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Freehand technique for C2 pedicle and pars screw placement: is it safe?
Accepted Manuscript Title: Freehand technique for C2 pedicle and pars screw placement: safe or not? Author: Prachya Punyarat, K. Daniel Riew, Benjamin T. Klawson, Colleen Peters, Thamrong Lertudomphonwanit, Jacob M. Buchowski PII: DOI: Reference:
S1529-9430(17)31163-4 https://doi.org/10.1016/j.spinee.2017.11.010 SPINEE 57542
To appear in:
The Spine Journal
Received date: Revised date: Accepted date:
2-8-2017 9-10-2017 9-11-2017
Please cite this article as: Prachya Punyarat, K. Daniel Riew, Benjamin T. Klawson, Colleen Peters, Thamrong Lertudomphonwanit, Jacob M. Buchowski, Freehand technique for C2 pedicle and pars screw placement: safe or not?, The Spine Journal (2017), https://doi.org/10.1016/j.spinee.2017.11.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1 1
Freehand Technique for C2 Pedicle and Pars Screw Placement: Safe or Not?
2
1.Prachya Punyarat, M.D.
3
Division of Neurosurgery, Department of Surgery, Faculty of Medicine, Thammasat
4
University, Pathumthani, Thailand
5
2. K. Daniel Riew, M.D.
6
Department of Orthopedic Surgery, Columbia University, New York, NY
7
3. Benjamin T. Klawson
8
Department of Orthopedic Surgery, Washington University School of Medicine in St.
9
Louis, MO
10
4. Colleen Peters, M.A
11
Department of Orthopedic Surgery, Washington University School of Medicine in St.
12
Louis, MO
13
5. Thamrong Lertudomphonwanit, M.D.
14
Department of Orthopedics, Faculty of Medicine Ramathibodi Hospital, Mahidol
15
University, Bangkok, Thailand
16
6.Jacob M. Buchowski, M.D., M.S.
17
Department of Orthopedic Surgery, Washington University School of Medicine in St.
18
Louis, MO
19 20
Name and address correspondence:
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Jacob M. Buchowski, M.D., M.S.
2
Department of Orthopedic Surgery, Washington University School of Medicine in St.
3
Louis
4
660 South Euclid Avenue, St. Louis, MO, 63110
5
Phone: (314) 747-4950 Fax: (314) 747-2599 Email: [email protected]
6
The manuscript submitted does not contain information about medical
7
device(s)/drug(s).
8
No funds were received in support of this work.
9
No relevant financial activities outside the submitted work.
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Abstract
2
Background Context: During placement of C2 pedicle and pars screws, intraoperative
3
fluoroscopy is used so that neurovascular complications can be avoided, and screws can
4
be placed in the proper position. However, this method is time consuming and increases
5
radiation exposure. Furthermore, it does not guarantee completely safe and accurate
6
screw placement.
7
Purpose: To evaluate the safety of the C2 pedicle and pars screw placement without
8
fluoroscopic or other guidance methods.
9
Study Design: Retrospective comparative study.
10
Patient Sample: One hundred and ninety-eight patients who underwent placement of
11
C2 pedicle or pars screws without any intraoperative radiographic guidance were
12
included.
13
Outcome Measures: Medical records and postoperative CT scans were evaluated.
14
Methods: Clinical data were reviewed for intraoperative and postoperative
15
complications. Accuracy of screw placement was evaluated with post-op CT scans using
16
a previously published cortical-breach grading system (described by location and
17
percentage of screw diameter over cortical edge (0 = none; grade I = < 25% of screw
18
diameter; grade II = 26-50%; grade III = 51-75%; and grade IV = 76-100%)).
19
Results: 148 pedicle and 219 pars screws were inserted by two experienced surgeons.
20
There were no cases of CSF leakage and no neurovascular complications during screw
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placement. Postoperative CT scans were available for 76 patients, which included 52
2
pedicle and 87 pars screws. For cases with C2 pedicle screws, there were 12 breaches
3
(23%); these included 10 screws with a grade I breach (19%), 1 screw with a grade II
4
breach (2%), and 1 screw with a grade IV breach (2%). Lateral breaches occurred in 7
5
screws (13%), inferior breaches in 3 (6%), and superior breaches in 2 (4%). For cases
6
with C2 pars screws, there were 10 breaches (11%); these included 6 screws with a
7
grade I breach (7%), 2 screws with a grade II breach (2%), and 2 screws with a grade IV
8
breach (2%). Medial breaches were found in 4 (5%), lateral breaches in 2 (2%), inferior
9
breaches in 2 (2%), and superior breaches in 2 (2%). 2 of the cases with superior
10
breaches (1 for pedicle and 1 for pars) experienced occipital neuralgia months after
11
surgery. There was no statistically significant difference in incidence of overall and high-
12
grade breaches between the groups (p = 0.07 and 1 respectively).
13
Conclusions: Although even in experienced hands up to 23% of C2 pedicle screws and
14
11% C2 pars screws placed using a freehand technique without guidance may be
15
malpositioned, a clear majority of malpositioned screws demonstrated a low-grade
16
breach and only 2 of 198 patients (1%) experienced complications related to screw
17
placement.
18
Keywords: Axial cervical spine; Pars screw; Pedicle screw; Freehand technique; fixation
19
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INTRODUCTION
3
Techniques for posterior stabilization of the upper cervical spine that address
4
atlantoaxial instability have been developed over decades. Originally, wiring techniques
5
described by Gallie [1], Brooks-Jenkins [2] and Dickman [3] were used, but they could
6
not provide sufficient biomechanical stability to prevent rotational force and resulted in
7
a high incidence of non-fusion [4]. To address this problem, Jeanneret and Magerl [5]
8
introduced the C1-2 transarticular screw fixation technique. This technique provides
9
optimal stability and yields an excellent fusion rate, though it has some limitations. First,
10
the C1-2 alignment must be correct before insertion of the screws. Also, this technique
11
is generally not feasible in patients with thoracic kyphosis as this would require a steep
12
angle of screw trajectory. Finally, anatomic studies of C2 found that up to 22% of
13
patients were not suitable candidates for transarticular screws due to an increased risk
14
of vertebral artery injury [6-8].
15
Compared to transarticular screws, C1 lateral mass screws combined with C2 pedicle or
16
C2 pars screws provide an alternative treatment for atlantoaxial instability. Several
17
studies show that this instrumentation leads to high rates of arthrodesis [9-19]. C2
18
pedicle and pars screws are also utilized in occipitocervical and subaxial fixation to
19
provide more rigid stability.
20
Despite their popularity, C2 pedicle and pars screw misplacement may result in
21
neurovascular complications – especially vertebral artery (VA) injury. Intraoperative
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fluoroscopy and other guidance methods have been used to assure safe placement of
2
screws. However, these methods are time consuming and often expose patients to
3
additional radiation. The aim of this study is to evaluate the safety of freehand
4
technique for C2 pedicle and pars screw placement as an alternative to intraoperative
5
fluoroscopy or other guidance methods.
6 7
MATERIALS AND METHODS
8
A retrospective study was conducted using data from January 2005 to December 2015
9
at a single institution. We included patients over 18 years old who underwent posterior
10
cervical fixation, without intraoperative radiographic guidance, with both C2 pedicle and
11
pars screw placement. We excluded any patient with an infection, tumor, or traumatic
12
fracture of the C2 vertebra that interfered with normal screw trajectory. Patients who
13
underwent prior C2 pedicle or pars screw insertion were excluded as well. All patients
14
were operated on by two experienced senior surgeons (K.D.R. or J.M.B.) with spine
15
fellows’ assistance. The Institutional Review Board at our institution approved the study.
16
For preoperative planning, all patients obtained cervical radiographs, cervical CT scans,
17
and MRIs. The cervical CT scan was essential for assessing screw size and determining
18
safe placement. When considering insertion of pedicle screws, the most important risk
19
factors to look for are the presence of a high riding vertebral artery and narrow pedicle
20
diameter (< 4 mm). The most common alternatives to pedicle screws are pars or laminar
21
screws. Less commonly, unilateral or other different screw types are used (seen in
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7 1
several patients in this study). Ultimately, the decision of screw type depends on the
2
surgeons’ preference. In this study, each singular pedicle or pars screw was analyzed
3
independently.
4
To assess the safety of these techniques, clinical data and operative reports were
5
reviewed for any intraoperative and postoperative complications. These included both
6
general complications and those related to screw placement.
7
Postoperative CT scans were analyzed for accuracy of screw position. At our institution,
8
plain radiographs are obtained in the immediate postoperative period for all patients to
9
confirm screw placement, while immediate postoperative CT scans are only performed
10
when radiographs are inadequate for evaluation or if the patient’s condition changes
11
during or after an operation. In addition, CT scans are sometimes obtained to assess
12
fusion status. All postoperative CT scans were included in this study to assess screw
13
placement accuracy.
14
Screw malposition was indicated by the presence of a cortical breach on CT images.
15
More specifically, conventional axial and sagittal views parallel to vertical and horizontal
16
planes respectively were reconstructed to make planes perpendicular to the axis of
17
screw (figure 1). The cortical-breached grading system is classified by Sciubba et al. [20],
18
and is described by location (lateral, medial, inferior and superior) and percentage of
19
screw diameter over cortical edge (0 = none; I = < 25% of screw diameter; II = 26-50%; III
20
= 51-75%; IV = 76-100%).
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Surgical Technique
2
Usually, the patient is placed in a prone position on a Jackson surgical table. The head is
3
held by Gardner-Wells tongs with 10-15 lb. traction. Intraoperative monitoring is set up.
4
A standard midline exposure is carried out until C2 and other necessary vertebrae are
5
clearly exposed.
6
C2 Pedicle Screw Insertion
7
Our preferred entry point is the intersection between the superior edge of the C2
8
lamina and midpoint of the C2 pars interarticularis. It is decorticated by a burr to create
9
a pilot hole – the trajectory of which is based on the pre-op CT finding. Usually, 20-30° in
10
both the medial and cranial directions is accepted. Intraoperatively, the medial edge of
11
the C2 pedicle, located both beneath and lateral to the spinal cord, is used as a
12
landmark for screw direction. A pedicle finder is advanced slowly through the pilot hole
13
in the planned direction. The tip is pointed medially to prevent vertebral artery injury
14
from a lateral breach. Because the tip is not sharp enough to violate the cortical bone
15
but sharp enough to penetrate the cancellous bone, feeling resistance to further
16
advancement of the pedicle finder indicates that the tip is touching the cortical bone.
17
Again, the tract should be parallel to the medial edge of the pedicle. A ball-tipped feeler
18
is used to confirm that there is no cortical breach, and it is marked to give the length of
19
the screw. Next, the tap, which is 0.5 mm smaller than the actual screw, is often used to
20
prepare the tract for the screw. If a tap is used, the integrity of tract is tested again with
21
the feeler, then the actual screw is put into place.
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Pars screw insertion
2
The entry point for the pars screw is 2-3 mm lateral and 2-3 mm rostral to the medial
3
edge of the C2-3 facet joint. Again, a burr is used to create a pilot hole. Next, a pedicle
4
finder is directed towards the C1-2 facet joint along the center of the pars
5
interarticularis and advanced forward until it touches the anterior cortex. This is
6
indicated by the resistance against further advancement of the pedicle finder as
7
described earlier. The rest of the procedure continues the same as for pedicle screw
8
insertion.
9
Intraoperative AP and lateral fluoroscopes or radiographs are only used as a final check
10
after screw placement is complete.
11
Statistical analysis
12
Statistical analysis was performed using SPSS version 18.0, (SPSS Inc., Chicago, IL, USA).
13
We used Fischer’s exact test or a Pearson chi-square test for categorical variables. A
14
probability value < 0.05 was considered statistically significant.
15 16
RESULTS
17
There were 198 cases enrolled in the study, including 90 males and 108 females (table
18
1). Ages ranged from 20 to 86 years (mean 59.9 years). The reasons for surgery were:
19
degenerative disease in 137 patients (69%), deformity in 51 (26%), trauma in 7 (3.5%),
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congenital condition in 2 (1%), and inflammation in 1 (0.5%). 122 patients (62%) had
2
prior cervical surgery before undergoing C2 instrumented surgery.
3
The most common procedure was a multi-level cervical fixation combined with occipital
4
and/or thoracic fixation in 91 patients (46%), followed by a multiple cervical fixation in
5
52 (26%). In total, 395 screws were placed, including 148 pedicle (37%), 219 pars (55%),
6
and 28 laminar screws (7%). Bilateral pedicle and pars screws were placed in 56 (28%)
7
and 93 (47%) patients respectively. When the fusion extended proximally to the occiput
8
or C1, either pars or pedicle screws were utilized (36 pars screws vs. 47 pedicle screws).
9
When the fusion extended proximally to C2, however, the authors’ preference was to
10
use C2 pars screw because it is generally easier to connect the C2 screws to the rods
11
(extending proximally to C2 from the subaxial spine where lateral mass screws were
12
utilized) without having to use offset connector or bending the rods laterally when pars
13
screws rather than pedicle screws are utilized (183 pars screws vs. 101 pedicle screws).
14
The length of C2 pars screws and pedicle screw averaged 20 mm (range 12-34 mm) and
15
24 mm (range 20-30 mm), respectively.
16
Incidental durotomies leading to CSF leakage occurred during exposure with the
17
electrocautery in 3 patients. During screw placement, there were no CSF leakages and
18
no neurological or vascular injuries. Only 1 pars screw was removed when the screw was
19
thought to be malpositioned during the fluoroscopic check. When the integrity of tract
20
was checked with the feeler again, there was no evidence of a cortical breach. The
21
screw was re-inserted into the same tract with no consequences. In the early
Comment [s1]: Phrasing changed as suggested by reviewer.
Comment [s2]: Additional information provided as requested.
Comment [JB3]: Clarification made as requested
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postoperative period, there were 4 cases of surgical infection (with 2 of these cases
2
requiring a reoperation for debridement). During the follow-up period, three patients
3
with bilateral C2 pars screws required revision surgery: 2 cases were due to unilateral C2
4
screw pullout and one case was for a symptomatic pseudarthrosis at C2-C3 without
5
instrumentation failure.
6
Postoperative CT scans were available for 76 patients. The most common reason for
7
obtaining a CT scan was persistent neck pain (34 patients). Other reasons included:
8
evaluation of instrumentation without any symptoms (14 patients), neurological deficits
9
(7 patients), new radicular pain (7 patients), trauma sustained after instrumentation (4
10
patients), instrumentation failure (3 patients), and other causes such as evaluation of
11
spinal metastases (7 patients).
12
Images for 139 screws were analyzed, including 52 pedicle screws and 87 pars screws
13
(table 2). In the C2 pedicle screw group, there were 12 breaches (23%); these included
14
10 screws with a grade I breach (19%), 1 screw with a grade II breach (2%) (figure 2), and
15
1 screw with a grade IV breach (2%). Lateral breaches occurred in 7 screws (13%),
16
inferior breaches in 3 (6%), and superior breaches in 2 (4%). There were no medial
17
breaches. The grade IV breach occurred superiorly into the C1-2 facet joint (figure 3).
18
There was no concern of joint degeneration because this patient underwent a C1-2
19
fusion. The other patient with a superior breach (grade I) had symptoms of occipital
20
neuralgia 6 months after surgery. CT evaluation showed tips of the breached screw
Comment [s4]: Long term complications provided as requested by the reviewer.
Comment [s5]: Inserted reference for figure 2.
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above the C1-2 joint and close to the C2 nerve. The screw was removed, and the
2
patient’s condition improved dramatically.
3
In the C2 pars screw group, there were 10 breaches (11%); these included 6 screws with
4
a grade I breach (7%), 2 screws with a grade II breach (2%), and 2 screws with a grade IV
5
breach (2%). Medial breaches were found in 4 screws (5%)(figure 4), inferior breaches in
6
2 (2%), superior breaches in 2 (2%), and lateral breaches in 2 (2%). Of the 2 screws with
7
grade IV breaches, one was located medially into the spinal canal and did not cause
8
neurological injury. The other (superior breach) was located near the C2 ganglion and
9
did not cause any early postoperative nerve root irritation. However, a new symptom of
10
occipital neuralgia appeared 18 months later, so the screw was removed.
11
There was no statistical significance between pedicle and pars C2 screws across all cases
12
of breaches (χ2 test, P= 0.07). There was also no statistical significance in the incidence
13
of high-grade breaches (breach grade III and IV) (Fisher exact test, P= 1).
14 15
DISCUSSION
16
Currently, pedicle and pars screws are accepted as the primary posterior C2 constructs
17
for atlantoaxial, occipitocervical, and subaxial fixation [21]. They provide immediate
18
stabilization and long-term fusion. Due to the variable anatomy of the C2 vertebra, a
19
preoperative CT scan is generally necessary for surgeons to clearly define bony
20
morphology and decide proper screw trajectory. If a preoperative CT scan is not
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13 1
available, an MRI scan can be utilized for the same purpose, although it is more difficult
2
to accurately determine the appropriate trajectory on an MRI compared to a CT as the
3
CT provides better bony detail compared to the MRI. Intraoperative CT scan is a
4
potential alternative. Pedicle diameter and vertebral artery position are analyzed to
5
determine whether pedicle screw placement is possible. Several studies show that the
6
incidence of narrow pedicle width and a high riding vertebral artery are up to 22.8% and
7
up to 31% respectively [22-24]. Both of these anatomic variations significantly increase
8
the risk of vertebral artery injury with pedicle screw placement [23]. In these cases,
9
pedicle screws should be avoided.
10
Since pedicle screws are placed near the spinal cord and vertebral artery, a misplaced
11
screw may lead to neurological and vascular injuries. To lessen this risk, intraoperative
12
fluoroscopy can be utilized during screw insertion. Though it does not guarantee
13
complete safety, the risk of vertebral artery injury is reduced. Out of 150 pedicle screw
14
placements under lateral fluoroscopic guidance, Ondra et al. [25] reported 1 case of
15
vertebral artery injury. Similarly, Bransford et al. [21] reported that 0.6% (2/339 screws)
16
of pedicle screws caused vertebral artery injuries. In most fluoroscopy-guided
17
operations, the screw tract is created using a drill, which lacks in tactile perception. It is
18
possible that cortical breaches can occur due to this. In contrast, the freehand
19
technique’s reliance on tactile feedback allows the surgeon to use anatomical landmarks
20
to prevent breaches. It also decreases both operative time and radiation exposure.
21
Nonetheless, there is a limited number of studies that report outcomes related to
22
freehand screw placement. In our study, there were no perioperative or early
Page 13 of 29
14 1
postoperative complications related to 148 pedicle screw placements using freehand
2
technique.
3
Postoperative CT scans in our study showed that the overall occurrence of cortical
4
breaches following pedicle screw placement was 23% (12/52 screws). Having said that,
5
one of the weakness of our study is that not all patients had a postoperative CT scan. In
6
their review of C2 pedicle screw placement, Elliott et al. [26] reported that the incidence
7
of malposition demonstrated by CT varied from 1.1 - 44% in cases with fluoroscopic
8
guidance. This wide range could be a result of varying standards of screw displacement
9
among studies. For example, Bransford et al.[21] defined unacceptable placement as
10
>50% of screw diameter out of cortical bone, and reported this in 1.2% of pedicle
11
screws. If breaches of less than 50% are included, the total incidence increased to 18%
12
(48/260 screws). This incidence is not much different from our study. Furthermore, a
13
freehand technique study by Sciubba and colleagues[20] recorded an overall incidence
14
of 15% while using the same classification method as ours. In both our study and
15
Sciubba’s, the majority of breaches were grade I (10/12 breaches and 13/15 breaches
16
respectively). This minor degree of breach rarely causes damage, as less than 1 mm of
17
screw is out of the cortical bone. In our study, a significant high-grade breach (at least
18
grade III) was only present in 1.9% of cases. This single case was a superior breach into
19
the C1-2 facet joint, which did not result in any clinical sequelae. Similarly, Sciubba et al.
20
reported a 2.0% incidence of high-grade breaches with no negative clinical
21
consequences. Therefore, the safety of freehand C2 pedicle screw insertion appears to
22
be comparable to that of fluoroscopic guidance.
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15 1
C2 Pars screws are usually reserved for patients with unfavorable anatomy for pedicle
2
screws. Thus, they are used infrequently compared to pedicle screws and reported
3
uncommonly in literature. In their review of C2 pars screw placement with fluoroscopic
4
guidance, Elliott et al. [26] reported that 3 - 8% of screws were malpositioned with no
5
arising complications. Regarding the freehand technique, a single cadaveric study [27]
6
reported 2 critical displacements in 16 screws, and concluded that freehand technique
7
was less reliable for pars screw than with pedicle screws. However, in our study there
8
were no intraoperative and early postoperative complications in 219 pars screw
9
placements. Postoperative CT scans revealed breaches in 11% of overall pars screws
10
(10/87). 2.3% (2/87) of cases were high-grade breaches, including 1 medial breach, and
11
1 superior breach. The patient with the medial breach into the spinal canal did not
12
experience any neurological deficits – likely due to the abundant space around the C2
13
level of the spinal cord. There was no statistically significant difference between
14
incidences of both overall and high-grade breaches when compared to pedicle screws in
15
our study. Based on these results, the safety of freehand insertion of C2 pars screws
16
appears to be similar to that of pedicle screws.
17
Out of the 22 total breaches, 2 pedicle and 2 pars screws were superior. One patient in
18
each group presented with occipital neuralgia months after surgery. Pain medication
19
provided insufficient relief, so the two patients underwent revision surgery to remove
20
the misplaced screw – and symptoms consequently improved. While superior breaches
21
were relatively uncommon in this study, they are especially rare in surgeries with
22
fluoroscopic guidance. Use of the lateral fluoroscope can prevent misplacement of
Page 15 of 29
16 1
screws in superior-inferior direction. Wang et al. [15] reported no cases of superior
2
breaches in 592 C2 pedicle screw insertions. Therefore, focusing on a possible superior
3
breach during the final fluoroscopic check is especially important when implementing
4
freehand technique.
5
A limitation of this study is its retrospective design. Immediate post-op CT scans were
6
not available for all patients. To address this, we included follow-up CT scans that
7
showed no change when compared to the immediate postoperative radiographs.
8
Overall, the freehand technique for both C2 pedicle and pars screws is a viable
9
alternative to intraoperative fluoroscopy, particularly since it significantly reduces
10
radiation exposure.
11
CONCLUSIONS
12
Use of freehand technique for C2 pedicle and pars instrumentation was safe without
13
critical neurovascular complications. Preoperative assessment of anatomy for surgical
14
planning combined with intraoperative tactile feedback ensured accurate screw
15
placement.
Comment [s6]: Change made as requested by the reviewer.
16
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References 1. Gallie W. Fractures and dislocations of the cervical spine. Am J Surg. 1939;46:495-9. 2. Brooks A, Jenkins E. Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978;60:702-5. 3. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg. 1991;74(2):190-8. 4. Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clinical orthopaedics and related research. 1999;(359):126-35. 5. Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. Journal of spinal disorders. 1992;5(4):464-75. 6. Mandel IM, Kambach BJ, Petersilge CA, Johnstone B, Yoo JU. Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws. Spine. 2000;25(12):1542-7. 7. Abou Madawi A, Solanki G, Casey AT, Crockard HA. Variation of the groove in the axis vertebra for the vertebral artery. Implications for instrumentation. The Journal of bone and joint surgery British volume. 1997;79(5):820-3. 8. Solanki GA, Crockard HA. Peroperative determination of safe superior transarticular screw trajectory through the lateral mass. Spine. 1999;24(14):1477-82. 9. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001;26(22):2467-71. 10. Goel A, Desai KI, Muzumdar DP. Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery. 2002;51(6):1351-6; discussion 6-7. 11. Chen JF, Wu CT, Lee SC, Lee ST. Posterior atlantoaxial transpedicular screw and plate fixation. Technical note. Journal of neurosurgery Spine. 2005;2(3):386-92. 12. Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr., Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. Journal of neurosurgery Spine. 2008;8(3):222-9. 13. Li L, Zhou FH, Wang H, Cui SQ. Posterior fixation and fusion with atlas pedicle screw system for upper cervical diseases. Chinese journal of traumatology = Zhonghua chuang shang za zhi. 2008;11(6):323-8. 14. Pan J, Li L, Qian L, Tan J, Sun G, Li X. C1 lateral mass screw insertion with protection of C1-C2 venous sinus: technical note and review of the literature. Spine. 2010;35(21):E1133-6. 15. Wang S, Wang C, Wood KB, Yan M, Zhou H. Radiographic evaluation of the technique for C1 lateral mass and C2 pedicle screw fixation in three hundred nineteen cases. Spine. 2011;36(1):3-8.
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16. Stokes JK, Villavicencio AT, Liu PC, Bray RS, Johnson JP. Posterior atlantoaxial stabilization: new alternative to C1-2 transarticular screws. Neurosurgical focus. 2002;12(1):E6. 17. Mummaneni PV, Lu DC, Dhall SS, Mummaneni VP, Chou D. C1 lateral mass fixation: a comparison of constructs. Neurosurgery. 2010;66(3 Suppl):153-60. 18. Thomas JA, Tredway T, Fessler RG, Sandhu FA. An alternate method for placement of C-1 screws. Journal of neurosurgery Spine. 2010;12(4):337-41. 19. Kang MM, Anderer EG, Elliott RE, Kalhorn SP, Frempong-Boadu A. C2 nerve root sectioning in posterior C1-2 instrumented fusions. World neurosurgery. 2012;78(12):170-7. 20. Sciubba DM, Noggle JC, Vellimana AK, et al. Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws. Clinical article. Journal of neurosurgery Spine. 2009;11(1):15-22. 21. Bransford RJ, Russo AJ, Freeborn M, et al. Posterior C2 instrumentation: accuracy and complications associated with four techniques. Spine. 2011;36(14):E936-43. 22. Wajanavisit W, Lertudomphonwanit T, Fuangfa P, Chanplakorn P, Kraiwattanapong C, Jaovisidha S. Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique. Asian spine journal. 2016;10(6):1141-8. 23. Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013;13(7):775-85. 24. Wakao N, Takeuchi M, Nishimura M, et al. Vertebral artery variations and osseous anomaly at the C1-2 level diagnosed by 3D CT angiography in normal subjects. Neuroradiology. 2014;56(10):843-9. 25. Ondra SL, Marzouk S, Ganju A, Morrison T, Koski T. Safety and efficacy of C2 pedicle screws placed with anatomic and lateral C-arm guidance. Spine. 2006;31(9):E263-7. 26. Elliott RE, Tanweer O, Boah A, Smith ML, Frempong-Boadu A. Comparison of safety and stability of C-2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review of the literature. Journal of neurosurgery Spine. 2012;17(6):577-93. 27. Helgeson MD, Lehman RA, Jr., Dmitriev AE, et al. Accuracy of the freehand technique for 3 fixation methods in the C-2 vertebrae. Neurosurgical focus. 2011;31(4):E11.
36
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Figure Legends
2
Figure 1. Postoperative lateral (D) and anteroposterior (E) radiographs with right pars
3
and left pedicle screws at C2. Postoperative CT scans were reformatted to identify a
4
cortical breach from a coronal view. The right side pars screw was in the correct place in
5
reconstructed coronal view (C), which is lined up orthogonally to the screw by using a
6
parallel plane in both the sagittal (A) and axial view (B). Also, there were no breaches of
7
the left pedicle screw on the reconstructed coronal view (H), again aligned from the
8
sagittal (F) and axial views (G).
9 10
Page 19 of 29
20 1
Page 20 of 29
21 1
Figure 2. Pedicle screw was misplaced with grade II (26-50%) and inferior breach on
2
coronal (A) and sagittal (B) views
3 4
Page 21 of 29
22 1
Figure 3. Reconstructed coronal (A) and sagittal (B) views demonstrated a grade IV (76-
2
100%) and superior breach into C1-2 facet joint in C1-2 fusion procedure.
3 4
Page 22 of 29
23 1
Figure 4. Reconstructed coronal (A), sagittal (B) and axial (C) CT scan showed grade I (1-
2
25%) and medial breach to spinal canal on left pars screw.
3 4 5
Table 1. Patient Data Characteristic Patients Female (%):Male(%) Mean Age –years (range) Diagnosis (%) Cervical spondylosis Cervical deformity Trauma RA Congenital (Os Odontoidium) Procedure (%) 1 level (C1-2 or C2-3) Multi-level cervical fixation Multi-level cervical fixation with either ..occipital or thoracic levels Single stage anterior-posterior surgery
Number 198 98(55%):90(45%) 60 (20-86) 137 (69%) 51 (26%) 7 (3.5%) 1 (0.5%) 2 (1%)
26 (13%) 52 (26%) 91 (46%) 29 (15%)
Total C2 screws (%) Pedicle Pars Intralaminar
395 148 (37%) 219 (55%) 28 (7%)
Mean follow-up in mos. (range)
22.6 (1-118)
Page 23 of 29
24
Complication CSF leakage during exposure Surgical site infection Occipital neuralgia
3 (1.5%) 4 (2%) 2 (1%)
1 2 3
Table 2. Accuracy of C2 screw placement under CT evaluation (L = lateral, M = medial, S
4
= superior, I = inferior)
5 Cortical breach Grade (location), (%)
I II III IV Overall Breach
Pedicle (n=52)
Pars (n=87)
P
10 (7L, S, 2I) (19%) 1 (I) (2%) 1 (S) (2%) 12 (23%)
6 (2L, 2M, S, I) (7%) 2 (M, I) (2%) 2 (S, M) (2%) 10 (11%)
1 0.07
6 7 8
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S1529-9430(17)31163-4 https://doi.org/10.1016/j.spinee.2017.11.010 SPINEE 57542
To appear in:
The Spine Journal
Received date: Revised date: Accepted date:
2-8-2017 9-10-2017 9-11-2017
Please cite this article as: Prachya Punyarat, K. Daniel Riew, Benjamin T. Klawson, Colleen Peters, Thamrong Lertudomphonwanit, Jacob M. Buchowski, Freehand technique for C2 pedicle and pars screw placement: safe or not?, The Spine Journal (2017), https://doi.org/10.1016/j.spinee.2017.11.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1 1
Freehand Technique for C2 Pedicle and Pars Screw Placement: Safe or Not?
2
1.Prachya Punyarat, M.D.
3
Division of Neurosurgery, Department of Surgery, Faculty of Medicine, Thammasat
4
University, Pathumthani, Thailand
5
2. K. Daniel Riew, M.D.
6
Department of Orthopedic Surgery, Columbia University, New York, NY
7
3. Benjamin T. Klawson
8
Department of Orthopedic Surgery, Washington University School of Medicine in St.
9
Louis, MO
10
4. Colleen Peters, M.A
11
Department of Orthopedic Surgery, Washington University School of Medicine in St.
12
Louis, MO
13
5. Thamrong Lertudomphonwanit, M.D.
14
Department of Orthopedics, Faculty of Medicine Ramathibodi Hospital, Mahidol
15
University, Bangkok, Thailand
16
6.Jacob M. Buchowski, M.D., M.S.
17
Department of Orthopedic Surgery, Washington University School of Medicine in St.
18
Louis, MO
19 20
Name and address correspondence:
Page 1 of 29
2 1
Jacob M. Buchowski, M.D., M.S.
2
Department of Orthopedic Surgery, Washington University School of Medicine in St.
3
Louis
4
660 South Euclid Avenue, St. Louis, MO, 63110
5
Phone: (314) 747-4950 Fax: (314) 747-2599 Email: [email protected]
6
The manuscript submitted does not contain information about medical
7
device(s)/drug(s).
8
No funds were received in support of this work.
9
No relevant financial activities outside the submitted work.
Page 2 of 29
3 1
Abstract
2
Background Context: During placement of C2 pedicle and pars screws, intraoperative
3
fluoroscopy is used so that neurovascular complications can be avoided, and screws can
4
be placed in the proper position. However, this method is time consuming and increases
5
radiation exposure. Furthermore, it does not guarantee completely safe and accurate
6
screw placement.
7
Purpose: To evaluate the safety of the C2 pedicle and pars screw placement without
8
fluoroscopic or other guidance methods.
9
Study Design: Retrospective comparative study.
10
Patient Sample: One hundred and ninety-eight patients who underwent placement of
11
C2 pedicle or pars screws without any intraoperative radiographic guidance were
12
included.
13
Outcome Measures: Medical records and postoperative CT scans were evaluated.
14
Methods: Clinical data were reviewed for intraoperative and postoperative
15
complications. Accuracy of screw placement was evaluated with post-op CT scans using
16
a previously published cortical-breach grading system (described by location and
17
percentage of screw diameter over cortical edge (0 = none; grade I = < 25% of screw
18
diameter; grade II = 26-50%; grade III = 51-75%; and grade IV = 76-100%)).
19
Results: 148 pedicle and 219 pars screws were inserted by two experienced surgeons.
20
There were no cases of CSF leakage and no neurovascular complications during screw
Page 3 of 29
4 1
placement. Postoperative CT scans were available for 76 patients, which included 52
2
pedicle and 87 pars screws. For cases with C2 pedicle screws, there were 12 breaches
3
(23%); these included 10 screws with a grade I breach (19%), 1 screw with a grade II
4
breach (2%), and 1 screw with a grade IV breach (2%). Lateral breaches occurred in 7
5
screws (13%), inferior breaches in 3 (6%), and superior breaches in 2 (4%). For cases
6
with C2 pars screws, there were 10 breaches (11%); these included 6 screws with a
7
grade I breach (7%), 2 screws with a grade II breach (2%), and 2 screws with a grade IV
8
breach (2%). Medial breaches were found in 4 (5%), lateral breaches in 2 (2%), inferior
9
breaches in 2 (2%), and superior breaches in 2 (2%). 2 of the cases with superior
10
breaches (1 for pedicle and 1 for pars) experienced occipital neuralgia months after
11
surgery. There was no statistically significant difference in incidence of overall and high-
12
grade breaches between the groups (p = 0.07 and 1 respectively).
13
Conclusions: Although even in experienced hands up to 23% of C2 pedicle screws and
14
11% C2 pars screws placed using a freehand technique without guidance may be
15
malpositioned, a clear majority of malpositioned screws demonstrated a low-grade
16
breach and only 2 of 198 patients (1%) experienced complications related to screw
17
placement.
18
Keywords: Axial cervical spine; Pars screw; Pedicle screw; Freehand technique; fixation
19
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5 1 2
INTRODUCTION
3
Techniques for posterior stabilization of the upper cervical spine that address
4
atlantoaxial instability have been developed over decades. Originally, wiring techniques
5
described by Gallie [1], Brooks-Jenkins [2] and Dickman [3] were used, but they could
6
not provide sufficient biomechanical stability to prevent rotational force and resulted in
7
a high incidence of non-fusion [4]. To address this problem, Jeanneret and Magerl [5]
8
introduced the C1-2 transarticular screw fixation technique. This technique provides
9
optimal stability and yields an excellent fusion rate, though it has some limitations. First,
10
the C1-2 alignment must be correct before insertion of the screws. Also, this technique
11
is generally not feasible in patients with thoracic kyphosis as this would require a steep
12
angle of screw trajectory. Finally, anatomic studies of C2 found that up to 22% of
13
patients were not suitable candidates for transarticular screws due to an increased risk
14
of vertebral artery injury [6-8].
15
Compared to transarticular screws, C1 lateral mass screws combined with C2 pedicle or
16
C2 pars screws provide an alternative treatment for atlantoaxial instability. Several
17
studies show that this instrumentation leads to high rates of arthrodesis [9-19]. C2
18
pedicle and pars screws are also utilized in occipitocervical and subaxial fixation to
19
provide more rigid stability.
20
Despite their popularity, C2 pedicle and pars screw misplacement may result in
21
neurovascular complications – especially vertebral artery (VA) injury. Intraoperative
Page 5 of 29
6 1
fluoroscopy and other guidance methods have been used to assure safe placement of
2
screws. However, these methods are time consuming and often expose patients to
3
additional radiation. The aim of this study is to evaluate the safety of freehand
4
technique for C2 pedicle and pars screw placement as an alternative to intraoperative
5
fluoroscopy or other guidance methods.
6 7
MATERIALS AND METHODS
8
A retrospective study was conducted using data from January 2005 to December 2015
9
at a single institution. We included patients over 18 years old who underwent posterior
10
cervical fixation, without intraoperative radiographic guidance, with both C2 pedicle and
11
pars screw placement. We excluded any patient with an infection, tumor, or traumatic
12
fracture of the C2 vertebra that interfered with normal screw trajectory. Patients who
13
underwent prior C2 pedicle or pars screw insertion were excluded as well. All patients
14
were operated on by two experienced senior surgeons (K.D.R. or J.M.B.) with spine
15
fellows’ assistance. The Institutional Review Board at our institution approved the study.
16
For preoperative planning, all patients obtained cervical radiographs, cervical CT scans,
17
and MRIs. The cervical CT scan was essential for assessing screw size and determining
18
safe placement. When considering insertion of pedicle screws, the most important risk
19
factors to look for are the presence of a high riding vertebral artery and narrow pedicle
20
diameter (< 4 mm). The most common alternatives to pedicle screws are pars or laminar
21
screws. Less commonly, unilateral or other different screw types are used (seen in
Page 6 of 29
7 1
several patients in this study). Ultimately, the decision of screw type depends on the
2
surgeons’ preference. In this study, each singular pedicle or pars screw was analyzed
3
independently.
4
To assess the safety of these techniques, clinical data and operative reports were
5
reviewed for any intraoperative and postoperative complications. These included both
6
general complications and those related to screw placement.
7
Postoperative CT scans were analyzed for accuracy of screw position. At our institution,
8
plain radiographs are obtained in the immediate postoperative period for all patients to
9
confirm screw placement, while immediate postoperative CT scans are only performed
10
when radiographs are inadequate for evaluation or if the patient’s condition changes
11
during or after an operation. In addition, CT scans are sometimes obtained to assess
12
fusion status. All postoperative CT scans were included in this study to assess screw
13
placement accuracy.
14
Screw malposition was indicated by the presence of a cortical breach on CT images.
15
More specifically, conventional axial and sagittal views parallel to vertical and horizontal
16
planes respectively were reconstructed to make planes perpendicular to the axis of
17
screw (figure 1). The cortical-breached grading system is classified by Sciubba et al. [20],
18
and is described by location (lateral, medial, inferior and superior) and percentage of
19
screw diameter over cortical edge (0 = none; I = < 25% of screw diameter; II = 26-50%; III
20
= 51-75%; IV = 76-100%).
Page 7 of 29
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Surgical Technique
2
Usually, the patient is placed in a prone position on a Jackson surgical table. The head is
3
held by Gardner-Wells tongs with 10-15 lb. traction. Intraoperative monitoring is set up.
4
A standard midline exposure is carried out until C2 and other necessary vertebrae are
5
clearly exposed.
6
C2 Pedicle Screw Insertion
7
Our preferred entry point is the intersection between the superior edge of the C2
8
lamina and midpoint of the C2 pars interarticularis. It is decorticated by a burr to create
9
a pilot hole – the trajectory of which is based on the pre-op CT finding. Usually, 20-30° in
10
both the medial and cranial directions is accepted. Intraoperatively, the medial edge of
11
the C2 pedicle, located both beneath and lateral to the spinal cord, is used as a
12
landmark for screw direction. A pedicle finder is advanced slowly through the pilot hole
13
in the planned direction. The tip is pointed medially to prevent vertebral artery injury
14
from a lateral breach. Because the tip is not sharp enough to violate the cortical bone
15
but sharp enough to penetrate the cancellous bone, feeling resistance to further
16
advancement of the pedicle finder indicates that the tip is touching the cortical bone.
17
Again, the tract should be parallel to the medial edge of the pedicle. A ball-tipped feeler
18
is used to confirm that there is no cortical breach, and it is marked to give the length of
19
the screw. Next, the tap, which is 0.5 mm smaller than the actual screw, is often used to
20
prepare the tract for the screw. If a tap is used, the integrity of tract is tested again with
21
the feeler, then the actual screw is put into place.
Page 8 of 29
9 1
Pars screw insertion
2
The entry point for the pars screw is 2-3 mm lateral and 2-3 mm rostral to the medial
3
edge of the C2-3 facet joint. Again, a burr is used to create a pilot hole. Next, a pedicle
4
finder is directed towards the C1-2 facet joint along the center of the pars
5
interarticularis and advanced forward until it touches the anterior cortex. This is
6
indicated by the resistance against further advancement of the pedicle finder as
7
described earlier. The rest of the procedure continues the same as for pedicle screw
8
insertion.
9
Intraoperative AP and lateral fluoroscopes or radiographs are only used as a final check
10
after screw placement is complete.
11
Statistical analysis
12
Statistical analysis was performed using SPSS version 18.0, (SPSS Inc., Chicago, IL, USA).
13
We used Fischer’s exact test or a Pearson chi-square test for categorical variables. A
14
probability value < 0.05 was considered statistically significant.
15 16
RESULTS
17
There were 198 cases enrolled in the study, including 90 males and 108 females (table
18
1). Ages ranged from 20 to 86 years (mean 59.9 years). The reasons for surgery were:
19
degenerative disease in 137 patients (69%), deformity in 51 (26%), trauma in 7 (3.5%),
Page 9 of 29
10 1
congenital condition in 2 (1%), and inflammation in 1 (0.5%). 122 patients (62%) had
2
prior cervical surgery before undergoing C2 instrumented surgery.
3
The most common procedure was a multi-level cervical fixation combined with occipital
4
and/or thoracic fixation in 91 patients (46%), followed by a multiple cervical fixation in
5
52 (26%). In total, 395 screws were placed, including 148 pedicle (37%), 219 pars (55%),
6
and 28 laminar screws (7%). Bilateral pedicle and pars screws were placed in 56 (28%)
7
and 93 (47%) patients respectively. When the fusion extended proximally to the occiput
8
or C1, either pars or pedicle screws were utilized (36 pars screws vs. 47 pedicle screws).
9
When the fusion extended proximally to C2, however, the authors’ preference was to
10
use C2 pars screw because it is generally easier to connect the C2 screws to the rods
11
(extending proximally to C2 from the subaxial spine where lateral mass screws were
12
utilized) without having to use offset connector or bending the rods laterally when pars
13
screws rather than pedicle screws are utilized (183 pars screws vs. 101 pedicle screws).
14
The length of C2 pars screws and pedicle screw averaged 20 mm (range 12-34 mm) and
15
24 mm (range 20-30 mm), respectively.
16
Incidental durotomies leading to CSF leakage occurred during exposure with the
17
electrocautery in 3 patients. During screw placement, there were no CSF leakages and
18
no neurological or vascular injuries. Only 1 pars screw was removed when the screw was
19
thought to be malpositioned during the fluoroscopic check. When the integrity of tract
20
was checked with the feeler again, there was no evidence of a cortical breach. The
21
screw was re-inserted into the same tract with no consequences. In the early
Comment [s1]: Phrasing changed as suggested by reviewer.
Comment [s2]: Additional information provided as requested.
Comment [JB3]: Clarification made as requested
Page 10 of 29
11 1
postoperative period, there were 4 cases of surgical infection (with 2 of these cases
2
requiring a reoperation for debridement). During the follow-up period, three patients
3
with bilateral C2 pars screws required revision surgery: 2 cases were due to unilateral C2
4
screw pullout and one case was for a symptomatic pseudarthrosis at C2-C3 without
5
instrumentation failure.
6
Postoperative CT scans were available for 76 patients. The most common reason for
7
obtaining a CT scan was persistent neck pain (34 patients). Other reasons included:
8
evaluation of instrumentation without any symptoms (14 patients), neurological deficits
9
(7 patients), new radicular pain (7 patients), trauma sustained after instrumentation (4
10
patients), instrumentation failure (3 patients), and other causes such as evaluation of
11
spinal metastases (7 patients).
12
Images for 139 screws were analyzed, including 52 pedicle screws and 87 pars screws
13
(table 2). In the C2 pedicle screw group, there were 12 breaches (23%); these included
14
10 screws with a grade I breach (19%), 1 screw with a grade II breach (2%) (figure 2), and
15
1 screw with a grade IV breach (2%). Lateral breaches occurred in 7 screws (13%),
16
inferior breaches in 3 (6%), and superior breaches in 2 (4%). There were no medial
17
breaches. The grade IV breach occurred superiorly into the C1-2 facet joint (figure 3).
18
There was no concern of joint degeneration because this patient underwent a C1-2
19
fusion. The other patient with a superior breach (grade I) had symptoms of occipital
20
neuralgia 6 months after surgery. CT evaluation showed tips of the breached screw
Comment [s4]: Long term complications provided as requested by the reviewer.
Comment [s5]: Inserted reference for figure 2.
Page 11 of 29
12 1
above the C1-2 joint and close to the C2 nerve. The screw was removed, and the
2
patient’s condition improved dramatically.
3
In the C2 pars screw group, there were 10 breaches (11%); these included 6 screws with
4
a grade I breach (7%), 2 screws with a grade II breach (2%), and 2 screws with a grade IV
5
breach (2%). Medial breaches were found in 4 screws (5%)(figure 4), inferior breaches in
6
2 (2%), superior breaches in 2 (2%), and lateral breaches in 2 (2%). Of the 2 screws with
7
grade IV breaches, one was located medially into the spinal canal and did not cause
8
neurological injury. The other (superior breach) was located near the C2 ganglion and
9
did not cause any early postoperative nerve root irritation. However, a new symptom of
10
occipital neuralgia appeared 18 months later, so the screw was removed.
11
There was no statistical significance between pedicle and pars C2 screws across all cases
12
of breaches (χ2 test, P= 0.07). There was also no statistical significance in the incidence
13
of high-grade breaches (breach grade III and IV) (Fisher exact test, P= 1).
14 15
DISCUSSION
16
Currently, pedicle and pars screws are accepted as the primary posterior C2 constructs
17
for atlantoaxial, occipitocervical, and subaxial fixation [21]. They provide immediate
18
stabilization and long-term fusion. Due to the variable anatomy of the C2 vertebra, a
19
preoperative CT scan is generally necessary for surgeons to clearly define bony
20
morphology and decide proper screw trajectory. If a preoperative CT scan is not
Page 12 of 29
13 1
available, an MRI scan can be utilized for the same purpose, although it is more difficult
2
to accurately determine the appropriate trajectory on an MRI compared to a CT as the
3
CT provides better bony detail compared to the MRI. Intraoperative CT scan is a
4
potential alternative. Pedicle diameter and vertebral artery position are analyzed to
5
determine whether pedicle screw placement is possible. Several studies show that the
6
incidence of narrow pedicle width and a high riding vertebral artery are up to 22.8% and
7
up to 31% respectively [22-24]. Both of these anatomic variations significantly increase
8
the risk of vertebral artery injury with pedicle screw placement [23]. In these cases,
9
pedicle screws should be avoided.
10
Since pedicle screws are placed near the spinal cord and vertebral artery, a misplaced
11
screw may lead to neurological and vascular injuries. To lessen this risk, intraoperative
12
fluoroscopy can be utilized during screw insertion. Though it does not guarantee
13
complete safety, the risk of vertebral artery injury is reduced. Out of 150 pedicle screw
14
placements under lateral fluoroscopic guidance, Ondra et al. [25] reported 1 case of
15
vertebral artery injury. Similarly, Bransford et al. [21] reported that 0.6% (2/339 screws)
16
of pedicle screws caused vertebral artery injuries. In most fluoroscopy-guided
17
operations, the screw tract is created using a drill, which lacks in tactile perception. It is
18
possible that cortical breaches can occur due to this. In contrast, the freehand
19
technique’s reliance on tactile feedback allows the surgeon to use anatomical landmarks
20
to prevent breaches. It also decreases both operative time and radiation exposure.
21
Nonetheless, there is a limited number of studies that report outcomes related to
22
freehand screw placement. In our study, there were no perioperative or early
Page 13 of 29
14 1
postoperative complications related to 148 pedicle screw placements using freehand
2
technique.
3
Postoperative CT scans in our study showed that the overall occurrence of cortical
4
breaches following pedicle screw placement was 23% (12/52 screws). Having said that,
5
one of the weakness of our study is that not all patients had a postoperative CT scan. In
6
their review of C2 pedicle screw placement, Elliott et al. [26] reported that the incidence
7
of malposition demonstrated by CT varied from 1.1 - 44% in cases with fluoroscopic
8
guidance. This wide range could be a result of varying standards of screw displacement
9
among studies. For example, Bransford et al.[21] defined unacceptable placement as
10
>50% of screw diameter out of cortical bone, and reported this in 1.2% of pedicle
11
screws. If breaches of less than 50% are included, the total incidence increased to 18%
12
(48/260 screws). This incidence is not much different from our study. Furthermore, a
13
freehand technique study by Sciubba and colleagues[20] recorded an overall incidence
14
of 15% while using the same classification method as ours. In both our study and
15
Sciubba’s, the majority of breaches were grade I (10/12 breaches and 13/15 breaches
16
respectively). This minor degree of breach rarely causes damage, as less than 1 mm of
17
screw is out of the cortical bone. In our study, a significant high-grade breach (at least
18
grade III) was only present in 1.9% of cases. This single case was a superior breach into
19
the C1-2 facet joint, which did not result in any clinical sequelae. Similarly, Sciubba et al.
20
reported a 2.0% incidence of high-grade breaches with no negative clinical
21
consequences. Therefore, the safety of freehand C2 pedicle screw insertion appears to
22
be comparable to that of fluoroscopic guidance.
Page 14 of 29
15 1
C2 Pars screws are usually reserved for patients with unfavorable anatomy for pedicle
2
screws. Thus, they are used infrequently compared to pedicle screws and reported
3
uncommonly in literature. In their review of C2 pars screw placement with fluoroscopic
4
guidance, Elliott et al. [26] reported that 3 - 8% of screws were malpositioned with no
5
arising complications. Regarding the freehand technique, a single cadaveric study [27]
6
reported 2 critical displacements in 16 screws, and concluded that freehand technique
7
was less reliable for pars screw than with pedicle screws. However, in our study there
8
were no intraoperative and early postoperative complications in 219 pars screw
9
placements. Postoperative CT scans revealed breaches in 11% of overall pars screws
10
(10/87). 2.3% (2/87) of cases were high-grade breaches, including 1 medial breach, and
11
1 superior breach. The patient with the medial breach into the spinal canal did not
12
experience any neurological deficits – likely due to the abundant space around the C2
13
level of the spinal cord. There was no statistically significant difference between
14
incidences of both overall and high-grade breaches when compared to pedicle screws in
15
our study. Based on these results, the safety of freehand insertion of C2 pars screws
16
appears to be similar to that of pedicle screws.
17
Out of the 22 total breaches, 2 pedicle and 2 pars screws were superior. One patient in
18
each group presented with occipital neuralgia months after surgery. Pain medication
19
provided insufficient relief, so the two patients underwent revision surgery to remove
20
the misplaced screw – and symptoms consequently improved. While superior breaches
21
were relatively uncommon in this study, they are especially rare in surgeries with
22
fluoroscopic guidance. Use of the lateral fluoroscope can prevent misplacement of
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screws in superior-inferior direction. Wang et al. [15] reported no cases of superior
2
breaches in 592 C2 pedicle screw insertions. Therefore, focusing on a possible superior
3
breach during the final fluoroscopic check is especially important when implementing
4
freehand technique.
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A limitation of this study is its retrospective design. Immediate post-op CT scans were
6
not available for all patients. To address this, we included follow-up CT scans that
7
showed no change when compared to the immediate postoperative radiographs.
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Overall, the freehand technique for both C2 pedicle and pars screws is a viable
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alternative to intraoperative fluoroscopy, particularly since it significantly reduces
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radiation exposure.
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CONCLUSIONS
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Use of freehand technique for C2 pedicle and pars instrumentation was safe without
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critical neurovascular complications. Preoperative assessment of anatomy for surgical
14
planning combined with intraoperative tactile feedback ensured accurate screw
15
placement.
Comment [s6]: Change made as requested by the reviewer.
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References 1. Gallie W. Fractures and dislocations of the cervical spine. Am J Surg. 1939;46:495-9. 2. Brooks A, Jenkins E. Atlanto-axial arthrodesis by the wedge compression method. J Bone Joint Surg Am. 1978;60:702-5. 3. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN. The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg. 1991;74(2):190-8. 4. Farey ID, Nadkarni S, Smith N. Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion. Clinical orthopaedics and related research. 1999;(359):126-35. 5. Jeanneret B, Magerl F. Primary posterior fusion C1/2 in odontoid fractures: indications, technique, and results of transarticular screw fixation. Journal of spinal disorders. 1992;5(4):464-75. 6. Mandel IM, Kambach BJ, Petersilge CA, Johnstone B, Yoo JU. Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws. Spine. 2000;25(12):1542-7. 7. Abou Madawi A, Solanki G, Casey AT, Crockard HA. Variation of the groove in the axis vertebra for the vertebral artery. Implications for instrumentation. The Journal of bone and joint surgery British volume. 1997;79(5):820-3. 8. Solanki GA, Crockard HA. Peroperative determination of safe superior transarticular screw trajectory through the lateral mass. Spine. 1999;24(14):1477-82. 9. Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine. 2001;26(22):2467-71. 10. Goel A, Desai KI, Muzumdar DP. Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery. 2002;51(6):1351-6; discussion 6-7. 11. Chen JF, Wu CT, Lee SC, Lee ST. Posterior atlantoaxial transpedicular screw and plate fixation. Technical note. Journal of neurosurgery Spine. 2005;2(3):386-92. 12. Aryan HE, Newman CB, Nottmeier EW, Acosta FL, Jr., Wang VY, Ames CP. Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. Journal of neurosurgery Spine. 2008;8(3):222-9. 13. Li L, Zhou FH, Wang H, Cui SQ. Posterior fixation and fusion with atlas pedicle screw system for upper cervical diseases. Chinese journal of traumatology = Zhonghua chuang shang za zhi. 2008;11(6):323-8. 14. Pan J, Li L, Qian L, Tan J, Sun G, Li X. C1 lateral mass screw insertion with protection of C1-C2 venous sinus: technical note and review of the literature. Spine. 2010;35(21):E1133-6. 15. Wang S, Wang C, Wood KB, Yan M, Zhou H. Radiographic evaluation of the technique for C1 lateral mass and C2 pedicle screw fixation in three hundred nineteen cases. Spine. 2011;36(1):3-8.
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16. Stokes JK, Villavicencio AT, Liu PC, Bray RS, Johnson JP. Posterior atlantoaxial stabilization: new alternative to C1-2 transarticular screws. Neurosurgical focus. 2002;12(1):E6. 17. Mummaneni PV, Lu DC, Dhall SS, Mummaneni VP, Chou D. C1 lateral mass fixation: a comparison of constructs. Neurosurgery. 2010;66(3 Suppl):153-60. 18. Thomas JA, Tredway T, Fessler RG, Sandhu FA. An alternate method for placement of C-1 screws. Journal of neurosurgery Spine. 2010;12(4):337-41. 19. Kang MM, Anderer EG, Elliott RE, Kalhorn SP, Frempong-Boadu A. C2 nerve root sectioning in posterior C1-2 instrumented fusions. World neurosurgery. 2012;78(12):170-7. 20. Sciubba DM, Noggle JC, Vellimana AK, et al. Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws. Clinical article. Journal of neurosurgery Spine. 2009;11(1):15-22. 21. Bransford RJ, Russo AJ, Freeborn M, et al. Posterior C2 instrumentation: accuracy and complications associated with four techniques. Spine. 2011;36(14):E936-43. 22. Wajanavisit W, Lertudomphonwanit T, Fuangfa P, Chanplakorn P, Kraiwattanapong C, Jaovisidha S. Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique. Asian spine journal. 2016;10(6):1141-8. 23. Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013;13(7):775-85. 24. Wakao N, Takeuchi M, Nishimura M, et al. Vertebral artery variations and osseous anomaly at the C1-2 level diagnosed by 3D CT angiography in normal subjects. Neuroradiology. 2014;56(10):843-9. 25. Ondra SL, Marzouk S, Ganju A, Morrison T, Koski T. Safety and efficacy of C2 pedicle screws placed with anatomic and lateral C-arm guidance. Spine. 2006;31(9):E263-7. 26. Elliott RE, Tanweer O, Boah A, Smith ML, Frempong-Boadu A. Comparison of safety and stability of C-2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review of the literature. Journal of neurosurgery Spine. 2012;17(6):577-93. 27. Helgeson MD, Lehman RA, Jr., Dmitriev AE, et al. Accuracy of the freehand technique for 3 fixation methods in the C-2 vertebrae. Neurosurgical focus. 2011;31(4):E11.
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Figure Legends
2
Figure 1. Postoperative lateral (D) and anteroposterior (E) radiographs with right pars
3
and left pedicle screws at C2. Postoperative CT scans were reformatted to identify a
4
cortical breach from a coronal view. The right side pars screw was in the correct place in
5
reconstructed coronal view (C), which is lined up orthogonally to the screw by using a
6
parallel plane in both the sagittal (A) and axial view (B). Also, there were no breaches of
7
the left pedicle screw on the reconstructed coronal view (H), again aligned from the
8
sagittal (F) and axial views (G).
9 10
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Figure 2. Pedicle screw was misplaced with grade II (26-50%) and inferior breach on
2
coronal (A) and sagittal (B) views
3 4
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Figure 3. Reconstructed coronal (A) and sagittal (B) views demonstrated a grade IV (76-
2
100%) and superior breach into C1-2 facet joint in C1-2 fusion procedure.
3 4
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Figure 4. Reconstructed coronal (A), sagittal (B) and axial (C) CT scan showed grade I (1-
2
25%) and medial breach to spinal canal on left pars screw.
3 4 5
Table 1. Patient Data Characteristic Patients Female (%):Male(%) Mean Age –years (range) Diagnosis (%) Cervical spondylosis Cervical deformity Trauma RA Congenital (Os Odontoidium) Procedure (%) 1 level (C1-2 or C2-3) Multi-level cervical fixation Multi-level cervical fixation with either ..occipital or thoracic levels Single stage anterior-posterior surgery
Number 198 98(55%):90(45%) 60 (20-86) 137 (69%) 51 (26%) 7 (3.5%) 1 (0.5%) 2 (1%)
26 (13%) 52 (26%) 91 (46%) 29 (15%)
Total C2 screws (%) Pedicle Pars Intralaminar
395 148 (37%) 219 (55%) 28 (7%)
Mean follow-up in mos. (range)
22.6 (1-118)
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Complication CSF leakage during exposure Surgical site infection Occipital neuralgia
3 (1.5%) 4 (2%) 2 (1%)
1 2 3
Table 2. Accuracy of C2 screw placement under CT evaluation (L = lateral, M = medial, S
4
= superior, I = inferior)
5 Cortical breach Grade (location), (%)
I II III IV Overall Breach
Pedicle (n=52)
Pars (n=87)
P
10 (7L, S, 2I) (19%) 1 (I) (2%) 1 (S) (2%) 12 (23%)
6 (2L, 2M, S, I) (7%) 2 (M, I) (2%) 2 (S, M) (2%) 10 (11%)
1 0.07
6 7 8
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