General Information

Bones of the skeleton meet in areas called joints or articulations. According to the amount of movement they permit, joints are classified as immovable, slightly movable, and freely movable.

Immovable joints or synarthrosis

These allow no appreciable movement and the bones are fastened together by cartilage or fibrous tissue.

The bones of the skull are united by one type of immovable joint called a suture.

Slightly movable joints or amphiarthroses

These permit limited movement and the bony surfaces are connected by fibrocartilage, often in the form of a disk. These joints are exemplified in the intervertebral spaces and in the symphysis pubis.

Freely movable joints or diarthroses

The freely movable joints permit varying types of movement as discussed below. The articular surfaces of these bones are covered with hyaline (articular) cartilage and encased by an articular capsule ligament that is attached to both bones near the articulating end, holding them together. The cavity of the capsule contains synovial fluid that lubricates the joint. In some joints, an articular disk is also found between the articulating layers. Most joints of the body are freely movable (diarthrodial).

Types of Joint Movement: Muscles are attached to bones by tendons (cords of white fibrous connective tissue). Contracting muscles provide the forces which, when transmitted to the bone, institute various movements. The different types of movement are described below.

Gliding movements

Limited to a sliding of articular surfaces over each other.

Angular movements

Adduction: Movement toward the median plane of the body.

Abduction: Movement away from the median plane of the body.

Flexion: Movement to decrease the angle between adjoining parts.

Extension: Movement to increase the angle between adjoining parts.

Circumduction: Movement in which the bone circumscribes a pointed cone. The base of the cone is distal to the joint; the apex is the joint.

Rotation: The part turns about its own axis without changing position.

Pronation: To turn the palm of the hand (from the normal anatomical position) posteriorly.

Supination: To turn the palm of the hand from posterior to anterior (thus regaining the normal anatomical position).

Inversion: To turn the sole of the foot inward.

Eversion: To turn the sole of the foot outward.

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