The six types of synovial joints are the
- pivot,
- hinge,
- saddle,
- plane,
- condyloid
- ball-and-socket joints.
Next, let's focus on hinge joints, shown as letter B on the diagram. Hinge joints are the synovial joint type referred to in our introductory section. These joints can be found between your upper and lower arm bones, otherwise called your elbow, as well as your ankles, fingers, toes, and knees.
Hinge joints operate just like the hinges on a door. They allow for a swinging motion, where bones can either flex toward one another or extend apart. Twisting or overextending a hinge joint can result in injury. If you've ever twisted your knee or rolled your ankle, it's likely that a hinge joint was forced to move in a manner it shouldn't have.
Saddle joints, indicated by letter C in our illustration, are similar to hinge joints but provide more range of motion. In the case of a saddle joint, the bone sitting on the saddle can move in an oval shape relative to the other bone. Our thumb is a classic example of a saddle joint in action. Thumbs can move using a hinge-like motion but can also rock side to side. This is because of a saddle joint. In fact, it's the saddle joint that makes our thumbs opposable, a trait that allows us to firmly grasp objects with our hands.
Plane joints, sometimes called gliding joints and shown as letter D on the diagram, are probably the most difficult joint type to visualize. They are usually associated with the small bones of your wrists and ankles. In this type of joint, bones slide along beside one another. This allows for movement in many directions, hence the flexibility of your wrists. Here is a picture highlighting the location and type of bones associated with plane joints in your wrist.