The Surgical Approach to Subaxial Cervical Spine Injuries

Subaxial Cervical Spine Injuries • Dvorak et al
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spectrum of injury from a simple unilateral facet subluxation
to bilateral perched facets. In each case, there is a
varying degree of disruption of not only the posterior
element ligamentous structures but also the posterior
anulus of the disc. These injuries are no longer distraction
and become translational injuries if the facet subluxation
or perch progresses to a dislocation or becomes
associated with a fracture. Magnetic resonance imaging
(MRI) has been shown to be effective in evaluating the
degree and type of soft tissue disruption associated with
these injuries. 42–45
The role of closed reduction and traction before definitive
surgical stabilization remains controversial. Regardless
of whether or not a closed reduction is attempted
the decision as to which surgical approach to
choose rests on a number of factors.
When an MRI shows a fragment of disc material displaced
dorsal to the posterior cortex of the more caudal
vertebral body, 46 then the surgeons preference should be
for an anterior approach. 2,7,9,21 This is another example
of the extent of the DLC disruption (anterior disc protrusion)
informing the choice of surgical approach. Anterior
discectomy can decompress the spinal canal directly
and can then be followed by an anterior closed
reduction of the facet subluxation (usually achieved by
placing the patient in some degree of cervical extension
and by removing any intraoperative traction), inserting
an interbody graft, and an anterior cervical
plate. 2,7,8,13,20,21 Ensuring tight, 100% apposition of the
facets, a trapezoidal interbody graft, and contouring of
the plate into lordosis will optimize the stability of this
anterior approach for what is primarily a posterior ligamentous
injury. Although some biomechanical studies
have identified the inferiority of anterior fixation when
compared with posterior fixation in these injuries, most
studies show that anterior fixation alone for these posterior
injuries returns the spine to at least the stability of
the intact motion segment and combined with clinical
case series provide a compelling case for this treatment
alternative. 16,41
When the disc is essentially intact or merely disrupted
without frank herniation, then the surgeon can make a
choice either anterior or posterior fixation based on patient
and surgeon preference. Variables that may influence
this decision include the available equipment and
the training and familiarity of the surgeon with each
approach. From the patients’ perspective, anterior issues
such as neck scar, the risk of temporary dysphagia or
hoarse voice, and injury to visceral structures (esophagus)
may be compared with the additional muscle dissection
and local wound infection risk found with posterior
approaches. When a pure ligamentous unilateral or bilateral
facet subluxation is treated posteriorly, the torn
ligamentum flavum and any intervening hematoma or
scar tissue should be resected (flavotomy) before compressing
to reduce the posterior elements. 47
Specific to bilateral facet subluxations, however, are
the findings of a study by Elgafy et al, 17 wherein patients
with bilateral facet subluxations (perched facets without
fracture) were found to develop higher degrees of kyphosis
after posterior instrumented fusion. They, and other
authors 6,21 postulated that the disruption of the disc that
occurs with these distraction injuries leads to progressive
disc space collapse, which the posterior fixation is not
able to overcome, thus allowing the spinal segment to
drift into kyphosis. This tendency of posterior fusions to
lead to kyphosis has been identified by Lifeso and
Colucci, who recommended anterior plating for these
injuries. 21 Fehlings et al identified 2 patients with significant
kyphosis after posterior fixation. 6 The long-term
clinical significance of segmental kyphosis remains to be
seen.
Translation or Rotation Injuries
Unilateral or Bilateral Facet Fracture Dislocation or Subluxation.
Translation or rotation injuries score the highest
number of points on the morphology scale (4 points)
and almost always are associated with significant ligamentous
disruption (DLC 2) (Figure 5). Before adding
the neurology score, these injuries already score 6 on the
SLIC scale and are thus the most unstable of all cervical
injuries. Although these injuries may consist of a variety of
posterior element pathologies spanning the spectrum from
fracture separation of the lateral mass 25,26 (with translation
or rotation since an undisplaced lateral mass fracture falls
within the compression morphology) through completely
dislocated or locked facets. There may be varying degrees of
posterior element fracture and comminution of the spinous
process, lamina, and lateral masses in association with
burst, sagittal and/or coronal fractures of the vertebral
body leading to the “so-called” teardrop fracture.
7,8,16,18,22,27
All of these injuries therefore exhibit translation of 1
vertebra relative to an adjacent vertebra. This occurs as
either pure translation (i.e., bilateral locked facets) or as
a rotational translation around a single intact facet (i.e.,
displaced unilateral facet fracture or dislocation). The
principal features that subcategorize and differentiate injuries
within the translation or rotation group are the
presence or absence of fractures affecting the vertebral
body and the presence, severity, and location of residual
compression of the neural elements.
End-Plate Compression Fracture With Facet Fracture/
Dislocation. The vertebral body fracture may simply be a
superior end-plate compression fracture that is often difficult
to see on plain radiographs because of the natural
shape and slope of the superior endplate of the subaxial
cervical vertebrae. Once a minimal end-plate compression
fracture is seen in association with a facet fracture,
subluxation, or dislocation, this in general is a contraindication
to anterior alone surgical fixation. Johnson et al
showed that fully two-thirds of patients with an endplate
compression fracture who were fused with an anterior
approach alone developed early mechanical failure