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Kern Singh, MD, Vincent J. Devlin, MD, Justin Munns, MD, Alexander R. Vaccaro, MD, PhD O

1. What are the indications for use of cervical spinal instrumentation?

• To immobilize an unstable segment • To correct spinal deformity

• To promote bony union • To decrease the need for external immobilization

• To improve soft tissue healing

2. How are the various types of cervical spinal implants classified?

No universal classification exists. Cervical spinal implants may be classified descriptively by:

• Location of implant: Anterior spinal column versus posterior spinal column

• Spinal region stabilized: Occipitocervical (O-C1); odontoid (C2); atlantoaxial (C1-C2); subaxial (C3-C7); cervicothoracic (C7-T2)

• Method of osseous attachment: Screw, hook, wire, cable

• Type of longitudinal member: Rod, plate, other (e.g. rib graft)

3. What types of cervical spinal implants are most commonly utilized today?

Posterior cervical instrumentation most commonly involves use of rod-screw systems. Screws may be placed in the occiput, C1 (lateral mass), and C2 (pedicle vs. pars vs. translaminar screws). In the subaxial cervical region, lateral mass screws are most commonly used at the C3 to C6 levels, whereas pedicle screws are typically used at C7 and distally in the thoracic region. Anterior cervical plates are the most commonly used implants in the C3 to C7 region. Reconstruction of the anterior spinal column following discectomy or corpectomy may be performed with bone graft or fusion cages (Fig. 28-1A and B).

Figure 28-1. A, Posterior occiput to C2 spinal instrumentation, B, Posterior spinal instrumentation C3 to T1 and anterior reconstruction with C3-C4 allograft bone graft and titanium mesh cage from C4-C7.

4. What are the indications for use of spinal instrumentation in the occipitocervical region?

• Ligamentous instability • Select skeletal dysplasias

• Select odontoid fractures • Arnold-Chiari malformations

Rheumatoid arthritis (basilar invagination) • Select metabolic bone diseases

5. What implant options are available for use at the occipitocervical junction?

• Anterior options: Implants are infrequently placed in this region because it is challenging to achieve surgical exposure here. Bone graft or cages are used to reconstruct osseous defects. Occasionally specialized plates (e.g. C2 to clivus plate) or C1-occipital condyle screws are used

• Posterior options: Rod-screw systems are the most commonly used implant. A hybrid rod-plate combination is an additional option. Contoured rods with wire or cable fixation are an option for special circumstances. Bone grafts and wires may be used in conjunction with other implants but are rarely used in isolation because they are not sufficiently stable to permit patient mobilization without extensive external immobilization, such as a halo device

6. Where can a surgeon safely place screws in the occiput when performing posterior occipitocervical instrumentation?

Occipital bone is thickest and most dense in the midline below the external occipital protuberance (inion). This region provides an excellent surface for screw purchase. Occipital bone thickness decreases laterally and inferiorly from the inion. Screws should be placed below the superior nuchal line that overlies the transverse sinuses, which can be injured during drilling or screw placement (Fig. 28-2).

Figure 28-2. Safe placement of occipital screws is in the region adjacent to the external occipital protuberance and below the superior nuchal line. (DePuy Spine, Inc. All rights reserved.)

Superior nuchal line

Superior nuchal line

Figure 28-2. Safe placement of occipital screws is in the region adjacent to the external occipital protuberance and below the superior nuchal line. (DePuy Spine, Inc. All rights reserved.)

foramen magnum

7. How are occipital screws connected to a rod system?

The surgeon has several options including:

• Modular midline screw-plates: A midline plate permits screw purchase in the thick midline bone and permits minor adjustments to facilitate linkage to an independent dual rod construct (Fig. 28-3A)

• Hybrid rod-plate fixation: Plates attach laterally to the midline of the occiput and connect with rods for fixation in the cervical spine distally. Specialized implants consisting of a single rod that transitions to a plate are available (Fig. 28-3B)

• Rod with specialized connectors: Occipital screws are linked to rods via offset screw-rod connectors (Fig. 28-3C)

Figure 28-3. Occipital screw linkage options. A, Midline screw-plate. B, Hybrid rod-plate. C, Rod with specialized connectors. (Synthes Spine. All rights reserved.)

8. How is posterior screw fixation performed at C1?

Two basic techniques are utilized:

• In the first technique, the screw is placed directly in the lateral mass of C1. The entry point is at the junction of the C1 lateral mass with the undersurface of the C1 posterior arch (Fig. 28-4A). The extensive venous plexus in this region makes dissection challenging. In addition, the C2 nerve root is in proximity to the screw entry point and must be retracted distally. A modified technique involves creation of a notch on the undersurface of the C1 arch to facilitate drill/screw placement to minimize dissection in the region of this venous plexus. Screws are directed with 5 to 10 degrees of convergence and parallel to the C1 arch (Fig. 28-4B)

Figure 28-4. A, Posterior landmark for C1 screw placement. B, C1 screw trajectory in the axial plane. (From Vaccaro AR, Baron EM. Spine Surgery: Operative Techniques. Philadelphia: Saunders; 2008, with permission.)

• The second technique uses an entry point on the C1 arch and places a screw through the pedicle analog of C1 and into the C1 lateral mass. The vertebral artery is at greater risk with this technique and one must not mistake a common anomaly in which a bony bridge, the arcuate foramen, overlies the vertebral artery or the screw will injure the vertebral artery. This osseous anomaly has been termed the ponticulus posticus. With either technique, excessive superior C1 screw angulation will violate the occiput-C1 joint. An excessively long C1 screw may potentially compromise the internal carotid artery or hypoglossal nerve.

9. What are the options for achieving screw fixation in C2?

Three options exist: C2 pars screws, C2 pedicle screws, and C2 translaminar screws.

10. How is a C2 pars screw placed?

The pars interarticularis is defined as the portion of the C2 vertebra between the superior and inferior articular processes. The screw entry point is 3 to 4 mm superior and 3 to 4 mm lateral to the inferior medial aspect of the C2-C3 facet joint. Screw trajectory is parallel to the C2 pars interarticularis with approximately 10 degrees of medial angulation (Fig. 28-5).

Figure 28-5. C2 pars screw placement. A, Lateral view. B, Anteroposterior view. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

11. How is a C2 pedicle screw placed?

The C2 pedicle is defined as the portion of the C2 vertebra connecting the posterior osseous elements with the vertebral body and consists of the narrow area between the pars interarticularis and the vertebral body. The entry point is approximated by the intersection of a vertical line through the center of the C2 pars interarticularis and a horizontal line through the center of the C2 lamina. The screw entry point is in the cranial and medial quadrant defined by these landmarks. The screw is placed with 15 to 30 degrees of medial angulation and parallel to the superior surface of the C2 pars interarticularis. The medial wall of the C2 pars can be palpated as an additional guide to placement (Fig. 28-6).

Figure 28-6. C2 pedicle screw placement. A, Lateral view. B, Anteroposterior view. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

Figure 28-6. C2 pedicle screw placement. A, Lateral view. B, Anteroposterior view. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

12. Compare and contrast a C2 pedicle screw with a C2 pars screw.

The C2 pedicle screw trajectory is more superior and medial than the pars screw and has less risk of injury to a highriding vertebral artery. A longer screw length may be achieved using a C2 pedicle screw than a C2 pars screw. A C2 pedicle screw can be safely placed with bicortical screw purchase. A C2 pars screw is typically a unicortical screw that stops short of the transverse foramen to prevent potential injury to the vertebral artery.

13. When might a C2 translaminar screw be preferred over alternative C2 screw fixation methods?

A translaminar screw is preferred when the trajectory for placement of a C2 pars or pedicle screw is compromised by an aberrantly coursing vertebral artery or aberrant osseous anatomy. The technique is straightforward and consists of creating a small entry window at the junction of the C2 spinous process and lamina. A blunt probe or hand drill is used to create a pathway for screw placement in the cancellous bone of the contralateral lamina. The process is repeated on the opposite side for placement of a second screw that crosses above or below the initial screw. An additional window can be created at the facet-laminar junction to visualize screw-exit to ensure that the screw has not inadvertently violated the inner cortical surface of the lamina (Fig. 28-7).

Figure 28-7. C2 translaminar screw placement technique. A, Creation of screw tract, B, Axial CT view after screw placement, C, Anteroposterior radiograph after screw placement. (A from Jea A, Sheth R, Vanni S, et al. Modification of Wright's technique for placement of C2 translaminar screws: technical note. Spine J 2008;8:656-60, with permission.)

Figure 28-7. C2 translaminar screw placement technique. A, Creation of screw tract, B, Axial CT view after screw placement, C, Anteroposterior radiograph after screw placement. (A from Jea A, Sheth R, Vanni S, et al. Modification of Wright's technique for placement of C2 translaminar screws: technical note. Spine J 2008;8:656-60, with permission.)

14. What are the indications for spinal implant placement in the atlantoaxial (C1-C2) region?

Atlantoaxial instability due to traumatic etiologies (e.g. unstable odontoid fractures), midtransverse ligament disruption, odontoid nonunion, an unstable os odontoideum, or nontraumatic disorders, such as rheumatoid arthritis, congenital malformations, and metabolic disorders.

15. What are the types of implants most commonly used to stabilize the atlantoaxial (C1-C2) joint?

C1-C2 stabilization is most commonly performed from a posterior approach using C1-C2 transarticular screws or C1-C2 screw-rod constructs. Posterior wire/cable techniques or rod-clamps are less frequently utilized. Anterior placement of transarticular screws is a specialized technique, which is occasionally used to salvage failed posterior C1-C2 fusions and for unique cases.

16. Describe the technique for posterior C1-C2 transarticular facet screw fixation.

The starting point for a transarticular screw is 3 to 5 mm above the C2-C3 facet joint and as medial as possible without breaking through the medial aspect of the C2 isthmus. Screw insertion can be guided by exposing the posterior C1-C2 facet complex and the isthmus of C2. The transarticular screws traverse the inferior articular process of C2, the isthmus of C2, the superior endplate of C2, the C1-C2 facet joint, and the lateral mass of C1 (Fig. 28-8).

Anteroposterior landmark

Anteroposterior landmark

Figure 28-8. C1-C2 transarticular screw placement. A, Lateral view, B, Anteroposterior view. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

Figure 28-8. C1-C2 transarticular screw placement. A, Lateral view, B, Anteroposterior view. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

17. What are some complications and challenges associated with transarticular screw placement?

The technique carries a risk of vertebral artery injury. It cannot be performed in up to 20% of patients due to vertebral artery anomalies. A preoperative computed tomography (CT) scan is required to look for a high-riding vertebral artery whose aberrant path is along the planned screw trajectory. Proper screw placement requires anatomic reduction of the C1-C2 joints prior to screw placement. Excessively long screws may injure the internal carotid artery or hypoglossal nerve. In addition, screw placement in patients with increased thoracic kyphosis is challenging because it is difficult to achieve the required screw trajectory in this setting.

18. Describe advantages of C1-C2 screw rod systems versus transarticular screws.

C1-C2 screw-rod systems have several advantages over transarticular screws for stabilization of the C1-C2 region. C1-C2 screw-rod systems are more versatile. Preoperative reduction of the C1-C2 joints is not required prior to instrumentation. In fact, the independent placement of screws in C1 and C2 can be used as a tool to facilitate reduction, which can be checked with fluoroscopy and modified without the need to replace screws. In addition, C1-C2 screw rod systems can be used in cases where transarticular screws are contraindicated (e.g. vertebral artery anomalies, severe kyphosis).

19. Why are transarticular screws or screw-rod constructs preferred over posterior wire or cable procedures?

Transarticular screws and screw rod techniques provide much greater stability than wire/cable techniques and avoid the need for postoperative external mobilization with a halo vest. In addition, these techniques are associated with higher rates of successful fusion than wire/cable techniques. Screw-based techniques avoid the risk of wire passage adjacent to the spinal cord. Screw-based techniques can be used in the presence of fractured or absent lamina, whereas wire/cable techniques rely on intact posterior elements to provide fixation.

20. Describe two common techniques used to achieve C1-C2 stabilization using wires or cables?

• The Gallie technique begins with sublaminar wire (double-looped) passage from caudal to cranial under the posterior arch of C1. Following wire passage, a structural corticocancellous iliac graft is harvested and shaped to conform to the posterior processes of C1 and C2. The two free ends of the wire are then passed through the leading wire loop and then passed over the graft and around or through the spinous process of the axis. The free ends of the wire are then twisted in the midline, thereby securing the graft position between C1 and C2 (Fig. 28-9A)

• The Brooks technique involves the passage of dual or doubled sublaminar wires (cables/tape) from caudal to cranial under the arch of C2 and then C1. Following the passage of the wire, two separate triangular or rectangular cortico-cancellous iliac grafts are harvested and placed over the posterior elements of C1 and C2. The ends of the wires on each side are then tightened together, thereby securing the position of the grafts (Fig. 28-9B)

Figure 28-9. C1-C2 wire techniques. A, Gallie technique, B, Brooks technique. (From McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005, with permission.)

21. Describe the fixation of choice for select odontoid fractures treated through an anterior approach.

One or two screws may be used to stabilize a type 2 odontoid fracture. The critical transverse outer diameter for the placement of two 3.5-mm cortical screws is 9 mm. Cadaveric biomechanical studies have demonstrated that one central screw, which engages the cortical tip of the dens, is just as effective as two screws. Two screws more effectively counter the rotational forces created by the alar ligaments. Single-screw options include the use of a single 4.5-mm cannulated Herbert screw or a single 3.5/4.0-mm standard lag screw (Fig. 28-10).

Figure 28-10. Odontoid screw fixation. Left, Lateral view. Right, Anteroposterior

Figure 28-10. Odontoid screw fixation. Left, Lateral view. Right, Anteroposterior

22. What are some contraindications for the use of odontoid screw fixation?

• Patients who possess anatomic obstructions to appropriate screw placement (e.g. short neck, excessive thoracic kyphosis, barrel chest deformity)

• Unfavorable fracture patterns (e.g. fracture obliquity in the same direction as screw placement—i.e., a sagittal plane fracture that courses posterior superiorly to anterior inferiorly, low type 3 odontoid fractures, fractures requiring a flexed neck position to maintain reduction)

• Poor bone quality (a pathologic fracture with compromised bone quality, significant osteoporosis)

23. What are the indications for posterior subaxial cervical instrumentation?

Fracture fusion and stabilization, posterior stabilization following an anterior nonunion, adjunctive stabilization following a long segment anterior fusion, or fusion and stabilization following a posterior decompression for cervical myelopathy.

24. Describe three techniques for placement of lateral mass screws.

Three commonly employed techniques for lateral mass screw placement (C3-C6) have been described by Roy-Camille, Magerl, and An and are summarized in Table 28-1. Laterally directed screws are not utilized at C2 due to concerns regarding vertebral artery proximity.

Table 28-1.

Recommended landmarks for lateral mass screw placement

1 TECHNIQUE

ROY-CAMILLE

MAGERL AN

Starting position Center (lateral mass)

1 mm medial and 1-2 mm 1 mm medial cephalad to the center to the center

Cephalad tilt

0

30 15

Lateral tilt

10

25 30

At C7, the lateral mass is frequently quite small, and a lateral mass screw risks causing C8 nerve root irritation. For this reason, pedicle screws are more commonly utilized at this level, although C7 lateral mass fixation remains a valid technique depending on individual patient anatomy (Fig. 28-11).

Figure 28-11. Techniques for lateral mass screw placement.

25. What is the role of pedicle screws in the cervical spine?

Pedicle screws are useful and relatively safe at the C2 and C7 levels. In the majority of patients, the vertebral artery enters the foramen transversarium of C6 and is not at risk with C7 pedicle screw placement. Pedicle screw placement at the C3 through C6 levels is not widely practiced in North America due to concern relating to the risk of vertebral artery injury.

26. Describe the most common technique used for C7 pedicle screw placement.

Most commonly, a laminoforaminotomy is created at C6-C7 to palpate and visualize the medial border of the C7 pedicle. Next, a small drill or pedicle probe can be used to cannulate the C7 pedicle while visualizing for a medial pedicle breech. This is followed by screw placement.

27. What are some advantages of lateral mass and pedicle screw fixation versus posterior wire or cable fixation?

Cervical lateral mass and pedicle screw fixation affords significantly increased stability in rotation and extension, compared with posterior wiring or cable fixation. Spinal implant fixation to the lateral mass and pedicles obviates the need for intact laminae or spinous processes, which are necessary for most wire/cable techniques. Rigid postoperative cervical immobilization is not required with screw fixation techniques. Loss of wire fixation, due to wire failure or bony pullout, is the most common complication associated with wire/cable techniques but is rarely seen with screw-based techniques.

28. What techniques have been described for use of wires and cables in the subaxial cervical region?

Wires or cables may be placed beneath the lamina (sublaminar), between adjacent spinous processes (interspinous or Rogers wiring), through the facet joints, or between the facet joint and the spinous process. The Bohlman triple-wire technique combines midline interspinous wiring with passage of separate wires through adjacent spinous processes, which are used to secure a corticocancellous bone graft to the decorticated posterior elements on each side of the spinous processes.

29. What are the indications for anterior cervical plating?

To decrease the incidence of graft or cage subsidence and dislodgement, to minimize kyphotic collapse of the fused interface, to improve fusion rates, and to minimize the need for postoperative external immobilization.

30. Describe the design features of the first anterior cervical plates.

The original Caspar (Aesculap Instrument Company) and Orozco (Synthes Spine) systems were non-constrained, load-sharing plates that required bicortical screw purchase. Due to the non-constrained nature of the screw plate interface, excessive motion at the screw plate junction occasionally led to screw loosening or pullout. Engagement of the posterior vertebral cortex was required to minimize screw loosening. This is technically challenging and an increased risk of neurologic injury is associated with this technique.

31. What solution was developed to address the difficulties associated with anterior cervical plates requiring bicortical screw purchase?

Because of the technical difficulty associated with bicortical screw purchase, constrained systems that firmly lock the screws to the plate were developed. The first solution was a plate system (cervical spine locking plate [CSLP]) that used a screw with an expandable cross-split head that locks into the plate after insertion of a small central bolt (Synthes Spine). Securing the screws to the plates allows a more direct transfer of the applied forces from the spine to the plate and improved construct stiffness without the need for bicortical screw purchase. Alternative methods were developed to secure the screw to the plate to prevent screw back-out and included a variety of screw head coverage mechanisms (ring locks, blocking heads, screw covers) (Fig. 28-12).

Figure 28-12. Anterior cervical locking plate (Synthes Spine). A, The screw head is locked to the plate by insertion of a conical bolt, thereby ensuring angular stability between the plate and the screws. B, Anterior cervical locking plate application after interbody fusion. Note that penetration of the posterior vertebral body cortex is not required to achieve a stable implant construct.

Figure 28-12. Anterior cervical locking plate (Synthes Spine). A, The screw head is locked to the plate by insertion of a conical bolt, thereby ensuring angular stability between the plate and the screws. B, Anterior cervical locking plate application after interbody fusion. Note that penetration of the posterior vertebral body cortex is not required to achieve a stable implant construct.

32. How are current anterior cervical plating systems classified?

Anterior cervical plate systems can be broadly classified as either static (constrained) plates or dynamic

(semi-constrained) plates.

• Static plates rely on screws, which are rigidly locked to the plate. A direct transfer of applied forces from spine to plate is assured, but the theoretical possibility of stress shielding of the anterior spinal column is present

• Dynamic plates utilize screws that are restricted from backing out from the plate but attempt to allow some degree of load sharing between the plate and the anterior spinal column. This load sharing is achieved through three mechanisms, which may be used singularly or in combination: screw rotation, screw translation, or plate shortening. Semiconstrained rotational plates permit rotation at the plate-screw interface as graft subsidence occurs. Semiconstrained translational plates permit screws to slide longitudinally (fixed screws) within slotted holes in the plate. Some designs permit only longitudinal translation (fixed screws), whereas others permit both longitudinal screw translation and screw rotation (variable screws). The last type of plate permits translation by means of plate shortening. The ends of the plate are rigidly fixed to adjacent vertebra, but the plate itself shortens under physiologic loading (Fig. 28-13)

Rotational vs. Translational

Figure 28-13. A, Rotational versus translational anterior cervical plate. B, Cervical translation through plate shortening. C, Note plate length intraoperatively compared with postoperatively, (A, from Medtronic Sofamor Danek, 2005. All rights reserved. B and C, from DePuy Spine, Inc. All rights reserved.)

Figure 28-13. A, Rotational versus translational anterior cervical plate. B, Cervical translation through plate shortening. C, Note plate length intraoperatively compared with postoperatively, (A, from Medtronic Sofamor Danek, 2005. All rights reserved. B and C, from DePuy Spine, Inc. All rights reserved.)

33. Which type of anterior cervical plate is superior—a static plate or a dynamic plate?

This is a controversial area. In the setting of trauma, a static plate is indicated because it provides greater immediate stability. In the treatment of degenerative disorders, no studies have established superiority of one particular type of plate. With use of dynamic plates, graft settling may lead to segmental kyphosis, foraminal stenosis, and plate impingement on the superior adjacent disc space. However, when multilevel corpectomies are stabilized with anterior plates, graft subsidence may be accommodated by translational plates and potentially decrease the rate of anterior plate fixation failure.

34. What is a buttress plate?

A buttress or junctional plate is an alternative to long segment anterior cervical plates that are subject to large cantilever forces, particularly at the caudal plate-screw-bone junction. The buttress plate spans only the caudal or cephalad graft-host junction, thereby theoretically preventing graft extrusion. The plate is most commonly used at the caudal end of the graft where the cantilever forces are the greatest. A surgeon should use supplemental posterior segmental fixation in the setting of a long anterior strut graft fusion and junctional plate stabilization to prevent dislodgement of the buttress plate with potentially catastrophic consequences (Fig. 28-14).

Figure 28-14. The buttress plate prevents anterior graft dislodgement in combination with posterior cervical instrumentation. (From Vaccaro AR, Baron EM: Spine Surgery: Operative Techniques. Philadelphia: Saunders; 2008, with permission.)

Key Points

1. Posterior cervical instrumentation typically involves use of rod-screw systems. Screws may be placed in the occiput, C1 (lateral mass), and C2 (pedicle vs. pars vs. translaminar screws). In the subaxial cervical region, lateral mass screws are most commonly used at the C3 to C6 levels, whereas pedicle screws are typically used at C7 and distally in the thoracic region.

2. Anterior cervical plates are the most commonly used implants in the C3 to C7 region and may be classified as static or dynamic plates.

3. The anterior spinal column may be reconstructed with autogenous bone graft (iliac or fibula), allograft bone graft, or synthetic materials (e.g. titanium mesh cages, carbon fiber cages, polyetheretherketone [PEEK] cages).

Websites

Anterior cervical plate nomenclature of cervical spine study group: http://cme.medscape.com/viewarticle/424941_1 Posterior occipital cervical fixation: http://www.spineuniverse.com/displayarticle.php/article288.html Trends in surgical management for type II odontoid fracture: 20 years of experience at a regional spinal cord injury center: http://www.orthosupersite.com/view.asp?rID=28891

BiBLiOGRAPHY

1. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 2001;26:2467-71.

2. Jea A, Sheth R, Vanni S, et al. Modification of Wright's technique for placement of C2 translaminar screws: technical note. Spine J 2008;8:656-60.

3. Jeanneret B, Magerl F. Primary posterior fusion C1 -2 in odontoid fractures: indications, technique and results of transarticular screw fixation. J Spinal Disord Tech 1992;5:464-75.

4. McLaughlin MR, Haid RW, Rodts GE. Atlas of Cervical Spine Surgery. Philadelphia: Saunders; 2005.

5. Reilly TM, Sasso RC. Anterior odontoid screw techniques. Tech Ortho 2002;17(3):306-15.

6. Rhee JM, Riew KD. Dynamic anterior cervical plates. J Am Acad Orthop Surg 2007;15(11):640-6.

7. Sekhon LH. Posterior cervical lateral mass screw fixation: analysis of 1026 consecutive screws in 143 patients. J Spinal Disord Tech 2005;18(4):297-303.

8. Stock GH, Vaccaro AR, Brown AK, et al. Contemporary posterior occipital fixation. J Bone Joint Surg 2006;88A:1642-9.

9. Vaccaro AR, Baron EM. Spine Surgery: Operative Techniques. Philadelphia: Saunders; 2008.

FDA Disclosure: The use of screw-based fixation in lateral mass or pedicle in the posterior cervical spine is not FDA cleared or approved.

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