The upper cervical spine is said to be consist of two unique vertebrae, the atlas (C1) and the axis C2). The skull base with its bony and ligamentous elements surrounding the foramen magnum plays an integral part in maintenance of the normal functional alignment of these two cervical vertebrae.
Technically however, skull base is not a part of upper cervical spine.
But the injuries to upper cervical spine also include all osseous and ligamentous structures between the skull base and the cranial side of the C-3 vertebra.
The integrity of the craniocervical junction is of crucial for survival and function. It is here that transition from brainstem to spinal cord occurs. These vertebra are shaped different from rest of cervical spine to protect these vital structures and allow for mobility of the head .
An injury to osseoligamentous components in this region may therefore compromise structural integrity of the entire craniocervical junction and therefore needs to be addressed separately from rest of cervical spine.
Because of compex anatomy and a major role played by ligaments in stability, this region is quite vulnerable to injury in high energy trauma. This unique composition also makes the assessment difficult and aid of imaging studies becomes very important.
The assessment should be performed according to standard guidelines and should include cranial nerve examination. Prior to advent of trauma management systems, these injuries were almost always fatal but the survival has been improving with better management.
In conscious, oriented patients the symptoms of neck pain, headache, and tenderness in the area might suggest the injury to this area.
Neurologic deficits range from complete high quadriplegia to incomplete injuries, such as cruciate paralysis or disorders affecting brainstem function.
Unconscious patients pose an increased diagnostic challenges and need to be scrutinized for possible spinal column and cord injury. The imaging studies play a greater role in these cases.
Biomechanics of Upper cervical Spine
The three bony components of the upper cervical spine are
- Skull base
these three components form a functional unit. There are five joints in the upper cervical spine which are stabilized by ligamentous check rein and muscular control.
Together these contribute to the movements in the neck substantially. This enables us for a rapid response and large-scale head excursion.
Upper cervical spine is thought to contribute approximately 60% of rotation, 40% of flexion-extension, and 45% of overall neck motion.
The normal axial plane C1–2 rotational excursion amounts to 80 to 88 degrees from left to right.
The Atlanto-occipital joint and C1–2 flexion/extension excursion is similar for both joints at 20 to 30 degrees at each level.
Total left to right lateral bending at the C1–2 segment amounts to 20 degrees.
The alar ligaments play a key role in protecting normal craniocervical motion. At midposition of the head these ligaments are slack.
By turning the head in one direction, the alar ligament contralateral to the direction of turning tightens, while the ipsilateral ligament slackens. Together with the tectorial membrane the alar ligaments limit flexion but they play no role in limiting extension.
The contralateral alar ligament limits lateral bending.
Other ligamentous stabilizers of the craniocervical junction are the cranial portions of the anterior longitudinal ligament and posterior longitudinal ligament of the spine and joint capsules of the respective articulations.
Anteriorly, the well-developed atlanto occipital membrane limits extension, with the thinner anterior atlantoaxial membrane contributing to a less significant degree.
A number of smaller ligaments, such as the apical and cruciate ligaments, the
obliquely aligned accessory atlantoaxial ligaments, the anterior atlantodental ligament, and the facet joint capsules also provide support.
The specific arrangement of ligaments at the craniocervical junction utilizes the atlas as a washer or base for a coupled, multiplanar motion.
The combination of a high degree of motility and relatively delicate ligamentous and bony structures makes the upper cervical spine susceptible to injury from indirect high-energy trauma.
Fracture-dislocations of the craniocervical junction is the leading cause of death of motor vehicle accidents.
The atlas is the most fragile vertebral segment in humans. It will fracture with as little as 1 to 2 mm of deformation and is very susceptible to bursting-type fractures with relatively low axial loads.
The two most vulnerable bony structures of the axis are the pars interarticularis and the odontoid waist. Forced hyperextension can lead to failure of either structure.
Flexion is believed to be causative in 80% of odontoid fractures by forcing the transverse ligament against the odontoid.
Atlantoaxial rotation of more than 50 degrees in either direction as measured by CT scan is suspicious for alar ligament insufficiency.
If it is more than 56 degrees, it is diagnostic of disruption.
An intact transverse ligament limits anterior subluxation of the atlas relative to the axis to 3 mm in adults and 5 mm in children.
Similarly, more than 5 degrees of atlantoaxial flexion is indicates transverse
If atlantoaxial translation exceeds 9 mm in adults, comprehensive failure of all key craniocervical ligaments has to be assumed.
Imaging in Upper Cervical Spine Injury
Lateral cervical spine xray is the most important trauma screening study . However, clearance of the cervical spine is not possible on basis of single lateral plane study. Moreover, the typical lateral cervical spine xray is centered in the midneck region and interpretation of the occipitocervical junction can be impaired.
To be able to rule out injury following bony structures need to be seen on xray
- Opisthion -On the occipital bone, the mid-point on the posterior margin of the foramen magnum
- Occipital condyles
- Mastoid processes
- Tip of the dens
- Outline of atlas and axis
These structures should be visualized in a trauma situation and looked for fracture, rotation, and displacement.
The occipitocervical and atlantoaxial joints should be assessed for congruence.
In adults, widening of the prevertebral soft tissue mass in the upper neck is an important warning sign of major underlying trauma.
Various Reference lines can help in identifying alteration in normal upper cervical spine outline.
Anteroposterior visualization of the upper cervical spine requires either an open-mouth odontoid view. Normally symmetrical articulating occipital condyles, C-1 lateral masses, and C-2 superior articular processes can be visualized. The odontoid is well centered between the lateral masses of C-1.
In this view, there should be no overhang, translation, or distraction between the lateral masses of C-1 and C-2. The articular surfaces of occipital condyles to the C-1 superior facets and those of the atlantoaxial articular surfaces should be equidistant to one another.
Other xrays that can be done to evaluate upper cervical spine are oblique views, one lower cervical spine anteroposterior x-ray, which usually exposes C4 to T4, and a swimmer’s lateral view.
Dynamic radiographs of cervical spine are used to find any ligamentous injury to the region.
Any odontoid asymmetry relative to the lateral masses of the atlas or any diastasis of the upper cervical spine articulations to one another is cause for concern about a ligamentous injury to this region.
Dynamic sudies should not be done in patients with with suspected occipitocervical dissociation because of their potential to inflict neurologic compromise. Also, flexion-extension radiographs are contraindicated for patients with known acute cervical spine fractures and dislocations.
Computed tomography is a crucial investigation tool in assessment of patients with known or suspected cervical spine fractures.
CT scans allows for high-resolution imaging and makes diagnosis easier. By digital reconstruction of the fracture fragments, articular incongruities, complex fracture patterns and visualizing axial plane fractures can be understood.
A head CT scan incorporating the craniovertebral junction, can be helpful in detecting subarachnoid craniovertebral junction hematoma, which is frequently associated with atlanto-occipital dissociation, and occipital condyle fractures, which are commonly missed on conventional radiography.
Magnetic Resonance Imaging
Magnetic resonance imaging of the craniovertebral junction is indicated for patients with spinal cord injury, and it can be helpful in assessing upper cervical spine ligament trauma. Subarachnoid and prevertebral hemorrhage can be readily demonstrated on MRI scans.
Radioisotope-based imaging tests, like technetium-99 bone scan, are rarely required in trauma but can be useful in assessing occult fractures, osteoarthritis affecting the upper cervical spine and in pediatric patients for detection of a nondisplaced growth plate injury.
Occipital Condyle Fractures and Occipitocervical Dissociation
Occipital condyle fractures have previously been viewed as relatively uncommon injuries; but with the increased utilization of CT scanning with reconstructions in the evaluation of suspected spine trauma patients, an increased incidence has been noted. It has been reported to occur in 3-15% of trauma patients. Presence of these fractures indicate high injury trauma.
Occipital condyle fractures may be stable or represent the bony component of occipitocervical dissociation.
Montesano classified these fractures into three categories.
Type I Fractures
These are usually stable fractures and thought to be the result of an impaction injury.
They occur as comminution of the tip of the occipital condyle.
Type II Fractures
These consist of an oblique fracture extending from the condylar surface into
the skull base. Fractures of this nature are likely caused by a shear mechanism and are likely unstable.
Type III Fractures
These are least common of the three.
They occur as a transverse fracture line through an occipital condyle. They are thought to occur as a result of an avulsion.
They are unstable and may represent the bony component of a craniocervical dissociation.
If a unilateral bony injury to an occipitocervical joint is identified, the contralateral side should be looked for any signs of a bony or ligamentous injury.
Due to association of occipitocervical dissociation, any occipital condyle fracture should be evaluated for it.
Type I and II fractures are usually treated conservatively with immobilization in a rigid cervical collar for 6-8 weeks.
Type III fractures should be treated with halo-vest immobilization if there is a suspicion of ligamentous instability. If there is evidence of craniovertebral subluxation, some authors advocate immediate occiput-to-C2 fusion.
Occipitocervical dissociation is an uncommon injury which can be difficult to identify and has a high mortality. The most common mechanism of injury is that of a pedestrian struck by a car, with a high incidence in pediatric patients.
Obvious signs of instability are translation or distraction of more than 2 mm in any plane, neurologic injury, or concomitant cerebrovascular trauma.
The classification of these injuries is based upon the displacement of the occiput.
- Type I injuries are anterior subluxations and are the most common.
- Type II injuries have vertical distraction greater than 2 mm of the atlanto-occipital joint.
- Type III injuries are posterior dislocations and are rarely reported.
Once an injury is identified, prompt management is of the utmost importance.
Traction is contraindicated.
Treatment consists of immediate halo vest application with reduction of the subluxation and confirmation by CT scanning.
An occiput-to-C2 fusion is required in most cases to provide longterm stability.
Fracture of C1 Vertebra or Atlas
Atlas fractures can be stable or unstable injuries. This fracture has very high association with injuries to other areas of the spine.
A fracture of atlas vertebra should cause enough alert to search for injuries in other region of the spine.
Almost 43% of all C-1 fractures are found to be associated with a C-2 fracture.
Atlas fractures have been divided into following 5 types.
- Transverse process fracture
- Postreior arch fracture
- Anterior arch fracture
- Comminuted or lateral mass fracture
- Burst fracture
Transverse Process Fracture
An extraarticular fractures of the transverse process. While these fractures are usually mechanically stable, involvement of the vertebral foramen may imply vertebral artery injury.
Posterior Arch Fracture
Posterior arch fractures are caused by a hyperextension mechanism. They are stable fractures.
Anterior Arch Fracture
Isolated anterior arch fractures are subdivided into minimally displaced, comminuted, and unstable. They are caused by a hyperextension mechanism in which the odontoid is thrust against the anterior arch of the atlas.
A blowout fracture of the anterior arch leads to displacement of the odontoid anterior to the lateral masses and is inherently unstable.
Lateral Mass Fracture
Lateral mass fractures are either unilateral intraarticular split type or occur as comminuted fractures. These fractures are caused by lateral flexion or rotational forces. These are unstable fractures.
Bursting-type fractures result from an axial load and split the ring of the atlas into several fragments.
Complete transverse ligament insufficiency is said to occur if the combined overhang of the C-1 lateral masses relative to the lateral mass walls of C-2 is 7 mm or more. Transverse ligament insufficiency signifies instability.
In normal conditions, the articulation of the odontoid process of C2 (axis) with the anterior arch of C1 (atlas) allows for 50% of cervical lateral rotation.
The liagments responsible for stability are transverse and alar ligaments. They maintain joint integrity and limit posterior motion of the odontoid process relative to the C1 anterior arch.
An acute injury to this area can cause cord compression and could be fatal.
Acute trauma, usually cervical hyperflexion, hyperextension, or a direct axial load on the head or cervical spine causes atlanto axial injuries. Certain conditions congenital odontoid anomalies, such as odontoid aplasia, odontoid hypoplasia, and a separate odontoid process or os odontoideum and inflammatory processes predispose an individual to these injuries.
Most of these injuries are the result of significant trauma to the head, although they may occur in older patients with a simple fall and striking of the occiput.
The individuals suffering from these injuries present with general symptoms of neck pain, limited range of motion, and torticollis. However, worsening of symptoms like headache, fatigue, transient upper-extremity paresthesias could be an indicator of this injury.
Quadriplegia due to cord compression may also be a presentation.
Standard protocol of spine injury examination must be followed. More Information on this available here
- Spine Injury initial evaluation
- Spine injury- Detailed Evaluation
An assessment of the airway, breathing, and circulation (ABCs), with immediate stabilization of the cervical spine in a neutral position must be done. While placing airway, a compromise to the injured spine should be avoided.
High-dose intravenous steroids should be considered in patients with suspected cervical cord injuries to reduce spinal cord swelling.
The findings may be completely normal in asymptomatic patients with radiographically documented injury .
An MRI may be used to investigate the integrity of the ligamentous complex.
Types of Atlanto axial Injuries
There are three patterns of atlantoaxial instability. These can present as isolated or combined injury
These injuries cause are rotational displacement in an axial plane. Fine-cut CT scans are of utmost importance in diagnosis and measurement of this condition.
These injuries are translationally unstable in a sagittal plane due to insufficiency of the transverse atlantal ligament. These are inherently unstable injuries.
Injuries are characterized by a multiplanar vertical atlantoaxial dissociation. Atlantoaxial distractive injuries are also referred to as atlantoaxial dissociation and constitute a variant of atlanto-occipital dissociation. This injury is a result of vertical separation as in judicial hanging. Often there is traumatic separation of both alar ligaments, rendering this injury highly unstable,
Treatment decisions should be always made on the basis of a comprehensive evaluation of the patient in general and the injury specifically.
Presence of a spinal cord injury usually requires definitive surgical decompression and instrumented fusion of the injury to maximize chances for neurologic recovery.
Ligament injuries heal poorly when treated nonoperatively.
Non operative treatments include bracing, halo vest and cervical traction.
Operative treatment consists of C1 -C2 fusion.
Rupture of Transverse Ligament
This is a pure ligamentous injury of upper cervical spine and behaves differently from other injuries of C1-C2 region.
Most common cause of this injury is blow on the back of the head following a fall.
How Does Transverse ligament Rupture?
The ligament may either be avulsed with a bony fragment from the lateral mass on either side or it may rupture in its substance.
The presentation would be like other injuries of upper cervical spine. The xrays may reveal anterior subluxation of ring of C1 on lateral views in flexion.
The instability can be reduced on extension.
These flexion and extension views should be made under supervision of a physician.
Presence of retropharyngeal hematoma suggests an acute injury.
A small fleck of the bone may suggest avulsion of the ligament.
Anterior widening of atlanto-dens interval of more than 5 mm in lateral view in flexion suggests that transverse ligament is incompetent.
Rupture of the transverse liagment is a ligamentous injury and non operative treatment is not effective in this type of injury.
Therefore surgery is almost always needed.
Initial treatment of this injuryis by stablization of the spine using traction.
Definitive treatment involves fusion of C1-C2 vertebrae.
Traumatic Spondylolisthesis of the Axis
Disruption of the neural arch of the axis predominately affects the narrow zone of the pars interarticularis and may be associated with more complex soft tissue injuries.
Injuries to this structure are popularly known as hangman’s fracture.
The term hangman’s fracture originally referred to neck injuries incurred during the hanging of criminals. The most common cause of hangman’s fracture now is a motor vehicle accident with hyperextension of the head on the neck. The occiput is forced down against the posterior arch of the atlas, which is forced against the pedicles of C2.
Hangman’s fractures are the second most common type of axis injuries after odontoid fractures.
A classification of these injuries has been given by Effendi et al. was later modified.
Type I Fractures
Type I fractures are minimally displaced and are believed to be caused by hyperextension and axial loading with failure of the neural arch in tension. Because ligamentous injury is minimal, these fractures are stable.
Atypical fractures that are obliquely displaced are unstable fractures.
Type II Fractures
Type II fractures have more than 3 mm of anterior translation and significant angulation. These injuries result from hyperextension and axial loading that cause the neural arch to fail with a predominantly vertical fracture line, followed by significant flexion resulting in stretching of the posterior anulus of the disc and significant anterior translation and angulation.
The C2-3 disc may be disrupted by the sudden flexion component involved in this injury.
A subtype Type IIa is unstable due to their associated C2–3 disc and interspinous ligament disruption.
Type III Fractures
Type III injuries are relatively rare and constitute a complete unilateral or bilateral C2–3 facet dislocation. A C2–3 dislocation is highly unstable and cannot be expected to be reducible by nonsurgical means
The instability of a traumatic spondylolisthesis of the axis largely hinges on the integrity of the C2–3 discoligamentous elements. These fractures frequently are associated with neurological deficits
The assessment of instability is determined by the amount of sagittal C2–3 translation, and angulation between the end plates and is then assigned to one of five categories
- Grade I – Translation < 3.5 mm, angulation < 11 degrees.
- Grade II- Translation< 3.5-mm , > 11 degrees of kyphosis.
- Grade III – Translation >3.5-mm, <than 11 degrees of kyphosis.
- Grade IV – >3.5-mm translation, >11 degrees of angulation.
- Grade V- Complete disc disruptions.
Type I fractures usually heal with 12 weeks of immobilization in a rigid cervical orthosis.
For type II treatment consists of application of skull traction through tongs or a halo ring with slight extension of the neck over a rolled-up towel for 3 to 6 weeks to maintain anatomical reduction. The patient can be mobilized in a halo vest for up to 3-month period.
These fractures usually unite with an initial gap in the neural arch and develop a spontaneous anterior fusion at C2-3
Type IIA fractures are a variant of type II fractures that show severe angulation between C2 and C3 with minimal translation.
They usually have a more horizontal than vertical fracture line through the C2 arch. The recommended treatment is application of a halo vest with slight compression applied under image intensification to achieve and maintain anatomical reduction.
When reduction has been obtained, halo vest immobilization is continued for 12 weeks until union occurs.
Type III injuries usually have severe angulation and translation of the neural arch fracture and an associated unilateral or bilateral facet dislocation at C2-3. Type III injuries are the only type of hangman’s fracture that commonly require surgical stabilization.
Open reduction and internal fixation usually are required because of inability to obtain or maintain reduction of the C2-3 facet dislocation.
After posterior cervical fusion at the C2-3 level, halo vest immobilization for 3 months is necessary for the bipedicular fracture and for consolidation of the fusion mass.
Rotary Subluxation of C1 Vertebra On C2 Vertebra
This is an uncommon injury in adults. Rotary C1-C2 subluxation is more common in children and that behaves differently from the injury in adults.
In adults, the injury is caused by motor vehicle accidents and often may be missed in initial evaluation of the patient.
Following an injury , the patient complains of torticollis and restricted neck motion.
An open mouth view may reveal wink sign. The wink sign is caused due to over riding of C1-2 joint on one side ans normal configuration on other side.
However, since the atlantoaxial joint permits flexion, extension, rotation, and lateral bending, radiographic asymmetry is produced when the head is tilted laterally or rotated or if a slightly oblique odontoid view is obtained.
CT scan is helpful in defining the injury clearly.
Acute rotary subluxation can be reduiced by closed methods. After applying a Halo ring, a gentel traction is used to derotate the skull and C1 vertebra. Spinal cord monitoring is done throughout the procedure.
if stable reduction is obtained, it is confirmed radiologically and Halo vest is applied.
Done in cases of late detections or failed closed reduction. Using a posterior incision on neck, the subluxation is reduced manually.
This is followed by C1-C2 fusion.
Immobilization in halo vest is recommended for 8-12 weeks in either type of treatment.
Approaches To Upper Cervical Spine Surgery
The cervical spine can be approached from front or from back respectively called anterior and posterior approaches.
Posterior approach is more common than anterior.
This approach is most commonly used in procedures such as C-1 laminectomy, posterior fossa decompression, and C-2 neurolysis to procedures aimed at achieving a fusion between the C1–2 segments with or without inclusion of the occiput.
Advantages of a posterior approach include a relatively simple anatomic exposure and the possibility to extend the
procedure cranially and caudally as needed. In general, posterior spinal instrumentation constructs are also stiffer than anterior stabilization methods.
- A longitudinal midline incision
- Development of an intermuscular plane down to the posterior elements aided by electrocautery, periosteal elevators, and self-retaining retractors.
- If the occiput is to be included in the fusion, the incision should start at the inion, a large, usually well-palpable bony midline protuberance.
The presence of the vertebral artery lateral to the joint should be taken into account.
There are three main indications for anterior upper cervical spine exposures in trauma:
- Screw fixation of a type II odontoid fracture
- Anterior cervical plating and fusion of the C2–3 interspace for a displaced type IIa hangman’s fracture
- Anterior arthrodesis of the C1–2 facet joints as a salvage
As in any anterior cervical procedure, correct placement of the incision is important in minimizing technical difficulties.
Some of the pathologies of upper cervical spine are approached through the mouth and the approach is called transoral approach.
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