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Natural History Spinal cord compression resulting from spondylotic changes in the cer-vical spine is typically a slowly pro-gressive process.. Minimal symptoms without hard evidence of g

Cervical spondylosis results from

the nearly universal process of

de-generation of the disks and joints of

the cervical spine These changes in

the spinal motion segments have

doubtless existed since the

evolu-tion of man, but our understanding

of the pathoanatomy and clinical

conditions associated with cervical

spondylosis is relatively recent

Classic anatomic studies by Brain et

al1and Payne and Spillane2in the

1950s began to clarify the disease

process and its effect on the neural

elements Surgical procedures

through a posterior approach for

decompression of the cervical spine

were available in the 1940s; how-ever, decompression from an ante-rior approach did not begin to be used until the late 1950s As cross-sectional imaging evolved—with computed tomographic (CT) scans

in the 1970s and later with magnetic resonance (MR) imaging—a better appreciation of the pathoanatomy emerged

A thorough understanding of the pathology of cervical spondylosis,

as well as the principles of clinical examination, radiologic evaluation, and surgical indications, is essential for optimal treatment planning

Complications as a consequence of

the treatment of cervical spondylotic myelopathy are intimately related

to the type and extent of surgical procedure selected

Natural History

Spinal cord compression resulting from spondylotic changes in the cer-vical spine is typically a slowly pro-gressive process Many patients have evidence of significant com-pression on neuroradiologic imag-ing but are relatively asymptomatic

It can be surprising how much chronic deformation the spinal cord can tolerate without interfering with patient function (Fig 1)

The natural history of cervical myelopathy has been described in classic papers by Lees and Turner3

and Clarke and Robinson.4 Lees and Turner described exacerbation

of symptoms followed by often long periods of static or worsening function or, in rare instances, im-provement Very few patients had

Dr Emery is Associate Professor, Department

of Orthopaedics, University Hospitals of Cleveland Spine Institute, Cleveland, Ohio Reprint requests: Dr Emery, University Hospitals of Cleveland Spine Institute, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106.

Copyright 2001 by the American Academy of Orthopaedic Surgeons.

Abstract

The delineation of cervical spondylotic myelopathy as a clinical entity has

improved with the development of high-quality cross-sectional neuroradiologic

imaging The natural history of this disorder is usually slow deterioration in a

stepwise fashion, with worsening symptoms of gait abnormalities, weakness,

sensory changes, and often pain The diagnosis can usually be made on the

basis of findings from the history, physical examination, and plain radiographs,

but confirmation by magnetic resonance imaging or computed tomography and

myelography is necessary Minimal symptoms without hard evidence of gait

disturbance or pathologic reflexes warrant nonoperative treatment, but patients

with demonstrable myelopathy and spinal cord compression are candidates for

operative intervention Both anterior and posterior approaches have been

uti-lized for surgical treatment of cervical myelopathy Anterior decompression

fre-quently requires corpectomy at one or more levels and strut grafting with bone

from the ilium or fibula Multilevel laminectomies were initially used for

poste-rior decompression but now are either combined with fusion or replaced by

laminoplasty Any operative technique requires proper patient selection and

demands adequate decompression of the canal to effect neurologic improvement.

Perioperative complications can be devastating in this group of high-risk

patients with cervical spondylotic myelopathy, but careful attention to detail,

meticulous technique, and experience can result in excellent outcomes.

J Am Acad Orthop Surg 2001;9:376-388

Diagnosis and Treatment

Sanford E Emery, MD

steady progressive deterioration.

Clarke and Robinson described a

similar stepwise pattern of

decreas-ing function Long periods of

sta-ble neurologic function, sometimes

lasting for years, were noted in

about 75% of their patients In the

majority, however, the condition

deteriorated between quiescent

streaks About 20% of patients had

a slow, steady progression of

symp-toms and signs without a stable

period, and 5% had rapid

deterio-ration of neurologic function

Generally, once moderate signs

and symptoms of myelopathy

de-velop, the ultimate prognosis is poor As cervical myelopathy has become better understood, most authors have recommended surgi-cal intervention for patients with moderate to severe myelopathy, taking into account both the clinical status and the neuroradiologic findings, to alter this unfavorable natural history

Pathology

The pathoanatomy of cervical spon-dylosis with myelopathy results

from the sequelae of the aging process in the spine (i.e., disk de-generation with hypertrophic os-seous and ligamentous changes) Disk desiccation is accompanied by biochemical changes, with a relative increase in the ratio of keratan sul-fate to chondroitin sulsul-fate The loss

of elasticity and total disk substance results in a decrease in disk height with annular bulging This altered biomechanical environment stimu-lates formation of chondro-osseous spurs at the annular insertion near the end-plates The uncovertebral joints hypertrophy, which may lead

Figure 1 Images of a 40-year-old man with severe cervical myelopathy who was able to ambulate with a walker and live independently

despite motor weakness in his arms and legs He underwent an anterior corpectomy with strut graft and halo vest placement Just prior

to discharge 1 week postoperatively, he died of an autopsy-proven acute coronary artery thrombosis A, Sagittal MR image demonstrates fixed subluxation of C3 on C4 with severe cord compression (arrowhead) B (top), Normal histologic cross section of the spinal cord at the C2 level (above the compression) B (bottom), Histologic cross section of the spinal cord at the level of maximal compression Note the

loss of central gray matter and disorganized architecture Arrowheads identify the dura (Reprinted with permission from Emery SE:

Cervical spondylotic radiculopathy and myelopathy: Anterior approach and pathology, in White AH, Schofferman JA [eds]: Spine Care.

St Louis: Mosby-Year Book, 1995, p 1370.)

to foraminal stenosis The posterior

zygoapophyseal joints can also

be-come arthritic, causing dorsal

foram-inal narrowing Thickening of the

ligamentum flavum occurs, as well

as buckling of the flavum due to loss

of disk height These degenerative

changes can result in cervical

steno-sis with spinal cord compression

(Fig 2, A), often in concert with disk

protrusions or frank herniations

Loss of cervical lordosis or even

ky-phosis may accentuate the problem

Instability can be another cause of

cord impingement (Fig 1) Cervical

spondylosis will typically result in

stiffening of the spinal motion

seg-ments It is not uncommon for the

motion segments one or two levels

above the stiff segments to become

hypermobile This is termed

“com-pensatory subluxation” (Fig 2, B)

Identification of this feature is

im-portant and often requires

flexion-extension lateral radiographs The

presence or absence of instability

will enter into the decision-making

process with regard to whether an

anterior or a posterior approach is

used, as well as the number of levels

requiring operative intervention

Cervical kyphosis is not uncom-mon in patients with significant spondylotic changes This deformity will aggravate the degree of com-pression in patients with cervical stenosis or disk herniations because the spinal cord will be stretched over the posterior aspect of the disks and vertebral bodies (Fig 2, C) The presence of kyphosis will typically dictate an anterior operative ap-proach to adequately decompress the canal as well as to achieve an improvement in the deformity, which augments the direct decom-pression

Ossification of the posterior lon-gitudinal ligament (OPLL) has also been described as a cause of cervi-cal myelopathy, with or without the presence of spondylotic changes.5

The etiology of this condition is unknown Genetic influences prob-ably predominate, with certain Asian populations, such as the Japanese, having a higher incidence

of OPLL than others The ossifica-tion can be at one level, can involve skip-type lesions at multiple levels,

or can be a continuous strip of bone (Fig 2, D) The ossified ligament is

often not a thin strip, but rather a bulbous mass that may be centrally

or eccentrically located (Fig 3) It can occur in conjunction with cervi-cal spondylosis and often produces severe anterior compression of the spinal cord Long-standing OPLL can ossify the adherent dura, which may create the problem of spinal fluid fistulae.6

Another important anatomic fac-tor underlying all of these patho-logic conditions is the initial size of the spinal canal.7,8 There is a cer-tain degree of variation in the size

of the space available for the spinal cord, which is probably genetically determined In the midcervical spine, the average midsagittal canal diameter is 17 to 18 mm (range, 13

to 20 mm in the normal spine) Be-cause spondylosis, disk herniations, and OPLL take up space, a patient with a congenitally narrow canal will have a higher risk of cord com-pression and myelopathy Neck extension decreases the spinal canal diameter even further, and patients can dynamically compress their cords with neck motion This phe-nomenon is exemplified by a

pa-Figure 2 Causes of spinal cord compression in cervical spondylotic myelopathy A, Cervical spondylosis with stenosis B, Compensatory

subluxation C, Cervical kyphosis D, Ossification of the posterior longitudinal ligament (segmental and continuous types).

tient with asymptomatic cervical

stenosis who sustains a

hyperexten-sion injury that results in acute

pin-cering of the spinal cord and central

cord syndrome

In patients with spondylosis, a

canal measurement on a lateral plain

radiograph of 12 mm or less often

indicates cord compression, which

may or may not be symptomatic, as

the average diameter of the spinal

cord in the midcervical spine is 10

mm However, plain radiographs

do not take into account soft-tissue

changes, such as disk herniations

and hypertrophied ligamentum

flavum, which can decrease the

space available for the cord

Fuji-wara et al9correlated the transverse

area of the spinal cord as measured

on CT-myelography with the severity

of pathologic changes in cadaveric

spinal cords Fujiwara et al10 and

Koyanagi et al11 have also found a

correlation between the preoperative

cross-sectional area of the cord and

the degree of postoperative

recov-ery; 30 mm2 was found to be a

watershed mark, with patients

hav-ing poorer neurologic recovery if the

preoperative cross-sectional area

was below this value

Pathophysiology of Spinal Cord Compression

The pathoanatomic changes that have been described have a direct compressive effect on the neural tissue with resultant spinal cord ischemia Ogino et al12 examined pathologic specimens and corre-lated their findings with the degree

of cord compression Mild to mod-erate compression was associated with degeneration of the lateral white-matter tracts More severe compression led to necrosis of the central gray matter This occurred when the ratio of the midsagittal diameter of the deformed cord to its width (the anterior-to-posterior compression ratio) was less than 1:5 The authors noted that the anterior white columns were rela-tively resistant to infarction, even

in cases of severe compression

Histologic changes associated with myelopathy include axonal demyelinization followed by cell necrosis and gliosis or scarring (Fig 1, B) Cystic cavitation can occur within the gray matter This more central destruction of the cord tissue is probably related to

ischemic changes caused by defor-mation of the cord Breig et al13

demonstrated that the vascular supply of the gray matter was from the transverse arterioles branching out from the anterior spinal artery system With flattening of the cord

in an anterior-to-posterior direc-tion, these transverse arterioles are subject to mechanical distortion, leading to relative ischemia of the gray matter and medial white mat-ter The pathophysiologic effects of cord compression are believed to

be a combination of ischemia and direct mechanical effects on the neural tissue

The complex biochemical and cel-lular mechanisms of acute spinal cord injury are an area of active cur-rent research Chemical and cellular mediators are being studied in both acute spinal cord injury and amyo-trophic lateral sclerosis to determine the role of glutamate toxicity, free-radical toxicity, cation-mediated cell injury, and programmed apoptosis (cell death) in both acute and pro-gressive deterioration of neural tis-sue Further research may allow investigators to relate these mecha-nisms to the chronic changes that occur with cervical myelopathy.14

Clinical Presentation

Patients with cervical spondylosis, either alone or in combination with root or cord compression, can pre-sent with a wide spectrum of clinical signs and symptoms Even patients with cord compression may be com-pletely asymptomatic with respect

to both pain and neurologic func-tion Others may have mild symp-toms with only neck pain or some component of radicular arm pain Paresthesias are common, typically occurring in a global, nonderma-tomal pattern in the upper extrem-ities Many patients with mye-lopathy will not appreciate their weakness; however, they may

com-Figure 3 Ossification of the posterior longitudinal ligament A, Sagittal section from

CT-myelographic study shows an osseous bar behind two vertebrae spanning the C5-C6 disk

space B, Cross-sectional view at C5 shows severe canal compromise from the

asymmetri-cal mass of OPLL extending from the posterior aspect of the vertebral body.

plain of subtle changes in gait and

balance This is often the first clue to

the presence of early myelopathy

If the cord compression and

myelopathy are either moderate or

severe, patients complain of gait

and balance abnormalities involving

the lower extremities They also

have numbness or paresthesias in

their upper extremities Fine motor

control is usually affected as well,

and they will note changes in their

handwriting or ability to

manipu-late buttons or zippers Arm

weak-ness is common in this group of

patients, either unilaterally or

bilat-erally Leg weakness can occur, and

patients may notice problems

mov-ing their body weight, such as is

necessary when rising out of a chair

or going up stairs In patients with

cervical myelopathy, the proximal

motor groups of the legs are more

involved than the distal groups

(which is the opposite of the pattern

with lumbar stenosis); thus,

presen-tation with foot-drop complaints is

rare Changes in bowel or bladder

function can occur in extremely

se-vere cases of myelopathy, but this is

quite rare Although most patients

with cervical spondylotic

myelopa-thy have neck pain, approximately

15% with moderate to severe

mye-lopathy do not This may cause

con-fusion or a delay in diagnosis.15

Spondylotic cord compression

can predispose a patient to spinal

cord injury (acute myelopathy) with

minor trauma This typically occurs

in elderly patients who sustain a

fall that results in a hyperextension

neck injury A central cord

syn-drome (motor weakness greater in

the arms than in the legs) often

ensues, with variable degrees of

paralysis The patient may

demon-strate obvious weakness,

prompt-ing immediate evaluation and

hos-pitalization At times, however, the

changes in the patient’s function

are minimal, and only with in-depth

history taking can one relate the

de-terioration to minor trauma

Physical Examination

The clinical evaluation should be-gin with an accurate description of the onset of symptoms and the time course over which they devel-oped Areas of neck tenderness and range of motion should then

be evaluated Neck extension is generally restricted and may be painful for patients with cervical stenosis or root compression This

is an important clinical feature and may indicate a narrowed canal and frank cord compression, which may be extremely important for patients undergoing procedures re-quiring general anesthesia Recog-nition of the decreased extension

and stenosis may prevent iatro-genic injury during intubation and operative positioning

A full neurologic examination is critical to detect motor weakness

or sensory changes Wasting of the intrinsic muscles of the hand and spasticity result in “myelopathy hand.”16 The “finger escape sign” may be evident (Fig 4, A) The pa-tient is asked to hold his or her fin-gers extended and adducted; if the two ulnar digits drift into abduc-tion and flexion in 30 to 60 sec-onds, cervical myelopathy is con-sidered to be present Similarly, the patient should be able to rapidly make a fist and release it in a re-petitive motion 20 times in 10

sec-B A

Figure 4 A, Finger-escape sign The patient holds his fingers extended and adducted In

patients with cervical myelopathy, the two ulnar digits will flex and abduct, usually in less

than 1 minute B, Grip-and-release test Normally, one can make a fist and rapidly release

it 20 times in 10 seconds; patients with myelopathy may be unable to do this that quickly.

C, Hoffmann reflex Snapping the distal phalanx of the patient’s middle finger downward

will result in spontaneous flexion of the other fingers in a positive test D, Inverted radial

reflex Tapping the distal brachioradialis tendon produces hyperactive finger flexion.

onds (Fig 4, B); slow or clumsy

performance on this

grip-and-release test is consistent with

cervi-cal cord compression

Wasting of the shoulder girdle

may be evident in patients with

stenosis at C4-5 and C5-6 due to loss

of anterior-horn cell function This

dropout of motor neurons may also

manifest as fasciculation in the

upper-extremity muscles This is a

nonspecific finding, however, and

can be present in degenerative

upper motor neuron diseases, such

as amyotrophic lateral sclerosis

Pinprick examination should be

done in the upper and lower

extrem-ities, looking for a global decrease in

sensation, dermatomal changes, and

dysesthesias Vibratory testing is

performed to test the function of the

posterior columns This finding, if

present, is typically found in severe

cases of long-standing myelopathy

Vibratory testing is also utilized to

help detect concomitant changes

due to peripheral neuropathy, such

as may be noted in patients with

diabetes, thyroid disease, or heavy

alcohol use

Reflex examination should show

hyperreflexia in both the upper and

the lower extremities, although

severe concomitant cervical root

compression may result in an absent

reflex in one or more muscle groups

Clonus and positive Babinski and

Hoffmann reflexes (Fig 4, C) are

abnormal long-tract signs consistent

with cord compression These are

found in varying degrees in patients

with moderate to severe

myelopa-thy The inverted radial reflex is

an-other pathologic change sometimes

evident in patients with cervical

stenosis and myelopathy If tapping

the brachioradialis tendon in the

dis-tal forearm elicits a hypoactive

bra-chioradialis reflex plus hyperactive

finger flexion, this is a positive radial

reflex This correlates with cord and

C5 root lesions that produce

spastic-ity distal to the compression and a

hypoactive response at the level of

root or anterior horn cells (Fig 4, D)

Cranial nerve abnormalities or a hyperactive jaw jerk can suggest a cranial or brainstem lesion, which should be evaluated with brain imaging and neurologic consul-tation

Patients with cervical complaints should have their gait examined for ability to toe-walk, heel-walk, and perform a toe-to-heel tightrope gait

Subtle myelopathy may be evident

on this provocative testing The Romberg test, in which the patient stands with the arms held forward and the eyes closed, is a test for position sense; loss of balance is

a positive result consistent with posterior-column dysfunction

Radiologic Evaluation

Radiographic changes of cervical spondylosis are age-related and occur in most people over the age

of 50 Typical radiographic mani-festations include disk-space nar-rowing, end-plate sclerosis, and osteophytic changes at the end-plates, uncovertebral joints, and facet joints Plain radiographs re-main an important part of the diagnostic workup, and anteropos-terior (AP), lateral, and flexion-extension views of the cervical spine should be obtained in essen-tially all patients in this age group

Oblique views are useful for visual-izing foraminal narrowing, which is typically due to uncovertebral joint spurs; however, the true utility of oblique views in evaluation of de-generative conditions is question-able The AP view allows identifi-cation of cervical ribs and scoliotic deformity The lateral view is most important, as it demonstrates the degree of disk narrowing, the size

of end-plate osteophytes, the size of the spinal canal, and sagittal align-ment In some cases, OPLL is visu-alized as a bar of bone running along the posterior aspect of the

vertebral bodies Overall sagittal alignment (lordosis versus kypho-sis) is also important in that it may influence the choice of surgical pro-cedure Flexion-extension views are critical to diagnose instability, which may not be evident on a neutral lateral view Patients with stiffening of the midcervical spine from spondylotic changes often have a compensatory subluxation one or two levels above the stiffer levels

Magnetic resonance imaging is the next step in the evaluation of the patient with a presumed diag-nosis of spondylosis with myelopa-thy However, this modality is cer-tainly not indicated for everyone who presents with neck pain Per-sistent neck or arm pain (present for more than 2 or 3 months), neuro-logic findings, or a worsening symp-tomatic picture warrants neuroradio-logic investigation If evidence of myelopathy is present on physical examination, MR imaging is indi-cated to assess the extent of patho-logic changes to the soft tissues (e.g., disk herniation, hypertrophy, and buckling of the ligamentum flavum) and the degree of cord compression One of the strengths

of MR imaging is the ability to visu-alize the spinal cord The size and shape of the cord are evident on both sagittal and transverse images Flattening of the cord over anterior compressive lesions, such as osteo-phytic ridging, OPLL, disk hernia-tions, and kyphotic deformities, can

be seen In long-standing cases of compression, cord atrophy is evi-dent It is important to identify pa-renchymal changes, such as syrinx formation, or high-intensity signal within the cord resulting from mye-lomalacia Although high-intensity signal change does not necessarily correlate with preoperative deficits

or postoperative recovery, it certainly identifies pathologic changes within the cord that should alert the treat-ing physician

Although MR imaging provides

optimal visualization of soft tissues,

CT-myelography offers better

defi-nition of bone spurs and OPLL The

exact degree of cord deformation in

the transverse plane is more sharply

visualized with CT-myelography

as well This modality is useful in

evaluating whether marginal levels

need to be included in an operative

procedure

Other forms of clinical

evalua-tion include electrodiagnostic

tech-niques For patients with cervical

radiculopathy, electromyographic–

nerve conduction studies may be

useful in considering the

differen-tial diagnosis of carpal tunnel

drome, ulnar cubital tunnel

syn-drome, or thoracic outlet syndrome

Electrodiagnostic modalities may

also help elucidate the confusing

clinical presentations of amyotrophic

lateral sclerosis, multiple sclerosis,

and severe peripheral neuropathy

Somatosensory-evoked

poten-tials and motor-evoked potenpoten-tials

are of limited utility during the

diagnostic evaluation but are used

intraoperatively A preoperative

baseline study can be very helpful,

especially in patients with severe

changes in latency and amplitude

Some authors advocate the use of

intraoperative spinal-cord evoked

potentials to identify the level of

greatest conduction delay and then

limit surgery to that level17;

how-ever, this approach risks leaving

clinically significant pathologic

changes in untreated areas

Nonoperative Treatment

Patients with neuroradiologic

evi-dence of spinal cord compression

but no symptoms or signs of

mye-lopathy should generally be

ob-served One exception would be a

patient with such severe

compres-sion that even low-energy trauma,

such as might occur with a rear-end

motor vehicle impact or a fall, could

predictably result in spinal cord injury It is extremely rare for a pa-tient with that degree of cord com-pression on imaging studies to be truly asymptomatic; nevertheless, these patients should be counseled to avoid high-risk situations in which a hyperextension injury might occur,

as they are at some increased risk for cord impingement

Patients with mild myelopathy may display findings such as slight gait disturbance and mild hyper-reflexia but may have no functional deficits and no weakness The indi-vidual clinical course and especially the pattern of deteriorations should

be well understood by both physi-cian and patient If the patient is in

a plateau period without recent ex-acerbation, nonoperative treatment may be indicated Reevaluation every 6 to 12 months to look for de-terioration of neurologic function or

a change in symptoms may be ap-propriate

Indications for Surgery

The natural history of cervical myelopathy for most patients is slow deterioration over time Typ-ically, this is in a stepwise fashion with variable periods of stable neuro-logic function If one assumes sig-nificant deterioration for all pa-tients with myelopathy, it can be argued that operative intervention

is indicated for everyone with this clinical and radiographic diagnosis

However, the decision making is much more complex, with the clini-cal severity of myelopathy being the most important issue

The extent of myelopathy is reflected predominantly by physi-cal examination findings such as balance deficits, gait, motor weak-ness, long-tract signs, and changes

in function (e.g., decreased fine motor control) All of these clinical findings provide evidence of the degree of cord dysfunction Other

important factors involved in the decision-making process include the amount of pain the patient is experiencing, the degree of change

of function that can be tolerated, and the evaluation of symptoms Patients with rapid neurologic de-terioration should undergo earlier operative intervention

Consideration of the severity of compression evident on neuroradio-logic studies is important, as the severity of cord compression gener-ally, but not always, correlates with the level of function For patients with equivalent signs and symp-toms of moderate myelopathy, operative intervention would be recommended earlier if there were more severe radiologic findings, such as smaller cord area, cord atro-phy, signal changes indicative of myelomalacia, or the presence of a kyphotic deformity Although not all neuroradiologic findings have been correlated with preoperative symptoms or postoperative out-come, more severe compression intuitively suggests more risk for the spinal cord

For patients with moderate to se-vere compression and myelopathy, surgical intervention is indicated to alter the natural history Surgery can be expected to halt progression

in neurologic function and may improve motor, sensory, and gait disturbance The degree of recovery depends largely on the severity of the myelopathy at the time of inter-vention.10,15 Other factors of posi-tive prognostic value include larger transverse area of the cord, younger patient age, shorter duration of symptoms, and single rather than multiple levels of involvement.10,11

Many patients with cervical spon-dylosis and myelopathy are elderly, but age alone is not a contraindica-tion to operative intervencontraindica-tion Patients with chronic cervical spondylosis who suffer acute minor trauma, particularly a hyperexten-sion injury, can sustain acute spinal

cord injuries of varying severity

superimposed on the long-standing

myelopathy Typically, this

pre-sents as a central cord syndrome

with greater weakness in the upper

extremities than in the lower

ex-tremities and proximal rather than

distal muscle involvement in each

extremity This can occur with or

without a prior history of

myelo-pathic symptoms Initial treatment

involves collar immobilization,

high-dose methylprednisolone, and

a neuroradiologic investigation If

neurologic function improves after

the injury, the plateau functional

level should be determined If

re-covery is complete or near

com-plete, surgery is not necessary

Residual deficits, as evidenced by

the appearance of cord compression

on imaging studies, warrant

opera-tive intervention to promote

neuro-logic recovery One recent

long-term study of patients with central

cord syndrome treated

nonopera-tively documented much poorer

recovery in patients over 50 years of

age compared with younger

pa-tients.18 There are no data

docu-menting a substantial difference in

recovery if diagnosis was early

rather than late

Surgical Approaches

The preferred approach for surgical treatment of cervical myelopathy continues to be controversial, as both anterior and posterior tech-niques have been used successfully

Posterior options include multilevel laminectomy,19 laminoplasty, and laminectomy plus fusion proce-dures Anterior options include multiple anterior diskectomies with fusion and corpectomy plus strut fusion techniques with or without the use of anterior instru-mentation The choice of approach

is determined on the basis of the existing lesion and surgeon experi-ence Factors to be considered in-clude the number of involved lev-els, overall sagittal alignment, the direction of compression, the pres-ence of instability, and clinical symptoms

Posterior Approach

For patients with diffuse canal stenosis or dorsal cord compres-sion due to buckling of the liga-mentum flavum posteriorly, a pos-terior decompression technique may

be ideal to achieve adequate decom-pression (Fig 5) However, most

patients with cervical spondylosis and certainly those with OPLL have predominantly anterior com-pression of the cervical cord Any posterior decompressive procedure

is an indirect technique that re-quires posterior shifting of the cord

in the thecal sac to diminish the effect of the anterior compression For this to occur, the preoperative sagittal alignment of the cervical spine must be at least straight or preferably lordotic A kyphotic spine

is less likely to allow sufficient pos-terior translation of the spinal cord

to diminish symptoms This is a key point in choosing between pos-terior and anpos-terior approaches for surgical treatment of myelopathy,

as is the presence of instability Laminectomy alone will only

wors-en preexisting instability Fusion must be added if the posterior ap-proach is the preferred route of de-compression

Multilevel laminectomy was ini-tially the only procedure available

to treat cervical stenosis and may still have a place for selected pa-tients The results after that proce-dure deteriorate due to the devel-opment of late instability, such as kyphosis or subluxation, although

Figure 5 Images of a 61-year-old man with moderate cervical spondylotic myelopathy, gait changes, upper-extremity neurologic signs

and symptoms, and minimal neck pain A, Sagittal MR image shows normal lordosis and suggests diffuse narrowing of the spinal canal over multiple levels B, Axial CT-myelographic image at C5 shows severe stenosis that is causing circumferential, rather than focal

anteri-or, cord impingement C, The patient underwent a laminoplasty from C3 to C7 performed with use of the Chiba method A postoperative

CT image demonstrates expansion of the spinal canal at C4 The clinical outcome at 3-year follow-up was rated as successful.

the exact incidence of this problem

is difficult to determine The

addi-tion of a multilevel fusion at the

time of laminectomy eliminates the

potential for development of late

postoperative kyphosis or

instabil-ity Although originally done with

bone graft wired to the facets, it is

now more easily achieved by lateral

mass plating and fusion

Laminoplasty evolved as a method

to eliminate postoperative

develop-ment of instability and kyphosis by

expanding the canal while retaining

the posterior elements.20,21 Several

techniques for performing

lamino-plasty have been devised, but all

adhere to the concept of canal

ex-pansion by opening the posterior

elements in a trapdoor fashion but

not completely removing the

osse-ous posterior arch By expanding

the size of the canal, the cord

com-pression can be alleviated or

less-ened, and the chance of

postopera-tive instability is minimized because

the posterior musculature can heal

to the residual posterior osseous

ele-ments Most methods are based on

either a unilateral hinge with a

one-way trapdoor opening to expand

the canal20 or a midline spinous

process–splitting procedure with

bilateral hinges to expand the canal

in a symmetrical fashion.22,23 A

small amount of bone graft or spacer

is often placed in the opening

de-fects, but arthrodesis of the motion

segments is not desirable

Lamino-plasty results in a 30% to 50% loss

of motion in the cervical spine,23,24

which is less than occurs with

mul-tilevel arthrodesis

Anterior Approach

Because the pathoanatomy of

cord compression in degenerative

conditions is typically anterior to

the spinal cord, an anterior

ap-proach allows direct

decompres-sion of the dura (Fig 6) Two

dif-ferent techniques can be utilized,

with selection dependent on

align-ment and the pathologic features

If the cord compression is present only at the disks at one, two, or three levels, an anterior cervical diskectomy with graft at each level

is appropriate In most patients with spondylotic myelopathy or OPLL, there is compression at the disk as well as above and below the disk space Usually, this is caused

by large osteophytes or ridging at the vertebral end-plates

Ossifica-tion of the posterior longitudinal ligament occurs behind the verte-bral body and may be focal or mul-tifocal or may appear as a continu-ous long ossecontinu-ous bar Because the surgeon cannot safely reach poste-rior to the vertebral bodies through the disk space, it is necessary to remove part or all of the midpor-tion of the vertebral body to ade-quately decompress the canal

A

C

B

D Figure 6 A, Sagittal T2-weighted MR image demonstrates spondylotic changes with

severe spinal cord compression predominantly at two levels B, Postoperative CT scan demonstrates decompression of the spinal canal and the fibular graft C, Lateral

radio-graph obtained immediately after two-level anterior cervical corpectomies and fibular

strut grafting (arrowheads) D, Lateral radiograph obtained 2 years later shows smooth

bone remodeling, indicating a solid arthrodesis.

Hemicorpectomies may be

per-formed for end-plate osteophytes

located near the disk spaces;

how-ever, full corpectomies are more

commonly performed to totally

decompress the canal at several

disk levels as needed The lateral

walls of the vertebral body are left

intact because they provide

protec-tion against vertebral artery injury

The typical midline channel for a

corpectomy is 16 to 18 mm, which

provides adequate decompression

for the entire canal if it is

appropri-ately centered in the midline

It is not uncommon for a patient

with cervical spondylotic

myelopa-thy to require a two- or three-level

corpectomy and then a strut graft

for fusion or to correct kyphosis

The degree of difficulty of the

proce-dure, the risk of postoperative graft

complications, and the potential for

soft-tissue complications increase

with the number of corpectomy

lev-els This limitation should enter into

the decision-making process

regard-ing choice of approach

Autograft, allograft, and even

metal cages with cancellous grafts

have been used as struts to

main-tain alignment and promote

ar-throdesis Autografts provide the

highest union rate Harvesting

large iliac-crest grafts may be

asso-ciated with local pain, fracture of

the ilium, and injury to the lateral

femoral cutaneous nerve

Autol-ogous fibular grafts have been

asso-ciated with less morbidity than long

iliac grafts, although tibial stress

fractures,25pain, and muscle

weak-ness26have been described

Allo-graft iliac-crest or fibular Allo-grafts are

used for single-level diskectomy

and fusion, with good success rates

reported in most studies27 but less

optimal results in others.28 Fibular

strut allografts have also been used

successfully29 for reconstruction

after multilevel corpectomy but are

slower to heal and have a higher

rate of pseudarthrosis Some

sur-geons use cancellous chips from the

vertebrectomy to augment the allo-graft; others prefer supplemental posterior fixation combined with anterior allograft struts to promote union Many surgeons utilize iliac-crest strut grafts for one- or two-level vertebrectomy procedures and fibular strut grafts for constructs to

be used at two or more levels

Theoretically, the use of anterior cervical plates provides additional stability, maintains correction of deformity, and promotes arthrode-sis, especially in longer or multilevel constructs There is considerable controversy concerning the use of plates for one-level anterior cervical diskectomy and fusion, unless there are certain coexisting circumstances, such as a history of smoking or the presence of adjacent segment fu-sions Anterior plate fixation after one-level corpectomy (two-level fusion) with iliac-strut fusion pro-vides increased stability and may allow less restrictive immobilization postoperatively

The use of anterior plates for multilevel corpectomy and strut-graft procedures is more controver-sial Because of the long lever arm with only two screws above and two screws below, a high rate of loosening and displacement has been described for these long-plate constructs.30 Three-level corpectomy procedures seem to be at higher risk for this complication than two-level procedures Also, plate fixa-tion does not allow settling of the graft into the vertebral-body dock-ing sites, which may actually inhibit arthrodesis Other authors have utilized a small buttress-type plate

at the inferior end of the strut-graft construct to help prevent graft dis-lodgment Failures with this tech-nique have also been reported.31

Meticulous preparation of the ver-tebral bodies, including centralizing the graft in the end-plate with sculpted mortices, will help mini-mize complications due to graft dis-lodgment

Choice of Approach

For each patient, the surgeon should weigh the relative advan-tages and disadvanadvan-tages of the anterior and posterior approaches Neither is optimal for every patient with cervical spondylotic myelopa-thy, although either may be appro-priate for some patients The rela-tive pros and cons of laminoplasty versus anterior corpectomy and strut grafting are summarized in Table 1

Anterior decompression and arthrodesis is a more direct decom-pression method that allows cor-rection of deformity and stabiliza-tion with fusion It is technically demanding, especially in multi-level cases, and one must be pre-pared to deal with graft-related complications Rigid postoperative bracing is necessary with an ortho-sis or a halo vest

The posterior approach is an in-direct method of decompression in most cases and relies on the spinal cord being able to shift posteriorly

in an expanded canal For this rea-son, patients with preoperative kyphosis are not good candidates for a posterior unroofing-type pro-cedure because the anterior im-pingement on the cord will remain Compensatory subluxation or other instability may also worsen with a posterior approach if fusion is not performed

Laminoplasty techniques are not

as technically demanding as multi-level anterior corpectomy and strut-grafting procedures There is less bracing required, as a soft collar will generally suffice for comfort after laminoplasty Although some loss

of motion is typical after lamino-plasty procedures, this would be expected to be less than occurs with long arthrodesis methods More re-cent data have suggested that lami-noplasty techniques may not provide consistent relief of axial neck pain,32

whereas anterior fusion procedures provide good axial pain relief.15