Types of Joints

Articulations, more commonly known as joints, are points in the body where two bones meet. There are three categories of joints which are classified as synarthrosis, amphiarthroses and diarthrosis.

Categories of Joints

• Joints that do not move fall under the category of synarthroses. These joints are those in which bones are in close contact, separated by fibrous connective tissues only, such as the joints or sutures that connect the bones of the skull. Amphiarthroses are joints that connect with hyaline or fibro cartilage and have very little movement, such as the intercostal joints of the ribcage. The majority of joints in the human body are diarthrosis, or free moving joints. Of these joints, there are six different types.

Ball and Socket Joints

• The hip and shoulder joints are obvious examples of ball and socket joints. Ball and socket joints allow the greatest range of motion of all joints. In these types of joints, the rounded end of a bone, or the "ball" end of the bone, fits into the socket or cup formation of another bone allowing rotation and four-way flexion.

Gliding Joints

• When bones have flat surfaces that slide against one another, they form gliding joints. These joints do not allow for circular motion, but can allow for some twisting movement. Examples of gliding joints include the articulations of carpals (wrist bones) and tarsals (ankle bones) in the hands and feet.

Condyloid Joints

• Metacarpals, or bones found in the palm of the hand, metatarsals or bones of the feet, as well as phalanges, or finger and toe bones, connect to form condyloid joints. These joints are formed when an oval shaped bone connects with the elliptical form of another to allow flexion and extension, but no rotation.

Hinge Joints

• Elbow and knee joints are considered hinge joints, and allow only extension and flexion. In these articulations, one bone with a convex, or outwardly round shaped end will fit into the concave or depressed portion of another.

Saddle Joints

• The saddle joint is a very important type of joint, as it is the articulation that gives us an opposable thumb. In fact, the thumb is the only saddle joint in the human body. These joints are formed when touching bones have both convex and concave portions, allowing a large range of motion and flexibility, including rotation.

Pivot Joints

• Finally, pivot joints are formed when a round surface of a bone fits into the ring shape of either a tendon or bone. The best example of a pivot joint in the body is the joint that connects the atlas and axis of the upper spinal column. This joint allows the full motion of the head and neck.