Youjeong Kim, Maneesh Bawa, and John G. Heller
DEFINITION
The term atlantoaxial instability encompasses a number of varied conditions that compromise the normal function of the C1–2 joint, resulting in either pain, spinal cord dysfunction, or the threat thereof.
Atlantoaxial instability can result from trauma, including rupture of the transverse ligament, odontoid fracture, or Jefferson fracture. Nontraumatic causes include inflammatory arthropathy, osteoarthritis, congenital anomalies, rotatory subluxation, tumor, and infection.
Several methods have been described for stabilizing the atlantoaxial complex, including wiring techniques, transarticular screw fixation, and, more recently, articular mass screws.
We describe our technique for transarticular screw fixation and articular mass screw and rod construct to achieve atlantoaxial arthrodesis.
ANATOMY
The first cervical vertebra, or the atlas, is unlike any other in that it lacks a vertebral body and spinous process. It consists of an anterior and posterior arch connected by two articular masses, forming a ring that pivots about the odontoid process of C-2 (FIG 1A).
On each side of the cranial surface of the C1 posterior arch there is a groove for the vertebral artery, the first cervical nerve, and their associated venous complex. In a small subset of the population, this groove is covered by an arch of bone, the ponticulus posticus. The resulting foramen is identified as the arcuate foramen15 (FIG 1B).
The articular masses of C1 give rise to the superior and inferior articular facets, which are broad and articulate with the occipital condyles superiorly and the axis inferiorly. A synovial joint also is located between the posterior aspect of C-1 and the odontoid process of the axis.
The axis (C2) has thicker laminae and a larger bifid spinous process than a typical cervical vertebra. It is characterized further by an odontoid process that projects upward from the vertebral body. Lateral to the odontoid process, or dens, are the sloping superior articular surfaces, which articulate with the inferior articular facets of C1, forming the atlantoaxial joint. The C2 pedicle can be identified in a zone between the lamina and vertebral body, projecting superomedially (FIG 1C,D).
C1–2 articulation: The C1–2 complex is composed of three articulations, two laterally comprised of the inferior C1 and superior C2 articular facets, and one anteriorly between the dens and the posterior aspect of the anterior C1 arch.
The C1–C2 articulation allows for 47 degrees of rotation to either side, which is approximately 50% of the lateral rotation of the entire cervical spine.16 Panjabi and associates14 showed that in the healthy spine C1–2 flexion is 11.5 degrees, extension is 10.9 degrees, lateral bending 6.7 degrees, and axial rotation to each side 38.9 degrees.
The vertebral artery, which is the first branch of the subclavian artery medial to the anterior scalene muscle, ascends behind the common carotid artery. It then ascends through the foramina transversaria from C6 to C1. After traversing through the foramina transverseria at C1, the artery takes a sharp turn medially and posteriorly to course behind the C1 articular mass along the groove in the posterior arch of C1. It then passes through the posterior atlanto-occipital membrane before ascending through the foramen magnum as it merges with its counterpart to form the basilar artery (FIG 1E,F).
The C1 nerve root, or the suboccipital nerve, exits cranial to the posterior arch of C1 and innervates muscles of the suboccipital triangle. The C2 nerve root, or greater occipital nerve, exits between the posterior arches of C1 and C2, posterior to the superior C1–2 articulation. It does not exit through a true foramen like the remaining subaxial cervical nerve roots. It traverses inferior to the obliquus capitus inferior to ascend through the semispinalis capitus to lie superficial to the rectus capitus. Injury to the greater occipital nerve can lead to dysesthesia of the posterior scalp and be troublesome to patients.
PATHOGENESIS
Stability of the C1–2 articulation relies heavily on its ligamentous restraints, including the transverse, alar, and apical ligaments, and the facet capsules. Trauma may disrupt these ligamentous restraints. Also, with the advanced degeneration found in arthritic conditions, these ligamentous structures may become incompetent.
Up to 3 mm of anterior translation of C1 on C2, as measured by the anterior atlantodental interval (AADI) on a lateral cervical radiograph, is normal. An atlantodental interval of 3.5 to 5 mm in an adult indicates potential damage to the transverse ligament, whereas an interval greater than 5 mm indicates probable injury to the transverse ligament and accessory ligaments (FIG 2A).
In cases of trauma, an atlantodental interval greater than 3.5 mm probably is an indication for further evaluation, and most likely requires C1–2 arthrodesis.
In patients with inflammatory arthropathy, including rheumatoid arthritis, a canal diameter identified as posterior atlantodenal interval (PADI) smaller than 14 mm is associated with a worse outcome and is an indication for decompression and fusion.1 The exact anterior atlantodental interval measurement is not as relevant in these patients as with trauma patients.
Fractures that involve the osseous structures of C1 and C2 also may result in atlantoaxial instability and require arthrodesis (FIG 2B).
FIG 1 • A. The atlas consists of an anterior and posterior arch connected by two articular masses. B. AP view of first and second cervical vertebrae. Anterior (C) and posterior (D) views of the axis, demonstrating the odontoid process projecting upward from the vertebral body. The pedicle connects the lamina and the vertebral body, projecting superomedially. The pars interarticularis lies between the superior and inferior articular processes. E. The vertebral artery ascends through the foramina transversaria from C6 to C3. It takes a turn laterally through C2 underneath the pars interarticularis. Once it traverses the transverse foramen at C1, it turns medially and lies on the superior surface of the C1 ring. F. After passing medially on the superior surface of the C1 ring, the vertebral artery passes through the foramen magnum and merges with its counterpart to form the basilar artery.
NATURAL HISTORY
In the event of C1–2 trauma, the potential need for surgery arises in the setting of ligamentous instability, fractures, or a combination of the two. Atlantoaxial instability due to rupture of the transverse ligament represents a threat to the cervical spinal cord with a low likelihood of successful healing. Thus C1–2 fusion is indicated.
Transverse ligament disruption in association with a Jefferson fracture may represent an exception to this rule, in that successful nonoperative fracture treatment (halo-vest) can lead to a “stable” C1–2 segment on flexion–extension radiographs.
Fractures of the odontoid process may represent a primary indication for C1–2 fusion if nonoperative means (eg, halovest immobilization) cannot obtain or maintain an appropriate reduction, or if a patient elects surgery to avoid the use of a halo. Displaced odontoid fractures have an increased likelihood of resulting in either nonor malunion in the cases of type II and III fractures, respectively (FIG 3A).
Primary atlanto-axial osteoarthritis is quite painful and responds poorly to nonoperative means. C1–2 fusion affords a high likelihood of symptom relief (FIG 3B).
Cervical myelopathy due to either rheumatoid pannus or pseudo-pannus formation, as seen in older individuals with extensive subaxial spondylosis and spontaneous fusion, is unlikely to improve without surgery (FIG 3C).
C1–2 instability due to rheumatoid arthritis may be neither symptomatic nor a neurologic threat. Thus, in this case, an ADI exceeding 3.5 mm is not, by itself, an indication for surgery. A PADI of less than 14 mm or the presence of myelopathy is a poor prognostic sign and indicates the need for fusion. Painful C1–2 rheumatoid involvement in the face of adequate medical therapy also indicates the need for fusion. Progressive C1–2 subluxation, especially with cranial settling, also has an unfavorable natural history. C1–2 fusion in this instance will obviate the need for a future occipitocervical fusion, which has a less favorable influence on the overall condition of the cervical spine (FIG 3D,E).
FIG 2 • A. An anterior atlantodental interval greater than 5 mm indicates likely injury to the transverse ligament and, in the setting of trauma, necessitates operative stabilization. B. An avulsion (arrow) of the transverse ligament from the ring of C1 indicates instability and may require arthrodesis of C1–2.
The natural history of asymptomatic C1–2 instability associated with miscellaneous conditions such as os odontoideum (FIG 3F) and Down syndrome is less clear. When such patients have symptoms, myelopathic signs, or an insufficient PADI, the potential benefits of a C1–2 fusion probably outweigh the risks of the natural history. The patient's age, lifestyle, and activity level also must be considered in determining the need for surgery.
HISTORY AND PHYSICAL FINDINGS
A complete history and physical examination, including a thorough neurologic examination, should be performed when evaluating a patient with C1–2 pathology. The complaints offered will vary with the presentation (eg, trauma, inflammatory arthritis, developmental, congenital).
Patients with a traumatic injury may complain of isolated pain but also may present with neurologic deficits. A low threshold of suspicion should be maintained for patients with blunt trauma to the head or face, or with known noncontiguous fractures of the spine.
FIG 3 • A. Displaced odontoid fractures (type 2) have a higher likelihood of a nonunion and may require a primary C1–2 fusion. B. Joint space narrowing is a sign of C1–2 osteoarthritis and responds poorly to nonoperative management. C. Pseudo-pannus formation behind the dens in patients with rheumatoid arthritis can lead to cervical stenosis and myelopathy. It rarely improves without surgery, but will dissolve after C1–2 fusion. Flexion (D) and extension (E) lateral radiographs demonstrate C1–2 instability in a patient with rheumatoid arthritis. F. Os odontoideum is another condition associated with instability in which part of the dens is not attached to the axis body.
Some patients with rheumatoid arthritis may complain only of axial neck pain, whereas others may present with deteriorating gait and bilateral hand numbness or clumsiness without significant neck pain.
Patients with primary atlantoaxial arthritis will complain of severe neck and head pain, most often unilateral, with varying degrees of refusal to rotate their head, especially ipsilaterally toward the pain. Locking or crepitation of the affected joint may be both audible and palpable.
Physical examination should include the following:
Active self-limited rotation of the head, especially toward the side of the pain. Normal rotation is up to 50 degrees of rotation to either side. C1–2 pathology often causes pain that limits rotation.
Palpation of the suboccipital area near the interval between the posterior arches of C1 and C2 will elicit pain. When asked, the patient often can point to the source of their pain.
Response to traction vs. compression combined with passive C1–2 rotation. The patient is examined supine with his or her head resting comfortably on a pillow. Passive lateral head rotation is measured with slight manual traction. In cases of C1–2 arthritis, this maneuver should provide more motion and less pain than similar motion with an axial vertex load. With slight manual traction, head rotation is increased, whereas an axial vertex load will cause pain and result in decreased rotation.
In the setting of potential traumatic instability, however, these examination maneuvers are not applicable. The cervical spine must be immobilized until the radiographic and CT findings are known.
IMAGING AND OTHER DIAGNOSTIC STUDIES
In the setting of blunt trauma, plain radiographs of the cervical spine, specifically the upper cervical spine, have been shown to be inadequate.
McCulloch et al12 reported that plain radiographs have a sensitivity of 52%, a specificity of 98%, a positive predictive value (PPV) of 81%, and a negative predictive value (NPV) of 93%, whereas helical CT had a sensitivity and specificity of 98%, PPV of 81%, and NPV of 93%.
They concluded that although helical CT has limited ability to detect pure ligamentous injury, it is superior to plain radiographs when evaluating patients with high-energy trauma for cervical spine fractures.
Other means may be required to evaluate potential ligamentous instability, such as an MRI scan or lateral flexion–extension radiographs under certain circumstances.
CT with sagittal and coronal reconstruction is done routinely for diagnostic purposes as well as for preoperative planning.
Fractures of either C1 or C2 indicate a significant likelihood of additional cervical spine fractures. As many as 50% of C1 fractures may be associated with other fractures.
A vertebral artery angiogram is recommended when there is any question of acute injury or history of injury to the vertebral arteries. A unilateral vertebral artery injury rarely is symptomatic because of sufficient collateral flow through the contralateral vertebral artery as well as the circle of Willis. A patient with a vertebral artery injury who presents with neurologic deficits due to a concomitant spinal cord injury may be especially difficult to diagnose clinically.
FIG 4 • Coronal reconstruction of a CT angiogram demonstrating occlusion of flow through the left vertebral artery (right side of the image) in a patient with a C4–5 facet fracture-subluxation.
We recommend imaging with either an angiogram or an MRA in all patients presenting with a significant flexion– distraction injury, fracture that extends into the transverse foramen, or facet dislocation (FIG 4).
When discovered, this should be treated with prompt anticoagulation to prevent thromboembolic complications. If a surgical procedure is necessary, anticoagulation is stopped before and restarted after surgery.3
DIFFERENTIAL DIAGNOSIS
Rheumatoid arthritis: instability, pannus accumulation, cranial settling.
Degenerative osteoarthritis
Trauma: odontoid fracture, Jefferson fracture, transverse ligament rupture
Tumor
Infection
Atlantoaxial rotatory subluxation: recurring subluxation, irreducible and fixed subluxation
Miscellaneous: Down syndrome, os odontoideum
NONOPERATIVE MANAGEMENT
In most instances a hard collar is not adequate for immobilizing an unstable C1–2 articulation, but one may be considered in an elderly patient who is not a surgical candidate and otherwise cannot tolerate a halo or Minerva vest (Variteks, Istanbul, Turkey).
For certain fractures, use of a halo-vest may be appropriate, and the patient is treated in the orthosis for 3 months. It is a time-tested “nonoperative” option with well-defined success/failure rates.
Some patients may require a halo for postoperative immobilization, depending on the fixation quality, the anticipated level of patient compliance with a hard collar, and other unusual circumstances.
SURGICAL MANAGEMENT
Several different techniques have been described for successful posterior C1–2 fixation and fusion.
Before Jeanneret and Magerl10 described the transarticular screw technique, posterior fixation was accomplished with Gallie's sublaminar wiring and grafting6 or by the Brooks wiring method.2
Some of the newer methods include the C1 articular mass and C2 pedicle screw and rod construct described by Goel and Laheri,7 and the use of a C2 interlaminar screw combined with C1 articular mass screw and rod construct.8
Biomechanically, the Magerl technique of transarticular fixation provides the best stability compared with traditional wiring methods, but it may be technically more demanding than either the Brooks or Gallie method of fixation.
Malreduction of C1–2, anomalous position or size of the vertebral arteries, and collapse of the lateral masses of C2 are relative contraindications to the use of the transarticular screw method because of the risk for inadvertent penetration of the vertebral artery.
Preoperative Planning
All imaging studies should be reviewed with regard to osseous anatomy as well as the course of the vertebral artery. Preoperative CT scanning with reconstructed images in the sagittal plane or in the plane of the transarticular screw is necessary to view the pertinent anatomy and to avoid injury to the vertebral artery.
Confirmation of an anatomic reduction of C1–2 intraoperatively is preferable to avoid vertebral artery injury, neurologic injury, and inadequate bony purchase of the screw. However, mild anterior displacement of C1 on C2 is well tolerated and may facilitate fixing the C1 lateral mass, as long as the PADI remains large enough to accommodate the spinal cord.
C1–2 reduction in most trauma conditions can be achieved with longitudinal traction in the awake patient. After successful reduction, a halo vest may be applied to facilitate prone positioning of the patient under anesthesia.
FIG 5 • The patient is positioned prone with the head flexed and posteriorly translated to allow the instruments to achieve the correct C1–2 trajectory. It is important to confirm reduction of an unstable C1–2 joint radiographically before proceeding further.
Positioning
The patient is placed in the prone position on bolsters with the head rigidly held in place using Mayfield tongs, or previously placed halo. The shoulders and arms are tucked at the patient's side.
The table is adjusted into a reverse Trendelenburg orientation, with the knees bent (FIG 5). The shoulders can be depressed with wide tape if necessary to obtain a true lateral view of the C1–2 complex.
After the patient is positioned, the proper alignment of an unstable C1–2 joint should be confirmed radiographically before proceeding further. It is important to confirm that the head is in neutral rotation, to avoid an iatrogenic torticollis.
TECHNIQUES
EXPOSURE
A midline posterior skin and subcutaneous incision is made from the occiput to the spinous process of C7. The deep subperiosteal dissection is confined from the upper edge of C1 to the inferior margin of the C2 laminae (TECH FIG 1).
The longer skin incision permits the correct trajectory of the drill guides, which often are tunneled through the posterior cervical extensor muscles.
A shorter skin incision could be used, with the drills, guides, and other instruments passed through percutaneous stab wounds, but we have found the cosmetic results less desirable.
Muscular infiltration with local anesthetic and epinephrine will reduce bleeding.
TECH FIG 1 • The posterior arch of C1 down to the inferior margin of the lamina of C2 is exposed with meticulous subperiosteal dissection.
MAGERL METHOD OF C1-2 TRANSARTICULAR SCREW FIXATION 10
Sagittal and axial CT images are scrutinized preoperatively. The isthmus of the C2 pars must measure at least 4.5 mm in height and width to accommodate a transarticular screw.11 An abnormally large or malpositioned vertebral artery might lead to increased risk of harm to this important structure.
C1–2 reduction and the ability to obtain a true lateral view of C1–2 with a fluoroscope are confirmed.
A midline incision is made from the occiput far enough caudally to allow a steep enough angulation of the drill and other instruments.
Posterior C1 and C2 exposure is carried out laterally to visualize the superior and medial surfaces of the C2 pars. Care also should be taken to avoid disturbing the C2–3 facet capsule.
The starting point for the transarticular screw is at the posterior cortex of the C2 inferior articular process 2 mm cephalad and 2 to 3 mm lateral to the medial border of the C2–3 facet joint.
The starting point is confirmed with a direct lateral C-arm image and marked with a 2-mm burr to provide a secure starting point for the tip of the drill bit. Caudal–cranial angulation is determined via lateral Carm fluoroscopic guidance. The sagittal plane orientation is confirmed visually with reference to the superior and medial sufaces of the C2 pars. A Penfield 4 dissector can be placed on the dorsal surface of the C2 pars to serve as a guide on the lateral fluoroscopy view.
The K-wire is directed superiorly along the C2 pars while aiming toward the anterior arch of C1 as seen on the lateral fluoroscopic images, with slight medial angulation of 0 to 10 degrees (TECH FIG 2A,B).
We recommend leaving the drill bit or K-wire in place on the initial side to transfix the C1–2 joint, then proceeding to the opposite side. The screw on the second side is inserted before returning to the initial side to remove the drill bit, then tap and insert the second screw. This avoids any problems with loss of reduction (TECH FIG 2C–F).
Bone grafting is performed with autologous iliac crest. After careful decortication of the posterior arches, a modified Gallie technique is employed using either heavy suture or braided titanium cable to secure the graft in place (as described under Gallie Method of Sublaminar Wiring and Grafting).
The extensors at C2 are repaired with drill holes placed through the spinous process.
TECH FIG 2 • A,B. The guidewire is placed superiorly through the pars, aiming toward the anterior arch of C1 on lateral fluoroscopic images. With the first guidewire in place, a second guidewire is placed on the other side. The K-wire is overdrilled with a drill bit (C,D) and tapped, and the screw is placed on the second side (E) before the same is done on the first side. F. Postoperative radiograph of transarticular screw fixation in a patient who sustained a C1–2 fracture-dislocation.
GOEL METHOD OF C1–2 ARTICULAR MASS FIXATION 7
The ponticulus posticus is a common anomaly that can easily be mistaken for a broad posterior arch of the atlas, and the lateral radiograph must be reviewed to check for the presence of an arcuate foramen to avoid injuring the vertebral artery.17
The starting point for the C1 screw is in the middle of the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral mass. The entry point is marked with a 2-mm high-speed burr.
The C2 nerve root is retracted in a caudal direction for proper screw placement. If divided proximal to the dorsal root ganglia, the patient may experience troubling neuralgia and numbness postoperatively.
The initial drill hole is made in a straight or slightly convergent trajectory in the sagittal plane and parallel to the plane of the C1 posterior arch in the coronal plane, with the tip of the drill aimed toward the anterior arch of C1 (TECH FIG 3A).
The hole is tapped and measured, and a 3.5-mm polyaxial screw of appropriate length is placed so that the screw head stays above the bony surface of the lateral mass to avoid any irritation to the greater occipital nerve.
Care should be taken when dissecting around the C1–2 articulation to avoid excessive bleeding from the epidural venous plexus in this area. Hemostasis can be achieved using bipoloar electrocautery, powdered Gelfoam with thrombin, and cotton pledgets.
The center of the lateral mass of C1 is the ideal exit point of the C1 lateral mass screw, and the proximity of the internal carotid artery (ICA) places it in danger when placing a bicortical screw. The ICA can vary in location from side to side and may be within 1 mm of the ideal exit point of a bicortical transarticular screw or a C1 lateral mass screw.4
Medial angulation of the screw in the lateral mass of C1 may increase the margin of safety for the ICA, but care should be taken to avoid penetrating the occipitocervical joint.
TECH FIG 3 • Postoperative CT scan (A) and lateral radiograph (B) of a patient with a displaced, kyphotic, chronic C2 fracture who underwent C1–2 posterior fusion using C1 articular mass screws and C2 pars screws.
The starting point of the C2 pedicle is in the midline of the C2–3 facet joint, 3 to 5 mm cranial to the C2–C3 articulation. The trajectory is 25 degrees of medial convergence and is aimed 25 degrees cephalad, while keeping in mind that individual anatomy will vary.
A no. 4 Penfield dissector is used to feel the medial border of the C2 pars interarticularis, and the superior and medial aspects of the isthmus are palpated during the drilling process.
The drilled hole is then palpated with a blunt ball-tipped probe. The hole is tapped, and a 3.5-mm polyaxial screw is inserted bicortically.
The polyaxial screw heads are connected with two rods. If necessary, a reduction of the C1–2 articulation is performed before fixation with the rods.
The posterior elements of C1 and C2 are decorticated, and a corticocancellous H-graft is secured using a modified Gallie technique (TECH FIG 3B).
The extensors at C2 are repaired using drill holes through the spinous process.
BROOKS METHOD OF WIRE FIXATION
Brooks wiring is the most reliable of the traditional wire fixation methods. It does not provide as much stability as other screw options, however, and so must be used in conjunction with significant postoperative immobilization, often a halo-vest, for optimal likelihood of fusion.2 It also requires passing sublaminar wires at C2, which can be technically demanding.
Midline posterior subperiosteal exposure of C1 and C2 laminae is carried out with careful attention to dissect from midline laterally at C1 to prevent injury to the vertebral artery. The occipital nerves emerge through the interlaminar space between C1 and C2.
The ligamentum flavum between C1 and the occiput and also between C1 and C2 is sharply divided. A Woodson instrument is used to confirm that there are no dural adhesions in the sublaminar space.
Although Brooks originally described use of two doubled 20-gauge stainless steel wires passed under each side of the arch of C1 followed by C2 with the aid of a no. 2 Mersilene suture in a cephalad-to-caudal direction, we routinely use pairs of braided titanium cables rather than stainless steel wire.
After the cables are passed with a loop at the end, two full-thickness rectangular bone grafts measuring approximately 1.25 × 3.5 cm are taken from the iliac crest. The sides of each graft are beveled to fit in the interval between the C1 and C2 laminae and placed on each side.
The bone grafts are then held in place by securing the cables (TECH FIG 4).
TECH FIG 4 • Brooks wiring technique.
GALLIE METHOD OF SUBLAMINAR WIRING AND GRAFTING
The Gallie method is less stable than the Brooks method and is relatively contraindicated in the presence of any posterior C1–2 instability.6 It also requires significant postoperative immobilization.
The sublaminar cable is passed under the laminae of C1 and C2. We use a suture for this technique when the Gallie graft is employed in conjunction with Magerl transarticular fixation, because the Gallie configuration is relied on for maintenance of graft position, not for mechanical stability.
A corticocancellous bone graft from the iliac crest (FIG 5A) is taken and placed with the cancellous side facing down on the posterior elements after the cortical bone has been burred to reveal a nice bleeding cancellous bed (TECH FIG 5B). The small grooves are placed on the superior and inferior edges of the graft to hold the sutures in place.
The cable is tightened, and the graft is secured (TECH FIG 5C).
TECH FIG 5 • A. The posterior arches of C1 and C2 are decorticated. B. A corticocancellous graft is taken from the iliac crest. This is fashioned into an H shape, and the cancellous side is placed facing down on the decorticated posterior elements of C1–2. C. A modified Gallie technique is used to secure the graft in place.
POSTOPERATIVE CARE
Whereas patients undergoing the Brooks or Gallie procedure obtain a maximal fusion rate with postoperative halovest immobilization, the modern screw fixation methods yield fusion rates in excess of 90% with only cervical collars worn for 6-12 weeks.
The type of collar used and duration of wear should be in accordance with surgeon judgment about host bone, security of fixation, anticipated patient compliance, etc.
OUTCOMES
Jeanneret and Magerl10 achieved solid fusion in 13 patients stabilized with the transarticular screw technique.
McGuire and Harkey13 showed solid fusion in 8 patients using a transfect screw technique.
Fielding and associates5 achieved fusion in 45 of 46 patients with fractures using the Gallie technique.
Brooks and Jenkins2 used a C1–2 sublaminar wiring technique to achieve fusion in 14 out of 15 patients.
Harms9 reported fusion in all 37 patients with C1 lateral mass and C2 pedicle minipolyaxial screw and rod construct.
Cost-effectiveness: The Goel C1–2 articular mass method has been popularized by Harms, and is offered as less risky than the Magerl method with respect to the vertebral artery. However, in the right patient, the Magerl method has proved to be quite safe. The cost of two 4.0-mm cannulated bone screws is substantially less than four polyaxial screws and a pair of rods.
COMPLICATIONS
Vertebral artery and internal carotid artery injuries
Infection
Malpositioned screw
Nonunion
C2 neuralgia
C1–2 hyperextension with Brooks or Gallie procedure if the C1 and C2 arches are compressed together.
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