Description of Neck Motion

One joy particular to the study of human motion is that of characterizing motion in specific human joints. Today's task for me has been developing an internal schema (a sort of mental map) for the motion relations between the base of the skull (occiput) and the first two neck bones--C1 and C2 which are respectively referred to as the atlas (for it's rotational role) and axis (for its phallic process). Below is a diagram of the occiput, atlas, and axis. This diagram depicts from top to bottom: the occiput of the skull (with the back of the skull sawed off), the atlas (with the back side of the atals' ring sawed off), and the axis (with the back side or spine of the axis sawed off). Notice that the dens is hidden by a dense connection of ligaments and proceeds upward from the back side of the axis. The ligaments most relevant to motion are: the alar, the apical, and the cruciform ligaments. Joint surfaces that exist between spinal bones are termed facets. These facet surfaces are planar in topography and glide upon one another to allow neck motion. Each neck bone contains two upper facets and two lower facets. The upper facets of C3-C7 are oriented upward (toward the skull), inward (toward midline) and backward (toward the back of the neck) at roughly 45-degrees from horizontal. The lower facets of C3-C7 are oriented downward (toward the feet), outward (toward the outer neck), and forward (toward the throat) at the same 45-degree angle. Consequently, when considering the component facets motions which make up forward bending of the neck, their motion are described as upward and forward. Likewise, during backward bending of the neck their motions are described as downward and backward. The depiction below is helpful for visualizing these mechanics.Furthermore, rotation of the neck to the left can be characterized as downward glide of the left facet and upward glide of the right fact. Interestingly, side-bending of the neck to the left is characterized by the identical facet motions (left downward glide and right upward glide). As such it is clear that when the neck is bent sideways to the left, rotation to the left occurs (this is termed ipsilateral rotation).

These mechanics do not hold true for the upper cervical spine (occiput, atlas, and axis). During left side bending of the skull on the atlas (C1), the atlas rotates to the opposite (right) side. This occurs to allow room for joint congruency between the concave facet of the right atlas as it travels up the convex surface of the right occiput (Hertling and Kessler 2006: page 714). Side-bending of the occiput is checked by the alar ligament. While viewing the alar ligament in the first diagram presented this checking mechanism can be conceptualized. Additionally, the axis (C2) is rotated to the left during left side bending of the occiput (this also can be visualized from the diagram).

The take home messages go somewhat like this:

C3-C7:

1) Forward bending of the C3-C7 can be diminished by restricted upward gliding at the facet joints.

2) Left side bending of C3-C7 can be diminished by restricted left downward gliding or right upward gliding at the facet joints.

3) Left rotation of C3-C7 can be diminished by restricted left downward gliding or right upward gliding at the facet joints.


Occiput-C2:

1) Forward bending at the occipitoatlanto joint can be diminished by restricted backward glide of the occiput on C1.

2) Backward bending at the occipitoatlanto joint can be diminished by restricted forward glide of the occiput on C1.

3) Left side bending of the occipitoatlanto joint can be diminished by restricted left backward glide or right forward glide of the occiput on C1. It can also be diminished by restricted left rotation of C2 (i.e. restricted inferior glide of left C1 facet on C2 and/or superior glide of superior glide of right C1 facet on C2).

4) Left rotation of atlas (C1) on axis (C2) can be diminished by restricted inferior glide of left facet joints or superior glide of right fact joints.