Axis of Rotation
If you’re having trouble understanding the concept of the axis of rotation, here is a great primer on this somewhat complex concept. Learn about the three axes of rotation and the various types of movements that occur at different types of joints.
Axis of rotation can be a complex concept to grasp. It is not visible or tangible. It is an imaginary line that is the pivotal/rotational point at a joint. Movement in the planes occurs around this point and it is perpendicular to the planes, meaning that both lines—the plane and the axis—create a right (90°) angle.
Just as there are three planes of motion, there are three axes of rotation: the anterior-posterior axis, the mediolateral axis and the longitudinal axis. Joints rotate in these axes, allowing movement to occur in the planes.
Anterior-posterior Axis (also known as the Sagittal Axis or Anteroposterior Axis): Imagine a pin that inserts through the joint from front to back (anteriorly and posteriorly). Because of the pin’s position, the only movement allowed around this axis is lateral movement (abduction or adduction) in the frontal plane.
Mediolateral Axis (also known as the Transverse Axis): Mediolateral means that we take our imaginary pin and insert it from a mid-point at the side of the body. The position of our pin allows only forward and backward movement (flexion and extension) in the sagittal plane around this axis.
Longitudinal Axis: If we insert our pin through the joint from top to bottom, it will allow movement in transverse plane only (i.e., rotation).
Joints rotate in these axes, allowing movement to occur in the planes. Some only rotate in one axis, while others rotate in multiple axes
Uniaxial or uniplanar joints (also called hinge joints) rotate in one axis, allowing movement in one plane. The elbow joint is a hinge joint because it only moves forward and backward (flexion and extension) in the sagittal plane.
Biaxial or biplanar joints rotate in two axes, allowing movement in two planes. The foot and hand are examples of biaxial/biplanar joints. They both move laterally or side to side in the frontal plane and forward and backward (flexion and extension) in the sagittal plane.
Multiplanar or triaxial joints rotate in all three axis, allowing movement in all three planes. The shoulder joint is an excellent example of a multiplanar/triaxial joint. It allows forward and backward movement in the sagittal plane, lateral or side-to-side movement in the frontal plane, and internal and external rotation in the transverse plane.