The four types of joints in the human body are fixed or fibrous joints, ball-and-socket joints, pivot joints and hinge joints. Joints occur at the point of articulation, or the point where two bones meet in the skeleton.
Joints can be movable or immovable. The fixed joints in the cranium are needed to protect the brain. They are immovable and separated only by a bit of connective tissue. There are also fixed joints between the teeth and the jawbone.
A ball-and-socket joint is found where the large, round head of a bone fits into the cup of another bone. These can be found in the way the femur fits into the hip bone. It can also be seen in how the humerus fits into the scapula that makes up part of the shoulder bone. Ball-and-socket joints allow for the greatest range of motion in the body.
A hinge joint permits forward and backward motion along one plane, like the hinge on a door. These joints can be seen at the knee and the fingers.
Pivot joints allow a rotating motion. This can be seen in the movement of the head from side to side. The elbow also has a pivot joint.
