Clinical and computed tomographic evaluation of safety and efficacy of facet screw fixation in the subaxial cervical spine.

ORIGINAL ARTICLE

Clinical and Computed Tomographic Evaluation of Safety and Efficacy of Facet Screw Fixation in the Subaxial Cervical Spine Yoichi Aota, MD, Atsushi Honda, MD, and Tomoyuki Saito, MD

Design: A retrospective study comparing screw positioning and associated complications between 2 different facet screw placement methods.

cable. Screw loosening was significantly reduced using this lateral screw direction. One of the disadvantages of this technique is that extensive cranial exposure is required to align the instruments in the proper sagittal trajectory.

Objective: To review the anatomic location, clinical safety, efficacy, and limitations of 2 facet screw placement techniques.

Key Words: cervical arthrodesis, computed tomographic evaluation, instrumentation, complication

Background: Facet screw fixation in the subaxial cervical spine penetrates 4 cortical layers and affords better stability than lateral mass screws. Takayasu and colleagues recommended placing screws in the sagittal plane. We modified the trajectory to direct the screws laterally from the sagittal plane to place the root at less risk and improve fixation by increasing the excursion of the screws into bone. No clinical reports exist describing the quadricortical facet screw placed in a lateral direction. Methods: A total of 95 screws were used in 18 consecutive patients who underwent posterior cervical stabilization for various spinal disorders: 34 screws used sagittal plane screw placement and 61 used our technique. Screw-related complications were reviewed. Screw trajectories and screw tip positions related to the ventral cortical margin and vertebral artery were evaluated using postoperative 3-dimensional computed tomograms taken within 6 months after surgery. Instrumentation failures were evaluated from postoperative 3-dimensional computed tomograms taken 2 years after surgery. Results: There was 1 complication, nerve root irritation due to screw malposition. Postoperative computed tomographic images revealed that drilling was 30 degrees lateral from the sagittal plane in our method. Fourth cortex penetration failed in 29% of the screws placed in the sagittal plane and in 5% by our method. Screw loosening was significantly increased using screws placed in the sagittal plane (24% vs. 2%). Conclusions: Quadricortical facet screw placement aimed at the juncture between the transverse process and the facet is practi-

Received for publication August 1, 2011; accepted February 1, 2012. From the Department of Orthopaedic Surgery, Yokohama City University Hospital, Yokohama City, Kanagawa Prefecture, Japan. This system has been approved by the Food and Drug Administration (FDA) for use in long bones and the pelvis. The authors declare no conflict of interest. Reprints: Yoichi Aota, MD, Department of Orthopaedic Surgery, Yokohama City University Hospital, Fukuura 3-9, Kanazawa-ku, Yokohama City 236-0004, Kanagawa Prefecture, Japan (e-mail: [email protected]). Copyright r 2012 by Lippincott Williams & Wilkins

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acet screw fixation was first described by King1 in 1944; short screws were placed directly across the facets of 2 vertebrae. The use of this fixation method for lower cervical facet joints was developed by Roy-Camille et al2,3 in 1972 to provide an alternative to lateral mass screw placement. Several screw insertion techniques have been reported. Takayasu et al4 published the results of a clinical series using the technique of placing screws in the sagittal plane with excellent outcomes. Miyanji et al5 compared the Takayasu technique to lateral mass screw placement in a C3–C6 fusion model and concluded that the 2 techniques are equivalent. Lee et al6 compared the biomechanical stability of the Takayasu technique to lateral mass screws in a multilevel corpectomy model. They concluded that facet screws were inferior to lateral mass screws in their ability to provide spinal stability. Klekamp et al7 inserted facet screws using a technique with a starting point 1–2 mm caudal and 1 mm medial to the midpoint of the lateral mass and aiming in a 40-degree caudal and 20-degree lateral position. They directly compared pullout strength of transfacet screws inserted 20-degree lateral to lateral mass screws and concluded that transfacet screws possessed more pullout strength (467 N) than lateral mass screws (359 N) because facet screws penetrate 4 cortical layers during screw purchase, whereas lateral mass screws penetrate only 2 cortical layers. DalCanto et al8 inserted facet screws with a starting point 2 mm caudal to the midpoint of the lateral mass and with the same insertion angle as Klekamp et al.7 DalCanto et al8 compared quadricortical transfacet screws inserted using their technique to lateral mass screws in 2-level instrumentation of intact cadaveric spines and concluded that the techniques are equivalent. Horn et al9 used short C7 facet screws, which were not intended to cross the C7–T1 facet joint. In their biomechanical study, constructs formed by a C7 facet screw and a T1 pedicle screw provided stability

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J Spinal Disord Tech

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Facet Screw Fixation in the Subaxial Spine

equivalent to the constructs formed by pedicle screws at both levels.10 Miyamoto et al11 used the tricortical facet screw technique and reported successful surgical results. Initially, we used the Takayasu technique, which utilizes quadricortical facet screws placed in the sagittal plane.4 We modified the trajectory to direct the screws laterally off the sagittal plane so that the nerve root and vertebral artery are not in the trajectory of the drill or screw and fixation is improved by increasing the excursion of the screw into the bone. Until now, no information has been published concerning quadricortical facet screws in a clinical setting. The purpose of this study was to compare the clinical safety and efficacy of sagittal plane screw placement and the authors’ technique by determining the anatomic location of the screws and screw loosening using computed tomographic (CT) images; clinical complications were also assessed.

pathy stenosis (2); athetoid cerebral palsy (2); metastatic spinal tumor (2); lymphoma (1); trauma (1); and destructive spondyloarthropathy (1). Except for 2 patients (cases 10 and 14), who died at 6 and 10 months, respectively, after surgery from metastatic cancer, follow-up periods ranged from 27 to 62 months with a mean of 46 months. Case 5, with athetoid cerebral palsy, had anterior fusion procedures as a concomitant procedure. Another patient with athetoid cerebral palsy (case 17) had prior anterior fusion procedures 9 years previously. Case 15 had 2 levels of surgery; all others in this study had 3 or more instrumented levels. Basically, bilateral facet screws were used at each level for intermediate fixation in combination with other posterior instrumentation techniques at the cephalad and caudad ends of the fusion. In 5 patients (cases 5, 13, and 15–17) only facet screws were used as stand-alone fixation. In case 11, an iatrogenic inferior facet fracture occurred during facet screw placement, precluding bilateral facet screw placement at C2/3 and C4/5. In case 14, the inferior facet was fractured during placement of lateral mass screws; unilateral C5/6 facet screws were placed as salvage. In all other patients, facet screw fixation was done according to the presurgical plan.

METHODS From 2003 to 2007, a total of 18 patients in the authors’ hospitals underwent posterior stabilization using facet screws for various cervical spinal disorders. Initially, screws were placed using the method of Takayasu et al.4 In June 2005, using cadaveric dissection, we identified the safest aiming point for placing quadricortical facet screws. On the basis of the findings from the dissections, facet screw placement was done in a lateral direction thereafter. Age, sex, etiology, fusion levels, number of screws used at each level, instrumentation systems used, and follow-up periods are listed in Table 1. The patients had a variety of diagnoses: rheumatoid arthritis (9); cervical spondylotic myelo-

Surgical Technique All surgeries were performed by an experienced spine surgeon. Under general anesthesia, the patient was positioned prone using 3-pin skull fixation. Full exposure of the posterior elements was obtained to the lateral edges of the lateral mass. Laminectomies, if required, were performed before drilling and placement of screws. The implants used were Olerud cervical systems with a

TABLE 1. Summary of Patient Characteristics of Cases Using Facet Screws Case Number

No. Facet Screws Age

Sex

Etiology

Fusion Levels

1

58

M

RA

2 3 4 5 6 7

76 74 61 49 65 66

F F F F F F

8 9 10 11 12 13 14

74 67 54 65 51 74 64

15 16 17 18

75 70 53 65

C2/3

C3/4

C4/5

C5/6

O–T2

2

2

2

Trauma RA RA ACP RA RA

O–C5 O–C7 O–C7 C3–C6 C2–T2 C1–T5

2

2 2 2 2 2 2

F F F F F F M

Lymphoma RA Metastasis RA RA RA Metastasis

O–C6 O–C6 O–C6 O–C7 C2–T1 C2–C5 C5–T3

M M M F

CSM CSM ACP DSA

C3–C5 C3–C7 C4–C6 C2–C7

2

1 2

2 2

1

1 2 2 2

2

2

2 2 2 1 2 2

2 2 2

C6/7

Associated Instrumentation

Device

Follow-up Periods (mo)

Olerud

62

2 2

Occipital plate; C1 LMS; C7, T1,T2 PS Occipital plate Occipital plate Occipital plate

Olerud Olerud Olerud Oasys Oasys Oasys

60 58 57 52 47 50

Oasys Oasys Oasys Oasys Oasys Oasys Oasys

27 37 6 49 47 40 10

Oasys Oasys Oasys Oasys

40 39 33 40

C2, C7, T1, T2 PS C1 LMS; C2, C7, T1, T3, T4, T5 PS Occipital plate; C6 hooks Occipital plate; C6 hooks Occipital plate, C1 LMS Occipital plate, C7 PS C2, C7, T1 PS

2 2 2 2 2 2 1

2 2

2 2 2 2

2 2 2

C5, C6 (L), C7 (R) LMS;T2, T3 (L) PS; T3 (R) hook 2 C2, C7 PS

Number of facet screws; 2 indicates bilateral screws and 1 indicates a unilateral screw. Under associated instrumentation, the side of unilateral fixation is indicated as left (L) or right (R). If not indicated, bilateral fixation was used. ACP indicates athetoid cerebral palsy; CSM, cervical spondylotic myelopathy; DSA, destructive spondyloarthropathy; F, female; LMS, lateral mass screw; M, male; PS, pedicle screw; RA, rheumatoid arthritis.

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diameter of 4.0 mm (Nordopedic AB, Uppsala, Sweden) in 4 patients and Oasys with a diameter of 3.5 mm (Stryker Spine, Cestas, France) in14 patients. Quadricortical purchase was attempted in all procedures. To align the air drill in the proper sagittal trajectory, fluoroscopy in the true lateral view was used. In either technique, pedicles were identified on the fluoroscopic image and were used as the radiologic landmark for the aiming point. Each hole was drilled with a 2.0-mm drill bit until the dorsal cortex of the upper facet was penetrated. Each trajectory was further probed until penetration of the ventral cortex of the upper facet with loss of resistance was achieved. The hole was then palpated with a flexible ball-tipped probe, tapped until the third cortical layer was reached, and repalpated. A depth gauge was used to measure the desired screw length. Except for the 2 metastatic cancer patients (cases 10 and 14), who were considered to have poor prognoses, the arthrodesis was completed by burring the exposed bone surfaces, curreting the facet joints, and placing a bone graft into the facets and over the lateral masses. Case 5 required halo immobilization; otherwise all patients were treated with a soft foam collar for 4 weeks after surgery.



Clinical and Radiologic Evaluations Patients were typically followed up with clinical evaluations and radiographs at 1, 3, 6, 12 months, and thereafter every year. All patient information was recorded and monitored for the occurrence of any potential screw-related complications, with special emphasis on neurologic signs and symptoms. Within 6 months after surgery, each patient received a 3D-CT scan with thin axial and sagittal reconstructed images at 2.0 mm intervals for screw position assessment. The screw trajectory was measured for lateral direction on axial images and for caudal direction on sagittal images (Fig. 2). The length of screw tips beyond the fourth cortical surface

Placement of Screws in the Sagittal Plane (Takayasu Technique) A total of 34 screws were placed in the sagittal plane in the initial 6 patients (cases 1–6); their mean age at the time of surgery was 56.0 years (range, 47–62 y). A conventional midline approach was performed. The entry point was made at the midpoint of the lateral mass. The average screw length was 17.1 mm with the following screw lengths utilized: 15 mm (1), 16 mm (17), 18 mm (13), and 20 mm (3).

Placement of Screws Lateral to the Sagittal Plane (Authors’ Technique) A total of 61 screws were placed in the lateral direction aiming at the juncture between the transverse process and the lateral mass in 12 cases (cases 7–18); their mean age at the time of surgery was 64.8 years (range, 51–75 y). Because the spinous process of the vertebra above the level of drilling interferes with proper positioning of the drill in the lateral direction, a spinous process splitting approach was introduced to achieve better alignment of the drill (Fig. 1).12,13 The entry point was made 2–4 mm medial to the center of the lateral mass. The lateral border of the isthmus, located just posterior to the juncture between the transverse process and the facet, was also used as a dorsal anatomic landmark to align the drill. Using fluoroscopy to aim the juncture, the entry point was chosen as far cephalad as possible in the lateral mass to avoid possible facet fracture. The average screw length was 20.9 mm with the following screw lengths utilized: 16 mm (4), 18 mm (13), 20 mm (19), 22 mm (11), 24 mm (6), 26 mm (6), and 28 mm (2).


FIGURE 1. Schematic drawings illustrate the technique developed by the authors. A spinous process splitting approach was used to achieve a sufficiently lateral alignment for the drill (top). Facet screw placement aimed at the juncture between the transverse process and the lateral mass was done (middle), followed by closure (bottom). r





FIGURE 2. Measurement of screw angles and screw tip penetration of the fourth cortex utilizing computed tomograms. Axial deviation angle: the angle between the screw and vertical line (A). Sagittal angle: the angle between the screw and the line joining the dorsal cortical margins of the lateral masses (B). To evaluate penetration of the fourth cortex, the distance between the screw tip and anterior cortical margin of the lateral mass (dotted line) is measured on the axial image (C). “Plus” data represent overpenetration.

was measured (plus data represent overpenetration into the cortical margin). Screws were defined as overpenetrating if they penetrated the cortical margin of the lateral mass 4.0 mm or more. If the tip of the screw did not reach the cortical margin with more than a 2 mm gap, those screws were considered to have tricortical purchase. To describe screw tip position, we used the Heller classification14 with modification by Graham et al15; this divides the cervical lateral masses into 3 zones in the sagittal and axial planes (Fig. 3). In the sagittal plane, zone I is the superior margin of the superior articular process that forms the roof of the neuroforamen, zone II is the ventral portion of the lateral mass that includes the transverse process, and zone III extends below the inferior origin of the transverse process. Zone II in the sagittal plane and the lateral zone in the axial plane represent the optimal location for the tip of a screw in the authors’ method. The influence of occipital exposure on caudal trajectories was determined by comparisons between the 56 screws used in the 9 patients who required occipital exposure (cases 1–4, 7–11) and the 39 screws used in the 9 patients with subaxial lesions, for whom surgeries without occiput occipital exposure were performed (cases 5, 6, 12–18). All facet screw tips were evaluated for encroachment into the spinal canal and foramen transversarium. Deviation of the screw into the foramen transversarium was classified into 4 grades according to the classification by Neo et al16: grade 0, no encroachment into the foramen transversarium; r


grade 1, encroachment 2 mm and 4 mm. CTs were repeated as frequently as necessary. At 24 months after surgery, a CT was taken for all patients except the 2 metastatic cancer patients (cases 10 and 14), who had both died within 1 year of the surgery. Hardware failures, including screw loosening, and screw or plate breakage, were evaluated in 16 patients. Anteroposterior and flexion-extension lateral radiographs taken at 2 years after surgery were also used to evaluate loss of fixation. For statistical analyses, the Fisher exact test and the independent t test were used. P < 0.05 was considered statistically significant.

FIGURE 3. Schematic drawings illustrate the assessment of screw tip placement in the lateral mass using computed tomography. The screw tip position in the axial plane (A) and in the sagittal plane (B) was classified into the 3 zones proposed by Graham et al.15 www.jspinaldisorders.com |

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FIGURE 4. Postoperative roentgenogram and axial computed tomogram (CT) image of case 15. The lateral roentgenogram demonstrates the insufficient caudal inclination of 4 screws with a mean caudal angle of 72.3 degrees (A). The axial CT image illustrates that the left C4/5 facet screw was placed with insufficient lateral direction (15 degrees laterally) and penetrated the fourth cortical margin by 4.8 mm with the malpositioned screw tip in the foramen (arrow, B).

RESULTS Screw-related Complications A screw-related complication (symptomatic nerve root irritation) occurred in case 15. This 75-year-old man with a diagnosis of myelopathy associated with spondylolisthesis at C4/5 and C5/6 underwent laminectomy of C3–C5 and posterior cervical fusion with C4/5 and C5/6 facet screw placement in our method. The postsurgical course passed uneventfully until 2 months after surgery, when he hit his forehead. Thereafter, radicular arm pain gradually developed and a left C5 motor deficit was present with 4/5 deltoid function and 3/5 biceps function. The x-rays revealed insufficient caudal inclination of 4 screws, possibly because of the limited exposure used in this patient. The CT scan revealed a malpositioned screw

tip within the left C4/5 foramen (Fig. 4). Revision surgery was performed 5 weeks after the onset of motor weakness. The bilateral C4/5 facet screws were first removed and anterior fusion at C4/5 was performed. The C5 radiculopathy disappeared immediately and completely after the second surgery. The patient had no pain or sensory deficit and had regained motor function with 5/5 deltoid strength at the final follow-up.

CT Outcome Drilling was at an average angle of 2.7 degrees laterally and 51.4 degrees caudally in the Takayasu sagittal plane screw placement method and at an average angle of 30.0 degrees laterally and 54.6 degrees caudally in our method (Table 2). Seventy-one percent of screws placed in the sagittal plane had tips positioned in the

TABLE 2. Screw Angle, Tip Location, and Malposition on Computed Tomograms Within 6 Months After Surgery Trajectory Angle Mean Degree ± SD (Range) Screw Placement Method Sagittal plane (Takayasu) (no. screws = 34)

Caudal Plane 51.4 ± 13.5 degrees (29–80 degrees)

Lateral to the 54.6 ± 16.4 sagittal plane (no. degrees screws = 61) (22–88 degrees)

Distance Between Tip of Screw and Fourth Cortex

Lateral Angle

Mean ± SD, Range

2.7 ± 16.5 degrees ( 41 to 24 degrees)

0.6 ± 2.4 mm ( 6.7 to 2.9)

30.0 ± 10.3 degrees (12–53 degrees)

1.7 ± 2.4 mm ( 4.6 to 8.3)

Underpenetration or Overpenetration

Deviations of the Screw into Tricortical Overpenetration Spinal Canal the Foramen (< 2 mm) (> 4 mm) Infringements Transversarium 10 (29%)

3 (5%)

0 (0%)

10 (16%)

1 (3%)

Grade 3

0 (0%)

Grade Grade Grade Grade

0

2 1 0 3

0 0 34 0

Grade 2 Grade 1 Grade 0

2 1 57

Deviation of the screw into foramen transversarium was classified into 4 grades according to the classification of Neo and colleagues: grade 0: no encroachment into the foramen transversarium, grade 1: encroachment 2 mm and 4 mm.


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TABLE 3. Screw Tip Position in Lateral Masses Based on the Zone Classification of Graham et al10 Axial Zone Sagittal Zone Zone I Zone II Zone III Total

Medial

Central

Lateral

Total

2/2 1/0 1/0 4/2

14/11 10/5 0/0 24/16

1/18 4/16 1/9 6/43

17/31 15/21 2/9 34/61

Number of screws shown as: Takayasu’s sagittal plane method/our lateral to the sagittal plane technique.

central axial zone, whereas in our method, 70% were in the lateral zone (Table 3). The percentages of zone I of the sagittal plane by the Takayasu method were 50% and 51% by our technique. The percentage of tricortical screws was significantly (P < 0.005) lower in our method (5%) than in the Takayasu method (29%) (Table 2). The percentage of overpenetration >4 mm was also significantly higher (P < 0.05) in our method (16%) than in the Takayasu method (0%). Three of the 10 screws in the cortical margin overpenetrating by 4 mm or more placed the vertebral artery at grade I (n = 1) or grade II (n = 2) risk (Fig. 5). No screws located in the foramen transversarium resulted in vertebral artery injury. Minimal spinal canal violation (< 2 mm) was noted in 1 case using the Takayasu method. Screws in patients with occipital exposure were significantly (P < 0.005) aligned caudally. The mean caudal angle was 47.2 ± 13.2 degrees (range, 22–80 degrees) in patients with occiput exposure, and 62.5 ± 13.9 degrees (range, 39–88 degrees) in patients without occiput exposure. The number of screws placed in each sagittal zone were as follows: 19 in zone I, 27 in zone II, and 10 in zone III in patients with occiput exposure. In patients without occiput exposure, 27 screws were placed in zone I, 12 in zone II, and none in zone III. The ratio of screws positioned in zone I was significantly increased (P < 0.005) in patients without occiput exposure; 34% versus 69%.

Careful reading of the CT images taken 2 years after surgery revealed that the only failure noted was the loosening of 9 screws in 3 patients with no evidence of backing out or breakage of instrumentation (Table 4). Eight screws inserted by the Takayasu method were surrounded by marked radiolucent areas, whereas 1 screw placed by our technique had a minimal radiolucent line. The Fisher exact test revealed that screw loosening was significantly higher (P < 0.005) in the Takayasu method than ours, 24% of 34 screws versus 2% of 61 screws, respectively. In case 1, although all instruments had obvious loosening on follow-up CT images, no motion was detected in fusion levels on functional x-rays. In case 4, obvious loosening was detected as early as 11 months after surgery (Fig. 6) and 12 degrees of hypermobility was seen on functional x-rays taken 6 years after surgery. Because these failures remained asymptomatic, revision was not indicated. In case 8, despite a minimal clear zone around a single screw, bone fusion was assumed to have been obtained because mobility on flexion-extension x-rays was not seen at the final follow-up.

DISCUSSION The purpose of the present study was to review the anatomic location, clinical safety, efficacy, and limitations of facet screw placement used by an experienced orthopedic spinal surgeon familiar with various posterior screw placement methods. It should be noted that this series reports the first 18 patients in whom the placement of facet screws was used and therefore represents the early portion of the learning curve of the use of our system. The theoretical advantage of our method over placement of screws in the sagittal plane is decreased risk to the spinal cord, nerve root, and vertebral artery.17 Thorough penetration into the ventral cortex of the facets and increased excursion of the screw into bone would provide a greater degree of stabilization. The significant reduction in the number of loosened screws in our method may have resulted from superior fixation.

FIGURE 5. Overpenetration on postoperative reconstructed computed tomography images (case 13). The bilateral C2/3 screw tips are excessively long and located in the transverse processes. The right screw tip is positioned in close proximity to the vertebral artery (arrow, A). Overpenetrations were 7.8 and 5.5 mm, respectively. The right C3/4 screw tip had grade II deviation of the screw into the foramen transversarium with 4.3 mm of overpenetration (arrow, B). r



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TABLE 4. Summary of Cases of Screw Loosening Case Number

Facet Screw Placement Method

No. Loosened Facet Screws

1

Sagittal plane

4

4 8

Sagittal plane Lateral to sagittal plane

4 1

Loosened Instrumentation Occipital plate; C1 LMS; C3/4, C4/5 facet screws C5/6, C6/7 facet screws C4/5 facet screw (R)

Mobility on FlexionExtension X-Rays (deg.) 0 12 0

The side was indicated as right (R). If not indicated, bilateral fixation had radiolucent area. LMS indicates lateral mass screw.

Before the clinical application of our technique, we examined its feasibility using a cadaver. The placement of facet screws into the lateral mass and their relationship to the neighboring anatomic structures were also examined. As the nerve root travels laterally, the volume of the neuroforamen increases, providing more space for the nerve root to accommodate a prominent screw tip.18 As in lateral mass screw placement, nerve root impingement is more likely with less lateral or less caudal drill trajectories.19 The starting point, degree in lateral direction, and aiming point for our technique are the same as for the An technique for lateral mass screw placement.19 Even in cases of involuntary overpenetration, if the screw is directed to the juncture between the transverse process and the facet, the screw tip is less likely to injure the nerve root because the screws are placed parallel to the nerve root (Fig. 7). In a recent cadaveric study,17 the risk for inferior facet fracture from the Dalcanto technique,8 inserting screws 2 mm caudal to the midpoint of the lateral mass was surprisingly high (17/65 screws). To preclude facet fracture, our method chooses the starting point as far cephalad as possible. Two inferior facet fractures occurred in 1 patient (case 11) from a total of 65 screw insertions using our technique.

Directing the screw tip toward the superior portion of the lateral mass places the root at greater risk. Overall, 48 screws (51% of 95 screws) were placed in zone I of the sagittal plane (Table 3). Of these 9 patients, case 15 had iatrogenic radicular complaints. As Takayasu et al4 stated, caudal alignment of the drill may be impeded by occipital bone protuberance. This was also observed in our cadaveric study (Fig. 7). Unless the occipital bone is exposed, however, the limited exposure increases the challenge of achieving proper screw trajectory because the drill impinges on the cranial wound margin. The ratio of zone I screws increased to 69% in 9 patients without occipital exposure. Thus, we believe that the indication for quadricortical facet screw placement is limited to patients who require occipitocervical fusion or extensive cranial exposure. Overpenetration of the drill, depth gauge, tap, or screw may expose the vertebral artery to additional risk if the lateral direction is insufficient. Perhaps because the ventral cortex was penetrated, on the basis of the surgeon’s tactile sense without use of fluoroscopy, 10 screws (16% of 61) penetrated the cortical margins by 4.0 mm or more and 3 screws are at risk of vertebral artery injury (Fig. 5). To prevent involuntary malposition into the

FIGURE 6. Axial computed tomography image of case 4 taken 11 months after surgery. Obvious screw loosening is seen around the bilateral C6/7 facet screws.


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FIGURE 7. Photographs demonstrating the authors’ technique in a cadaver. The C4 nerve root is parallel to the left C3/4 screw tip, which is overpenetrated approximately 1 cm (A). The caudal inclination in the left C5/6 screw (white arrow) is limited by the occipital bone protuberance (black arrow, B).

foramen transversarium, fluoroscopy should be used during penetration of the ventral cortex. Care should be taken not to probe beyond the posterior margin of the vertebral body.20 The appropriate screw trajectory in the sagittal plane can also be monitored by fluoroscopy; this would improve the consistency of the surgeon obtaining a particular angle of screw insertion, although excessive radiation exposure should be avoided. When the occipital bone protuberance or the cranial wound margin impedes achieving proper caudal direction, the tricortical facet screw technique may be used to decrease the risk of radiculopathy.11 However, even using tricortical fixation, we believe the trajectory should be in the lateral direction to increase the excursion of the screw into bone. Clinical studies comparing the safety and efficacy of quadricortical compared with tricortical screw purchase will be required before final recommendations are made about their clinical safety and efficacy. The challenge to the surgeon is in balancing what is safe versus what is biomechanically sound. This study concludes that placing facet screws lateral to the sagittal plane is a feasible procedure. Our fixation technique has theoretical advantages over the Takayasu sagittal plane screw placement technique. Fixation utilizing longer screws with decreased risk of nerve root injuries compared with lateral mass screw placement makes our technique appealing. The major disadvantage of our method is relatively low versatility. Indications for quadricortical facet screw placement are limited to patients who require long fusion in the occipitocervical area with no need for reduction. The surgeon should recognize that each technique offers both advantages and potential risks and should consider these factors for every patient. REFERENCES 1. King D. Internal fixation of lumbosacral fusion. J Bone Joint Surg Am. 1948;30:560–565. 2. Roy-Camille R, Mazel C, Saillant G. Treatment of cervical spine injuries by a posterior osteosynthesis with plates and screws. In: Kehr P, Weidner A, eds. Cervical Spine. Vienna: Springer-Verlag; 1987:163–174. 3. Roy-Camille R, Saillant G. Cervical spine surgery: fracture dislocation. Nouvelle Presse Medicale. 1972;1:2484–2485.

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4. Takayasu M, Hara M, Yamauchi K, et al. Transarticular screw fixation in the middle and lower cervical spine. Technical note. J Neurosurg Spine. 2003;99(suppl 1):132–136. 5. Miyanji F, Mahar A, Oka R, et al. Biomechanical differences between transfacet and lateral mass screw-rod constructs for multilevel posterior cervical spine stabilization. Spine (Phila Pa 1976). 2008;33:E865–E869. 6. Lee YP, Robertson C, Mahar A, et al. Biomechanical evaluation of transfacet screw fixation for stabilization of multilevel cervical corpectomies. J Spinal Disord Tech. 2011;24:258–263. 7. Klekamp JW, Ugbo JL, Heller JG, et al. Cervical transfacet versus lateral mass screws: a biomechanical comparison. Spinal Disord. 2000;13:515–518. 8. DalCanto RA, Lieberman I, Inceoglu S, et al. Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine. Spine. 2005;30:897–902. 9. Horn EM, Theodore N, Crawford NR, et al. Transfacet screw placement for posterior fixation of C-7. J Neurosurg Spine. 2008;9:200–206. 10. Horn EM, Reyes PM, Baek S, et al. Biomechanics of C-7 transfacet screw fixation. J Neurosurg Spine. 2009;11:338–343. 11. Miyamoto H, Sumi M, Uno K. Utility of modified transarticular screw in the middle and lower cervical spine as intermediate fixation in posterior long fusion surgery. J Neurosurg Spine. 2009;11:555–561. 12. Shiraishi T. Skip laminectomy—a new treatment for cervical spondylotic myelopathy, preserving bilateral muscular attachments to the spinous processes: a preliminary report. Spine J. 2002;2:108–115. 13. Aota Y, Honda A, Uesugi M, et al. Vertebral artery injury. J Neurosurg (Spine). 2007;7:112–113. 14. Heller JG, Carlson GD, Abitbol JJ, et al. Anatomic comparison of the Roy-Camille and Magerl techniques for screw placement in the lower cervical spine. Spine. 1991;16(suppl 10):S552–S557. 15. Graham AW, Swank ML, Kinard RE, et al. Posterior cervical arthrodesis and stabilization with a lateral mass plate. Clinical and computed tomographic evaluation of lateral mass screw placement and associated complications. Spine (Phila Pa 1976). 1996;21:323–328. 16. Neo M, Sakamoto T, Fujibayashi S, et al. The clinical risk of vertebral artery injury from cervical pedicle screws inserted in degenerative vertebrae. Spine (Phila Pa 1976). 2005;30:2800–2805. 17. Zhao L, Xu R, Liu J, et al. The study on comparison of three techniques for transarticular screw placement in the lower cervical spine. Spine (Phila Pa 1976). 2011;37:E468–E472. 18. Jonsson H, Rauschning W. Anatomical and morphometric studies in posterior cervical spinal screw-plate systems. J Spinal Disord. 1994;7:429–438. 19. An HS, Gordin R, Renner K. Anatomic considerations for platescrew fixation of the cervical spine. Spine. 1991;16(suppl):E548–E551. 20. Xu R, Zhao L, Chai B, et al. Lateral radiological evaluation of transarticular screw placement in the lower cervical spine. Eur Spine J. 2009;18:392–397.


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Safety Eevaluation of Free-Hand Lateral Mass Screw Fixation in the Subaxial Cervical Spine; Evaluation of 1256 Screws.

Radiographic and clinical assessment of a freehand lateral mass screw fixation technique: is it always safe in subaxial cervical spine?

Laminar screw fixation in the subaxial cervical spine: A report on three cases.

Anatomic Study of Anterior Transdiscal Axial Screw Fixation for Subaxial Cervical Spine Injuries.

Lateral Mass Fixation in the Subaxial Cervical Spine.

Posterior Fixation Techniques in the Subaxial Cervical Spine.

Computed tomographic morphometric analysis of cervical pedicles in a multi-ethnic Asian population and relevance to subaxial cervical pedicle screw fixation.

Facet joint degeneration of the cervical spine: a computed tomographic analysis of 320 patients.

The safety and accuracy of freehand pedicle screw placement in the subaxial cervical spine: a series of 45 consecutive patients.

Lateral mass fixation in subaxial cervical spine: anatomic review.

Detecting Facet Joint and Lateral Mass Injuries of the Subaxial Cervical Spine in Major Trauma Patients.

The accuracy of 3D fluoroscopy-navigated screw insertion in the upper and subaxial cervical spine.

The feasibility of transpedicular screw fixation of the subaxial cervical spine in the Arab population: a computed tomography-based morphometric study.

Anatomic considerations for plate-screw fixation of the cervical spine.

Subaxial cervical spine trauma: evaluation and surgical decision-making.

Lateral mass screw fixation in the cervical spine.

Occipital condyle to cervical spine screw and rod fixation.

Morphological character of cervical spine for anterior transpedicular screw fixation.

The risk of translaminar screw fixation to the transverse foramen of the lower cervical spine: a computed tomography study.

AOSpine subaxial cervical spine injury classification system.

Efficacy of Pedicle Screw Fixation in Unstable Upper and Middle Thoracic Spine Fractures.

The role and limitations of computed tomographic scanning in the evaluation of cervical trauma.

Morphometric evaluation of subaxial cervical spine using multi-detector computerized tomography (MD-CT) scan: the consideration for cervical pedicle screws fixation.

Cervical spine dislocations with unilateral facet interlocking.