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Operative Treatment of Cervical Spondylotic Myelopathy

¹ Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, WI 53226

The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

	Introduction

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 

• Nonoperative treatment with collar immobilization and modification of activities improves functional status in selected patients with mild cervical spondylotic myelopathy. Careful monitoring of these patients is necessary as neurological deterioration can occur in spite of this treatment.
  
• Early operative management is beneficial for most patients with moderate or severe myelopathy.
  
• The primary aims of operative intervention for the treatment of cervical spondylotic myelopathy are decompression of the spinal cord and stabilization of levels at which excessive motion may be contributing to the myelopathy.
  
• Anterior operative approaches are preferred in patients with compression of the spinal cord at one, two, or three disc levels and those with loss of cervical lordosis. A higher rate of approach and graft-related complications generally favor a posterior approach when more than three levels are involved.
  
• Appropriate operative management results in satisfactory recovery from myelopathy in most cases, with improvement more likely in patients who have operative treatment earlier in the course of the disease and in those with less comorbidity.
  

Cervical spondylotic myelopathy is a leading cause of spinal cord dysfunction in the adult population. Affected patients represent a large subset of individuals who undergo operative treatment of degenerative cervical conditions. In a study of 450 patients undergoing anterior neck surgery for the treatment of degenerative disc disease, 61% presented with radicular symptoms, 16% had pure myelopathic symptoms, and the remaining 23% had a combination of myelopathy and radiculopathy¹.

The subtle clinical findings of early cervical spondylotic myelopathy make diagnosis difficult, and true natural history studies are unavailable. The patients or their relatives notice increasing awkwardness with gait and balance that they attribute to old age or arthritis of the lower extremity joints. Patients may report an insidious onset of clumsiness or diffuse numbness in the hands, resulting in worsening of handwriting or other fine motor skills and difficulty with grasping or holding. Physical examination shows exaggerated deep tendon reflexes, clonus, diminished superficial reflexes, and the presence of pathologic reflexes. Spasticity, motor weakness, and loss of proprioception contribute to the functional disability of the upper and lower limbs. Severely affected individuals are quadriparetic or quadriplegic when first seen². In an effort to describe the natural history of this condition, Clarke and Robinson described the progression of disease in a group of 120 patients (including thirty-seven patients who did not receive treatment, twenty-nine patients who were treated medically, and an additional fifty-four patients) until the time of surgery³. Medical treatment consisted of varying periods of collar immobilization, bed rest, and neck traction. The authors found that 5% of their patients had a rapid onset of symptoms followed by a long period of quiescence, 20% showed gradual but steady progression of signs and symptoms, and 75% showed stepwise deterioration of clinical function with intervening variable periods of quiescent disease. Operative intervention is a consideration in the cases of most patients with clinically evident cervical spondylotic myelopathy, given the risk of neurologic deterioration. However, a standard treatment algorithm is precluded by (1) the variability in initial presentation and subsequent course of the disease and (2) the lack of prospective, randomized studies that stratify treatment options for patients with varying severity of myelopathy. A prospective multicenter study conducted by the Cervical Spine Research Society demonstrated that operative and nonoperative treatment were equally prescribed to patients with cervical spondylotic myelopathy even when the difference between the two groups with regard to the clinical stage at the time of presentation was "not unusually large."⁴

The operative treatment of degenerative cervical disorders has evolved over the past seventy-five years. Mixter and Barr initially described a posterior approach in 1934, when they performed cervical laminectomy⁵. In the 1970s, various techniques of laminoplasty were introduced as a less destabilizing alternative to laminectomy^6,7. Concurrently, the 1950s saw increasing popularity of anterior procedures, with Robinson and Smith⁸, Cloward⁹ and Simmons and Bhalla¹⁰ describing anterior decompression and fusion techniques involving the use of iliac crest bone graft. Increasing familiarity with the anterior approach led to the development of multiple-level anterior reconstruction and instrumentation. The goals of operative treatment with all of these techniques have been to prevent deterioration and, in some cases, to reverse the myelopathy by (1) decompressing the spinal cord, (2) stabilizing the spine in cases in which segmental motion may be a contributory factor, and (3) secondarily improving cord perfusion by decompressing obstructed spinal vessels.

	Nonoperative Treatment of Cervical Myelopathy

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Patients with mild myelopathy are occasionally offered a trial of observation or nonoperative management, but nonoperative management is generally not successful in reversing or permanently halting the progress of cervical spondylotic myelopathy. In a prospective, randomized study of patients with "mild to moderate" cervical spondylotic myelopathy, Kadanka et al. reported similar outcomes following either conservative or operative treatment after a follow-up period of three years¹¹. Conservative treatment consisted of intermittent cervical immobilization in a soft collar, anti-inflammatory medications and bed rest, active discouragement of high-risk activities, and avoidance of physical overloading, exposure to cold, movement on slippery surfaces, manipulation therapies, and vigorous or prolonged flexion of the head. In a more recent study, the authors reported that a greater anteroposterior diameter of the spinal canal, larger transverse area of the spinal cord, and old age were associated with a better response to this conservative treatment¹². Matsumoto et al. retrospectively reviewed the results of conservative management in a study of twenty-seven patients with mild to moderate myelopathy due to soft disc herniation¹³. Conservative treatment consisted of cervical bracing with a rigid neck brace and restriction of activities. Seventeen (63%) of the twenty-seven patients had improvement or stabilization of clinical function, and an operation was avoided over a mean duration of follow-up of 3.9 years. Ten (37%) of the twenty-seven patients showed neurologic deterioration or failed to show an improvement and were offered an operation at a mean of nine months after the time of presentation. Operatively and nonoperatively managed patients showed similar recovery at the time of the final follow-up, suggesting that a trial of nonoperative treatment did not decrease the potential for ultimate recovery of patients with mild myelopathy.

	Indications for Operative Treatment of Cervical Myelopathy

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Patients with severe or progressive clinical myelopathy with concordant radiographic evidence of spinal stenosis are candidates for operative intervention. For patients with clinically evident but nonprogressive disease, there are no clearly established guidelines with regard to the indications for operative treatment. Most studies on the operative treatment of cervical spondylotic myelopathy have been retrospective in nature. A constellation of findings, including patient symptoms, alteration in gait, other evidence of long tract dysfunction, decreased function in the upper or lower extremities, the duration of symptoms, comorbidities, and radiographic findings all contribute to the surgeon's decision to recommend operative intervention.

The Role of Clinical Findings in Indicating Operative Treatment
Symptoms and signs of long tract dysfunction, including motor weakness, hyperreflexia, spasticity, ataxia, pathologic reflexes, and myelopathic hand findings, are evaluated in combination to help to determine whether operative intervention is indicated¹⁴. In a study of 146 patients who underwent an operation for the treatment of myelopathy, motor weakness (129 patients; 88.4%) and spasticity (115 patients; 78.8%) were the two most common preoperative findings¹⁵. Wada et al. used a combination of neurological symptoms, preoperative functional scoring with use of the Japanese Orthopaedic Association (JOA) system (Table I), and radiographic findings to determine the need for operative treatment¹⁶. The most commonly seen myelopathic symptoms in that series were clumsiness of the hands, unsteady gait, and numbness in the extremities. Operative treatment was recommended when these symptoms were present in combination with a JOA score of <13 points and spinal cord compression on imaging studies.

Development of a myelopathic gait is an important indication for operative intervention. The gait abnormality may be spastic or ataxic, depending on whether the lateral or posterior cord is primarily affected. Bohlman, in a study of seventeen patients who underwent an operation for the treatment of cervical myelopathy, reported gait disturbances in all seventeen patients, with fifteen patients demonstrating stumbling and falling¹⁷. Okada et al. reported on thirty-seven patients with either myelopathy (thirty-two patients) or myeloradiculopathy (five patients) who underwent anterior corpectomy¹⁸. All patients had sensory abnormalities and hyperreflexia, but the authors used gait disturbance as the primary indication for operative treatment.

Axial pain along the posterior part of the neck or radiating into the shoulder girdles is frequently present in patients with cervical spondylotic myelopathy and does not play a major role in indicating operative treatment. The axial pain in these patients may represent muscle fatigue or referred pain from degenerative changes in the spinal column, or it may be a manifestation of upper cervical radiculopathy. The Lhermitte sign, or shock-like sensations in the trunk and legs provoked by neck movement, coughing, or sneezing, is found in some patients with cervical spondylotic myelopathy.

The Role of Duration of Symptoms in the Operative Decision
Prolonged compression of the spinal cord can result in irreversible histological and physiological changes such as intraneural fibrosis, demyelination, and loss of neurons within the spinal cord¹⁹. The results of operative treatment generally are better in patients who undergo decompression early rather than late^20,21. In a prospective study of 146 patients with cervical spondylotic myelopathy, Suri et al. noted that patients with less than a one-year duration of symptoms showed significantly greater motor recovery following operation than did those with a longer duration of symptoms (p < 0.05)¹⁵. Tanaka et al., in a study of forty-seven patients who were more than sixty-five years old, found that the preoperative duration of symptoms strongly influenced recovery of function following operative treatment²⁰. The authors recommended that decompressive surgery should be attempted even in patients who are more than eighty years old, provided that the duration of symptoms is less than three years, the inability to walk has been present for less than three months, and the patient is physically able to undergo an operation. In another study, improvement in gait following laminoplasty was reported in 92% (eleven) of twelve patients in whom symptoms had been present for less than eighteen months, as opposed to 77% (ten) of thirteen patients with a longer duration of symptoms before the operation²¹.

In contrast, some authors have reported no correlation between the duration of preoperative symptoms and the clinical outcome following an operation. Arnasson et al. reported on a group of thirty-eight patients with cervical myelopathy who underwent anterior decompression with or without fusion (five patients), laminectomy (twenty-nine patients), or nonoperative treatment (four patients)²². The authors found that the clinical outcome following operative intervention was not influenced by the duration of preoperative symptoms.

Radiographic Factors Indicating Operative Management
Measurement of the midsagittal canal diameter may be carried out on plain radiographs (Fig. 1, a) or, more accurately, on axial computed tomography images or magnetic resonance images. The normal midsagittal canal diameter from C3 to C7 is 17 to 18 mm, and patients with an osseous canal measuring <13 mm are considered developmentally stenotic²³. Many patients with symptomatic cervical spondylotic myelopathy have some degree of developmental osseous canal stenosis, with superimposed degenerative changes at the facet joints, discs, and ligamentum flavum that further contribute to canal and neuroforaminal narrowing. Static or dynamic translation between vertebral bodies may further decrease the available canal area and precipitate the development of myelopathy (Fig. 1). Although evidence to support these radiographic criteria in the degenerative cervical spine is lacking, vertebral olisthesis of >3.5 mm between adjacent cervical vertebral bodies frequently is used in clinical practice as an indicator of excessive translation between the vertebral bodies, favoring surgical intervention. So-called dynamic stenosis is a more recently described measure of canal space and mobility and is assessed on a lateral radiograph made with the neck in extension. A distance of <12 mm between the posteroinferior lip of the vertebral body and the anterosuperior margin of the immediately caudal lamina is suggestive that the spinal cord is being pinched with intersegmental motion.

View larger version (28K): [in this window] [in a new window]   Fig. 1 Illustration depicting the radiographic criteria used in the assessment of cervical stenosis and myelopathy. a, The midsagittal diameter of the spinal canal is measured as the distance from the middle of the dorsal surface of the vertebral body to the nearest point on the spinolaminar line. Patients in whom the osseous canal measures <13 mm are considered to be developmentally stenotic. b, A distance of <12 mm from the posteroinferior corner of a vertebral body to the anterosuperior edge of the lamina of the immediately caudal vertebra with the neck in extension is suggestive of dynamic stenosis. c, Olisthesis of >3.5 mm is a measure of excessive translation between the vertebral bodies. The signal changes within the substance of the spinal cord, noted on T1 and T2-weighted magnetic resonance imaging in some patients, are represented diagrammatically.

Comorbidity Affecting Operative Intervention
The patient's overall medical condition should be considered in the decision leading to operative treatment because outcome is influenced by underlying medical comorbidity, particularly in elderly patients. Hypertension, diabetes mellitus, coronary insufficiency, cardiomyopathy, pulmonary problems, previous cerebral infarction, gastrointestinal ulcers, and benign prostatic hypertrophy may be present; in two previous studies, such comorbidities were found in up to 70% (fourteen) of twenty patients with an age of more than seventy years for whom operative intervention was being considered for the treatment of cervical spondylotic myelopathy^27,28. Close medical monitoring in the perioperative period is essential, but surgery can nevertheless result in aggravation of the underlying medical conditions or delirium in these patients²⁷. Functional deterioration in the postoperative period may also result from cerebral infarction or aggravation of diabetes mellitus²⁸. Age-related changes in the spinal cord, coexistent osteoarthritis of the lower limbs, lumbar spinal stenosis, and peripheral neuropathy can hamper recovery following operative treatment^28,29. Although the rates of functional recovery are lower in older patients^27,28, the potential for neurologic stabilization or improvement makes operative treatment a consideration in this age-group even in the presence of comorbid factors^20,27,28.

	Choosing the Operative Procedure

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
The primary goal of surgical intervention in patients with cervical spondylotic myelopathy, regardless of whether an anterior or posterior approach is used, is expansion of the spinal canal. Appropriate and early decompression restores and improves spinal cord morphology²³, reverses cord edema^15,30, and likely improves blood supply to the cord, aiding neurological recovery. The secondary goals of operative treatment are to achieve a successful fusion where abnormal segmental mobility may contribute to repeated injury of the cord and to prevent development of late deformity that can compromise the surgical outcome.

Both anterior and posterior approaches to the cervical spine allow decompression of the spinal cord and nerve roots, correction of deformity, and stabilization of the spinal column. The choice between an anterior, posterior, or combined approach for decompression of a stenotic spinal canal is based primarily on (1) the sagittal alignment of the spinal column, (2) the extent of disease, (3) the location of compressive abnormality, (4) the presence of preoperative neck pain, and (5) previous operations. Additional considerations that influence the choice of approach include (1) the increased risk of postoperative dysphagia and laryngeal nerve injury following multiple-level or prolonged anterior surgery, (2) injury to the stabilizing posterior muscular and ligamentous structures with the posterior approach, and (3) inadequate exposure at the C7-T1 level through the anterior approach in individuals with a short, muscular neck.

Role of Cervical Spine Alignment in Selection of Operative Approach
Posterior decompression for the treatment of myelopathy is generally contraindicated for patients who have neutral or kyphotic sagittal alignment of the cervical spinal column. Laminectomy or laminoplasty in a patient with a kyphotic or neutrally aligned spinal column will not allow posterior translation of the spinal cord away from the anterior compressive abnormality. Sodeyama et al. showed that the peak postoperative dorsal translation of the spinal cord was greatest (peak shift, 3.1 mm) in patients who had a lordotic spinal curve, less (peak shift, <3 mm) in patients who had a straight spine, and least (peak shift, <2 mm) in patients who had a kyphotic or an S-shaped cervical spinal curve³¹. Better recovery of myelopathy has also been reported following laminoplasty in patients without preoperative kyphosis³².

Kawakami et al. reported that preoperative and postoperative cervical spine sagittal alignment had no bearing on postoperative recovery of myelopathy³³. The authors recommended anterior discectomy and fusion for patients with one or two-level disc involvement without developmental canal stenosis (anteroposterior diameter, 13 mm) and laminoplasty for those with involvement of three levels or more and for those with developmental stenosis (even if they had a one-level lesion). Chiba et al. hypothesized that slack in the spinal cord induced by decreased disc height in patients with multiple-level cervical spondylotic myelopathy allowed for an acceptable recovery following posterior decompression, even in the presence of a kyphotic or straight spine³⁴.

Role of Extent of Disease Involvement
For patients with one or two-level involvement, most surgeons prefer an anterior procedure^33,35. Yonenobu et al., in a study of patients with cervical spondylotic myelopathy, reported that patients with one or two-level involvement were managed with anterior cervical discectomy or corpectomy, patients with involvement of four levels or more were managed with laminectomy, and patients with involvement of three levels were managed with any of the three procedures³⁵. Patients who underwent corpectomy maintained the gain in functional recovery better than those who underwent either of the other two procedures. The authors recommended that corpectomy should be used for the treatment of spondylosis involving as many as three levels and that laminectomy be reserved for the treatment of spondylosis involving four levels or more.

Corpectomy may be considered (1) for a patient with developmental stenosis as evidenced by an osseous anteroposterior canal diameter of <13 mm, (2) for a patient with a large posterior osteophyte adjacent to the end plate, (3) for a patient who has a free disc fragment that has migrated posterior to the vertebral body, and (4) as an alternative to multiple-level interbody fusion to reduce the number of required fusion surfaces. Correction of a fixed kyphotic deformity in the cervical spine can be more reliably achieved with corpectomy than with multiple-level anterior cervical discectomy and fusion.

The prevalence of dysphagia and graft-related complications increases as the number of levels that are included in an anterior fusion increases, and this fact must be kept in mind when deciding on the approach. Persistent difficulty with swallowing or potentially substantial voice changes can occur in some patients following prolonged or difficult anterior surgery.

Role of Dimensions of the Cervical Spinal Canal
Severe developmental stenosis involves the entire cervical spine and generally requires a posterior approach. Sodeyama et al. recommended posterior decompression of the cervical spinal cord in patients with myelopathy who had a spinal canal diameter of <11 mm and multiple-level impingement of the spinal cord³¹. Conversely, Kadoya et al. thought that multiple-level anterior discectomy and fusion accompanied by osteophyte removal provided satisfactory decompression of the spinal cord in patients with myelopathy even in the presence of a congenitally stenotic canal (<12 mm)³⁶. The authors based their choice on myelographic findings, which showed that the cord compression was primarily due to the osteophytes and not to the canal stenosis.

Role of the Location of the Abnormality
The choice between an anterior and a posterior approach for the treatment of a stenotic spinal canal should take into consideration the anatomic location of the abnormality. Anterior approaches allow good visualization of abnormalities that are located ventral to the cord and obviate the need to work around the cord. Herkowitz et al. reported an excellent or good result in ten (91%) of eleven patients undergoing anterior discectomy and fusion for the treatment of myelopathy or axial neck pain resulting from central soft disc herniations³⁷. Posterior compression of the spinal cord resulting from buckling of the ligamentum flavum or shingling of the laminae in a patient with hyperlordosis favors a posterior approach³¹.

Role of Preoperative Neck Pain
Preoperative neck pain is a relative contraindication to laminoplasty. Disruption of the posterior paraspinal musculature from a posterior approach can aggravate axial neck pain. Ratliff and Cooper, in a review of the literature on laminoplasty, reported that the postoperative prevalence of neck pain ranged from 6% to 60% among different series and suggested that the true prevalence may actually be higher as neck pain was frequently not reported in the studies that were reviewed³⁸. Axial pain is not a major concern following anterior surgery.

Role of Previous Surgery
In patients who have undergone previous operations on the cervical spine through an anterior or posterior approach, revision surgery that is performed through an alternate approach avoids having to dissect through scar tissue and disrupted anatomic planes. Scar tissue tethering the esophagus, trachea, and laryngeal neurovascular structures makes an injury to these structures more likely with repeat intervention. Additional factors that should be considered when deciding on the approach for revision surgery include the time that has elapsed since the previous operation, the maturity of scar tissue, and the ease of performing the planned intervention through the approach. Revision anterior surgery is best carried out through the previous approach when feasible. When a contralateral anterior approach is contemplated, preoperative laryngoscopy will rule out subclinical vocal cord paresis on the previously treated side.

	Operative Options for and Issues Related to Anterior Surgical Approaches to Cervical Spondylotic Myelopathy

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Anterior Cervical Discectomy and Fusion
Anterior cervical discectomy and fusion allows for the removal of disc material and posterior osteophytes impinging on the spinal cord and nerve roots at or immediately adjacent to the level of the disc space (Fig. 2, A). The cartilaginous end plate is completely removed, but we prefer to maintain the integrity of the thin osseous end plate because we think that this contributes to the mechanical stability of the graft-host interface and helps to maintain lordotic alignment. Distraction of the disc space results in indirect decompression of the foramen and canal to a varying degree and is followed by insertion of an appropriately sized bone graft into the interspace. The recommended height of the graft in most cases is 2 mm more than the initial disc height in order to avoid the loss of height that sets in after graft incorporation³⁹.

View larger version (41K): [in this window] [in a new window]   Fig. 2 Illustration depicting common anterior procedures used in cervical myelopathy. A, Anterior cervical discectomy and insertion of a bone spacer for fusion. B, Anterior cervical corpectomy and insertion of a bone strut graft. C, Anterior cervical discectomy followed by insertion of a bone spacer for fusion and anterior plating. D, Anterior cervical corpectomy, strut graft insertion, and anterior plating.

Cervical Corpectomy
The term subtotal corpectomy refers to removal of a 15 to 19-mm anterior midline trough in the vertebral body down to the posterior longitudinal ligament or dura, with removal of the cephalad and caudad discs (Figs. 2, B and Figs. 3-A, 3-B, 3-C, 3-D and 3-E 3-F and 3-G). Corpectomy allows expansion of a narrow osseous canal and allows for simultaneous removal of large osteophytes from the vertebral end plates impinging on the spinal cord or nerve roots. Undercutting large osteophytes from adjacent levels is also safer through a corpectomy trough as opposed to working through a narrow disc space with limited visualization. The lateral extent of decompression is limited by the foramen transversarium, which houses the vertebral artery. Computerized tomography shows that a total central decompression of approximately 15 mm at C3 to 19 mm at C6 provides a safety margin of 5 mm to the medial border of the foramen transversarium^40,41. The superior surfaces of the subaxial cervical vertebrae are marked by an upward ridge on their lateral and posterior lateral margins, known as the uncus. Anatomic landmarks such as the medial margin of the uncus, the medial margin of the longus colli muscle, and the natural curve of the vertebral end plate can be used to maintain midline orientation. This helps to avoid inadvertent vertebral artery injury resulting from lateral wall violation.

View larger version (683K): [in this window] [in a new window]   Fig. 3-A, Fig. 3-B, Fig. 3-C, Fig. 3-D and Fig. 3-E Figs. 3-A through 3-G A forty-seven-year-old woman presented with a six-month history of neck pain, numbness in both upper extremities, and profound weakness with hand function bilaterally. Figs. 3-A through 3-E Preoperative T2-weighted sagittal image (Fig. 3-A) and axial images at C3-C4 (Fig. 3-B), C4-C5 (Fig. 3-C), C5-C6 (Fig. 3-D), and C6-C7 (Fig. 3-E), showing severe stenosis, particularly at C4-C5 and C5-C6, resulting from a combination of spondylotic changes and superimposed disc protrusion. Signal changes within the substance of the spinal cord can be seen posterior to the C4-C5 disc space.

View larger version (228K): [in this window] [in a new window]   Fig. 3-F and Fig. 3-G Figs. 3-F and 3-G Radiographs made after the patient was managed with corpectomy of the C5 and C6 vertebral bodies, strut-grafting with use of a titanium mesh cage packed with local autogenous bone, and the application of an anterior cervical plate from C4 to C7.

Various modifications of the corpectomy technique have been described. For patients without developmental stenosis of the canal but with large osteophytes adjacent to the disc space at one level, some authors have combined a discectomy with limited resection of the adjacent vertebral body¹⁴. The authors of one report described resection of the anterior two-thirds of the vertebral body⁴⁴. Those authors suggested that this partial anterior corpectomy allowed greater intraoperative visualization of the interface between the adjacent discs and the posterior longitudinal ligament, allowed easier removal of osteophytes, and decreased the number of surfaces at which fusion was required in comparison with a multiple-level discectomy and fusion. Combining a corpectomy with an adjacent discectomy may avoid the biomechanical instability associated with multiple-level corpectomies.

Resection of Posterior Osteophytes as Part of the Decompression
Resection of posterior osteophytes has been reported to allow earlier decompression of the spinal cord and improved recovery³⁶. Resection of posterior and lateral osteophytes also may allow more reliable improvement in patients with associated radicular symptoms. However, the removal of osteophytes is associated with an increased risk of injury to the spinal cord. Yonenobu et al. reported worsening of myelopathy in one of seventy-five patients as a result of cord damage that occurred in association with the resection of osteophytes during anterior cervical discectomy and fusion⁴⁵. The authors recommended corpectomy over anterior cervical discectomy and fusion for patients with posterior osteophytes that are large enough to require removal.

There is conflicting information on whether osteophytes will resorb following a solid fusion. Connolly et al.⁴⁶ and Robinson et al.⁴⁷ reported complete resorption of osteophytes following a solid fusion. Conversely, Stevens et al.⁴⁸ reviewed computerized tomographic myelograms for fifty-three patients twelve years following anterior interbody fusion and reported that osteophyte resorption did not occur in any patient. They recommended that all osteophytes should be systematically removed during the operation to minimize the chances of persistent symptoms.

Removal of the Posterior Longitudinal Ligament as Part of the Decompression
Removal of a thickened or ossified posterior longitudinal ligament during anterior cervical discectomy and fusion allows for more thorough decompression but increases the risk of cord contusion and postoperative hematoma^1,17. An intact posterior longitudinal ligament contributes to the stability of the spinal column and adds a margin of safety by helping to prevent graft extrusion posteriorly into the spinal cord. Yamamoto et al. reported the presence of a disc fragment behind the posterior longitudinal ligament in three (5%) of fifty-five patients⁴⁹. If a rent in the posterior longitudinal ligament is noted during the operation, or if imaging studies suggest that there is a fragment behind the posterior longitudinal ligament, resection of the posterior longitudinal ligament allows for the performance of a safe exploration to rule out persistent compression of the spinal cord and/or nerve roots by an extruded disc fragment.

Addition of Levels with Mild Radiographic Findings to the Operation
With multiple-level degenerative disc changes, a single level that is responsible for the myelopathy frequently cannot easily be identified. In addition, there is concern that untreated segments showing mild degenerative changes or intervertebral translation adjacent to the site of the proposed operative intervention may result in recurrent postoperative myelopathic changes. For these reasons, some authors have suggested that all levels of radiographically demonstrable compression should be dealt with at the time of surgery^35,42. Shoda et al. recommended extending the fusion to any adjacent segment that displayed dynamic stenosis in addition to the primary stenotic levels⁵⁰. Tani et al. attempted to minimize perioperative complications in patients with multiple-level disease by limiting operative intervention to a single most symptomatic level⁵¹. Those authors used intraoperative spinal cord evoked potentials to identify the disc level that was causing the greatest conduction delay. This approach risks leaving behind clinically important compressive abnormalities in untreated areas. The benefits of including all levels must be weighed against the increased time and risk of the operation.

Bone Graft Options Following Discectomy and Corpectomy
Autogenous iliac crest bone traditionally has been the preferred choice of bone graft for multiple-level anterior cervical discectomy and fusion. A tricortical horseshoe-shaped graft is harvested from the iliac crest with use of a low-speed oscillating saw and is inserted into the interspace with the cortical portion facing anteriorly. The use of allograft bone avoids the morbidity associated with the harvesting of autogenous bone but traditionally has been associated with higher rates of nonunion following arthrodeses involving more than one level⁵². Samartzis et al. recently described equivalent rates of fusion in association with allograft and autograft when used for procedures involving as many as three levels that were performed with current surgical techniques and anterior cervical plates⁵³. Those authors suggested that preparation of the end plates, sizing of the graft, recessing the graft 2 mm from the anterior margin of the vertebral body, and segmental screw fixation were more important than the type of graft used. The use of structural supports such as metallic cages (Fig. 3-F) or synthetic spacers in conjunction with local autograft or allograft avoids the morbidity associated with the harvesting of autogenous bone, but long-term results will be needed before this method achieves general acceptance.

Autogenous iliac crest bone is also the preferred graft choice to span the defect created by a one-level or two-level corpectomy. For patients with longer corpectomy defects or those in whom the iliac crest is mechanically insufficient, a fibular strut is preferred. A fibular allograft avoids donor-site morbidity, reduces operative time and intraoperative blood loss, and has been shown to be biomechanically superior to the iliac crest when tested under axial loading⁵⁴. The risk of disease transmission is low⁵⁵.

Graft failure following anterior discectomy or corpectomy occurs through displacement, fracture, resorption, collapse, or penetration of the graft into the cephalad or caudad vertebral bodies. Autogenous iliac crest graft has been associated with rates of collapse ranging from 4% (four of 100)⁵⁶ to 14% (nine of sixty-three)⁵⁷. Allograft generally has been associated with higher rates of collapse. Brown et al. reported collapse in 28% (fifteen) of fifty-three patients who were managed with iliac crest allograft as compared with 16% (seven) of forty-five patients who were managed with iliac crest autograft⁵⁷. The number of graft-related complications increases as the number of levels undergoing corpectomy increases⁵⁸. Anterior plating can help to decrease the prevalence of graft displacement following multiple-level corpectomy, but some authors nevertheless have recommended second-stage posterior stabilization following a corpectomy of three levels or more^59,60.

Role of Anterior Plating in Reconstruction of the Cervical Spinal Column Following Anterior Cervical Discectomy and Fusion or Corpectomy
Plate fixation following anterior cervical discectomy and fusion or cervical corpectomy (Fig. 2, C and D) does not add substantially to the duration of an operation or the prevalence of complications. Anterior plating improves the rate of fusion, reduces the length and type of postoperative immobilization, reduces the prevalence of graft-related complications, and leads to less postoperative kyphosis, particularly in patients undergoing two or more levels of anterior cervical discectomy and fusion^61-63. An appropriate plate length is selected to maintain a minimum distance of 5 mm between the ends of the plate and the adjacent discs. This helps to decrease adjacent disc level ossification⁶⁴. Segmental screw fixation should be obtained when possible, and all screws should be locked to the plate⁵³. Dynamic or semiconstrained devices that allow sliding or toggling of the screw within the plate were developed to reduce stress-shielding of the graft and to allow for increased compressive forces on the graft. The inherent lack of longitudinal rigidity of dynamic systems can be a disadvantage in some situations, allowing migration of the graft into adjacent end plates or drifting of the plate toward adjacent disc spaces. Drawbacks of anterior plate fixation include (1) difficulties with fixation in osteoporotic bone, (2) the risk of esophageal injury or airway obstruction from loose and migrating implants, (3) increased cost, and (4) the slight increase in operative duration, blood loss, and intraoperative risk that the added procedure entails.

When plating has been performed following single-level anterior cervical discectomy and fusion, some authors have reported no improvement in fusion rates or overall clinical outcome^61,65. Conversely, Wang et al. reported less graft subsidence, less segmental kyphosis, a lower prevalence of pseudarthrosis (4.5% [two of forty-four] compared with 8.3% [three of thirty-six]; p = 0.653), and a higher percentage of good or excellent outcomes when patients who had been managed with plating were compared with patients who had not been managed with plating⁶⁶. In another study, computerized analysis of the lateral radiographs for fifty-one patients who had had single or multiple-level anterior cervical discectomy and fusion demonstrated a significant (p = 0.0001) beneficial effect of the plate in maintaining sagittal alignment postoperatively⁶⁷.

Anterior cervical plating has been shown to decrease the prevalence of graft-related complications following corpectomy. Epstein compared patients who underwent single-level corpectomy with and without plating. Among the forty-eight patients who were managed without an anterior cervical plate, 73% went on to have fusion whereas 10.3% required reoperation for graft-related complications or a pseudarthrosis⁶⁸. Among the eight patients who were managed with an anterior cervical plate, there were no graft-related complications. However, one patient had development of a pseudoarthrosis and underwent elective posterior wiring and fusion six months after the index procedure to prevent future plate loosening. Failure rates of 50% (six of twelve)⁵⁹ to 71% (five of seven)⁶⁰ following three-level corpectomy, grafting, and plating have prompted some authors to recommend the addition of posterior instrumentation whenever three-level corpectomy and fusion are performed.

Success of Fusion Following Anterior Operative Treatment
Fusion following anterior discectomy or corpectomy is determined by the radiographic observation of bridging trabeculae across all graft-host bone interfaces, with no motion at the fused levels noted on dynamic radiographs. A change in interspinous distance on flexion and extension radiographs is an accurate technique for detecting lack of fusion^69,70. The rate of fusion following single-level anterior cervical discectomy and fusion generally ranges from 80% to 95% (88% of 202 in the study by Cauthen et al.⁷⁰, 90% [242 of 269] in the study by Martin et al.⁷¹, and 95% [thirty-nine of forty-one] in the study by Zdeblick and Ducker⁵²). Some authors have reported higher nonunion rates following multiple-level anterior cervical discectomy and fusion, with the rates increasing as the number of fused levels increases. Bohlman et al. reported that the rate of fusion following anterior cervical discectomy and fusion without instrumentation was 89% (fifty-five of sixty-two) after one-level procedures, 73% (thirty-five of forty-eight) after two-level procedures, and 73% (eight of eleven) after three-level procedures, with a failure of fusion in the one patient who underwent a four-level procedure⁶⁹. The lower fusion rate following operative intervention at multiple levels is explained by the increased number of fusion interfaces, increased motion resulting from multiple discectomies, and increased compressive loads across multiple segments leading to a higher rate of graft failure. More recent long-term studies have demonstrated no significant difference (p > 0.05) in fusion rates in association with the use of either allograft or autograft at two and three levels with anterior discectomy and anterior plating⁵³. Compared with multiple-level anterior cervical discectomy and fusion, anterior cervical corpectomy reduces the number of surfaces at which fusion is required but creates a mechanically more demanding environment for the graft resulting from greater bone resection and graft lengths. In a retrospective review of 249 cases of anterior corpectomy over one to five vertebral levels with use of autogenous iliac crest or fibular graft without instrumentation, Wang et al. reported fusion with no displacement of the graft in 94% (233) of their 249 patients⁵⁸. The authors reported that graft displacement was directly related to the number of vertebral bodies removed, the use of longer grafts, and fusions ending caudally at the C7 level.

Immobilization Following Anterior Surgery
Following anterior surgery, patients are immobilized in a cervical or cervicothoracic orthosis, depending on the number of levels involved and the use of internal fixation. While some authors have recommended immobilization in a soft brace for one or two weeks following a single level anterior discectomy and fusion with instrumentation⁶⁵, most have recommended the use of a rigid cervical orthosis for four to six weeks. Some authors have recommended that patients undergoing multiple-level corpectomy without internal fixation should be immobilized in a halo orthosis until the fusion shows signs of consolidation⁵⁸. We prefer to use internal fixation supplemented with a rigid cervicothoracic orthosis for these patients. Skin under the brace should be checked regularly for areas of breakdown, and halo pins should be cleaned daily. These braces restrict the ability of the patient to look down at the feet, and myelopathic patients need to be particularly careful during the first few days of brace wear to avoid falling.

	Posterior Surgery in Cervical Spondylotic Myelopathy

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Laminoplasty
Laminoplasty increases the effective diameter of the spinal canal from C3-C7 by shifting the laminae dorsally with use of either a so-called single door with a single lateral hinge or a double door with lateral hinges on both sides (Fig. 4). In contrast to laminectomy, laminoplasty retains a covering of posterior laminar bone and ligamentum flavum over the spinal cord, minimizes instability, limits constriction of the dura from extradural scar formation^72,73, and obviates the need for fusion.

View larger version (36K): [in this window] [in a new window]   Fig. 4 Illustrations depicting common techniques used for cervical laminoplasty. A, Single-door laminoplasty. Sutures are placed through the spinous process to the articular capsule on the hinge side to hold the lamina elevated. B, Double-door laminoplasty. The spinous process is osteotomized in the midline, and the two halves are pried open on laterally based hinges. Structural bone graft or a spacer fills the defect between the split spinous processes and prevents closure of the laminoplasty doors. C, Single-door laminoplasty with use of bone graft or spacer to prop the door open. D, Single-door laminoplasty with use of a laminoplasty plate. E, Unilateral muscle-stripping approach to maintain the integrity of soft tissues on the contralateral side. The laminae on one side are exposed with preservation of the nuchal, supraspinous, and interspinous ligaments. The spinous processes are osteotomized at their bases and are reflected to the intact side, allowing exposure of the posterior laminar bone. The arrows indicate the plane of the osteotomy and exposure.

Earlier descriptions of laminoplasty kept the door open with use of suture or wire tethering the spinous process to the hinge side facet joint or capsular tissue⁷⁴. More recent techniques include insertion of an autogenous spinous process graft, allograft bone, or synthetic spacers to keep the door open (Fig. 4, C). Fixation with use of miniplates fixed to the lamina and lateral mass has been reported by multiple authors, without major complications (Fig. 4, D and Figs. 5-A, 5-B, 5-C, 5-D and 5-E, 5-F)^77-79.

View larger version (761K): [in this window] [in a new window]   Fig. 5-A, Fig. 5-B, Fig. 5-C, Fig. 5-D and Fig. 5-E Figs. 5-A through 5-F A forty-eight-year-old man presented with a three-year history of diffuse numbness in both upper extremities, difficulty with fine-motor skills in the hands, and neck pain. Figs. 5-A through 5-E Preoperative T2-weighted sagittal image (Fig. 5-A) and axial images at C3-C4 (Fig. 5-B), C4-C5 (Fig. 5-C), C5-C6 (Fig. 5-D), and C6-C7 (Fig. 5-E), showing degenerative changes, multiple-level stenosis, and high-intensity changes within the substance of the spinal cord posterior to the C3-C4 disc space.

View larger version (103K): [in this window] [in a new window]   Fig. 5-F Radiograph made after the patient underwent a laminoplasty with use of mini-plates. After surgery, the patient reported improvement in upper-extremity sensations and function and resolution of neck pain.

Laminectomy
Laminectomy is a useful alternative for multiple-level decompression in patients with preserved cervical lordosis, particularly elderly patients, in whom comorbidities increase the operative risk. The lateral margins of the laminectomy are at the junctions of the lateral masses and laminae. Foraminotomy is considered following both laminectomy and laminoplasty in patients who have foraminal stenosis resulting from a disc protrusion or foraminal osteophytes and concordant radicular symptoms. Segmental stability is maintained during the foraminotomy by resecting no more than 25% of the facet joint^80,81.

All levels with radiographic evidence of stenosis should be included in the decompression. Limiting the number of segments that are decompressed does not influence the development of postlaminectomy kyphosis or instability^82-84 and may result in recurrent symptoms resulting from progression of disease at adjacent segments⁸⁵. A laminectomy that does not extend cephalad enough may result in dorsal kinking of the spinal cord and increased postoperative neurologic findings. Inclusion of C2 and T1 in the laminectomy increases the likelihood of kyphosis and instability. Concern about postlaminectomy kyphosis and instability has led to the development of the laminectomy with fusion and posterior instrumentation.

Adequacy of Decompression
Visible expansion of the dural sac intraoperatively and pulsation of the dura after opening of the laminoplasty doors or following laminectomy suggest good canal expansion⁷⁴. A laminoplasty opening gap of 8 to 10 mm results in adequate decompression, with an average increase in the canal diameter of 3 to 4.6 mm⁸⁶. Ishida et al. found better recovery from myelopathy in patients in whom the transverse width of the laminoplasty window was at least 70% of the transverse width of the spinal canal and in whom the sagittal diameter of the canal was increased to 15 mm⁷³. The degree of canal expansion that is achieved correlates with recovery following surgery. Hirabiyashi et al. reported a significant difference in the recovery rate between patients with an increase of >5 mm in the anteroposterior canal diameter and patients with an increase of <2 mm (p < 0.05)⁸⁷. Kohno et al. found that patients who showed good recovery from myelopathy after laminoplasty had expansion of the anterior-posterior canal diameter to 12.8 mm⁸⁸.

Itoh and Tsuji did not find any correlation between canal expansion and recovery from myelopathy in a series of thirty patients who underwent laminoplasty⁸⁶. Increased expansion of the canal does not result in better decompression in all cases because the spinal cord is limited in its capacity to migrate dorsally as a result of the tether of the roots anteriorly or adhesions between an ossified posterior longitudinal ligament and the dura. Attempting excessive canal expansion may also predispose the patient to nerve-root palsy resulting from undue stretch on the tethering nerve roots.

Instrumentation Following Laminectomy
Instrumentation provides immediate stability to the cervical spine, increases the fusion rate, and obviates dynamic factors contributing to cord compression and myelopathy^89-93. Instrumentation options for posterior cervical fixation include sublaminar and facet wires connected to a longitudinal rod or rectangular construct⁹¹ and interspinous wires⁹³. Lateral mass and cervical pedicle-based screw fixation systems^92,94,95 are alternative options for patients with deficient posterior elements but currently are not approved for clinical use in the United States by the Food and Drug Administration.

Heller et al. reported on complications following instrumentation with use of 654 lateral mass screws in seventy-eight patients⁹⁶. Nerve-root injury was the most common complication, associated with 0.6% (four) of the 654 screws placed, and was related to improper drilling technique or the use of an excessively long screw. Facet violation was seen in association with 0.2% (one) of the 654 screws. No case of vertebral artery injury was reported in that series. The rate of reoperation due to radiculopathy resulting from malpositioned lateral mass screws has been reported to range from 3% (one of thirty-eight patients)⁹² to 14% (three of twenty-one patients)⁹⁷.

Pedicle screws have a higher pullout strength than lateral mass screws do⁹⁸, and they may allow for better correction of deformity. Abumi et al., in a study of forty-six patients who underwent cervical pedicle fixation, reported that the prevalence of pedicle cortical penetration was 5.3% (ten of 190)⁹⁵. None of the patients had a neurovascular complication. There were no cases of screw pullout, breakage, or loosening. Preoperative evaluation with use of computerized tomography helps to ensure adequate pedicle morphology and surgical planning.

Posterior Fusion Following Laminectomy
The rate of fusion following laminectomy and bone-grafting alone has been reported to range from 65.2% (thirty of forty-six patients)⁹⁹ to 79% (twenty-seven of thirty-four patients)¹⁰⁰. The addition of instrumentation enhances the fusion rate. Callahan et al. reported a fusion rate of 96% (fifty of fifty-two) in association with posterolateral bone-grafting and facet wiring; both cases of pseudarthrosis in that series were attributed to improper bone-grafting technique⁸⁹. Using clearly defined and much stricter criteria to determine nonunion (abnormal motion between segments, hardware failure, and radiolucency around the screws), Heller et al. reported nonunion in 38% (five) of thirteen patients who underwent laminectomy with lateral mass screw-and-plate instrumentation⁹⁴.

Immobilization Following Posterior Surgery
Following laminoplasty, patients are mobilized in a soft or rigid cervical collar. Patients may begin isometric neck exercises while still wearing the collar. The cervical orthosis is generally worn for six³³ to twelve weeks¹⁶, but shorter periods of brace wear may reduce the prevalence of posterior neck and shoulder girdle pain^16,101 following laminoplasty. Unrestricted activity, including sports activity, was permitted in one series after the graft on the open-door side of the laminoplasty showed radiographic evidence of union¹⁰². Following laminectomy with fusion and posterior instrumentation, a rigid cervical collar is worn for four to eight weeks^92,97. This time is increased to two to three months for patients with osteoporosis or those with fixation at more than four levels⁹⁵.

	Outcome Following Operative Treatment of Cervical Myelopathy

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Predictive Factors for Outcome
Patients who are more than seventy-five years old generally have greater comorbidity and do not have the recovery following an operation that can be expected from younger patients²⁸. Lumbar canal stenosis, hip osteoarthritis, and cardiac dysfunction can all contribute to overall disability, impaired walking ability, and a worsening Nurick grade¹⁰³ (Table II). Kawaguchi et al. reported less improvement following surgery for the treatment of myelopathy in patients who were more than seventy years old and attributed this finding to age-related changes within the myelinated fibers and motor neurons of the spinal cord²⁷. Operative intervention that is carried out earlier in the course of the disease also appears to result in a better prognosis in terms of neurological recovery. In one study, patients in whom the operation was performed within three years after the onset of symptoms and within three months after the loss of walking capacity had a better chance of recovery of gait and upper limb function²⁰. In another study, 92% (eleven) of twelve patients who had had symptoms for less than eighteen months had an improvement in gait as opposed to 77% (ten) of thirteen patients who had presented later²¹. Other factors that have been linked with poorer outcomes following operative treatment include more severe myelopathy at the time of presentation^104,105, preoperative bladder dysfunction²¹, and postoperative kyphosis^88,106.

Increased T2-weighted magnetic resonance imaging signal changes are frequently present within the substance of the cervical spinal cord and may represent cord edema or irreversible changes such as gliosis or microcavitation. Some authors have reported that isolated T2-weighted signal changes have no correlation with the severity of myelopathy^15,24, but there appears to be consensus that recovery from myelopathy following an operation is better in patients who do not demonstrate these signal changes^24,25.

The degree of preoperative cord compression has been related to postoperative recovery. Fukushima et al. reported that patients in whom the transverse area of the cord measured <0.45 cm² at the site of maximum compression on preoperative axial magnetic resonance imaging scans had less recovery of neurologic function following surgery¹⁰⁷. In a similar study, Fujiwara et al. found better recovery following surgery in patients in whom the transverse area of the cord measured 0.30 cm² on preoperative computed tomography myelography²³. Patients with multisegmental areas of cord compression also have been reported to have poorer results following surgery than those with focal areas of compression¹⁵.

Recovery of Neurologic Function
Decompression of the spinal cord in patients with cervical myelopathy results in stabilization of or improvement in long-tract spinal cord function in most cases. Function is better in patients who have good restoration of spinal canal dimensions following decompression, those who have earlier decompression, and those without substantial comorbidity. Gait improves in patients with cervical myelopathy following both anterior and posterior decompression of the spinal cord. Emery et al. reported on 106 patients with cervical myelopathy who underwent either anterior discectomy or corpectomy and fusion¹⁴. Eighty-two (77%) of the 106 patients had preoperative gait abnormalities. Thirty-eight (46%) of these eighty-two patients had recovery of normal gait and thirty-three (40%) had an improvement in gait, with the average Nurick grade improving from a preoperative value of 2.4 to a postoperative value of 1.2. Okada et al. reported on thirty-seven patients who had had one to four-level decompression and arthrodesis¹⁸. The average duration of follow-up was four years. No patient had had normal lower limb motor function preoperatively, but normal function was seen in seventeen (46%) of the thirty-seven patients postoperatively. Improvement in gait and lower extremity function is similar to that following laminoplasty¹⁰⁸.

Patients with cervical spondylotic myelopathy may present with predominantly hand symptoms, with motor and sensory abnormalities in the upper and lower extremities being apparent on further examination. Myelopathic hand manifestations are commonly described as "numb, clumsy hands"¹⁰⁹. These findings are more frequent in patients with upper cervical spine stenosis and may result from a combination of anterior horn cell dysfunction, venous stasis, and ischemia of the central grey matter and/or the pyramidal tract^110-112. Most patients have substantial improvement in hand function after the operation. Lee et al. reported improvement in terms of nondermatomal hand tingling and numbness in 87% (thirteen) of fifteen patients and improvement in terms of upper extremity weakness in 71% (ten) of fourteen patients eighteen to forty-three months following laminoplasty²¹. Other authors have reported an increased ability to rapidly grip and release the hand following surgery for the treatment of cervical spondylotic myelopathy^27,113.

The prevalence of sensory abnormalities has varied widely among various reports on patients undergoing operative treatment of cervical myelopathy, from 58% (sixty-one of 105)¹¹⁴ to 84% (eighty-nine of 106)¹⁴. Sensory deficits have included dermatomal anesthesia, nondermatomal paresthesias, and loss of pinprick, proprioceptive, and vibratory sensations in the upper and/or lower extremities. Emery et al., in a study of eighty-nine patients managed with anterior discectomy or corpectomy, reported complete recovery of sensory deficit in forty-three patients (48%), partial recovery in thirty-five patients (39%), no change in ten patients (11%), and worsening in one patient (1%)¹⁴. Okada et al., in a study of thirty-seven patients with cervical myelopathy, reported that definite preoperative sensory loss was noted in the upper limbs, trunk, and lower limbs of twenty-seven, thirteen, and twenty-four patients, respectively¹⁸. Following anterior corpectomy, these changes were noted in only eight, zero, and three patients, respectively. Edwards et al. reported improvement in sensory symptoms in 69% of thirteen patients who had undergone laminoplasty for the treatment of cervical spondylotic myelopathy¹¹⁵.

Comparative Outcome Between Anterior and Posterior Surgery
Wada et al.¹⁶ retrospectively reviewed the clinical course of twenty-three patients who had been managed with subtotal corpectomy and fusion and twenty-four patients who had been managed with laminoplasty over a ten to eighteen-year period. Spondylotic myelopathy was present over an average 2.3 levels in the corpectomy group and 2.5 levels in the laminoplasty group. No significant difference in neurological recovery was found between the two groups at one or five years after the operation or at the time of the final follow-up. Sakaura et al. compared two groups of patients ten and fifteen years after laminoplasty and anterior cervical discectomy and fusion, respectively¹¹⁶. The preoperative extent of disease was similar in both groups. Neurological function improved after surgery in both groups, with no significant differences between the two groups with regard to the JOA score or the recovery rate. Those authors found greater adjacent-segment deterioration following the use of an anterior operative approach and increased postoperative kyphosis and axial pain following the use of a posterior approach. The authors recommended laminoplasty for patients with cervical myelopathy due to disc herniations, except for patients with a single-level disc herniation without developmental canal stenosis. Yonenobu et al. reported an overall slightly higher recovery from myelopathy in patients who underwent anterior subtotal corpectomy and fusion as compared with patients who underwent laminoplasty¹¹⁷. On further analysis, those authors found that patients with a canal diameter of <12 mm had better recovery following laminoplasty, suggesting that this was a better option for patients with a developmentally narrow canal.

Maintenance of Neurological Recovery Over the Long-Term
A general trend is observed in the pattern of recovery following the operative treatment of myelopathy. Recovery that is obtained in the immediate postoperative period is followed by continued improvement over the next few years and then by some deterioration in functional status thereafter. This pattern is seen following both anterior and posterior operative treatment. Wada et al., in a retrospective review of twenty-three patients with cervical spondylotic myelopathy who were managed with anterior subtotal corpectomy and fusion, reported an improvement in the mean JOA score from 7.9 preoperatively to 13.3 at one year and to 13.9 at five years¹⁶. At a mean of fifteen years after surgery, the mean JOA score was 13.4. In a cohort of twenty-four patients who underwent laminoplasty, the average JOA score was 7.4 preoperatively, 13.1 at one year, 12.9 at five years, and 12.2 at a mean 11.7 years¹⁶. Kawaguchi et al., in a study of the results of laminoplasty, reported that the mean preoperative JOA score of 9.1 points improved to 13.4 at six months and to 13.9 at five years and then decreased to 13.4 at the time of the final follow-up at an average of 13.2 years²⁹.

The causes of late deterioration are distinct following anterior and posterior procedures. The most common cause of recurrent symptoms following anterior operative treatment is deterioration of an adjacent segment; other causes may include inadequate decompression at the time of the initial operation, pseudarthrosis, graft or implant failure, continued growth of osteophytes, or ligamentum flavum infolding. Common causes of recurrent myelopathy following posterior operative treatment include the development of kyphosis, instability, the spread of ossification of the posterior longitudinal ligament, and the development of stenosis at new levels. Late deterioration of neurological symptoms is more frequent following laminectomy without fusion^85,118.

	Consequences and Complications Following Operative Treatment

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Postoperative Neck Pain
In the study by Hosono et al., posterior neck and shoulder girdle pain was present following laminoplasty in 60% (forty-three) of seventy-two patients, with 25% (eighteen) of the seventy-two patients reporting severe axial pain as the chief complaint¹¹⁹. Soft-tissue injury following a posterior approach, facet arthrosis, preoperative stiffness, and older age have all been implicated in the pathogenesis of axial pain. Operative modifications such as coronal osteotomy of the spinous processes during the approach with subsequent reattachment after laminoplasty¹²⁰ (Fig. 4, E)¹²⁰ or combining laminectomy at selected levels with either partial laminectomy or interlaminar decompression¹²¹ help to preserve some of the extensor muscle and ligament attachments and have been reported to lower the prevalence of axial pain and stiffness following multiple-level posterior decompression^122,123. The duration of postoperative immobilization also may have a bearing on the prevalence of postoperative axial pain^16,101, leading some authors to encourage early active mobilization. Many patients have resolution of symptoms within a year.

Yonenobu et al. noted that the prevalence of postoperative pain was highest following laminoplasty (60% of 203), followed by laminectomy (27% of 115) and then by anterior decompression (19% of 209)¹¹⁸. Wada et al. reported moderate to severe axial neck pain in 40% of twenty-four patients at an average 11.7 years following laminoplasty and in 15% of twenty-three patients an average of fifteen years following subtotal corpectomy (p < 0.05)¹⁶. Conversely, Kawakami et al. reported less axial pain at 5.6 years following laminoplasty than following anterior cervical fusion at one or two levels and suggested that a shorter period of immobilization following laminoplasty prevents muscle atrophy and facet joint contracture, thereby minimizing postoperative stiffness³³.

Postoperative Stiffness
A decrease in the range of motion of the neck occurs in some patients following laminoplasty and is presumed to occur as a result of interlaminar or facet fusion on the hinge side or contracture of the posterior muscles and ligaments. Kawai et al. reported an appreciable loss in range of motion in thirty-four (72%) of forty-seven patients who were followed for two to fifteen years after laminoplasty¹²⁴. Range of motion is also lost following laminectomy with fusion, and Callahan et al. reported that as much as 12° of flexion, 16° of rotation, and 6° of lateral flexion can be expected to be lost for each level included in the posterior fusion⁸⁹. Some authors believe that the decrease in range of motion following laminoplasty is beneficial because it prevents further instability and retards the progression of spondylosis^74,125.

A decrease in the range of motion of the neck following anterior cervical discectomy and fusion is not an important concern. Many patients will note an increase in range of motion accompanying the pain relief following the operation. One study demonstrated no difference in the range of motion of the neck following anterior cervical discectomy and fusion at one and two levels but revealed a slight decrease in range of motion one year after anterior cervical discectomy and fusion at four levels¹²⁶. Range of motion decreases following corpectomy and fusion and is proportional to the number of levels fused. Hanai et al. reported on thirty myelopathic patients who were followed for three years after corpectomy and fusion involving an average of 3.4 levels¹²⁷. The average preoperative sagittal range of motion was 56°. The range of motion decreased by an average 15.2° in the three-level corpectomy group (eighteen patients) and by an average of 29.6° in the four-level corpectomy group (twelve patients).

Postoperative Stability
Laminectomy alone, especially in children and young adults or in patients with preexisting kyphosis or segmental mobility, can result in further instability, kyphosis, and worsening of neurologic deficit. Yonenobu et al., in a report on 115 patients who were managed with laminectomy for the treatment of myelopathy resulting from either spondylosis or ossification of the posterior longitudinal ligament, noted that 21% of the patients had postoperative neurologic deterioration due to instability of the cervical spine¹¹⁸. In another study of patients who underwent laminectomy without fusion for the treatment of cervical spondylotic myelopathy, 14% (three) of twenty-two patients with a preoperative lordotic cervical spine had development of postoperative kyphosis whereas 30% (six) of twenty patients with a straight spine and 67% (two) of three patients with preoperative kyphosis had an increase in kyphosis⁸³. In studies in which posterior instrumentation has been used, laminectomy with fusion has maintained lordosis close to the preoperative value^90,92.

The development of instability following laminectomy may be partly dependent on the degree of degenerative changes already present in the cervical spine. Yasuoka et al. reported on a large series of 1577 adult patients who had been followed for a minimum of five years after laminectomy⁸⁴. When the patients who had had trauma and those who had been managed with facetectomy were excluded, none of the patients had development of a deformity substantial enough to warrant a second operation.

Some loss of lordosis is common, but severe postoperative kyphosis is infrequent following laminoplasty^115,116,128. Preservation of the soft-tissue attachments to the C2 spinous process following laminoplasty decreases the likelihood of development of deformity in the cervical spine. In patients undergoing laminoplasty, unilateral exposure followed by coronal osteotomy of the spinous process and en bloc reflection of the spinous processes and attached soft tissues to the contralateral side minimizes the injury to the posterior soft-tissue tether^120,122.

Development of overt instability following anterior discectomy is uncommon even without an attempt at fusion. Many patients will go on to have spontaneous fusion¹¹⁴. The insertion of a graft and anterior plating following discectomy helps to maintain, and in some cases increases, cervical lordosis⁶⁷. Multiple-level anterior corpectomy with grafting and anterior instrumentation effectively reconstructs cervical alignment; in one study, it led to improved lordosis compared with laminoplasty¹¹⁵.

Adjacent Segment Degeneration Following Operation
In many cases, loss of recovery from myelopathy over the long term is attributed to degenerative changes adjacent to previously fused segments in the cervical spine. However, the occurrence of these degenerative changes needs to be viewed in the context of the natural progression of the spondylotic process with age and the ubiquitous presence of degenerative changes in an elderly but asymptomatic population. In an analysis of 374 patients at a maximum of twenty-one years following anterior cervical fusion, Hilibrand et al. reported that 2.9% of the patients had development of symptomatic adjacent-segment disease each year¹²⁹. Kaplan-Meier survivorship analysis indicated that the risk of development of adjacent-segment disease within ten years following anterior cervical fusion was 25.6%. Adjacent-segment disease developed earlier in patients who had preexisting degenerative changes at segments adjacent to the fusion. The C5-C6 and C6-C7 levels were most vulnerable to adjacent-segment disease but are also naturally most likely to show degenerative changes. The authors concluded that adjacent-segment disease was more likely to be a manifestation of the natural history of spondylosis rather than a consequence of fusion. Recently published biomechanical data suggest that anterior cervical discectomy and fusion with anterior plating does not predispose to adjacent-segment deterioration¹³⁰.

Adjacent-segment degeneration also has been reported following other forms of operative intervention on the cervical spine. In one study, 3.8% (three) of seventy-eight patients had development of adjacent-segment degeneration within 2.5 years after laminectomy and fusion, with two patients requiring a repeat operation for this condition⁹⁶. Wada et al. studied adjacent-segment degeneration in twenty-three patients following anterior corpectomy and fusion over an average of 2.5 levels and found that 38% of the patients had development of olisthesis at an adjacent segment and that 54% of the patients had development of osteophytes and disc-space narrowing at adjacent levels¹⁶. However, only one patient required a repeat operation for recurrent myelopathy over a follow-up period of fifteen years.

Neurological Complications
Patients with myelopathy are at risk for worsening of the neurological status intraoperatively. Active range of motion of the neck should be provocatively tested prior to the induction of anesthesia, and care should be taken to avoid intubation or intraoperative alignment of the neck in positions that result in neurological symptoms. Manipulation of the vertebral bodies during the operation should be minimized. Somatosensory and motor evoked potentials should be checked prior to positioning and throughout the procedure to help to detect any injury to the spinal cord.

Intraoperative spinal cord injury can result from direct trauma, ischemia, stretch, or hypothermia. In a survey of surgeons who performed anterior discectomy and fusion procedures, 311 neurological complications were reported among 36,657 cases¹³¹. The most common postoperative complications were radiculopathy (40%; 124 of 311), substantial permanent myelopathy (25%; seventy-eight of 311), and recurrent laryngeal nerve palsy 17% (fifty-two of 311). Yonenobu et al. reported that the prevalence of spinal cord dysfunction following laminectomy was 3.5% (three of eighty-five) and attributed this finding to the development of an epidural hematoma and postoperative swelling of the nuchal muscles, compressing the exposed spinal cord¹³². No myelopathic complications occurred in ninety-five patients who were managed with laminoplasty.

Postoperative C5 radiculopathy is a well-recognized complication that occurs following both anterior and posterior decompression of the spinal cord. Possible etiologies for the palsy include traction on the short C5 root resulting from posterior migration of the cord into the space created by a laminoplasty, closure of the laminoplasty door resulting in nerve impingement, and impingement of the ventral aspect of the spinal cord against the edges of a corpectomy trough^118,132,133. Yonenobu et al. reported that the prevalence of C5 palsy was 3.9% (eight of 204) following anterior procedures, 4.2% (four of ninety-five) following laminoplasty, and 1% (one of eighty-five) following laminectomy¹³². The clinical presentation is usually one of severe shoulder and upper arm pain, followed by weakness of the biceps and deltoid occurring one to three days after the operation. Spontaneous recovery can be expected, although this may take twelve months in some cases. Concurrent foraminotomy may help to diminish the prevalence of this condition following laminoplasty¹³⁴.

The prevalence of recurrent laryngeal nerve palsy following an anterior cervical approach has been reported to range from 2% (thirteen of 650)¹³⁵ to 11% (nine of eighty-five)¹³⁶. The actual prevalence of this complication may be underreported because common symptoms of hoarseness, aspiration, or cough are minor, transient, and frequently seen in association with endotracheal intubation. Mechanisms of injury to the nerve include direct surgical trauma, pressure or stretch-induced neurapraxias, postoperative edema, and stretch resulting from retraction on the intralaryngeal course of a laryngeal nerve tethered by the endotracheal tube¹³⁵. Avoidance of prolonged retraction, knowledge of the anatomy, careful dissection, and deflation of the endotracheal tube cuff after retractor placement all may help to diminish the prevalence of this complication. The course of the recurrent laryngeal nerve is more protected within the tracheoesophageal groove on the left side, but it is unclear whether the laterality of the approach affects the prevalence of this complication. Injury to the superior laryngeal nerve leads to easy voice fatigue and difficulty with high-pitched tones. It most frequently occurs inadvertently during anterior approaches to the upper cervical segments.

Injury to the sympathetic nerves results in Horner syndrome and commonly occurs in association with prolonged or more vigorous retraction, revision surgery, and operations involving lower cervical and cervicothoracic levels. Patients generally do not have symptoms other than a drooping eyelid, and most patients have resolution of these findings within six months. Bertalanffy and Eggert reported Horner syndrome in five (1.1%) of 450 patients who underwent anterior cervical discectomy for the treatment of myelopathy, radiculopathy, and myeloradiculopathy¹.

Dysphagia
Dysphagia is a frequent and transient occurrence following anterior cervical spinal approaches. Hematomas; local edema; denervation of the pharyngeal plexus; adhesions between the esophagus, trachea, and prevertebral fascia; and displaced graft or instrumentation are all potential causes. Bazaz et al. reported that the prevalence of dysphagia was as high as 50% (ninety-nine of 197) at one month after the operation and decreased to 12.5% (nineteen of 152) at one year¹³⁷. Dysphagia occurred more frequently when the procedure involved multiple levels or was performed in women. There was no correlation with the type of procedure (corpectomy or discectomy, primary or revision surgery), the vertebral level at which the operation was performed, or the addition of anterior plating. Esophageal perforation resulting from anterior migration of screws or plates occurs infrequently^138,139.

Vertebral Artery Injuries
Vertebral artery injuries occur during operations performed through an anterior approach for the treatment of cervical spondylotic myelopathy; such injuries can result from a loss of orientation to the midline during corpectomy, lateral dissection in the foraminal region, or unrecognized anomalies in the course of the vessel¹⁴⁰. The width of the corpectomy trough should be restricted to 15 to 19 mm to avoid inadvertent injury to the vertebral artery. The medial margin of the longus colli muscles, uncovertebral joints, and the natural curvature of the vertebral end plates all help to orient the surgeon with respect to the midline. Eleraky et al.¹⁴¹ reported vertebral artery injury in four of 185 patients undergoing corpectomy. Treatment options include ligation, exposure and direct repair, and endovascular stent placement. In most cases, the contralateral vertebral artery provides sufficient collateral circulation to the hindbrain, but neurologic deficit can occasionally result.

	Intraoperative Spinal Cord Monitoring

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Electrophysiologic monitoring aims to detect intraoperative compromise of the long tracts of the spinal cord and to allow earlier correction of any surgical or anesthetic event that may have precipitated these changes. Somatosensory evoked potentials represent potentials conducted from the ulnar, median, or posterior tibial nerves through the dorsal columns to electrodes located over the cranium or the upper cervical spine. Motor evoked potentials monitor the ventral columns of the spinal cord and are frequently used in combination with somatosensory evoked potentials for intraoperative monitoring. Motor evoked potentials record peripheral muscle potentials in response to transcranial stimulation with a needle or surface electrode. Continuous or so-called free-running electromyogram recording of upper extremity muscle groups helps to monitor cervical nerve roots during the operation¹⁴².

Somatosensory evoked potentials can vary in response to the dose of inhalational anesthetic agents, and the rate of false-positive recordings is high. In one study, sixty (86%) of seventy patients with an amplitude decrease of >50% had no neurological deficit postoperatively¹⁴³. False-negative somatosensory evoked potentials are rare with proper technique and appropriate threshold selection¹⁴⁴. Motor evoked potentials are more specific but are blunted by neuromuscular blocking agents and in more severe cases of myelopathy. Motor evoked potentials should not be used in children or in patients with metallic aneurysmal clips, cardiac pacemakers, or epilepsy.

At our institution, baseline recordings are obtained for the patient after the induction of anesthesia but before final positioning. A change in spinal cord function is indicated when somatosensory evoked potentials decrease in amplitude by 50% and increase in latency by 10% or when the stimulation threshold for motor evoked potentials is exceeded by 100 mV.

	Overview

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 
Operative management is indicated for most patients with clinically evident cervical spondylotic myelopathy. Patients with very early or mild clinical findings are clinically and radiographically assessed with regard to their level of disability, the duration of symptoms, the degree of stenosis, and evidence of progression, and a decision regarding treatment is made by weighing these factors against the risks of operative intervention. The objective of operative treatment is to adequately decompress the spinal cord and to maintain the stability of the spinal column.

A choice of operative techniques is available for the surgical treatment of cervical spondylotic myelopathy, and the specific procedure that is chosen is based on multiple factors, including the location of the compressive pathology, the longitudinal extent of disease, the alignment of the spinal column, and the dimensions of the spinal canal. Appropriate operative surgical treatment of cervical spondylotic myelopathy will result in satisfactory recovery from myelopathy in most cases, with improvement being higher in younger patients, patients in whom operative treatment is performed earlier in the course of the disease, and patients with less comorbidity.

	References

Top Introduction Nonoperative Treatment of... Indications for Operative... Choosing the Operative Procedure Operative Options for and... Posterior Surgery in Cervical... Outcome Following Operative... Consequences and Complications... Intraoperative Spinal Cord... Overview References

 

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				R. D. Rao, B. L. Currier, T. J. Albert, C. M. Bono, S. V. Marawar, K. A. Poelstra, and J. C. Eck Degenerative Cervical Spondylosis: Clinical Syndromes, Pathogenesis, and Management J. Bone Joint Surg. Am., June 1, 2007; 89(6): 1360 - 1378. [Full Text] [PDF]

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