Injuries to the Cervicocranium
The cervicocranium consists of the osseoligamentous and neurovascular structures that extend from the skull base to C2. It includes the craniocervical junction and the articulations between the first and second cervical vertebrae.
The cervicocranium′s susceptibility to injury is related to (1) the large lever arm induced by the mass and immobility of the cranium, combined with (2) the relative freedom of movement more caudally, which relies on ligamentous structures rather than on intrinsic bony stability to preserve craniocervical alignment. This tenuous functional unit is maintained by highly specialized C1 and C2 bony segments interconnected via a complex and incompletely understood ligamentous system whose vulnerability to injury may compromise the structural integrity of the entire craniocervical junction.
Due to the nearby neurovascular structures, injury to the upper cervical spine that results in loss of craniocervical integrity carries a high likelihood of death. However, improved trauma care has increased the likelihood of survival in patients with craniocervical injuries, raising the burden of responsibility to appropriately identify and treat these life-threatening injuries.
This chapter focuses primarily on the treatment of six injury types, many of which coexist: (1) occipital condyle fractures, (2) craniocervical dissociation, (3) fractures of the atlas, (4) C1-C2 instability patterns, (5) odontoid fractures, and (6) C2 neural arch fractures (i.e., traumatic spondylolisthesis or hangman′s fractures) of C2. In trying to achieve our main goal of describing the surgical treatment of craniocervical injuries, we also aim to impart a fundamental and prerequisite understanding of craniocervical instability patterns, the complexities involved in their diagnosis and classification, and the manner in which these principles apply to evolving treatment methods.
Nonoperative Treatment
General Concepts
The crucial first treatment step is timely injury recognition and determination of stability. Reduction maneuvers are typically performed with cranial skeletal traction in the emergency room using fluoroscopy. However, traction is contraindicated in distractive cervical spine injuries. Closed reduction of such distractive injuries may necessitate early application of a halo or postural reduction in a RotoRest® bed (Kinetic Concepts Inc., San Antonio, TX) or with sandbags surrounding the head, both of which are usually temporizing measures pending operative stabilization.
Accompanying resuscitation efforts include vasopressor support for suspected neurogenic shock and emergent assessment for potential intracranial trauma. Although patients with neurologic injuries may be considered for intravenous methylprednisolone as per the National Acute Spinal Cord Injury Study (NASCIS) II or III protocols, the role of steroids in the treatment of acute spinal cord injuries has become increasingly unclear. Many trauma centers have discontinued the routine use of high-dose corticosteroid treatment for acute spinal cord injuries. Although the balance between the risk of steroid-related complications versus their beneficial effect on spinal cord injury remains controversial, the most recently published American Association of Neurological Surgeons guidelines recommend against the use of high-dose methylprednisolone in the treatment of acute spinal cord injuries.1
Emergent surgical intervention for patients with upper cervical spine injuries is rarely necessary. Open reduction and stable internal fixation are helpful strategies for patients with dislocations and distractive upper cervical spine injuries. The presence of a spinal cord injury usually suggests the need for surgical stabilization and, possibly, decompression to maximize the chance for neurologic recovery.
Nonoperative treatment options consist of recumbent skeletal traction, bracing, and halo immobilization. Vertebral reduction can be assessed by obtaining lateral recumbent and upright radiographs. The duration of external immobilization usually ranges from 2 to 4 months, and depends on the type of injury and age of the patient. External immobilization is also commonly used for 6 to 12 weeks postoperatively after surgical stabilization. Recommendations vary widely with regard to the need for and duration of external support.
Bracing
In the presence of minimally or nondisplaced fractures of the upper cervical spine, external bracing alone can be considered. Sternal occipital mandibular immobilization (SOMI)-type devices have been shown to allow the least upper cervical spine motion of non-halo devices in cadaveric testing.2
Halo Orthosis
Halo ring and vest orthotics offer the most stable form of external upper cervical spine immobilization.2 The halo has been recommended for patients with isolated occipital condyle fractures, unstable atlas ring fractures, odontoid fractures, and displaced neural arch fractures of the axis.3,4 Unlike bracing, the halo allows for some fracture manipulation and correction of malalignment. However, secondary loss of reduction has been noted in approximately one half of patients.5 A common mechanism of fracture displacement in a halo consists of a “snaking” of the cervical spine between the supine and upright positions.6 Although this phenomenon may not adversely affect the healing of inherently stable upper cervical spine fractures with large cancellous bone surfaces, unstable fractures with a small bony contact surface, such as type II odontoid fractures, may not be effectively immobilized.7,8
Skeletal Traction
Aside from its role in acute fracture reduction, traction can be used to maintain spinal alignment and stability for an extended period of time in an attempt to achieve initial consolidation of an unstable fracture prior to mobilizing the patient with a halo or rigid brace. Although there are no fixed guidelines for such a management strategy for cervical spine injuries, suggested time frames for traction have usually ranged from several days to weeks.5,9 However, prolonged recumbency carries an increased morbidity and mortality risk, and consideration should be given to the use of a RotoRest bed and mechanical as well as pharmacological thromboembolism prophylaxis.10
Injury Classification and Indications for Surgical Treatment
Occipital Condyle Fractures
Classification
Although often inherently stable, occipital condyle fractures may be highly unstable if they represent bony avulsion of major craniocervical stabilizers. Anderson and Montesano11 described a classification system consisting of three categories (Fig. 9.1). Type I fractures are usually stable, comminuted axial loading injuries. Type II injuries are potentially unstable injuries caused by a shear mechanism that results in an oblique fracture extending from the condyle into the skull base. Type III injuries are unstable avulsion injuries that result in a transverse fracture line through the occipital condyle (Fig. 9.2). Any occipital condyle fracture should be considered a possible component of craniocervical dissociation.
Indications for Surgery
Operative treatment of occipital condyle fractures is generally reserved for the type III injuries that represent alar ligament avulsions and result in craniocervical instability (Fig. 9.2). Surgical indications are therefore equivalent to those described below for craniocervical dissociation.12,13
Craniocervical Dissociation
Classification
Traynelis et al14 identified three craniocervical dissociation patterns according to the direction of displacement of the cranium relative to the cervical spine (Fig. 9.3). However, the severe instability of these injuries renders the position of the head relative to the neck completely arbitrary and more dependent on external forces than on any intrinsic injury characteristic. In addition, this classification does not reflect injury severity or the potential for spontaneously reduced dislocations. These issues render directional classification systems less useful, because the magnitude of displacement may underestimate the degree of instability, and the direction of displacement has little influence on prognosis or treatment method.
A useful classification system should quantify the stability of the craniocervical junction. Signs of instability are translation or distraction of more than 2 mm in any plane,15 neurologic injury, and concomitant cerebrovascular trauma.16 The problem lies in segregating patients with minimally displaced (≤ 2 mm) craniocervical injuries into those with relatively stable injuries who can be treated nonoperatively, and those with highly unstable but partially reduced injuries who require operative stabilization in spite of a misleadingly low degree of displacement. We have found it useful to categorize these patients by using manual provocative traction testing in minimally displaced injuries (≤ 2 mm), reserving surgical stabilization for patients with type II and III injuries of the craniocervical junction, which we define as dissociations (Table 9.1).17
Stage | Description of Injury |
1 | MRI evidence of injury to craniocervical osseoligamentous stabilizers Craniocervical alignment within 2 mm of normal Distraction of 2 mm or less on provocative traction radiograph |
2 | MRI evidence of injury to craniocervical osseoligamentous stabilizers Craniocervical alignment within 2 mm of normal Distraction of more than 2 mm on provocative traction radiograph |
3 | Craniocervical malalignment of more than 2 mm on static radiographic studies |
Note: Shaded areas represent injuries defined as craniocervical dissociation.
Indications for Surgery
Displacement of greater than 2 mm at the atlanto-occipital joint, either on static imaging studies or with provocative traction testing (Fig. 9.4 and Table 9.1), or the presence of neurologic injury is an indication for craniocervical stabilization. Particularly in the presence of neurologic deficits, stabilization is performed as early as reasonably possible in the context of the frequently guarded condition of these polytraumatized patients.17
Fractures of the Atlas
Classification
Atlas fractures are best described as either stable or unstable injuries,18 based on the status of the transverse atlantal ligament (TAL). The integrity of the TAL can be diagnosed either by direct means, such as by identifying bony avulsion on computed tomography (CT) scan or ligament rupture on magnetic resonance imaging (MRI), or indirectly by identifying widening of the lateral masses (Fig. 9.5) with ≥ 7 mm lateral overhang relative to the lateral masses of C2,19 appropriately corrected for radiographic magnification (see below).20
Levine and Edwards21 described a useful four-part classification system: (1) posterior arch fractures, (2) lateral mass fractures, (3) isolated anterior arch fractures, and (4) bursting type fractures. As mentioned above, the extent of lateral mass separation is more relevant than the number of fracture fragments. A transverse fracture of the anterior arch has been identified as a tension injury that can be seen in association with craniocervical dissociation, and should be treated accordingly.22
Indications for Surgery
Most C1 fractures are treated by nonoperative methods. Indications for operative management are related mainly to the loss of TAL integrity, as suggested by a combined lateral mass displacement of ≥ 7 mm on nonmagnified radiographs, which introduces the potential for progressive lateral mass separation, C1-C2 instability, and pseudarthrosis.19,20,23 Halo immobilization alone may be insufficient to maintain acceptable alignment in these patients. If upright radiographs in a halo show further lateral mass displacement or an anterior atlanto–dens interval (ADI) of > 3 mm, patients must be treated either with prolonged recumbency in cranial tong traction (Fig. 9.5) or with operative stabilization, generally with posterior C1-C2 or occiput-C2 fixation.
Surgical stabilization options consist of C1-C2 transarticular screw fixation or segmental fixation with C1 lateral mass connected by a rod to C2 pedicle, pars, or translaminar screws.24 The latter method provides the opportunity to correct C1 lateral mass widening by approximating the two rods with a cross-connector. Internal fixation of the C1 ring, by simply reapproximating the lateral masses to each other through lateral mass screws connected to a transversely oriented rod (Fig. 9.6), is a potentially useful treatment option that theoretically preserves C1-C2 motion, but with an indication profile that has yet to be fully understood.25 A potential deficiency of directly repairing unstable C1 fractures is that the associated TAL deficiency may result in persistent C1-C2 instability. However, unlike with shear or distractive injuries, the axial loading mechanism that causes TAL rupture in displaced C1 ring fractures generally allows secondary restraints to remain intact, thus minimizing any remaining atlantoaxial instability once the atlas has been stabilized.26
Atlantoaxial Instability
Classification
Three atlantoaxial instability patterns present either as isolated or combined injuries. Type A injuries are rotationally displaced in the transverse plane. Type B injuries are translationally unstable in the sagittal plane due to TAL insufficiency. Type C injuries are characterized by vertical atlantoaxial dissociation and represent a variant of craniocervical dissociation.
In type A injuries (Fig. 9.7), rotational displacement of the atlantoaxial motion segment is most commonly nontraumatic, and will therefore not be described in detail. However, traumatic causes have been described, and range in severity from mild rotational subluxation to complete dislocation of the atlantoaxial lateral masses.27
In type B injuries (Fig. 9.8), acute translational atlantoaxial instability is the result of TAL insufficiency. Treatment of these highly unstable injuries may depend on differentiating a ligamentous tear (type I) from a bony avulsion injury (type II).18,28
In type C injuries (Fig. 9.9), distractive atlantoaxial injuries (atlantoaxial dissociation) constitute variants of craniocervical dissociation because the disrupted major ligamentous stabilizers—the alar ligaments and tectorial membrane—extend from C2 to the occiput. They frequently coexist with overt atlanto-occipital distraction injuries (Fig. 9.10).
Indications for Surgery
Translational Instability
This highly unstable injury generally requires posterior atlantoaxial arthrodesis. However, in the presence of bony avulsion, successful healing may occur in approximately three fourths of patients with a period of recumbent traction followed by patient mobilization in a halo or SOMI.18 An ADI of greater than 3 mm on flexion radiographs after 3 months of immobilization constitutes a failure of closed treatment and indicates the need for atlantoaxial arthrodesis.
Distraction Injuries
A distraction injury of C1-C2 with ≥ 2 mm of displacement requires surgical stabilization. This injury is analogous to craniocervical dissociation at the atlanto-occipital joint, and should be treated under similar guidelines.
Odontoid Fractures
Classification
Fractures of the odontoid process are the most common of axis fractures (41%).29 Anderson and D′Alonzo′s30 threepart system of odontoid fracture classification has become the basis for odontoid fracture management (Fig. 9.11). Type I injuries are considered bony avulsions of the alar ligament from the superolateral site of odontoid insertion, and represent a component of craniocervical dissociation. Type II injuries are located at the odontoid waist in the area covered by the TAL and have the highest propensity for pseudarthrosis, probably due to their small cross-sectional fracture surfaces and interruption in blood supply to the cephalad fragment. A IIa subtype of odontoid fracture has been described by Hadley et al,31 which consists of a highly unstable, segmentally comminuted injury extending from the waist of the odontoid into the body of the axis. Fracture characteristics, such as the angle of obliquity, displacement, and comminution, also help guide treatment. Fracture characteristics (high/low, obliquity, displacement, comminution) guide treatment. Type III fractures extend into the cancellous vertebral body and have wider, well-vascularized cancellous fracture surfaces. Distractive type II or III injuries may also occur, which should be considered highly unstable and stabilized accordingly.
Indications for Surgery
Type I
Because the treatment of type I odontoid fractures relates to how their associated alar ligament incompetence affects craniocervical stability,30 indications for surgical management of these injuries are the same as those discussed for the treatment of craniocervical instability (Fig. 9.10c).
Type II
The management of type II odontoid fractures remains controversial, although recent publications have suggested better overall results with surgical intervention.32–34
We advocate surgical stabilization of irreducible fractures with distractive patterns of displacement or fractures with associated spinal cord injury (Fig. 9.12). Relative indications include multiply injured patients, associated closed head injury, initial displacement of ≥ 4 mm, angulation > 10 degrees,7,35 delayed presentation (> 2 weeks), multiple risk factors for nonunion,31 the inability to treat with a halo due to advanced age,10 associated cranial or thoracoabdominal injury or other medical factors, and the presence of associated upper cervical fractures.
Noncomminuted fractures in patients with favorable bone quality and appropriate body habitus are ideal for anterior odontoid screw fixation,36 which allows preservation of some atlantoaxial motion. In patients with extensive fracture comminution or compromised bone quality, or in whom achieving the required anterior odontoid screw trajectory is not feasible due to body habitus or the neck position required to maintain reduction, we favor a posterior atlantoaxial fusion using either transarticular screw fixation or segmental C1-C2 screw and rod fixation.24,37 Posterior atlantoaxial fusion is the recommended treatment for the two following subcategories of type II odontoid fractures that are not suitable for either nonoperative management or internal fixation with odontoid compression screws: (1) type IIa dens fractures, which are inherently unstable due to a zone of segmental comminution at the odontoid base31; and (2) sagittally oblique fractures,38 in which the fracture line parallels the typical odontoid screw trajectory, leading to loss of reduction and inadequate fixation with attempts at interfragmentary compression.39,40 Posterior C1-C2 arthrodesis with transarticular or screw-and-rod fixation is expected to have the most predictable healing results in the management of these two injury subtypes.6,37,38
Proper patient selection helps minimize the high complication rate of up to 28% that has been reported using anterior odontoid screw fixation.36,38,41
Type III
Type III odontoid fractures do not commonly require surgical stabilization. As with type II odontoid fractures, we advocate operative stabilization of fractures with associated spinal cord injury or distractive instability patterns (Fig. 9.13). Posterior C1-C2 arthrodesis is the surgical treatment method of choice, because anterior odontoid screw fixation has a high failure rate with these injury types.40 Relative indications include highly displaced irreducible fractures; patients with displaced injuries who cannot, for reasons cited above, be treated with a halo; and fractures with initial displacement of ≥ 5 mm, which have a high potential for nonunion, particularly in the elderly population.35 Results may be less predictable than is generally acknowledged, however. Delayed unions or pseudarthroses have been reported in up to 54% of nonoperatively treated patients,35 and are generally amenable to posterior C1-C2 fixation.
Neural Arch Fractures of the Axis (Traumatic Spondylolisthesis or Hangman′s Fractures)
Classification
Hangman′s fractures are the second most common type of axis fracture (38%).29 Effendi et al42 have formulated the following simple classification, as subsequently modified by Levine and Edwards43 and Starr and Eismont44 (Fig. 9.14).
Type I injuries consist of a minimally displaced, relatively stable fracture of the pars interarticularis that results from hyperextension and axial loading. Type IA fractures are atypical, unstable lateral bending fractures that are obliquely displaced and usually involve only one pars, extending anterior to the pars into the vertebral body on the contralateral side.39 The oblique plane of these fractures makes them less obvious on lateral radiographs, giving the appearance of an elongated pars (Fig. 9.15).
Type II fractures are displaced injuries that result when a flexion force follows the initial hyperextension and axial loading insult. Type II injuries appear similar to type I injuries on supine radiographs, but displace to a greater extent on upright radiographs. Physician-supervised flexion-extension radiographs of type I injuries have been advocated to differentiate them from spontaneously reduced type II injuries, in order to determine appropriate treatment.7 Type IIA injuries are thought to occur from a flexion-distraction mechanism, and are more unstable due to their associated C2-C3 disk and interspinous ligament disruption. Because they are flexion-distraction injuries, kyphosis is the prevailing deformity rather than translation (Fig. 9.16). An inconsistent feature of type IIA injuries is that, because of the injury mechanism, the pars interarticularis fractures tend to be more horizontal than in standard type II injuries. Levine and Edwards postulated that any injury where distraction of the C2-3 disk space occurs with only 10 lb of traction should be considered type IIA.
Type III injuries are unusual and highly unstable injuries in which the neural arch fractures are associated with a unilateral or bilateral C2-C3 facet dislocation, which is not generally reducible by nonoperative means. On rare occasions, these injuries may also spontaneously reduce and have the more benign appearance of a type I injury on initial supine lateral radiographs (Fig. 9.17).
Other classification systems have evaluated fracture stability based on the degree of translational and angulatory displacement as a measure of the integrity of C2-C3 diskoligamentous elements.45
Indications for Surgery
Operative stabilization is rarely indicated for traumatic spondylolisthesis of the axis.32 Most injuries can be treated with early ambulatory immobilization with 12 weeks of bracing for type I (and most IA) fractures and of halo immobilization for most type II fractures.42
Because the kyphotic deformity in type IIA injuries cannot generally be controlled with a halo, surgery is the recommended treatment. Traction is contraindicated in these injuries, as it accentuates their kyphotic deformity. A C2-C3 anterior cervical diskectomy and fusion (ACDF) with plating enables fusion across the least number of levels, and preserves atlantoaxial motion (Fig. 9.17).46,47 However, because the anterior longitudinal ligament is often the only remaining intact C2-C3 stabilizing structure, posterior stabilization remains an appropriate option. A disadvantage of the posterior approach is that, absent the ability to gain acceptable purchase with C2 screws directly across the fracture, loss of atlantoaxial motion results from the need to extend the fixation to the C1 level (Fig. 9.16).
Type III injuries generally cannot be reduced by traction and require operative reduction and stabilization. Stabilization options include (1) posterior C1-C3 fusion (Fig. 9.18); (2) posterior C2-C3 fusion using interfragmentary C2 screws across the fracture; (3) converting the fracture to a type I or II injury by posterior C2-C3 facet fusion using C2 screws that stop short of the fracture, followed by collar or halo immobilization as per the usual treatment for type I and II injuries; and (4) anterior C2-C3 ACDF (Fig. 9.17), in the unusual event that reduction is achieved by closed methods. The advantage of the latter three options is their preservation of atlantoaxial motion.7
Surviving the Night
In general, upper cervical injuries should be treated in centers that have specialized spine trauma care and the ability to perform surgery on unstable injuries even in the middle of the night, when warranted. Injuries that should be treated as soon as reasonably possible, taking into account associated injuries and the patient′s overall physiological condition, usually consist of spinal cord injuries with persistent spinal cord compression, as with type III hangman′s fractures or atlanto-axial dislocation, or severely unstable ligamentous injuries that are so unstable as to not be amenable to external immobilization regardless of neurologic integrity, such as occipitocervical or atlantoaxial dissociation. Upper cervical fractures associated with ankylosing spine conditions may also merit fixation as soon as possible due to the presence of stiff adjacent lever arms that render the fracture atypically unstable.
However, even when the intent is to proceed with operative intervention, most other unstable injuries in patients with either an intact neurologic exam or a neurologic deficit but absence of persistent spinal cord compression can reasonably be observed overnight with external immobilization and appropriate spine precautions. Examples of this type of injury include unstable odontoid fractures, C1 ring fractures, and certain hangman′s fracture variants, such as atypical hangman′s fractures, type IIA hangman′s fractures, and highly displaced type II hangman′s fractures.
External immobilization generally consists of a rigid cervical collar with supine positioning and either log-rolling or the use of a RotoRest bed. Halo-vest immobilization can be useful as well, particularly in situations that require frequent patient transfers for therapeutic or diagnostic procedures. Provisional Gardner-Wells tong traction is primarily useful when realignment is deemed to be essential prior to surgery, to remove compression from the spinal cord, to protect against what is believed to be a significant risk of spinal cord injury, or to facilitate the eventual operative treatment of the injury. Examples of injuries in which traction may be useful include highly displaced odontoid fractures, unstable C1 ring Jefferson-type fractures, and highly displaced type II hangman′s fractures. Traction is to be specifically avoided in distractive injuries or injuries suspected to involve severe ligamentous instability, such as occipitocervical or atlantoaxial dissociation. Traction is generally not recommended in certain specific injuries, such as type IIA hangman′s fractures, in which traction tends to accentuate the deformity and is usually not successful for the reduction of type III hangman′s fractures, in which the pars interarticularis fracture results in lack of continuity between the anterior part of the upper cervical spine and the dislocated C2-C3 facets.
Surgical Treatment
General Concepts
Surgical Options
Basic surgical options consist of decompressive procedures, fracture osteosynthesis, and fusion of vertebral motion segments.
Decompression
Because of the normally wide spinal canal diameter at this level, decompression of neural elements is rarely necessary in the treatment of upper cervical spine fractures. In general, surgical decompression should be performed only if fracture reduction maneuvers fail to achieve adequate indirect decompression. Moreover, the posterior elements of the craniocervical junction provide important surfaces for bony healing of fusions and anchor points for surgical stabilization, and therefore should not be removed as a matter of routine. Case reports have described transoral dens resections for hypertrophic nonunion of dens fractures.48 Occasionally, a depressed fracture of the atlas or the axis may have to be surgically elevated and removed. Posterior fossa decompression may be required in selected patients.
Osteosynthesis
The two indications for direct fracture repair in the upper cervical spine relate to the treatment of type II odontoid fractures with anterior odontoid screw fixation,49 and surgical repair of a type II hangman′s fracture with posterior interfragmentary screw fixation. The validity of direct osteosynthesis for type II hangman′s fractures has been questioned because this technique does not address the associated injury to the C2-3 intervertebral disk.
Fusion
The mainstay of operative treatment of upper cervical fractures and dislocations remains fusion with instrumentation, most commonly performed from the posterior approach. In order of frequency, the most common upper cervical fusion procedures are atlantoaxial fusion, occipitocervical fusion, and, less commonly, C1-C3 fusion. Anterior upper cervical stabilization usually involves odontoid screw fixation and C2-C3 fusion for type IIa or atypical hangman′s fractures. Anterior atlantoaxial and occipitocervical fusion techniques as salvage procedures for previously failed posterior upper cervical fusions are rarely indicated and are not discussed here.
Patient Positioning
An unstable upper cervical spine fracture/dislocation requires atraumatic endotracheal airway access with minimal manipulation. Awake, fiberoptic intubation and positioning of a patient enable clinical neurologic monitoring. Electrophysiological neuromonitoring can be used as an alternative to awake positioning. For upper cervical spine injuries the patient′s head is generally secured with either Gardner-Wells or Mayfield three-pin tongs in patients without skull fractures. Operating tables should accommodate unobstructed image-intensifier access.
Supine positioning is used for odontoid screw placement and anterior C2-C3 diskectomy and fusion. Rarely, anterior approaches including transoral and submandibular lateral approaches are used. Prone positioning is used for atlantoaxial and occipitocervical fusions and most neural element decompressions. A slightly reversed Trendelenburg position reduces venous congestion in the upper cervical spine and may minimize blood loss, but should be avoided, if possible, in distractive injury patterns to prevent the traction effect of the body on the fixed skull. After patient positioning, fracture reduction is checked with image intensifier, and neurologic assessment is repeated with clinical exam of an awake patient or with repeat electrophysiological testing.
Radiographic Imaging
Given the proximity of neural and vascular structures to the bony elements of the upper cervical spine, precise hardware placement requires intraoperative imaging. We favor fluoroscopic imaging, using concurrent biplanar fluoroscopy for selected procedures such as anterior odontoid screw placement, over more cumbersome three-dimensional navigation systems. Visualization on the anteroposterior (AP) odontoid view can be enhanced with a radiolucent bite block.
Approaches
Posterior Upper Cervical Approach
Video 9.1 Posterior Instrumentation and Fusion C1-C3
Indications
Most upper cervical fractures are treated through the posterior approach. Indications range from purely decompressive procedures, such as removal of the C1 posterior arch and posterior fossa decompression, to procedures aimed at achieving a fusion between the C1-C2 segments alone or with the occiput. The posterior approach has the advantage of providing an anatomically familiar and extensile exposure. In addition, posterior spinal instrumentation techniques are generally biomechanically superior to anterior stabilization methods.
Technique
Posterior element integrity should be verified on imaging studies before performing a posterior dissection of the spine. Following a midline longitudinal incision, the midline intermuscular plane is developed, enabling subperiosteal exposure of the posterior elements. If the occiput is to be exposed, the incision is extended rostrally to the inion. The large, bifid spinous process of the axis is a helpful orientation aid during the early dissection. The C2-3 interspinous ligament should be preserved if the intended fusion will not extend below C2. The atlas should be dissected in a strictly subperiosteal plane, keeping in mind the course of the vertebral artery on the superior aspect of its posterolateral arch. Blunt dissection along the posterior C1 arch, after release of the midline ligament insertions, minimizes the risk of injury to the vertebral arteries during exposure. For the same reason sublaminar wire or cable passage around the atlas should be performed in an atraumatic, subperiosteal manner.
If screw fixation of the axis with pedicle or transarticular screws is desired, visualization of the superior and medial walls of the C2 pedicles as a reference point is strongly recommended, which requires dissection of the atlantoaxial membrane off the superior lamina of the axis.50 Exposure of the C1-C2 joints may be necessary for a formal intra-articular arthrodesis of this motion segment, for instance in the absence of an intact posterior arch of C1.37 This dissection can result in considerable hemorrhage due to the overlying extensive epidural venous plexus. To facilitate exposure of the C1-C2 joint, the C2 nerve root is reflected cranially. When denuding or decorticating the atlantoaxial joint, the vertebral artery′s course immediately lateral to the joint should be taken into account.
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