joint in the human body. Unfortunately, this flexibility also makes it the most likely to become dislocated.

Cartilaginous

• A cartilaginous joint offers limited flexibility, with bones joined by pads of cartilage, as it has no hinge. The vertebrae in the back -- held together by cartilaginous joints -- contain 33 bones in the spine, which surrounds the spinal cord. Each vertebrae remains sandwiched by a disc of cartilage on the top and bottom, and by ropes of ligaments that run on either side down the length of the back. This configuration provides protection and support, but not movement.

Semi-Mobile

• The ribs hold to the sternum by semi-mobile joints, which have very little flexibility, and offer none of the movement allowable by hinge or ball-and-socket joints. The ribs have to move slightly -- otherwise breathing would be impossible -- providing nearby organs with room to expand.