Download Surgical management of cervical myelopathy: indications and *

The Spine Journal 6 (2006) 252S–267S
Surgical management of cervical myelopathy: indications and
techniques for laminectomy and fusion
Ricardo J. Komotar, MD, J. Mocco, MD, Michael G. Kaiser, MD*
Department of Neurological Surgery, The Neurological Institute of New York, Columbia University Medical Center,
710 West 168th Street, Room 504, New York, NY 10032, USA
Abstract
BACKGROUND: Cervical spondylotic myelopathy (CSM) is a commonly encountered surgical
disease that may be approached through a variety of operative techniques. Operative goals in the
treatment of CSM include effective neural element decompression and maintaining spinal stability
to avoid delayed deformity progression and neurologic compromise. Determining the most appropriate operative approach requires careful consideration of the patient’s clinical presentation and
radiographic imaging.
PURPOSE: To review the indications and techniques for multilevel laminectomy and fusion in the
treatment of CSM.
CONCLUSIONS: When indications permit, a multilevel laminectomy is an effective and safe
method of neural element decompression. Recognizing the potential for spinal instability is essential to prevent neurologic compromise and intractable axial neck pain caused by deformity progression. A variety of techniques have been described to supplement the posterior tension band after
laminectomy; however, lateral mass fixation has evolved into the preferred stabilization technique.
Although clinical success is well documented, a successful outcome is dependent on a comprehensive, individualized evaluation of each patient presenting with CSM. Ó 2006 Elsevier Inc. All
rights reserved.
Keywords:
Cervical; Fusion; Indications; Laminectomy; Myelopathy; Techniques
Introduction
Cervical spondylotic myelopathy (CSM) is a common
diagnoses requiring surgical intervention among patients
presenting with disorders of the spine [1–8]. A variety of
well-known pathological processes, both congenital and acquired, can lead to canal compromise and myelopathy;
however, the presentation and history are difficult to predict
[1,3,4,8]. Thus, the prognosis and management of this
patient population may be challenging. Although well-designed clinical outcome trials are lacking, the existing literature suggests that operative intervention reliably arrests
the progression of myelopathy and may lead to functional
FDA device/drug status: approved for this indication (pedicle screws).
Nothing of value received from a commercial entity related to this
manuscript.
* Corresponding author. Department of Neurological Surgery, The
Neurological Institute of New York, Columbia University Medical Center,
710 West 168th Street, Room 504, New York, NY 10032. Tel.: (212) 3050378; fax: (212) 305-2026.
E-mail address: [email protected] (M.G. Kaiser)
1529-9430/06/$ – see front matter Ó 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.spinee.2006.04.029
improvement in the majority of patients [1,2,4–6,8–20].
The success of any operative procedure is dependent on
a comprehensive evaluation of the individual patient’s clinical and radiographic characteristics.
Both static and dynamic forces contribute to direct compression, distortion, and ischemia of the spinal cord, resulting in injury that often extends beyond the limits of the
compressive pathology [21]. Degenerative changes compromising the spinal canal are exaggerated by stretching
the spinal cord across ventral pathology during flexion
and in-folding of the ligamentum flavum with extension
[22]. Repeated microtrauma contributes to a chronic progressive course, while acute deterioration due to irreversible cord injury may result from hyperextension. Patients
suffering from CSM typically manifest signs and symptoms
including upper extremity weakness and paresthesias, loss
of hand dexterity, gait instability, or bowel and bladder dysfunction. Foraminal impingement will produce radicular
complaints with pain and sensorimotor loss in a specific
nerve root distribution.
The goals of operative intervention in the treatment of
cervical spondylotic myelopathy include the following:
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(a) decompression of the spinal cord and nerve roots; (b)
deformity prevention by maintaining or supplementing spinal stability; and (c) alleviating pain. Achieving these goals
will translate into improved clinical outcomes with stabilization or reversal of neurologic deficits, decreased pain,
and maximal functional restoration.
A number of surgical strategies exist, including anterior,
posterior, or circumferential approaches. Under most circumstances one approach will produce optimal results.
The surgical management of patients presenting with
CSM requires a comprehensive and individualized approach.
Designing the most effective surgical plan is dependent on
numerous factors, including the pathoanatomy of the patient,
the patient’s neurologic presentation, medical comorbidity,
assessment of procedure-specific risks, and the surgeon’s experience and comfort level with specific procedures.
The multilevel cervical laminectomy has been proven to
be a safe and effective means to decompress the spinal canal and nerve roots [6]. Although this procedure carries the
risk of a late kyphotic deformity, improved neurologic outcome is possible under the appropriate conditions. Absence
of a fixed kyphotic deformity is mandatory when considering a multilevel laminectomy. Disregarding this basic
premise will lead to suboptimal surgical results or worsening neurologic deficits.
The presence or possibility of spinal instability must be
anticipated in order to avoid a postoperative deformity that
could lead to delayed neurologic deterioration. Selecting
the optimal posterior stabilization technique requires a thorough understanding of cervical biomechanics and the available techniques of spinal reconstruction. Points of fixation
to stabilize the cervical spine after resection of the lamina
are limited to the lateral masses and pedicles. The choice
of fixation construct is dependent on the nature and extent
of instability and the surgeon’s experience and comfort
level [23]. Under the appropriate conditions, however,
a multilevel laminectomy with or without an arthrodesis
is a valuable and effective management strategy in the treatment of CSM.
Once the decision to proceed with surgery is finalized,
a comprehensive radiographic evaluation of the pathologic
spine is absolutely necessary to determine the most appropriate operative approach. Several important questions that
should be considered when choosing the most appropriate
operative approach include:
Preoperative surgical planning
Advantages of the posterior cervical approach
Deciding on the most appropriate surgical strategy is dependent on several factors, including neurologic presentation, pathologic anatomy, and medical comorbidity. The
decision to pursue surgery and its timing is influenced by
a patient’s neurological presentation. A rapid neurologic
decline will require more urgent intervention whereas a stable deficit may be approached on an elective basis. Prophylactic surgery for patients with stable deficits is
controversial and requires careful consideration by both
the patient and surgeon. The decision is dependent on
a careful assessment of the individual’s clinical and radiographic findings as well as the risk, whether operative or
conservative, that the patient is willing to accept.
A major advantage of the posterior approach in the management of CSM is the familiarity with the surgical procedure. A multilevel laminectomy is a commonly performed
procedure, considered technically easier, with shorter operative times and fewer perioperative complications when
compared with an equivalent anterior procedure [6]. Anterior exposure may prove exceedingly difficult for obese patients or patients with short thick necks. There is less risk of
unintentional durotomy and cerebrospinal fluid leak with
a posterior approach, particularly in patients with ossification of the posterior longitudinal ligament where the ventral
dura is attenuated or absent. The risk of swallowing dysfunction or recurrent laryngeal nerve palsy is eliminated
(a) What is the alignment of the cervical spine? Is the
spine lordotic, straight, or kyphotic? Posterior procedures are primarily indicated for lordotic, and possibly straight, spinal configurations.
(b) How rigid is the deformity? A single-stage posterior
approach with stabilization remains an option even in
the presence of a kyphosis if postural reduction restores
sagittal balance. Fixed kyphotic deformities are an absolute contraindication to the posterior approach.
(c) What is the nature of the pathologic process? How
many spinal levels are involved? Does the patient
demonstrate congenital stenosis? Anterior interbody
strut grafting beyond two levels is associated with
an increased failure rate. In such cases supplemental
posterior stabilization is required or a single-stage
posterior approach may be more appropriate.
(d) Does a static or mobile subluxation exist? Severe subluxation or any increase visualized on dynamic imaging would eliminate the possibility of a stand-alone
laminectomy and require inclusion of a stabilization
and fusion.
(e) What is the patient’s baseline medical status? Older
patients typically are more prone to complications related to swallowing dysfunction with anterior approaches [7]. Severe osteoporosis will increase the
chance of interbody graft subsidence. Under both
circumstances a posterior approach may be more
appropriate.
(f) Does the patient complain of significant axial neck
pain? The presence of axial neck pain, if attributed
to motion across a spondylotic segment, may support
the addition of an arthrodesis.
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with the posterior approach. Finally, posterior fusion techniques eliminate the complications associated with
intervertebral strut grafting, such as subsidence or dislodgement, particularly in the osteoporotic patient.
Disadvantages of the posterior cervical approach
The indirect mechanism of neural element decompression is one limitation of a multilevel laminectomy in the
treatment of CSM. In the presence of ventral pathology, operative success is dependent on the dorsal translation of the
neural elements. The posterior approach is therefore ideally
suited for patients demonstrating a minimal degree of lordosis. The presence of a straight or kyphotic alignment, especially if associated with significant ventral pathology,
will limit dorsal migration and cause the spinal cord and
nerve roots to drape across ventral pathology, leading to
further neurologic compromise [24].
The posterior approach also tends to be associated with
increased postoperative pain and morbidity owing to the denervation and devascularization of the paraspinal muscles.
Unsightly cosmetic defects resulting from atrophy of the
paraspinal muscles may be cause for concern in certain patients. Release of the posterior tension band increases the
risk of postoperative kyphotic deformity. The potential for
this complication is influenced by numerous factors, including the underlying pathologic process, the number of spinal
levels involved, the extent of the decompression, and the
patient’s age and underlying medical condition (eg, presence
of osteoporosis) [6]. Although the theoretical risk of spinal
cord injury may be lower with posterior approaches, there
are more specific neurologic deficits that are associated with
a posterior decompression, in particular dysfunction of the
C5 nerve root producing dissociated motor loss [25].
Flexible deformities or subluxation may be exacerbated
with a stand-alone multilevel laminectomy, and therefore
the inclusion of a posterior stabilization construct must be
considered. The potential for open deformity reduction is
limited with the more common posterior cervical fixation
techniques because of the limited purchase of lateral mass
screws. Although the use of cervical pedicle screws may
provide a biomechanical advantage, the insertion of these
devices is technically demanding with the potential for catastrophic neurovascular complications.
Indications for multilevel cervical laminectomy
For patients presenting with CSM, poor prognostic indicators and, therefore, absolute indications for surgery are:
(1) progression of neurologic signs and symptoms; (2) presence of myelopathy for 6 months or longer; or (3) severe
spinal cord compression, defined by a compression ratio approaching 0.4 or transverse spinal cord area of 40 square
millimeters or less [1,2,4,6,9,12,18,26,27]. Under these
circumstances, conservatively treated patients nearly always experience neurological deterioration [19], with surgical intervention being the most reliable method to
prevent disease progression.
Factors that influence the surgical decision-making process include the extent of disease, location of compressive
pathology, spinal alignment, and the presence of congenital
canal stenosis (Table 1). For cases with anterior compression limited to one or two levels, fixed kyphotic deformity,
and no significant developmental narrowing of the canal, an
anterior or circumferential decompression and stabilization
is favored [12,14,15,18,26,28]. In contrast, patients with
compression extending more than two levels, developmental narrowing of the canal, lordotic alignment, and primary
posterior compressive pathology are candidates for the multilevel laminectomy (Fig. 1) [9,16,20,24,29–32].
Among these factors, appropriate assessment of the cervical alignment is the most important factor when determining if a multilevel laminectomy is appropriate. Benzel
defines an ‘‘effective’’ cervical lordosis as the configuration
where no dorsal component of C3 to C7 crosses a line from
the posterior caudal corner of C2 to an identical point on
C7. Associated with this line is a zone of uncertainty, where
a surgeon’s bias and experience determine if the global configuration is consistent with a lordosis or kyphosis. Others
consider a configuration that falls into this ‘‘gray’’ zone
as a ‘‘straightened’’ spine [33]. The decision to perform
a multilevel laminectomy in the presence of a straight spine
requires consideration of additional factors, such as the degree of canal encroachment. Dorsal migration of the spinal
cord away from ventral pathology may be insufficient with
a straight cervical spine. Limits of ventral encroachment
have been suggested; however, no definitive value exists.
Hamanishi and Tanaka considered a minimum lordosis of
10 degrees required for adequate dorsal migration of the
spinal cord [34]. Yamazaki and coworkers observed continued ventral compression after posterior decompression
when the lordosis was less than 10 degrees and the extent
of ventral canal encroachment exceeded 7 mm in patients
presenting with ossification of the posterior longitudinal ligament [35]. Under these questionable circumstances, the decision often rests on the surgeon’s clinical experience and
procedural bias as there are no defined standards of treatment.
After the decision has been made to perform a multilevel
Table 1
Indications for anterior and posterior approaches for
cervical spondylotic myelopathy
Anterior approach
Posterior approach
Primarily anterior compression
1-2 level of disease
Kyphotic deformity
Absence of congential canal
stenosis
Associated radiculopathy
Absence of OPLL
Primarily posterior compression
$3 levels of disease
Normal or lordotic deformity
Presence of congenital canal stenosis
No radiculopathy
Presence of OPLL
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more than 4 mm of subluxation on dynamic views [17]. Under these circumstances a posterior decompression without
stabilization is likely to lead to a progressive deformity that
will require intervention at a future date.
Although not an absolute indication for supplemental
posterior stabilization, the presence of a straight cervical
spine should alert the surgeon to an increased potential
for a postlaminectomy kyphosis. The extent of decompression may prove more significant under these circumstances,
and has been correlated to postoperative spinal instability,
deformity progression, accelerated spondylotic changes,
and constriction of the dura mater by formation of extradural scar tissue [6,8,11,16,20,24,27,32,38]. In vitro studies
have demonstrated significant mobility and potential for
postoperative instability with the resection of 50% of the
facet complex [39,40]. Age has also been correlated to
the development of a postlaminectomy kyphosis, requiring
the surgeon to consider a stabilization when performing
a multilevel decompression in a younger patient [41–43].
Contraindications to the posterior approach
Fig. 1. Sagittal T2-weighted magnetic resonance imaging demonstrating
spinal cord compression and characteristics considered appropriate for
a multilevel laminectomy approach including a lordotic alignment, the
presence of posterior compressive pathology, and multilevel degenerative
disease.
laminectomy, the surgeon must then decide whether the addition of a posterior cervical fusion is indicated.
Indications for posterior cervical fusion
The primary surgical goals when performing a posterior
cervical stabilization and fusion include restoring stability,
maintaining alignment, providing stability until fusion has
matured, and alleviation of pain. These constructs provide
stability by reinforcing the posterior tension band that is
compromised by the pathologic process or surgical decompression. Determining the presence and extent of instability
rests on careful assessment of both static and dynamic imaging. There have been numerous models and definitions
created in an attempt to identify and quantify spinal instability [36,37]. Although these models provide a foundation
for operative decision making, each has limitations and
cannot be universally applied to all clinical situations. From
a practical standpoint, the presence of instability must be
determined on an individual basis. Findings on radiographs
that are suggestive of instability include: subluxation of
more than 3.5 mm on static lateral radiographs; more than
11 degrees of angulation between adjacent segments; and
Specific to the posterior approach, the presence of a fixed
kyphotic deformity is an absolute contraindication when
considering a multilevel laminectomy, even with the inclusion of a posterior cervical arthrodesis. These patients often
require a circumferential approach to adequately decompress the neural elements, stabilize the spine, and optimize
sagittal balance. A similar approach may be considered for
patients with severe osteoporosis, who require 360 degree
stabilization to prevent construct failure. Chronic injury
to the spinal cord, as demonstrated on preoperative magnetic resonance imaging, is also considered a contraindication. Imaging characteristics consistent with intramedullary
cystic necrosis, syrinx formation, or myelomalacia indicate
permanent cord injury that is unlikely to improve with
operative intervention [44].
Relative contraindications, not specific to the posterior
approach, include a history of significant medical comorbidity, such as older age (O70 years), diabetes, coronary
disease, obstructive pulmonary disease, peripheral vascular
disease, stroke, and social history of tobacco use or alcoholism [45–47]. Under these circumstances the risks of operative intervention often do outweigh the benefits,
particularly if there is no chance of neurologic recovery.
Surgical technique
Patient positioning/operative setup
An awake, fiberoptic intubation is preferred for symptomatic patients with severe cord compression. During the
induction of general anesthesia the natural protective mechanisms resisting neck motion are inhibited, allowing unrestricted cervical manipulation that could result in spinal
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cord injury. Accurate blood pressure monitoring is required
to avoid hypotension that could result in spinal cord ischemia or infarction. Before patient positioning, baseline electrophysiological monitoring, including somatosensory
evoked potentials, motor evoked potentials, and free running electromyography, is obtained, particularly for patients with severe cord compression. Although the value
of electrophysiological monitoring is debatable, it can provide useful information during reversible maneuvers, such
as patient positioning [48–50]. Monitoring, however,
should not be regarded as an insurance policy for poor surgical technique.
The patient is positioned prone with the arms tucked at
the sides and appropriate padding to prevent pressure neuropathies. A Mayfield head holder or tongs with traction are
used to secure the head (Fig. 2). A neutral position is
favored because prolonged periods in either a flexed or
extended posture may not be tolerated, especially in the
presence of severe spinal cord compression. A second traction line is set up to extend the neck and maximize lordosis
once neurologic decompression is achieved. After final positioning, repeat electrophysiological monitoring is performed. If a change is identified, factors that may affect
potentials such as anesthetics or alterations in blood
pressure should be verified and corrected. Neck position
should be rechecked and returned to a more neutral position. Intraoperative fluoroscopic imaging is useful to verify
cervical alignment after final positioning and confirm spinal
level during the operative procedure. Also alignment may
be rechecked during the procedure to optimize sagittal balance before any stabilization is performed.
Multilevel laminectomy
Once the patient is positioned and skin localization confirmed, the spine is exposed through a midline incision.
Maintaining a midline approach in the avascular fascial
plane will help decrease blood loss and minimize postoperative pain. The paraspinal muscles are elevated in a subperiosteal fashion using monopolar cautery. Dissection of the
facet joints is completed if an arthrodesis is intended. Care
is taken not to disrupt the facet capsule of uninvolved adjacent segments or if only a laminectomy is intended (Fig. 3).
Localization can be performed with anatomic landmarks,
such as the prominent C2 spinous process; however, confirmation with intraoperative imaging is recommended.
Resection of the lamina en bloc is the favored approach.
If required, keyhole foraminotomies are performed before
Fig. 2. Patient placed in a prone position for multilevel laminectomy and arthrodesis with Gardner Wells tongs and traction. Initially a neutral alignment is
preferred; however, a second traction line, with an upward directed vector, will enhance lordosis once the decompression is completed by placing the neck in
extension.
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Fig. 3. The paraspinal muscle and soft-tissue dissection necessary to expose the posterior cervical spine are depicted in a schematic and corresponding intraoperative photograph. If no fusion is intended, violation of the facet capsule should be avoided.
resection of the lamina so that the lamina can act as a protective barrier during drilling of the foramen. The en bloc
resection tends to be less time-consuming and avoids the
insertion of any instrument into the central canal before
the decompression. Using a high-speed drill equipped with
a matchstick or small round burr, troughs are drilled bilaterally at the lamina–facet junction. The drill is held perpendicular to the dorsal surface of the lamina to provide the
shortest route to the canal and avoid drilling of the lateral
mass (Fig. 4). Drilling initially passes through the dorsal
cortex followed by the soft cancellous core, and finally the
dense ventral cortex of the lamina. Bleeding from the medial
wall of the trough is easily controlled with wax. Although
a diamond bit may be used, this tends to slow the process
and generate more heat. Regardless of the drill bit used, continuous irrigation is recommended to avoid thermal injury.
The rostral aspect of the lamina tends to dive deep and requires more extensive drilling to completely disarticulate
the lamina. Entry into the epidural space is confirmed with
gentle palpation with either the drill bit or nerve hook. The
ventral cortex may also be resected by inserting a small footplated rongeur into the trough.
Once the bony troughs are completed, the spinous processes at the rostral and caudal extremes of the decompression are elevated with clamps and the ligamentous
attachments of the ligamentum flavum within the troughs
are stripped with rongeurs. Epidural bleeding encountered
during this maneuver is easily controlled with bipolar cautery and gelfoam. Symmetric elevation of the lamina is required to avoid levering the bone into the spinal canal
(Fig. 5). Once all ligamentous attachments are resected,
the entire complex is removed. The underlying dura is inspected and epidural bleeding controlled. If no fusion is intended, a hemovac drain is placed to prevent postoperative
hematoma and a multilayer closure is performed. The hemovac drain is typically removed within 24 hours of the operation. Patients may be placed in a soft cervical collar for
comfort measure for several weeks.
Posterior cervical stabilization and fusion
The earliest attempts at stabilizing the subaxial cervical
spine involved the placement of autologous bone along the
posterior elements; however, this approach lacked immediate stability and required prolonged periods of immobilization. Wiring techniques were first described in 1891 by
Hadra [51], and since that time a variety of posterior wiring
techniques have been developed that have demonstrated acceptable fusion potential with relatively low complication
rates [52–56]. Postlaminectomy wiring techniques required
the wire to be passed between adjacent facets or tied to either bone grafts or metallic rods (Fig. 6) [57,58]. Although
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Fig. 4. The en bloc laminectomy approach avoids placement of instruments into the central canal before the decompression. Bilateral troughs are drilled at
the lamina–facet junction with the drill bit oriented perpendicular to the dorsal surface of the lamina to avoid violation of the lateral mass.
facet wiring techniques have largely been replaced by more
rigid, newer generation constructs, wiring continues to be
a viable option.
Over the last several decades the emergence of lateral
mass fixation has become the stabilization technique of
choice [59–63]. Lateral mass fixation has proven to be a safe
and biomechanically superior technique when compared
with wiring procedures. Gill et al. demonstrated the increased rigidity and fusion potential with lateral mass fixation compared with posterior wiring techniques [64]. The
intrinsic strength of the lateral mass screw provides immediate stabilization, allowing early mobilization and possibly
eliminating the need for external bracing. The placement
of cervical pedicle screws has also been described, demonstrating superior fixation when compared with lateral mass
and anterior plating techniques [65]. Despite the biomechanical rationale for inserting cervical pedicle screws, this technique is not routinely practiced because of the technical
demands and the potential neurovascular complications [66].
Lateral mass fixation
Fixation to the lateral masses has evolved from early
generation screw-plate constructs to more versatile multiaxial screw-rod constructs. Plating systems were generally
unyielding because of the predetermined position of the
screw hole within the plate. These constructs could not
adapt well to variations in the patient’s anatomy, instead
the patient’s anatomy was forced to conform to the construct. Because of the rigidity of the plate in the coronal
plane, all screws had to be positioned in line. In addition,
points of fixation were sacrificed if the plate hole did not
match the entry site within the lateral mass (Fig. 7). Due
to the dynamic interface between the screw and plate, the
potential to maintain reduction was limited and required bicortical screw purchase to obtain maximal stability [67].
Surface area for fusion formation was compromised because the plate was positioned flush against the dorsal wall
of the lateral mass. Finally, revision surgery required removal of all the screws in order to disengage the plate.
These deficiencies have largely been overcome with the
evolution of multi-axial screw rod constructs [62].
Various lateral mass screw insertion techniques have
been described in the literature (Fig. 8). The Roy-Camille
technique uses the midpoint of the lateral mass as the insertion site and directs the screw without any rostral or caudal
angulation and 10 degrees laterally [68]. Jeanneret and Magerl describe a starting point 1 to 2 mm medial and superior
to the midpoint of the lateral mass with the trajectory aimed
30 degrees superior and 15 to 25 degrees lateral [69]. An
and colleagues recommended a starting point 1 mm medial
to the lateral mass center and angled 15 degrees cranial and
30 degrees lateral [70]. Finally, Anderson et al. modified
the Magerl technique with a starting point 1 mm medial
to the lateral mass center and aimed 20 to 30 degrees cranially and 10 to 20 degrees laterally [71].
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Fig. 5. The posterior elements, including the lamina and spinous processes, are resected en bloc making sure the rostral and caudal ends are
simultaneously elevated to avoid leveraging one end into the spinal canal.
Curettes or rongeurs are inserted into the troughs to release any ligamentous tissue tethering the lamina.
Several studies have investigated the biomechanical
characteristics and anatomic relationships of the various
lateral mass screw techniques [72–75]. Montesano and coworkers demonstrated a 40% greater pullout strength when
screws were placed using the Magerl compared with the
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Roy-Camille technique [74]. From a clinical perspective,
however, there has been no difference in the complication
rate between the different techniques [73]. Bicortical purchase of the lateral mass is associated with greater complications without a clear biomechanical advantage [75,76].
Ultimately measurement of exact angles for screw placement is impractical, and a trajectory with a bias in the medial to lateral direction with a rostral angulation starting
close to the lateral mass midpoint will create an appropriate
screw trajectory (Fig. 9). The surgeon needs to develop
a clear understanding of the anatomy, perform an appropriate exposure, and study preoperative imaging in order to
obtain the optimal screw insertion.
Exposure for lateral mass fixation requires soft-tissue
dissection to be extended until the far lateral margin of
the facet is identified. To avoid compromise of uninvolved
segments, care must be taken to maintain the facet capsule at the rostral and caudal extremes of the intended fusion. Lateral mass landmarks must be clearly identified for
appropriate placement of screws. The medial border is defined by the valley at the lamina–lateral mass junction. The
rostral and caudal boundaries are defined by the adjacent facet
joints; and the lateral boundary by the exposed lateral edge.
Although the relationship of the vertebral artery and nerve
root to the subaxial lateral masses is generally consistent, appropriate screw placement requires a detailed understanding
of these anatomical relationships. The vertebral artery lies anterior to the lamina–lateral mass junction whereas the nerve
root passes anterolaterally, deep to the caudal superior facet.
Once the soft-tissue exposure is completed, entry sites
for the lateral screws are marked by scoring the dorsal
cortical wall with a high-speed drill. This site is typically
in close proximity to the midpoint of the lateral mass. The
drill bit is placed into the entry site, perpendicular to the
dorsal cortex. Once the bit engages the bone, the trajectory is altered aiming from the infero-medial quadrant toward the supero-lateral quadrant, away from the nerve
root and vertebral artery. Resection of the spinous
Fig. 6. Wiring techniques used to stabilize the cervical spine after a multilevel laminectomy include passage of the wire between adjacent facets, securing
individual wires to a structural graft, or to a rigid rod, such as the Hartshill rectangle.
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processes may be necessary to obtain the optimal trajectory (Fig. 10). Laminectomies are not performed until after the holes are drilled to protect the dura and neural
elements. Once completed, the screw holes may be tapped
and filled with bone wax to prevent excessive bleeding.
The lamina are then resected with the en bloc technique
(Fig. 11). If a fusion is performed, all bone resected is
saved as autograft. Lateral mass screws are inserted into
the predrilled holes aiming in a supero-lateral direction
(Fig. 12). Malleable rods are cut and contoured, and locking mechanisms are engaged. Rods should be contoured
so that significant force is not required to seat the rod
within the screw. The posterolateral spine, including the
facet joints, is decorticated and the grafting material is impacted across the spine and into the facet joints (Fig. 13).
Closure is performed in the same manner as for an
isolated laminectomy.
Cervical pedicle screws
Fig. 7. This anterior-posterior radiograph demonstrates how plate constructs have a limited ability to conform to the surgical anatomy. The right
sided screw hole second from the top is positioned over the facet joint,
eliminating the possibility for screw placement.
Specific indications for cervical pedicle screws have
not been defined. With the exception of C7, the placement
of subaxial cervical pedicle screws is not routinely performed due to the potential for catastrophic neurovascular
injury, morphologic characteristics and variation of the
cervical pedicles [77], the technical difficulty involved with
Fig. 8. The entry site for the screw with the Roy-Camille method is the midpoint of the lateral mass, perpendicular to the dorsal cortex in the sagittal plane.
The screw is directed laterally by 10 . Using the Magerl technique the screw entry site is located slightly medial and cranial to the midpoint of the lateral
mass. The screw trajectory is parallel to the facet joint in the sagittal plane and directed 25 laterally in the transverse plane. The entry site for the Anderson
technique is located approximately 1 mm medial to the lateral mass midpoint with a rostral angulation of 30–40 and a lateral angle of 10 . Finally, the An
technique uses an entry site similar to the Anderson technique but only 15 of rostral angulation and a lateral angulation of 30 . These trajectories are intended for placement of screws into the lateral masses of C3 to C6. (Reprinted with permission from Barrey et al. [72] and Xu et al. [75])
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Fig. 9. The drawing demonstrates the general trajectory required for effective and safe lateral mass screw placement. A lateral trajectory directs the screw
away from the transverse foramen and vertebral artery, while the rostral angle avoids the nerve root traversing deep to the superior facet of the caudal spinal
segment. Bone volume is sufficient with this trajectory to enhance screw purchase.
insertion, and the lack of clinical data supporting the superiority of cervical pedicle screws over lateral mass screws. Despite the technical difficulties, placement of cervical pedicle
screws may serve as a pragmatic solution under unusual circumstances where lateral mass fixation cannot be achieved.
In animal and cadaveric biomechanical studies, the
placement of cervical pedicle screws has demonstrated superior stability, fixation, and reduction potential when compared with lateral mass fixation [65,78].
In vitro studies have demonstrated an unacceptable potential for injury when depending only on anatomic topography for the placement of cervical pedicle screws [79,80].
Fig. 10. Lamina are left intact during drilling of the lateral masses to act as a protective barrier. The prominent spinous processes can obstruct the trajectory
for appropriate lateral mass drilling; therefore resection will allow the optimal screw trajectory. Once drilling of the lateral masses is completed, the lamina
are resected.
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of critical injury to the vertebral artery, nerve root, or spinal
cord in a cadaveric model.
Based on the available literature, it seems that successful
placement of cervical pedicle screws not only requires
a comprehensive understanding of the three-dimensional
pedicle anatomy and the surrounding neurovascular tissues,
but also requires supplementation with direct visualization
of the pedicle or utilization of advanced navigational techniques. Despite these maneuvers, considerable risks remain
and more conventional methods of posterior cervical stabilization should strongly be considered before the placement
of these implants.
Complications
Fig. 11. An intraoperative photograph showing the thecal sac after the
lamina has been resected and the lateral masses drilled. Bleeding in the
epidural space is controlled with bipolar cautery and hemostatic agents,
such as gelfoam. Bone wax or gelfoam are inserted into the screw holes
to prevent continuous bleeding during the laminectomies.
The inability for accurate insertion based on visualized anatomic landmarks is primarily due to the inherent morphologic variability of the cervical pedicle trajectories and the
minimal margin of error allowed for appropriate screw
placement (Fig. 14). Increased accuracy has been observed
with direct exposure of the pedicle through a laminoforaminotomy and the addition of computer-assisted navigational
techniques [79–81]. Even with a laminoforaminotomy,
however, in vitro studies have demonstrated a 39.6%
incidence of critical violation, with possible nerve root or
vertebral artery injury [66].
Abumi et al. have published extensively on the placement of cervical pedicle screws [66,82–86]. They chose
an entry site just lateral to the midpoint of the lateral mass
in close proximity to the posterior edge of the superior articular surface. The cortical bone is drilled away to expose
the dorsal cancellous bone of the pedicle. Trajectory
through the pedicle is created with a hand-held probe with
a lateral to medial inclination ranging from 25 to 45 degrees. Cannulation of the pedicle is performed with realtime fluoroscopic imaging to supplement tactile feedback.
Using this technique, Abumi and colleagues reported rates
of pedicle violation ranging from 5.3% to 6.9%; however,
no injury to the vertebral artery was observed. Using the
same technique, Ludwig et al. [97] reported a 12% rate
Iatrogenic deformity, as a result of a previous laminectomy, is considered one of the more common causes of
a progressive cervical kyphosis. Because of the increased
flexibility of the cervical spine, stability is more dependent on the integrity of the posterior muscles and ligaments. The posterior exposure causes denervation and
atrophy of the posterior cervical musculature and compromises the ligamentous capsule of the facet joints
[42,87,88]. The incidence of kyphosis after dorsal cervical procedures has been reported to be as high as 21%
[88]. As many as 53% of patients under 18 years of
age who undergo a multilevel laminectomy will develop
a progressive kyphosis [41]. Younger patients are at an
increased risk as a result of incomplete ossification of
the vertebral bodies and reduced resistance to the incremental compressive forces that develop with compromise
of the posterior tension band [42,43]. Additional risk factors include compromised preoperative sagittal balance,
extent of posterior element disruption, and the number
and location of lamina resected [42,89–91]. Cadaveric
studies have demonstrated a significant increase in cervical mobility after resection of more than 50% of the facet
complex [39,40].
Neurologic complications can be divided into cord and
root injuries. The incidence of spinal cord injury ranges
from 0% to 3%, whereas injury to an individual nerve root
has been reported as high as 15% [47,92]. Technical error,
introduction of instruments under the central lamina, as
well as ischemic injury due to hypoperfusion or aggressive distraction can lead to irreversible spinal cord injury.
Nerve root injury may result from direct manipulation but
has also been attributed to the dorsal translation of the spinal cord after midline decompression [47]. The resulting
loss of motor function in the absence of sensory loss
has been termed dissociated motor loss. Radicular complaints are more commonly described in the C5 and C6
nerve root distributions. Symptom onset typically occurs
within hours to days after surgery, with specific pain
and weakness. Spontaneous recovery is the general rule;
however, deficits may persists for months. Isolated reports
have been published that demonstrate neurologic recovery
R.J. Komotar et al. / The Spine Journal 6 (2006) 252S–267S
263S
Fig. 12. Once the decompression is completed, the lateral mass screws are inserted. The screws are inserted with a rostral and lateral angulation with respect
to the lateral mass. The computed tomographic image demonstrates appropriately placed screws and their relationship to the transverse foramen.
with aggressive posterior decompression after onset of
symptoms [25].
Complications associated with lateral mass fixation result from impingement of the traversing nerve root or penetration of the vertebral artery. Potential for nerve root
injury is increased when attempting bicortical purchase.
Cadaveric studies have investigated the potential for inappropriate placement with the various fixation techniques
[75,76]. Seybold and colleagues using a modified Magerl
technique, demonstrated a 17.4% incidence of nerve root
impingement and 5.8% incidence of potential vertebral
artery injury when placing bicortical screws [76]. No such
injuries were recorded with unicortical screws, and no
significant difference in pullout strength was observed between unicortical and bicortical screws. Xu and coworkers
observed a 95%, 90%, and 60% incidence of nerve root
violation with the Magerl, Anderson, and An techniques respectively [75]. In this study a fixed screw length of 20 mm
was used to ensure bicortical purchase. The Magerl technique commonly violated the dorsal ramus, whereas the
An technique violated the ventral ramus.
The risk of injury is not only related to the technique but
also to the morphology of the lateral masses. Barrey et al.
observed an increased incidence of poor screw position at
C3–C4 with the Magerl technique and at C5–C6 with the
Roy-Camille technique [72]. This variation was attributed
to the change in the height/thickness ratio as one descends
down the spine, with more caudal lateral masses becoming
longer and thinner. These authors concluded that variations
in the technique of lateral mass screw placement should be
considered to achieve optimal purchase and reduce incidence of nerve injury. Despite the potential for neurovascular injury, most studies have demonstrated that fixation to
the lateral masses is a safe and effective means of posterior
cervical stabilization [93].
Insertion of cervical pedicle screws is associated with
risks to the vertebral artery, nerve root, and spinal cord. Because of the technical difficulty, small size, and morphological variation in the cervical pedicle, the risk is considered
greater than observed with lateral mass fixation. The greatest
potential for injury is to the vertebral artery injury owing to
the steep lateral to medial inclination required for appropriate
screw placement. Abumi and Kaneda observed a 6.7% incidence of pedicle penetration; however, only 4% of these
screws produced a clinically significant radiculopathy [66].
In vitro studies have demonstrated rates of critical pedicle violation as high as 65.5% depending on the insertion technique [79,81]. A greater degree of accuracy was achieved
when direct visualization of anatomic landmarks was supplemented with computer-assisted stereotactic navigation techniques. Pedicle screw placement is generally reserved for
levels with larger diameter pedicles, such as C7, when crossing the cervicothoracic junction, or when fixation to the lateral masses is not possible.
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R.J. Komotar et al. / The Spine Journal 6 (2006) 252S–267S
Fig. 13. The final stabilization construct is depicted in the schematic and intraoperative photograph. The lateral masses and facet joints are decorticated and
the bone graft impacted along these surfaces. To enhance stability, the newer generation screw-rod constructs allow insertion of cross-links to create a rectangular construct. Placing bone graft along the exposed dural surfaces, especially along a decompressed nerve root, should be avoided to prevent the possibility of recurrent stenosis.
Outcomes
Under the appropriate conditions, a multilevel laminectomy with or without arthrodesis is an effective
management strategy when treating cervical myelopathy.
Most clinical series are retrospective in nature and describe
an individual surgeon’s experience. Laminectomy as
a stand-alone procedure has demonstrated comparable
Fig. 14. The drawings demonstrate the trajectories required for appropriate cervical pedicle screw placement in both the sagittal and axial planes. A steep lateral to
medial inclination and the significant variability of the pedicle trajectory make the insertion of cervical pedicle screws technically demanding. Potential for neurovascular injury exists because of the proximity of the vertebral artery, nerve root, and spinal cord. (Reprinted with permission from Ladd et al. [98] and Abumi et al. [99])
R.J. Komotar et al. / The Spine Journal 6 (2006) 252S–267S
immediate postoperative results to anterior procedures and
laminoplasty [18]. Other series report a significant incidence of delayed deterioration, with rates as high as 40%
[10,18,94].
Herkowitz, in 1988, compared results of patients undergoing anterior decompression and strut grafting, laminoplasty, and laminectomy without fusion [15]. Only 66%
of patients after laminectomy reported good to excellent
outcomes, whereas the anterior group and laminoplasty
group reported good to excellent outcomes in 92% and
86% respectively. Twenty-five percent of the patients in
the laminectomy group developed a postlaminectomy
kyphosis within 2 years of the operation.
Outcomes after multilevel laminectomy and arthrodesis
for cervical degenerative disease have been favorable
[71,95,96]. Long-term improved neurologic status and
maintenance of cervical alignment have been demonstrated
[3]. Retrospective studies have compared the complexity,
safety, and clinical results of laminectomy versus corpectomy in patients with multilevel cervical spondylosis
[6,9,11,15,18,26,28]. Whereas anterior decompression and
fusion procedures at one or two motion segments have predictable results, procedures involving three or more levels
are associated with increased morbidity. Outcome parameters have included operative time, blood loss, length of stay,
and rate of complications. These investigations have concluded that posterior decompression by laminectomy for
multilevel stenosis (O2 levels) requires shorter operative
time and results in fewer complications than anterior cervical decompression with similar clinical results. Factors that
have been shown to correlate with poor outcome after laminectomy for CSM include advanced age (O70 years at the
time of the first surgery), severe original myelopathy, and
recent trauma [7,20,32,38]. In short, laminectomy, with or
without fusion, may be successfully employed to address
multilevel cervical pathology in carefully selected patients.
Cervical laminectomy with posterior fusion is valuable
in cases of CSM when preoperative dynamic imaging demonstrates instability. Several retrospective studies have focused on this topic. One review by Huang et al. involving
32 patients with multilevel CSM treated by laminectomy
and lateral mass plate fusion confirmed the clinical utility
of this procedure [38]. The etiology of disease in these
patients was either cervical spondylosis or ossification of
the posterior longitudinal ligament, the mean postoperative
follow-up was over 15 months, and in all cases myelopathy
was graded using the Nurick system. The authors noted the
mean Nurick score improved from 2.6 (range 1–4) to 1.8
(range 0–3) postoperatively (p!.0001). More specifically,
22 patients (71%) had an improvement in Nurick grade
of at least one point and nine showed no improvement.
Of note, no patients had neurologic deterioration. Severe
myelopathy, advanced age, and myelomalacia on preoperative magnetic resonance imaging had no prognostic value
for improvement of myelopathy. Overall, this study demonstrated that laminectomy and fusion may result in excellent
265S
outcomes for carefully selected patients with multilevel
cervical myelopathy.
Conclusions
Under the appropriate conditions, a multilevel cervical
laminectomy with or without a supplemental fusion is an
effective management strategy for the treatment of CSM.
Careful preoperative assessment of the pathologic anatomy,
clinical presentation, and medical comorbidity is essential
to achieve operative success. Patients requiring surgery
with evidence of a reducible deformity or static lordosis
are ideal candidates for a posterior decompression. The potential or presence of instability must be recognized and
prevented with a supplemental stabilization technique. Lateral mass fixation is the stabilization procedure of choice,
demonstrating superior biomechanical properties, technical
simplicity, and low complication rate. These operative techniques are essential to the surgeon’s armamentarium when
treating patients with CSM.
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