Spinal stability: general definition is that motion segment provides mobility while at the same time protecting neurologic structures and function and implies non-painful movement.

White and Panjabi.

Cervical spine stability when less than 3.5 mm of translation at each segment and less than 11° of flexion relative to adjacent motion segments.

Motion at each segment of the spine largely defined by facet joint orientation.

Occiput-C1 provides for flexion/extension.

C1/C2 provides for rotation due to unique anatomy.

Subaxial cervical spine provides flexion/extension and lateral bending coupled with rotation.

Thoracic motion is rotational.

Lumbar motion is combined. Flexion and extension with lateral bending and rotation which are limited by the unique orientation of the lumbar facet joints, lateral bending, and rotation are coupled.

Instantaneous axis of rotation is the posterior half of the disc.

In general, the anterior column experiences compression forces; cages and structural grafts best resist this compression; anterior plates confer some advantage but do not resist flexion well.

Lateral plates are a little better.

In general, the posterior column experiences tension forces, and a screw and rod construct resists this best and also resists shear forces.