Management of Traumatic Atlantoaxial Subluxations

h1 class=”calibre8″>8 Management of Traumatic Atlantoaxial Subluxations

Alexander D. Ghasem, Frank J. Eismont, Evan J. Trapana, and Joseph P. Gjolaj

Abstract

Most patients with type I (posterior C-1 arch) fractures and type III (C-1 lateral mass) atlas fractures will not have any C1–C2 subluxation. Type I fractures can be treated in a soft collar and type III fractures can be treated in a standard rigid cervical collar for 6 weeks. Most patients with traumatic atlantoaxial subluxation due to type II atlas fractures (Jefferson fractures) or transverse ligament injuries with a bony avulsion can be successfully treated with a rigid occipito-cervical-thoracic orthosis for 2 to 3 months. Surgery should be limited to patients with intrasubstance transverse ligament tears, patients with Jefferson fractures and C1–C2 instability after failure of appropriate bracing, and patients with bony avulsion transverse ligament injuries who do not heal after conservative care. C1‒C2 posterior instrumented fusion is the usual type of surgery when surgery is indicated, but O–C2 fusion is sometimes necessary for treatment of patients with type II atlas fractures as described within the text of this chapter.

Keywords: atlas, facets, transverse ligament, apical ligament, alar ligament, atlantoaxial joint, atlanto-dens interval (ADI), posterior atlanto-dens interval (PADI), sum of lateral mass displacement, atlas fracture

8.1 Introduction

The upper cervical spine is composed of the occiput, atlas, and axis and is often described as the craniocervical junction (CCJ). The unique anatomical relationships within this osseoligamentous complex account for the injury patterns seen in the occipitoatlantoaxial spine. Unrecognized trauma to the upper cervical spine can result in devastating outcomes with injury to the brainstem and spinal cord. Nowadays, continually improving resuscitation protocols and lifesaving measures have increased the incidence of patients surviving high-energy trauma with concomitant atlantoaxial injury. Radiographs and advanced imaging techniques are utilized to assist surgeons in diagnosis and treatment planning. In this chapter, the authors discuss the diagnosis, anatomy, clinical evaluation, and surgical stabilization techniques for traumatic atlantoaxial subluxation.

8.2 Epidemiology and Associated Conditions

The etiologies for atlantoaxial instability are wide-ranging and include congenital (os odontoideum), infectious (Grisel syndrome), metabolic (Down syndrome), arthritic (rheumatoid arthritis), neoplastic, and traumatic causes. The focus of this chapter is on the traumatic causes of atlantoaxial subluxation and their respective management. Traumatic atlantoaxial instability is notably seen in a bimodal distribution in younger patients as well as those over the age of 60 years. ¹ In pediatric patients, CCJ injury accounts for 56 to 73% of all cervical spine trauma. ²^,³ Moreover in patients over the age of 60 years, C1‒C2 injury accounts for 70% of all cervical trauma cases. ¹ In both cohorts, atlantoaxial instability may result in unsatisfactory outcomes. Pediatric patients with cervical spine injuries and concomitant head injuries experience mortality rates as high as 41%. ⁴ Similarly, older patients with concomitant cervical spine injuries and neurological injuries have 2-year mortality rates of 41%. ⁵^,⁶^,⁷ Thoughtful consideration and a thorough understanding of upper cervical injury is crucial to the early recognition and appropriate management of atlantoaxial trauma.

8.3 Anatomy

Understanding the anatomy of the occipitoatlantoaxial complex is critical in evaluating upper cervical spine trauma and developing a treatment plan. The CCJ comprises the occiput, the atlas, and the axis, as well as their associated articulations and ligamentous attachments. There are six articular surfaces of the CCJ that allow for multiplanar motion. The conjoining surfaces between occiput–C1 and C1–C2 account for 50% of the total cervical flexion/extension and cervical rotation, respectively. The anterior atlanto-odontoid articulation is interposed between the posterior aspect of the anterior arch of the atlas and the anterior portion of the dens.

Conversely, the posterior atlanto-odontoid articulation is positioned between the posterior aspect of the dens and the anterior surface of the transverse ligament. The atlantoaxial joints are shallow, providing for increased rotation across C1–C2. Mechanical stability within the atlantoaxial complex is derived from the surrounding ligaments.

The ligaments spanning the CCJ include the transverse ligament, paired alar ligaments, the rudimentary apical ligament, the anterior longitudinal ligament, and the posterior longitudinal ligament (tectorial membrane). The transverse portion of the cruciform ligament is commonly referred to as the transverse ligament. The transverse ligament is attached to the tubercles on the medial aspect of each lateral mass of the atlas and is essential in maintaining atlantoaxial stability. Positioned anterior to the transverse ligament, the apical ligament extends from the tip of the dens to the basion. It is rudimentary and relatively weak. The paired alar ligaments connect the lateral aspect of the odontoid to the medial aspect of the occipital condyles and limit lateral bending forces as well as rotational forces. ⁸ They are strong and essential for stability. Barring vertebral artery anomalies, the paired arteries extend through the transversarium at the level of the axis and into a transverse groove above the superior articular facet of the atlas. Due to their proximity, the vertebral arteries, internal carotid vasculature, and cranial nerves are all vulnerable to injury and require special attention during examination.

8.4 Clinical Evaluation and Associated Conditions

Cervical spine injuries have been closely associated with high-energy accidents, focal neurological deficits, and severe head injury. As with any trauma evaluation, the airway must be secured first. In the setting of upper cervical spine injury, diaphragm and intercostal musculature may paralyze and result in respiratory failure. Large prevertebral hematomas may also produce airway obstruction. The remainder of the spine should also be evaluated as noncontiguous spine injuries are as high as 6% in trauma patients.

Patients often complain of suboccipital neck pain and a feeling of instability. It is difficult to assess focal injury since there is no dermatomal sensory or motor loss associated with this level. Posterior scalp sensation in the distribution of the greater occipital nerve may be diminished and cranial nerve injury is possible. Vaccaro et al demonstrated a 20% risk of vertebral artery injury in nonpenetrating cervical spine trauma. ⁹ This may result in severe sequelae such as blindness, quadriplegia, and death. However, many of these vascular injuries are clinically silent.

8.5 Imaging

A complete series of cervical radiographs is the principal means for evaluating cervical spine injuries and includes anteroposterior, lateral, and open-mouth odontoid views. Flexion-extension views are omitted due to risk of progressive neurological injury in the setting of instability as well as patient guarding.

8.5.1 Lateral X-ray

The lateral radiograph aids in evaluating prevertebral edema, sagittal balance, and instability. As a general rule for evaluating prevertebral swelling, soft-tissue shadows measured on the lateral radiograph should not exceed 10 mm at C1, 5 mm at C3, and 20 mm at C6. Sagittal balance is maintained in the cervical spine when lines drawn between the anterior border of the vertebral bodies, posterior border of the vertebral bodies, anterior aspect of the lamina, and spinous processes, are all continuous. Instability and potential spinal cord compression are assessed on the basis of following measurements:

Atlanto-dens interval (ADI): This is measured from the posterior border of the anterior arch of the atlas to the anterior border of the odontoid process. Accepted parameters for instability are ADIs measuring greater than 3.5 mm in adults and greater than 5 mm in children. ²^,¹⁰
Space available for the cord (SAC) and posterior ADI (PADI): This is measured from the anterior border of the posterior arch of the atlas to the posterior border of the odontoid process. Patients are at risk of neurological deterioration when the PADI is less than 14 mm and many consider this an indication for surgical intervention. ²

8.5.2 Open-Mouth Odontoid X-ray

Sum of lateral mass displacement: Bilateral increased C1 lateral mass translation relative to the lateral mass of C2 indicates the presence of a bony fracture at C1 and possible transverse ligament disruption. In adults, when the sum of lateral mass displacement is greater than 6.9 mm, then a transverse ligament rupture is likely to be present, and this may be confirmed with magnetic resonance imaging (MRI) in equivocal cases. ¹¹^,¹²^,¹³

8.5.3 Advanced Imaging Modalities

Computed tomography (CT) has been shown to be cost effective and the most sensitive tool for detecting and delineating fracture patterns in the upper cervical spine. ¹⁴^,¹⁵ MRI has been shown to be less cost effective and less accurate at detecting upper cervical spine fractures with a sensitivity ranging from 11 to 37%. ¹⁶^,¹⁷^,¹⁸ However, advantages of using MRI include further delineation of soft-tissue structures (including the intervertebral discs, the spinal cord, and ligaments such as the transverse ligament), as well as detection of compressive soft-tissues lesions such as hematomas.

8.6 Atlas Fractures

Most atlas fractures result from axial loading injuries and occur in the anterior and posterior arches. They account for an estimated 10% of all cervical spine fractures and 25% of injuries to the atlantoaxial complex. ³ The risk of having a spinal cord neurological injury caused by atlas fractures is low when occurring in isolation, although patients may have damage to the greater occipital nerve or to cranial nerves. ¹⁹ However, they are often observed in polytrauma patients with a multitude of injuries including other spine injuries which may have associated spinal cord injuries. Half of patients with atlas fractures have one or more other cervical spine fractures and 40% are associated with fractures of the axis. ²⁰

Atlas fractures are best visualized on thin-cut CT imaging and they are most commonly categorized according to Landells’ fracture classification ²¹ which is as follows:

Type I: These fractures only include one arch, anterior or posterior, and do not cross the equator of the atlas. The two posterior arch fractures are usually due to hyperextension and abutment of the C1–arch against the occiput (▶ Fig. 8.1). The anterior arch fractures are due to abutment against the dens. Treatment usually consists of soft cervical collar immobilization for a short time since this is a stable injury. It is not necessary to wait for fracture union to occur.
Type II: Also known as a “Jefferson fracture.” These fractures are the result of axial loading mechanisms of injury (▶ Fig. 8.2). This injury type produces bilateral anterior and posterior arch fractures and may cause C1–C2 instability depending on the integrity of the transverse ligament. If coronal displacement of the combined lateral masses exceeds 6.9 mm, then transverse ligament injury and resulting instability are present. In the setting of instability, C1–C2 or occiput–C2 fusion may be required for maintenance of neurological status and initiating early rehabilitation. However, the timing of any surgical fusion and the role for using a halo vest or other occipito-cervical-thoracic orthoses are not agreed upon. ²⁰^,²¹^,²²^,²³^,²⁴^,²⁵^,²⁶ The senior authors would recommend initial treatment with a rigid orthosis including either a halo vest or an occipito-cervical-thoracic brace for 2 to 3 months depending on the degree of instability present. The patient would then be reevaluated with X-rays and CT scans to assess bony healing and callus formation. The final test would then be cervical flexion and extension X-rays out of the orthosis (▶ Fig. 8.3). If there is no C1–C2 translation, then the patient would be changed to a soft collar for 1 month and then allowed to resume normal low-impact activities. On the other hand, if it remains unstable with C1–C2 translation after 2 to 3 months of immobilization, then surgery would be proposed and would be either a C1–C2 or an occiput–C2 fusion. The levels of the fusion would depend on the local bony anatomy, the degree of malalignment of the occipitocervical joint, and the location and patency of the vertebral arteries. It should be emphasized that drilling, tapping, and screw insertion into the atlas lateral masses can be extremely challenging and may not be possible if the atlas lateral masses are completely loose and independently mobile. In Landells series of 13 patients with type II atlas fractures, all were treated conservatively with a rigid orthosis and only one required C1–C2 fusion 1 year later after initial bracing because of lateral C1–C2 instability.
Type III: Fractures of a unilateral mass of the atlas are classified as type III. These may be subclassified as displaced and nondisplaced for treatment purposes. Lateral mass fractures with greater than 5 mm of displacement should be immobilized using a rigid cervical collar or rarely using a rigid occipito-cervical-thoracic brace. Minimal or nondisplaced injuries should be treated definitively with rigid cervical collar immobilization for 6 weeks. ²¹ In Landells series of 35 patients with atlas fractures, there were 16 type I, 13 type II, and 6 type III fractures. Of the 23 patients with more than 1-year follow-up, 57% reported significant symptoms including neck pain, scalp dysesthesias, and/or neck stiffness. Only one patient was treated surgically for late instability. ²¹

$This axial CT scan demonstrates a C1 posterior arch fracture that is minimally displaced, and this typically occurs at the vertebral artery groove. Provided there are no other associated injuries, the$

Fig. 8.1 This axial CT scan demonstrates a C1 posterior arch fracture that is minimally displaced, and this typically occurs at the vertebral artery groove. Provided there are no other associated injuries, the treatment would usually be immobilization in a soft collar for a short time for comfort only. This by itself is a stable injury. (Reproduced with permission from Tay B, Eismont J. Injuries of the upper cervical spine. In: Garfin SR, Eismont FJ, Gordon R. Bell GR, Fischgrund JS, Bono CM, eds. Rothman-Simeone and Herkowitz’s The Spine, Vol 2. Elsevier; 2017: 1285-1309.)

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