Spinal fusion-hardware construct: Basic concepts and imaging review

Table 1 Denis’s three spinal column theory

Spinal column	Components	Primary function	Secondary function
Anterior	ALL, anterior 2/3 of the vertebral body and annulus fibrosus	Bears axial load	Resist extension
Middle	Posterior 2/3 of the vertebral body and annulus fibrosus, nucleus bulbosus and PLL	Resist flexion	Shares in axial loading
Posterior	Posterior vertebral arch elements	Spinal stability during rotational movements	Resist flexion

ALL: Anterior longitudinal ligament; PLL: Posterior longitudinal ligament; Posterior vertebral arch elements include: Pedicles, facets, ligamentum flavum, interspinous, and supraspinous ligaments.