Eur Spine J (2016) 25:1716–1723 DOI 10.1007/s00586-016-4470-z
ORIGINAL ARTICLE
An RCT study on the feasibility of anterior transpedicular screw fixation in the cervicothoracic junction Liujun Zhao1 • Jinjiong Hong1 • Meghan E. Wandtke2 • Rongming Xu1 • Weihu Ma1 • Weiyu Jiang1 • Yongjie Gu1 • Jianqing Chen1 • Liran Wang1 Jiayong Liu2 • Nabil A. Ebraheim2
•
Received: 26 March 2015 / Revised: 18 February 2016 / Accepted: 19 February 2016 / Published online: 1 March 2016 Ó Springer-Verlag Berlin Heidelberg 2016
Abstract Study design We evaluated the trajectory and the entry points of anterior transpedicular screws (ATPS) in the cervicothoracic junction (CTJ). Objective This study aimed at investigating the feasibility of ATPS fixation in the CTJ. Summary of background data Application of an ATPS in the lower cervical spine has been reported; however, there were no reports exploring the feasibility of anterior transpedicular screw fixation in the CTJ. Methods CT scans were performed in 50 cases and multiplanar reformation was used to measure the related parameters on pedicle axis view at C6–T2. Transverse pedicle angle, outer pedicle width, pedicle axis length, distance transverse intersection point (DtIP), sagittal pedicle angle, anterior vertebral body height, outer pedicle height, and distance sagittal intersection point (DsIP) were measured. The prozone of CTJ was divided into three different regions, which were named as the ‘‘manubrium region’’, the region ‘‘above’’ and ‘‘below’’ the manubrium. The distribution of the trajectory of sagittal pedicle axes was recorded in the three regions and the related data were statistically analyzed. Results There was no statistical difference in gender (P [ 0.05). The transverse pedicle angle decreased from C6 (46.77° ± 2.72°) to T2 (20.62° ± 5.04°). DtIP increased from C6 to T2. DsIP was an average of 7.17 mm.
& Liujun Zhao [email protected] 1
Department of Orthopaedic Surgery, Ningbo 6th Hospital, Ningbo University, 1059#, Zhongshan Dong Road, Ningbo, Zhejiang, People’s Republic of China
2
Department of Orthopaedic Surgery, University of Toledo Medical Center, Toledo, OH 43614, USA
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The sagittal pedicle axis lines of the C6 and C7 were located in the region above the manubrium. T1 was mainly in the manubrium region followed by the region above the manubrium. T2 was mainly located in the manubrium region followed by the region below the manubrium. Conclusion Implantation of ATPS at C6, C7, and some T1 is feasible through the low anterior cervical approach, while it is almost impossible to approach T2 that way. Keywords Cervicothoracic junction Anterior approach Pedicle screw Tomography Spiral computed
Introduction Cervicothoracic pathologies such as metastasis, trauma, degeneration, or infection are not rare and usually occur in the anterior segment of the vertebrae, which frequently determines the instability of the cervicothoracic junction (CTJ) and may require immediate stabilization, neural decompression, or restoration of anatomical spinal alignment [1–11]. However, ventral exposure of the CTJ is difficult because of the deep location of the vertebral bodies caused by the thoracic kyphosis and the crossing of vital structures over the operative field in the upper mediastinum [6, 11–13]. Furthermore, the CTJ is one of the most challenging regions in spinal surgery, anterior stabilization alone reveals a high incidence of construct failure, and supplementary fixation should be considered to augment the construct [14, 15]. Since Aramomi et al. first introduced the concept of anterior transpedicular screw fixation (ATPSF) and successfully applied it to the lower cervical spine, many scholars have begun to accept it [16]. With the recent development in anatomic and radiological studies of ATPSF and in its respective clinical applications,
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we now propose an operational scheme to solve the problem of anterior approach stability of reconstruction in the CTJ using a one-stage operation through the use of ATPSF [17]. Up to date, there are few radiologic studies on relevant parameters and feasibility of insertion of ATPS in the CTJ. We explored the entry points and the directions of the pedicle axis in the CTJ by spiral CT multiplanar reconstruction and analyzed the anatomical relationship between the trajectory of the pedicle axis and the thoracic outlet to provide the basis for its clinical application in the future.
Patients and methods From January to June 2014, CT scans of the cervical and upper thoracic spine including an intact thoracic outlet and manubrium were performed on 50 patients, who were selected from our institution, including 29 males and 21 females with ages ranging from 22 to 60 years (average 36.4 years). The following exclusion criteria were used: severe degenerative changes, traumatic fracture and dislocation, obvious bone defect caused by infection or tumor, dysplasia of the cervicothoracic spine and congenital spinal malformation, significant scoliosis or kyphosis, history of spine surgery, and severe osteoporosis. All patients, in a comfortable supine position, had CT scans performed using axial thickness of 0.6 mm, slice spacing of 0.5 mm. Reconstructed 2D images of axial pedicles were obtained from the original images. The clearest axial reconstructed 2D images showing both pedicles and an intact anterior vertebral edge were selected. C6, C7, T1, and T2 axial and sagittal images were reconstructed, respectively (Figs. 1, 2a). The clearest sagittal reconstructed images showing the unilateral cervicothoracic pedicle and intact anterior vertebral edge were chosen (Fig. 2b–e). On middle sagittal plane, the prozone of the CTJ was divided into three different regions by two lines, a line horizontal to the suprasternal notch and a line horizontal to the inferior edge of the manubrium, respectively. They were named as the region above the manubrium (zone A), the manubrium region (zone B), and the region below the manubrium (zone C) (Fig. 3). The distribution of the trajectory of the sagittal pedicle axis in these regions was recorded. All selected images were measured bilaterally and the related data were statistically analyzed, as listed below (Figs. 1, 2a): tPA sPA
Angle between the transverse pedicle axis and mid-sagittal line; Angle formed by a line from the sagittal intersection point vertical to the plane of the anterior vertebral body wall and the sagittal pedicle axis;
Fig. 1 Horizontal axis including pedicles of the CTJ. tPA angle formed between the transverse pedicle axis and the mid-sagittal line, DtIP distance between the transverse intersection point and the midsagittal line at the anterior vertebral body wall at each level C6–T2, OPW distance from the lateral border of pedicle to the medial border of pedicle, PAL distance between the anterior vertebral body wall and the posterior margin of the vertebra along the transverse pedicle axis
DtIP
DsIP
OPW PAL
OPH aVBH
Distance between the transverse intersection point and the mid-sagittal line at the anterior vertebral body wall at each cervicothoracic level C6–T2. Those pedicle axes that crossed the mid-sagittal line were scaled as ‘negative’ values, and those intersecting the anterior vertebral body lateral to the mid-sagittal line were scaled as ‘positive’ values; Distance between the sagittal intersection point and the cephalad endplate at each cervicothoracic level C6–T2; Distance between the lateral and medial border of the pedicle; Distance from the anterior vertebral body wall to the posterior margin of the vertebra along the transverse pedicle axis; Distance from the cephalad to the caudad endplate; Distance from the upper to the lower pedicle surface in the sagittal plane.
Statistical analysis was performed and was expressed by the mean ± standard deviation. Student’s tests were performed comparing the data (sPA, tPA, DtIP, DsIP, OPW, PAL, OPH, aVBH) between sexes. Chi square Test was conducted to test whether there was a significant difference between genders. n \ 0.05 indicated a significant difference.
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Fig. 2 a Sagittal view including the pedicles of the CTJ. b–e Sagittal pedicle axis of the CTJ at each segment, respectively. sPA angle formed by a line from the sagittal intersection point vertical to the plane of the anterior vertebral body wall and the sagittal pedicle axis,
DsIP distance between the sagittal intersection point and the cephalad endplate at each level C6–T2, OPH distance from the cephalad to the caudad endplate, aVBH distance from the upper to the lower pedicle surface in sagittal plane
Results
32.84 ± 2.30 mm. The aVBH had a tendency to increase from cephalad C6 to caudad T2 in all patients. Table 2 lists the data of tPA and sPA for anterior transpedicular screw in the CTJ. Transverse pedicle angle of the CTJ decreased from C6 (46.77° ± 2.72°) to T2 (20.02° ± 3.40°) on transverse pedicle view. On sagittal pedicle view, the pedicles of C6–T2 were all caudally tilted and the sPA of T2 (20.62° ± 5.04°) was the largest of all (Fig. 2b–e). Table 3 provides the data of DtIP and DsIP on the axial and sagittal view in the CTJ. The DtIP had the tendency to
The data of aVBH, OPW, OPH, and PAL were recorded in Table 1. The OPW showed a tendency to increase from cephalad C6 to caudad T1 in all patients with a reversal decrease of OPW from T1 to T2. The OPH demonstrated a tendency to increase from cephalad C6 to caudad T2 in all patients. In the t test, OPH at the same vertebral level was shown to be significantly larger than OPW (P \ 0.05) (Fig. 4). There was no increasing or decreasing trend of PAL at cervicothoracic levels C6–T2, on an average of
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Fig. 3 The trajectory of ATPS in the CTJ on sagittal view. A region above the manubrium, B manubrium region, C region below the manubrium. The top yellow line is horizontal to the suprasternal notch, and the line below is horizontal to the inferior edge of manubrium
Table 1 Measurements of aVBH, OPW, OPH, and PAL in the cervicothoracic junction (mean ± SD, mm) Level C6 C7 T1 T2
aVBH (range)
OPW (range)
OPH (range)
12.13 ± 0.73
5.95 ± 0.45
6.12 ± 0.90
33.20 ± 2.30
11.11–13.42
4.96–7.21
5.10–8.02
29.11–36.42
13.90 ± 0.99 12.21–16.32
6.52 ± 0.91 5.27–8.42
7.25 ± 0.80 6.21–9.32
32.63 ± 2.58 28.21–38.32
increase from cephalad C6 to caudad T2 in all patients in an average of 2.60 ± 3.02 mm. On sagittal view, the DsIP of all the patients averaged 7.17 ± 2.22 mm and the DsIP in T2 (9.41 ± 2.23 mm) was the largest of them all. The entry point of C6 was located in the mid-sagittal line and 5 mm to the upper endplate. The entry point of T2, the majority of C7, and all of T1 were found in the same side of the proposed screw-setting pedicle; T2 was approximately 9 mm from the upper endplate and T1 and C7 were approximately 7 mm (Fig. 5). All sagittal pedicle axes of C6 and C7 were located in zone A. The sagittal pedicle axis of T1 was mainly in zone B followed by zone A. The sagittal pedicle axis of T2 was mainly located in zone B followed by zone C (Table 4). On the sagittal axis view, 20 sagittal pedicle axes of T1 were located in zone A, accounting for 40 % of all the regions. We reconstructed those 20 cases on the transverse pedicle axis plane and found that the screw-setting direction of 12 of them was hindered by bony obstructions such as the sternoclavicular joint and clavicle. Five of them passed through the space between the two sternal ends of the clavicle to the T1 vertebral arch (Fig. 6b) and only three of them were above the line connecting the superior borders of the two sternal ends of the clavicle.
PAL (range)
Discussion
15.20 ± 1.19
8.23 ± 0.98
9.03 ± 0.94
32.63 ± 2.08
13.65–18.38
6.81–10.46
7.65–11.38
26.65–35.38
16.87 ± 1.46
6.53 ± 1.04
10.38 ± 1.39
33.13 ± 1.71
14.46–20.07
4.63–9.25
8.46–14.07
30.46–37.07
Merged data for male and female patients
Fig. 4 The correlation between mean OPH and mean OPW
The cervicothoracic junction (CTJ) refers to the region between C6 and T2. Gaining anterior access to this region is difficult and potentially dangerous not only because of the nearby vital, complex anatomical structures, but also because of the bony obstructions [5, 12, 18–20]. This region is a transition area from a mobile cervical spine to a rigid thoracic spine. In those vertebral segments, physiologic cervical lordosis and thoracic kyphosis create a unique biomechanical feature [19]. Consequently, many scholars believe that there is a higher demand for the biomechanical stability of implant systems for reconstructing the stability of the CTJ, anterior stabilization alone may not be sufficient, and ventral corpectomies across the CTJ should be supplemented with dorsal instrumentation [10, 14, 21]. In recent years, as the new stabilization technique of anterior transpedicular screw fixation (ATPSF) has appeared, scholars have recognized that combining ATPS and an anterior locking plate provides good stability immediately after implantation [17, 22–24]. The technique allows anterior decompression and reconstruction of the CTJ to help increase three-column stabilization using a one-stage operation with an anterior only surgical approach. During the screw fixation, the key to inserting the screw accurately depends on the appropriate length and diameter
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1720 Table 2 Date of tPA and sPA for anterior transpedicular screw in the CTJ (mean ± SD, °)
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Level
tPA M (n = 29)
sPA F (n = 21)
Sum (n = 50)
M (n = 29)
F (n = 21)
Sum (n = 50)
C6
47.19 ± 2.52
46.20 ± 2.93
46.77 ± 2.72
18.17 ± 4.98
18.00 ± 3.64
18.10 ± 4.43
Range
41.56–51.03
40.38–51.09
40.38–51.09
7.91–25.99
10.30–25.60
7.91–25.99
C7
33.18 ± 2.15
33.99 ± 3.01
33.52 ± 2.55
15.52 ± 5.51
16.25 ± 4.62
15.83 ± 5.12
Range
29.27–38.21
29.27–42.01
29.27–42.01
6.57–24.55
9.62–24.79
6.57–24.79
T1
30.59 ± 3.04
28.18 ± 4.19
29.58 ± 3.73
14.81 ± 4.10
14.18 ± 3.17
14.54 ± 3.71
Range
25.34–36.76
20.70–35.77
20.70–36.76
7.94–23.70
9.22–23.29
7.93–23.70
T2
19.98 ± 3.27
20.08 ± 3.66
20.02 ± 3.40
19.23 ± 4.56
22.53 ± 5.15
20.62 ± 5.04
Range
11.54–26.17
12.28–24.88
11.54–26.17
11.12–31.28
10.14–34.68
10.14–34.68
There is no significant difference between males and females at the same vertebrae, either tPA or sPA (P [ 0.05) There is no significant difference between the left and right tPA at the same vertebrae of the same subject (P [ 0.05)
Table 3 Measurements of DtIP and DsIP for anterior transpedicular screw in the CTJ (mean ± SD, mm)
Level
C6 (range)
C7 (range)
T1 (range)
T2 (range)
C6–T2 (range)
DtIP
-0.13 ± 2.77
1.80 ± 2.55
3.68 ± 2.17
5.03 ± 1.50
2.60 ± 3.02
-5.50 to 5.66
-3.87 to 6.60
0.50–7.02
2.18–8.98
-5.50 to 8.98
5.45 ± 1.77
6.98 ± 1.45
6.86 ± 1.80
9.41 ± 2.23
7.17 ± 2.22
3.01–8.37
4.13–10.54
3.42–10.63
5.05–15.10
3.01–15.10
DsIP
Merged data for male and female patients
of the screw and finding the reasonable fixation angle and entry point. The current study showed that outer pedicle height (OPH) is greater than outer pedicle width (OPW) at each segment of the CTJ. Consequently, the smaller OPW decides the diameter of the screw. In general, to ensure safe screw placement 0.5 mm of bone around each screw was determined as the critical value, furthermore, to place a 3.5- or 4.0-mm ATPS in C6, C7, and T2 is suitable. However, in T1, a 4.5- or 5.0-mm ATPS can be selected because it has the biggest OPW. Our research showed PAL was on average 26.65–38.32 mm. When an ATPS breaches the lateral mass or the posterior margin of the vertebra, bicortical screws yield the best possible anchoring force. Depending on the needs of the situation, either bicortical or unicortical fixation can be utilized with a screw ranged from 30 mm to 40 mm in length. The results indicated that the entry points of T2, T1 and the majority of C7 were found on the same side of proposed screw-setting pedicle except the entry point of C6 was in the mid-sagittal line. The tPA decreased from C6 to T2, but the distance between the transverse intersection point and mid-sagittal line increased, with T2 (about 5 mm) being the largest. Supplemental anterior plate fixation provides immediate stabilization, prevents graft extrusion, and decreases the need for extended external immobilization. Furthermore, anterior plate fixation helps maintain the restored sagittal
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alignment through the prevention of graft collapse and extrusion. Combined with the superior biomechanical characteristics of ATPSF, the screw-and-plate system can increase three-column structure rigidity and diminish early failure rates. The study found that the sagittal pedicle axes of C6 and C7 vertebrae were all located in zone A. T1 was mainly found in zone B followed by zone A. T2 was mainly located in zone B followed by zone C, with none being found in zone A. T1 was primarily in zone B, which constituted 56.0 percent of all three regions, followed by 20 cases residing in zone A, with only 4.0 percent located in zone C. After the reformation of the T1 pedicle whose sagittal axis was in zone A, we found that 12 of them were limited by the clavicle and sternoclavicular joint anteriorly, and 5 of them passed through the space between the two sternal ends of clavicle (Fig. 7b), and only three of them were located above the line connecting the two superior borders of the sternal end of the clavicle. Based on the results, it appeared that nearly all of the sagittal pedicle axes of T2 were limited by bony obstructions, followed by 84.0 percent of T1. However, during surgery, operators will have to avoid the bony obstructions such as the manubrium or clavicle, to gain access to the entry point, which greatly increases the difficulty of screw placement. The cervical pad can effectively increase cervical lordosis preoperatively, and surgical field exposure of C7, especially in
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Fig. 5 Graph illustrating the entry point of the anterior transpedicular screw in the cervicothoracic junction. The black spots indicate the entry points at each segment
Table 4 The distribution of the trajectory of ATPS in 50 cases at cervicothoracic junction on sagittal view Level
Male (n = 29)
Female (n = 21)
Sum (n = 50)
A
A
A
B
0 0
21 21
B
C6 C7
29 29
T1
12
15
2
8
T2
0
18
11
0
70
33
13
50
24
Sum
0 0
C
0 0
C
B 0 0
C
0 0
50 50
0 0
13
0
20
28
2
11
10
0
29
21
10
120
57
23
There was no statistical significance of the regional distribution between sexes (P [ 0.05)
obese people with a short neck. Furthermore, the cervicothoracic alignment does not change with position for T1 and under. The thorax has many associated bony structures, such as the manubrium, clavicle, and the thoracic vertebrae with their corresponding ribs which allow the anatomical relationship between T1 and the manubrium to be constant [25]. Therefore, we could not extend the scope in the direction of the T1 pedicle axis and the manubrium with the use of a pad for those T1 pedicle axes in zone A (Fig. 8).
Fig. 6 a, b Reconstructed 2D image of the sagittal pedicle. The entry angle indicates the angle between the sagittal pedicle axis and the vertical line
The direction of ATPS is much different with traditional anterior screws; we use a semi-constrained, rotational plate with variable-angle locking as an example for illustrations. The direction of ATPS is caudally tilted on sagittal plane so as to pass through the pedicle strictly and accurately, especially in the distal screws. Therefore, to meet the needs of the entry angle, it might be necessary for ATPS instrumentation to expose the surgical field much more adequately. This study indicates that the low anterior cervical approach (LACA) can satisfy the needs of ATPS placement in C6, C7, and some T1, theoretically. It is almost impossible to approach T2 that way. When anterior approach fixation is involved with the vertebrae T1 and under, LACA combined sternotomy, unilateral or bilateral manubriotomy, or clavicular dissection is required for
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Fig. 8 The anatomic relationship between the thoracic inlet and the T1 vertebrae. E the entry point of the fixation of the T1 anterior transpedicular screw, ET the direction of the fixation of the T1 anterior transpedicular screw, M manubrium, N suprasternal notch, TEN an area formed by the direction of the fixation of the T1 anterior transpedicular screw and a line connecting the entry point of the fixation of the T1 anterior transpedicular screw and the suprasternal notch
Fig. 7 a, b Reconstructed 2D image of the transverse pedicle. Figure 6b illustrates the transverse pedicle axis of the T1 vertebra passing through the space between the two sternal ends of the clavicle to the T1 vertabral arch
exposure due to the bony obstructions of the thorax. In turn, it is associated with a relatively high risk of neurovascular injury within the thoracic outlet, infections, bone instability, and may even influence the function of the shoulder joint [26]. We suggest that the technology of ATPS in the CTJ be used in the following circumstances in particular: (1) patients who underwent anterior/anteroposterior approach
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surgery and need an anterior revision surgery; and (2) patients who have planned to have an anteroposterior approach surgery, which could be replaced by an anterior only approach. The advantage of ATPSF is that it allows anterior decompression and reconstruction of the CTJ to obtain a solid three-column stabilization using a one-stage operation that is utilizing an anterior only approach. This implant system’s biomechanical stability is excellent due to the use of a combination of anterior locking plates. Currently, the benefit versus the risk needs to be taken into account when considering the anterior versus posterior approach in this region. There were limitations in this study: (1) data deviation, due to all the data from spiral CT multiplane reformation, (2) the research mainly focuses on the anatomical relationship between the direction of ATPS placement in the CTJ and bone structures of thoracic outlet, and ignores other important structures like the esophagus, trachea, and great vessels of the upper mediastinum. This paper
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implements CT images only due to the focus being on the screw trajectory within the bone, but future studies should be aimed at studying the soft tissue structures and their respective obstacles to the clinical application of ATPSF, which would be better illustrated by MRI scans. Acknowledgments
No funds were received in support of this work.
Compliance with ethical standards Conflict of interest
None.
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ORIGINAL ARTICLE
An RCT study on the feasibility of anterior transpedicular screw fixation in the cervicothoracic junction Liujun Zhao1 • Jinjiong Hong1 • Meghan E. Wandtke2 • Rongming Xu1 • Weihu Ma1 • Weiyu Jiang1 • Yongjie Gu1 • Jianqing Chen1 • Liran Wang1 Jiayong Liu2 • Nabil A. Ebraheim2
•
Received: 26 March 2015 / Revised: 18 February 2016 / Accepted: 19 February 2016 / Published online: 1 March 2016 Ó Springer-Verlag Berlin Heidelberg 2016
Abstract Study design We evaluated the trajectory and the entry points of anterior transpedicular screws (ATPS) in the cervicothoracic junction (CTJ). Objective This study aimed at investigating the feasibility of ATPS fixation in the CTJ. Summary of background data Application of an ATPS in the lower cervical spine has been reported; however, there were no reports exploring the feasibility of anterior transpedicular screw fixation in the CTJ. Methods CT scans were performed in 50 cases and multiplanar reformation was used to measure the related parameters on pedicle axis view at C6–T2. Transverse pedicle angle, outer pedicle width, pedicle axis length, distance transverse intersection point (DtIP), sagittal pedicle angle, anterior vertebral body height, outer pedicle height, and distance sagittal intersection point (DsIP) were measured. The prozone of CTJ was divided into three different regions, which were named as the ‘‘manubrium region’’, the region ‘‘above’’ and ‘‘below’’ the manubrium. The distribution of the trajectory of sagittal pedicle axes was recorded in the three regions and the related data were statistically analyzed. Results There was no statistical difference in gender (P [ 0.05). The transverse pedicle angle decreased from C6 (46.77° ± 2.72°) to T2 (20.62° ± 5.04°). DtIP increased from C6 to T2. DsIP was an average of 7.17 mm.
& Liujun Zhao [email protected] 1
Department of Orthopaedic Surgery, Ningbo 6th Hospital, Ningbo University, 1059#, Zhongshan Dong Road, Ningbo, Zhejiang, People’s Republic of China
2
Department of Orthopaedic Surgery, University of Toledo Medical Center, Toledo, OH 43614, USA
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The sagittal pedicle axis lines of the C6 and C7 were located in the region above the manubrium. T1 was mainly in the manubrium region followed by the region above the manubrium. T2 was mainly located in the manubrium region followed by the region below the manubrium. Conclusion Implantation of ATPS at C6, C7, and some T1 is feasible through the low anterior cervical approach, while it is almost impossible to approach T2 that way. Keywords Cervicothoracic junction Anterior approach Pedicle screw Tomography Spiral computed
Introduction Cervicothoracic pathologies such as metastasis, trauma, degeneration, or infection are not rare and usually occur in the anterior segment of the vertebrae, which frequently determines the instability of the cervicothoracic junction (CTJ) and may require immediate stabilization, neural decompression, or restoration of anatomical spinal alignment [1–11]. However, ventral exposure of the CTJ is difficult because of the deep location of the vertebral bodies caused by the thoracic kyphosis and the crossing of vital structures over the operative field in the upper mediastinum [6, 11–13]. Furthermore, the CTJ is one of the most challenging regions in spinal surgery, anterior stabilization alone reveals a high incidence of construct failure, and supplementary fixation should be considered to augment the construct [14, 15]. Since Aramomi et al. first introduced the concept of anterior transpedicular screw fixation (ATPSF) and successfully applied it to the lower cervical spine, many scholars have begun to accept it [16]. With the recent development in anatomic and radiological studies of ATPSF and in its respective clinical applications,
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we now propose an operational scheme to solve the problem of anterior approach stability of reconstruction in the CTJ using a one-stage operation through the use of ATPSF [17]. Up to date, there are few radiologic studies on relevant parameters and feasibility of insertion of ATPS in the CTJ. We explored the entry points and the directions of the pedicle axis in the CTJ by spiral CT multiplanar reconstruction and analyzed the anatomical relationship between the trajectory of the pedicle axis and the thoracic outlet to provide the basis for its clinical application in the future.
Patients and methods From January to June 2014, CT scans of the cervical and upper thoracic spine including an intact thoracic outlet and manubrium were performed on 50 patients, who were selected from our institution, including 29 males and 21 females with ages ranging from 22 to 60 years (average 36.4 years). The following exclusion criteria were used: severe degenerative changes, traumatic fracture and dislocation, obvious bone defect caused by infection or tumor, dysplasia of the cervicothoracic spine and congenital spinal malformation, significant scoliosis or kyphosis, history of spine surgery, and severe osteoporosis. All patients, in a comfortable supine position, had CT scans performed using axial thickness of 0.6 mm, slice spacing of 0.5 mm. Reconstructed 2D images of axial pedicles were obtained from the original images. The clearest axial reconstructed 2D images showing both pedicles and an intact anterior vertebral edge were selected. C6, C7, T1, and T2 axial and sagittal images were reconstructed, respectively (Figs. 1, 2a). The clearest sagittal reconstructed images showing the unilateral cervicothoracic pedicle and intact anterior vertebral edge were chosen (Fig. 2b–e). On middle sagittal plane, the prozone of the CTJ was divided into three different regions by two lines, a line horizontal to the suprasternal notch and a line horizontal to the inferior edge of the manubrium, respectively. They were named as the region above the manubrium (zone A), the manubrium region (zone B), and the region below the manubrium (zone C) (Fig. 3). The distribution of the trajectory of the sagittal pedicle axis in these regions was recorded. All selected images were measured bilaterally and the related data were statistically analyzed, as listed below (Figs. 1, 2a): tPA sPA
Angle between the transverse pedicle axis and mid-sagittal line; Angle formed by a line from the sagittal intersection point vertical to the plane of the anterior vertebral body wall and the sagittal pedicle axis;
Fig. 1 Horizontal axis including pedicles of the CTJ. tPA angle formed between the transverse pedicle axis and the mid-sagittal line, DtIP distance between the transverse intersection point and the midsagittal line at the anterior vertebral body wall at each level C6–T2, OPW distance from the lateral border of pedicle to the medial border of pedicle, PAL distance between the anterior vertebral body wall and the posterior margin of the vertebra along the transverse pedicle axis
DtIP
DsIP
OPW PAL
OPH aVBH
Distance between the transverse intersection point and the mid-sagittal line at the anterior vertebral body wall at each cervicothoracic level C6–T2. Those pedicle axes that crossed the mid-sagittal line were scaled as ‘negative’ values, and those intersecting the anterior vertebral body lateral to the mid-sagittal line were scaled as ‘positive’ values; Distance between the sagittal intersection point and the cephalad endplate at each cervicothoracic level C6–T2; Distance between the lateral and medial border of the pedicle; Distance from the anterior vertebral body wall to the posterior margin of the vertebra along the transverse pedicle axis; Distance from the cephalad to the caudad endplate; Distance from the upper to the lower pedicle surface in the sagittal plane.
Statistical analysis was performed and was expressed by the mean ± standard deviation. Student’s tests were performed comparing the data (sPA, tPA, DtIP, DsIP, OPW, PAL, OPH, aVBH) between sexes. Chi square Test was conducted to test whether there was a significant difference between genders. n \ 0.05 indicated a significant difference.
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Fig. 2 a Sagittal view including the pedicles of the CTJ. b–e Sagittal pedicle axis of the CTJ at each segment, respectively. sPA angle formed by a line from the sagittal intersection point vertical to the plane of the anterior vertebral body wall and the sagittal pedicle axis,
DsIP distance between the sagittal intersection point and the cephalad endplate at each level C6–T2, OPH distance from the cephalad to the caudad endplate, aVBH distance from the upper to the lower pedicle surface in sagittal plane
Results
32.84 ± 2.30 mm. The aVBH had a tendency to increase from cephalad C6 to caudad T2 in all patients. Table 2 lists the data of tPA and sPA for anterior transpedicular screw in the CTJ. Transverse pedicle angle of the CTJ decreased from C6 (46.77° ± 2.72°) to T2 (20.02° ± 3.40°) on transverse pedicle view. On sagittal pedicle view, the pedicles of C6–T2 were all caudally tilted and the sPA of T2 (20.62° ± 5.04°) was the largest of all (Fig. 2b–e). Table 3 provides the data of DtIP and DsIP on the axial and sagittal view in the CTJ. The DtIP had the tendency to
The data of aVBH, OPW, OPH, and PAL were recorded in Table 1. The OPW showed a tendency to increase from cephalad C6 to caudad T1 in all patients with a reversal decrease of OPW from T1 to T2. The OPH demonstrated a tendency to increase from cephalad C6 to caudad T2 in all patients. In the t test, OPH at the same vertebral level was shown to be significantly larger than OPW (P \ 0.05) (Fig. 4). There was no increasing or decreasing trend of PAL at cervicothoracic levels C6–T2, on an average of
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Fig. 3 The trajectory of ATPS in the CTJ on sagittal view. A region above the manubrium, B manubrium region, C region below the manubrium. The top yellow line is horizontal to the suprasternal notch, and the line below is horizontal to the inferior edge of manubrium
Table 1 Measurements of aVBH, OPW, OPH, and PAL in the cervicothoracic junction (mean ± SD, mm) Level C6 C7 T1 T2
aVBH (range)
OPW (range)
OPH (range)
12.13 ± 0.73
5.95 ± 0.45
6.12 ± 0.90
33.20 ± 2.30
11.11–13.42
4.96–7.21
5.10–8.02
29.11–36.42
13.90 ± 0.99 12.21–16.32
6.52 ± 0.91 5.27–8.42
7.25 ± 0.80 6.21–9.32
32.63 ± 2.58 28.21–38.32
increase from cephalad C6 to caudad T2 in all patients in an average of 2.60 ± 3.02 mm. On sagittal view, the DsIP of all the patients averaged 7.17 ± 2.22 mm and the DsIP in T2 (9.41 ± 2.23 mm) was the largest of them all. The entry point of C6 was located in the mid-sagittal line and 5 mm to the upper endplate. The entry point of T2, the majority of C7, and all of T1 were found in the same side of the proposed screw-setting pedicle; T2 was approximately 9 mm from the upper endplate and T1 and C7 were approximately 7 mm (Fig. 5). All sagittal pedicle axes of C6 and C7 were located in zone A. The sagittal pedicle axis of T1 was mainly in zone B followed by zone A. The sagittal pedicle axis of T2 was mainly located in zone B followed by zone C (Table 4). On the sagittal axis view, 20 sagittal pedicle axes of T1 were located in zone A, accounting for 40 % of all the regions. We reconstructed those 20 cases on the transverse pedicle axis plane and found that the screw-setting direction of 12 of them was hindered by bony obstructions such as the sternoclavicular joint and clavicle. Five of them passed through the space between the two sternal ends of the clavicle to the T1 vertebral arch (Fig. 6b) and only three of them were above the line connecting the superior borders of the two sternal ends of the clavicle.
PAL (range)
Discussion
15.20 ± 1.19
8.23 ± 0.98
9.03 ± 0.94
32.63 ± 2.08
13.65–18.38
6.81–10.46
7.65–11.38
26.65–35.38
16.87 ± 1.46
6.53 ± 1.04
10.38 ± 1.39
33.13 ± 1.71
14.46–20.07
4.63–9.25
8.46–14.07
30.46–37.07
Merged data for male and female patients
Fig. 4 The correlation between mean OPH and mean OPW
The cervicothoracic junction (CTJ) refers to the region between C6 and T2. Gaining anterior access to this region is difficult and potentially dangerous not only because of the nearby vital, complex anatomical structures, but also because of the bony obstructions [5, 12, 18–20]. This region is a transition area from a mobile cervical spine to a rigid thoracic spine. In those vertebral segments, physiologic cervical lordosis and thoracic kyphosis create a unique biomechanical feature [19]. Consequently, many scholars believe that there is a higher demand for the biomechanical stability of implant systems for reconstructing the stability of the CTJ, anterior stabilization alone may not be sufficient, and ventral corpectomies across the CTJ should be supplemented with dorsal instrumentation [10, 14, 21]. In recent years, as the new stabilization technique of anterior transpedicular screw fixation (ATPSF) has appeared, scholars have recognized that combining ATPS and an anterior locking plate provides good stability immediately after implantation [17, 22–24]. The technique allows anterior decompression and reconstruction of the CTJ to help increase three-column stabilization using a one-stage operation with an anterior only surgical approach. During the screw fixation, the key to inserting the screw accurately depends on the appropriate length and diameter
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1720 Table 2 Date of tPA and sPA for anterior transpedicular screw in the CTJ (mean ± SD, °)
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Level
tPA M (n = 29)
sPA F (n = 21)
Sum (n = 50)
M (n = 29)
F (n = 21)
Sum (n = 50)
C6
47.19 ± 2.52
46.20 ± 2.93
46.77 ± 2.72
18.17 ± 4.98
18.00 ± 3.64
18.10 ± 4.43
Range
41.56–51.03
40.38–51.09
40.38–51.09
7.91–25.99
10.30–25.60
7.91–25.99
C7
33.18 ± 2.15
33.99 ± 3.01
33.52 ± 2.55
15.52 ± 5.51
16.25 ± 4.62
15.83 ± 5.12
Range
29.27–38.21
29.27–42.01
29.27–42.01
6.57–24.55
9.62–24.79
6.57–24.79
T1
30.59 ± 3.04
28.18 ± 4.19
29.58 ± 3.73
14.81 ± 4.10
14.18 ± 3.17
14.54 ± 3.71
Range
25.34–36.76
20.70–35.77
20.70–36.76
7.94–23.70
9.22–23.29
7.93–23.70
T2
19.98 ± 3.27
20.08 ± 3.66
20.02 ± 3.40
19.23 ± 4.56
22.53 ± 5.15
20.62 ± 5.04
Range
11.54–26.17
12.28–24.88
11.54–26.17
11.12–31.28
10.14–34.68
10.14–34.68
There is no significant difference between males and females at the same vertebrae, either tPA or sPA (P [ 0.05) There is no significant difference between the left and right tPA at the same vertebrae of the same subject (P [ 0.05)
Table 3 Measurements of DtIP and DsIP for anterior transpedicular screw in the CTJ (mean ± SD, mm)
Level
C6 (range)
C7 (range)
T1 (range)
T2 (range)
C6–T2 (range)
DtIP
-0.13 ± 2.77
1.80 ± 2.55
3.68 ± 2.17
5.03 ± 1.50
2.60 ± 3.02
-5.50 to 5.66
-3.87 to 6.60
0.50–7.02
2.18–8.98
-5.50 to 8.98
5.45 ± 1.77
6.98 ± 1.45
6.86 ± 1.80
9.41 ± 2.23
7.17 ± 2.22
3.01–8.37
4.13–10.54
3.42–10.63
5.05–15.10
3.01–15.10
DsIP
Merged data for male and female patients
of the screw and finding the reasonable fixation angle and entry point. The current study showed that outer pedicle height (OPH) is greater than outer pedicle width (OPW) at each segment of the CTJ. Consequently, the smaller OPW decides the diameter of the screw. In general, to ensure safe screw placement 0.5 mm of bone around each screw was determined as the critical value, furthermore, to place a 3.5- or 4.0-mm ATPS in C6, C7, and T2 is suitable. However, in T1, a 4.5- or 5.0-mm ATPS can be selected because it has the biggest OPW. Our research showed PAL was on average 26.65–38.32 mm. When an ATPS breaches the lateral mass or the posterior margin of the vertebra, bicortical screws yield the best possible anchoring force. Depending on the needs of the situation, either bicortical or unicortical fixation can be utilized with a screw ranged from 30 mm to 40 mm in length. The results indicated that the entry points of T2, T1 and the majority of C7 were found on the same side of proposed screw-setting pedicle except the entry point of C6 was in the mid-sagittal line. The tPA decreased from C6 to T2, but the distance between the transverse intersection point and mid-sagittal line increased, with T2 (about 5 mm) being the largest. Supplemental anterior plate fixation provides immediate stabilization, prevents graft extrusion, and decreases the need for extended external immobilization. Furthermore, anterior plate fixation helps maintain the restored sagittal
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alignment through the prevention of graft collapse and extrusion. Combined with the superior biomechanical characteristics of ATPSF, the screw-and-plate system can increase three-column structure rigidity and diminish early failure rates. The study found that the sagittal pedicle axes of C6 and C7 vertebrae were all located in zone A. T1 was mainly found in zone B followed by zone A. T2 was mainly located in zone B followed by zone C, with none being found in zone A. T1 was primarily in zone B, which constituted 56.0 percent of all three regions, followed by 20 cases residing in zone A, with only 4.0 percent located in zone C. After the reformation of the T1 pedicle whose sagittal axis was in zone A, we found that 12 of them were limited by the clavicle and sternoclavicular joint anteriorly, and 5 of them passed through the space between the two sternal ends of clavicle (Fig. 7b), and only three of them were located above the line connecting the two superior borders of the sternal end of the clavicle. Based on the results, it appeared that nearly all of the sagittal pedicle axes of T2 were limited by bony obstructions, followed by 84.0 percent of T1. However, during surgery, operators will have to avoid the bony obstructions such as the manubrium or clavicle, to gain access to the entry point, which greatly increases the difficulty of screw placement. The cervical pad can effectively increase cervical lordosis preoperatively, and surgical field exposure of C7, especially in
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Fig. 5 Graph illustrating the entry point of the anterior transpedicular screw in the cervicothoracic junction. The black spots indicate the entry points at each segment
Table 4 The distribution of the trajectory of ATPS in 50 cases at cervicothoracic junction on sagittal view Level
Male (n = 29)
Female (n = 21)
Sum (n = 50)
A
A
A
B
0 0
21 21
B
C6 C7
29 29
T1
12
15
2
8
T2
0
18
11
0
70
33
13
50
24
Sum
0 0
C
0 0
C
B 0 0
C
0 0
50 50
0 0
13
0
20
28
2
11
10
0
29
21
10
120
57
23
There was no statistical significance of the regional distribution between sexes (P [ 0.05)
obese people with a short neck. Furthermore, the cervicothoracic alignment does not change with position for T1 and under. The thorax has many associated bony structures, such as the manubrium, clavicle, and the thoracic vertebrae with their corresponding ribs which allow the anatomical relationship between T1 and the manubrium to be constant [25]. Therefore, we could not extend the scope in the direction of the T1 pedicle axis and the manubrium with the use of a pad for those T1 pedicle axes in zone A (Fig. 8).
Fig. 6 a, b Reconstructed 2D image of the sagittal pedicle. The entry angle indicates the angle between the sagittal pedicle axis and the vertical line
The direction of ATPS is much different with traditional anterior screws; we use a semi-constrained, rotational plate with variable-angle locking as an example for illustrations. The direction of ATPS is caudally tilted on sagittal plane so as to pass through the pedicle strictly and accurately, especially in the distal screws. Therefore, to meet the needs of the entry angle, it might be necessary for ATPS instrumentation to expose the surgical field much more adequately. This study indicates that the low anterior cervical approach (LACA) can satisfy the needs of ATPS placement in C6, C7, and some T1, theoretically. It is almost impossible to approach T2 that way. When anterior approach fixation is involved with the vertebrae T1 and under, LACA combined sternotomy, unilateral or bilateral manubriotomy, or clavicular dissection is required for
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Fig. 8 The anatomic relationship between the thoracic inlet and the T1 vertebrae. E the entry point of the fixation of the T1 anterior transpedicular screw, ET the direction of the fixation of the T1 anterior transpedicular screw, M manubrium, N suprasternal notch, TEN an area formed by the direction of the fixation of the T1 anterior transpedicular screw and a line connecting the entry point of the fixation of the T1 anterior transpedicular screw and the suprasternal notch
Fig. 7 a, b Reconstructed 2D image of the transverse pedicle. Figure 6b illustrates the transverse pedicle axis of the T1 vertebra passing through the space between the two sternal ends of the clavicle to the T1 vertabral arch
exposure due to the bony obstructions of the thorax. In turn, it is associated with a relatively high risk of neurovascular injury within the thoracic outlet, infections, bone instability, and may even influence the function of the shoulder joint [26]. We suggest that the technology of ATPS in the CTJ be used in the following circumstances in particular: (1) patients who underwent anterior/anteroposterior approach
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surgery and need an anterior revision surgery; and (2) patients who have planned to have an anteroposterior approach surgery, which could be replaced by an anterior only approach. The advantage of ATPSF is that it allows anterior decompression and reconstruction of the CTJ to obtain a solid three-column stabilization using a one-stage operation that is utilizing an anterior only approach. This implant system’s biomechanical stability is excellent due to the use of a combination of anterior locking plates. Currently, the benefit versus the risk needs to be taken into account when considering the anterior versus posterior approach in this region. There were limitations in this study: (1) data deviation, due to all the data from spiral CT multiplane reformation, (2) the research mainly focuses on the anatomical relationship between the direction of ATPS placement in the CTJ and bone structures of thoracic outlet, and ignores other important structures like the esophagus, trachea, and great vessels of the upper mediastinum. This paper
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implements CT images only due to the focus being on the screw trajectory within the bone, but future studies should be aimed at studying the soft tissue structures and their respective obstacles to the clinical application of ATPSF, which would be better illustrated by MRI scans. Acknowledgments
No funds were received in support of this work.
Compliance with ethical standards Conflict of interest
None.
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