Eur Spine J (2014) 23:2175–2181 DOI 10.1007/s00586-014-3473-x
ORIGINAL ARTICLE
Radiological studies on the best entry point and trajectory of anterior cervical pedicle screw in the lower cervical spine Liujun Zhao • Guoqing Li • Jiayong Liu • Gregory M. Benedict Nabil A. Ebraheim • Weihu Ma • Shaohua Sun • Rongming Xu • Chaoyue Ruan
•
Received: 25 August 2013 / Revised: 30 April 2014 / Accepted: 14 July 2014 / Published online: 24 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Objective To explore the best entry point and trajectory of anterior cervical transpedicular screws in the lower cervical spine by radiological studies, and provide reference for clinical application. Methods Fifty patients were scanned by computed tomography and confirmed no obvious defect of the cervical spine. On horizontal axis, camber angle (a) and axial length (AL) were measured from C3 to C7. On sagittal view, the cranial or caudal angle (b) and sagittal length (SL) were also measured from C3 to C7. On the sagittal and horizontal planes vertebrae were respectively divided into four areas, ordered 1–4, on the anterior side of the pedicle. The areas and angles of pedicle intersect into the vertebral body were recorded. We inserted six anterior pedicle screws into the lower cervical spine of three patients by this technique. Results On transverse plane, camber angle (a) of C3–C5 increased gradually, while it decreased from C5 to C7. On sagittal view, C3 and C4 pedicles showed cranial tilting, while C5 to C7 were caudally tilted. AL and SL values increased gradually from C3 to C7. The number of the intersections of C3–C7 in each area was also different. Six pedicle screws of three cases were inserted into the lower cervical spine with proper placement and no complications. Conclusion Anterior transpedicular screw (ATPS) is a theoretically feasible option for internal fixation. The L. Zhao G. Li W. Ma (&) S. Sun R. Xu C. Ruan Department of Orthopedics, The Sixth Hospital of Ningbo, 1059 Zhongshan East Road, Ningbo 315040, People’s Republic of China e-mail: [email protected] J. Liu G. M. Benedict N. A. Ebraheim Department of Orthopedic Surgery, University of Toledo Medical Center, 3065 Arlington Ave., Toledo, OH 43614, USA
technique described in this paper was subsequently used in three patients without complication. Future improvement of ATPS insertion remains necessary for this technically demanding procedure. Keywords Cervical vertebrae Tomography, spiral computed Fracture fixation, internal
Introduction The clinical interest in anterior transpedicular screw (ATPS) fixation increased after Aramomi et al. [1] first introduced the concept and successfully applied it in nine cases under visualization of the pedicles to affix fibular grafts to cervical pedicles. Since then, more and more articles had reported on the ex vivo anatomic and in vivo clinical feasibility of ATPS fixation [2–9]. Current anterior cervical spine screw-and-plate systems are limited by their mechanical strength because the screws are solely anchored into the anterior and middle columns of the spine with a lack of posterior column support. ATPS strengthens screw anchorage by fixation into the stronger pedicle, as opposed to the cortex of the vertebral body, which should serve to counteract pull-out forces. New transpedicular screws combine the strength of the posterior column screws with lower complication rates of the anterior approach [2, 10–12]. Increased stability offered by ATPS becomes imperative in multi-level and severe threecolumn injuries that have, in the past, required an anterior cervical implant combined with posterior cervical pedicle screw fixation. The improved complication rates seen from the anterior approach mainly stem from the lower rate of neurovascular and muscular compromise due to the location of the
123
2176
vertebral arteries, the nerve roots of the spinal cord, and a lack of damage to the paravertebral muscles [2]. Due to the anatomical complexity of the cervical spine and the mentioned possibility of severe complications, the accurate insertion of ATPS is very desirable. In recent years, different methods to correctly place anterior pedicle screws have been described with some success. Since the safety of this procedure depends on the placement of screws exploring the best entry point and trajectory of anterior cervical screws by computed tomography (CT) studies may prove useful for clinical application. With few landmarks on the anterior surface of cervical vertebrae and a relatively long distance between the anterior surface and the pedicle, insertion of ATPS is more difficult and dangerous than posterior transpedicular fixation. To address this challenge our study was designed to observe and calculate the projection point of the pedicle axis on the lower cervical vertebral body by CT-assisted horizontal and sagittal views which allows exploration for precise anterior cervical transpedicular screw placement. We adopted a new strategy to explore a safe technique, entry point, and trajectory of the anterior cervical screw by CT studies and successfully placed cervical transpedicular screws in three patients.
Eur Spine J (2014) 23:2175–2181
Fig. 1 Horizontal axis including pedicles of the lower cervical spine. 1–4 The divided regions on the anterior border of the lower cervical spine in axial view. AL The distance between the anterior vertebral body insertion point and the trailing edge of lateral mass on horizontal axis view. a Camber angle of anterior pedicle vertebral screws of lower cervical spine
Materials and methods Patient data From January 2008 to December 2011, 50 patients scanned by cervical CT were selected from our institution and confirmed no obvious defect of the lower cervical spine. In addition, all patients included had no history of cervical spine surgery. Of these, 27 cases were males and 23 were females, ranging in age from 38 to 83 years (mean 58.5 years). Three patients underwent anterior cervical pedicle screw and plate fixation. Two of these patients (age 26 and 74 years) were diagnosed with cervical spine fracture dislocation with incomplete paralysis. The third patient (age 56 years) was diagnosed with cervical spondylotic myelopathy. Radiographic assessment All patients were imaged using a Brilliance CT 16-channel scanner (Philips, Eindhoven, The Netherlands). In-plane pixel size was 0.5 mm and slice thickness was 1.0 mm. 3D reconstructions were obtained from the original images. The clearest axial reconstructive images showing both cervical pedicles and an intact anterior vertebral edge were selected (Fig. 1). C3–C7 axial images were reconstructed respectively. The clearest sagittal reconstructive images
123
Fig. 2 Sagittal view including the pedicle of the lower cervical spine. 1–4 The divided regions on the anterior border of the lower cervical spine in sagittal view; SL the distance between the anterior vertebral body insertion point and the trailing edge of lateral mass in sagittal axis view. b Cranial tilted angle of the anterior pedicle vertebral screws of the lower cervical spine
showing the unilateral lower cervical pedicle and intact anterior vertebral edge were chosen (Fig. 2). C3–C7 sagittal images were reconstructed respectively. On the sagittal and horizontal planes, vertebrae were divided into four subsequent areas. These vertebral areas were sequentially ordered from 1 to 4, and the area of pedicle vertebral body intersects into the vertebrae was recorded. All selected images had measures taken bilaterally, as listed below: 1.
AL axial length—the distance between the screw insertion point of the anterior vertebral body and the trailing edge of lateral mass on horizontal axis view.
Eur Spine J (2014) 23:2175–2181
2. 3.
4.
2177
a camber angle of anterior pedicle vertebral screws of lower vertical spine. SL sagittal length—the distance between the screw insertion point of the anterior vertebral body and the trailing edge of lateral mass on sagittal view. b cranial/caudal tilted angle of anterior pedicle vertebral screws of the lower cervical spine. Cranially-tilted angle was recorded as positive, and a caudally-tilted angle was recorded as negative.
All the measurements mentioned earlier were performed, separately, by two experienced radiologists. The data was collected, and the average value of the two groups was used as the final actual value. The projection area of the pedicle vertebral body intersection was recorded according to the different vertebral sections (Figs. 1, 2). Surgical procedure for anterior transpedicular screw fixation All patients were placed on surgical beds in the supine position before induction of anesthesia. The head was placed on a special head frame with the neck slightly extended and the head fixed. Then, the C-arm was placed at 45° to obtain the correct axial pedicle image of the lower cervical spine. The surgical level of the cervical spine was positioned by Kirschner wire pre-operatively. The surgical incision was performed by left anterior Smith-Robinson approach. The anterior aspect of the cervical vertebrae was exposed followed by thorough decompression and subtotal corpectomy of C5–7. Spinal reconstruction stability was obtained by inserting titanium mesh cages into the excavated vertebral body (Fig. 4i). Prepared iliac bone graft was placed in and around the mesh. The pre-operatively determined camber angle (a), tilt angle (b), and projection area of pedicle vertebral body intersection were subsequently used under C-arm fluoroscopic imaging to guide the 1.5 mm Kirschner wire placement into the left pedicles of C5 and C7. The sagittal imaging of the lower cervical
pedicle indicated satisfactory kirschner placement. Cervical transpedicular screws were then inserted along the guide-wires into each pedicle. The appropriate length plate (Medtronic Inc, USA) was placed along the contour of the physiological lordosis of the cervical spine. The diameter of the screws used was 3.5 mm with a length of 30–34 mm which was determined intra-operatively. Structural stability of the anterior cervical reconstruction was confirmed before placing drainage tubing. After the bleeding stopped completely, the surgical incision was closed. Precise placement of the anterior cervical transpedicular screws was confirmed post-operatively by CT scan (Fig. 4g–i). Statistical analysis SPSS 11.5 was used for statistical analysis. Student’s t tests were performed comparing the data (a, b, AL, SL) between men and women. Chi square Test was conducted to test whether there was significant difference in the number of pedicle vertebral body intersections in the different projection areas. P \ 0.05 indicated a significant difference.
Results There was no significant difference between males and females at the same vertebral level, either a or b (P [ 0.05). The difference was not significant between the left and right angles at the same vertebrae of the same subject (P [ 0.05) (Table 1). Camber angle of C3–C7 was 38°–45° on transverse plane with C3–C5 increasing gradually and C5–C7 decreasing. On sagittal view, C3, C4 pedicles showed cranial tilting while C5–C7 were caudally tilted with C3–C4 decreasing, and C5–C7 becoming more caudally tilted (Table 1). These changes were vividly reflected on the schematic (Fig. 3). The AL and SL values increased gradually from C3 to C7 (Table 2). The difference was not significant between the left and right at the same vertebrae of the same subject (P [ 0.05).
Table 1 Data of a and b for anterior pedicle screws in the lower cervical spine (Mean ± SD, °) Level
a M (n = 27)
b F (n = 23)
Sum (n = 50)
M (n = 27)
F (n = 23)
Sum (n = 50)
C3
43.6 ± 4.3
43.9 ± 5.2
43.8 ± 5.5
8.5 ± 1.3
8.9 ± 1.2
8.8 ± 1.5
C4
44.6 ± 4.8
44.5 ± 5.1
44.6 ± 3.8
4.5 ± 0.6
4.1 ± 0.5
4.3 ± 0.8
C5
45.7 ± 3.6
45.0 ± 5.7
45.1 ± 5.3
-(1.1 ± 0.8)
-(1.0 ± 0.3)
-(1.0 ± 0.6)
C6
40.2 ± 3.9
40.9 ± 4.8
40.6 ± 4.6
-(4.5 ± 1.7)
-(4.6 ± 1.5)
-(4.6 ± 1.0)
C7
38.8 ± 5.2
39.0 ± 3.5
38.9 ± 5.0
-(8.9 ± 1.4)
-(8.3 ± 1.8)
-(8.5 ± 1.5)
There is no significant difference between male and female at the same vertebrae, either a or b (P [ 0.05) M male, F female
123
2178
Eur Spine J (2014) 23:2175–2181
Measurement in males was longer than females, but the difference was not significant (P [ 0.05). On axial and sagittal views, the area of pedicle intersection into the vertebral body was recorded and statistically analyzed (Table 3). On horizontal axis, the majority of the intersections in C3, C4 and C5 were in the second area. The intersections in C6 were in the second and third area, while the intersections in C7 were mostly in the third
area. Horizontal intersections in the first and fourth areas were minimal. On sagittal view, the majority of the intersections in C3, C4 and C5 were in the first area. The majority of intersections in C6 were in the first and second areas, and the majority of intersections in C7 were in the second area. Sagittal intersections in the third and fourth areas were minimal. According to the above findings and technique, the author preliminarily applied this technology in three selected patients with cervical myelopathy. A total of six anterior pedicle screws were inserted, and all screws were placed precisely in the pedicles. Post-operative X-ray and CT showed satisfactory insertion of screws. There were no neurovascular complications. These patients were followed up for 6 months after surgery, and no associated complications occurred. Images of a typical case are shown in Fig. 4.
Discussion
Fig. 3 The safe and ideal trajectory (arrows) of ATPS. On sagittal view C3 and C4 were cranially tilted at a decreasing angle. C5 was near level. C6 and C7 pedicles were caudally tilted at an increasing angle
Nowadays, anterior plate fixation in the cervical spine is widespread in cases having anterior etiologies such as anterior neural compression or severe kyphosis. These anterior screw-and-plate systems have been successful in those with normal bone quality and those with injuries involving the anterior and middle columns of the spine. For certain subsets of cervical spinal injury this form of screw anchorage has been prone to complication. Single-level three-column injuries or multi-level anterior compression treated with anterior vertebral body screws has resulted in only modest success. Non-union rates of anterior fixation alone in multi-level anterior cervical discectomy and fusion has been reported as high as 20–50 % [12, 13]. This may be partly due to a lack of posterior column support. Koller et al. [14] looked at cervical prototype reconstructions after multi-level corpectomy and compared biomechanical stability of ATPS with other anterior and posterior techniques finding relative success with anterior pedicle screws.
Table 2 Measurement of theoretical pedicle length on the axial and sagittal view (AL and SL) in the lower cervical spine (Mean ± SD, mm) Level
AL M (n = 27)
SL F (n = 23)
Sum (n = 50)
M (n = 27)
F (n = 23)
Sum (n = 50)
C3
34.2 ± 2.4
31.0 ± 2.8
32.4 ± 2.7
33.7 ± 1.8
31.7 ± 2.1
32.4 ± 3.1
C4
34.3 ± 2.8
32.5 ± 2.2
33.5 ± 2.5
34.5 ± 2.5
32.0 ± 2.7
33.5 ± 2.3
C5
34.3 ± 1.9
32.5 ± 2.0
33.6 ± 2.8
34.7 ± 2.2
32.8 ± 2.8
33.7 ± 2.7
C6
35.4 ± 2.9
33.8 ± 3.0
34.8 ± 3.1
35.7 ± 3.9
34.0 ± 3.6
34.8 ± 3.5
C7
36.0 ± 2.7
33.9 ± 2.3
35.2 ± 2.4
36.2 ± 2.3
34.9 ± 2.0
35.2 ± 2.4
The difference is not significant between left and right at the same vertebrae of the same subject (P [ 0.05). Measurement in males is longer than females, the difference is not significant (P [ 0.05) M male, F Female
123
Eur Spine J (2014) 23:2175–2181
2179
Table 3 The projection area of the pedicle on axial and sagittal views in the lower cervical spine (point) Level
Axial view N1
Sagittal view
N2
N3
N4
Sum
N1
N2
N3
N4
Sum
C3
0
82
18
0
100
90
10
0
0
100
C4
0
79
21
0
100
83
17
0
0
100
C5 C6
0 0
74 58
26 42
0 0
100 100
63 45
35 52
2 3
0 0
100 100
C7
0
24
74
2
100
38
55
6
1
100
SUM
0
317
181
2
500
319
169
11
1
500
The projection areas (1–4) were respectively recorded as N1, N2, N3 and N4
Stability is limited even more so in elderly patients with poor quality bone making supplemental posterior stabilization a reasonable option in these situations due to improved screw anchorage by fixation into the stronger pedicle [15, 16]. Although added posterior plate fixation is used to increase the stability of the constructs it requires longer anesthesia and is very laborious, including a change of the patient’s surgical position. What’s more, complications such as infection and neurovascular injury are increased, and can be fatal in the elderly. The ATPS technique allows for support in the anterior, middle, and posterior columns of the spine from a single approach. It has been shown in a previous cadaver study that transpedicular screws can resist 2.5 times the pull-out force than that of vertebral body screws [3]. With this increased anchorage it has allowed the design of some ATPS constructs to be anchored solely into the cervical level immediately above and below the pathological vertebra, as opposed to many vertebral body constructs that employ screws in two levels above and below the pathological vertebra. Hence, to avoid additional posterior stabilization or the involvement of extra vertebral levels, the ATPS technique may be promising for selected cases. Multiple techniques have been described for anterior pedicle screws. Aramomi et al. introduced a method that included excavation of much of the vertebral body before inserting guide wires under fluoroscopy into the pedicle. After which fibular autograft was tapped around the wire and a cannulated screw was inserted along the guide wire [1]. Pedicle-axis view imaging assisted by fluoroscopy was later used by Yukawa et al. in the successful insertion of anterior pedicle screws in six patients. However, the sample number was small, and both operative time and intraoperative bleeding were increased [5]. Subsequently, Koller et al. introduced their technique in an ex vivo study using pre-implantation CT imaging and intra-operative ‘‘fluoroscopic pedicle axis view.’’ Using pre-implantation CT imaging to map the angulation and fluoroscopy to guide
the k-wire tip into the pedicle center Koller still demonstrated 21.7 % ‘‘critical’’ pedicle breach of all ATPS inserted [3]. Later Koller et al. proposed to refine the insertion technique using an electronic conductivity device (ECD) similar to that used in many thoracolumbar procedures [4]. They used fluoroscopy to control the entry point and then demonstrated manual insertion supported by an ECD equaling the favorable results with their previous manually fluoroscopically-assisted technique introducing a possible adjunctive technique to improve accuracy. Subsequently, Ikenaga et al. described an anterior transpedicular technique that increases construct stability in patients after a 4-level corpectomy for patients with multi-level cervical myelopathy. They described a segmental screw and rod construct to increase middle segment stability along with plates at the cranial and caudal ends to increase upper and lower interface stability. This technique provided further evidence of the stability of anterior pedicle screws as well as demonstrates the advantage of segmental pedicle screw fixation being performed at each level after long segmental corpectomy in efforts to increase stability [8]. Another unique technique examined in an in vitro study illustrated the use of a cervical drill template modeled after patient-specific morphology. This technique created a bone cement template with pin tracts that was placed on the anterior surface of the vertebra to guide kirschner wire placement, although some grade 3 screw positions penetrating the cortex were witnessed [9]. This technique could also increase patient cost, and until now no articles have reportedly tested its clinical applications. Since the safety of ATPS depends on the placement of screws, further exploration of the best entry point and trajectory of anterior cervical screws by CT studies should prove useful for clinical application. With few landmarks on the anterior surface of cervical vertebrae and a relatively long distance between the anterior surface and the pedicle, insertion of ATPS is more difficult than either anterior vertebral body screws or posterior transpedicular fixation. This study demonstrated average entry points and angles of insertion for C3 to C7 to better characterize screw placement. Yukawa’s previous technique used a consistent camber angle of 45° for segments C3–C6 and 40° for C7 [5]. While the anatomical CT portion of the current study yielded similar results, we demonstrated that segment C6 may actually be closer to 40° for more precise placement (Table 1). Additionally, with CT-assisted pedicle horizontal and sagittal views this study helped to determine the entry point that coincided with the appropriate trajectory angle for each cervical vertebra in sagittal as well as transverse planes. This technology combined with the described surgical technique resulted in precise placement of six pedicle screws in three patients. In these three
123
2180
Eur Spine J (2014) 23:2175–2181
Fig. 4 A 74-year-old male patient with C5,6 fracture-dislocation and subsequent incomplete paraplegia caused by a fall. a–c AP and lateral X-rays, and CT showed the C5,6 fracture dislocation. d MRI showed posterior cervical ligament complex injury, anterior C5,6, C6,7 protrusion of intervertebral disks, and compression of
endorhachis. e, f Postoperative AP and bilateral X-ray showed adequate reduction and screw positioning. g, h Postoperative axial view of C5 and C7 showed satisfactory insertion of screws. i Sagittal reconstruction showed good reduction of anterior cervical pedicle screws
patients imaging findings provided a very useful reference for clinical application. However, the study has some drawbacks. First, ATPS was used on a small number of patients. Therefore, careful investigations of additional cases are needed. Second, patients were followed for 6 months, so in the future extended follow-up should be used to fully monitor outcomes and complication rates. Last, there are different degrees of cervical pedicular pathology in most patients who are selected to undergo surgery. Therefore, this requires surgeons to individualize treatment for differing patients and not blindly reference the results of this study. At this stage, we believe this technique should be restricted to one-level three column injuries, multi-level anterior
decompression, patients with poor bone quality or who may need anterior revision surgery, especially in the elderly. In conclusion, the author considers that pre-operative CT studies for optimal entry point may theoretically be a feasible and practical option for internal fixation. This technique demands a high level of surgical skill in addition to expert knowledge of anterior and posterior cervical procedure and anatomy. Additional studies are required to improve the existing ATPS technique.
123
Conflict of interest No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
Eur Spine J (2014) 23:2175–2181
References 1. Aramomi M, Masaki Y, Koshizuka S, Kadota R, Okawa A, Koda M, Yamazaki M (2008) Anterior pedicle screw fixation for multilevel cervical corpectomy and spinal fusion. Acta Neurochir (Wien) 150:575–582 2. Koller H, Hempfing A, Acosta F, Fox M, Scheiter A, Tauber M, Holz U, Resch H, Hitzl W (2008) Cervical anterior transpedicular screw fixation. Part I: Study on morphological feasibility, indications, and technical prerequisites. Eur Spine J 17:523–538 3. Koller H, Acosta F, Tauber M, Fox M, Martin H, Forstner R, Augat P, Penzkofer R, Pirich C, Ka¨ssmann H (2008) Cervical anterior transpedicular screw fixation (ATPS)—Part II. Accuracy of manual insertion and pull-out strength of ATPS. Eur Spine J 17:539–555 4. Koller H, Hitzl W, Acosta F, Tauber M, Zenner J, Resch H, Yukawa Y, Meier O, Schmidt R, Mayer M (2009) In vitro study of accuracy of cervical pedicle screw insertion using an electronic conductivity device (ATPS part III). Eur Spine J 18:1300–1313 5. Yukawa Y, Kato F, Ito K, Nakashima H, Machino M (2009) Anterior cervical pedicle screw and plate fixation using fluoroscope-assisted pedicle axis view imaging: a preliminary report of a new cervical reconstruction technique. Eur Spine J 18:911–916 6. Marchesi DG (2009) Reviewer’s comment concerning ‘‘Anterior cervical pedicle screw and plate fixation using fluoroscopeassisted pedicle axis view imaging: a preliminary report of a new cervical reconstruction technique’’ by Y. Yukawa et al. Eur Spine J 18:917. doi:10.1007/s00586-009-0949-1 7. Zhao Lj Xu, Rm Jiang Wy, Ma Wh, Xu Nj HuY (2011) A new technique for anterior cervical pedicle screw implantation. Orthop Sur 3:193–198 8. Ikenaga M, Mukaida M, Nagahara R, Yasunaga T, Ueda Y, Sohma Y (2012) Anterior cervical reconstruction with pedicle screws after a 4-level corpectomy. Spine 37:E927–E930
2181 9. Fu M, Lin L, Kong X, Zhao W, Tang L, Li J, Ouyang J (2013) Construction and accuracy assessment of patient-specific biocompatible drill template for cervical anterior transpedicular screw (ATPS) insertion: an in vitro study. PLoS One 8:e53580 10. Acosta FL Jr, Aryan HE, Chou D, Ames CP (2008) Long-term biomechanical stability and clinical improvement after extended multi-level corpectomy and circumferential reconstruction of the cervical spine using titanium mesh cages. J Spinal Disord Tech 21:165–174 11. Brazenor GA (2007) Comparison of multisegment anterior cervical fixation using bone strut graft versus a titanium rod and buttress prosthesis: analysis of outcome with long-term follow-up and interview by independent physician. Spine 32:63–71 12. Koller H, Hempfing A, Ferraris L, Maier O, Hitzl W, MetzStavenhagen P (2007) 4-and 5-level anterior fusions of the cervical spine: review of literature and clinical results. Eur Spine J 16:2055–2071 13. Daubs MD (2005) Early failures following cervical corpectomy reconstruction with titanium mesh cages and anterior plating. Spine 30:1402–1406 14. Koller H, Schnidt R, Mayer M, Hitzl W, Zenner J, Midderhoff S, Graf N, Resch H, Wilke HJ (2010) The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping. Eur Spine J 19:2137–2148 15. Epstein NE (2000) The value of anterior cervical plating in preventing vertebral fracture and graft extrusion after multi-level anterior cervical corpectomy with posterior wiring and fusion: indications, results, and complications. J Spinal Disord Tech 13:9–15 16. Singh K, Vaccaro AR, Kim J, Lorenz EP, Lim T-H, An HS (2003) Biomechanical comparison of cervical spine reconstructive techniques after a multi-level corpectomy of the cervical spine. Spine 28:2352–2358
123
ORIGINAL ARTICLE
Radiological studies on the best entry point and trajectory of anterior cervical pedicle screw in the lower cervical spine Liujun Zhao • Guoqing Li • Jiayong Liu • Gregory M. Benedict Nabil A. Ebraheim • Weihu Ma • Shaohua Sun • Rongming Xu • Chaoyue Ruan
•
Received: 25 August 2013 / Revised: 30 April 2014 / Accepted: 14 July 2014 / Published online: 24 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Objective To explore the best entry point and trajectory of anterior cervical transpedicular screws in the lower cervical spine by radiological studies, and provide reference for clinical application. Methods Fifty patients were scanned by computed tomography and confirmed no obvious defect of the cervical spine. On horizontal axis, camber angle (a) and axial length (AL) were measured from C3 to C7. On sagittal view, the cranial or caudal angle (b) and sagittal length (SL) were also measured from C3 to C7. On the sagittal and horizontal planes vertebrae were respectively divided into four areas, ordered 1–4, on the anterior side of the pedicle. The areas and angles of pedicle intersect into the vertebral body were recorded. We inserted six anterior pedicle screws into the lower cervical spine of three patients by this technique. Results On transverse plane, camber angle (a) of C3–C5 increased gradually, while it decreased from C5 to C7. On sagittal view, C3 and C4 pedicles showed cranial tilting, while C5 to C7 were caudally tilted. AL and SL values increased gradually from C3 to C7. The number of the intersections of C3–C7 in each area was also different. Six pedicle screws of three cases were inserted into the lower cervical spine with proper placement and no complications. Conclusion Anterior transpedicular screw (ATPS) is a theoretically feasible option for internal fixation. The L. Zhao G. Li W. Ma (&) S. Sun R. Xu C. Ruan Department of Orthopedics, The Sixth Hospital of Ningbo, 1059 Zhongshan East Road, Ningbo 315040, People’s Republic of China e-mail: [email protected] J. Liu G. M. Benedict N. A. Ebraheim Department of Orthopedic Surgery, University of Toledo Medical Center, 3065 Arlington Ave., Toledo, OH 43614, USA
technique described in this paper was subsequently used in three patients without complication. Future improvement of ATPS insertion remains necessary for this technically demanding procedure. Keywords Cervical vertebrae Tomography, spiral computed Fracture fixation, internal
Introduction The clinical interest in anterior transpedicular screw (ATPS) fixation increased after Aramomi et al. [1] first introduced the concept and successfully applied it in nine cases under visualization of the pedicles to affix fibular grafts to cervical pedicles. Since then, more and more articles had reported on the ex vivo anatomic and in vivo clinical feasibility of ATPS fixation [2–9]. Current anterior cervical spine screw-and-plate systems are limited by their mechanical strength because the screws are solely anchored into the anterior and middle columns of the spine with a lack of posterior column support. ATPS strengthens screw anchorage by fixation into the stronger pedicle, as opposed to the cortex of the vertebral body, which should serve to counteract pull-out forces. New transpedicular screws combine the strength of the posterior column screws with lower complication rates of the anterior approach [2, 10–12]. Increased stability offered by ATPS becomes imperative in multi-level and severe threecolumn injuries that have, in the past, required an anterior cervical implant combined with posterior cervical pedicle screw fixation. The improved complication rates seen from the anterior approach mainly stem from the lower rate of neurovascular and muscular compromise due to the location of the
123
2176
vertebral arteries, the nerve roots of the spinal cord, and a lack of damage to the paravertebral muscles [2]. Due to the anatomical complexity of the cervical spine and the mentioned possibility of severe complications, the accurate insertion of ATPS is very desirable. In recent years, different methods to correctly place anterior pedicle screws have been described with some success. Since the safety of this procedure depends on the placement of screws exploring the best entry point and trajectory of anterior cervical screws by computed tomography (CT) studies may prove useful for clinical application. With few landmarks on the anterior surface of cervical vertebrae and a relatively long distance between the anterior surface and the pedicle, insertion of ATPS is more difficult and dangerous than posterior transpedicular fixation. To address this challenge our study was designed to observe and calculate the projection point of the pedicle axis on the lower cervical vertebral body by CT-assisted horizontal and sagittal views which allows exploration for precise anterior cervical transpedicular screw placement. We adopted a new strategy to explore a safe technique, entry point, and trajectory of the anterior cervical screw by CT studies and successfully placed cervical transpedicular screws in three patients.
Eur Spine J (2014) 23:2175–2181
Fig. 1 Horizontal axis including pedicles of the lower cervical spine. 1–4 The divided regions on the anterior border of the lower cervical spine in axial view. AL The distance between the anterior vertebral body insertion point and the trailing edge of lateral mass on horizontal axis view. a Camber angle of anterior pedicle vertebral screws of lower cervical spine
Materials and methods Patient data From January 2008 to December 2011, 50 patients scanned by cervical CT were selected from our institution and confirmed no obvious defect of the lower cervical spine. In addition, all patients included had no history of cervical spine surgery. Of these, 27 cases were males and 23 were females, ranging in age from 38 to 83 years (mean 58.5 years). Three patients underwent anterior cervical pedicle screw and plate fixation. Two of these patients (age 26 and 74 years) were diagnosed with cervical spine fracture dislocation with incomplete paralysis. The third patient (age 56 years) was diagnosed with cervical spondylotic myelopathy. Radiographic assessment All patients were imaged using a Brilliance CT 16-channel scanner (Philips, Eindhoven, The Netherlands). In-plane pixel size was 0.5 mm and slice thickness was 1.0 mm. 3D reconstructions were obtained from the original images. The clearest axial reconstructive images showing both cervical pedicles and an intact anterior vertebral edge were selected (Fig. 1). C3–C7 axial images were reconstructed respectively. The clearest sagittal reconstructive images
123
Fig. 2 Sagittal view including the pedicle of the lower cervical spine. 1–4 The divided regions on the anterior border of the lower cervical spine in sagittal view; SL the distance between the anterior vertebral body insertion point and the trailing edge of lateral mass in sagittal axis view. b Cranial tilted angle of the anterior pedicle vertebral screws of the lower cervical spine
showing the unilateral lower cervical pedicle and intact anterior vertebral edge were chosen (Fig. 2). C3–C7 sagittal images were reconstructed respectively. On the sagittal and horizontal planes, vertebrae were divided into four subsequent areas. These vertebral areas were sequentially ordered from 1 to 4, and the area of pedicle vertebral body intersects into the vertebrae was recorded. All selected images had measures taken bilaterally, as listed below: 1.
AL axial length—the distance between the screw insertion point of the anterior vertebral body and the trailing edge of lateral mass on horizontal axis view.
Eur Spine J (2014) 23:2175–2181
2. 3.
4.
2177
a camber angle of anterior pedicle vertebral screws of lower vertical spine. SL sagittal length—the distance between the screw insertion point of the anterior vertebral body and the trailing edge of lateral mass on sagittal view. b cranial/caudal tilted angle of anterior pedicle vertebral screws of the lower cervical spine. Cranially-tilted angle was recorded as positive, and a caudally-tilted angle was recorded as negative.
All the measurements mentioned earlier were performed, separately, by two experienced radiologists. The data was collected, and the average value of the two groups was used as the final actual value. The projection area of the pedicle vertebral body intersection was recorded according to the different vertebral sections (Figs. 1, 2). Surgical procedure for anterior transpedicular screw fixation All patients were placed on surgical beds in the supine position before induction of anesthesia. The head was placed on a special head frame with the neck slightly extended and the head fixed. Then, the C-arm was placed at 45° to obtain the correct axial pedicle image of the lower cervical spine. The surgical level of the cervical spine was positioned by Kirschner wire pre-operatively. The surgical incision was performed by left anterior Smith-Robinson approach. The anterior aspect of the cervical vertebrae was exposed followed by thorough decompression and subtotal corpectomy of C5–7. Spinal reconstruction stability was obtained by inserting titanium mesh cages into the excavated vertebral body (Fig. 4i). Prepared iliac bone graft was placed in and around the mesh. The pre-operatively determined camber angle (a), tilt angle (b), and projection area of pedicle vertebral body intersection were subsequently used under C-arm fluoroscopic imaging to guide the 1.5 mm Kirschner wire placement into the left pedicles of C5 and C7. The sagittal imaging of the lower cervical
pedicle indicated satisfactory kirschner placement. Cervical transpedicular screws were then inserted along the guide-wires into each pedicle. The appropriate length plate (Medtronic Inc, USA) was placed along the contour of the physiological lordosis of the cervical spine. The diameter of the screws used was 3.5 mm with a length of 30–34 mm which was determined intra-operatively. Structural stability of the anterior cervical reconstruction was confirmed before placing drainage tubing. After the bleeding stopped completely, the surgical incision was closed. Precise placement of the anterior cervical transpedicular screws was confirmed post-operatively by CT scan (Fig. 4g–i). Statistical analysis SPSS 11.5 was used for statistical analysis. Student’s t tests were performed comparing the data (a, b, AL, SL) between men and women. Chi square Test was conducted to test whether there was significant difference in the number of pedicle vertebral body intersections in the different projection areas. P \ 0.05 indicated a significant difference.
Results There was no significant difference between males and females at the same vertebral level, either a or b (P [ 0.05). The difference was not significant between the left and right angles at the same vertebrae of the same subject (P [ 0.05) (Table 1). Camber angle of C3–C7 was 38°–45° on transverse plane with C3–C5 increasing gradually and C5–C7 decreasing. On sagittal view, C3, C4 pedicles showed cranial tilting while C5–C7 were caudally tilted with C3–C4 decreasing, and C5–C7 becoming more caudally tilted (Table 1). These changes were vividly reflected on the schematic (Fig. 3). The AL and SL values increased gradually from C3 to C7 (Table 2). The difference was not significant between the left and right at the same vertebrae of the same subject (P [ 0.05).
Table 1 Data of a and b for anterior pedicle screws in the lower cervical spine (Mean ± SD, °) Level
a M (n = 27)
b F (n = 23)
Sum (n = 50)
M (n = 27)
F (n = 23)
Sum (n = 50)
C3
43.6 ± 4.3
43.9 ± 5.2
43.8 ± 5.5
8.5 ± 1.3
8.9 ± 1.2
8.8 ± 1.5
C4
44.6 ± 4.8
44.5 ± 5.1
44.6 ± 3.8
4.5 ± 0.6
4.1 ± 0.5
4.3 ± 0.8
C5
45.7 ± 3.6
45.0 ± 5.7
45.1 ± 5.3
-(1.1 ± 0.8)
-(1.0 ± 0.3)
-(1.0 ± 0.6)
C6
40.2 ± 3.9
40.9 ± 4.8
40.6 ± 4.6
-(4.5 ± 1.7)
-(4.6 ± 1.5)
-(4.6 ± 1.0)
C7
38.8 ± 5.2
39.0 ± 3.5
38.9 ± 5.0
-(8.9 ± 1.4)
-(8.3 ± 1.8)
-(8.5 ± 1.5)
There is no significant difference between male and female at the same vertebrae, either a or b (P [ 0.05) M male, F female
123
2178
Eur Spine J (2014) 23:2175–2181
Measurement in males was longer than females, but the difference was not significant (P [ 0.05). On axial and sagittal views, the area of pedicle intersection into the vertebral body was recorded and statistically analyzed (Table 3). On horizontal axis, the majority of the intersections in C3, C4 and C5 were in the second area. The intersections in C6 were in the second and third area, while the intersections in C7 were mostly in the third
area. Horizontal intersections in the first and fourth areas were minimal. On sagittal view, the majority of the intersections in C3, C4 and C5 were in the first area. The majority of intersections in C6 were in the first and second areas, and the majority of intersections in C7 were in the second area. Sagittal intersections in the third and fourth areas were minimal. According to the above findings and technique, the author preliminarily applied this technology in three selected patients with cervical myelopathy. A total of six anterior pedicle screws were inserted, and all screws were placed precisely in the pedicles. Post-operative X-ray and CT showed satisfactory insertion of screws. There were no neurovascular complications. These patients were followed up for 6 months after surgery, and no associated complications occurred. Images of a typical case are shown in Fig. 4.
Discussion
Fig. 3 The safe and ideal trajectory (arrows) of ATPS. On sagittal view C3 and C4 were cranially tilted at a decreasing angle. C5 was near level. C6 and C7 pedicles were caudally tilted at an increasing angle
Nowadays, anterior plate fixation in the cervical spine is widespread in cases having anterior etiologies such as anterior neural compression or severe kyphosis. These anterior screw-and-plate systems have been successful in those with normal bone quality and those with injuries involving the anterior and middle columns of the spine. For certain subsets of cervical spinal injury this form of screw anchorage has been prone to complication. Single-level three-column injuries or multi-level anterior compression treated with anterior vertebral body screws has resulted in only modest success. Non-union rates of anterior fixation alone in multi-level anterior cervical discectomy and fusion has been reported as high as 20–50 % [12, 13]. This may be partly due to a lack of posterior column support. Koller et al. [14] looked at cervical prototype reconstructions after multi-level corpectomy and compared biomechanical stability of ATPS with other anterior and posterior techniques finding relative success with anterior pedicle screws.
Table 2 Measurement of theoretical pedicle length on the axial and sagittal view (AL and SL) in the lower cervical spine (Mean ± SD, mm) Level
AL M (n = 27)
SL F (n = 23)
Sum (n = 50)
M (n = 27)
F (n = 23)
Sum (n = 50)
C3
34.2 ± 2.4
31.0 ± 2.8
32.4 ± 2.7
33.7 ± 1.8
31.7 ± 2.1
32.4 ± 3.1
C4
34.3 ± 2.8
32.5 ± 2.2
33.5 ± 2.5
34.5 ± 2.5
32.0 ± 2.7
33.5 ± 2.3
C5
34.3 ± 1.9
32.5 ± 2.0
33.6 ± 2.8
34.7 ± 2.2
32.8 ± 2.8
33.7 ± 2.7
C6
35.4 ± 2.9
33.8 ± 3.0
34.8 ± 3.1
35.7 ± 3.9
34.0 ± 3.6
34.8 ± 3.5
C7
36.0 ± 2.7
33.9 ± 2.3
35.2 ± 2.4
36.2 ± 2.3
34.9 ± 2.0
35.2 ± 2.4
The difference is not significant between left and right at the same vertebrae of the same subject (P [ 0.05). Measurement in males is longer than females, the difference is not significant (P [ 0.05) M male, F Female
123
Eur Spine J (2014) 23:2175–2181
2179
Table 3 The projection area of the pedicle on axial and sagittal views in the lower cervical spine (point) Level
Axial view N1
Sagittal view
N2
N3
N4
Sum
N1
N2
N3
N4
Sum
C3
0
82
18
0
100
90
10
0
0
100
C4
0
79
21
0
100
83
17
0
0
100
C5 C6
0 0
74 58
26 42
0 0
100 100
63 45
35 52
2 3
0 0
100 100
C7
0
24
74
2
100
38
55
6
1
100
SUM
0
317
181
2
500
319
169
11
1
500
The projection areas (1–4) were respectively recorded as N1, N2, N3 and N4
Stability is limited even more so in elderly patients with poor quality bone making supplemental posterior stabilization a reasonable option in these situations due to improved screw anchorage by fixation into the stronger pedicle [15, 16]. Although added posterior plate fixation is used to increase the stability of the constructs it requires longer anesthesia and is very laborious, including a change of the patient’s surgical position. What’s more, complications such as infection and neurovascular injury are increased, and can be fatal in the elderly. The ATPS technique allows for support in the anterior, middle, and posterior columns of the spine from a single approach. It has been shown in a previous cadaver study that transpedicular screws can resist 2.5 times the pull-out force than that of vertebral body screws [3]. With this increased anchorage it has allowed the design of some ATPS constructs to be anchored solely into the cervical level immediately above and below the pathological vertebra, as opposed to many vertebral body constructs that employ screws in two levels above and below the pathological vertebra. Hence, to avoid additional posterior stabilization or the involvement of extra vertebral levels, the ATPS technique may be promising for selected cases. Multiple techniques have been described for anterior pedicle screws. Aramomi et al. introduced a method that included excavation of much of the vertebral body before inserting guide wires under fluoroscopy into the pedicle. After which fibular autograft was tapped around the wire and a cannulated screw was inserted along the guide wire [1]. Pedicle-axis view imaging assisted by fluoroscopy was later used by Yukawa et al. in the successful insertion of anterior pedicle screws in six patients. However, the sample number was small, and both operative time and intraoperative bleeding were increased [5]. Subsequently, Koller et al. introduced their technique in an ex vivo study using pre-implantation CT imaging and intra-operative ‘‘fluoroscopic pedicle axis view.’’ Using pre-implantation CT imaging to map the angulation and fluoroscopy to guide
the k-wire tip into the pedicle center Koller still demonstrated 21.7 % ‘‘critical’’ pedicle breach of all ATPS inserted [3]. Later Koller et al. proposed to refine the insertion technique using an electronic conductivity device (ECD) similar to that used in many thoracolumbar procedures [4]. They used fluoroscopy to control the entry point and then demonstrated manual insertion supported by an ECD equaling the favorable results with their previous manually fluoroscopically-assisted technique introducing a possible adjunctive technique to improve accuracy. Subsequently, Ikenaga et al. described an anterior transpedicular technique that increases construct stability in patients after a 4-level corpectomy for patients with multi-level cervical myelopathy. They described a segmental screw and rod construct to increase middle segment stability along with plates at the cranial and caudal ends to increase upper and lower interface stability. This technique provided further evidence of the stability of anterior pedicle screws as well as demonstrates the advantage of segmental pedicle screw fixation being performed at each level after long segmental corpectomy in efforts to increase stability [8]. Another unique technique examined in an in vitro study illustrated the use of a cervical drill template modeled after patient-specific morphology. This technique created a bone cement template with pin tracts that was placed on the anterior surface of the vertebra to guide kirschner wire placement, although some grade 3 screw positions penetrating the cortex were witnessed [9]. This technique could also increase patient cost, and until now no articles have reportedly tested its clinical applications. Since the safety of ATPS depends on the placement of screws, further exploration of the best entry point and trajectory of anterior cervical screws by CT studies should prove useful for clinical application. With few landmarks on the anterior surface of cervical vertebrae and a relatively long distance between the anterior surface and the pedicle, insertion of ATPS is more difficult than either anterior vertebral body screws or posterior transpedicular fixation. This study demonstrated average entry points and angles of insertion for C3 to C7 to better characterize screw placement. Yukawa’s previous technique used a consistent camber angle of 45° for segments C3–C6 and 40° for C7 [5]. While the anatomical CT portion of the current study yielded similar results, we demonstrated that segment C6 may actually be closer to 40° for more precise placement (Table 1). Additionally, with CT-assisted pedicle horizontal and sagittal views this study helped to determine the entry point that coincided with the appropriate trajectory angle for each cervical vertebra in sagittal as well as transverse planes. This technology combined with the described surgical technique resulted in precise placement of six pedicle screws in three patients. In these three
123
2180
Eur Spine J (2014) 23:2175–2181
Fig. 4 A 74-year-old male patient with C5,6 fracture-dislocation and subsequent incomplete paraplegia caused by a fall. a–c AP and lateral X-rays, and CT showed the C5,6 fracture dislocation. d MRI showed posterior cervical ligament complex injury, anterior C5,6, C6,7 protrusion of intervertebral disks, and compression of
endorhachis. e, f Postoperative AP and bilateral X-ray showed adequate reduction and screw positioning. g, h Postoperative axial view of C5 and C7 showed satisfactory insertion of screws. i Sagittal reconstruction showed good reduction of anterior cervical pedicle screws
patients imaging findings provided a very useful reference for clinical application. However, the study has some drawbacks. First, ATPS was used on a small number of patients. Therefore, careful investigations of additional cases are needed. Second, patients were followed for 6 months, so in the future extended follow-up should be used to fully monitor outcomes and complication rates. Last, there are different degrees of cervical pedicular pathology in most patients who are selected to undergo surgery. Therefore, this requires surgeons to individualize treatment for differing patients and not blindly reference the results of this study. At this stage, we believe this technique should be restricted to one-level three column injuries, multi-level anterior
decompression, patients with poor bone quality or who may need anterior revision surgery, especially in the elderly. In conclusion, the author considers that pre-operative CT studies for optimal entry point may theoretically be a feasible and practical option for internal fixation. This technique demands a high level of surgical skill in addition to expert knowledge of anterior and posterior cervical procedure and anatomy. Additional studies are required to improve the existing ATPS technique.
123
Conflict of interest No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
Eur Spine J (2014) 23:2175–2181
References 1. Aramomi M, Masaki Y, Koshizuka S, Kadota R, Okawa A, Koda M, Yamazaki M (2008) Anterior pedicle screw fixation for multilevel cervical corpectomy and spinal fusion. Acta Neurochir (Wien) 150:575–582 2. Koller H, Hempfing A, Acosta F, Fox M, Scheiter A, Tauber M, Holz U, Resch H, Hitzl W (2008) Cervical anterior transpedicular screw fixation. Part I: Study on morphological feasibility, indications, and technical prerequisites. Eur Spine J 17:523–538 3. Koller H, Acosta F, Tauber M, Fox M, Martin H, Forstner R, Augat P, Penzkofer R, Pirich C, Ka¨ssmann H (2008) Cervical anterior transpedicular screw fixation (ATPS)—Part II. Accuracy of manual insertion and pull-out strength of ATPS. Eur Spine J 17:539–555 4. Koller H, Hitzl W, Acosta F, Tauber M, Zenner J, Resch H, Yukawa Y, Meier O, Schmidt R, Mayer M (2009) In vitro study of accuracy of cervical pedicle screw insertion using an electronic conductivity device (ATPS part III). Eur Spine J 18:1300–1313 5. Yukawa Y, Kato F, Ito K, Nakashima H, Machino M (2009) Anterior cervical pedicle screw and plate fixation using fluoroscope-assisted pedicle axis view imaging: a preliminary report of a new cervical reconstruction technique. Eur Spine J 18:911–916 6. Marchesi DG (2009) Reviewer’s comment concerning ‘‘Anterior cervical pedicle screw and plate fixation using fluoroscopeassisted pedicle axis view imaging: a preliminary report of a new cervical reconstruction technique’’ by Y. Yukawa et al. Eur Spine J 18:917. doi:10.1007/s00586-009-0949-1 7. Zhao Lj Xu, Rm Jiang Wy, Ma Wh, Xu Nj HuY (2011) A new technique for anterior cervical pedicle screw implantation. Orthop Sur 3:193–198 8. Ikenaga M, Mukaida M, Nagahara R, Yasunaga T, Ueda Y, Sohma Y (2012) Anterior cervical reconstruction with pedicle screws after a 4-level corpectomy. Spine 37:E927–E930
2181 9. Fu M, Lin L, Kong X, Zhao W, Tang L, Li J, Ouyang J (2013) Construction and accuracy assessment of patient-specific biocompatible drill template for cervical anterior transpedicular screw (ATPS) insertion: an in vitro study. PLoS One 8:e53580 10. Acosta FL Jr, Aryan HE, Chou D, Ames CP (2008) Long-term biomechanical stability and clinical improvement after extended multi-level corpectomy and circumferential reconstruction of the cervical spine using titanium mesh cages. J Spinal Disord Tech 21:165–174 11. Brazenor GA (2007) Comparison of multisegment anterior cervical fixation using bone strut graft versus a titanium rod and buttress prosthesis: analysis of outcome with long-term follow-up and interview by independent physician. Spine 32:63–71 12. Koller H, Hempfing A, Ferraris L, Maier O, Hitzl W, MetzStavenhagen P (2007) 4-and 5-level anterior fusions of the cervical spine: review of literature and clinical results. Eur Spine J 16:2055–2071 13. Daubs MD (2005) Early failures following cervical corpectomy reconstruction with titanium mesh cages and anterior plating. Spine 30:1402–1406 14. Koller H, Schnidt R, Mayer M, Hitzl W, Zenner J, Midderhoff S, Graf N, Resch H, Wilke HJ (2010) The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping. Eur Spine J 19:2137–2148 15. Epstein NE (2000) The value of anterior cervical plating in preventing vertebral fracture and graft extrusion after multi-level anterior cervical corpectomy with posterior wiring and fusion: indications, results, and complications. J Spinal Disord Tech 13:9–15 16. Singh K, Vaccaro AR, Kim J, Lorenz EP, Lim T-H, An HS (2003) Biomechanical comparison of cervical spine reconstructive techniques after a multi-level corpectomy of the cervical spine. Spine 28:2352–2358
123
