Anatomy of a Hinge Joint

There are six types of freely movable joints in the human body. Joints connect bones and with the help of muscles, allow for movements such as hugging or running. Both running and hugging require movement of hinge joints: the elbows and the knees.

Structure

• A hinge joint is similar in operation to a door hinge.

  In a hinge joint, the rounded-end portion of one bone fits into the bowl-shaped portion of an adjoining bone. A hinge joint is similar to a door hinge: just as a door can only open or close, a hinge joint can only extend or flex.

Function

• The knee is a hinge joint.

  Muscles pull on bones to create movement. As regards the hinge joint, this movement is allowed in only two directions: flexion, which occurs when the joint is as closed as possible; and extension, when the joint is as open as possible.

Try It

• Fingers have hinge joints, and to make a fist, those joints must flex.

  In a standing position, the hinge joint in the knee is extended. If the heel of the foot is lifted up towards your back, however, the knee is in flexion. Similarly, a fist requires the hinge joints in the fingers to be flexed, while an open palm shows finger joint extension.