Pivot joint
Encyclopedia
A Pivot joint is a type of diarthrosis, or synovial joint
. In pivot joints, the axis of a convex articular surface is parallel with the longitudinal axis of the bone.
, which can be external (for example when rotating an arm outward), or internal (as in rotating an arm inward). When rotating the forearm, these movements are typically called pronation
and supination
. In the standard anatomical position, the forearms are supinated, which means that the palms are facing forward, and the thumbs are pointing away from the body. In contrast, a forearm in pronation would have the palm facing backward and the thumb would be closer to the body, pointing medially.
Note that spherical joints (ball and socket joints), such as the hip joint, also permit rotation (among all other possible motions), and should thus not be confused with pivot joints, where rotation is the only possible movement.
Synovial joint
A Synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones....
. In pivot joints, the axis of a convex articular surface is parallel with the longitudinal axis of the bone.
Movements
Pivot joints allow for rotationRotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
, which can be external (for example when rotating an arm outward), or internal (as in rotating an arm inward). When rotating the forearm, these movements are typically called pronation
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
and supination
Supination
Supination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...
. In the standard anatomical position, the forearms are supinated, which means that the palms are facing forward, and the thumbs are pointing away from the body. In contrast, a forearm in pronation would have the palm facing backward and the thumb would be closer to the body, pointing medially.
Examples
Examples of a pivot joint include:- Proximal radioulnar joint
- Distal radioulnar joint
- Median atlanto-axial jointAtlanto-axial jointThe Atlanto-axial joint is of a complicated nature. It consists of no fewer than four distinct joints....
Note that spherical joints (ball and socket joints), such as the hip joint, also permit rotation (among all other possible motions), and should thus not be confused with pivot joints, where rotation is the only possible movement.
External links
- Synovial Joints-Pivot Joints from The University of Michigan Medical SchoolUniversity of Michigan Health SystemThe University of Michigan Health System is the wholly owned academic medical center of the University of Michigan in Ann Arbor. UMHS includes the U-M Medical School, with its Faculty Group Practice and many research laboratories; the U-M Hospitals and Health Centers, which includes University...