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A joint is defined as the point in the body where two bones meet. As a result, a joint doesn’t just include obvious articulations such as the knee and shoulder but also features such as the joins between bones in the skull.
Joints balance the properties of movement and stability. This means that joints with a high range of movement are often more unstable, such as the shoulder joint, which dislocates relatively easily. It also means that joints with lower range of movement are often more stable such as the sutures in the skull.
There are three main types of joint in the body:
Fibrous joints are extremely stable joints, with fibrous connective tissue stabilising the joint. As a result, fibrous joints have very limited movement. An example of this would be the joints between skull bones, known as sutures. These joints need to be as stable as possible to protect the brain, and do not require any movement.
Cartilaginous joints unite bones through cartilage and provide stability. Primary cartilaginous joints, or synchondroses, use hyaline cartilage and are functionally immobile; growth plates in growing bones are examples. Secondary cartilaginous joints, or symphyses, use fibrocartilage and allow slight movement. Examples include the pubic symphysis and the intervertebral discs between adjacent vertebral bodies.
Synovial joints are the most mobile of all the types of joints. The bone ends are capped with articular hyaline cartilage and are surrounded by a sack of synovial fluid contained within a fibrous capsule. These joints often have associated ligaments or menisci. There are six main types of synovial joints in the human body:
This type of joint is relatively simple. It involves one bone with a rounded end inserting into a corresponding cup. Common examples of this in the body are the hip joint and the shoulder joint. This is type of joint allows multidirectional movement, including rotation, flexion, extension, abduction and adduction. Range of movement in the joint is limited by muscles and ligaments which support and move the joint.
Diagram of a ball and socket joint.
SimpleMed original by Dr. Maddie Swannack.
This type of joint is very similar to a ball and socket joint except that the ball is elliptical in shape. Also known as a condyloid joint, this joint allows flexion, extension, abduction, adduction and circumduction, but not true axial rotation (as the oval shape of the bone cannot spin in the oval shaped socket). An example of this is the radio-carpal joint.
This type of joint involves one bone ending in a cylindrical shape, which fits into a trough in another bone. An example of this would be the elbow. Due to the cylindrical shape of the articular surface (where the bones contact each other) this joint only allows for unidirectional movement, like a hinge in a door can only allow movement along one axis.
Diagram of a hinge joint.
SimpleMed original by Dr. Maddie Swannack.
This type of joint is made up of a peg in a hole. This joint only allows rotational movement. This joint occurs between the atlas (C1) and the dens process of the axis (C2) vertebrae (atlantoaxial joint). The range of movement of the atlantoaxial joint is limited by the many ligaments and muscles of the spine, making it a very stable joint.
Diagram of a pivot joint.
SimpleMed original by Dr. Maddie Swannack.
Plane joints have relatively flat articular surfaces that allow small gliding movements, limited by the joint capsule and ligaments. Examples include the intercuneiform joints between the cuneiform bones of the foot and the second to seventh sternocostal joints. The first sternocostal joint is a primary cartilaginous synchondrosis, rather than a plane synovial joint.
Diagram of a plane joint.
SimpleMed original by Dr. Maddie Swannack
Saddle joints are probably the hardest joint type to describe. The articular surfaces are shaped like Pringles and allow movement in two arcs that are perpendicular to each other. An example of this joint in the body is between the trapezium (one of the carpal bones) and the 1st metacarpal bone.
Diagram of a saddle joint.
SimpleMed original by Dr. Maddie Swannack
For information about the pathology of each type of joint, check out the Clinical Conditions section of the Musculoskeletal unit.
Edited by: Dr. Ben Appleby
Reviewed by: Dr. Marcus Judge
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