Neurologic Complications of Common Spine Operations

Summary of Key Points

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A surgical complication can result in a return for a subsequent operation, longer hospital stay after the initial operation, or an additional need for subsequent care (rehab, therapy, assistive devices).
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The spinal cord is at risk in any spine surgery above the conus.
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Posterior occipitocervical or cervical procedures risk injury to the vertebral artery, and C5 palsy is the most common nerve root injury.
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Anterior cervical operations can lead to injury to the carotid sheath, recurrent laryngeal nerve, and esophagus.
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Posterior thoracic cases put the spinal cord at greatest risk.
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Lumbar surgery may lead to lower extremity deficit from nerve root injury, and cerebrospinal fluid leak is common, particularly in revision cases.
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Suspected cerebrospinal fluid leaks, new neurologic deficits, and medically intractable postsurgical pain require imaging as an early step in management to identify surgically correctible problems.

Neurologic complications can be devastating for the patient, stressful for the surgeon, and costly for health care. Even with the best intentions, techniques, and care, neurologic complications may still occur. This chapter discusses common and uncommon neurologic complications, subdivided into the surgical approaches involving the different regions of the spine.

Neurologic complications have wide-ranging impacts on patients and health care costs. A surgical complication can result in a return for a subsequent operation, longer hospital stay after the initial operation, or an additional need for subsequent care (rehab, therapy, assistive devices). We first describe complications by anatomic region and approach and later discuss management strategies for some common complications.

Occipitocervical Junction Operations

Neurologic complications can occur during surgery at the occipitocervical junction, but compared to other regions of spine, complications in this location are rare. The underlying anatomic and biomechanical complexity of the occipitocervical junction poses unique challenges that may lead to complications. Operative complications could result in compromise to neural, biomechanical, or vascular structures in this region. One possible complication is C2 neuralgia, which can occur from manipulation, thermal injury, or stretch injury during placement of C1 lateral mass screws or exposure of the C1-2 facet capsule. Mortality for occipitocervical fixation cases is low, at 1.7%. Serious complications may occur either from injury from instrumentation or from surgical exposure.

Given that complications at the occipitocervical junction may cause more severe consequences, liberal use of fluoroscopy or image-guidance is a common mitigating technique. Anatomic foramen in the cervical spine house critical structures that include exiting nerves or blood vessels, and they may be compromised with improperly placed instrumentation. Improper screw placement into the transverse foramen may cause vertebral artery injury. Intracranial extension of occipital screws could cause occipital meningismus resulting in persistent headaches, hemorrhage, or spinal fluid leak. Instrumentation into the neural foramen may cause focal radiculopathies.

Avoiding vital structures becomes increasingly difficult when the underlying anatomy is remodeled in the setting of prior surgery, bone pathology, or anatomic variants. Surgical exposure with electrocautery can itself cause vertebral artery injury, spinal fluid leak, or nerve injury because of the proximity of such vital structures to the exposure area. Although complications in this region could result in irreversible and devastating injuries, careful and meticulous surgical technique helps prevent neurologic complications.

Anterior Cervical Operations

Anterior approaches to the cervical spine provide visualization or proximity to vital anatomic structures such as the carotid sheath, recurrent laryngeal nerve, esophagus, and spinal cord. Anterior approaches can result in significant morbidity by injuring any one of these vital anatomic structures.

The anterior transcervical approach is the most common for anterior cervical discectomy and corpectomy. Anterior cervical complications usually occur as a result of the surgeon not being able to identify the midline or other anatomic landmarks in the neck. If the surgeon is unable to identify landmarks while approaching the spine (especially in morbidly obese patients or revision cases), one can stop the deep dissection, start again more superficially, identifying superficial landmarks before carrying on with the deep dissection. We also recommend a limited use of scissors and cutting tools within the deep dissection so as to avoid the possibility of cutting any vital nerves or structures. We prefer blunt dissection down to the spine to avoid any permanent transection of traversing nerves or arteries. Extreme care must be taken to avoid esophageal injury, which can occur even with blunt dissection. Once at the level of the spine, judicious and meticulous surgical technique can reduce uncommon neurologic complications including injury to the spinal cord, exiting nerve root(s), sympathetic plexus (resulting in a Horner syndrome), and vertebral artery injury. Sometimes it is helpful to mark the midline of the spine before performing the main procedure because the retractors can shift, and the surgeon can become disoriented with the location of midline, especially in multilevel procedures.

Neurologic complication rates are low for anterior cervical procedures. One retrospective national database study showed 30-day neurologic complication rates of only 0.09% to 0.13% for single-level anterior cervical discectomy and fusion (ACDF). However, this report failed to specifically quantify rates of postoperative C5 palsy. Other studies have shown C5 palsy rates of 1.7% to 11.5%. Higher complication rates correlate with increasing age and number of segmental levels treated. It is important to warn the patient preoperatively of possible C5 palsy because of its profound and visible effect on arm function postoperatively. With significant advance warning, patients are more likely to tolerate the usually transient loss of deltoid or biceps function as a known, possible outcome from the surgery.

Vertebral artery injury has a lower incidence with anterior approaches compared to posterior. Rates range from 0.07% to 0.14%. Careful review of preoperative imaging studies for the location of the transverse foramen, size of the foramen, proximity to the vertebral artery, and uncovertebral joint may help to avoid vertebral artery injury. During the dissection, the use of electrocautery should be minimized as the dissection over the vertebral body becomes more lateral and deep. Extra care should be taken near the transverse foramen, especially when exposing the nerve root laterally or widening the corpectomy with the drill. The surgeon should also keep in mind that there is often a bias toward the contralateral side of the spine because of the inherent nature of a non-midline approach. For instance, if the surgeon performs a right anterior approach, the decompression may be skewed toward the left side of the spine; thus, the surgeon needs to be cognizant of not going too far laterally on the left.

Delayed postoperative neurologic complications, including a postoperative hematoma causing mass effect either on the spinal cord or exiting nerve roots, is a feared but rarely encountered complication for anterior approaches. The postoperative hematoma rate is less than 1% and may be lower when a surgical drain is left in place. The most significant danger of a postoperative hematoma in the anterior cervical spine is potential compromise of the trachea and airway. If there is airway compromise, emergent intubation or emergent evacuation of the hematoma should be performed.

Injury to the recurrent laryngeal nerve (RLN) is a more commonly encountered neurologic complication. Injury occurs by stretching, dividing, ligating, or avulsing the nerve, causing postoperative voice change or hoarseness. RLN injury may result in transient vocal cord paresis or permanent vocal cord paralysis in addition to severe dysphagia secondary to an inability to protect the airway during swallowing. Anterior cervical approaches are associated with 5% to 11% rates of voice change, with most changes being transient and likely secondary to edema and eventually resolving over a 3-month period of time. Permanent unilateral nerve damage occurs in 2% to 4% of cases. Given these rates, professional singers should be warned that an anterior cervical approach could cause irreversible vocal changes. For these reason, singers and other vocal professionals may prefer a posterior approach if possible, which avoids this risk. When injuries do occur, an otolaryngology consult is appropriate to evaluate vocal cord function.

Multiple strategies can be employed to prevent RLN injury, which can be caused by transection or prolonged retraction. The first strategy is careful and meticulous dissection with thorough knowledge of anatomy. The recurrent laryngeal nerves each branch off from the descending vagus nerve in the carotid sheath. The right RLN loops around the subclavian artery, while the left RLN loops around the arch of the aorta. On either side, it then ascends lateral to the trachea in the tracheoesophageal groove before innervating the larynx. Because of the differing bilateral anatomy, left-sided approaches have been suggested to cause lower rates of RLN injury, but most right-handed neurosurgeons prefer a right-sided approach. There are data to support that neither side has a higher complication rate than the other. Retractor-related injury may be mitigated by minimizing the intubation time, limiting the degree of retraction, and avoiding excessive endotracheal cuff pressures. After retractors are placed, some have advocated for deflating the endotracheal tube cuff and then reinflating to the minimum necessary pressure.

Posterior Cervical Operations

Posterior cervical operations are commonly used for decompression, and various techniques have been utilized, including laminectomy, laminectomy and fusion, and laminoplasty. Laminectomy performed for decompression is generally safe, but there have been reports of uncommon delayed complications and postlaminectomy kyphosis causing myelopathy. Laminoplasty was originally developed as a potential means of treating cervical spondylotic myelopathy (CSM) while preserving motion. One retrospective study showed improved pain scores with laminectomy and fusion compared to laminoplasty for cervical spondylotic myelopathy, but with higher implant cost ($12,000 for C3-6 fusion versus $4200 for C3-6 laminoplasty) and higher rates of reoperation and complications. There were similar improvements in walking ability on the Nurick scale in both groups. When excluding fusion cases involving the cervicothoracic junction, reoperation rates were 13% in both groups.

Postlaminectomy kyphosis is an infrequent complication that occurs more commonly in cases of preoperative kyphosis or preoperative instability. There is an increased risk of kyphosis associated with extensive facet resection, detachment of cervical extensor musculature (especially at C2), or multiple-level decompressions without fusion. To minimize the risk of postlaminectomy kyphosis, a lateral upright radiograph should be obtained to evaluate the alignment of the cervical spine (alignment of C2 above C7), assessing risk factors such as preoperative kyphosis. Cervical alignment should be taken into context with the overall global alignment of the spine. Obtaining flexion and extension radiographs could provide further insight to an underlying instability. Although postlaminectomy kyphosis is rare, prevention through adequate preoperative assessment is critical.

Another complication is the C5 palsy, as in the anterior approach. The incidence of C5 palsy ranges from 0% to 13.6%, depending on the operation, with lower rates seen in laminoplasty versus laminectomy. The overall incidence of C5 palsy in the posterior approach is approximately 5.8%. Risk factors for postoperative C5 palsy include ossification of the posterior longitudinal ligament (OPLL), narrow intervertebral foramen, and male gender. Patients with OPLL in the cervical spine have an overall greater incidence of surgical complications. Preoperative C4-5 foraminal stenosis appears to be a risk factor for postoperative C5 palsy, and some authors have advocated for a prophylactic C4-5 foraminotomy; however, it is unclear if prophylactic foraminotomy truly decreases the risk of C5 palsy. A prospective cohort study of prophylactic bilateral C4-5 foraminotomy showed reduction of C5 palsy rates from 7.0% to 1.7% in open-door laminoplasty cases, without changing range of motion, rates of hinge fracture, or nonunion. One must be cautious, however, because the foraminotomy itself may cause a C5 palsy if not done gently. Thus, surgeons should take into consideration their own technique of decompression, avoiding the use of large Kerrison rongeurs into the foramen, using steady control of the drill over the nerve root, and minimizing overall manipulation of the C5 nerve.

The etiology of neurologic complications can be further divided into two categories: direct trauma to neural tissue, and progression of symptoms related to spine instability. Instability of the cervical spine can lead to spinal cord tension and ischemia, which can cause direct neuronal injury with cord changes manifesting in myelomalacia and cord atrophy. To further minimize disease progression and prevent neurologic complications following cervical laminectomy, studies have shown the importance of fusion for stability. Fusion may also prevent delayed kyphosis. Fusion can be helpful in patients who lack lordosis of their cervical spine. In a neutral spine, extension can be achieved after laminectomy and facetectomy, and subsequent internal fixation can be used to recreate cervical lordosis.

Thoracic Spine Operations

Operations in the thoracic spine are generally less common than those in the cervical or lumbar spine. Surgical approaches have evolved to minimize spinal cord manipulation because of potential poor outcomes and neurologic deterioration. Thoracic disc herniations, although they make up less than 1% of all intervertebral disc operations, can carry significant risks especially when encountering large or even giant calcified disc herniations that are medially located and indenting the spinal cord. Anterolateral approaches are generally recommended for these challenging disc herniations. Transpedicular and costotransversectomy approaches have proved successful for treating soft discs. However, extreme caution should be taken when trying to remove a midline calcified disc from a posterior approach, which risks significant loss of neurologic function postoperatively. Additionally, dural erosion by calcified discs can lead to ventral cerebrospinal fluid (CSF) leaks during discectomy, and these leaks can be notoriously difficult to repair.

Figure 202-1 demonstrates an attempt at an outside hospital to remove an anterior thoracic disc via a posterior approach for a patient with a large medially located T11-12 herniated disc ( Fig. 202-1A ). The edema caused by this approach and the significant residual disc herniation can be appreciated on magnetic resonance imaging (MRI) ( Fig. 202-1B ). A subsequent anterior operation was needed to fully resect the remaining herniated disc via a thoracotomy approach ( Fig. 202-1C ).