C1 (Atlas) Fractures 

Updated: Aug 04, 2021
Author: J Allan Goodrich, MD; Chief Editor: Jeffrey A Goldstein, MD 

Overview

Practice Essentials

The C1 vertebra (atlas) is a closed ring. A fracture of a closed ring necessarily results in at least two areas of ring disruption. These disruptions are customarily accompanied by a spread of the C1 ring fragments as a result of the axial loading mechanism of this injury and the weight of the head.[1]  Sir Geoffrey Jefferson, a British neurologist and neurosurgeon, originally described this type of C1 fracture in 1920, reporting on four cases in addition to reviewing other previously reported cases.[2]  Accordingly, the term Jefferson fracture is also used to denote burst fractures of the ring of C1, usually involving four bony fractures of the anterior and posterior arch.

In addition to anteroposterior (AP) and lateral views, radiographs of the upper cervical spine include the open-mouth view. This view may identify spreading or widening of the lateral masses or asymmetry of the separation of the odontoid from the lateral masses, which, in an appropriately centered radiograph, may be consistent with spreading of the C1 ring or a C1 fracture. Increased overhang of the lateral masses over the C2 facet totaling more than 6.9 mm suggests a fracture with disruption of the transverse odontoid ligament that may otherwise constrain displacement.

Fractures of the ring of C1 may be associated with an odontoid fracture; thus, the combination of the two fractures should be considered. Furthermore, congenital anomalies of the arch (eg, agenesis of the posterior ring) may be present. Anterior subluxation of C1 on C2 may be present and, if so, often indicates a disruption of the transverse odontoid ligament.

The principal treatment is with a cervical collar or halo vest, which remains an effective current treatment for many of these fractures.

Anatomy

The upper cervical spine is defined by the two most cephalad cervical atypical vertebrae, C1 (the atlas) and C2 (the axis). This region is distinct in anatomic shape and is more mobile than the lower cervical spine (ie, the subaxial cervical spine). The occipital condyles of the head (or the globe) rest upon the lateral masses of C1. These articular facets allow most of the flexion and extension of the head on the neck as the occipital condyles articulate on the atlas.[3, 4, 5, 6]

The ring of C1 has no vertebral body; the vertebral body that would correspond to C1 is connected or contiguous with the vertebral body of C2 and projects up as the dens (tooth), also known as the odontoid of C2. Most of the lateral rotation of the neck actually occurs at the C1-C2 junction; the remaining motion of the cervical spine is distributed among the subaxial spine vertebral motion segments as a fractional amount (~7%) per level and is less in total than the C1-C2 lateral rotation. Up to 50% of cervical flexion/extension and rotation are thought to occur at these levels.

This area of the upper cervical spine is extremely mobile, and its stability is dependent on ligamentous structures. In unresponsive patients or those who are unable to report symptoms or pain, a C1 fracture or an occipital cervical dislocation must be excluded by radiographic screening. Also, displacement of the C1 ring may occur if the capsule or ligaments are disrupted, even without a C1 fracture; hence, the head may be displaced on the neck, and the atlas may also rotate around the odontoid or sustain a fracture of the dens.

The care of any fracture requires attention to the joint above and below. This cervical complex has often been treated as two separable articulations, C0-C1 and C1-C2, but the concept of the three-unit occipitoatlantoaxial complex (C0-C1-C2) articulation is much more functionally relevant.

The significance is the proximity to the brain, brainstem, and upper cervical spinal cord, but that is contrasted with the very significant motion that occurs in this area. Although patients are routinely asked to flex and extend their necks to determine range of motion (ROM), some of the motion observed is between the occiput and the atlas, and as the patient rotates laterally, at least 50% of that motion is atlantoaxial.

The stability of the injury depends on the ligaments between the bony structures. On the frontal view, the projecting occipital condyles are supported by the lateral masses (observed as wedges that are narrow medially and expanding laterally), resting on the corresponding superior articular surface of C2. Consequently, the lateral masses provide inherent stability because of this bony shape and also illustrate the extent of the instability when this bony structure is disrupted, particularly when these wedges displace laterally.

The projecting condyles of the occiput are stabilized with the occipitoatlantal capsule, as well as anterior and posterior atlanto-occipital membranes. The ligamentum nuchae is a significant stabilizing structure; its specific relevance to the atlanto-occipital axial complex is controversial but should be considered. Connections from the occiput to the axis are the tectorium membrane and the alar and apical ligaments, which do not appear to be bulky enough to be independently significant restraints.

The dentate ligaments (ie, the alar ligament and the apical ligaments) attach to the dorsal lateral surface of the dens and run obliquely to the medial surfaces of the occipital condyles. In 1974, Anderson and D'Alonzo classified a type 1 odontoid fracture as an avulsion fracture of the odontoid tip caused by the apical ligament, suggesting that these ligaments impart a significant degree of stability.[7] Modifications aimed at expanding the Anderson-D'Alonzo classification have been proposed.[8]  The Roy-Camille system has also been used to classify odontoid fractures.[9]

The transverse ligament goes from the medial surface of one side of the atlas to the other side and essentially constrains the axis to rotate around the odontoid in a closed ring of bone and the transverse ligament. As a consequence, the atlas can displace and embarrass the brainstem and spinal cord if this ligament ruptures or if an associated fracture of the odontoid is present as a result of this specific anatomic arrangement.

Pathophysiology

The ring of C1 is a structural member of the cervical spine. Because it is a ring and because fracture results in disruption of this ring, more than one location is affected.

The fragments have a propensity to shift laterally, both from the weight of the head and from the muscular contraction acting through this articulation; thus, occipital condylar support for the head is lost. The absence of the rigid bony structure and the lack of interconnection or interrelation of the attached ligamentous structures meet the definition of instability, particularly in that the bony protective function of C1 for the neural elements is lost.

Vertebral artery injuries have been reported as a result of C1 fractures in as many as 7% of cases, especially with atlanto-occipital dislocations; small excursions of displacement can be fatal.[10] In addition, vertebral artery injuries can occur and have been reported in the absence of severe trauma as a result of cervical traction, chiropractic manipulation, overhead work, or yoga exercises. Hyperextension is customarily accompanied by rotation; when this is not limited by normal restraints, it becomes excessive, severely diminishing blood flow through the vertebral arteries.

This diminished blood flow is a particular problem in the posterior inferior cerebellar artery and may result in Wallenberg syndrome, which is characterized by ipsilateral loss of cranial nerves V, IX, X, and XI with cerebellar ataxia.

Horner syndrome may occur and, in some cases, may involve contralateral loss of pain and temperature sensation; involvement can extend up from a lateral medullary infarct and spread to the basilar superior cerebellar or the inferior cerebral artery, leading to sudden death, quadriplegia, and the locked-in syndrome, in which quadriplegia occurs with loss of lower cranial nerves and only eye-blinking is possible.

Etiology

The Jefferson fracture most commonly occurs as the result of axial loading on the head through the occiput, which leads to a burst-type fracture of C1. Diving is the most frequent cause of this fracture, when it results from striking the head on an obstacle in shallow water; hence, the national program "Feet first, first time" (North American Spine Society, 2005) provides a motto for diving in unknown waters or shallow collections of water and has been an effective deterrent.[11]

The next most frequent cause of this fracture is being thrown up against the roof of a motor vehicle, a car or bus, or even an aircraft, with the forces being distributed to the body through the neck. The third most frequent cause of these injuries is falls onto the head, except in toddlers, who are predisposed to injury from falls because of their disproportionate head size.[3]

Less frequently, when a significant rotatory force is exerted, an atlanto-occipital junction dislocation may occur, or the force may also be dissipated through the odontoid as an associated fracture.

Epidemiology

Fractures of the atlas account for 25% of atlantoaxial complex bony injuries, 10% of cervical spine injuries, and 2% of all spine injuries. Injury to the cervical spine occurs infrequently in pediatric populations, and although C1 represents only 1-2% of pediatric trauma and 2-10% of all cervical injuries in this population, the associated mortality is 16%.

Prognosis

Patients with Jefferson fractures are expected to heal and have an excellent prognosis for resumption of activity in the absence of associated injuries. Any surgical stabilization severely restricts the motion of the head, because the occipitoatlantoaxial complex represents over 50% of the motion of the head on the trunk. Healing time is generally 12 weeks with or without surgery.

Platzer et al studied nine patients (average age, 54 years) who underwent anterior plate fixation of an odontoid fracture because of unsuitability for anterior screw fixation.[12]  After plate fixation, eight of the nine returned to their preinjury activity level and were satisfied with the treatment; one reported chronic pain and decreased cervical spine motion. Bony fusion was achieved in all patients; reduction or fixation failed in two. These findings suggested that anterior plate fixation may be a practical option for odontoid fractures requiring additional stabilization.

Al Eissa et al performed a retrospective review of 17 patients with isolated C1 and C2 fractures who experienced significant airway compromise.[13]  Older age and male gender were found to be significant risk factors. Most patients also exhibited prevertebral swelling, significant degenerative changes, and significant fracture displacement. Of the 17 patients, 12 required intubation and admission to the intensive care unit (ICU); four died. The findings suggested that all patients with isolated C1 and C2 fractures should be assessed for potential airway compromise.

 

Presentation

History and Physical Examination

Patients with C1 (atlas) fractures customarily present with a history of trauma and a symptom of pain in the neck. Among the massive number of patients who qualify as having this history and symptom, a few patients have an unstable C1 injury and may present in a neurologically intact state, but they are at grave risk for neurologic compromise if not promptly diagnosed and appropriately stabilized and treated.

Patients with a complete spinal cord injury (SCI) and no neurologic function continue to have only sensation on the face and motor control of the facial muscles from the cranial nerves. A tracheostomy is essential; the patient requires respiratory assistance and a volume respirator. If the C3-C5 area is intact, the phrenic nerve may often be stimulated to contract the diaphragm. If stimulation of the phrenic nerve does not contract the diaphragm, then the spinal cord is no longer functioning; the cell body is dead, and a phrenic electrical stimulator is not effective.

Classification

The Gehweiler classification is commonly used to categorize C1 fractures. This sytem divides fractures of the atlas into the following five types[14] : 

  • Type I - Fracture of the anterior arch
  • Type II - Fracture of the posterior arch
  • Type IIIa/ IIIb - Combined fracture of both the anterior and the posterior arch (Jefferson fracture), either nondisplaced (IIIa) or displaced (IIIb) 
  • Type IV - Fracture of the massa lateralis
  • Type V - Fracture of the transverse process
 

Workup

Imaging Studies

Historically, cervical spine radiographs were routinely obtained in the emergency department (ED) for patients with a history of pain or of trauma, as well as for nonresponsive patients who are unable to report pain.

In 2013, the American Association of Neurological Surgeons (AANS) and the Congress of Neurological Surgeons (CNS) released updated guidelines for the management of acute cervical spine and spinal cord injury. In these guidelines, radiographic assessment was based on the presentation of the patient as falling into one of the following categories[15] :

  • Awake, asymptomatic patient
  • Awake, symptomatic patient
  • Obtunded or unevaluable patient

Briefly, for awake, asymptomatic patients who are without neck pain or tenderness, who have a normal neurologic examination, who do not have an injury hindering accurate evaluation, and who are able to complete a functional range-of-motion examination; radiographic evaluation of the cervical spine is not recommended.[15]

For symptomatic or obtunded or unevaluable patients, high-quality computed tomography (CT) of the cervical spine is recommended, if available; routine three-view cervical spine radiography is not recommended.[15] If high-quality CT is not available, a cervical spine series with anteroposterior, lateral, and odontoid views is recommended and should be supplemented with CT for areas that are suspicious or are not well visualized.  

Radiographs should specifically include the open-mouth view (see the image below). After confirmation that neutral rotation is present and the radiograph is reliable (eg, as determined by looking at the incisors to confirm lack of rotation of the head), the odontoid should appear symmetrically centered between the lateral masses. A C1 (atlas) fracture is often associated with lateral displacement; thus, if the ring of C1 overhangs or extends laterally more than 6.9 mm over the lateral mass, a fracture of the ring of C1 is established. However, less excursion does not exclude this fracture, particularly if there is minimal displacement in the supine patient.

Fracture of C1 ring may result in lateral displace Fracture of C1 ring may result in lateral displacement and subsequent overhang on open-mouth view in radiographs.

The lateral view is also crucial because the atlanto-occipital membranes may be disrupted and an occipitoatlantal dislocation may be observed; the normal anatomy must be confirmed. If any suspicion of disruption or dislocation exists, traction must be avoided, as well as any subsequent flexion-extension maneuvers or inappropriate manipulation, until that possibility can be excluded.

The odontoid should be well imaged from the lateral view; any lack of alignment or discontinuity that suggests fracture also suggests instability of the upper cervical spine, which may be associated with a C1 fracture but indicates very significant instability that necessitates immobilization of the occipitoatlantoaxial complex.

On the lateral view, the Power ratio may be used to evaluate for possible atlanto-occipital dislocation: A ratio greater than 1 of the basion to the posterior arch of C1 (BC) over the anterior arch of C1 to the opisthion (AO) is suspicious for anterior dislocation.

If the ring is not clearly observed to overhang but asymmetry is present between the atlas and the odontoid, a C1-C2 problem may be present, particularly atlantoaxial rotary subluxation, which may be a result of one of the facets between these two vertebrae being displaced or locked in a dislocated position.

Unfortunately, a possible C1-C2 instability, particularly the cock-robin position of the head that may be present with displacement of C1 on one side (most often anteriorly), makes obtaining the standard open-mouth and other radiographic views difficult. CT (see the images below) facilitates those investigations wherein thin cuts best demonstrate the pattern of disruption for evaluating the location and displacement of suspected fractures of C1.

Computed tomography is often best for visualizing Computed tomography is often best for visualizing C1 ring fractures. Note anterior disruption, which must be accompanied by another break in ring.
Computed tomography sagittal views can be used to Computed tomography sagittal views can be used to evaluate atlantodental (or atlantodens or atlas-dens) interval or to visualize C1 fractures.

Unilateral posterior displacement of the atlas also produces the cock-robin position, but this displacement is usually without a fractured dens. In trauma cases, most commonly, a unilateral combined anterior-posterior subluxation occurs when the transverse ligament is disrupted. The C1 ring may displace anteriorly and reduce the space available for the spinal cord.

CT angiography (CTA)[16] or magnetic resonance angiography (MRA) may be valuable to detect occlusion, thrombosis, or intimal tear in patients with suspected vascular compromise or symptoms consistent with a vascular insult. Digital subtraction angiography (DSA) may also help evaluate collateral circulation. If any circulatory problems are diagnosed, immediate anticoagulation with heparin prevents further extension of thrombosis, and administration of oxygen maintains cerebral oxygenation.

 

Treatment

Approach Considerations

Recognition and identification of a Jefferson fracture is the indication for treatment. Treatment consists of spinal stabilization to protect the patient from nervous system damage. Children may represent less unstable cases, presumably because of periosteal stability, and they are often treated with a collar. The body of C1 (the atlas) is not visible radiographically until age 1 year.

Even in the absence of a C1 fracture, assessment of stability must include the associated structures. An atlanto-occipital dislocation or disruption and C1-C2 instability, particularly when the transverse ligament may be disrupted, poses severe risk to the brainstem and upper spinal cord. Furthermore, with a C1 fracture, associations exist with unstable injuries such as odontoid fractures and other injuries to the upper cervical spine. In addition, the odontoid fragment may migrate into the foramen magnum, endangering the brainstem and upper spinal cord.  

The images below illustrate a type II odontoid symptomatic nonunion in a patient with continued neck pain followed by another fall, resulting in bilateral fractures of the posterior arch of C1.

Sagittal reformat of CT cervical spine showing pos Sagittal reformat of CT cervical spine showing posterior displacement and chronic nonunion of the dens.
Bilateral posterior arch fractures in the axial pl Bilateral posterior arch fractures in the axial plane of the CT cervical spine in the same patient after a second fall.
Lateral radiograph after C1-2 posterior fusion. Lateral radiograph after C1-2 posterior fusion.
AP radiograph showing hybrid C1-2 posterior fixati AP radiograph showing hybrid C1-2 posterior fixation with bilateral C1 screws and right sided C2 pedicle screw with a left to right intralaminar or translaminar C2 screw.

Specific treatment should be based on analysis of the mechanism and extent of the injury. In a younger patient with limited displacement of the C1, immobilization with a collar or halo and vest may be adequate.

In more severe cases, particularly with associated injuries such as odontoid fracture, bypassing the C1 ring with an occipital-to-cervical fusion extending to C2 or lower may be necessary. Instrumentation spanning that area may stabilize the C1 ring, which otherwise cannot easily be addressed directly, because both the anterior and posterior components of the ring are disconnected by the fracture and are not amenable to instrumentation or direct repair.

No significant contraindications for treatment exist, because the lack of stabilization, which commonly is initially provided either with traction or with a halo brace, can have fatal consequences. Any contraindications are mitigated by the potential for serious and even fatal neurologic consequences without treatment, as well as by the observation that halo with vest or traction can be relatively effective in immobilizing the upper cervical spine, with low associated morbidity.

Primary internal fixation of C1 fractures with lateral mass screws and transverse connector has been reported without the need for C1-C2 arthrodesis, resulting in preservation of cervical motion.[17]  Anterior transoral, isolated posterior, and combined posterior–anterior transoral approaches have been reported. For each approach, only small case series are available.[18]

Medical Therapy

Patients with C1 fractures typically have sustained some form of trauma. Prehospital care recommended by Emergency Medical Services and the American College of Surgeons dictates immediate stabilization of the cervical spine at the scene with the use of a hard backboard, a rigid cervical collar, lateral support and a mechanism to stap all the above to the backboard. Of course, the customary attention to the ABCs (airway, breathing, and circulation) is expected. If the airway is compromised or air exchange is inadequate, intubation without moving the head is crucial (C-spine protection).

Careful evaluation and frequent reassessment are essential because the patient may have sustained a concussion with the impact to the head (the common injury that produces the C1 fracture) and, because of a clouded sensorium, may not be able to be fully evaluated or to report neck pain. Patients with a diminished alertness and orientation should carefully undergo imaging studies to exclude underlying pathology.

Vertebral artery dissection and neurologic decline may occur with cervical trauma, emphasizing the above recommendation for arteriography. Basilar artery occlusion has been reported with chemical and mechanical thrombolysis, resulting in basilar artery patency and clinical improvement,[19] whereas prior cases of basilar artery occlusion reported death and locked-in syndrome.

Surgical Therapy

Choice of approach

Treatment of a C1 fracture consists of stabilization or immobilization in a satisfactorily reduced position to allow reliable healing. This illustrates the necessity of identifying associated injuries; for example, if a Jefferson fracture is identified but an associated odontoid fracture, transverse ligament rupture, or other problem is present, halo treatment may be modified or less successful. The transverse ligament is not necessarily expected to heal tightly or reliably, though a fractured bone may have its mechanical integrity restored if the fracture fragments are well opposed when healed.

With a C1 fracture, the posterior aspect of the ring becomes disconnected from the anterior aspect, which is stabilized around the odontoid; thus, a posterior fusion of the occiput to C1 would be inadequate to stabilize the spine and consequently would extend at a minimum to C2. Customarily, instrumentation attaches a type of contoured rod or plate from the occiput down to C2 to stabilize the area and facilitate healing.

Direct lateral mass screws have been reported, allowing reduction and compression across the fracture but also, more significantly, preserving upper cervical motion segments.[20]  This technique has been reported to be associated with occipital neuralgia[21] ; it will find its place in the author’s armamentarium as further experience is amassed. A computer-aided analysis by Krassnig et al suggested that such screws should be positioned with a slightly converging 16° angle and a slightly ascending 10° angle and that intraoperative multiplanar imaging should be employed to minimize the risk of harm to the vertebral artery or the spinal canal.[22]

A fractured odontoid fragment cannot be removed via the posterior approach; if a neurologic deficit or threat to the brainstem is present (the alar ligament may have an attached portion of the odontoid migrate superiorly into the foramen magnum to compress the brainstem at the pontomedullary junction), neurosurgical posterior decompression of the foramen magnum could be performed in a halo.

Alternative consideration may be given to a transoral approach or an anterior retropharyngeal approach for the combination of a Jefferson fracture and a fracture of the odontoid. The traditional treatment is a halo vest or cast until the Jefferson fracture is healed. Then, additionally, if the odontoid fracture healing has become delayed or a nonunion is present, this can be treated by a C1-C2 arthrodesis, but the procedure must be delayed for the ring of C1 to heal.

For this combined fracture, anterior open reduction and internal fixation (ORIF) of the odontoid may be performed, with two screws placed in an oblique fashion, starting at the inferior anterior edge of C2 and directed cephalad to engage the odontoid. With a C1 fracture, this is done in conjunction with a halo vest.

An alternative would be a Magerl approach of a posterior open reduction, accompanied by internal fixation of C1-C2. For this procedure, two screws are placed in an oblique fashion starting at the inferior edge of the C2 lamina, and then they cross the C1-C2 facet joint between the vertebral artery, which is lateral, and the spinal cord and brainstem, which are medial.

The use of intraoperative navigation has been reported to be useful in helping guide the placement of screws during surgical treatment of C1 and C2 fractures. In one study involving 17 patients (median age, 47.6 years), a total of 67 screws were placed.[23] Intraoperative computed tomography (CT) revealed that 62 screws (92.6%) were placed correctly, four (5.9%) with minor cortical violation, and one (1.5%) incorrectly (immediately corrected). The findings suggested that intraoperative CT reduces the risk of screw misplacement and consequent complications.

In a study of 10 patients with unstable hangman fracture (age range, 17-81 years), 52 screws were placed under O-arm guidance (20 in C2 pedicle, 20 in C3 lateral mass, and 12 in C4 lateral mass).[24] One C2 pedicle screw (5%) was misplaced. At follow-up (range, 3-21 months), no new-onset neurologic deficits had developed. Bony fusion was achieved in all patients, and full rotation at C1-C2 was preserved. The findings suggested that C2 pedicle screws can be precisely placed with O-arm guidance and that intraoperative CT can confirm screw position.

Alternative approaches

Disruption of the ring of C1 makes stabilization by a C1-C2 fusion in the customary posterior fashion impossible; however, a C1-C2 direct fixation with Magerl screws may stabilize the anterior ring to the body of C2. The role of this C1-C2 fusion is not yet universally accepted, but with experience, the indications and role will be more clearly defined.

A transoral resection of C1 may be preferred to an alternative technique, decompression posteriorly to the foramen magnum, particularly for a migrating odontoid fragment from an associated type 2 Anderson-D'Alonzo odontoid fracture with a Jefferson fracture. A significant amount of rotation of the atlas on the axis would be lost with this fusion, but the fusion would preserve the flexion and extension of the occipital condyle and head on the lateral masses, which would also be lost in an occipital C2 fusion (the traditional approach).

With regard to C1-C2 fixation, wires have been used for a significant time with excellent results. Gallie described fusion where wires are passed onto the arch of C1 and into the spinous process of C2.[25]

In 1978, Brooks and Jenkins then presented a more stable construct.[26]  Rather than placing the bone graft over the posterior elements, grafts are wedged between the posterior arch of C1 and C2, and the wires are passed under both C1 and C2, so that they can more effectively stabilize the bone grafts in their respective positions and increase the area for fusion. However, this procedure requires passing the wires more laterally, with careful attention to the vascular structures.

In 2002, Richter et al presented six different techniques for biomechanical comparison, preferring transarticular screws but considering isthmic screws with a claw or lateral mass screws and isthmic screws as an alternative with somewhat less immediate stability.[27]

In 2003, Cornefjord et al reported on a series of patients treated with Olerud cervical fixation.[28]  In this report, odontoid fracture occurred in 18 patients, rheumatoid instability in six, and odontoid nonunion and os odontoideum in one patient each, with clinical follow-up (20 patients followed for 6-27 months) suggesting no serious complications and a high frequency of fusion healing.

The posterior arch at C1 has minimal bone for the fusion to heal, and claw techniques to avoid passing sublaminar wires over the brainstem had some early discouraging results and were generally abandoned, leading to refinements and further investigation. Various techniques will continue to be compared and studied; this is clearly a challenging area.

Operative details

Patients must be maintained in protective immobilization, which, for adults, means more than just a soft collar. Ideally, they should be are in a halo from the point of initial treatment. Reduction of an atlas fracture may be achieved by means of ligamentotaxis with mild traction; however, traction is very risky, and such highly unstable injuries must be monitored extremely closely. Associated fractures must be promptly identified to direct subsequent treatment. Congenital abnormalities of the arch (eg, agenesis of the posterior ring) must be identified and taken into account in the treatment plan.

If the patient is awake and has a halo and vest applied, then the conversation and discussion with him or her during the procedure serves to demonstrate maintenance of safety and neurologic status. Patients who undergo surgical correction, particularly posterior arthrodesis, may be monitored with somatosensory evoked potentials.

After application of a halo, close radiographic follow-up is required to demonstrate that the fracture is maintained in a satisfactory position for healing. If surgical stabilization is appropriate, then monitoring the healing of the bone fusion with radiographs is also crucial postoperatively.

C1 lateral mass fixation[29]  involves a midline approach from the base of the skull to the subaxial spine, with the length of the incision depending on the number of levels to be incorporated. If occipitocervical fusion is planned, a longer incision will be necessary. C2 pedicle screw or pars fixation will require anatomic exposure of C2-C3; the procedure is fluoroscopically assisted, or O-arm navigation can be employed.

Careful exposure of the ring of C1 is carried out laterally, and the neurovascular bundle arising beneath the ring tracking laterally is exposed and dissected with a Penfield dissector so as to allow palpation of the lateral mass. Brisk venous bleeding is frequently encountered and can be controlled with a hemostatic agent (eg, Floseal; Baxter, Deerfield, IL) and a bipolar cautery. Packing with cottonoids and addressing the other side is an efficient way of achieving hemostasis.

A pilot hole with a 1- to 2-mm cylindrical burr followed by a 2.4-mm drill allows drilling of the lateral mass under fluroscopic control. Obtaining bicortical purchase improves biomechanical stability. The ideal starting point is the midpoint of the C1 lateral mass. The vertebral artery passes laterally and the spinal canal medially.

According to a study by Simsek et al, the ideal amount of medial angulation is 13.5º ± 1.9º, with a maximum medial angulation of 29.4º ± 3º; further medial angulation will result in penetration of the spinal canal.[30]  The ideal sagittal angle is 15.2º ± 2.6º, with a maximum cephalic angle of 29.6º ± 2.6º. Higher trajectories will result in screw penetration into the atlanto-occipital joint.

Neurovascular structures of concern include the vertebral artery laterally and superiorly and the internal carotid artery anteriorly. Careful analysis of preoperative imaging studies must be undertaken to recognize anomalous path of the vertebral artery

Postoperative Care

Mobilization after C1 fixation, C1-C2 fixation, or occipitocervical instrumentation and fusion is generally possible on the day of surgery or postoperative day 1. In the polytrauma patient, mobilization may depend on the coexisting injuries. A hard cervical collar is generally utilized for comfort and support.

Surgical drains are removed after output decreases a day or two after surgery. Incentive spirometry is encouraged on the day of surgery and as long as the patient remains hospitalized. Routine deep vein thrombosis (DVT) prophylaxis is performed by mechanical means. If there is a history of DVT or multiple risk factors for DVT, then anticoagulation can generally be started on postoperative day 1.

Complications

Patients with upper cervical instability are at risk for death; this risk is increased if the injury is not identified and recognized. Neurologic damage at this level could make the patient dependent on a ventilator; thus, extreme care is necessary in handling these patients during fracture healing.

Associated injuries to the occipitoatlantoaxial complex (C0-C2) must be considered and included in the treatment plan. Devastating neurologic injuries may develop as a consequence of vascular embarrassment resulting from the instability of these injuries.

C1 lateral mass fractures with displacement can result in settling of the occipital condyle and a cock-robin deformity of the head neck clinically. This usually necessitates complex reconstruction with occipital-to-subaxial fusion.

Long-Term Monitoring

Patients in the cervical collar or halo will require at least 8 weeks—most likely, 12 or more weeks—of immobilization until healing is documented on radiographs. This period is followed by one in which the patient is placed in a collar to protect the neck while he or she is being weaned from the halo and while the neck is gradually being rehabilitated in terms of intrinsic muscle stability and range of motion.