Correct interpretation of imaging studies of the postoperative cervical spine requires knowledge of the underlying pathology and of the surgical procedures performed. The authors review imaging of the upper cervical spine and the lower cervical spine following surgery with anterior or posterior approaches.
is an Associate Professor of Radiology,
is a 2nd-year Radiology Resident, and
is an Assistant Professor of Radiology in the Department of
Radiology, Section of Neuroradiology, Louisiana State University,
New Orleans, LA.
is Chief of Neuroradiology and a Professor of Radiology in the
Department of Radiology, Section of Neuroradiology, University of
North Carolina School of Medicine, Chapel Hill, NC.
Correct interpretation of imaging studies of the postoperative
cervical spine requires knowledge of the underlying pathology and
of the surgical procedures performed. This paper is divided into
two sections: the upper cervical spine (defined as the base of the
skull to C2) and the lower cervical spine (C3C7).
Surgical techniques used in these regions are divided into anterior
and posterior approaches. Most patients require radiographs, plain
computed tomography (CT) or post-CT myelography, and magnetic
resonance imaging (MRI). MRI has not been widely used in these
patients because of potential artifacts; however, artifacts can
often be reduced using imaging sequences that decrease magnetic
Upper cervical spine
Fixation and fusion of the upper cervical spine is difficult due
to its location and unusual biomechanics. The posterior approach
affords the surgeon a better view of the spinous processes,
laminae, facets, and spinal cord than the anterior approach.
Advantages of this approach include safety and greater facility to
apply bone grafts and hardware.
Anterior transoral approach--
The indications for this approach include C1C2 abscess drainage,
biopsy of tumor, and congenital neck deformities. Risks of this
approach include infection and limited surgical exposure.
The procedure is performed as follows. The patient is placed in
a supine position with the neck fully extended, and the face and
oropharynx are prepped with retraction for good exposure. The
surgeon palpates the anterior tubercle of C1 with the anterior body
of C2. Fluoroscopy and plain radiographs can aid the surgeon as
needed. A midline incision is made through the posterior pharyngeal
wall, including the retropharyngeal tissue and anterior
longitudinal ligament from C1 to C3, providing access to the
vertebrae and disk spaces. Proper closure of the pha-ryngeal layers
Anterior lateral retropharyngeal approach
The indications for this approach include C1C2 fusion when the
posterior ring is hypoplastic or absent. For this procedure, the
patient is placed in the supine position with neck extended and the
head turned. Traction is provided via tongs and a halo device. An
incision is made along the anterior border of the
sternocleidomastoid muscle crossing the temporal bone base. The
sternocleidomastoid is mobilized and everted with external jugular
vein and occipital artery ligation. The dissection is continued to
the retropharyngeal space laterally and posteriorly to the carotid
artery sheath. The alar and prevertebral fasciae are dissected to
expose the vertebral bodies with the anterior longitudinal ligament
incised in the midline.
Posterior occipitocervical fusion--
The indications for this approach are instability, intractable neck
pain, cervical osteoporosis, severe rheumatoid arthritis, and
trauma (ie, unstable C2 teardrop fracture). The techniques and
devices used in this approach include the following.
: This device is contoured and shaped for the individual patient
(Figure 1). It provides occipitocervical and atlantoaxial stability
by preventing vertical migration of the dens. It can be used for
rheumatoid arthritis, congenital malformations, tumors, complicated
fractures, spondylosis, and osteogenesis imperfecta.
These are smooth rods that are shaped to accommodate the
occipitocervical junction (Figure 2). These rods are fixed to the
occiput with wires placed in the outer table of the calvarium.
These rectangles are then fixed to the cervical spine with
sublaminar wires. They may also require bone grafting.
The occipitocervical plates are metal plates that are preformed to
accommodate the base of the skull. The plates help maintain an
occipitocervical angle of ~105š and are fixed with screws to the
occiput superiorly and with screws at the articular masses of C1/C2
inferiorly. There is increased morbidity from penetrating the inner
table of the skull.
This procedure addresses atlantoaxial instability that is >2.5
mm between the dens and the atlas in adults and 4.5 to 5.0 mm in
children. This fusion of C1C2 requires passing a stainless steel
wire around the posterior arch of C1 and under the spinous process
Songer cables are passed under the arch of C1 and around the lamina
of C2 (Figure 3). This procedure prevents subluxation of C1 and
Posterior transarticular screw fixation:
This technique is a conventional means for wiring of C1C2. Screws
are placed through the articular pillars of C2 and into the lateral
masses of C1.
Laminar clamps (Halifax clamps):
This technique is used for atlantoaxial fixation. Two C-clamps grip
the laminae with threaded screws that keep the clamps in place.
Fusion is acquired in 12 weeks in ~80% of patients.
Lower cervical spine
In this segment, the anterior approaches are the most direct
method for decompression of the cervical canal. These methods are
also used to decompress the cervical nerve roots or spinal cord
compression secondary to osteophytes, ossification of the posterior
longitudinal ligament, congenitally narrowed canal, and herniated
disks. The indications include cervical myelopathy (gait
disturbance, parasthesias, neck pain) and radicular signs. Once the
cause for the symptoms has been identified, it is important to
recommend surgical therapy, anterior diskectomy/fusion, or subtotal
The diskectomy with fusion is performed with the patient in a
head-holder traction or in a neutral position via a left-sided neck
approach with incision of the prevertebral fascia exposing the
vertebrae and disk spaces. After radiographic confirmation, the
disk is removed to the level of the posterior longitudinal ligament
and laterally to the unconvertebral joints. Osteophytes are removed
and the vertebral bodies are then spread. An iliac crest graft is
placed in the disk space, and the graft is locked into place
(Figure 4). This method is considered the gold standard for
anterior cervical fusions. Six to 12 weeks after surgery, the graft
becomes incorporated. The variation to this procedure is the
Bailey-Badgley procedure that utilizes bone strut grafts; the
patient wears a brace for approximately 6 weeks
Anterior cervical vertebrectomy/ fusion--
This procedure is performed via a transverse neck incision with
mobilization of the deep cervical fascia. A diskectomy is performed
and the central portion of the vertebral body is removed. End
plates and cortical lips are prepared and grafts locked into place.
Postoperative patients are placed into a halo vest for 8 to 12
weeks of immobilization. Physical therapy and rehabilitation are
required. Placement of metallic plates and/or screw fixation are
required for burst fractures, traumatic disk herniation, tumor
resection, and unstable injuries. Following corpectomy and removal
of disk material below or above the level of corpectomy, bone
grafts are placed. Afterward, a cervical plate is placed anteriorly
across the bone graft. Screws secure adjacent vertebral bodies.
Different plates are available for fusions.
The Caspar plate has three rows of holes and is concave
anteriorly. The plate is trapezoidal and bicortical screws are used
for greater stability (Figure 5).
The Morscher plate is an H-shaped titanium plate with
self-locking screws. (Figures 6 and 7). These screws have spiral
fenestrations that allow the ingrowth of cancellous bone. Titanium
hardware has great tissue compatibility and stealthiness over
stainless steel especially when imaged with MR.
This type of posterior approach is used in the decompression of the
posterior cervical disk herniations and osteophytes at one level.
The patient is placed in a prone position with appropriate traction
applied. A 3- to 4-cm incision is followed by retraction of the
paraspinous muscles. This process exposes the spinous processes.
The laminae are drilled with removal of ligamentum flavum and
epidural venous plexuses and nerve root retraction. This
facilitates the exposure of the lateral disk space.
This is a treatment for multilevel spondylitic radiculopathy. The
patient is placed in a prone position and a midline incision is
made. The spinous processes are removed to adequately expose the
soft tissues and ligaments.
This procedure is performed on cases of myelopathy secondary to
canal stenosis, multilevel spondylosis, and ossification of the
posterior longitudinal ligament. This technique increases the canal
diameter. The spinous processes and laminae are partially resected
with a bony gutter drilled laterally, and the thinned border of the
laminae are excised. The second bony gutter is drilled into the
contralateral laminae and sutured to prevent the laminar door from
closing. The canal diameter is increased to 5 mm, which may
necessitate the need for posterior stabilization via interspinous
wiring, wrap-around interspinous wiring, facet wiring with bone
graft, interfacet wiring, or interspinous wiring with
Holes are drilled into the outer cortex of the spinous processes
near the laminae. Wires are then passed through the holes into the
adjacent vertebrae. The ends of these wires are twisted.
Holes are drilled into the posterior pillars of the facets. Wires
are passed through the holes and then tied around the bone graft
struts. This promotes strong fusion.
In this procedure, wire loops are placed around both sides of the
laminae using 16- to 18-gauge Luque wires or braided Songer steel
cables; then bone grafts are placed over the fusion site.
Complications of cervical spine surgery
Complications associated with anterior approaches
Intraoperative complications associated with the use of plates
include arterial/venous laceration, spinal cord injury,
esophageal/tracheal injury, and recurrent laryngeal nerve injury.
Injury to the recurrent laryngeal nerve is the most common
complication with plate placement anteriorly. The symptoms of such
an injury include temporary/permanent hoarseness.
Postoperative infection/abscesses are also common. Imaging
modalities commonly employed for these conditions include MRI with
gadolinium and contrast-enhanced CT. T1-postcontrast images
demonstrate an area of thickened epidural enhancement with mass
effect and posterior displacement of the thecal sac. There is
occasional spinal cord compression. The necrotic center will not
Within a few days of the surgical intervention, MRI reveals
discrete areas of signal abnormality at the superior and inferior
corpectomy sites. The vertebral bodies demonstrate low T1 and high
T2 signal intensities that are consistent with edema. These changes
often persist for a few weeks with signal intensity abnormalities
within the adjacent vertebral bodies that vary from isointense to
hypointense on T1-weighted images and from isointense to
hyperintense on T2-weighted images (Figure 8). Graft sites that are
not stable will have prolonged edema while stable graft sites tend
to have fatty infiltration and sclerosis. The graft always remains
rectangular in shape. These findings should not be confused with
Autologous bone graft imaging often depends upon the state of
the marrow, ie, fatty vs. cellular. The cortex of the graft is low
in signal on both T1- and T2-weighted spin-echo sequences. The
marrow cavity is usually of intermediate signal intensity on T1-
and T2-weighted imaging. Bone graft struts without bone marrow have
no specific signal centrally.
Cervical canal stenosis is defined as an anteroposterior canal
diameter of less than 1 cm. Significant abnormal postoperative
findings result from hypertrophic bone formation at the level above
and below the fusion sites. Due to increased biomechanical stress
at these levels, there is increased propensity for degenerative
changes. New bone is isointense to the vertebral body on
T1-weighted images and tends to cause mass effect on the
subarachnoid space and the spinal cord. Osteophytes on T2-weighted
images and gradient spin-echo sequences produce a low signal
intensity. Graft extrusion can produce functional canal stenosis
and cord compression. Graft material hypertrophy can also lead to
spinal canal stenosis.
Complications associated with posterior surgical
Complications from this technique include arterial/venous
injury, tracheoesophageal tears, and recurrent laryngeal nerve
injury. Other complications such as air embolism and wound
infections are less common.
Special imaging considerations
Multiple metallic substances may preclude MR imaging because of
patient safety considerations and imaging quality.
Metallic fragments that originate from the drill bit can cause
image degradation (Figure 9). These artifacts are described as
producing a blooming artifact on MRI.
MR is vital in the evaluation of the postoperative patient.
Fast-spin-echo sequences demonstrate increased amounts of T2
information in the presence of metallic artifact because of
decreased magnetic susceptibility.
Magnetic susceptibility can cause field inhomogeneity and image
distortions created by dephasing of spins. This effect increases
with the length of time the spins have to dephase.
Factors that influence magnetic susceptibility include field
strength, chemical structure, density, spatial resolution, echo
spacing, and sampling bandwidth.
Ferromagnetic substances have a greater effect than paramagnetic
substances. Fast-spin-echo is a sequence that is performed at a
faster rate than the standard spin-echo pulse sequence with
improved signal-to-noise ratio and contrast. Use of short-spin-echo
spacing allows for decreased magnetic susceptibility effect.
A reduction of magnetic susceptibility may be a disadvantage for
detecting hemorrhage; however, this technique has a great advantage
in the postoperative spine. Half-Fourier acquisition single-shot
turbo-spin-echo (HASTE) images are also advantageous with regards
to decreasing metal-induced artifacts at the expense of lower
Correct imaging evaluation of the postoperative spine requires
an understanding of the surgical principles, different surgical
approaches, and recognition of the various available fixation
devices. As most fixation devices are metallic, they often preclude
interpretation secondary to image degradation. A reduction of these
artifacts produced from the hardware is important when evaluating
the postoperative spine. The use of short-spin echo, fast-spin
echo, or HASTE is effective when imaging the postoperative patient.