A hinge joint is a joint that moves like the hinge on a door with movement occurring in only one plane, hence its name. It requires flexion and extension muscles to control its movement. Flexion muscles decrease the angle of the joint, whereas extension muscles increase the angle of the joint.
For example, the knee is one such hinge joint. The femur (bone above the knee) acts as the fixed point from which movement occurs and the and tibia (bone below the knee) acts as the lever in the joint that the muscles act on. The quadriceps act to extend the knee in extension by contracting and pulling the tibia upwards increasing the angle of the joint and the hamstrings act to flex the knee in flexion by contracting and pulling the tibia downwards decreasing the angle of the joint.