Throughout any anterior surgical procedure on the cervical spine, the surgeon must always know the location of the midline. This is reliably done by marking the midline before dissection of the longus colli and identifying the medial portion of the uncovertebral joints and using them as a continuous reference for bone and soft-tissue removal.
When dissecting laterally under the longus colli with monopolar electrocautery, it should be set at a low intensity to minimize the transduction of heat through surrounding structures, which can cause vertebral artery injury. Similarly, bipolar electrocautery or transcollation technology can be used for this portion of a surgical procedure to prevent arterial injuries caused by the arcing of energy. Venous bleeding should be controlled with topical hemostatic agents and paddies as opposed to being chased into the lateral vertebral body with the electrocautery device.
A recommended width for safe vertebral body removal during corpectomy is approximately 15 mm, given that the average interforaminal distance varies from 26 to 29 mm. An off-center, asymmetric, or oblique corpectomy trough can put the vertebral artery at risk of injury. The wall of the vertebral body opposite the chief surgeon is generally more prone to injury secondary to an oblique corpectomy trough. During diskectomies and corpectomies, trumpet laminectomy, creating a space >15 mm, can be used for the optimal lateral decompression of neural structures (Figure 3).
In the instance of a vertebral artery injury, the therapeutic goals include control of local hemorrhage, prevention of immediate vertebrobasilar ischemia, and prevention of cerebrovascular complications (Figure 4). Efforts should be made immediately after injury to tamponade bleeding with local pressure, using thromboplastic agents and surgical patties. The use of bone wax or other particulate materials should be avoided if possible, given the theoretical risk of embolization. After bleeding is controlled, surgeons should avoid the temptation to definitively treat a vertebral artery injury solely with packing or tamponade because of the risk of delayed hemorrhage or creation of a fistula or pseudoaneurysm.
During the process of tamponade and before any further surgical exploration is attempted, the operating room staff and anesthesiologists should be immediately notified, and the protocol for massive transfusion should be activated because of the potential for 3 to 5 L of rapid blood loss from vertebral artery injury. Intraoperative consultation with a vascular surgeon should also be considered. In addition, the head of the bed should be immediately returned to the neutral position to ensure the contralateral vertebral artery will not be mechanically occluded.
At this point, the decision must be made either to have the patient undergo immediate angiography evaluation and possible coil/stent treatment or further surgical exploration with a possible repair or direct ligation. This decision is based on the stability of the patient and area of tamponade, availability and proximity of angiographic services, anatomic site and mechanism of injury, and vertebral artery dominance, if it is known. A patient who remains in an unstable state or in whom active bleeding persists despite efforts at hemostasis should not be transported from the operating room to an angiography suite. If the injured vertebral artery is known to be dominant or the contralateral artery is not patent because of prior pathology, repair of the injured artery should be undertaken.
The direct repair or ligation of an injured vertebral artery requires that the ipsilateral artery be clearly exposed above and below the site of injury. For an arterial injury during an anterior procedure, the skin incision made for the latter can be extended and the sternocleidomastoid muscle partially transected at the level of the arterial injury to create an improved working area. The ipsilateral longus colli is dissected laterally over the transverse processes above and below the site of injury. For the distal control of bleeding, the injured vertebral artery is dissected out and a temporary clamp applied at the C6-C7 level before the artery enters the C6 transverse foramen (Figure 5). For proximal control, the transverse process directly cephalad to the site of injury is unroofed using a 2- or 3-mm Kerrison rongeur and the intertransversarii muscles are carefully removed. Before a clamp is applied proximally, determination is made of the presence or absence of retrograde flow from the injury site. If good backfilling of the artery is seen, the patient can be presumed to have a patent circle of Willis or collateral antegrade flow, allowing direct ligation to remain a potentially viable option if the repair is unsuccessful.7 In addition, any significant changes in baseline neurologic function observed in neuromonitoring should be taken into account when assessing for adequate perfusion.
With clamps in place cephalad and caudal to the injury site, surgical repair is done with 7-0 or 8-0 nonabsorbable polypropylene suture. If repair is unsuccessful or technically impossible, direct ligation with hemoclips should be considered. Blind placement of clamps should be avoided because of the potential for damaging exiting nerve roots.
Although most patients who sustain a vertebral artery injury can tolerate unilateral ligation of the injured artery, it poses a grave risk of neurologic compromise in those with an absent, hypoplastic, or stenotic contralateral artery. Wallenberg syndrome, cerebellar infarction, cranial nerve palsies, and quadriparesis have been reported in such patients, with death occurring in as many as 12%.8 The reported incidences of hypoplasia and the absence of the left vertebral artery are 5.7% and 1.3%, respectively, and of the right vertebral artery are 8.8% and 3.1%, respectively.9
If arterial injury occurs posteriorly at C1 or C2, direct repair and even ligation can be technically difficult because of poor visualization. If injury occurs during exposure of these cervical vertebrae, an approach similar to that described earlier is taken to expose the artery above and below the site of injury. This can entail removing the lateral masses of C2 and C3 and/or the posterior ring of C1. If injury is noted when drilling or tapping for screw placement, the screw can be placed to plug the drill hole, and bleeding and hemodynamic stability in the surrounding area can be reassessed. Following the procedure, the patient should be sent for angiography for potential coiling.
Following any vertebral artery injury, the integrity of the repair or ligation is confirmed with angiography. The patient is admitted to the intensive care unit for monitoring. The latter should include vigilance for pseudoaneurysm or late hemorrhage. Anticoagulation and/or antiplatelet therapy should also be considered to reduce the risk of vertebrobasilar thromboembolism.
Reported rates of esophageal injury during anterior cervical spine surgeries are 0.3% for diskectomy and fusion, 1.6% for corpectomy, and 1.5% for fracture repair.10 Causes of injury can include trauma, erosion by anterior osteophytes, intraoperative injury, and delayed injury from instrumentation-related erosion (eg, prominent plates or loose screws).
The esophagus sits immediately posterior to the longus colli muscle, requiring that retractors be placed around it for visualization of the midline during procedures on the cervical spine. The use of retractors, as well as the coverage of the posterior esophageal mucosa by only a thin layer of connective tissue, makes injury to the esophagus possible, especially proximally at the Lannier triangle (dorsal midline area just below cricopharyngeus muscle). The importance of careful manual retraction should be stressed to novice surgical assistants. When self-retaining retractors are placed, special attention should be given to ensuring that no esophageal folds are protruding into the surgical field, making them susceptible to injury by a burr or drill.
Weakened and/or distorted esophageal anatomy can be expected in cases of surgical revision, tumor, or infection. Steps to avoid esophageal injury include careful dissection and retraction, and placement of a nasogastric or orogastric tube to help locate the esophagus during dissection.
Evaluation and Treatment
The most important step in treating an esophageal injury is recognizing it initially. Intraoperative injury can sometimes be noted with direct visualization. However, this can be unreliable, especially with small tears. In a cadaver study of esophageal perforations, poor sensitivity was seen with reliance only on intraesophageal dye injection (methylene blue/indigo carmine) via a nasogastric tube.11 Better, although still limited, detection was achieved with the addition of a Foley catheter distal to the suspected area of injury.
Early in the postoperative period, perforation of the esophagus in a missed intraoperative injury may present as neck pain, dysphagia, odynophagia, fever, swelling of the neck, wound drainage of food, or subcutaneous emphysema/crepitus. An injury with delayed presentation, caused by instrument-related erosion, presents in a similar manner with dysphagia or pneumonia of new onset.
The evaluation of an esophageal injury includes radiography with or without CT to assess the position of instrumentation and/or a graft and for soft-tissue swelling, pneumomediastinum, or abscess/fluid collection. Contrast esophagoscopy can also be considered but has a false-negative rate of 10%, with barium being slightly more sensitive than diatrizoate meglumine for detecting esophageal tears.12 If, after an initial study that is read as normal, a patient’s clinical symptoms raise high suspicion of a tear, direct visualization via surgical exploration can be considered. However, a less invasive method of assessment involves performing serial esophagrams, with surgical exploration done only after a tear is identified on imaging.
If an esophageal tear is detected during surgery on the cervical spine, primary repair is the standard of care, performed preferably by an otolaryngologist or general surgeon. The patient should remain on status of no oral foods or liquids (ie, NPO), with a nasogastric or Dobhoff tube in place, until a swallowing study yields a normal result. In addition, an esophagram is commonly done at 7 to 10 days after the repair of an esophageal tear. A muscle flap may be required to allow the tension-free closure of a delayed or late perforation, with a pedicled graft of the sternocleidomastoid muscle most commonly used.
Spinal Cord Injury
Scant literature exists on perioperatve injury to the spinal cord in cervical spine surgery, but it has been reported to have a low incidence (<1%).13,14 Such injury can occur during any phase of the perioperative process, with potential causes including hyperextension of the neck during intubation/positioning, hypotension, hematoma, inadequate decompression, interbody graft/cage dislodgement, and surgical trauma. Certain patients may be at particularly high risk of cord injury, such as those with severe myelopathy (myelomalacia), spinal instability, and ankylosing spondylitis, and those undergoing correction of a significant deformity.
The keys to avoiding a perioperative cord injury are communication with the operating room staff and anesthesia team and vigilant attention to detail. Before intubating the patient, the surgical team should directly communicate with the anesthesia team about the severity of any spinal stenosis and not restrict this communication to any traumatic instability. A review of the American Society of Anesthesiologists Closed Claims database found that 57% of perioperative injuries to the cervical spinal cord occurred in patients with underlying stenosis and/or herniation, as opposed to only 24% of such injuries occurring in patients with notable cervical instability.15 For this reason, fiberoptic intubation, rather than direct laryngoscopy, should be strongly considered in patients with instability or a tenuous cord resulting from compressive cord pathology. Furthermore, mean arterial pressures (MAPs) should be kept >85 mm Hg until decompression is done or the correction of a deformity has been completed.16 If possible, this pressure should also be maintained during intubation and all subsequent positioning of the patient. Similarly, a cognizant neuromonitoring team can be especially helpful in minimizing neurologic injury. Any signs of lability should be immediately relayed to the surgical and anesthesia teams.
The spine surgeon should have a memorized checklist for review in the event of a major neuromonitoring alert to allow prompt and aggressive management of its source. When running through the list, the surgeon should also keep in mind that false-positive neuromonitoring alerts can occur and that some interventions may cause harm. A typical series of items for swift review include ensuring that the patient has a MAP >85 mm Hg, temperature >36.5° C, hemoglobin >8 g/dL, and whether the patient has recently undergone untaping of the shoulders, repositioning of the neck, release of a deformity correction, or removal of an implant (Figure 6). Depending on the stage of an operation on the cervical spine, aborting the procedure or a wake-up test can also be considered.
If a cord injury persists postoperatively, potentially reversible causes for it are investigated with MRI and/or CT. Patients with persisting injury are admitted to the intensive care unit to maintain the MAP >85 mm Hg and hemoglobin >10 g/dL for 3 to 5 days, and may be treated with intravenous steroids.17
Peripheral nerve injuries during cervical spine surgery are most often the result of improper positioning, with the most frequent injuries being ulnar neuropathy and brachial plexus injury. Although rare, both types of injury can lead to devastating deficits in upper extremity function.
Ulnar neuropathy is the most common type of perioperative peripheral nerve injury in cervical spine surgery, being responsible for 28% of all claims for anesthesia-related nerve injury.18 Its end result can be loss of intrinsic hand function and a clawlike deformity of the hand. Preexisting subclinical neuropathy can manifest in the perioperative period when patients undergoing cervical spine surgery are subjected to certain predisposing factors, such as prolonged hypotension. Other patient-related risk factors for perioperative ulnar neuropathy include extreme thinness and obesity, older age, and male sex.19 Men are more susceptible to direct pressure on the unmyelinated fibers of the ulnar nerve than are women.20
Initial symptoms of ulnar neuropathy in patients undergoing cervical spine surgery are usually noted >24 hours postoperatively,19,21 with <10% of instances of such neuropathy having been noted in the postoperative recovery unit in a large retrospective study.19 In this study, 47% of ulnar neuropathies presented as sensory deficits, with the remaining 53% presenting as mixed sensory and motor deficits. At 1 year postoperatively, 41% of the patients who had experienced postoperative deficits had persistent deficits. Patients with mixed deficits were less likely to have a complete recovery (35%) than were patients with purely sensory deficits (80%).19
Before positioning the arms of patients in preparation for surgery on the cervical spine, the elbows of both arms should be wrapped with gel or foam pads, with care taken to ensure that the caudal surfaces of the elbows are adequately protected (Figure 7). Similarly, the number of lines and/or wires that traverse the arms should be minimized, especially over the medial side of the elbow.
If no significant improvements in symptoms of apparent ulnar neuropathy are seen at 6 weeks, electromyographic testing should be considered and, if necessary, the patient should be referred to a hand specialist.
Brachial Plexus Injury
Brachial plexus injury can result from the stretching or compression of nerves with subsequent ischemia of the vasa nervorum. During procedures on the cervical spine, traction injuries are most commonly the result of taping the patient’s shoulders to optimally visualize the level of interest on the localizing lateral radiograph. Under general anesthesia, especially with the use of muscle relaxants for intubation, patients have reduced defensive muscle tone, making it easy for an inattentive surgeon to apply too much traction. After affixing tape to the shoulder, the surgeon can place one hand over the tape and gently pull the shoulder down until the desired degree of tension is achieved (Figure 8). With this hand kept in place over the shoulder, the surgeon can then use the other hand (or ask an assistant) to affix the distal end of the tape to the operating table. Taping in this manner allows the surgeon to better gauge the tension on the patient’s brachial plexus rather than pulling distally using only the affixed tape.
If neuromonitoring is being used and baseline values are recorded before the patient is positioned, they should be recorded before taping to provide the surgical team with a set of baseline values with which to determine whether the tape needs to be relaxed. Likewise, if adequate visualization cannot to obtained without excessive traction, further dissection can be carried cephalad until adequate radiographic localization occurs at a more cephalad level. From this point, the surgeon can manually count down to the cervical level of interest.
In the case of a new postoperative deficit thought to be potentially related to injury of the brachial plexus, an MRI of the cervical spine should be done to rule out a compressive disorder masquerading as a plexus injury. Given that most brachial plexus injuries in the setting of cervical spine surgery are traction-related injuries to upper nerve roots (C5 and C6), patients who manifest signs of such injury can be given a sling for comfort and physical therapy to prevent adhesive capsulitis of the shoulder and/or elbow contractures.
Cerebrospinal Fluid Leaks
CSF leaks in the cervical spine are rare, with a 1% (n = 20) incidence seen in a retrospective review of 1,994 patients who underwent cervical spine surgery from 1994 through 2005.22 A 12.5% rate of CSF leakage was seen in patients who had ossification of the posterior longitudinal ligament, and a 1.9% rate in patients who had anterior revision procedures. Seventy percent of anterior dural tears were caused by a Kerrison rongeur and 20% of posterior tears were caused by Bovie electrocautery or in opening of the lamina during laminoplasty. Eleven leaks were treated without repair or lumbar drainage, five with direct repair, and four without repair but with lumbar drainage. Only one patient (who had no repair or lumbar drainage) required a second operation for persistent leakage of CSF.22
CSF leaks in cervical trauma are also rare, with higher-energy injuries more likely to cause a dural tear. More common patterns of injury associated with CSF leaks include bilateral facet dislocations and compression-flexion injuries (stages IV and V). Most leaks associated with bilateral facet dislocations occur posteriorly and usually do not need to be repaired because of coverage by bone and/or ligamentum flavum of the dural tear through which they occur, allowing the tear to seal itself. In severe compression-flexion injuries, the retropulsed vertebral body tears into the dura, causing an anterior leak. These leaks are more likely to be persistent and often require a decompressive corpectomy and direct repair, if possible.
Many cervical CSF leaks are unavoidable, particularly in the setting of trauma and ossification of the posterior longitudinal ligament. However, careful use of Kerrison and pituitary rongeurs is critical to minimizing the tears responsible for cervical CSF leaks. During posterior dissection with unipolar electrocautery, special attention should be given to avoid falling into an interlaminar space. This is especially true in patients with widened interlaminar spaces.
Early diagnosis is key, with direct visualization of a leak being optimal. Occult leaks can be diagnosed based on clear drainage from surgical incision, CT myelography, and/or clinical signs (eg, blurred vision, headaches, light sensitivity, bogginess in the vicinity of the incision).
Treatment strategies for cervical CSF leaks include direct repair, counterpressure, and the placement of diverting drains. Whenever possible, a leak should be directly repaired with a Gore-Tex (Gore Medical) or silk suture. Postoperatively, the head of the patient’s bed should be raised to ≥30° to maintain a low intrathecal pressure. For posterior cervical leaks, maintaining the head of the bed at 90° can help in reducing CSF pressure at the site of the repair. Dural sealants can be used to reinforce “leaky” repairs; however, the surgeon must beware of sealant expansion, which can lead to neural compression.
When direct repair of a cervical CSF leak is impossible, autologous fascia, fat, or collagen matrix can be used as a dural graft. If possible, stay sutures are placed at the corners of the graft, holding it in place before a dural sealant further secures the graft. This technique can be valuable in the setting of an anterior cervical CSF leak that cannot be adequately exposed for repair. In such a case, a fascia graft or collagen matrix is laid over the defect and held in place with dural sealant and Gelfoam (Pfizer) before a tricortical bone graft or cage is placed in the usual fashion. More dural sealant can then be added in the lateral gutters.
If a CSF leak cannot be directly repaired, placement of a lumbar shunt should be considered, with the flow of CSF titrated to 10 mL/h. Also, a low threshold should be set for lumbar drainage in ventilator-dependent patients because positive-pressure ventilation increases intradural pressure, potentially causing CSF leaks.
Complications of Instrumentation
The increasing use of spinal instrumentation expands the realm of complications of its use, especially with a growing osteoporotic population. Many surgeons are aware of various techniques of such instrumentation and the potential for immediate complications associated with the nonanatomic placement of spinal instrumentation. However, it is important to be familiar with salvage or bailout techniques to help mitigate intraoperative complications of spinal instrumentation.
During posterior procedures on the subaxial cervical spine, lateral-mass fixation can at times be tenuous because of poor screw purchase. If the walls of the pilot hole for a screw remain intact, a larger diameter salvage screw can be used with the hope of gaining better purchase. However, this sometimes still provides poor fixation, especially when the superolateral quadrant of a lateral mass sustains a blowout fracture during drilling or screw insertion. In this situation, conversion to a Roy-Camille technique or the use of a transfacet screw can be considered as a salvage procedure. In the Roy-Camille technique for lateral mass fixation with screws, the screw trajectory is more horizontal and perpendicular to the lateral mass, in contrast to the parallel articular facet in most other insertion techniques. Transfacet screws provide purchase of the ventral cortex of the inferior articular process when directed distally across the facet joint. Failure of a lateral-mass screw inserted at C7 is not an exceedingly rare event, given the small anteroposterior dimensions and steep surface of this vertebra. However, pedicle-screw placement at this level provides a robust rescue option in this situation.
In the case of poor screw purchase in the atlantoaxial region, supplemental laminar wiring and cortical bone grafting remain viable salvage options. Additionally, the utilization of laminar screws at C2 should be remembered in the setting of a failed pars/pedicle screw or anatomic limitations created by the vertebral artery.
Before the placement of an anterior plate in the cervical spine, anterior osteophytes should be burred down to allow the plate to rest flat against the bone, providing the best biomechanical environment for screw fixation. If screw purchase is poor, larger diameter and/or longer screws may be placed. Another option to address poor screw purchase in placing an anterior plate in the cervical spine is bicortical screw fixation. This can be done through stepwise drilling and the use of a depth gauge, together with fluoroscopy to avoid catastrophic complications. If anterior fixation remains poor despite these options, especially in a patient with considerable cervical spinal instability, a low threshold should exist for supplemental posterior fixation.
Intraoperative complications during cervical spine surgery are rare. Having a systematic approach to preventing and immediately managing such complications, and especially vertebral artery and neurologic injuries, can potentially reduce any associated morbidity.
Evidence-based Medicine: Levels of evidence are described in the table of contents. In this article, reference 20 is a level I study. References 12, 21, and 22 are level II studies. References 1, 6, 13, 15, 18, and 19 are level III studies. References 7, 8, and 10 are level IV studies. References 2-5, 9, 11, 14, 16, and 17 are level V expert opinion.
References printed in bold type are those published within the past 5 years.
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Keywords:© 2015 by American Academy of Orthopaedic Surgeons
cervical; complications; intraoperative; spinal cord; vertebral