Joints, also called articulations, are where two bones come together. There are three main types of joints. Synarthroses are joints that do not move, such as those that connect the bones of the skull. Amphiarthroses are joints with a limited range of motion, such as where the ribs connect to the sternum. The third and most common type of joint is the diarthroses, those joints that provide movement within the body. There are six different types of diarthroses in the human body.
Ball and Socket Joints
Ball and socket joints are those that are formed when the round head of one end of a bone fits into the cavity of another bone. These types of joints provide the most range of movement, as reported by Inner Body. The shoulder joint, one example of a ball and socket joint, is formed by the humerus (the upper arm bone) fitting into the socket of the shoulder blade. This joint is the body's most mobile joint as it is very shallow. The hip joint, in contrast, is a deep ball and socket joint that provides less motion but is very stable.
Hinge Joints
A hinge joint is the simplest type of joint. As the name suggests, it provides flexion and extension movement similar to a hinge on a door. The knee joint, the largest joint in the body according to Inner Body, is a hinge joint as well as the elbow.
Gliding Joints
A gliding joint occurs when a flat, or slight flat, surface of the two bones glide along each other. This type of joint allows for movement in one direction without any circular motion. The carpal bones in the wrist and the tarsal bones in the ankle form gliding joints.
Saddle Joints
A saddle joint is formed when the surfaces of both bones that are joined have a concave and a convex region. This allows the two bones to complement each other and provides a wide range of motion. The only saddle joint in the human body, according to Minnesota State University, is the thumb.
Pivot Joints
A pivot joint is formed when the round or conical part of a bone fits into a ring formed by a tendon at the other bone. This allows for rotation at the joint. The top of the spine that connects to the neck is one example of a pivot joint.
Condyloid Joints
A condyloid joint is formed when the oval portion of a bone fits into an elliptical part of the other bone. Condyloid joints allow for angular movement without rotation. An example of a condyloid joint is where the metacarpals (the bones in the palm of the hand) join with the phalanges (the bones of the fingers).
