Ventral Cervical Surgery

Ventral cervical surgery, whether for discectomy or corpectomy, has many potential neurologic complications, but devastating neurologic injuries are a rarity.¹

Specific complication types and rates vary with the side selected for the approach. Injury to the cervical sympathetic chain can occur during dissection of the longus colli muscles from the ventral cervical spine.² The cervical sympathetic chain ascends on the lateral border of the longus colli muscles and has three ganglionic enlargements. The superior cervical ganglion is at the level of C2-3, the middle ganglion is at the level of C6, and the stellate ganglion is at the level of C7-T1. Injury to the sympathetic chain can be prevented by limiting dissection of the longus colli muscles to their medial aspect only and by careful positioning of the self‑retaining retractor blades on the medial side only of the dissected muscle. The stellate ganglion may occasionally be observed during low dissection in the neck. If it is observed, injury may be avoided by repositioning the retractor to move this structure out of the operating field. Injury to the cervical sympathetic nerves is manifested clinically by Horner syndrome (miosis, anhydrosis, and ptosis). Injury of the cervical sympathetic chain is seldom of any clinical significance, and recovery is usually spontaneous. Injury to the superior laryngeal nerve can occur during ventral cervical discectomy. This usually occurs during dissection in the deep cervical fascia because the superior laryngeal nerve is in close proximity to the superior and inferior thyroidal vessels.³

Injury to the recurrent laryngeal nerve may occur during ventral cervical discectomy, resulting in vocal cord paralysis.² The nerve is more often injured during a right‑sided operative approach because of the anatomic course of the nerve. In some instances, the right recurrent laryngeal nerve does not loop around the subclavian artery and takes a more direct course, making the nerve more vulnerable to surgical injury. For this reason, some surgeons prefer a left‑sided approach because the left recurrent laryngeal nerve has a more predictable course and has a more medial position between the trachea and the esophagus. However, the left nerve has a higher incidence of idiopathic palsy.³ Vocal cord paralysis from recurrent laryngeal nerve palsy is usually the result of a stretch injury from retraction and usually resolves spontaneously within 6 months after injury. In some patients with vocal cord paralysis, the opposite vocal cord hypertrophies, allowing normal phonation. In any patient who has repeat ventral surgery to the cervical spine, either the approach should be through the previously operated side or the patient should have an otolaryngologic evaluation to confirm normal vocal cord function on both sides before surgery. If vocal cord paralysis is noted, the operative approach should be on the side of the paralyzed vocal cord. Voice hoarseness is often attributable to swelling and does not reflect recurrent laryngeal nerve injury. The incidence of postoperative hoarseness may be lessened by placing a closed suction drain.⁴ Direct injury to the spinal cord and nerve roots has been reported with an incidence of approximately 2% after ventral cervical operations for myelopathy. These can be avoided only by meticulous operating technique and proper visualization.⁵

Dural tear is an uncommon intraoperative complication during ventral cervical surgery, more common when the posterior longitudinal ligament is taken down to complete a neural decompression or when corpectomy is carried out. Direct trauma caused by cutting instruments such as the bur or Kerrison rongeurs is the most common cause, but dural defect can be caused by cautery and even by focused application of the bipolar. Dural repair is desirable whenever possible, but access to the site of the leak and consideration for the dangers of retracting and manipulating the cord itself make many repairs unfeasible. In a large series of cervical surgeries that was reviewed for incidence and care of durotomies, laterally located leaks and those occurring behind the vertebral body were found to be unrepairable. Fibrin glue, mobilization precautions, bedrest in a partially seated position, and occasional use of a subarachnoid drain were required to obtain closure in these patients. While successful resolution was inevitably accomplished, additional care and prolonged hospitalization had a significant cost.⁶

Late postoperative complications of radiculopathy and myelopathy have been reported after ventral cervical discectomy and fusion. Five percent of patients developed myelopathy or radiculopathy an average of 5.5 years after ventral cervical discectomy and fusion, with myelography revealing pathology one level above or below the site of previous fusion. No compression was found at the previously operated site, and only 2.5% of these patients required reoperation at a second level.⁷ Other researchers have obtained different statistics. Deterioration within the first year after ventral decompression from advancing osteophytic spurring at adjacent levels occurred in 5% of cases, and deterioration in the second and third years after ventral decompressive surgery occurred in another 5% of cases because of osteophytic processes, for a total deterioration rate of 10% within 3 years of surgery.⁵ This deterioration may be preventable only by postoperative surveillance, reoperating on symptomatic patients, and considering the inclusion of all spondylotic levels in the fusion.⁵ Complications caused by bone grafts have an incidence of 13%. Nonunion of bone graft was also noted in 7% of patients as an early cause of deterioration and in 4% of patients in the second and third years, for a combined total of 11% for deterioration caused by nonunion.^5,8 Nonunion rates may be lowered by paying meticulous attention to bone grafting and by adding ventral cervical instrumentation in multilevel decompressions. Spinal cord compression from malpositioning of the bone graft occurs less often. Bilateral brachial paresis has been reported after ventral cervical surgery for spondylosis. This occurred in a delayed fashion and was associated with angulation at the surgical site, with extrusion of the bone graft.⁹ Worsening of neurologic function has been reported after ventral cervical fusion from cord compression by the bone graft. Neurologic function improved after removal of the offending graft.⁵ Proper morticing of the graft bed is key to preventing compression of the spinal cord during graft placement. Precise measurements must be obtained of the depth of the decompression at the superior, inferior, and both lateral walls, as well as the length and width of the graft bed, because these measurements are not uniform. A minimum buffer of 3 mm must be preserved between the decompressed spinal cord and the bone graft, with the mortices cut to provide a dorsal shelf that will prevent the graft from compressing the spinal cord.

Dorsal Cervical Surgery

Central cord syndrome has been reported as a delayed complication that occurs several days after dorsal cervical decompressive laminectomy for cervical stenosis. Central cord syndrome occurred after a period of hypotension and was often associated with abnormal neck position. It is recommended that laminectomy be avoided in patients with abnormal cervical lordosis; that hypotension be avoided, especially when the patient is mobilized for the first time postoperatively; and that a cervical collar be used in the immediate postoperative period.¹⁰ Jackson and Simmons¹¹ have reported a case of cervical laminectomy in a markedly kyphotic patient who had local anesthesia, with the patient serving as his own monitor. During the operation, the patient lost neurologic function. This rapidly reversed when the dura was opened. Other reported complications of dorsal cervical surgery include death from air embolism when the sitting position was used, neurologic deterioration from poor positioning of the cervical spine during operation, and tetraplegia from epidural hematoma.¹² Neurologic worsening has been noted in myelopathic patients if a laminectomy of inadequate length or width is performed. Laminectomy should extend to the lateral margin of the thecal sac, and if more than 50% of the medial facet is resected, fusion should be considered to lessen the risk of instability. Laminectomy should extend one level higher and one level lower than the highest and lowest compressive lesions.¹³ Syringomyelia has become symptomatic after cervical decompressive laminectomies for cervical stenosis in patients with an unrecognized syrinx. It is postulated that decompression changes the transmural pressures across the syrinx wall, causing an increase in syrinx size and the appearance of symptoms. This is a rare complication that is lessened by obtaining preoperative MRI to differentiate between syrinx and cervical stenosis.¹⁴

Cervical laminectomy may cause instability if more than one half of the medial facet is removed. Other risk factors for postlaminectomy kyphosis include young age and preoperative kyphosis.⁵ Kyphosis may result in progressive angulation with pain and cervical spondylotic myelopathy. This complication can be lessened by restricting decompression to less than one half of the medial facet or, when more lateral decompression is needed, by performing a fusion.¹⁵ During dorsal cervical fusion, spinal cord injury has been reported in a case in which the dorsal bone graft loosened, compressing the spinal cord and causing Brown‑Séquard syndrome.¹⁵

Dorsal cervical foraminotomy may worsen radiculopathy.¹⁵ Care must be taken not to place any instruments into the narrowed foramen because this will further compress the nerve root, and the nerve root should not be retracted until the foramen is opened, allowing easy retraction of the nerve root.

Thoracic Spine Surgery

Ventral approaches to the thoracic and lumbar spine can cause ischemia to the spinal cord by interrupting the blood supply to the cord. Approaches to the ventral thoracic spine at levels T4-9 are especially dangerous. The risk of causing spinal cord ischemia can be lessened by performing preoperative angiography to localize the artery of Adamkiewicz and then planning surgery to avoid this artery. In addition, temporary segmental artery occlusion with somatosensory-evoked potential (SSEP) monitoring has been advocated to help identify key intersegmental arteries supplying the cord. The segmental arteries are identified and temporarily occluded during a ventral approach to the thoracic spine while SSEP monitoring is carried out. If the SSEP waveform deteriorates, the occlusion is released, and that segmental vessel is spared.¹⁶ Thoracic disc herniations may be operated on via a variety of approaches. Neurologic complications are highest with central thoracic disc herniations approached from a dorsal laminectomy. In this setting, the paraplegia rate approaches 18% and is due to excessive spinal cord retraction. Complications may be lessened by a lateral extracavitary approach, costotransversectomy approach, or transthoracic approach.¹⁷ Complications may be lessened further by performing preoperative spine angiography to avoid damage to the radiculomedullary artery of the spinal cord.

Lumbar Spine Surgery

Injuries to the dura mater and nerve roots may occur during lumbar disc surgery. Nerve root injury may occur from laceration, thermal injury, and excessive retraction. Lacerations to the nerve root most commonly occur because of lack of identification of the nerve root or because of failure to recognize a flattened root spread over the top of a herniated disc. Adequate illumination and magnification are extremely helpful in locating lumbar nerve roots. The anulus should never be cut until the nerve root has been positively identified. Bone and ligament should be removed until the root can be easily retracted. Further dissection of bone is often needed in the lateral direction to accomplish this goal. Bipolar electrocautery is useful for providing hemostasis, but no cauterization should be attempted until the nerve root is identified to avoid electrical or thermal injury to the nerve root.¹⁸ Dural tears may occur during lumbar surgery with an incidence of approximately 4%. Care must be taken to avoid aspirating multiple nerve roots into the suction device and thereby causing neurologic deficit. The dural tear should be covered with a cottonoid, a smaller-diameter suction device should be inserted into the field, and exposure should be improved until the dural tear is fully exposed and then closed, if possible, in a watertight fashion.¹⁸

Lumbar discectomy in patients with cauda equina syndrome requires rapid evaluation and treatment. Some authors have found that persistent urinary incontinence is common in patients who are operated on 48 hours or more after presentation of symptoms but is uncommon in those who are operated on within 48 hours.¹⁹ Kostuik et al. found two separate modes of presentation in patients with cauda equina syndrome to an acute mode with rapid onset, more severe symptoms, and a poorer prognosis after decompression and a mode with more gradual onset of symptoms. In both groups of patients, those with complete perineal anesthesia tended to have permanent bladder paralysis. Kostuik et al. also found no correlation between timing of surgery and extent of recovery. Despite this lack of correlation, they recommend early surgery for patients with cauda equina syndrome.²⁰

Acute postdiscectomy cauda equina syndrome occurs at a rate of approximately 0.2%.²¹ The majority of these patients develop symptoms of perineal numbness, urinary retention, motor weakness, and multidermatomal numbness in the recovery room. Stenosis of the lumbar spinal canal at the operative level with anteroposterior dimension of 13 mm or less was the most common factor found in postdiscectomy cauda equina syndrome, with swelling, hematoma, retained disc fragments, and hemostatic gelatin (Gelfoam) contributing to the compression. A large epidural fat graft has also been a reported cause of cauda equina syndrome after lumbar discectomy.²² In this case, a large fat graft herniated into the spinal canal on the first postoperative day, causing cauda equina syndrome. These complications may be avoided by limiting the size of the fat graft to between 5 and 8 mm and by suturing the graft to adjacent paraspinous muscle tissue, by measuring the lumbar canal preoperatively, and, if stenosis is present, by avoiding use of keyhole laminotomy to provide the approach to the disc space. Additionally, hemostasis should be obtained to avoid hematoma formation.²³ The operation for lumbar disc herniation causing cauda equina syndrome differs from the usual lumbar discectomy in that a much wider bony exposure is required. Complete hemilaminectomy is recommended to provide space to remove the disc herniation while lessening retraction that could cause permanent deficit. Microdiscectomy should be avoided in these patients because it provides less bony exposure.²⁴

Cauda equina syndrome has also been reported after surgery for lumbar spinal stenosis. Compressive hematoma has been implicated as a cause of cauda equina syndrome after decompressive laminectomy. Cauda equina syndrome has been reported to occur after application of large epidural fat grafts in lumbar decompressive laminectomies.²⁵ This may occur by the fat graft acting to seal a hematoma against the thecal sac or by compression of the large fat graft by the paraspinal muscles. This complication may be prevented by limiting the size of the fat graft to a thickness of 0.5 to 1.0 cm and to a height less than the height of the spinous processes.²⁵ Several cases of cauda equina syndrome have resulted after decompressive laminectomies in which a higher lesion, such as a herniated disc, was later identified. To minimize these complications, the following steps should be taken: Hemostasis should be obtained before closure, or a closed suction drain should be placed if hemostasis cannot be obtained. The entire lumbar spine and thoracolumbar junction should be visualized by MRI or myelography preoperatively so that pathology in the upper portions of the spinal canal is not overlooked. Lumbar decompression should have sufficient length to include all compressed elements. Cauda equina syndrome may also occur on a vascular basis, as the artery of Adamkiewicz may enter at the upper lumbar segments and may be damaged during operation at the thoracolumbar junction. Preoperative spine arteriography should be considered carefully to verify the presence or absence of vascular supply to the spinal cord in the area of the proposed operation if the operation is to be performed in the regions from T4 to L2. In postoperative cauda equina syndrome, mechanical causes must be ruled out and, if present, removed in an urgent fashion. Only after all mechanical causes have been included should a vascular etiology be diagnosed.²¹

Automated percutaneous discectomy carries risk. The most severe reported complication is one of cauda equina syndrome caused by improper placement of the nucleotome probe in the thecal sac. In animal tests, the device could pierce dura, amputate nerve roots, and make holes in intravascular structures. Complications with the nucleotome probe can be minimized by the following procedures: The nucleotome should never be placed outside the disc space; once properly positioned, the device cannot incise the anulus and therefore cannot exit the disc space. The thecal sac is outlined by the line of the dorsal vertebral bodies ventrally, the line of the junction of the lamina and spinous processes dorsally, and the medial borders of the pedicles laterally; therefore, the probe should be placed under radiographic guidance using these landmarks to avoid the thecal sac. The device should be used only by an operator who has been trained in its proper usage. The procedure should be performed only under local anesthesia, as patient discomfort will alert the operator to any potential injury.^26–28

Surgery for lumbosacral spondylolisthesis may also cause cauda equina syndrome even with no attempt at reduction of alignment.²⁹ Paresis of proximal roots after reduction of lumbosacral spondylolisthesis has also been reported and is caused by stretching of proximal nerve roots after reduction of the spine.³⁰ The L5 nerve root is the most often damaged during reduction of lumbosacral spondylolisthesis, followed in frequency by the S1 and S2 nerve roots.^30,31 To lessen these complications, SSEP monitoring and prereduction decompression of the nerve roots should be performed. When the patient awakens from surgery, a thorough neurologic examination should be performed on the lumbosacral nerve roots, and if new deficit is found, the patient should be returned to the operating room for decompression of the involved root.²⁹