- Email: [email protected]
Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment
Original Article
Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment Jun Xuan1, Chen-Long Xie2, Yang Wu1, Jian Chen2, Xin Tong1, Xiang-Yang Wang2, Hui Xu2
OBJECTIVE: To assess an alternative method of cortical bone trajectory (CBT) screw placement in the thoracic spine from T1 to T8 and to investigate the proper entry point, screw insertion angle, screw length, and diameter.
-
METHODS: Computed tomography images of 80 patients were used to measure all related parameters. Ten cadaveric spines were studied and 4.5-mm screws were inserted into both sides of the vertebrae. Computed tomography of all vertebrae previously inserted with CBT screws was performed and lateral or medial pedicle wall violation was checked.
-
RESULTS: Of the inserted 160 CBT screws, 41.25% (66/160) penetrated the lateral pedicle wall, and the proportion of medial pedicle wall violation accounted for 0.625% (1/160). Maximal screw length tended to gradually increase from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8). Compared with T4 and T5, maximal screw diameters of other thoracic levels were wider, ranging from 4.63 mm at T4 to 5.53 mm at T8. The greatest lateral angle was 8.66 in men and 8.39 in women at T8, whereas the smallest lateral angle was 4.97 in men and 4.67 in women at T1. The cephalad angle ranged from 17.23 at T7 to 31.50 at T1 and it was significantly larger in men at T7 (P < 0.05), T6 and T8 (P < 0.01).
-
CONCLUSIONS: Based on the results of this study, we suggest that patients could be placed with 4.5 3 25.0e30.0 mm CBT screws from T1 to T8 through the pedicle or pedicle rib unit.
-
Key words Cervicothoracic junction - Cortical bone trajectory screw - Less invasive - Pedicle rib unit - Rescue failed screw -
Abbreviations and Acronyms CBT: Cortical bone trajectory CT: Computed tomography LA: Lateral angle MSL: Maximal screw length PLIF: Posterior lumbar interbody fusion TPA: Transverse pedicle angle
WORLD NEUROSURGERY -: e1-e9, - 2018
INTRODUCTION
T
ranspedicular screw instrumentation of thoracic spinal segments has been described for various indications such as fracture, tumor, and deformity (scoliosis and kyphosis). Moreover, the thoracic pedicle screw has been reported to have the advantages of better curve correction, less loss of correction, and shorter fusion length when it is used in idiopathic scoliosis surgery instead of other spinal anchoring devices.1-3 However, anatomic studies have reported that thoracic pedicles are small and the three-dimensional orientation of pedicles is complex and variable among patients,4-8 leading to transpedicular screw fixation in the thoracic spine, which has a high risk of injury to nerve roots, pleura, and large vessels. In 2009, Santoni et al.9 investigated cortical bone trajectory (CBT) for the lumbar pedicle screw (Figure 1). Their biomechanical tests showed a 30% increase in uniaxial yield pullout load and equivalency in mixed loading compared with the traditional trajectory. Many biomechanical or anatomic studies and clinical trials have been performed in the lumbar spine, showing that the CBT screw is a more rigid, safe, and minimally invasive technique.10-14 It has been expanded down to the lower thoracic spine (T9-T12),15,16 and Matsukawa et al.15 found that its insertional torque was 53.8% higher than that of the conventional technique. Although Sheng et al.17 investigated CBT screw placement in the mid and upper thoracic spine (T3-T8), their study has some disadvantages. At first, they determined whether the CBT screw penetrated medial or lateral pedicle wall only by performing radiography to obtain an anteroposterior radiograph. The method could not accurately determine whether the pedicle wall was penetrated or not. Second, Zhuang et al.18 reported that the percentage of pedicle width <4.5 mm was extremely high at T3eT8 in women (52.54%e80.51%) and T4eT7 in men
From the 1Department of Orthopaedic Surgery, Jinhua Municipal Central Hospital, Jinhua Hospital, Zhejiang University School of Medicine, Jinhua; and 2Department of Orthopaedic Surgery, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University, Wenzhou, People’s Republic of China To whom correspondence should be addressed: Hui Xu, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.05.152 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
e1
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 1. The trajectory of the lumbar cortical bone trajectory screw. (A) Lateral view. (B) Anteroposterior
(12.69%e40.30%). Moreover, the result also showed a high percentage of pedicle width <4.0 mm and 3.5 mm in women. Sheng et al.17 used a 5.0-mm-diameter CBT screw to perform their study; however, it was difficult to place a 5.0-mm CBT screw in patients with a pedicle width <4.5 mm without lateral or medial pedicle violation, especially some female patients whose pedicle width was <4.0 mm or 3.5 mm. Third, Zhuang et al.18 did not mention whether the connection between the screw head and the rod could be completed when using CBT screws on a multilevel. Fourth, these investigators excluded 2 segments of T1 and T2 in their study, but we found that T1 and T2 could be placed into CBT screws. Fifth, they did not provide the standard anteroposterior and lateral radiographs of the thoracic CBT screw, which could be used to preliminarily determine whether the CBT screw had been inserted correctly. Thus, we investigated the feasibility of CBT screw instrumentation via pedicle or pedicle rib unit in the thoracic spine (T1-T8). We inserted a CBT screw in cadaveric specimens to evaluate the incidence of medial and lateral pedicle wall violation. In addition, we conducted morphometric measurements on the thoracic CBT screw by 2-dimensional multiplanar reconstruction using computed tomography (CT). METHODS The research was approved by the institutional ethics review board of the hospital and carried out following the Declaration of Helsinki principles.
e2
www.SCIENCEDIRECT.com
view. (C) Axial view. (D) Cross section to show the trajectory of the lumbar cortical bone trajectory screw.
Study of Thoracic CBT Screw Violation on Cadavers Ten cadaveric specimens (6 men and 4 women) were provided by the Department of Anatomy, Wenzhou Medical University. The mean age of spine donors was 51.10 10.97 years (range, 30e70 years). Before the experiment, lateral and anteroposterior radiograms were taken on all cadavers to exclude congenital deformities, trauma, tumor, earlier surgery, or infection. Two fellowship-trained spinal surgeons dissected the thoracic spines and the study was carried out bilaterally on 160 pedicles between the first and eighth thoracic vertebrae. The screw insertion point was made using an electric drill equipped with a 2.0-mm Kirschner wire. The thoracic gearshift was inserted into the body to a depth of around 25e30 mm at T8 and 20e25 mm at the remaining levels from T1 to T7. Then, a flexible ball-tipped palpating device was introduced to palpate the bottom and 4 walls of the pedicle tract. Special attention must be paid to the first approximately 15 mm of the hole. If a breach is discovered, the pedicle finder should be redirected. The pedicle was tapped with a 4.5-mm-diameter tap. Once again, the pedicle tract was palpated to make sure that no wall had been violated. All CBT screws were inserted in the middle and proximal thoracic spine. We used 4.50 30.00 mm at T8 and 4.50 25.00 mm at the other levels from T1 to T7 in both sides, respectively. The position of the screw was identified by anteroposterior and lateral radiographs, and thoracic CBT screws were placed approximately at the 5 (7) o’clock orientation and aimed in the 11e12 (12e1) o’clock direction of the pedicle (Figure 2). CT scans of cadaveric specimens previously inserted with CBT screws were performed and vertebrae were dissected as well. We checked lateral or
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 2. The position of the screw was identified by anteroposterior and lateral radiographs. (A) The marker was inserted almost at the 5 (7) o’clock orientation and aimed in the 11e12 (12e1) o’clock direction. (B) The
medial pedicle wall violation. The thoracic CBT screw entry point is shown in Figure 3. Study of Morphometric Measurements on Thoracic CBT Screw We performed the study on patients who came to the Second Affiliated Hospital of Wenzhou Medical University for CT scans from January 2011 to October 2015. CT images were acquired by Philips Brilliance 256 IT scan machine (Philips Medical Systems, Eindhoven, the Netherlands). Scan parameters included 120 kV, 180 MA, 512 512 matrix, layer thickness of 0.9 mm, collimation of 128 0.625 mm, pitch of 0.6 mm, DoseRight of Z-DOM, and 250 mAs/slice. CT scans of 80 adults (45 males and 35 females; 49.52 10.35 years old; range, 30e68 years) who underwent examination for lung conditions were randomly enrolled, and the reformatted images with a thickness 1.0 mm were once again acquired from those images. None of the patients showed any evidence of infection, tumor, traumatic diseases, or spinal deformity. Measurements were acquired by the specially trained spine surgeon, who was acquainted with the anatomy and the thoracic
WORLD NEUROSURGERY -: e1-e9, - 2018
marker was placed via the caudal portion of the pedicle. The anteroposterior (C) and lateral radiographic (D) images showing that the position of the cortical bone trajectory screw accorded with that of the marker.
pedicle screw. Every parameter was measured 3 times in 1 patient, and we regarded the average of each parameter as the final value. At first, we drew an angle of 45 to make its extension line overlap the thoracic pedicle, identifying the intersection point which was located approximately at the 5 o’clock orientation of the pedicle, which was the entry point of the thoracic CBT screw. To obtain a novel axial plane, the horizontal axis was adjusted to overlap the anatomic axis of the thoracic pedicle. We measured the following parameters through the plane (Figures 4 and 5): 1) maximal screw length, 2) maximal screw diameter, 3) lateral angle (LA), and 4) cephalad angle. Statistical Analysis Statistical analysis was performed using SPSS statistical software program version 22.0 (IBM Corp., Armonk, New York, USA). Results were presented as mean standard deviation and the independent sample t test was used to compare the differences between males and females. One-way analysis of variance and the Tukey analysis were performed for statistical comparison among
www.WORLDNEUROSURGERY.org
e3
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 3. The starting point of the thoracic cortical bone trajectory screw. (Black dotted line) 1/2 of the base of transverse process; (yellow dotted line) medial 1/3 of the superior facet; (green dotted line) inferior 1/3 of the base of transverse process. (A) The entry point (T1-T2) was the point of intersection between 1/2 of the base
each segment. In the present study, we used a P value of <0.05 to represent statistical significance. RESULTS Incidence of Thoracic Pedicle Violation A total of 160 thoracic CBT screws, 96 in males and 64 in females, were inserted in the middle and upper thoracic spine. All of the
of transverse process and the medial 1/3 of the superior facet. The starting point (T3-T8) was the point of intersection between the inferior 1/3 of the base of transverse process and the medial 1/3 of the superior facet. (B) Cortical bone trajectory screws were inserted in the cadaveric thoracic spine.
inserted CBT screws, (41.25% [66/160]) penetrated the lateral pedicle wall, and the proportion of the medial pedicle wall violation accounted for 0.625% (1/160) (Table 1). Maximal Screw Length and Maximal Screw Diameter Maximal screw length tended to increase gradually from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8), and maximal screw length of males was longer than that of females. There were significant differences between males and females (P < 0.01) (Table 2) and among all levels (P < 0.01). Compared with T4 and T5, the maximal screw diameter of other thoracic levels was wider, ranging from 4.63 mm at T4 to 5.53 mm at T8 (Table 2). There were significant differences among all levels (P < 0.01). Differences also reached significance level between males and females for maximal screw diameter (P < 0.01). LA and Cephalad Angle The greatest LA was at T8 (8.66 in men and 8.39 in women), whereas the smallest LA was at T1 (4.97 in men and 4.67 in women) in both sexes. LA was significantly larger in men at all levels compared with women (P < 0.01) (Table 2). The difference reached significance level among all levels (P < 0.01). The cephalad angle showed a decrease from T1 to T6 followed by an increase from T7 to T8 in both sexes. The cephalad angle ranged from 17.23 at T7 to 31.50 at T1 and it was significantly larger in men at T7 (P < 0.05), T6, and T8 (P < 0.01) (Table 2). There were significant differences among all levels (P < 0.01). DISCUSSION
Figure 4. The length and diameter of the thoracic cortical bone trajectory screw. 1, screw insertion point; 2, maximal screw length; 3, maximal screw diameter.
e4
www.SCIENCEDIRECT.com
Lumbar CBT screw fixation was first advocated by Santoni et al. in 2009,9 following a mediolateral and caudocranial directed path, with a novel screw design that was shorter and smaller than the conventional pedicle screw to maximize thread contact with the
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Table 1. The Incidence of Thoracic Pedicle Violation (160 Cortical Bone Trajectory [CBT] Screws, 6 Males, 96 CBT Screws, 4 Females, 64 CBT Screws)
T4
T5
T6
WORLD NEUROSURGERY -: e1-e9, - 2018
M
0
3 (3/12)
F
0
3 (3/8)
All
0
6 (6/160, 3.75%)
M
0
3 (3/12)
F
0
2 (2/8)
All
0
5 (5/160, 3.125%)
M
0
4 (4/12)
F
0
3 (3/8)
All
0
7 (7/160, 4.375%)
M
0
7 (7/12)
F
1 (1/8)
5 (5/8)
T1
T3
highest concentration of cortical bone (Figure 1). These investigators found that the CBT screw showed a 30% increase in uniaxial yield pullout load and equivalent characteristics of the screw-rod constructs stability. It was reported that the insertional torque using CBT screw was 71% higher than that of the traditional pedicle screw, in terms of the mechanical behavior in vivo.12 Baluch et al.10 also studied the fixation strength of the CBT screw, showing that it had superior resistance to craniocaudal toggling compared with a traditional pedicle screw. Snyder et al.14 evaluated the perioperative outcomes and safety of the CBT screw and found that it was safe and also had acceptable perioperative outcomes. Moreover, posterior lumbar interbody fusion (PLIF) with a CBT screw for degenerative lumbar spondylolisthesis could provide comparable postoperative improvement of clinical symptoms and reduce the incidence of symptomatic adjacent segment disease.13 Gonchar et al.11 compared outcomes of single-level PLIF using a CBT screw versus percutaneous pedicle screw, reporting that singlelevel PLIF with a CBT screw showed a significantly lower rate of screw loosening and less loss of correction and was also less invasive. Thoracic pedicle screw placement has been commonly used as one of the most rigid posterior fixation techniques in various spinal surgeries. Thoracic pedicle morphometry has been researched extensively during the past 2 decades, either directly or by radiographic measurement. Zhuang et al.18 found that the percentage of pedicles with diameter 4.5 mm was extremely high from T3 to T8 in women; T3, 59.32%; T4, 80.51%; T5, 79.66%; T6, 67.80%; T7, 61.86%; and T8, 52.54%. Men had a significantly smaller percentage than did women and the
Lateral Pedicle Wall Violation
Sex
T2
Figure 5. The lateral and cephalad angle of the thoracic cortical bone trajectory screw. 1, lateral angle, the angle between axis line of maximal screw length and the midline; 2, cephalad angle, the angle between the upper end plate and the anatomic axis line of the pedicle.
Medial Pedicle Wall Violation
Level
T7
T8
All
1 (1/160, 0.625%)
12 (12/160, 7.5%)
M
0
6 (6/12)
F
0
6 (6/8)
All
0
12 (12/160, 7.5%)
M
0
5 (5/12)
F
0
4 (4/8)
All
0
9 (9/160, 5.625%)
M
0
4 (4/12)
F
0
4 (4/8)
All
0
8 (8/160, 5%)
M
0
4 (4/12)
F
0
3 (3/8)
All
0
7 (7/160, 4.375%)
1 (1/160, 0.625%)
160 (66/160, 41.25%)
All segments F, female; M, male.
percentage of pedicles with width 4.5 mm was relatively high from T3 to T8: T3, 16.42%; T4, 40.30%; T5, 38.81%; T6, 24.63%; T7, 19.40%; and T8, 12.69%. Liau et al.19 reported that most women had a diameter of <4.5 mm from T4 to T8, ranging from 44.4% to 82.2%. Besides, a significant percentage was found only at T4 (51.1%), ranging from T8 (17.8%) to T5 (39.9%). Many investigators have shown that the transverse pedicle angle (TPA) decreased gradually from T1 to T12,18-21 and hence, the TPA of the upper thoracic vertebrae from T1 to T3 was larger than that of other thoracic segments. However, the trajectory of the CBT screw was medial to lateral in the transverse plane, increasing the occurrence of lateral pedicle wall violation at T1, T2, and T3. As the findings showed, T1-T8 pedicles were difficult to
www.WORLDNEUROSURGERY.org
e5
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Table 2. Morphometric Measurements of Thoracic Cortical Bone Trajectory Screws (Mean Standard Deviation) Level
Sex
T1
M
T2
T3
T4
T5
T6
T7
T8
Maximal Screw Length (mm)
Maximal Screw Diameter (mm)
Lateral Angle ( )
Cephalad Angle ( )
24.95 0.54*
5.30 0.34*
4.97 0.35*
32.56 6.00
F
24.01 0.49
5.03 0.18
4.67 0.40
30.12 4.16
All
24.54 0.69
5.18 0.30
4.84 0.36
31.50 5.14
M
25.04 0.48*
5.26 0.26*
5.06 0.27*
31.92 6.24
F
24.16 0.41
5.02 0.12
4.79 0.31
29.64 4.52
All
24.65 0.63
5.15 0.24
4.95 0.31
30.92 5.64
M
25.69 0.46*
5.08 0.19*
5.59 0.30*
30.01 5.11
F
24.83 0.40
4.91 0.12
5.32 0.32
28.16 3.68
All
25.31 0.61
5.00 0.19
5.47 0.34
29.19 4.61
M
26.41 0.55*
4.68 0.10*
6.25 0.35*
26.97 5.37
F
25.47 0.44
4.55 0.07
5.93 0.41
25.80 4.15
All
26.00 0.69
4.63 0.11
6.11 0.41
26.46 4.88
M
27.36 0.43*
4.86 0.11*
6.91 0.33*
23.20 4.70
F
26.25 0.38
4.71 0.09
6.60 0.38
22.68 3.68
All
26.87 0.69
4.80 0.13
6.78 0.38
22.97 4.27
M
28.26 0.44*
5.08 0.13*
7.55 0.25*
21.33 5.37*
F
27.08 0.40
4.90 0.09
7.21 0.30
17.99 3.74
All
27.74 0.72
5.00 0.15
7.40 0.32
19.87 4.99
M
29.04 0.36*
5.37 0.21*
8.13 0.21*
17.95 3.30y
F
28.05 0.44
5.07 0.11
7.79 0.33
16.29 2.11
All
28.61 0.63
5.24 0.23
7.98 0.32
17.23 2.94
M
29.94 0.35*
5.74 0.22*
8.66 0.18*
19.77 3.01*
F
29.00 0.24
5.27 0.13
8.39 0.28
17.59 2.52
All
29.53 0.56
5.53 0.30
8.54 0.27
18.82 2.99
M, male; F, female. Comparison between men and women: *statistically significant difference (P < 0.01). ystatistically significant difference (P < 0.05).
optimally accommodate a 4.5-mm CBT screw without penetrating the lateral pedicle wall, especially in women, because of the narrower pedicle (T4-T8) and bigger TPA (T1-T3). O’Brien et al.22 found that T1-T12 pedicle width ranged from 4.6 to 8.25 mm, and the pedicle rib unit width ranged from 12.6 to 17.9 mm. Liljenqvist et al.23 reported that narrower pedicles on the concave side at the apex of the curve (range, 2.3e3.2 mm compared with the convex side, 3.9e4.4 mm), whereas the pedicle rib unit width was wider (range, 11 mm in the cephalad aspect to 14 mm in the caudad aspect of the thoracic spine). Husted et al.24 reported that mean pedicle width and mean pedicle rib unit width of all levels was 5.98 mm and 14.93 mm, respectively. These results show that the pedicle rib unit could provide an ample target for thoracic screw insertion. In our study, we used the dimension of the medial pedicle wall to the medial rib head wall as the maximal screw diameter, which ranged from 4.63 mm at T4 to 5.53 mm at T8. Theoretically, the diameter of the CBT screw could vary from 4.5e5.0 mm from
e6
www.SCIENCEDIRECT.com
T1-T7 to 5.5 mm at T8. Maximal screw length tended to gradually increase from T1 to T8 (24.54 mm at T1 to 29.53 mm at T8) so a CBT screw 25.0e30.0 mm long can be used. There was a tendency for the LA to increase from T1 to T8; however, the cephalad angle decreased with cephalad to caudal progression. In our study, when pedicle violation using the technique was considered, 0.625% of CBT screws showed medial pedicle violation, whereas 41.25% of CBT screws penetrated the lateral pedicle wall. Most of the violations were at T4 and T5, particularly in women. It was possible that the T4-T5 pedicle diameter was smaller than that of other levels. Therefore, both morphometric measurements and results of screw insertion in cadaveric specimens showed that the CBT screw should be inserted through the pedicle or pedicle rib unit from T1 to T8. Furthermore, the occurrence of pedicle rib unit fixation increased at the midthoracic level, especially in females. The in-out-in technique, using intentional perforation of the lateral pedicle cortex (with violation of the costovertebral joint), has been frequently performed,
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 6. Computed tomography scans of cadaveric specimens inserted with cortical bone trajectory screws at cervicothoracic junction. (A) T1, (B) T2, (C) T3.
especially in the upper and middle thoracic spine, where the pedicle width typically measures only 4.0e5.0 mm.18,25 Numerous studies have shown that the posterolateral portion of the vertebral end plate, the dorsal vertebral cortex, and caudad half of the
Figure 7. The reconstructed three-dimensional image showing that thoracic cortical bone trajectory screws combined with lateral mass screws fixation in the cadaveric spine and the bone widow were made transparent to view
WORLD NEUROSURGERY -: e1-e9, - 2018
pedicle were regions with higher density bone.26-30 The CBT screw in the middle and upper thoracic spine makes full use of cortically based track and acquire 6 or 7 points of cortex purchase: the dorsal cortex of the lamina, medial pedicle wall, caudad part of the
inserted screws. (A) Anterior view, (B) lateral view, (C) posterior view, (D) axial view.
www.WORLDNEUROSURGERY.org
e7
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
pedicle, medial wall of the rib head or lateral pedicle wall, lateral margin of the vertebral body, and subeend plate cortical bone (Figures 6 and 7). In theory, CBT screw fixation in the upper and midthoracic spine could provide 5 advantages. Ugur et al.31 found that pedicle dural sac distance ranged from 0 to 0.5 mm (T1-T8), and therefore, an inappropriate screw insertion angle can result in neurologic complications. The direction of the CBT screw was away from neural elements (i.e., a medial to lateral approach), reducing the possibility of damaging the spinal cord. Particularly at the cervicothoracic junction, it may be safer to use a CBT screw compared with a conventional pedicle screw, because the quality of C-Arm fluoroscopy in these segments was not optimal. Traditional pedicle screw instrumentation required a more lateral starting point and a lateral to medial approach. On the contrary, the entry point of the CBT screw was more medial and its trajectory was medial to lateral, enabling shorter incision length and less muscle dissection to minimize approach-related trauma. In addition, the CBT screw was a salvage method to rescue failed pedicle screws or an alternative trajectory to achieve solid fixation when the vertebra was destroyed, such as in infection. Fourth, screw heads of CBT screws (T1-T8) could line up in the sagittal plane to capture the rod without complicated rod bending, even combined with lateral mass screws at the cervicothoracic junction (Figure 7C). Screw tips of CBT screws in the mid and upper thoracic spine consistently located approximately costovertebral joints (Figure 7D), which may decrease the risk of pleura injury
REFERENCES 1. Delorme S, Labelle H, Aubin CE, de Guise JA, Rivard CH, Poitras B, et al. A three-dimensional radiographic comparison of Cotrel-Dubousset and Colorado instrumentations for the correction of idiopathic scoliosis. Spine (Phila Pa 1976). 2000;25: 205-210. 2. Liljenqvist UR, Halm HF, Link TM. Pedicle screw instrumentation of the thoracic spine in idiopathic scoliosis. Spine (Phila Pa 1976). 1997;22: 2239-2245. 3. Suk SI, Lee CK, Min HJ, Cho KH, Oh JH. Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Int Orthop. 1994;18:341-346. 4. Cinotti G, Gumina S, Ripani M, Postacchini F. Pedicle instrumentation in the thoracic spine. A morphometric and cadaveric study for placement of screws. Spine (Phila Pa 1976). 1999;24:114-119. 5. Ebraheim NA, Xu R, Ahmad M, Yeasting RA. Projection of the thoracic pedicle and its morphometric analysis. Spine (Phila Pa 1976). 1997; 22:233-238. 6. Panjabi MM, O’Holleran JD, Crisco JJ 3rd, Kothe R. Complexity of the thoracic spine pedicle anatomy. Eur Spine J. 1997;6:19-24. 7. Vaccaro AR, Rizzolo SJ, Allardyce TJ, Ramsey M, Salvo J, Balderston RA, et al. Placement of pedicle screws in the thoracic spine. Part I: Morphometric analysis of the thoracic vertebrae. J Bone Joint Surg Am. 1995;77:1193-1199.
e8
www.SCIENCEDIRECT.com
because the rib head could shield the intrathoracic contents. However, clinical studies are needed to further clarify above advantages. Some limitations should be noted in the present study. First, different human races might influence anatomic measurement; however, our CT scans and cadaveric specimens included for studying were all taken from Asian patients. Thus, further investigation is needed to evaluate if findings vary with race. Moreover, we assessed the feasibility of the CBT screw from the viewpoint of anatomy without biomechanical study; however, we will further study screw stability of the thoracic CBT screw. Meanwhile, further clinical research should be performed to prove the results of CBT screw fixation in the upper and middle thoracic spine. We will further study the key points of inserting a thoracic CBT screw via clinical research and design a corresponding navigation template to reduce the rate of pedicle wall penetration.
CONCLUSIONS Based on the anatomic measurements and cadaveric results of the current study, we suggest that a CBT screw 4.5 mm in diameter and 25.0e30.0 mm long could be inserted from T1 to T8 through the pedicle or pedicle rib unit. Furthermore, the results of our study provide insights into screw insertion angle when performing surgery in the middle thoracic spine and at the cervicothoracic junction.
8. Vaccaro AR, Rizzolo SJ, Balderston RA, Allardyce TJ, Garfin SR, Dolinskas C, et al. Placement of pedicle screws in the thoracic spine. Part II: an anatomical and radiographic assessment. J Bone Joint Surg Am. 1995;77:1200-1206. 9. Santoni BG, Hynes RA, McGilvray KC, RodriguezCanessa G, Lyons AS, Henson MA, et al. Cortical bone trajectory for lumbar pedicle screws. Spine J. 2009;9:366-373. 10. Baluch DA, Patel AA, Lullo B, Havey RM, Voronov LI, Nguyen NL, et al. Effect of physiological loads on cortical and traditional pedicle screw fixation. Spine (Phila Pa 1976). 2014;39: E1297-E1302. 11. Gonchar I, Kotani Y, Matsumoto Y. Cortical bone trajectory versus percutaneous pedicle screw in minimally invasive posterior lumbar fusion. Spine J. 2014;14:S114-S115. 12. Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K. In vivo analysis of insertional torque during pedicle screwing using cortical bone trajectory technique. Spine (Phila Pa 1976). 2014;39:E240-E245. 13. Sakaura H, Miwa T, Yamashita T, Kuroda Y, Ohwada T. Posterior lumbar interbody fusion with cortical bone trajectory screw fixation versus posterior lumbar interbody fusion using traditional pedicle screw fixation for degenerative lumbar spondylolisthesis: a comparative study. J Neurosurg Spine. 2016;25:591-595. 14. Snyder LA, Martinez-del-Campo E, Neal MT, Zaidi HA, Awad A-W, Bina R, et al. Lumbar spinal
fixation with cortical bone trajectory pedicle screws in 79 patients with degenerative disease: perioperative outcomes and complications. World Neurosurg. 2016;88:205-213. 15. Matsukawa K, Yato Y, Hynes RA, Imabayashi H, Hosogane N, Asazuma T, et al. Cortical bone trajectory for thoracic pedicle screws: a technical note. Clin Spine Surg. 2017;30:E497-E504. 16. Xuan J, Zhang D, Jin HM, Chen JX, Xu DL, Xu HM, et al. Minimally invasive cortical bone trajectory screws placement via pedicle or pedicle rib unit in the lower thoracic spine: a cadaveric and radiographic study. Eur Spine J. 2016;25: 4199-4207. 17. Sheng SR, Chen JX, Chen W, Xue EX, Wang XY, Zhu QA. Cortical bone trajectory screws for the middle-upper thorax: an anatomico-radiological study. Medicine (Baltimore). 2016;95:e4676. 18. Zhuang Z, Chen Y, Han H, Cai S, Wang X, Qi W, et al. Thoracic pedicle morphometry in different body height population: a three-dimensional study using reformatted computed tomography. Spine (Phila Pa 1976). 2011;36:E1547-E1554. 19. Liau KM, Yusof MI, Abdullah MS, Abdullah S, Yusof AH. Computed tomographic morphometry of thoracic pedicles: safety margin of transpedicular screw fixation in malaysian Malay population. Spine (Phila Pa 1976). 2006;31:E545-E550. 20. Datir SP, Mitra SR. Morphometric study of the thoracic vertebral pedicle in an Indian population. Spine (Phila Pa 1976). 2004;29:1174-1181.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
21. Kim NH, Lee HM, Chung IH, Kim HJ, Kim SJ. Morphometric study of the pedicles of thoracic and lumbar vertebrae in Koreans. Spine (Phila Pa 1976). 1994;19:1390-1394. 22. O’Brien MF, Lenke LG, Mardjetko S, Lowe TG, Kong Y, Eck K, et al. Pedicle morphology in thoracic adolescent idiopathic scoliosis: is pedicle fixation an anatomically viable technique? Spine (Phila Pa 1976). 2000;25:2285-2293. 23. Liljenqvist UR, Allkemper T, Hackenberg L, Link TM, Steinbeck J, Halm HF. Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction. J Bone Joint Surg Am. 2002;84A:359-368. 24. Husted DS, Haims AH, Fairchild TA, Kershaw TS, Yue JJ. Morphometric comparison of the pedicle rib unit to pedicles in the thoracic spine. Spine (Phila Pa 1976). 2004;29:139-146. 25. McLain RF, Ferrara L, Kabins M. Pedicle morphometry in the upper thoracic spine: limits to safe screw placement in older patients. Spine (Phila Pa 1976). 2002;27:2467-2471.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
26. Grant JP, Oxland TR, Dvorak MF. Mapping the structural properties of the lumbosacral vertebral endplates. Spine (Phila Pa 1976). 2001;26:889-896. 27. Karataglis D, Kapetanos G, Lontos A, Christodoulou A, Christoforides J, Pournaras J. The role of the dorsal vertebral cortex in the stability of transpedicular screws. A biomechanical study in human cadaveric vertebrae. J Bone Joint Surg Br. 2006;88:692-695. 28. Lehman RA Jr, Helgeson MD, Dmitriev AE, Paik H, Bevevino AJ, Gaume R, et al. What is the best way to optimize thoracic kyphosis correction? A micro-CT and biomechanical analysis of pedicle morphology and screw failure. Spine (Phila Pa 1976). 2012;37:E1171-E1176. 29. Wu SS, Edwards WT, Yuan HA. Stiffness between different directions of transpedicular screws and vertebra. Clin Biomech (Bristol, Avon). 1998;13:S1-S8.
ported by less-dense trabecular bone. Bone. 2009; 44:372-379. 31. Ugur HC, Attar A, Uz A, Tekdemir I, Egemen N, Genc Y. Thoracic pedicle: surgical anatomic evaluation and relations. J Spinal Disord. 2001;14:39-45.
Conflict of interest statement: This work was supported by a grant from the National Nature Foundation of China (grant number 81371988), the Natural Science Foundation of Zhejiang Province (grant number CF18H060026), and the Zhejiang Medical and Health Science and Technology Plan Project (grant number 2015RCB022). Received 18 March 2018; accepted 22 May 2018 Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.05.152 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
30. Zhao FD, Pollintine P, Hole BD, Adams MA, Dolan P. Vertebral fractures usually affect the cranial endplate because it is thinner and sup-
WORLD NEUROSURGERY -: e1-e9, - 2018
1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
e9
Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment Jun Xuan1, Chen-Long Xie2, Yang Wu1, Jian Chen2, Xin Tong1, Xiang-Yang Wang2, Hui Xu2
OBJECTIVE: To assess an alternative method of cortical bone trajectory (CBT) screw placement in the thoracic spine from T1 to T8 and to investigate the proper entry point, screw insertion angle, screw length, and diameter.
-
METHODS: Computed tomography images of 80 patients were used to measure all related parameters. Ten cadaveric spines were studied and 4.5-mm screws were inserted into both sides of the vertebrae. Computed tomography of all vertebrae previously inserted with CBT screws was performed and lateral or medial pedicle wall violation was checked.
-
RESULTS: Of the inserted 160 CBT screws, 41.25% (66/160) penetrated the lateral pedicle wall, and the proportion of medial pedicle wall violation accounted for 0.625% (1/160). Maximal screw length tended to gradually increase from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8). Compared with T4 and T5, maximal screw diameters of other thoracic levels were wider, ranging from 4.63 mm at T4 to 5.53 mm at T8. The greatest lateral angle was 8.66 in men and 8.39 in women at T8, whereas the smallest lateral angle was 4.97 in men and 4.67 in women at T1. The cephalad angle ranged from 17.23 at T7 to 31.50 at T1 and it was significantly larger in men at T7 (P < 0.05), T6 and T8 (P < 0.01).
-
CONCLUSIONS: Based on the results of this study, we suggest that patients could be placed with 4.5 3 25.0e30.0 mm CBT screws from T1 to T8 through the pedicle or pedicle rib unit.
-
Key words Cervicothoracic junction - Cortical bone trajectory screw - Less invasive - Pedicle rib unit - Rescue failed screw -
Abbreviations and Acronyms CBT: Cortical bone trajectory CT: Computed tomography LA: Lateral angle MSL: Maximal screw length PLIF: Posterior lumbar interbody fusion TPA: Transverse pedicle angle
WORLD NEUROSURGERY -: e1-e9, - 2018
INTRODUCTION
T
ranspedicular screw instrumentation of thoracic spinal segments has been described for various indications such as fracture, tumor, and deformity (scoliosis and kyphosis). Moreover, the thoracic pedicle screw has been reported to have the advantages of better curve correction, less loss of correction, and shorter fusion length when it is used in idiopathic scoliosis surgery instead of other spinal anchoring devices.1-3 However, anatomic studies have reported that thoracic pedicles are small and the three-dimensional orientation of pedicles is complex and variable among patients,4-8 leading to transpedicular screw fixation in the thoracic spine, which has a high risk of injury to nerve roots, pleura, and large vessels. In 2009, Santoni et al.9 investigated cortical bone trajectory (CBT) for the lumbar pedicle screw (Figure 1). Their biomechanical tests showed a 30% increase in uniaxial yield pullout load and equivalency in mixed loading compared with the traditional trajectory. Many biomechanical or anatomic studies and clinical trials have been performed in the lumbar spine, showing that the CBT screw is a more rigid, safe, and minimally invasive technique.10-14 It has been expanded down to the lower thoracic spine (T9-T12),15,16 and Matsukawa et al.15 found that its insertional torque was 53.8% higher than that of the conventional technique. Although Sheng et al.17 investigated CBT screw placement in the mid and upper thoracic spine (T3-T8), their study has some disadvantages. At first, they determined whether the CBT screw penetrated medial or lateral pedicle wall only by performing radiography to obtain an anteroposterior radiograph. The method could not accurately determine whether the pedicle wall was penetrated or not. Second, Zhuang et al.18 reported that the percentage of pedicle width <4.5 mm was extremely high at T3eT8 in women (52.54%e80.51%) and T4eT7 in men
From the 1Department of Orthopaedic Surgery, Jinhua Municipal Central Hospital, Jinhua Hospital, Zhejiang University School of Medicine, Jinhua; and 2Department of Orthopaedic Surgery, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University, Wenzhou, People’s Republic of China To whom correspondence should be addressed: Hui Xu, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.05.152 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
e1
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 1. The trajectory of the lumbar cortical bone trajectory screw. (A) Lateral view. (B) Anteroposterior
(12.69%e40.30%). Moreover, the result also showed a high percentage of pedicle width <4.0 mm and 3.5 mm in women. Sheng et al.17 used a 5.0-mm-diameter CBT screw to perform their study; however, it was difficult to place a 5.0-mm CBT screw in patients with a pedicle width <4.5 mm without lateral or medial pedicle violation, especially some female patients whose pedicle width was <4.0 mm or 3.5 mm. Third, Zhuang et al.18 did not mention whether the connection between the screw head and the rod could be completed when using CBT screws on a multilevel. Fourth, these investigators excluded 2 segments of T1 and T2 in their study, but we found that T1 and T2 could be placed into CBT screws. Fifth, they did not provide the standard anteroposterior and lateral radiographs of the thoracic CBT screw, which could be used to preliminarily determine whether the CBT screw had been inserted correctly. Thus, we investigated the feasibility of CBT screw instrumentation via pedicle or pedicle rib unit in the thoracic spine (T1-T8). We inserted a CBT screw in cadaveric specimens to evaluate the incidence of medial and lateral pedicle wall violation. In addition, we conducted morphometric measurements on the thoracic CBT screw by 2-dimensional multiplanar reconstruction using computed tomography (CT). METHODS The research was approved by the institutional ethics review board of the hospital and carried out following the Declaration of Helsinki principles.
e2
www.SCIENCEDIRECT.com
view. (C) Axial view. (D) Cross section to show the trajectory of the lumbar cortical bone trajectory screw.
Study of Thoracic CBT Screw Violation on Cadavers Ten cadaveric specimens (6 men and 4 women) were provided by the Department of Anatomy, Wenzhou Medical University. The mean age of spine donors was 51.10 10.97 years (range, 30e70 years). Before the experiment, lateral and anteroposterior radiograms were taken on all cadavers to exclude congenital deformities, trauma, tumor, earlier surgery, or infection. Two fellowship-trained spinal surgeons dissected the thoracic spines and the study was carried out bilaterally on 160 pedicles between the first and eighth thoracic vertebrae. The screw insertion point was made using an electric drill equipped with a 2.0-mm Kirschner wire. The thoracic gearshift was inserted into the body to a depth of around 25e30 mm at T8 and 20e25 mm at the remaining levels from T1 to T7. Then, a flexible ball-tipped palpating device was introduced to palpate the bottom and 4 walls of the pedicle tract. Special attention must be paid to the first approximately 15 mm of the hole. If a breach is discovered, the pedicle finder should be redirected. The pedicle was tapped with a 4.5-mm-diameter tap. Once again, the pedicle tract was palpated to make sure that no wall had been violated. All CBT screws were inserted in the middle and proximal thoracic spine. We used 4.50 30.00 mm at T8 and 4.50 25.00 mm at the other levels from T1 to T7 in both sides, respectively. The position of the screw was identified by anteroposterior and lateral radiographs, and thoracic CBT screws were placed approximately at the 5 (7) o’clock orientation and aimed in the 11e12 (12e1) o’clock direction of the pedicle (Figure 2). CT scans of cadaveric specimens previously inserted with CBT screws were performed and vertebrae were dissected as well. We checked lateral or
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 2. The position of the screw was identified by anteroposterior and lateral radiographs. (A) The marker was inserted almost at the 5 (7) o’clock orientation and aimed in the 11e12 (12e1) o’clock direction. (B) The
medial pedicle wall violation. The thoracic CBT screw entry point is shown in Figure 3. Study of Morphometric Measurements on Thoracic CBT Screw We performed the study on patients who came to the Second Affiliated Hospital of Wenzhou Medical University for CT scans from January 2011 to October 2015. CT images were acquired by Philips Brilliance 256 IT scan machine (Philips Medical Systems, Eindhoven, the Netherlands). Scan parameters included 120 kV, 180 MA, 512 512 matrix, layer thickness of 0.9 mm, collimation of 128 0.625 mm, pitch of 0.6 mm, DoseRight of Z-DOM, and 250 mAs/slice. CT scans of 80 adults (45 males and 35 females; 49.52 10.35 years old; range, 30e68 years) who underwent examination for lung conditions were randomly enrolled, and the reformatted images with a thickness 1.0 mm were once again acquired from those images. None of the patients showed any evidence of infection, tumor, traumatic diseases, or spinal deformity. Measurements were acquired by the specially trained spine surgeon, who was acquainted with the anatomy and the thoracic
WORLD NEUROSURGERY -: e1-e9, - 2018
marker was placed via the caudal portion of the pedicle. The anteroposterior (C) and lateral radiographic (D) images showing that the position of the cortical bone trajectory screw accorded with that of the marker.
pedicle screw. Every parameter was measured 3 times in 1 patient, and we regarded the average of each parameter as the final value. At first, we drew an angle of 45 to make its extension line overlap the thoracic pedicle, identifying the intersection point which was located approximately at the 5 o’clock orientation of the pedicle, which was the entry point of the thoracic CBT screw. To obtain a novel axial plane, the horizontal axis was adjusted to overlap the anatomic axis of the thoracic pedicle. We measured the following parameters through the plane (Figures 4 and 5): 1) maximal screw length, 2) maximal screw diameter, 3) lateral angle (LA), and 4) cephalad angle. Statistical Analysis Statistical analysis was performed using SPSS statistical software program version 22.0 (IBM Corp., Armonk, New York, USA). Results were presented as mean standard deviation and the independent sample t test was used to compare the differences between males and females. One-way analysis of variance and the Tukey analysis were performed for statistical comparison among
www.WORLDNEUROSURGERY.org
e3
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 3. The starting point of the thoracic cortical bone trajectory screw. (Black dotted line) 1/2 of the base of transverse process; (yellow dotted line) medial 1/3 of the superior facet; (green dotted line) inferior 1/3 of the base of transverse process. (A) The entry point (T1-T2) was the point of intersection between 1/2 of the base
each segment. In the present study, we used a P value of <0.05 to represent statistical significance. RESULTS Incidence of Thoracic Pedicle Violation A total of 160 thoracic CBT screws, 96 in males and 64 in females, were inserted in the middle and upper thoracic spine. All of the
of transverse process and the medial 1/3 of the superior facet. The starting point (T3-T8) was the point of intersection between the inferior 1/3 of the base of transverse process and the medial 1/3 of the superior facet. (B) Cortical bone trajectory screws were inserted in the cadaveric thoracic spine.
inserted CBT screws, (41.25% [66/160]) penetrated the lateral pedicle wall, and the proportion of the medial pedicle wall violation accounted for 0.625% (1/160) (Table 1). Maximal Screw Length and Maximal Screw Diameter Maximal screw length tended to increase gradually from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8), and maximal screw length of males was longer than that of females. There were significant differences between males and females (P < 0.01) (Table 2) and among all levels (P < 0.01). Compared with T4 and T5, the maximal screw diameter of other thoracic levels was wider, ranging from 4.63 mm at T4 to 5.53 mm at T8 (Table 2). There were significant differences among all levels (P < 0.01). Differences also reached significance level between males and females for maximal screw diameter (P < 0.01). LA and Cephalad Angle The greatest LA was at T8 (8.66 in men and 8.39 in women), whereas the smallest LA was at T1 (4.97 in men and 4.67 in women) in both sexes. LA was significantly larger in men at all levels compared with women (P < 0.01) (Table 2). The difference reached significance level among all levels (P < 0.01). The cephalad angle showed a decrease from T1 to T6 followed by an increase from T7 to T8 in both sexes. The cephalad angle ranged from 17.23 at T7 to 31.50 at T1 and it was significantly larger in men at T7 (P < 0.05), T6, and T8 (P < 0.01) (Table 2). There were significant differences among all levels (P < 0.01). DISCUSSION
Figure 4. The length and diameter of the thoracic cortical bone trajectory screw. 1, screw insertion point; 2, maximal screw length; 3, maximal screw diameter.
e4
www.SCIENCEDIRECT.com
Lumbar CBT screw fixation was first advocated by Santoni et al. in 2009,9 following a mediolateral and caudocranial directed path, with a novel screw design that was shorter and smaller than the conventional pedicle screw to maximize thread contact with the
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Table 1. The Incidence of Thoracic Pedicle Violation (160 Cortical Bone Trajectory [CBT] Screws, 6 Males, 96 CBT Screws, 4 Females, 64 CBT Screws)
T4
T5
T6
WORLD NEUROSURGERY -: e1-e9, - 2018
M
0
3 (3/12)
F
0
3 (3/8)
All
0
6 (6/160, 3.75%)
M
0
3 (3/12)
F
0
2 (2/8)
All
0
5 (5/160, 3.125%)
M
0
4 (4/12)
F
0
3 (3/8)
All
0
7 (7/160, 4.375%)
M
0
7 (7/12)
F
1 (1/8)
5 (5/8)
T1
T3
highest concentration of cortical bone (Figure 1). These investigators found that the CBT screw showed a 30% increase in uniaxial yield pullout load and equivalent characteristics of the screw-rod constructs stability. It was reported that the insertional torque using CBT screw was 71% higher than that of the traditional pedicle screw, in terms of the mechanical behavior in vivo.12 Baluch et al.10 also studied the fixation strength of the CBT screw, showing that it had superior resistance to craniocaudal toggling compared with a traditional pedicle screw. Snyder et al.14 evaluated the perioperative outcomes and safety of the CBT screw and found that it was safe and also had acceptable perioperative outcomes. Moreover, posterior lumbar interbody fusion (PLIF) with a CBT screw for degenerative lumbar spondylolisthesis could provide comparable postoperative improvement of clinical symptoms and reduce the incidence of symptomatic adjacent segment disease.13 Gonchar et al.11 compared outcomes of single-level PLIF using a CBT screw versus percutaneous pedicle screw, reporting that singlelevel PLIF with a CBT screw showed a significantly lower rate of screw loosening and less loss of correction and was also less invasive. Thoracic pedicle screw placement has been commonly used as one of the most rigid posterior fixation techniques in various spinal surgeries. Thoracic pedicle morphometry has been researched extensively during the past 2 decades, either directly or by radiographic measurement. Zhuang et al.18 found that the percentage of pedicles with diameter 4.5 mm was extremely high from T3 to T8 in women; T3, 59.32%; T4, 80.51%; T5, 79.66%; T6, 67.80%; T7, 61.86%; and T8, 52.54%. Men had a significantly smaller percentage than did women and the
Lateral Pedicle Wall Violation
Sex
T2
Figure 5. The lateral and cephalad angle of the thoracic cortical bone trajectory screw. 1, lateral angle, the angle between axis line of maximal screw length and the midline; 2, cephalad angle, the angle between the upper end plate and the anatomic axis line of the pedicle.
Medial Pedicle Wall Violation
Level
T7
T8
All
1 (1/160, 0.625%)
12 (12/160, 7.5%)
M
0
6 (6/12)
F
0
6 (6/8)
All
0
12 (12/160, 7.5%)
M
0
5 (5/12)
F
0
4 (4/8)
All
0
9 (9/160, 5.625%)
M
0
4 (4/12)
F
0
4 (4/8)
All
0
8 (8/160, 5%)
M
0
4 (4/12)
F
0
3 (3/8)
All
0
7 (7/160, 4.375%)
1 (1/160, 0.625%)
160 (66/160, 41.25%)
All segments F, female; M, male.
percentage of pedicles with width 4.5 mm was relatively high from T3 to T8: T3, 16.42%; T4, 40.30%; T5, 38.81%; T6, 24.63%; T7, 19.40%; and T8, 12.69%. Liau et al.19 reported that most women had a diameter of <4.5 mm from T4 to T8, ranging from 44.4% to 82.2%. Besides, a significant percentage was found only at T4 (51.1%), ranging from T8 (17.8%) to T5 (39.9%). Many investigators have shown that the transverse pedicle angle (TPA) decreased gradually from T1 to T12,18-21 and hence, the TPA of the upper thoracic vertebrae from T1 to T3 was larger than that of other thoracic segments. However, the trajectory of the CBT screw was medial to lateral in the transverse plane, increasing the occurrence of lateral pedicle wall violation at T1, T2, and T3. As the findings showed, T1-T8 pedicles were difficult to
www.WORLDNEUROSURGERY.org
e5
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Table 2. Morphometric Measurements of Thoracic Cortical Bone Trajectory Screws (Mean Standard Deviation) Level
Sex
T1
M
T2
T3
T4
T5
T6
T7
T8
Maximal Screw Length (mm)
Maximal Screw Diameter (mm)
Lateral Angle ( )
Cephalad Angle ( )
24.95 0.54*
5.30 0.34*
4.97 0.35*
32.56 6.00
F
24.01 0.49
5.03 0.18
4.67 0.40
30.12 4.16
All
24.54 0.69
5.18 0.30
4.84 0.36
31.50 5.14
M
25.04 0.48*
5.26 0.26*
5.06 0.27*
31.92 6.24
F
24.16 0.41
5.02 0.12
4.79 0.31
29.64 4.52
All
24.65 0.63
5.15 0.24
4.95 0.31
30.92 5.64
M
25.69 0.46*
5.08 0.19*
5.59 0.30*
30.01 5.11
F
24.83 0.40
4.91 0.12
5.32 0.32
28.16 3.68
All
25.31 0.61
5.00 0.19
5.47 0.34
29.19 4.61
M
26.41 0.55*
4.68 0.10*
6.25 0.35*
26.97 5.37
F
25.47 0.44
4.55 0.07
5.93 0.41
25.80 4.15
All
26.00 0.69
4.63 0.11
6.11 0.41
26.46 4.88
M
27.36 0.43*
4.86 0.11*
6.91 0.33*
23.20 4.70
F
26.25 0.38
4.71 0.09
6.60 0.38
22.68 3.68
All
26.87 0.69
4.80 0.13
6.78 0.38
22.97 4.27
M
28.26 0.44*
5.08 0.13*
7.55 0.25*
21.33 5.37*
F
27.08 0.40
4.90 0.09
7.21 0.30
17.99 3.74
All
27.74 0.72
5.00 0.15
7.40 0.32
19.87 4.99
M
29.04 0.36*
5.37 0.21*
8.13 0.21*
17.95 3.30y
F
28.05 0.44
5.07 0.11
7.79 0.33
16.29 2.11
All
28.61 0.63
5.24 0.23
7.98 0.32
17.23 2.94
M
29.94 0.35*
5.74 0.22*
8.66 0.18*
19.77 3.01*
F
29.00 0.24
5.27 0.13
8.39 0.28
17.59 2.52
All
29.53 0.56
5.53 0.30
8.54 0.27
18.82 2.99
M, male; F, female. Comparison between men and women: *statistically significant difference (P < 0.01). ystatistically significant difference (P < 0.05).
optimally accommodate a 4.5-mm CBT screw without penetrating the lateral pedicle wall, especially in women, because of the narrower pedicle (T4-T8) and bigger TPA (T1-T3). O’Brien et al.22 found that T1-T12 pedicle width ranged from 4.6 to 8.25 mm, and the pedicle rib unit width ranged from 12.6 to 17.9 mm. Liljenqvist et al.23 reported that narrower pedicles on the concave side at the apex of the curve (range, 2.3e3.2 mm compared with the convex side, 3.9e4.4 mm), whereas the pedicle rib unit width was wider (range, 11 mm in the cephalad aspect to 14 mm in the caudad aspect of the thoracic spine). Husted et al.24 reported that mean pedicle width and mean pedicle rib unit width of all levels was 5.98 mm and 14.93 mm, respectively. These results show that the pedicle rib unit could provide an ample target for thoracic screw insertion. In our study, we used the dimension of the medial pedicle wall to the medial rib head wall as the maximal screw diameter, which ranged from 4.63 mm at T4 to 5.53 mm at T8. Theoretically, the diameter of the CBT screw could vary from 4.5e5.0 mm from
e6
www.SCIENCEDIRECT.com
T1-T7 to 5.5 mm at T8. Maximal screw length tended to gradually increase from T1 to T8 (24.54 mm at T1 to 29.53 mm at T8) so a CBT screw 25.0e30.0 mm long can be used. There was a tendency for the LA to increase from T1 to T8; however, the cephalad angle decreased with cephalad to caudal progression. In our study, when pedicle violation using the technique was considered, 0.625% of CBT screws showed medial pedicle violation, whereas 41.25% of CBT screws penetrated the lateral pedicle wall. Most of the violations were at T4 and T5, particularly in women. It was possible that the T4-T5 pedicle diameter was smaller than that of other levels. Therefore, both morphometric measurements and results of screw insertion in cadaveric specimens showed that the CBT screw should be inserted through the pedicle or pedicle rib unit from T1 to T8. Furthermore, the occurrence of pedicle rib unit fixation increased at the midthoracic level, especially in females. The in-out-in technique, using intentional perforation of the lateral pedicle cortex (with violation of the costovertebral joint), has been frequently performed,
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
Figure 6. Computed tomography scans of cadaveric specimens inserted with cortical bone trajectory screws at cervicothoracic junction. (A) T1, (B) T2, (C) T3.
especially in the upper and middle thoracic spine, where the pedicle width typically measures only 4.0e5.0 mm.18,25 Numerous studies have shown that the posterolateral portion of the vertebral end plate, the dorsal vertebral cortex, and caudad half of the
Figure 7. The reconstructed three-dimensional image showing that thoracic cortical bone trajectory screws combined with lateral mass screws fixation in the cadaveric spine and the bone widow were made transparent to view
WORLD NEUROSURGERY -: e1-e9, - 2018
pedicle were regions with higher density bone.26-30 The CBT screw in the middle and upper thoracic spine makes full use of cortically based track and acquire 6 or 7 points of cortex purchase: the dorsal cortex of the lamina, medial pedicle wall, caudad part of the
inserted screws. (A) Anterior view, (B) lateral view, (C) posterior view, (D) axial view.
www.WORLDNEUROSURGERY.org
e7
ORIGINAL ARTICLE JUN XUAN ET AL.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
pedicle, medial wall of the rib head or lateral pedicle wall, lateral margin of the vertebral body, and subeend plate cortical bone (Figures 6 and 7). In theory, CBT screw fixation in the upper and midthoracic spine could provide 5 advantages. Ugur et al.31 found that pedicle dural sac distance ranged from 0 to 0.5 mm (T1-T8), and therefore, an inappropriate screw insertion angle can result in neurologic complications. The direction of the CBT screw was away from neural elements (i.e., a medial to lateral approach), reducing the possibility of damaging the spinal cord. Particularly at the cervicothoracic junction, it may be safer to use a CBT screw compared with a conventional pedicle screw, because the quality of C-Arm fluoroscopy in these segments was not optimal. Traditional pedicle screw instrumentation required a more lateral starting point and a lateral to medial approach. On the contrary, the entry point of the CBT screw was more medial and its trajectory was medial to lateral, enabling shorter incision length and less muscle dissection to minimize approach-related trauma. In addition, the CBT screw was a salvage method to rescue failed pedicle screws or an alternative trajectory to achieve solid fixation when the vertebra was destroyed, such as in infection. Fourth, screw heads of CBT screws (T1-T8) could line up in the sagittal plane to capture the rod without complicated rod bending, even combined with lateral mass screws at the cervicothoracic junction (Figure 7C). Screw tips of CBT screws in the mid and upper thoracic spine consistently located approximately costovertebral joints (Figure 7D), which may decrease the risk of pleura injury
REFERENCES 1. Delorme S, Labelle H, Aubin CE, de Guise JA, Rivard CH, Poitras B, et al. A three-dimensional radiographic comparison of Cotrel-Dubousset and Colorado instrumentations for the correction of idiopathic scoliosis. Spine (Phila Pa 1976). 2000;25: 205-210. 2. Liljenqvist UR, Halm HF, Link TM. Pedicle screw instrumentation of the thoracic spine in idiopathic scoliosis. Spine (Phila Pa 1976). 1997;22: 2239-2245. 3. Suk SI, Lee CK, Min HJ, Cho KH, Oh JH. Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Int Orthop. 1994;18:341-346. 4. Cinotti G, Gumina S, Ripani M, Postacchini F. Pedicle instrumentation in the thoracic spine. A morphometric and cadaveric study for placement of screws. Spine (Phila Pa 1976). 1999;24:114-119. 5. Ebraheim NA, Xu R, Ahmad M, Yeasting RA. Projection of the thoracic pedicle and its morphometric analysis. Spine (Phila Pa 1976). 1997; 22:233-238. 6. Panjabi MM, O’Holleran JD, Crisco JJ 3rd, Kothe R. Complexity of the thoracic spine pedicle anatomy. Eur Spine J. 1997;6:19-24. 7. Vaccaro AR, Rizzolo SJ, Allardyce TJ, Ramsey M, Salvo J, Balderston RA, et al. Placement of pedicle screws in the thoracic spine. Part I: Morphometric analysis of the thoracic vertebrae. J Bone Joint Surg Am. 1995;77:1193-1199.
e8
www.SCIENCEDIRECT.com
because the rib head could shield the intrathoracic contents. However, clinical studies are needed to further clarify above advantages. Some limitations should be noted in the present study. First, different human races might influence anatomic measurement; however, our CT scans and cadaveric specimens included for studying were all taken from Asian patients. Thus, further investigation is needed to evaluate if findings vary with race. Moreover, we assessed the feasibility of the CBT screw from the viewpoint of anatomy without biomechanical study; however, we will further study screw stability of the thoracic CBT screw. Meanwhile, further clinical research should be performed to prove the results of CBT screw fixation in the upper and middle thoracic spine. We will further study the key points of inserting a thoracic CBT screw via clinical research and design a corresponding navigation template to reduce the rate of pedicle wall penetration.
CONCLUSIONS Based on the anatomic measurements and cadaveric results of the current study, we suggest that a CBT screw 4.5 mm in diameter and 25.0e30.0 mm long could be inserted from T1 to T8 through the pedicle or pedicle rib unit. Furthermore, the results of our study provide insights into screw insertion angle when performing surgery in the middle thoracic spine and at the cervicothoracic junction.
8. Vaccaro AR, Rizzolo SJ, Balderston RA, Allardyce TJ, Garfin SR, Dolinskas C, et al. Placement of pedicle screws in the thoracic spine. Part II: an anatomical and radiographic assessment. J Bone Joint Surg Am. 1995;77:1200-1206. 9. Santoni BG, Hynes RA, McGilvray KC, RodriguezCanessa G, Lyons AS, Henson MA, et al. Cortical bone trajectory for lumbar pedicle screws. Spine J. 2009;9:366-373. 10. Baluch DA, Patel AA, Lullo B, Havey RM, Voronov LI, Nguyen NL, et al. Effect of physiological loads on cortical and traditional pedicle screw fixation. Spine (Phila Pa 1976). 2014;39: E1297-E1302. 11. Gonchar I, Kotani Y, Matsumoto Y. Cortical bone trajectory versus percutaneous pedicle screw in minimally invasive posterior lumbar fusion. Spine J. 2014;14:S114-S115. 12. Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K. In vivo analysis of insertional torque during pedicle screwing using cortical bone trajectory technique. Spine (Phila Pa 1976). 2014;39:E240-E245. 13. Sakaura H, Miwa T, Yamashita T, Kuroda Y, Ohwada T. Posterior lumbar interbody fusion with cortical bone trajectory screw fixation versus posterior lumbar interbody fusion using traditional pedicle screw fixation for degenerative lumbar spondylolisthesis: a comparative study. J Neurosurg Spine. 2016;25:591-595. 14. Snyder LA, Martinez-del-Campo E, Neal MT, Zaidi HA, Awad A-W, Bina R, et al. Lumbar spinal
fixation with cortical bone trajectory pedicle screws in 79 patients with degenerative disease: perioperative outcomes and complications. World Neurosurg. 2016;88:205-213. 15. Matsukawa K, Yato Y, Hynes RA, Imabayashi H, Hosogane N, Asazuma T, et al. Cortical bone trajectory for thoracic pedicle screws: a technical note. Clin Spine Surg. 2017;30:E497-E504. 16. Xuan J, Zhang D, Jin HM, Chen JX, Xu DL, Xu HM, et al. Minimally invasive cortical bone trajectory screws placement via pedicle or pedicle rib unit in the lower thoracic spine: a cadaveric and radiographic study. Eur Spine J. 2016;25: 4199-4207. 17. Sheng SR, Chen JX, Chen W, Xue EX, Wang XY, Zhu QA. Cortical bone trajectory screws for the middle-upper thorax: an anatomico-radiological study. Medicine (Baltimore). 2016;95:e4676. 18. Zhuang Z, Chen Y, Han H, Cai S, Wang X, Qi W, et al. Thoracic pedicle morphometry in different body height population: a three-dimensional study using reformatted computed tomography. Spine (Phila Pa 1976). 2011;36:E1547-E1554. 19. Liau KM, Yusof MI, Abdullah MS, Abdullah S, Yusof AH. Computed tomographic morphometry of thoracic pedicles: safety margin of transpedicular screw fixation in malaysian Malay population. Spine (Phila Pa 1976). 2006;31:E545-E550. 20. Datir SP, Mitra SR. Morphometric study of the thoracic vertebral pedicle in an Indian population. Spine (Phila Pa 1976). 2004;29:1174-1181.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2018.05.152
ORIGINAL ARTICLE JUN XUAN ET AL.
21. Kim NH, Lee HM, Chung IH, Kim HJ, Kim SJ. Morphometric study of the pedicles of thoracic and lumbar vertebrae in Koreans. Spine (Phila Pa 1976). 1994;19:1390-1394. 22. O’Brien MF, Lenke LG, Mardjetko S, Lowe TG, Kong Y, Eck K, et al. Pedicle morphology in thoracic adolescent idiopathic scoliosis: is pedicle fixation an anatomically viable technique? Spine (Phila Pa 1976). 2000;25:2285-2293. 23. Liljenqvist UR, Allkemper T, Hackenberg L, Link TM, Steinbeck J, Halm HF. Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction. J Bone Joint Surg Am. 2002;84A:359-368. 24. Husted DS, Haims AH, Fairchild TA, Kershaw TS, Yue JJ. Morphometric comparison of the pedicle rib unit to pedicles in the thoracic spine. Spine (Phila Pa 1976). 2004;29:139-146. 25. McLain RF, Ferrara L, Kabins M. Pedicle morphometry in the upper thoracic spine: limits to safe screw placement in older patients. Spine (Phila Pa 1976). 2002;27:2467-2471.
CBT SCREW FIXATION IN THE UPPER AND MIDDLE THORACIC SPINE
26. Grant JP, Oxland TR, Dvorak MF. Mapping the structural properties of the lumbosacral vertebral endplates. Spine (Phila Pa 1976). 2001;26:889-896. 27. Karataglis D, Kapetanos G, Lontos A, Christodoulou A, Christoforides J, Pournaras J. The role of the dorsal vertebral cortex in the stability of transpedicular screws. A biomechanical study in human cadaveric vertebrae. J Bone Joint Surg Br. 2006;88:692-695. 28. Lehman RA Jr, Helgeson MD, Dmitriev AE, Paik H, Bevevino AJ, Gaume R, et al. What is the best way to optimize thoracic kyphosis correction? A micro-CT and biomechanical analysis of pedicle morphology and screw failure. Spine (Phila Pa 1976). 2012;37:E1171-E1176. 29. Wu SS, Edwards WT, Yuan HA. Stiffness between different directions of transpedicular screws and vertebra. Clin Biomech (Bristol, Avon). 1998;13:S1-S8.
ported by less-dense trabecular bone. Bone. 2009; 44:372-379. 31. Ugur HC, Attar A, Uz A, Tekdemir I, Egemen N, Genc Y. Thoracic pedicle: surgical anatomic evaluation and relations. J Spinal Disord. 2001;14:39-45.
Conflict of interest statement: This work was supported by a grant from the National Nature Foundation of China (grant number 81371988), the Natural Science Foundation of Zhejiang Province (grant number CF18H060026), and the Zhejiang Medical and Health Science and Technology Plan Project (grant number 2015RCB022). Received 18 March 2018; accepted 22 May 2018 Citation: World Neurosurg. (2018). https://doi.org/10.1016/j.wneu.2018.05.152 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
30. Zhao FD, Pollintine P, Hole BD, Adams MA, Dolan P. Vertebral fractures usually affect the cranial endplate because it is thinner and sup-
WORLD NEUROSURGERY -: e1-e9, - 2018
1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved.
www.WORLDNEUROSURGERY.org
e9