A hinge joint is a point of connection between two objects that allow movement, backward and forward, on one plane. The joint does not allow side-to-side movement. Hinge joints are found in the human skeleton and other animal skeletons, as well as in objects that allow single plane motion like doors, box lids and cupboards.
The elbow joint on a human skeleton is an example of a hinge joint. The ulna bone of the lower arm is connected to the humerus of the upper arm, and the joint allows back and forth movement on one 180-degree plane. In the body, the back and forth movement is called flexion and extension. Flexion brings the lower arm and hand toward the upper arm and shoulder. Extension brings the lower arm away from the upper arm until they form a straight line. The joint does not allow movement beyond that straight line, which is what makes it a hinge joint.
Finger and Toe Joints
Finger and toe joints are other examples of human skeletal hinge joints. These small hinges include the second joints on the fingers, toes and thumbs, and the third joints on the fingers and toes, excluding the big toe. The first joint, the one that connects the hand and finger, or carpals and metacarpals, are not examples of hinge joints because, although they allow back-and-forth movement, they also allow movement from side to side. The joints and muscles work together to flex and extend the fingers and toes along their 180-degree plane of movement.
Mechanical hinges make daily living more convenient because they help construct many of the structures and objects people use on a day-to-day basis. Hinges are found on standard doors that open and close on 180-degree planes, jewellery box lids and toy box lids that open and close and cupboard doors. Types of mechanical hinges include a butt hinge, strap hinge, reversible or double-folding screen hinge, non-reversible screen hinge for screen doors, back flap hinge, rising butt hinge and pivot hinge. Hinges must be installed properly, with precision, because if they are not aligned correctly, the hinged object will not operate the way it is intended. There are different ways to install hinges, like on the outside or inside of a door or lid. Each way allows the hinge joint to operate on its intended plane.