Cervical spondylosis results from the nearly universal process of degeneration of the disks and joints of the cervical spine. These changes in the spinal motion segments have doubtless existed since the evolution of man, but our understanding of the pathoanatomy and clinical conditions associated with cervical spondylosis is relatively recent. Classic anatomic studies by Brain et al1 and Payne and Spillane2 in 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; however, decompression from an anterior approach did not begin to be used until the late 1950s. As crosssectional 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.
Spinal cord compression resulting from spondylotic changes in the cervical spine is typically a slowly progressive process. Many patients have evidence of significant compression on neuroradiologic imaging 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, improvement. Very few patients had steady progressive deterioration. Clarke and Robinson described a similar stepwise pattern of decreasing function. Long periods of stable 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 symptoms and signs without a stable period, and 5% had rapid deterioration of neurologic function.
Generally, once moderate signs and symptoms of myelopathy develop, the ultimate prognosis is poor. As cervical myelopathy has become better understood, most authors have recommended surgical 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.
The pathoanatomy of cervical spondylosis with myelopathy results from the sequelae of the aging process in the spine (i.e., disk degeneration with hypertrophic osseous and ligamentous changes). Disk desiccation is accompanied by biochemical changes, with a relative increase in the ratio of keratan sulfate to chondroitin sulfate. The loss of elasticity and total disk substance results in a decrease in disk height with annular bulging. This altered biomechanical environment stimulates formation of chondro-osseous spurs at the annular insertion near the end-plates. The uncovertebral joints hypertrophy, which may lead to foraminal stenosis. The posterior zygoapophyseal joints can also become arthritic, causing dorsal foraminal 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 stenosis with spinal cord compression (Fig. 2, A), often in concert with disk protrusions or frank herniations. Loss of cervical lordosis or even kyphosis 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 segments. It is not uncommon for the motion segments one or two levels above the stiff segments to become hypermobile. This is termed “compensatory subluxation” (Fig. 2, B). Identification of this feature is important and often requires flexionextension 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 uncommon in patients with significant spondylotic changes. This deformity will aggravate the degree of compression 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 approach to adequately decompress the canal as well as to achieve an improvement in the deformity, which augments the direct decompression.
Ossification of the posterior longitudinal ligament (OPLL) has also been described as a cause of cervical myelopathy, with or without the presence of spondylotic changes.5 The etiology of this condition is unknown. Genetic influences probably predominate, with certain Asian populations, such as the Japanese, having a higher incidence of OPLL than others. The ossification 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 cervical 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 factor underlying all of these pathologic conditions is the initial size of the spinal canal.7,8 There is a certain 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). Because spondylosis, disk herniations, and OPLL take up space, a patient with a congenitally narrow canal will have a higher risk of cord compression and myelopathy. Neck extension decreases the spinal canal diameter even further, and patients can dynamically compress their cords with neck motion. This phenomenon is exemplified by a patient with asymptomatic cervical stenosis who sustains a hyperextension injury that results in acute pincering 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. Fujiwara et al9 correlated 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 recovery; 30 mm2 was found to be a watershed mark, with patients having 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 correlated their findings with the degree of cord compression. Mild to moderate 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 relatively 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 deformation 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 direction, these transverse arterioles are subject to mechanical distortion, leading to relative ischemia of the gray matter and medial white matter. 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 cellular mechanisms of acute spinal cord injury are an area of active current research. Chemical and cellular mediators are being studied in both acute spinal cord injury and amyotrophic lateral sclerosis to determine the role of glutamate toxicity, freeradical toxicity, cation-mediated cell injury, and programmed apoptosis (cell death) in both acute and progressive deterioration of neural tissue. Further research may allow investigators to relate these mechanisms to the chronic changes that occur with cervical myelopathy.14
Patients with cervical spondylosis, either alone or in combination with root or cord compression, can present with a wide spectrum of clinical signs and symptoms. Even patients with cord compression may be completely asymptomatic with respect to both pain and neurologic function. Others may have mild symptoms with only neck pain or some component of radicular arm pain. Paresthesias are common, typically occurring in a global, nondermatomal pattern in the upper extremities. Many patients with myelopathy will not appreciate their weakness; however, they may complain 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 manipulate buttons or zippers. Arm weakness is common in this group of patients, either unilaterally or bilaterally. Leg weakness can occur, and patients may notice problems moving 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, presentation with foot-drop complaints is rare. Changes in bowel or bladder function can occur in extremely severe cases of myelopathy, but this is quite rare. Although most patients with cervical spondylotic myelopathy have neck pain, approximately 15% with moderate to severe myelopathy do not. This may cause confusion 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 syndrome (motor weakness greater in the arms than in the legs) often ensues, with variable degrees of paralysis. The patient may demonstrate obvious weakness, prompting immediate evaluation and hospitalization. At times, however, the changes in the patient’s function are minimal, and only with in-depth history taking can one relate the deterioration to minor trauma.
The clinical evaluation should begin with an accurate description of the onset of symptoms and the time course over which they developed. 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 requiring general anesthesia. Recognition of the decreased extension and stenosis may prevent iatrogenic 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 patient is asked to hold his or her fingers extended and adducted; if the two ulnar digits drift into abduction and flexion in 30 to 60 seconds, cervical myelopathy is considered to be present. Similarly, the patient should be able to rapidly make a fist and release it in a repetitive motion 20 times in 10 sec onds (Fig. 4, B); slow or clumsy performance on this grip-and-release test is consistent with cervical 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 extremities, 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 myelopathy. The inverted radial reflex is another pathologic change sometimes evident in patients with cervical stenosis and myelopathy. If tapping the brachioradialis tendon in the distal forearm elicits a hypoactive brachioradialis reflex plus hyperactive finger flexion, this is a positive radial reflex. This correlates with cord and C5 root lesions that produce spasticity 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 consultation.
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.
Radiographic changes of cervical spondylosis are age-related and occur in most people over the age of 50. Typical radiographic manifestations include disk-space narrowing, end-plate sclerosis, and osteophytic changes at the endplates, uncovertebral joints, and facet joints. Plain radiographs remain an important part of the diagnostic workup, and anteroposterior (AP), lateral, and flexion-extension views of the cervical spine should be obtained in essentially all patients in this age group. Oblique views are useful for visualizing foraminal narrowing, which is typically due to uncovertebral joint spurs; however, the true utility of oblique views in evaluation of degenerative conditions is questionable. The AP view allows identification 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 alignment. In some cases, OPLL is visualized as a bar of bone running along the posterior aspect of the vertebral bodies. Overall sagittal alignment (lordosis versus kyphosis) is also important in that it may influence the choice of surgical procedure. 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 diagnosis of spondylosis with myelopathy. However, this modality is certainly not indicated for everyone who presents with neck pain. Persistent neck or arm pain (present for more than 2 or 3 months), neurologic findings, or a worsening symptomatic picture warrants neuroradiologic investigation. If evidence of myelopathy is present on physical examination, MR imaging is indicated to assess the extent of pathologic 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 visualize 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 osteophytic ridging, OPLL, disk herniations, and kyphotic deformities, can be seen. In long-standing cases of compression, cord atrophy is evident. It is important to identify parenchymal changes, such as syrinx formation, or high-intensity signal within the cord resulting from myelomalacia. 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 treating physician.
Although MR imaging provides optimal visualization of soft tissues, CT-myelography offers better definition 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 evaluation include electrodiagnostic techniques. For patients with cervical radiculopathy, electromyographic-nerve conduction studies may be useful in considering the differential diagnosis of carpal tunnel syndrome, ulnar cubital tunnel syndrome, 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 potentials and motor-evoked potentials 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; however, this approach risks leaving clinically significant pathologic changes in untreated areas.
Patients with neuroradiologic evidence of spinal cord compression but no symptoms or signs of myelopathy should generally be observed. One exception would be a patient with such severe compression 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 patient with that degree of cord compression 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 hyperreflexia but may have no functional deficits and no weakness. The individual clinical course and especially the pattern of deteriorations should be well understood by both physician and patient. If the patient is in a plateau period without recent exacerbation, nonoperative treatment may be indicated. Reevaluation every 6 to 12 months to look for deterioration of neurologic function or a change in symptoms may be appropriate.
Indications for Surgery
The natural history of cervical myelopathy for most patients is slow deterioration over time. Typically, this is in a stepwise fashion with variable periods of stable neurologic function. If one assumes significant deterioration for all patients 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 clinical severity of myelopathy being the most important issue.
The extent of myelopathy is reflected predominantly by physical examination findings such as balance deficits, gait, motor weakness, 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 deterioration should undergo earlier operative intervention.
Consideration of the severity of compression evident on neuroradiologic studies is important, as the severity of cord compression generally, but not always, correlates with the level of function. For patients with equivalent signs and symptoms of moderate myelopathy, operative intervention would be recommended earlier if there were more severe radiologic findings, such as smaller cord area, cord atrophy, 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 outcome, more severe compression intuitively suggests more risk for the spinal cord.
For patients with moderate to severe 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 intervention.10,15 Other factors of positive 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 spondylosis and myelopathy are elderly, but age alone is not a contraindication to operative intervention.
Patients with chronic cervical spondylosis who suffer acute minor trauma, particularly a hyperextension injury, can sustain acute spinal cord injuries of varying severity superimposed on the long-standing myelopathy. Typically, this presents as a central cord syndrome with greater weakness in the upper extremities than in the lower extremities and proximal rather than distal muscle involvement in each extremity. This can occur with or without a prior history of myelopathic 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 recovery is complete or near complete, surgery is not necessary. Residual deficits, as evidenced by the appearance of cord compression on imaging studies, warrant operative intervention to promote neurologic recovery. One recent longterm study of patients with central cord syndrome treated nonoperatively documented much poorer recovery in patients over 50 years of age compared with younger patients.18 There are no data documenting a substantial difference in recovery if diagnosis was early rather than late.
The preferred approach for surgical treatment of cervical myelopathy continues to be controversial, as both anterior and posterior techniques have been used successfully. Posterior options include multilevel laminectomy,19 laminoplasty, and laminectomy plus fusion procedures. Anterior options include multiple anterior diskectomies with fusion and corpectomy plus strut fusion techniques with or without the use of anterior instrumentation. The choice of approach is determined on the basis of the existing lesion and surgeon experience. Factors to be considered include the number of involved levels, overall sagittal alignment, the direction of compression, the presence of instability, and clinical symptoms.
For patients with diffuse canal stenosis or dorsal cord compression due to buckling of the ligamentum flavum posteriorly, a posterior decompression technique may be ideal to achieve adequate decompression (Fig. 5). However, most patients with cervical spondylosis and certainly those with OPLL have predominantly anterior compression of the cervical cord. Any posterior decompressive procedure is an indirect technique that requires 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 posterior translation of the spinal cord to diminish symptoms. This is a key point in choosing between posterior and anterior approaches for surgical treatment of myelopathy, as is the presence of instability. Laminectomy alone will only worsen preexisting instability. Fusion must be added if the posterior approach is the preferred route of decompression.
Multilevel laminectomy was initially the only procedure available to treat cervical stenosis and may still have a place for selected patients. The results after that procedure deteriorate due to the development of late instability, such as kyphosis or subluxation, although the exact incidence of this problem is difficult to determine. The addition of a multilevel fusion at the time of laminectomy eliminates the potential for development of late postoperative kyphosis or instability. 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 development of instability and kyphosis by expanding the canal while retaining the posterior elements.20,21 Several techniques for performing laminoplasty have been devised, but all adhere to the concept of canal expansion by opening the posterior elements in a trapdoor fashion but not completely removing the osseous posterior arch. By expanding the size of the canal, the cord compression can be alleviated or lessened, and the chance of postoperative instability is minimized because the posterior musculature can heal to the residual posterior osseous elements. Most methods are based on either a unilateral hinge with a oneway 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 defects, but arthrodesis of the motion segments is not desirable. Laminoplasty results in a 30% to 50% loss of motion in the cervical spine,23,24 which is less than occurs with multilevel arthrodesis.
Because the pathoanatomy of cord compression in degenerative conditions is typically anterior to the spinal cord, an anterior approach allows direct decompression of the dura (Fig. 6). Two different techniques can be utilized, with selection dependent on alignment 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. Ossification of the posterior longitudinal ligament occurs behind the vertebral body and may be focal or multifocal or may appear as a continuous long osseous bar. Because the surgeon cannot safely reach posterior 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 adequately decompress the canal.
Hemicorpectomies may be performed for end-plate osteophytes located near the disk spaces; however, 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 protection 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 appropriately centered in the midline.
It is not uncommon for a patient with cervical spondylotic myelopathy 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 procedure, the risk of postoperative graft complications, and the potential for soft-tissue complications increase with the number of corpectomy levels. This limitation should enter into the decision-making process regarding choice of approach.
Autograft, allograft, and even metal cages with cancellous grafts have been used as struts to maintain alignment and promote arthrodesis. Autografts provide the highest union rate. Harvesting large iliac-crest grafts may be associated with local pain, fracture of the ilium, and injury to the lateral femoral cutaneous nerve. Autologous fibular grafts have been associated with less morbidity than long iliac grafts, although tibial stress fractures,25 pain, and muscle weakness26 have been described. Allograft iliac-crest or fibular 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 surgeons use cancellous chips from the vertebrectomy to augment the allograft; others prefer supplemental posterior fixation combined with anterior allograft struts to promote union. Many surgeons utilize iliaccrest 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 arthrodesis, 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 fusions. Anterior plate fixation after one-level corpectomy (two-level fusion) with iliac-strut fusion provides increased stability and may allow less restrictive immobilization postoperatively.
The use of anterior plates for multilevel corpectomy and strutgraft procedures is more controversial. 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 fixation does not allow settling of the graft into the vertebral-body docking 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 dislodgment. Failures with this technique have also been reported.31 Meticulous preparation of the vertebral bodies, including centralizing the graft in the end-plate with sculpted mortices, will help minimize complications due to graft dislodgment.
Choice of Approach
For each patient, the surgeon should weigh the relative advantages and disadvantages of the anterior and posterior approaches. Neither is optimal for every patient with cervical spondylotic myelopathy, although either may be appropriate for some patients. The relative pros and cons of laminoplasty versus anterior corpectomy and strut grafting are summarized in Table 1.
Anterior decompression and arthrodesis is a more direct decompression method that allows correction of deformity and stabilization with fusion. It is technically demanding, especially in multilevel cases, and one must be prepared to deal with graft-related complications. Rigid postoperative bracing is necessary with an orthosis or a halo vest.
The posterior approach is an indirect method of decompression in most cases and relies on the spinal cord being able to shift posteriorly in an expanded canal. For this reason, patients with preoperative kyphosis are not good candidates for a posterior unroofing-type procedure because the anterior impingement 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 multilevel anterior corpectomy and strutgrafting 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 laminoplasty procedures, this would be expected to be less than occurs with long arthrodesis methods. More recent data have suggested that laminoplasty techniques may not provide consistent relief of axial neck pain,32 whereas anterior fusion procedures provide good axial pain relief.15
The preoperative symptoms play a role in the decision-making process as well. Patients with diffuse canal stenosis and a congenitally narrow canal may require decompression of virtually the entire cervical spine. This is more readily achieved with laminoplasty techniques. Some authors prefer the anterior approach for patients with pathologic changes at one or two levels and posterior surgery for those with involvement at three or more levels.33 With proper patient selection, both anterior and posterior techniques will provide comparable rates of neurologic recovery and improvement of function.34,35
There are cases in which anterior multilevel decompression and strut grafting followed by posterior stabilization is indicated. Postlaminectomy kyphosis is perhaps the best example of this. Anterior decompression will typically be needed because of the degree of deformity and anterior-cord compression. Prior removal of the posterior elements predisposes them to graft complications if only an anterior approach is performed36; immediate posterolateral mass plating will help protect the graft, maintain alignment, and promote successful arthrodesis. The circumferential approach is also preferable for patients with severe osteoporosis, because it avoids fracture of the inferior end-plate due to loading by the graft. In multilevel cases requiring corpectomies at three or more levels, supplemental posterior fixation may increase fusion rates and decrease complications.
Complications can generally be categorized as: (1) approach-related, (2) decompression-related, (3) graft-related, and (4) long-term. Risks incurred with the anterior approach to the cervical spine include stretch injuries to the recurrent laryngeal nerve, which produce hoarseness. The incidence of this injury is believed to be approximately 1% to 2%.37 Dysphagia is experienced transiently by most patients after an anterior surgical approach, but can be a persistent problem for some. Upper airway compromise from edema or hematoma formation is more likely after multilevel corpectomy procedures.38 Drains should be utilized, and patients frequently are monitored for 24 to 48 hours postoperatively. The airway should be evaluated before extubation to minimize the risk of airway obstruction.
Both nerve root and spinal cord injury may occur during the decompression. Good visualization, careful technique, and experience are mandatory to avoid devastating results. The incidence of neurologic injury is approximately 1% to 2%.15 Spinal cord monitoring should be used for most, if not all, of these procedures. Corticosteroids may be given prophylactically in high-risk cases. During the procedure, any change in spinal cord monitoring considered to be significant should be treated with the same dose of methylprednisolone used for traumatic spinal cord injury (loading dose of 30 mg per kilogram of body weight, followed by 5.4 mg/kg per hour for 23 hours).
Motor palsy of the C5 root in patients who have undergone laminoplasty procedures has been well described. The etiology of this postoperative deficit is not clear but is thought to be related to the short length of the C5 root and the maximal lordosis at that level; when the spinal cord shifts posteriorly after decompression, the C5 root is believed to sustain a stretch injury. The incidence of this complication is 1% to 3%,24 and slow but progressive recovery has been reported in most, but not all, patients. C5 root palsy can also occur following anterior decompression and fusion procedures but is relatively rare.
Injury to the vertebral artery is also possible during anterior vertebral corpectomies.39 Strict orientation to the midline is necessary to help avoid this complication. Management includes exposure of the artery above and below the corpectomy, with ligation or microscopic repair. Spinal fluid leaks can occur during both anterior and posterior procedures. Because patients with long-standing OPLL may have erosion of the dura,6 gelatin-foam sponge and fibrin glue, fascial patching, or a lumbar cerebrospinal fluid drain may be needed to prevent a persistent fistula.40
Graft-related complications after an anterior strut-graft procedure may include dislodgment, fracture, and severe settling into the cancellous bone of the vertebral bodies. With long fibular grafts, the docking site in the inferior vertebral body can split due to axial loading, and the inferior end of the graft can displace anteriorly. If there is no longer bone contact, if the esophagus is threatened, or if significant kyphosis ensues, operative revision is indicated.
Long-term complications from anterior decompression and arthrodesis procedures include pseudarthrosis and adjacent-segment degeneration. Patients with recurrent myelopathy should be evaluated for pseudarthrosis and for compression at levels adjacent to the long fusion that have undergone further degenerative changes. It appears to be true that fusions accelerate spondylotic changes at adjacent disk levels; however, a recent study suggests it may not be higher than would be attributable to the natural history of spondylosis.41
Laminectomy procedures are associated with an increased risk of postlaminectomy kyphosis, swanneck deformity, or instability with late neurologic deterioration. Laminoplasty techniques decrease these risks, but add the potential complication of inadvertent closure of the opened lamina with recurrent stenosis. Incomplete decompression may necessitate a second-stage anterior procedure.
Operative intervention for cervical myelopathy has consistently been shown to improve the neurologic function of a high percentage of patients. Neurologic outcomes appear to improve to a similar degree, regardless of whether anterior or posterior techniques are utilized, provided the guidelines discussed earlier are taken into consideration.
As with other types of spine surgery, careful patient selection remains the cornerstone of good surgical results. This, combined with high-quality imaging studies and meticulous surgical technique, will result in gratifying results with respect to neurologic recovery, function, and pain relief.
Acknowledgment: The author wishes to thank Val Schmedlen for her assistance in the preparation of the manuscript.
1. Brain WR, Northfield D, Wilkinson M: The neurological manifestations of cervical spondylosis. Brain
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