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.

Table 2 Summarizes imaging techniques and indications[6]

Technique	Indications
Radiographs	Instrument failure, infection, failed fusion
Fluoroscopic positioned spot views	Instrument position
Radionuclide scans/PET	Infection
Ultrasonography	Fluid collections, abscesses
CT	Instrument position, pseudo-arthrosis, infection, fragments in spinal canal, vertebral alignment
MR imaging	Infection, failed back, recurrent disc, recurrent tumor
Diagnostic injection/aspiration	Confirm source of pain, aspiration of pseudo-bursae or organisms for infection

CT: Computed tomography; MR: Magnetic resonance; PET: Positron emission tomography.

Table 3 Ray’s criteria for evaluation of spinal bony fusion[107]

Ray’s criteria for radiographic assessment of bridging osseous fusion

Less than 3 degrees of inter-segmental position change on lateral flexion and extension views

No lucent area around the implant

Minimal loss of disk height

No fracture of the device, graft, or vertebra

No sclerotic changes in the graft or adjacent vertebra

Visible bone formation in or about the graft material