Cervical Myelopathy spine journal.pdf

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Surgical management of cervical myelopathy: indications andtechniques for laminectomy and fusion

Ricardo J. Komotar, MD, J. Mocco, MD, Michael G. Kaiser, MD* Department of Neurological Surgery, T he Neurological Institute of New York, Colu mbia 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 appro-

priate operative approach requires careful consideration of the patient’s clinical presentation andradiographic 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 essen-

tial to prevent neurologic compromise and intractable axial neck pain caused by deformity progres-

sion. 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 comprehen-

sive, 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 ac-

quired, 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-de-

signed clinical outcome trials are lacking, the existing liter-ature suggests that operative intervention reliably arrests

the progression of myelopathy and may lead to functional

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 clin-

ical and radiographic characteristics.

Both static and dynamic forces contribute to direct com-

pression, distortion, and ischemia of the spinal cord, result-

ing in injury that often extends beyond the limits of the

compressive pathology [21]. Degenerative changes com-

promising 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 pro-

gressive course, while acute deterioration due to irrevers-

ible 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 dys-

function. 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:

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) 305-

0378; 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

The Spine Journal 6 (2006) 252S–267S

mailto:[email protected]

mailto:[email protected]



(a) decompression of the spinal cord and nerve roots; (b)

deformity prevention by maintaining or supplementing spi-

nal stability; and (c) alleviating pain. Achieving these goals

will translate into improved clinical outcomes with stabili-

zation 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 cir-

cumstances 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 ex-

perience and comfort level with specific procedures.

The multilevel cervical laminectomy has been proven to

be a safe and effective means to decompress the spinal ca-

nal and nerve roots [6]. Although this procedure carries the

risk of a late kyphotic deformity, improved neurologic out-come is possible under the appropriate conditions. Absence

of a fixed kyphotic deformity is mandatory when consider-

ing a multilevel laminectomy. Disregarding this basic

premise will lead to suboptimal surgical results or worsen-

ing 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 thor-

ough understanding of cervical biomechanics and the avail-

able techniques of spinal reconstruction. Points of fixation

to stabilize the cervical spine after resection of the laminaare 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 treat-

ment of CSM.

Preoperative surgical planning

Deciding on the most appropriate surgical strategy is de-

pendent on several factors, including neurologic presenta-tion, 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 sta-

ble deficit may be approached on an elective basis. Prophy-

lactic 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 radio-

graphic findings as well as the risk, whether operative or

conservative, that the patient is willing to accept.

Once the decision to proceed with surgery is finalized,

a comprehensive radiographic evaluation of the pathologic

spine is absolutely necessary to determine the most appro-

priate operative approach. Several important questions that

should be considered when choosing the most appropriate

operative approach include:

(a) What is the alignment of the cervical spine? Is thespine lordotic, straight, or kyphotic? Posterior proce-

dures are primarily indicated for lordotic, and possi-

bly 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 ab-

solute 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 sub-

luxation or any increase visualized on dynamic imag-

ing 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 re-

lated to swallowing dysfunction with anterior ap-

proaches [7]. Severe osteoporosis will increase the

chance of interbody graft subsidence. Under bothcircumstances 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.

Advantages of the posterior cervical approach

A major advantage of the posterior approach in the man-

agement of CSM is the familiarity with the surgical proce-dure. A multilevel laminectomy is a commonly performed

procedure, considered technically easier, with shorter oper-

ative times and fewer perioperative complications when

compared with an equivalent anterior procedure [6]. Ante-

rior exposure may prove exceedingly difficult for obese pa-

tients 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 ossifica-

tion of the posterior longitudinal ligament where the ventral

dura is attenuated or absent. The risk of swallowing dys-

function or recurrent laryngeal nerve palsy is eliminated

253S R.J. Komotar et al. / The Spine Journal 6 (2006) 252S–267S



with the posterior approach. Finally, posterior fusion tech-

niques eliminate the complications associated with

intervertebral strut grafting, such as subsidence or dislodge-

ment, particularly in the osteoporotic patient.

Disadvantages of the posterior cervical approach

The indirect mechanism of neural element decompres-

sion is one limitation of a multilevel laminectomy in the

treatment of CSM. In the presence of ventral pathology, op-

erative 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 lor-

dosis. The presence of a straight or kyphotic alignment, es-

pecially 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 withincreased postoperative pain and morbidity owing to the de-

nervation and devascularization of the paraspinal muscles.

Unsightly cosmetic defects resulting from atrophy of the

paraspinal muscles may be cause for concern in certain pa-

tients. Release of the posterior tension band increases the

risk of postoperative kyphotic deformity. The potential for

this complication is influenced by numerous factors, includ-

ing 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, thereare 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 cat-

astrophic neurovascular complications.

Indications for multilevel cervical laminectomy

For patients presenting with CSM, poor prognostic indi-

cators and, therefore, absolute indications for surgery are:

(1) progression of neurologic signs and symptoms; (2) pres-

ence of myelopathy for 6 months or longer; or (3) severe

spinal cord compression, defined by a compression ratio ap-

proaching 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 al-

ways experience neurological deterioration [19], with sur-

gical intervention being the most reliable method to

prevent disease progression.

Factors that influence the surgical decision-making pro-

cess include the extent of disease, location of compressive

pathology, spinal alignment, and the presence of congenital

canal stenosis (Table 1). For cases with anterior compres-

sion 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, developmen-

tal narrowing of the canal, lordotic alignment, and primary

posterior compressive pathology are candidates for the mul-

tilevel laminectomy (Fig. 1) [9,16,20,24,29–32].

Among these factors, appropriate assessment of the cer-

vical alignment is the most important factor when deter-

mining if a multilevel laminectomy is appropriate. Benzel

defines an ‘‘effective’’ cervical lordosis as the configurationwhere 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 con-

figuration 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 de-

gree of canal encroachment. Dorsal migration of the spinal

cord away from ventral pathology may be insufficient with

a straight cervical spine. Limits of ventral encroachmenthave 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 contin-

ued 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 lig-

ament [35]. Under these questionable circumstances, the de-

cision often rests on the surgeon’s clinical experience and

procedural bias as there areno definedstandards 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 Primarily posterior compression

1-2 level of disease $3 levels of disease

Kyphotic deformity Normal or lordotic deformity

Absence of congential canal

stenosis

Presence of congenital canal stenosis

Associated radiculopathy No radiculopathy

Absence of OPLL Presence of OPLL




laminectomy, the surgeon must then decide whether the addi-

tion 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 decom-

pression. Determining the presence and extent of instabilityrests on careful assessment of both static and dynamic im-

aging. There have been numerous models and definitions

created in an attempt to identify and quantify spinal insta-

bility [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

more than 4 mm of subluxation on dynamic views [17]. Un-

der 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 decompres-

sion 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 extradur-

al 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

Specific to the posterior approach, the presence of a fixed

kyphotic deformity is an absolute contraindication when

considering a multilevel laminectomy, even with the inclu-

sion of a posterior cervical arthrodesis. These patients often

require a circumferential approach to adequately decom-

press 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 mag-netic resonance imaging, is also considered a contraindica-

tion. 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 comor-

bidity, such as older age (O70 years), diabetes, coronary

disease, obstructive pulmonary disease, peripheral vascular

disease, stroke, and social history of tobacco use or alcohol-

ism [45–47]. Under these circumstances the risks of ope-

rative 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 symp-

tomatic patients with severe cord compression. During the

induction of general anesthesia the natural protective mech-

anisms resisting neck motion are inhibited, allowing unre-

stricted cervical manipulation that could result in spinal

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.




cord injury. Accurate blood pressure monitoring is required

to avoid hypotension that could result in spinal cord ische-

mia or infarction. Before patient positioning, baseline elec-

trophysiological monitoring, including somatosensory

evoked potentials, motor evoked potentials, and free run-

ning electromyography, is obtained, particularly for pa-

tients with severe cord compression. Although the value

of electrophysiological monitoring is debatable, it can pro-

vide useful information during reversible maneuvers, such

as patient positioning [48–50]. Monitoring, however,

should not be regarded as an insurance policy for poor sur-

gical technique.

The patient is positioned prone with the arms tucked at

the sides and appropriate padding to prevent pressure neu-

ropathies. 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 trac-

tion line is set up to extend the neck and maximize lordosisonce neurologic decompression is achieved. After final po-

sitioning, repeat electrophysiological monitoring is per-

formed. 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 posi-

tion. 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 bal-

ance before any stabilization is performed.

Multilevel laminectomy

Once the patient is positioned and skin localization con-

firmed, the spine is exposed through a midline incision.

Maintaining a midline approach in the avascular fascial

plane will help decrease blood loss and minimize postoper-

ative pain. The paraspinal muscles are elevated in a subper-

iosteal 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 adja-

cent 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, confir-

mation 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.




resection of the lamina so that the lamina can act as a pro-

tective 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 bilat-

erally at the lamina–facet junction. The drill is held perpen-

dicular 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, con-tinuous irrigation is recommended to avoid thermal injury.

The rostral aspect of the lamina tends to dive deep and re-

quires 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 foot-

plated rongeur into the trough.

Once the bony troughs are completed, the spinous pro-

cesses at the rostral and caudal extremes of the decompres-

sion 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 cau-

tery and gelfoam. Symmetric elevation of the lamina is re-

quired 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 in-

spected and epidural bleeding controlled. If no fusion is in-

tended, a hemovac drain is placed to prevent postoperative

hematoma and a multilayer closure is performed. The he-

movac drain is typically removed within 24 hours of the op-

eration. Patients may be placed in a soft cervical collar for

comfort measure for several weeks.

Posterior cervical stabilization and fusionThe earliest attempts at stabilizing the subaxial cervical

spine involved the placement of autologous bone along the

posterior elements; however, this approach lacked immedi-

ate stability and required prolonged periods of immobiliza-

tion. 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 ac-

ceptable fusion potential with relatively low complication

rates [52–56]. Postlaminectomy wiring techniques required

the wire to be passed between adjacent facets or tied to ei-

ther bone grafts or metallic rods (Fig. 6) [57,58]. Although

Fig. 3. The paraspinal muscle and soft-tissue dissection necessary to expose the posterior cervical spine are depicted in a schematic and corresponding intra-

operative photograph. If no fusion is intended, violation of the facet capsule should be avoided.




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 in-

creased rigidity and fusion potential with lateral mass fixa-

tion compared with posterior wiring techniques [64]. The

intrinsic strength of the lateral mass screw provides immedi-

ate stabilization, allowing early mobilization and possibly

eliminating the need for external bracing. The placement

of cervical pedicle screws has also been described, demon-

strating superior fixation when compared with lateral mass

and anterior plating techniques [65]. Despite the biomechan-

ical rationale for inserting cervical pedicle screws, this tech-nique 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 multi-

axial 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 con-

struct. 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 bi-

cortical screw purchase to obtain maximal stability [67].

Surface area for fusion formation was compromised be-

cause the plate was positioned flush against the dorsal wall

of the lateral mass. Finally, revision surgery required re-

moval 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 inser-tion site and directs the screw without any rostral or caudal

angulation and 10 degrees laterally [68]. Jeanneret and Ma-

gerl 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 cra-

nially and 10 to 20 degrees laterally [71].

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.




Several studies have investigated the biomechanical

characteristics and anatomic relationships of the various

lateral mass screw techniques [72–75]. Montesano and co-

workers demonstrated a 40% greater pullout strength when

screws were placed using the Magerl compared with the

Roy-Camille technique [74]. From a clinical perspective,

however, there has been no difference in the complication

rate between the different techniques [73]. Bicortical pur-

chase of the lateral mass is associated with greater compli-

cations without a clear biomechanical advantage [75,76].

Ultimately measurement of exact angles for screw place-

ment is impractical, and a trajectory with a bias in the me-

dial 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 appropri-

ate 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 cap-

sule at the rostral and caudal extremes of the intended fu-

sion. Lateral mass landmarks must be clearly identified for

appropriate placement of screws. The medial border is de-fined by the valley at the lamina–lateral mass junction. The

rostral andcaudal boundaries aredefined by theadjacentfacet

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, ap-

propriate screw placement requires a detailed understanding

of these anatomical relationships. Thevertebral arterylies an-

terior 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 typicallyin 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 trajec-

tory is altered aiming from the infero-medial quadrant to-

ward the supero-lateral quadrant, away from the nerve

root and vertebral artery. Resection of the spinous

Fig. 5. The posterior elements, including the lamina and spinous pro-

cesses, 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 ligamen-

tous tissue tethering the lamina.

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.




processes may be necessary to obtain the optimal trajec-

tory (Fig. 10). Laminectomies are not performed until af-

ter 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 lock-

ing 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 im-

pacted 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

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 per-

formed due to the potential for catastrophic neurovascular

injury, morphologic characteristics and variation of the

cervical pedicles [77], the technical difficulty involved with

Fig. 7. This anterior-posterior radiograph demonstrates how plate con-

structs 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.

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 in-

tended 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])




insertion, and the lack of clinical data supporting the superi-

ority of cervical pedicle screws over lateral mass screws. De-

spite the technical difficulties, placement of cervical pedicle

screws may serve as a pragmatic solution under unusual cir-

cumstances where lateral mass fixation cannot be achieved.

In animal and cadaveric biomechanical studies, the

placement of cervical pedicle screws has demonstrated supe-

rior stability, fixation, and reduction potential when com-

pared with lateral mass fixation [65,78].

In vitro studies have demonstrated an unacceptable po-

tential for injury when depending only on anatomic topog-

raphy for the placement of cervical pedicle screws [79,80].

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.

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.




The inability for accurate insertion based on visualized an-

atomic landmarks is primarily due to the inherent morpho-

logic 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 laminoforami-

notomy 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 place-

ment of cervical pedicle screws [66,82–86]. They chose

an entry site just lateral to the midpoint of the lateral massin close proximity to the posterior edge of the superior ar-

ticular 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 de-

grees. Cannulation of the pedicle is performed with real-

time 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

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 tech-

niques. Despite these maneuvers, considerable risks remain

and more conventional methods of posterior cervical stabi-

lization should strongly be considered before the placement

of these implants.

Complications

Iatrogenic deformity, as a result of a previous laminec-

tomy, 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 depen-

dent on the integrity of the posterior muscles and liga-ments. The posterior exposure causes denervation and

atrophy of the posterior cervical musculature and compro-

mises the ligamentous capsule of the facet joints

[42,87,88]. The incidence of kyphosis after dorsal cervi-

cal 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 incre-

mental compressive forces that develop with compromise

of the posterior tension band [42,43]. Additional risk fac-tors 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 cervi-

cal 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 aggres-

sive 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 spi-

nal cord after midline decompression [47]. The resulting

loss of motor function in the absence of sensory loss

has been termed dissociated motor loss. Radicular com-

plaints 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

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.




with aggressive posterior decompression after onset of

symptoms [25].

Complications associated with lateral mass fixation re-

sult from impingement of the traversing nerve root or pen-

etration of the vertebral artery. Potential for nerve root

injury is increased when attempting bicortical purchase.

Cadaveric studies have investigated the potential for inap-

propriate 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 be-

tween unicortical and bicortical screws. Xu and coworkers

observed a 95%, 90%, and 60% incidence of nerve rootviolation with the Magerl, Anderson, and An techniques re-

spectively [75]. In this study a fixed screw length of 20 mm

was used to ensure bicortical purchase. The Magerl tech-

nique 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 inci-

dence of nerve injury. Despite the potential for neurovascu-

lar 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. Be-

cause of the technical difficulty, small size, and morpholog-

ical 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

thesteep lateral to medial inclinationrequired forappropriate

screw placement. Abumi and Kaneda observed a 6.7% inci-dence of pedicle penetration; however, only 4% of these

screws produced a clinically significant radiculopathy [66].

In vitro studies have demonstrated rates of critical pedicle vi-

olation as high as 65.5% depending on the insertion tech-

nique [79,81]. A greater degree of accuracy was achieved

when direct visualization of anatomic landmarks was supple-

mented with computer-assisted stereotactic navigation tech-

niques. Pedicle screw placement is generally reserved for

levels with larger diameter pedicles, such as C7, when cross-

ing the cervicothoracic junction, or when fixation to the lat-

eral masses is not possible.

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.




Outcomes

Under the appropriate conditions, a multilevel laminec-

tomy 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. 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 rect-

angular construct. Placing bone graft along the exposed dural surfaces, especially along a decompressed nerve root, should be avoided to prevent the pos-

sibility of recurrent stenosis.

Fig. 14. The drawings demonstratethe trajectoriesrequired for appropriate cervical pediclescrew placement in both the sagittal andaxial planes. A steep lateral to

medialinclination andthe significant variability of thepedicle trajectory make theinsertion of cervicalpedicle screwstechnically demanding. Potentialfor neurovas-

cular injury existsbecause of theproximity of thevertebralartery, nerve root, andspinal cord. (Reprinted with permission from Laddet al. [98] and Abumi etal. [99])




immediate postoperative results to anterior procedures and

laminoplasty [18]. Other series report a significant inci-

dence of delayed deterioration, with rates as high as 40%

[10,18,94].

Herkowitz, in 1988, compared results of patients under-

going anterior decompression and strut grafting, lamino-

plasty, 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 corpec-

tomy 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 pre-

dictable results, procedures involving three or more levels

are associated with increased morbidity. Outcome parame-

ters have included operative time, blood loss, length of stay,

and rate of complications. These investigations have con-

cluded that posterior decompression by laminectomy for

multilevel stenosis (O2 levels) requires shorter operative

time and results in fewer complications than anterior cervi-

cal decompression with similar clinical results. Factors that

have been shown to correlate with poor outcome after lam-

inectomy for CSM include advanced age (O

70 years at thetime 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 dem-

onstrates instability. Several retrospective studies have fo-

cused 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 postoperativefollow-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 preopera-

tive magnetic resonance imaging had no prognostic value

for improvement of myelopathy. Overall, this study demon-

strated that laminectomy and fusion may result in excellent

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 aneffective 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 po-

tential or presence of instability must be recognized and

prevented with a supplemental stabilization technique. Lat-

eral mass fixation is the stabilization procedure of choice,

demonstrating superior biomechanical properties, technical

simplicity, and low complication rate. These operative tech-

niques are essential to the surgeon’s armamentarium when

treating patients with CSM.

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