Nonaxial

Nonaxial is an anatomical and biomechanical term used to describe joints or movements that do not involve rotation around a fixed axis. In nonaxial joints, the articulating surfaces are nearly flat, allowing gliding movements confined to a plane and little or no rotation about a principal axis. This type of motion is primarily translational rather than angular.

In anatomy, nonaxial motion is typically associated with plane (gliding) joints. Examples include the intercarpal joints of the wrist, the intertarsal joints of the ankle, and the facet joints between vertebrae. These joints permit sliding movements between adjacent bones when subjected to forces, with movement occurring mainly in two-dimensional space rather than around an axis.

Nonaxial movement is often contrasted with other joint classifications based on the number of axes allowed. Uniaxial joints move around a single axis (such as hinge and pivot joints), biaxial joints accommodate movement around two axes (such as some saddle and condyloid joints), and multiaxial joints permit motion around three or more axes. Nonaxial joints, in contrast, offer limited angular mobility and are characterized by planar articulation rather than rotational freedom.

Etymology-wise, nonaxial comes from the Latin non- meaning not and axis, indicating the absence of rotation about a fixed axis. The term is used primarily in human anatomy and biomechanics, though it can appear in broader discussions of motion and design where planar, non-rotational movement is relevant.