Accepted Manuscript Radiographic and Clinical Assessment of a Freehand Lateral Mass Screw Fixation Technique : Is it always safe in subaxial cervical spine? In-Hoo Ra, M.D. Woo-Kie Min, M.D, Ph.D. PII:
S1529-9430(14)00354-4
DOI:
10.1016/j.spinee.2014.03.046
Reference:
SPINEE 55841
To appear in:
The Spine Journal
Received Date: 7 January 2014 Accepted Date: 25 March 2014
Please cite this article as: Ra I-H, Min W-K, Radiographic and Clinical Assessment of a Freehand Lateral Mass Screw Fixation Technique : Is it always safe in subaxial cervical spine?, The Spine Journal (2014), doi: 10.1016/j.spinee.2014.03.046. 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.
ACCEPTED MANUSCRIPT
Radiographic and Clinical Assessment of a Freehand Lateral Mass Screw Fixation Technique
In-Hoo Ra, M.D., Woo-Kie Min, M.D.Ph.D.
RI PT
: Is it always safe in subaxial cervical spine?
EP
TE D
M AN U
SC
Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, South Korea
※ Correspondence to: Woo-Kie Min, MD
AC C
Department of Orthopaedic Surgery, Kyungpook National University Hospital Postgraduate School of Medicine, Kyungpook National Universtiy 130 Dongdeok-ro, Jung-gu, Daegu, 700-721, Korea Fax: 82-53-422-6605
Tel : 82-53-420-5638
E-mail : [email protected]
1
ACCEPTED MANUSCRIPT
Abstract
2
BACKGROUND CONTEXT: Many spine surgeons use the freehand technique for lateral
3
mass(LM) screw fixation. However, issues about its safety still exist.
4
PURPOSE: This radiological and clinical assessment examines the safety of the freehand
5
technique after LM screw insertion.
6
STUDY DESIGN: Retrospective case series
7
PATIENT SAMPLE: A total of 26 patients (21 males and five females) who underwent LM
8
screw fixation via the freehand technique were included.
9
OUTCOME MEASURES: Postoperative computed tomography(CT) images and medical
M AN U
SC
RI PT
1
records were analyzed.
11
METHODS: During surgery, the lateral trajectory of screws was set using the adjacent SP
12
after the cranial trajectory was set by palpating the joint surface. CT analyses were performed
13
for measurement of screw angles and axial images were evaluated in order to determine the
14
SP length that would be long enough not to involve the transverse foramen. The medical
15
records were evaluated for investigation of the surgery-related complications. No funds were
16
received in support of this work and no potential conflict of interest relavant to this article
17
was reported.
18
RESULTS: Each axial and sagittal angle of the screws showed a significant difference. A
19
total of 18 screws (13.5%) involved the transverse foramen and the mean axial angle of the
20
screws was significantly smaller than the group not involving the foramen (P=0.0078). A
21
total of eight screws (6.0%) violated the facet and the mean sagittal angle was significantly
22
smaller than the group not violating the facet. The average difference in angle between the
23
screw and the actual joint surface was largest at C6 (P=0.0472). The mean maximum length
24
of the SP long enough not to involve the transverse foramen was significantly short at C3 and
AC C
EP
TE D
10
1
ACCEPTED MANUSCRIPT C6(P=0.0015). The actual SP length in one patient was longer than the maximum SP length
2
determined through analysis in the case of C6. And if the SP of C7 was used in C6, the SP
3
length would not be safe in six patients.
4
CONCLUSIONS: Excellent outcomes were observed with use of the freehand technique for
5
insertion of the LM screw at the subaxial C spine. However, this technique using the SP may
6
pose a relative risk at C6.
RI PT
1
7
Keywords: subaxial cervical spine, lateral mass screw, facet joint surface, spinous process,
9
freehand technique, maximum allowance length
M AN U
10 11 12 13
TE D
14 15
19 20 21
AC C
18
EP
16 17
SC
8
22 23 24
2
ACCEPTED MANUSCRIPT
Introduction
2
Lateral mass (LM) screws are commonly used for posterior fixation of the cervical spine,
3
particularly the subaxial cervical spine, which be unstable due to trauma, degenerative
4
diseases, tumors, rheumatoid arthritis, etc. Since introduction of posterior cervical LM screw
5
fixation for the first time in 1972 by Roy-Camille et al., many authors have proposed various
6
methods depending on the screw entry point and lateral and cranial angles; the techniques
7
proposed by Roy-Camille, Magerl, and Anderson and An are used most frequently [1-4]. LM
8
screws are known to be safer compared to pedicle screws [5,6], and several authors have
9
reported excellent outcomes using the freehand technique without image guidance with
10
relative ease of insertion [7,8,15]. However, because the surgeon decides on the screw entry
11
point and entry angle based on his/her experience and feeling, complications, including injury
12
to the spinal cord, vertebral artery, nerve root, facet joint, and adjacent LM, may result due to
13
wrong angles of entry [9]. Thus, some have proposed the need for safer freehand techniques,
14
which are easier to perform, using the surrounding constructs, such as the lamina and the
15
spinous process (SP) as the reference points [10-14].
16
Based on these previous studies, assuming that the possibility of violating the facet joints or
17
the lateral masses of the adjacent levels is low if LM screws were to be inserted parallel to the
18
facet joint surface, we used the freehand technique without fluoroscopy guidance, in which
19
the cranial trajectory was decided in parallel to the facet joint surface after visually
20
confirming this surface and determining the lateral trajectory using the adjacent SP. The
21
purpose of this study was to perform radiological and clinical evaluation of the results
22
obtained from cases in which the freehand technique was used with the goal of determining
23
the safety of this technique.
AC C
EP
TE D
M AN U
SC
RI PT
1
24 3
ACCEPTED MANUSCRIPT
Materials and methods
2
We obtained Institutional Review Board (IRB) approval for the current study. Then, the
3
medical records of patients who underwent cervical LM screw fixation at the our institute
4
were reviewed retrospectively. We investigated the records of 29 patients who had undergone
5
LM screw fixation using the freehand technique from September 2011 to June 2013. Of these
6
29 patients, 26 patients (21 males, five females) were finally selected for this study; we
7
excluded two patients whose LM screws were inserted only to C1 and one whose LM screws
8
were inserted to C3 and C4, but in whom we could not perform an evaluation since this
9
patient had no postoperative computed tomography(CT) images. The average age of these 26
10
patients was 56 years (range: 28~75 years) and the average follow-up period was 10.3
11
months (range: 5~35 months). Their diagnoses before the procedure included degenerative
12
disorders (cervical spondylotic myelopathy and ossification of the posterior longitudinal
13
ligament; OPLL) in 13 patients, trauma in 11 patients, and tumor in two patients. We did not
14
review C2 to C7 since pedicle screws were used on these segments; we only examined C3 to
15
C6, where a total of 133 LM screws were used (Table 1). The OASYS system (Stryker Spine,
16
France) was used for screw fixation in all patients.
17
EP
TE D
M AN U
SC
RI PT
1
Surgical Procedure
19
After endotracheal intubation, the patient was placed in the prone position and a sponge
20
pillow was used as padding in order to protect the patient’s face. In order to protect the
21
cranium, we did not use 3-point fixation, which is routinely used in this type of procedure;
22
only simple taping was used in order to stabilize the head. We then placed the patient in the
23
reverse Trendelenburg position in order to secure haemodynamic benefits, and taping was
24
also performed at the shoulders in order to prevent formation of skin folds at the incision site.
AC C
18
4
ACCEPTED MANUSCRIPT The standard midline posterior approach was used to open the surgical site, and the posterior
2
element was completely exposed.
3
Thus, the lateral edges of the LM and the top and bottom faces of the facet joint could be seen
4
at the time of screw insertion. The entry point was determined at 1 mm medially from the
5
midpoint of the LM, where marking was made using a burr. After palpation of the joint
6
surface of the superior or inferior articular facet using the Freer elevator, the angle formed by
7
the elevator was set as the sagittal trajectory (Fig 1). At this time, the joint surfaces of facet
8
joints that were not to be used in fusion or to obtain fixation using instrumentation were not
9
separated in order to protect the facet joint. A drill bit was then placed on the entry point
10
along with the sagittal trajectory and leaned to the adjacent SP in order to determine the
11
lateral trajectory before drilling. The size of all screws used was 3.5 X 14 mm, in which the
12
rod was bent after screw insertion. Then, decortication and fusion were performed, if
13
necessary. The screw was inserted before laminectomy in patients needing laminectomy.
14
Fluoroscopy was only used to confirm preoperative alignment and postoperative screw
15
fixation.
TE D
M AN U
SC
RI PT
1
EP
16 Evaluation
18
CT scan was taken and examined in all patients within postoperative two weeks. CT images
19
were taken at 2-mm intervals, and the screw trajectory angle was measured using the method
20
proposed by Seybold et al. [16] from the axial and sagittal views (Fig 2). The angles of the
21
surface joints of LM in which each screw was inserted were also measured, and the
22
difference in the angle with the actually inserted screw was calculated. When the top and
23
bottom angles formed at the surface joint were not uniform, the average of these two angles
24
was set as the joint surface angle. Since the probability of invading the transverse foramen is
AC C
17
5
ACCEPTED MANUSCRIPT high as the lateral trajectory angle decreases with longer SP lengths when the entry points are
2
consistent, in order to determine the safety of this technique, we attempted to calculate the
3
maximum length, i.e. the “maximum SP allowance length”, which is the length needed in
4
order not to invade the transverse foramen on CT. Taking into account the screw diameter of
5
3.5 mm, the maximum value of the SP tip was assumed where the line extended from the line
6
drawn between 1.75 mm away from the vertebral foramen and the entry point, i.e., 1 mm
7
medially away from the LM, met the line bisecting the vertebral body. The distance from this
8
maximum value to the point where the lines passing the entry point met perpendicularly was
9
defined as the “maximum SP allowance length” (Fig 3). This maximum SP allowance length
10
was measured in all patients from C3 to C6. And it was investigated whether there is a case
11
with the “allowance length” longer than the length from each LM to SP of the same level or
12
lower level cervical vertebra.
13
The presence or absence of transverse foramen invasion was verified on CT axial images, and
14
facet violation was verified on sagittal images (Fig 4). Upon this verification, analysis of the
15
difference in trajectory angles was performed between the transverse foramen involvement
16
group (FI) and the non-involvement group (non-FI) and between the facet violation group
17
(FV) and the non-involvement group (non-FV). Angles were compared between the
18
complication group and non-complication group by dividing the patients using the follow-up
19
investigation data, including screw loosening and breakage using anteroposterior or flexion–
20
extension lateral radiographs and nerve root injury, including paresthesia and loss of motor
21
function. Postoperative medical records were reviewed in order to verify vertebral artery
22
injury during surgery.
AC C
EP
TE D
M AN U
SC
RI PT
1
23 24
Statistical analysis 6
ACCEPTED MANUSCRIPT Statistical analysis was performed using SAS 9.13. Linear mixed models were used since
2
measurements were performed twice from the left and right sides in each patient. All values
3
were shown as mean ± SD. Unpaired t-test was used for comparison of the difference in
4
angles between each level and between each group. The maximum allowance SP length was
5
compared using ANOVA. Significance was determined at P
S1529-9430(14)00354-4
DOI:
10.1016/j.spinee.2014.03.046
Reference:
SPINEE 55841
To appear in:
The Spine Journal
Received Date: 7 January 2014 Accepted Date: 25 March 2014
Please cite this article as: Ra I-H, Min W-K, Radiographic and Clinical Assessment of a Freehand Lateral Mass Screw Fixation Technique : Is it always safe in subaxial cervical spine?, The Spine Journal (2014), doi: 10.1016/j.spinee.2014.03.046. 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.
ACCEPTED MANUSCRIPT
Radiographic and Clinical Assessment of a Freehand Lateral Mass Screw Fixation Technique
In-Hoo Ra, M.D., Woo-Kie Min, M.D.Ph.D.
RI PT
: Is it always safe in subaxial cervical spine?
EP
TE D
M AN U
SC
Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, South Korea
※ Correspondence to: Woo-Kie Min, MD
AC C
Department of Orthopaedic Surgery, Kyungpook National University Hospital Postgraduate School of Medicine, Kyungpook National Universtiy 130 Dongdeok-ro, Jung-gu, Daegu, 700-721, Korea Fax: 82-53-422-6605
Tel : 82-53-420-5638
E-mail : [email protected]
1
ACCEPTED MANUSCRIPT
Abstract
2
BACKGROUND CONTEXT: Many spine surgeons use the freehand technique for lateral
3
mass(LM) screw fixation. However, issues about its safety still exist.
4
PURPOSE: This radiological and clinical assessment examines the safety of the freehand
5
technique after LM screw insertion.
6
STUDY DESIGN: Retrospective case series
7
PATIENT SAMPLE: A total of 26 patients (21 males and five females) who underwent LM
8
screw fixation via the freehand technique were included.
9
OUTCOME MEASURES: Postoperative computed tomography(CT) images and medical
M AN U
SC
RI PT
1
records were analyzed.
11
METHODS: During surgery, the lateral trajectory of screws was set using the adjacent SP
12
after the cranial trajectory was set by palpating the joint surface. CT analyses were performed
13
for measurement of screw angles and axial images were evaluated in order to determine the
14
SP length that would be long enough not to involve the transverse foramen. The medical
15
records were evaluated for investigation of the surgery-related complications. No funds were
16
received in support of this work and no potential conflict of interest relavant to this article
17
was reported.
18
RESULTS: Each axial and sagittal angle of the screws showed a significant difference. A
19
total of 18 screws (13.5%) involved the transverse foramen and the mean axial angle of the
20
screws was significantly smaller than the group not involving the foramen (P=0.0078). A
21
total of eight screws (6.0%) violated the facet and the mean sagittal angle was significantly
22
smaller than the group not violating the facet. The average difference in angle between the
23
screw and the actual joint surface was largest at C6 (P=0.0472). The mean maximum length
24
of the SP long enough not to involve the transverse foramen was significantly short at C3 and
AC C
EP
TE D
10
1
ACCEPTED MANUSCRIPT C6(P=0.0015). The actual SP length in one patient was longer than the maximum SP length
2
determined through analysis in the case of C6. And if the SP of C7 was used in C6, the SP
3
length would not be safe in six patients.
4
CONCLUSIONS: Excellent outcomes were observed with use of the freehand technique for
5
insertion of the LM screw at the subaxial C spine. However, this technique using the SP may
6
pose a relative risk at C6.
RI PT
1
7
Keywords: subaxial cervical spine, lateral mass screw, facet joint surface, spinous process,
9
freehand technique, maximum allowance length
M AN U
10 11 12 13
TE D
14 15
19 20 21
AC C
18
EP
16 17
SC
8
22 23 24
2
ACCEPTED MANUSCRIPT
Introduction
2
Lateral mass (LM) screws are commonly used for posterior fixation of the cervical spine,
3
particularly the subaxial cervical spine, which be unstable due to trauma, degenerative
4
diseases, tumors, rheumatoid arthritis, etc. Since introduction of posterior cervical LM screw
5
fixation for the first time in 1972 by Roy-Camille et al., many authors have proposed various
6
methods depending on the screw entry point and lateral and cranial angles; the techniques
7
proposed by Roy-Camille, Magerl, and Anderson and An are used most frequently [1-4]. LM
8
screws are known to be safer compared to pedicle screws [5,6], and several authors have
9
reported excellent outcomes using the freehand technique without image guidance with
10
relative ease of insertion [7,8,15]. However, because the surgeon decides on the screw entry
11
point and entry angle based on his/her experience and feeling, complications, including injury
12
to the spinal cord, vertebral artery, nerve root, facet joint, and adjacent LM, may result due to
13
wrong angles of entry [9]. Thus, some have proposed the need for safer freehand techniques,
14
which are easier to perform, using the surrounding constructs, such as the lamina and the
15
spinous process (SP) as the reference points [10-14].
16
Based on these previous studies, assuming that the possibility of violating the facet joints or
17
the lateral masses of the adjacent levels is low if LM screws were to be inserted parallel to the
18
facet joint surface, we used the freehand technique without fluoroscopy guidance, in which
19
the cranial trajectory was decided in parallel to the facet joint surface after visually
20
confirming this surface and determining the lateral trajectory using the adjacent SP. The
21
purpose of this study was to perform radiological and clinical evaluation of the results
22
obtained from cases in which the freehand technique was used with the goal of determining
23
the safety of this technique.
AC C
EP
TE D
M AN U
SC
RI PT
1
24 3
ACCEPTED MANUSCRIPT
Materials and methods
2
We obtained Institutional Review Board (IRB) approval for the current study. Then, the
3
medical records of patients who underwent cervical LM screw fixation at the our institute
4
were reviewed retrospectively. We investigated the records of 29 patients who had undergone
5
LM screw fixation using the freehand technique from September 2011 to June 2013. Of these
6
29 patients, 26 patients (21 males, five females) were finally selected for this study; we
7
excluded two patients whose LM screws were inserted only to C1 and one whose LM screws
8
were inserted to C3 and C4, but in whom we could not perform an evaluation since this
9
patient had no postoperative computed tomography(CT) images. The average age of these 26
10
patients was 56 years (range: 28~75 years) and the average follow-up period was 10.3
11
months (range: 5~35 months). Their diagnoses before the procedure included degenerative
12
disorders (cervical spondylotic myelopathy and ossification of the posterior longitudinal
13
ligament; OPLL) in 13 patients, trauma in 11 patients, and tumor in two patients. We did not
14
review C2 to C7 since pedicle screws were used on these segments; we only examined C3 to
15
C6, where a total of 133 LM screws were used (Table 1). The OASYS system (Stryker Spine,
16
France) was used for screw fixation in all patients.
17
EP
TE D
M AN U
SC
RI PT
1
Surgical Procedure
19
After endotracheal intubation, the patient was placed in the prone position and a sponge
20
pillow was used as padding in order to protect the patient’s face. In order to protect the
21
cranium, we did not use 3-point fixation, which is routinely used in this type of procedure;
22
only simple taping was used in order to stabilize the head. We then placed the patient in the
23
reverse Trendelenburg position in order to secure haemodynamic benefits, and taping was
24
also performed at the shoulders in order to prevent formation of skin folds at the incision site.
AC C
18
4
ACCEPTED MANUSCRIPT The standard midline posterior approach was used to open the surgical site, and the posterior
2
element was completely exposed.
3
Thus, the lateral edges of the LM and the top and bottom faces of the facet joint could be seen
4
at the time of screw insertion. The entry point was determined at 1 mm medially from the
5
midpoint of the LM, where marking was made using a burr. After palpation of the joint
6
surface of the superior or inferior articular facet using the Freer elevator, the angle formed by
7
the elevator was set as the sagittal trajectory (Fig 1). At this time, the joint surfaces of facet
8
joints that were not to be used in fusion or to obtain fixation using instrumentation were not
9
separated in order to protect the facet joint. A drill bit was then placed on the entry point
10
along with the sagittal trajectory and leaned to the adjacent SP in order to determine the
11
lateral trajectory before drilling. The size of all screws used was 3.5 X 14 mm, in which the
12
rod was bent after screw insertion. Then, decortication and fusion were performed, if
13
necessary. The screw was inserted before laminectomy in patients needing laminectomy.
14
Fluoroscopy was only used to confirm preoperative alignment and postoperative screw
15
fixation.
TE D
M AN U
SC
RI PT
1
EP
16 Evaluation
18
CT scan was taken and examined in all patients within postoperative two weeks. CT images
19
were taken at 2-mm intervals, and the screw trajectory angle was measured using the method
20
proposed by Seybold et al. [16] from the axial and sagittal views (Fig 2). The angles of the
21
surface joints of LM in which each screw was inserted were also measured, and the
22
difference in the angle with the actually inserted screw was calculated. When the top and
23
bottom angles formed at the surface joint were not uniform, the average of these two angles
24
was set as the joint surface angle. Since the probability of invading the transverse foramen is
AC C
17
5
ACCEPTED MANUSCRIPT high as the lateral trajectory angle decreases with longer SP lengths when the entry points are
2
consistent, in order to determine the safety of this technique, we attempted to calculate the
3
maximum length, i.e. the “maximum SP allowance length”, which is the length needed in
4
order not to invade the transverse foramen on CT. Taking into account the screw diameter of
5
3.5 mm, the maximum value of the SP tip was assumed where the line extended from the line
6
drawn between 1.75 mm away from the vertebral foramen and the entry point, i.e., 1 mm
7
medially away from the LM, met the line bisecting the vertebral body. The distance from this
8
maximum value to the point where the lines passing the entry point met perpendicularly was
9
defined as the “maximum SP allowance length” (Fig 3). This maximum SP allowance length
10
was measured in all patients from C3 to C6. And it was investigated whether there is a case
11
with the “allowance length” longer than the length from each LM to SP of the same level or
12
lower level cervical vertebra.
13
The presence or absence of transverse foramen invasion was verified on CT axial images, and
14
facet violation was verified on sagittal images (Fig 4). Upon this verification, analysis of the
15
difference in trajectory angles was performed between the transverse foramen involvement
16
group (FI) and the non-involvement group (non-FI) and between the facet violation group
17
(FV) and the non-involvement group (non-FV). Angles were compared between the
18
complication group and non-complication group by dividing the patients using the follow-up
19
investigation data, including screw loosening and breakage using anteroposterior or flexion–
20
extension lateral radiographs and nerve root injury, including paresthesia and loss of motor
21
function. Postoperative medical records were reviewed in order to verify vertebral artery
22
injury during surgery.
AC C
EP
TE D
M AN U
SC
RI PT
1
23 24
Statistical analysis 6
ACCEPTED MANUSCRIPT Statistical analysis was performed using SAS 9.13. Linear mixed models were used since
2
measurements were performed twice from the left and right sides in each patient. All values
3
were shown as mean ± SD. Unpaired t-test was used for comparison of the difference in
4
angles between each level and between each group. The maximum allowance SP length was
5
compared using ANOVA. Significance was determined at P
