In
animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of
synovial joint
A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulat ...
whose
movement axis is parallel to the
long axis Long axis may refer to:
* Long axis of organs in anatomy
* Longitudinal axis of flight control surfaces
{{dab ...
of the proximal bone, which typically has a convex
articular surface.
According to one classification system, a pivot joint like the other synovial joint —the
hinge joint
A hinge joint (ginglymus or ginglymoid) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having ...
has one
degree of freedom.
[Platzer, Werner (2008) ''Color Atlas of Human Anatomy'', Volume 1]
p.28
/ref> Note that the degrees of freedom
Degrees of freedom (often abbreviated df or DOF) refers to the number of independent variables or parameters of a thermodynamic system. In various scientific fields, the word "freedom" is used to describe the limits to which physical movement or ...
of a joint is not the same as the same as joint's range of motion
Range of motion (or ROM), is the linear or angular distance that a moving object may normally travel while properly attached to another. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanic ...
.
Movements
Pivot joints allow for rotation
Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
, 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
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
and supination
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
. In the standard anatomical position
The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for Anatomical terms of location, anatomical location terms. Standard anatomical positions are used to standardise the position of ...
, 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
The proximal radioulnar articulation, also known as the proximal radioulnar joint (PRUJ), is a synovial pivot joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament.
...
* Distal radioulnar joint
The distal radioulnar articulation (also known as the distal radioulnar joint, or inferior radioulnar joint) is a synovial pivot joint between the two bones in the forearm; the radius and ulna. It is one of two joints between the radius and ulna, ...
* Median atlanto-axial joint
The atlanto-axial joint is a joint in the upper part of the neck between the atlas bone and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint.
Structure
The atlanto-axial joint is a joint between the atlas bo ...
In contrast, spherical joints (or ball and socket joints
The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...
) such as the hip joint permit rotation and all other directional movement, while pivot joints only permit rotation.
References
External links
Synovial Joints-Pivot Joints
from The University of Michigan Medical School
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Joints