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Clinical Application and Efficacy Analysis of 3D Navigation Module

in the Treatment of Atlantoaxial Instability

Research article

Clin Surg Res Commun 2018; 2(4):

1-11

DOI: 10.31491

CSRC.2018.12.023

Yong-xiong He

et al

Bo-kang Lv

, Yong-xiong He

Abstract

Background:

Posterior cervical atlantoaxial pedicle screw fixation is a very effective treatment for atlantoaxial

instability (AAI). However, due to the complex anatomy of the cranial-cervical junction, the accuracy and safety

of posterior atlantoaxial pedicle screw placement remains extremely challenging.

Objective:

To quantitatively evaluate the safety and accuracy of the 3D navigation module to assist the

posterior atlantoaxial fixation.

Methods:

A total of 20 AAI patients were selected between June 2014 and September 2015. The Mimics v10.1

and 3-matic software were used. The 3D navigation module was designed as a double-sided positioning hole

guide with a guide rod. All patients underwent posterior atlantoaxial posterior pedicle screw fixation with

3D navigation module. The actual entry point and screw trajectory were measured after operation, which

were compared with the ideal entry point and screw trajectory. The Japanese Orthopaedic Association (JOA)

score was measured before and after surgery to evaluate the neurological function improvement. The average

operation time, blood loss, and frequency of intraoperative fluoroscopy were counted.

Results:

The posterior atlantoaxial pedicle screw fixation with a 3D navigation module was successfully

performed in all patients. A total of 80 atlantoaxial pedicle screws were implanted in the 20 patients.

Postoperative CT scan showed that two pedicle screws deviated from the medial aspect of the atlas pedicle

cortex and entered the spinal canal approximately 1 mm, without causing neurological complications. There

was no significant difference between the ideal and actual entry points or ideal and actual screw trajectories

of the atlas and axis (P > 0.05). The preoperative JOA score was 12.45 ± 1.15 and postoperative JOA score was

15.5 ± 0.89, with statistically significant difference (P < 0.05).

Conclusion:

It was safe and effective to use the 3D navigation module to assist the posterior atlantoaxial

pedicle insertion, with a high accuracy of pedicle screw placement.

Keywords:

atlantoaxial instability; pedicle screw; 3D navigation module; rapid prototyping

*Corresponding author: Yong-xiong He

Mailing address: Department of Spine Surgery, Inner Mongolia

People’s Hospital, Saihan District Zhao wuda road No.42,

Hohhot 010017, Inner Mongolia, China.

E-mail: spinedoctor@sina.com

Tel: +86-0471-2243347

Received: 15 November 2018 Accepted: 15 December 2018

screw fixed the three columns (anterior, median, and

posterior) of the vertebral body and thus provided a

good three-dimensional fixed pattern, it has obvious

advantages compared with other fixed methods by

biomechanics

[5]

. However, as the cervical vertebra has

a complex anatomical structure and an important adja-

cent relationship, and the pedicle is relatively slender

with great angle change, the most common and most

serious surgical complications are C2 nerve root and

vertebral artery injures that are caused by the pedicle

screw trajectories deviating from the pedicle cortex

[6]

which makes the clinical application of posterior cervi-

cal pedicle screw fixation extremely limited. Therefore,

how to improve the accuracy of screw placement and

reduce surgical complications is an important problem

that needs to be solved urgently in clinical work.

The cervical pedicle screw fixation methods currently

used in the clinic include bare-handed screw-setting

[7]

, screw-setting assisted by the imaging techniques,

INTRODUCTION

In recent years, patients with atlantoaxial instabili-

ty (AAI) have been routinely treated with posterior

atlantoaxial pedicle screw fixation

[1-3]

. The cervical

spondylosis requiring internal fixation was generally

caused by multiple injuries and such injuries were

often combined with fracture dislocation, leading to

the destruction of its three-column structure. In 1994,

Abumi, et al.

[4]

successfully applied and promoted

the posterior cervical pedicle screw fixation in the

treatment of lower cervical injury. Because the pedicle

Department of Spine Surgery, Inner Mongolia People’s Hospital, Hohhot 010017, Inner Mongolia, China.

Published online: 25 December 2018

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Yong-xiong He et al

computer-assisted orthopaedics surgery (CAOS)

[8]

, and

3D printing technology that was also called comput-

er-aided design-rapid prototyping (CAD-RP technolo-

gy). The key points of the bare-handed screw-setting

are the accuracy of the point and direction of the screw,

rich experience, and intraoperative fluoroscopy. The

screw-setting assisted by the imaging techniques has

high requirements for doctors' knowledge accumu-

lation, experience judgment, and spatial imagination,

causing certain subjectivity and lacking objective mea-

surement standards. CAOS makes intraoperative sur-

gery more precise, safe and effective, but its expensive

equipment costs and operational complexity limit its

promotion and application

[9-11]

. The CAD-RP technique

was first applied to lumbar pedicle screw placement

by Radermacher

et al.

[12]

. It is a kind of modern digital

orthopedic technology. Its principle is to scan the struc-

ture of tissue and organ through CT, generate a propor-

tional 3D module corresponding to the real object, and

make a solid model proportional to the patient through

the 3D printer; through the solid model, the surgical

simulation and intraoperative reference and appli-

cation are performed

[10]

. The rapid prototyping drill

guide template designed by 3D printing technology can

help improve the accuracy of the screw placement

[13-16]

In this prospective clinical study, we designed a drill

guide template for atlantoaxial pedicle screw place-

ment. The purpose of this study was to quantitatively

evaluate the accuracy of placement of atlantoaxial ped-

icle screws using a drill guide template.

MATERIALS AND METHODS

Subjects

All patients signed written informed consent. In ad-

dition, this study followed the principles outlined in

the Helsinki Declaration. Patients with atlantoaxial

instability (AAI) who were hospitalized and surgically

treated in our hospital from June 2014 to September

2015 were enrolled in this prospective study. A total

of 20 patients who underwent AAI posterior approach

(17 Male and 3 female), with an average age of 42.6

years (age range 22-46 years), were selected based on

the inclusion and exclusion criteria. All AAI patients

underwent posterior atlantoaxial pedicle screw fixa

tion with a drill guide template. All protocols have been

approved by the Committee of Inner Mongolia People’s

Hospital.

Diagnostic criteria:

All patients were diagnosed with

AAI by clinical and imaging examinations and had clini-

cal symptoms.

Inclusion criteria:

patients who meet the diagnostic

criteria; patients who can be placed with the atlantoax-

ial pedicle screw by X-ray, computed tomography (CT),

and magnetic resonance imaging (MRI) examinations;

patients whose surgeries were performed by the same

senior physician.

Exclusion criteria:

patients with severe vertebral injury,

malformation, small posterior arch, etc.; patients with

advanced age, combined with serious medical diseases

and osteoporosis, unable to tolerate surgery; patients

with infection, tuberculosis, tumor, and other complica-

Figure 1. A. The atlantoaxial and drilling guides produced by Mimics software. B. Atlantoaxial models and drilling guides
generated using rapid prototyping techniques. C. 3D module disinfection backup and 3D module placed on the spinous

process of the axon. D. The accurate internal fixation showed by postoperative X-ray.

Yong-xiong He et al

Clin Surg Res Commun 2018; 2(4):

1-11

tions; patients who had a mental illness.

Construction of 3D navigation module

Software Platform

Mimics (Materialise's interactive medical image con-

trol system), known as "Dream Factory of Medical

Imaging", is a medical image control system developed

by Materialise of Belgium to realize interoperability.

Through this software, various medical imaging mate-

rials such as CT, MRI, and other two-dimensional data

are imported, and then the image data are analyzed

by the clinician on three different orthogonal planes:

cross-section, coronal plane, and sagittal plane. The

valuable areas are optimized to get the desired data,

and then the 3D data model is rebuilt. Through the sur-

gical simulation operation, virtual surgical operations

can be performed in the software, such as pre-surgical

program and prosthesis placement. Mimics can per-

form 3D reconstruction of imaging data, providing sup-

port for a variety of supporting software applications

such as virtual reality (VR), computer-aided design

(CAD), finite element analysis (FEA), and rapid proto

typing (RP). Therefore, Mimics can be used for clinical

diagnosis, surgical simulation (pre-surgical program,

virtual surgery operation, prediction and analysis

of surgical risk), and can also be applied to anatomy

teaching and scientific research. It has great potential

for functional development

[17]

3-matic is a forward engineering based on Digital

Standard Triangle Language (STL) produced by Ma-

terialise. It can directly edit and modify STL format

files to implement FEA/CFD processing in various STL

formats. All operations of 3-matic are based on digital

form (triangle based) for stretching, rotation, array-

ing, etc. It can directly copy and paste the anatomical

data in Mimics software, and can input them into any

CAD document. Through 3-matic, we can implement

3D measurement and engineering analysis, design

implants and surgical guidelines for specific patient

surgeries, and prepare anatomical data or implants for

finite element simulations. This study used 3-matic to

create a personalized navigation template for atlanto-

axial pedicles, which greatly reduced the time required

to create navigation templates using traditional reverse

engineering

[17]

Atlantoaxial pedicle screw simulation placement

All patients underwent cervical CT with a tomographic

thickness of 0.625 mm. CT images were imported into

Mimics software and the atlantoscopic 3D model was

constructed. In the virtual environment of the Mimics

software, a cylinder (3.5 mm in diameter) was created

as an atlantoaxial pedicle screw, which is because it is

easier to make and adjust the position of the cylinder

in the software. The ideal trajectory of the atlantoaxial

pedicle screw was created and adjusted by directly ob-

serving the relationship between the cylinder and the

pedicle cortical bone in different planes.

Production of atlantoaxial 3D guide module

Then the 3D model of the atlantoaxial vertebral body

and the cylinder was introduced into the 3-matic (Ma-

terialise) software to design a 3D drilling guide module

with drilling guidance. In the 3-matic software, the sur-

face of the template (2.5-mm thickness) was created as

DOI: 10.31491

CSRC.2018.12.023

Figure 2. A. Postoperative images of C1. B. Preoperative images of C1. C. Superimposition of preoperative and postoperative

images of C1. D, E: Adjusted C1 coordinate axis. F. Adjusted C2 coordinate axis.

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Yong-xiong He et al

the Mayfield head frame. The median incision of the

posterior neck was taken and separated layer by layer

to fully reveal the posterior structure of the atlanto-

axial vertebrae, including the posterior tibial tuber-

osity and posterior arch, lamina, and lateral vertebral

blocks. The soft tissue covering the bony structure was

completely peeled off by subperiosteal peeling to make

the drill guide template to be fully compatible with the

posterior surface of the vertebra. The drill guide was

fixed and the guide hole was drilled through the tem

plate positioning hole, followed by the drilling of the

trajectory parallel to the guide rod of the template. The

probe was used to detect the four walls of the nailing

channel were leaking. The intraoperative fluoroscopy

was used to confirm that the drilled trajectory was

ideal. If the actual trajectory deviated from the ideal

trajectory due to the poor fit between the template

and the posterior atlantoaxial surface, the direction

of the drill was adjusted according to the template.

After achieving the ideal spiral path, a 3.5-mm screw

was inserted. The pre-bent rods were then secured

to the sides of the atlantoaxial pedicle screws (Fig. 1).

Decompression of the occipital foramen was then per-
formed if necessary.

Postoperative treatment

The patient’s vital signs were closely observed. Post-

operative routine hormones were given to prevent

spinal cord inflammation and edema; antibiotics were

given to prevent infection; meeobalamin was used for

nourishing nerves. The drainage tube was routinely

removed within 48 hours. The patient was routinely

bedridden 3-5 d, with the axis turned over; after 3-5d,

the opposite side of the posterior atlantoaxial surface,

thus providing a perfect fit between the template and

the posterior atlantoaxial surface. Using a Boolean

subtraction operation, two position holes (3.5-mm

diameter) were created on both sides of the template

surface based on the data of the cylinder. After the

cylinder was interactively translated, two guide holes

(3.5-mm diameter) were created on the optimum en-

try points on either side of the template surface. The

direction of the drill guide hole was exactly the same

as the optimum nailing direction. The local Boolean

operation was used to combine the drill guide hole

and the template surface with the positioning hole

into one unit .

Physical molding of 3D guides

The DICOM format of the cervical CT of the patient

was introduced into the Mimics software, and the at-

las template of interest was obtained by operation of

thresholding, region growing, crop mask, editing mask,

etc. Then the atlas template selected, followed by the

click of the “Calculate 3D” button to complete the 3D

reconstruction of the atlas. The 3D model of the atlas

was displayed in the 3D viewport and was smoothed,

reduced by triangle reduction, etc. The final 3D model

of the atlas was obtained, and then imported into a 3D

printer to print out the patient’s atlantoaxial model

using a photosensitive resin material.

Surgical procedures

All operations were performed by the same senior

surgeon. The patient was placed in the prone position

under general anesthesia and the head was fixed by

Figure 3. A. Cross-sectional angle of the actual screw trajectory of C1. B. Sagittal angle of the actual screw trajectory of C1. C.
Entry point of the actual screw trajectory of C1. D. Transverse angle of the ideal screw trajectory of C1. E. Sagittal angle of the

Yong-xiong He et al

Clin Surg Res Commun 2018; 2(4):

1-11

patients would go to the ground. The neck brace was

worn for 3 months after operation, followed by the

X-ray examination of the cervical spine. According to

the results of the review, the neck brace was removed.

Evaluation of outcomes

Evaluation of screw trajectories

The accuracy of the atlantoaxial pedicle screw was

analyzed by a physician who did not participate in sur-

gical stapling. All patients had cervical CT scans after

surgery. Preoperative and postoperative CT images

were imported into Mimics software. The preopera-

tive atlantoaxial 3D model and cylinder as well as the

postoperative atlantoaxial 3D model and screw were

reconstructed. The "global registration" operation was

used to superimpose the preoperative 3D model with

the cylinder and the postoperative 3D model with the

screw. This overlay facilitated the comparison of the

cross-sectional angle and sagittal angle between the

ideal screw trajectory with the actual screw trajectory

(Fig. 2 and 3). Besides, the patient was routinely ex-

amined by CT after surgery, and the picture archiving

and communication system (PACS) measurement tool

was used to display the relative positional relationship

between the screw and the pedicle according to the

CT slice. Screw-setting accuracy was evaluated by the

methods provided by Yoshiharu

et al

[18]

, Miyamoto

et al

[19]

, and Yasutsugu

et a

[20]

. Grade 0: The screw

is completely placed inside the pedicle; Grade I: the

screw penetrates the pedicle bone cortex ≤ 2 mm,

without neurological or vertebral artery injury and

other complications associated with screw placement;

Grade II: screw penetrates the pedicle bone cortex>

2mm, without neurological or vertebral artery injury

and other complications related to nailing; Grade III:

neurological or vertebral artery injury and other com-

plications related to screw placement occur.

Evaluation of the entry points

In order to properly compare the ideal and actual

coordinates of the entry point, the axis of the atlanto-

axial axis was adjusted. For C1, the front nodule was

treated as the origin of the coordinate axis. The x-axis

passed through the origin of the coronal plane and

was parallel to the line connecting the lowest points of

the lower articular processes on both sides. The y-axis

and the z-axis passed through the origin and were per-

pendicular to the x-axis of the horizontal and coronal

planes, respectively. In the case of the C2 vertebra, the

midpoint of the line connecting the lowest points of

DOI: 10.31491

CSRC.2018.12.023

Figure 5. Comparison of the angle between the ideal and actual screw trajectory in (A) C1 and (B) C2. ls, lateral section; sp,
sagittal plane.

Figure 4. Schematic diagram of JOA scores before

and after surgery. *P < 0.05.

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Yong-xiong He et al

the articular processes on both sides was regarded as

the origin. The y-axis and the z-axis passed through the

origin and were perpendicular to the x-axis of the hori-

zontal and coronal planes, respectively (Fig. 2).

Evaluation of neurological function improvement

The JOA score was used to evaluate the neurological

function of the patient before and 6 months after sur-

gery. The score was divided into 17 points. The higher

the score, the better the neurological function.

Statistical analysis

Statistical analysis was performed using SPSS 13.0

statistical software. Data were expressed as mean ±

standard deviation. The comparisons were performed

using paired-sample t-test. P < 0.05 was considered as

significantly different.

RESULTS

Statistics of postoperative general results

All patients successfully underwent surgery with the

aid of a drill guide template. Five of the 80 screws were

placed in a direction that was adjusted during surgery,

and a satisfactory screw trajectory was achieved after

adjustment. No complications such as vertebral artery

injury, cerebrospinal fluid leakage or spinal cord injury

were found. Three patients developed venous plexus

hemorrhage. The mean operative time was 174.3 ±

27.6 minutes and the mean bleeding volume was 312.9

± 13.5 ml. The mean frequency of intraoperative fluo

roscopy was 2.60 ± 0.68.

Comparison of JOA scores before and after

surgery

The scores of the Japanese Orthopaedic Association

(JOA) were compared between pre-surgery and 6

months after surgery. The preoperative JOA score was

12.45 ± 1.15 and postoperative JOA score was 15.5 ±

0.89, with statistically significant difference (P < 0.05)

(Fig. 4).

Comparisons between the ideal and actual

screw trajectories, entry points

A total of 80 atlantoaxial pedicle screws were placed

in 20 AAI patients. Postoperative CT scan showed 79

grade 0 screws and 1 grade I screw. One of the pivot-

al screws deviated inwardly from the pedicle cortex

and entered the spinal canal approximately 1 mm,

but no neurological and surgical complications oc-

curred. There was no significant difference in the mean

cross-sectional angle between the left (P = 0.45), right

(P = 0.79) ideal screw trajectory and actual screw tra-

jectory of atlas. No significant difference in the mean

sagittal angle was observed between the left (P = 0.30),

right (P = 0.10) ideal screw trajectory and the actual

screw trajectory of atlas (Table 1 and Fig. 5A). Be-

sides, there was no significant difference in the mean

cross-sectional angle between the left (P = 0.39), right

(P = 0.11) ideal screw trajectory and actual screw tra-

jectory of axis. No significant difference in the mean

sagittal angle was observed between the left (P = 0.17),

right (P = 0.33) ideal screw trajectory and the actual

screw trajectory of axis (Table 2 and Fig. 5B). As for the

screw entry point coordinates, there was no significant

difference between the ideal entry point and the actual

entry point on both sides of the atlases, axises (P > 0.05)
(Table 3 and Table 4).

Comparison between bare-handed or naviga-

tion module-assisted screw-setting in previ-

ous study

[17]

and navigation module-assisted

screw-setting in our study

Screw

trajectory

C1 left (°)

C1 right (°)

Cross-sectional angle

Sagittal angle

Cross-sectional angle

Sagittal angle

Ideal trajectory

7.92 ± 2.37

7.75 ± 0.81

8.59 ± 0.70

8.70 ± 1.05

Actual trajectory

7.82 ± 1.85

8.02 ± 0.55

8.51 ± 0.71

8.36 ± 1.11

0.45

0.30

0.79

0.10

Screw

trajectory

C2 left (°)

C2 right (°)

Cross-sectional angle

Sagittal angle

Cross-sectional angle

Sagittal angle

Ideal trajectory

23.68 ± 3.62

25.59 ± 1.62

22.82 ± 1.46

24.57 ± 1.33

Actual trajectory

24.59 ± 3.86

25.42 ± 1.55

21.93 ± 1.67

25.07 ± 1.86

0.39

0.17

0.11

0.33

Table 1 Comparison of the angle between the ideal and actual screw trajectory in C1.

Table 2 Comparison of the angle between the ideal and actual screw trajectory in C2.

Yong-xiong He et al

Clin Surg Res Commun 2018; 2(4):

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DOI: 10.31491

CSRC.2018.12.023

In our study, using navigation module-assisted

screw-setting, 40 screws were placed in the atlas with

40 screws of grade 0 (100%) and 40 screws were

placed in the axis with 39 screws of grade 0 (97.5%)

and 1 screw of grade I (2.5%).

In the reference

[17]

, using bare-handed screw-setting,

44 screws were placed in the atlas, with 21 screws

of grade 0 (47.7%), 17 screws of grade I (38.6%), 4

screws of grade II (9.14%), and 2 screws of grade III

(4.5%); using navigation module-assisted screw-set-

ting, a total of 38 screws were placed with 35 screws of

grade 0 (92. 1%) and 3 screws of grade I (7.9%).

In our study, grade 0 and grade I screws were consid-

ered as satisfactory screws. The satisfaction rate of

atlantoaxial screw placement in this study was 100%

(40/40; 40/40). In the reference

[17]

, the satisfaction

rate was 86. 3% (38/44) for bare-handed screw-setting

and was 100% (38/38) for navigation module-assisted

screw-setting.

Using the rank sum test analysis, the accuracy of

screw-setting was significantly improved in our study

compared with the bare-handed screw-setting group

of the reference (P < 0.01). Further, there was no sig-

nificant difference in the accuracy of navigation mod

ule-assisted screw-setting between our study and the

reference (P > 0.05)(Tables 5 and 6).

Comparison of postoperative general results

between the previous study

[17]

and our study

The average operation time of our study was 174.3 ±

27.6 min, with the average blood loss of 312.9 ± 13.5ml.

Referring to the previous literature

[17]

, for bare-hand-

ed screw-setting and navigation module-assisted

screw-setting, the average operation time was 175 ±

41 min and 175 ± 41 min with the average blood loss

of 407 ± 116 ml and 428 ± 104 ml, respectively. Since

there was no detailed data in the reference, simple

comparisons can only be made with mean ± standard

deviation. The average operation time of this study was

similar to that of the reference, but the average amount

of bleeding was slightly reduced (Fig. 6A and B).

Finally, typical cases and special cases were shown in

supplementary Fig. 1-3.

DISCUSSION

Cervical pedicle screw placement is a difficult point

in spinal surgery. This is related to the particularity of

the atlantoaxial anatomy, which also leads to the risk

of surgery under normal anatomy, and surgery is more

challenging when fractures and dislocations occur in

Figure 6. Comparison of the (A) mean blood loss volume and (B) mean operation time between the three groups.

Entry point

C1 left (°)

C1 right (°)

Ideal point

25.59 ± 1.63

30.70 ± 0.97

0.49 ± 0.73

-15.02 ± 0.74

32.06 ± 1.07

0.01 ± 0.47

Actual point

25.42 ± 1.55

31.36 ± 1.12

0.55 ± 0.15

-15.24 ± 0.80

31.67 ± 1.09

0.23 ± 0.57

0.78

0.13

0.19

0.30

0.23

0.18

Table 3 Comparison of the ideal entry point and actual entry point in C1.

x, coronal axis; y, sagittal axis; z, vertical axis.

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Yong-xiong He et al

this area

[21]

. Therefore, clinically, atlantoaxial fixation

is difficult and has a high potential risk, and it has been

called a surgical "forbidden zone". CAD-RP technology

can accurately control the patient's anatomy and indi-

vidual differences before surgery, thus improving the

accuracy of atlantoaxial screw-setting. Jiang

et al.

[22]

used 3D navigation modules to assist the placement

of 128 atlantoaxial pedicle screws in 32 patients with

AAI. Postoperative CT showed that the atlas had two

screws protruding into the spinal canal < 1mm without

causing related complications. Although the anatomi-

cal structure of the lower cervical vertebra is not more

specific than the atlantoaxial vertebrae, it is one of the

difficult factors for screw placement due to individual

differences and damage

[23-25]

. In addition, Kaneyamade

et al.

[26]

applied a 3D navigation module to assist the

placement of 80 screws in the lower cervical spines of

20 patients; after surgery, all 80 screws were found in

the pedicle without related complications.

In the present study, the guide template of this study

also selects the type of single-vertebral double-sided

drilling guide plate which is currently used more. This

type of drilling guide plate can select the spinous pro-

cess as a fixed site and has double-sided drilling guide

plate, which can be well fixed during operation. The

drill guide has the advantage of drilling direction, and

intuitively presents the direction of the screw. If neces-

sary, it can help to adjust the direction of the screw. We

found that a screw of the vertebral pedicle deviated in-

wardly from the pedicle cortex and entered the spinal

canal approximately 1 mm, but there was no symptom.

This deviation may be caused by the failure to remove

the soft tissue during surgery, possibly resulting in

insufficient fit between the template and the posterior

vertebral surface. Therefore, the soft tissue on the pos-

terior arch surface of the atlas should be completely

removed before applying the drill guide template. In

previous studies, the efficacy of spinal screw place

ment was demonstrated in a bilateral guide template.

In the cadaveric study, Hu et al.

[27]

placed 64 C1 pedicle

screws and 64 C2 pedicle screws without causing a

screw to penetrate the cortex. However, it should be

noted that the subject is a cadaver. The factors that may

affect the results are listed as follows: preoperative and

postoperative CT scans can be consistent in position;

during the operation, the exposure and peeling of the

operation area can be revealed and peeled off as much

as possible.

Regarding the assessment of screw placement accu-

racy, some studies have simply reported the extent of

screw insertion into the spinal canal in postoperative

CT scans

[28]

. In this study, we also made more accurate

evaluation criteria in addition to the statistics of the

degree of screw insertion into the spinal canal. After

using the 3D navigation module to assist the placement

of the screw, the CT scan was first performed on the

postoperative patients. The high-quality rate of the

screw-setting was evaluated by the method developed

by Yoshiharu

et al

[18]

. A total of 80 individual screws

were placed in the personalized navigation template

group, of which 79 were grade 0 and 1 was grade I,

with the screw-setting satisfaction rate was 100%. Al-

though this CT scan-based method helps to make the

overall evaluation of the screw position, it cannot help

Groups

No. of screws

Grade 0

Grade I

Grade II

Grade III

Bare-handed screw-setting in
previous study

[52]

Navigation-assisted screw-setting
in our study

420

< 0.01

Table 5 Comparison of the accuracy between bare-handed screw-setting in previous study

[52]

and navigation mod-

ule-assisted screw-setting in our study.

Entry point

C2 left (°)

C2 right (°)

Ideal point

19.22 ± 0.71

22.70 ± 1.57

-2.28 ± 0.61

-19.38 ± 0.78

-2.02 ± 0.48

Actual point

19.34 ± 1.07

22.35 ± 0.98

-2.40 ± 0.55

-19.28 ± 0.88

-19.28 ± 0.87

-2.22 ± 0.64

0.19

0.31

0.55

0.17

0.16

0.33

Table 4 Comparison of the ideal entry point and actual entry point in C2.

x, coronal axis; y, sagittal axis; z, vertical axis.

Yong-xiong He et al

Clin Surg Res Commun 2018; 2(4):

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DOI: 10.31491

CSRC.2018.12.023

to effectively compare the ideal and actual trajectories

of the screw. Hu

et al.

[27]

analyzed the positional devi-

ation of C2 laminar screws from the ideal and actual

entry points as well as trajectory directions. Hu et al.

superimposed the preoperative and postoperative at-

lantoaxial models in Mimics software and compared

the ideal and actual screw trajectories. This is a more

efficient way to compare the ideal and actual screw

trajectories. In this study we also used this method to

compare the ideal and actual screw trajectories. The

results showed that the application of the drill guide

module to assist the placement of the pedicle screw

was extremely accurate, and there was no statistical

difference between the two screw trajectories. The

evaluation of the two screw trajectories can not only

overall reflects the satisfaction rate of screw-setting,

but also analyzes the ideal and actual screw trajectory

angles in different planes, making the evaluation of

screw-setting accuracy more perfect.

The

average operation time in this study was similar

to that in

the previous study

[17]

. However, the

average

blood loss of this study was significantly lower than

that in the reference

[17]

, possibly due to the

following

points. First, there were differences in the number of

experimental subjects: 20 subjects in this study, 22

cases in the

bare-handed screw-setting

group of the

reference, and 19 cases in the

navigation module-

assisted screw-setting

group of the reference. Second,

the differences in the intraoperative situation and

the patient's own situation. The age of patients in our

study was significantly different from the overall age

of the reference. The maximum age of the experiment

was 46 years, and the maximum age of the reference

was 64 years. Finally, intraoperative application of

devices and personal operating habits may also be the

cause. Besides, we found that the amount of bleeding

in the

navigation module-assisted screw-setting

group

was higher than that in the

bare-handed screw-setting

group

[17]

, possibly resulting from the pursuit of the

fitting degree of the guide to increase the extent of

the vision field and soft tissue peeling during the use

of guide templates. We believe that when using 3D

navigation templates, we should combine the actual

situation in the operation, and reduce the degree of

peeling as much as possible without affecting the

accuracy of screw placement.

During the operation of this study, it was found that

the texture of the material used in the navigation

template, a photosensitive resin material, was rela-

tively soft and slight deformation occurred during

use, which may be one of the causes of errors in this

experiment. Owing to the diversity of materials of 3D

printing technology, metal materials would be used

to make navigation templates in the subsequent sur-

geries, which may eliminate related problems in this

study. Besides, considering that the operating rooms of

most lower-level hospitals may not be equipped with

plasma disinfection equipment, the upgraded mate-

rials can also be used in the operating room without

plasma disinfection equipment, which is conducive to

clinical promotion. Further, in the early stage of the

surgery, the surgeon with relatively lack of experience

was selected for operation, resulting in a decrease in

the satisfaction rate of the screw-setting. The postop-

erative X-ray film clearly showed the screw offset, but

no neurological complications. Therefore, we believe

that 3D navigation template-assisted screw-setting can

greatly improve the accuracy of screw placement, but it

is not omnipotent. This method still requires the oper-

ation of a physician with certain experience, and there

is also a certain requirement for the understanding and

proficiency of the use of the guide in case of emergen

cy. However, the guide template is still positive for the

guidance of young physicians, which can greatly reduce

the learning curve and improve the accuracy of screw

placement.

After this stage of surgery accumulation, we have two

thoughts on the 3D navigation module. First of all, most

of the currently used navigation module materials are

photosensitive resin materials. In this study, the prob-

lems caused by the disinfection and use of materials

have highlighted the limitation of the 3D navigation

module itself. We consider further optimized materials

as metal 3D navigation modules. Secondly, we encoun-

Groups

No. of screws

Grade 0

Grade I

Grade II

Grade III

Navigation-assisted screw-setting
in previous study

[17]

Navigation-assisted screw-setting
in our study

700

0.072

Table 6 Comparison of the accuracy of navigation module-assisted screw-setting between the previous study

[17]

and

our study.

ANT PUBLISHING CORPORATION

Published online: 25 December 2018

Yong-xiong He et al

tered a deviation in the use of navigation templates due

to poor chimerism, affecting the accuracy and safety of

the screw placement. We believe that if the guide rod of

the external screw-setting angle can be added during

the production of the navigation template, the accura-

cy and safety of the screw-setting may be further im-

proved. When a similar problem is encountered, even if

the navigation template is not well fitted, the guide rod

can still guide the screw placement.

In conclusion, the use of 3D navigation module is safe

and effective for atlantoaxial pedicle screw implanta-

tion, which can significantly improve the accuracy of

screw placement and prevent surgical complications.

Therefore, the 3D navigation module-assisted posterior

atlantoaxial fixation is worthy of clinical application.

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