Management of Injuries of the Cervical Spine and Spinal Cord

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Chapter 174 Management of Injuries of the Cervical Spine and Spinal Cord

The cervical spine is the most frequently injured portion of the spinal column, with the most common causes being automobile accidents, violent trauma, and sports-related injuries. An understanding of radiographic features allows a more accurate determination of which injuries are unstable and may require external orthoses, cervical traction, surgical fixation, or emergent decompression of the spinal cord.

Upper Cervical Spine

The upper cervical spine consists of the occipital condyles: atlas (C1) and axis (C2). At the craniocervical junction, the two main injuries include occipitocervical dislocations and occipital condyle fractures. These injuries are often the result of high-energy trauma in children or young adults and typically result in severe neurological deficit or even death at the scene. In elderly patients, the majority of spinal column injuries occur at the C1-C2 level following relatively minor trauma, and they are associated with a much lower rate of neurological compromise.

Occipitocervical Dislocations

Atlanto-occipital dislocation (AOD) is the most unstable and dangerous injury of the cervical spine. It results from ligamentous disruption between the occiput and the cervical spine. Severe neurological morbidity and mortality are due to the combination of extreme instability and the possibility of a high cervical cord injury that can lead to quadriparesis and diaphragm paralysis. Fewer than 20% of patients with this devastating injury have a normal neurological examination. In these patients, neurological deficits occur as a result of injuries to the caudal cranial nerves, the brain stem, the upper cervical cord, and the nerve roots. Vertebral artery injuries resulting in brain stem stroke may also occur.

A number of radiographic techniques are used to diagnose AOD. The Powers ratio provides a mathematical relationship between the basion (B), the opisthion (O), the anterior arch of C1 (A), and the posterior arch of C1 (C).¹ To apply this ratio, two lines are drawn: one from the basion to the posterior arch of C1 and another from the opisthion to the anterior arch of C1. The ratio of the lengths of these two lines defines Powers ratio, with a value of B×C/O×A >1 raising concern for atlanto-occipital dislocation. This ratio may be unreliable C1 fracture or posterior subluxation cases. The method of Harris et al.² uses a combination of basion-dental interval to detect longitudinal displacement (normal, less than 12 mm) and basion-axial interval to detect anterior and posterior displacement (normal, 0 to 12 mm). Imaging studies should involve reconstructed computed tomographic scans and MRI studies, with the latter invariably showing ligamentous injury. Because of the extreme instability of occipitocervical dislocations, flexion-extension x-rays are absolutely contraindicated.

A classification scheme developed by Traynelis et al ³ involves three types of injury. Type I injuries include anterior displacement of the skull in relation to the cervical spine, type II injuries involve longitudinal displacement, and type III injuries include posterior displacement. The authors suggest that traction with less than 5 lb can be used under radiographic guidance to reduce and stabilize the injury, but such traction should be immediately discontinued following realignment. With type II injuries, traction should never be used, as this may result in the progression of neurological deficits. Despite these recommendations, these injuries are considered highly unstable; thus most clinicians avoid traction but instead provide immediate halo immobilization and/or internal occipitocervical fixation.

Occipital Condyle Fractures

Occipital condyle injures are relatively rare and often associated with an occipitocervical dislocation. They are frequently unilateral and are often isolated cervical spine injuries in patients with head injuries. If such fractures are not associated with the more ominous AOD, patients usually present without neurological deficit and complain only of upper cervical pain. On plain radiographs, a retropharyngeal hematoma or other soft-tissue swelling may be the only sign of injury. The diagnosis is usually on the basis of computed tomography (CT), and MRI may be useful in determining the extent of associated ligamentous injuries, although this has little utility from a treatment perspective.

Such fractures have also been classified on the basis of their radiographic appearance. CT reveals that type I injuries involve comminution of the condyle without fragment displacement. Type II injuries are characterized by continuation of a basilar skull fracture into the condyle. Type III injuries involve complete avulsion of the condyle and are presumed to result from excessive loading in rotation or lateral bending.⁴

According to the classification scheme originally described by Anderson and Montesano,⁴ the fracture pattern determines treatment. Type II injuries are classified as stable and can be treated with or without a rigid external orthosis for pain control. Types I and III injuries result in ipsilateral alar ligament disruption; thus patients are treated with an external orthosis or a halo vest if the injury is more profound. Surgical intervention is rare but may be indicated when fracture fragments compromise the spinal canal or cause chronic pain as a result of presumed instability.

Atlas (C1)

The atlas supports the skull and allows the greatest range of flexion-extension and rotation in the cervical spine because of its unique articulation with both the occiput and C2, respectively. Injuries to the atlas account for up to 15% of all cervical injuries. There are four major patterns of C1 fracture: burst fracture (Jefferson fracture), posterior arch fracture, lateral mass fracture, and horizontal fracture of the anterior arch. In addition, atlantoaxial dislocations can occur with ligamentous injury.

C1 Burst Fracture (Jefferson Fracture)

C1 burst fractures are presumed to result from direct axial loading that causes lysis of both the anterior and posterior arches, leading to spreading of the lateral masses. Neurological injury is rare, owing to pathological enlargement of the spinal canal. Stability is determined by assessing the extent of injury to the transverse ligament of C1. On open-mouth plain film views, the Rule of Spence states that more than 6.9 mm of combined lateral displacement of the lateral masses over the C2 articular pillars represents an indirect measurement indicating that the transverse ligament has been disrupted.⁵ Such an injury can be confirmed by noting ligamentous disruption on MRI scans.⁶ With disruption, the patient may require surgical stabilization if there is purely ligamentous injury; however, some think that if the ligament is intact and the disruption occurs because of a small bony avulsion off C1, then immobilization with a rigid collar or halo vest can be used with the goal of the avulsion fracture’s re-fusing to C1.

C1 Posterior Arch Fracture

Posterior arch fractures are caused by a compression-hyperextension injury, which results in the occiput’s compressing the posterior arch. Like Jefferson fractures, the canal diameter is usually increased in these injuries, rendering patients neurologically intact. These injuries are relatively stable and thus can be safely treated with the patient in a cervical collar.

C1 Lateral Mass Fracture

It is presumed that axial loading and lateral bending may result in lateral mass fracture at C1. These injuries may be seen on odontoid view radiographs, but CT is the preferred method of detection. Minimally displaced injuries (less than 2 mm) can be treated with a rigid cervical collar; otherwise, halo immobilization or internal fixation may be required.

Horizontal Fractures of the Anterior Arch

Horizontal anterior arch fractures, which are relatively rare, are avulsion injuries due to the superior attachment of the longus colli. These fractures heal well with conservative treatment with the patient in a rigid cervical collar.

Atlantoaxial Instability

Traumatic atlantoaxial instability is secondary to rupture of the transverse ligament of C1, resulting in an increase in the atlantodental interval (ADI). The ADI is measured from the posterior aspect of the anterior arch of C1 to the anterior aspect of the odontoid process. In adults, an ADI less than 3 mm is considered normal. An ADI between 3 and 5 mm suggests transverse ligament disruption. An ADI greater than 5 mm suggests disruption of both the transverse and accessory ligaments.⁷ Dickman et al⁶ described two types of isolated transverse atlantal ligament injuries identified on MRI studies. Type I involves ligament injury without associated fracture of the atlas, and type II involves an avulsion fracture of the atlas at the insertion of the transverse atlantal ligament. The authors concluded that patients with type I injuries should be treated with early surgical fixation because of the inherent instability at C1-C2 following ligamentous disruption, whereas type II injuries require rigid external immobilization.

With such ligamentous injury, surgery is indicated to regain stability, and there exist numerous techniques to stabilize the C1-C2 complex. The original techniques of Gallie,⁸ Brooks and Jenkins,⁹ and Dickman et al¹⁰ involve placing a structural bone graft between the C1 arch and C2 spinous process and supplementing it by posterior wiring around C1 and C2. Although they are rigid in flexion-extension, these constructs are less stable in rotation and require halo immobilization. More recently, techniques involving screw fixation have been developed that provide added stability in all loading modes. C1-C2 transarticular screws directly fix the C1-C2 joints bilaterally. They were originally used in conjunction with posterior wiring techniques. Unfortunately, such screws can be challenging to place, as the course of the vertebral artery may be prohibitive in relation to the screw trajectory. More recently, posterior screw-rod constructs based on the method of Harms and colleagues¹¹ have gained popularity In these constructs, C1 lateral mass screws are attached to screws in the C2 pedicle, the pars interarticularis, or the laminae.

Axis (C2)

The odontoid process (dens) of the axis allows articulation with C1. Some theorize that during developmental formation, there may be an inherent weakness between the C2 body and the dens, as the latter originates from a separate cartilaginous growth center. Incomplete fusion at this junction is termed an os odontoideum, which is believed to be congenital. Others hypothesize that such a floating fragment is the result of a previous fracture at this junction. Full cortication of the fragment may help distinguish this abnormality radiographically from an acute odontoid fracture.

Odontoid Fracture

Odontoid fractures are relatively common cervical fractures and have been classified into three types by Anderson and D’Alonzo.¹² Type 1 fractures occur at the tip of the dens and are considered avulsion fractures of the alar ligaments. Although relatively rare, these injuries are considered stable and heal well with a rigid collar. Type 2 fractures occur through the odontoid process and are generally considered unstable injuries. Type 3 fractures occur in the cancellous bone of the C2 body. These are more stable than type 2 fractures and usually heal with 12 weeks of immobilization.

Type 2 fractures may be challenging to treat. Nonoperative treatment may be attempted, as many of these fractures occur in the elderly. Treatment may include closed reduction prior to stabilization in an external orthosis. Immobilization is associated with a 68% bony union rate, and factors implicated in lower fusion rates include increased age, greater displacement of the fracture plane at final reduction, and a history of smoking. Enthusiasm for halo use in the elderly must also be tempered by a high medical complication rate, as mobility, nutrition, and sanitation are greatly compromised. Although a rigid cervical collar does not provide the same degree of immobilization, it may be preferable in certain instances.

Operatively, anterior screw fixation leads to a higher rate of fusion than the use of an external orthosis (Figure 174-1). However, three anatomical characteristics may affect the technical success of screw placement. First, the patient cannot be significantly kyphotic in the cervical or cervicothoracic spine, as this will prevent the surgeon from obtaining the correct trajectory to place the screw. Second, the fracture fragment must be straight or angled posteriorly so that while the surgeon is reducing the fragment to the C2 body using a lag screw, the fracture planes can be opposed. Third, a comminuted fracture or a poorly angled fracture may not be satisfactorily realigned with the anterior screw and thus may never heal. In these cases, a posterior fusion may be appropriate, using a C1-C2 construct to stabilize the fractured axis.