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Analysis of Cervical Pedicle With Reconstructed Computed Tomography Imaging in Korean Population Feasibility and Surgical Anatomy Soo-Hoon Oh, MD and Woo-Kie Min, MD, PhD
Study Design: We analyzed the anatomy of C3–C6 cervical pedicles with reconstructed computed tomography images. Objectives: The objective of the study was to estimate the feasibility and to understand the surgical anatomy in order to reduce pedicle penetration. Summary of Background Data: It is necessary to minimize pedicle penetration by anatomic analysis of cervical pedicles. Many studies have been conducted on cervical pedicle anatomy and cervical pedicle screw fixation, yet there are debates about the feasibility and surgical anatomy. Methods: Oblique axial and oblique sagittal images were reconstructed from a 1 mm cut computed tomography image. The pedicle transverse diameter, pedicle length, pedicle convergence angle (CA), and pedicle distance were measured on the oblique axial images. The pedicle sagittal diameter, pedicle sagittal angle (SA), and lateral mass index were measured on the oblique sagittal images. The multiple t test was used for statistical analysis. Results: The averages of the pedicle transverse diameter ranged from 5.79 to 6.19 mm, the pedicle length ranged from 16.24 to 17.56 mm, the CA ranged from 47.49 to 48.86 degrees, the pedicle distance ranged from 22.67 to 24.93 mm, the SA ranged from 15.43 to 19.98 degrees, and the lateral mass index ranged from 0.64 to 1.25. Conclusions: Because of a tight safe margin, to reduce pedicle penetration the screw should be inserted along the pedicle. With regard to SA, C3 and C4 have a risk of upper end plate penetration. However, C5 and C6 have a risk of facet joint violation, which needs C4 and C5 inferior articular process removal for screw placement. The entry point at C3 and C4 is near one third of the lateral mass height from the posterior border of the superior articular process at the posterolateral border of the lateral mass. The entry point at C5 is near the posterolateral border of the superior articular process and that at C6 is superior to the Received for publication September 23, 2012; accepted March 11, 2013. From the Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, Korea. The authors declare no conflict of interest. Reprints: Woo-Kie Min, MD, PhD, Department of Orthopedic Surgery, Kyungpook National University Graduate School of Medicine, PO Box 700-721, 130 Dongduk-ro, Jung-gu, Daegu, Korea (e-mail: [email protected]). Copyright r 2013 by Lippincott Williams & Wilkins
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posterior border of the superior articular process at a line medial to the posterolateral border of the C5 lateral mass. During insertion, not only CA but even SA should be considered carefully to reduce pedicle penetration. Key Words: pedicle screw, cervical, penetration, entry point, feasibility (J Spinal Disord Tech 2014;27:E99–E103)
S
urgical options for stabilization of the cervical vertebrae are the anterior cervical plate fixation, posterior wiring, lateral mass screw fixation, and cervical pedicle screw (CPS) fixation. The anterior cervical plate fixation allows immediate rigid fixation, but in a vertebral fracture with incompetent posterior elements and ligamentous structures or in a multilevel disease, the anterior cervical plate fixation alone usually is insufficient. Moreover, in a patient who needs posterior decompression, the anterior cervical plate fixation demands another posterior approach.1 The wiring technique may be sufficient for cervical vertebra fixation, but in case of a deficient spinous process due to a trauma or disease and in case of a multilevel instability, the wiring technique is inadequate.1–3 The lateral mass screw fixation provides firm fixation and is safer than the CPS screw fixation, but if the lateral mass is small or if the lateral mass or facet joint has been fractured, the lateral mass screw fixation may face the problem of screw loosening.2,4,5 The CPS screw fixation is most stable when compared with others. However, the CPS screw fixation has a risk of causing neurovascular injury due to the anatomy around the pedicle. The nerve root passes the upper and lower surface of the pedicle, the spinal cord passes the inner surface of the pedicle, and the vertebral artery passes the outer surface of the pedicle.6–8 Some surgeons who have performed the CPS fixation reported that screw penetration did not cause serious neurovascular complications.9–11 Abumi et al3,9,12 reported a screw penetration rate of 1%–10% with few cases having neurovascular injury. However, in recent study, Nakashima et al13 reported that screw misplacement occurred in 76 of 390 screws placed, and 5 screws caused neurovascular injury. Although some report that the CPS is safe, possible disastrous complications lead most surgeons to hesitate using the CPS. To date many www.jspinaldisorders.com |
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studies have been performed, yet there are debates about the feasibility and surgical anatomy.2,3,6–9,11,12,14–20 This study was conducted to estimate the feasibility of the CPS fixation in Korean population and to study pedicle orientation for minimizing pedicle screw penetration, by analyzing the anatomy of the cervical vertebrae (C3–C6) using reconstructed computed tomography (CT) imaging.
MATERIALS AND METHODS Among 4173 patients, who underwent CT of the cervical vertebrae in the Kyungpook National University Hospital (Daegu, Korea) from April 2004 to March 2008, 2589 patients were excluded from the study because of age (age restriction was over 20 y and under 65 y) and diagnosis (patients with diagnosis of tumor, infection, congenital deformity, and C3–C6 level fracture were excluded). The included 2589 patients were divided into 2 groups on the basis of sex. From each group, 100 male and 100 female patients were selected to perform the measurements. Only chart numbers were given to the observer when selecting patients. From these 200 patients, 800 right pedicles (C3–C6) were evaluated. From 1 mm axial cut CT images, oblique axial and oblique sagittal images were reconstructed. Oblique axial images were reconstructed parallel to the superior and inferior border of each pedicle. Among the reconstructed oblique axial images, those in which the pedicle diameters were the largest were used to perform the measurements. The pedicle transverse diameter (PTD), pedicle length (PL), pedicle convergence angle (CA), and pedicle distance (PD) were measured on the oblique axial images. The PTD was defined as the width of the pedicle. A pedicle longitudinal axis was defined as the line parallel to and in the middle of the lateral and medial border of the pedicle. The point where the pedicle longitudinal axis and lateral mass posterior cortex meet was termed projection point. The area where the pedicle and the vertebral body meet was termed contact area. The PL was defined as a length of the longitudinal axis of the pedicle from the projection point to the contact area. The CA was defined as the angle between the midline and the longitudinal axis of the pedicle. The PD was defined as the shortest distance from the midline to the projection point (Fig. 1). Oblique sagittal images for measurement were made along with the longitudinal axis of the pedicle. The pedicle sagittal diameter (PSD), pedicle sagittal angle (SA), and lateral mass index (MI) were measured on the oblique sagittal images. The PSD was defined as the width of the pedicle. The SA was defined as the angle between the upper end plate of the vertebral body and the longitudinal axis of the pedicle. The MI was calculated as the ratio (the length of the posterior border of the inferior articular process to the projection point divided by the posterior height of the lateral mass) (Fig. 2). All measurements were made twice in an interval of 2 weeks by 1 observer with picture archiving and communication system; the average values of the 2
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FIGURE 1. Oblique axial image of the C4 vertebra from a 57year-old man who had C2 fracture. P indicates the projection point; a, pedicle transverse diameter (PTD); b, pedicle length (PL); c, pedicle distance (PD); d, pedicle convergence angle (CA).
measurements were used. The multiple t test was used for statistical analysis.
RESULTS The average age of the study participants was 46.3 years (range, 23–64 y). The average and SD of the body mass index was 26.3 ± 4.4 kg/m2. The averages and SDs of each parameter on the oblique axial images (Table 1) and the oblique sagittal images (Table 2) were calculated. Statistical results of the PTD showed significant difference between C3 and C5, C3 and C6, and C4 and C6 (P < 0.05). Statistical results of the PL showed significant difference between all levels from C3 to C6 except C3 and C4 (P < 0.05). Statistical results of the CA showed significant difference between C3 and C4, C3 and C5, C4 and C6, and C5 and C6 (P < 0.05). Statistical results of the PD showed significant difference between all levels from C3 to C6 (P < 0.05). Statistical results of the PSD
FIGURE 2. Oblique sagittal image of the C4 vertebra from a 57-year-old man who had C2 fracture. a indicates pedicle sagittal diameter (PSD); b, pedicle sagittal angle (SA); c, posterior height of lateral mass; and d/c, lateral mass index (MI). The entry point is near one third of the lateral mass height from the posterior border of the superior articular process. r
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Reconstructed CT in Analysis of Cervical Pedicle
TABLE 1. Averages and SDs of Measured Parameters at the Oblique Axial Images Cervical Level
PTD (mm)
PL (mm)
CA (deg.)
PD (mm)
C3 C4 C5 C6
5.76 ± 0.83 5.86 ± 0.73 6.07 ± 0.69 6.19 ± 0.76
17.31 ± 1.15 17.56 ± 0.91 16.71 ± 0.97 16.24 ± 1.01
48.86 ± 3.56 50.90 ± 3.51 50.49 ± 3.35 47.49 ± 3.67
22.67 ± 1.70 23.44 ± 1.61 24.93 ± 1.70 24.25 ± 1.59
CA indicates pedicle convergence angle; PD, pedicle distance; PL, pedicle length; PTD, pedicle transverse diameter.
showed significant difference between all levels from C3 to C6 except C3 and C6 (P < 0.05). Statistical results of the SA showed significant difference between all levels from C3 to C6 (P > 0.05). Statistical results of the MI showed significant difference between all levels from C3 to C6 except C3 and C4 (P < 0.05). The PSD was significantly larger than the PTD from C3 to C6 (P < 0.05).
DISCUSSION Because PTD is larger than PSD, PTD is more important than PSD when evaluating the feasibility of screw insertion. From our result and other previous studies, the cervical pedicle size has a tight safe margin when considering 3.5 mm CPS. Tan et al,17 in a study of a Singaporean Chinese population, reported that averages of PTD (C3– C7) ranged from 4.4 to 5.7 mm, with the smallest diameter at C3 and the largest at C7. Yusof et al,18 in a study of a Malaysian population, reported that averages of PTD (C2–C7) ranged from 5.1 to 6.5 mm in the male population and from 4.6 to 5.6 mm in the female population, with the smallest diameter at C3 and the largest at C7. Hacker et al,11 in a study of a British population, reported that averages of PTD (C3–C7) ranged from 4.9 to 6.6 mm. Sakamoto et al,15 in a study of a Japanese population, reported that averages of PTD (C3–C7) ranged from 5.5 to 7.4 mm, with the smallest diameter at C3 and the largest at C7. Su et al,20 in a study of a South Chinese population, reported that averages of PTD (C3–C7) ranged from 5.2 to 6.6 mm, with the smallest diameter at C3 and the largest at C7. Our result showed that averages of PTD (C3–C6) ranged from 5.76 to 6.19 mm, with the smallest diameter at C3 and the largest at C6. Owing to the tight safe margin and the surrounding neurovascular structure, if CPS fixation is needed, the TABLE 2. Averages and SDs of Measured Parameters at the Oblique Sagittal Images Cervical Level
PSD (mm)
SA (deg.)
C3 C4 C5 C6
7.21 ± 0.71 8.08 ± 0.69 7.67 ± 0.61 7.02 ± 0.63
19.98 ± 6.84 8.59 ± 6.47 2.04 ± 6.71* 15.43 ± 7.81*
MI 0.66 ± 0.03 0.64 ± 0.03 0.91 ± 0.02 1.25 ± 0.07
*Negative value of SA; caudal tilt of pedicle. MI indicates lateral mass index; PSD, pedicle sagittal diameter; SA, pedicle sagittal angle.
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FIGURE 3. Three-dimensional reconstruction image of the cervical vertebrae. White dot is the entry point, and the white arrow is insertion angle of each vertebra. The entry point at C6 is on the inferior articular process of the C5 lateral mass.
screw has to be inserted more precisely. To fulfill this criterion, pedicle orientation and the entry point should be thoroughly understood. There are several studies on pedicle orientation and entry point. Jeanneret et al14 suggested that the entry point is 3 mm beneath the facet joint on a vertical line in the middle of the articular mass, and the insertion angle is close to 45 degrees. Abumi et al2 suggested that the entry point is slightly lateral to the center of the lateral mass and close to the posterior margin of the superior articular surface, and the insertion angle is 25–45 degrees toward the midline. Meanwhile, Sakamoto et al15 suggested, by analyzing the axial CT of cervical pedicles, that the entry point is located as laterally as possible on the posterior surface of the lateral mass, and the insertion angle is close to 50 degrees in the transverse plane. Authors of these previous studies focused mostly on pedicle orientation and the entry point in a horizontal plane. In addition, they regarded the entry point in the sagittal plane as slightly inferior to the posterior border of the facet joint and inserted screws along the upper end plate of each vertebral body. Although PSD is larger than PTD, this roughly measured entry point and screw insertion angle in the sagittal plane may cause root injury. According to our result of CA and PD, the entry point in the horizontal plane is close to the posterolateral border of the lateral mass, and the insertion angle in the horizontal plane is close to 50 degrees, which is somewhat similar to the previous studies.2,14,15 However, according www.jspinaldisorders.com |
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FIGURE 4. Oblique sagittal image of C3 (left) and C6 (right) from a 40-year-old man who had C7–T1 fracture dislocation. Screw insertion along the pedicle hazards the upper end plate of the vertebral body at C3 (left) and the facet joint at C6 (right).
to our result of SA and MI, the entry point and screw insertion angle in the sagittal plane is different from those reported in previous studies. From our SA result, C3 and C4 pedicles and C5 and C6 pedicles have different orientations. C3 and C4 pedicles are in the posteroinferior to anterosuperior direction, whereas the C5 pedicle is almost parallel to the upper end plate of the vertebral body, and the C6 pedicle is in the posterosuperior to anteroinferior direction. From our MI result, the entry point in the sagittal plane is near one third of the lateral mass height from the posterior border of the superior articular process at C3 and C4, near the posterior border of the superior articular process at C5, and superior to the posterior border of the superior articular process at C6 (Fig. 3). This result implicates that C3 and C4 have a risk of penetration of the upper end plate, and C5 and C6 have a risk of facet joint violation when the screw is inserted along the pedicle (Fig. 4). Therefore, at C3 and C4, consideration of the screw length is important when the screw is inserted along the pedicle. Jones et al4 reported that, in a mechanical study, the amount of cortical purchase in the pedicle canal is important for screw pull-out strength, whereas the amount of cancellous purchase in the vertebral body has little relation to the screw pull-out strength. If this experiment is right, the screw size should be carefully checked to have full cortical purchase and to not penetrate the upper end plate for C3 and C4. The average screw length for C3 and C4 might be 18–20 mm from our PL measurement result. At C5 and C6, to insert along the pedicle, the screw should be inserted more caudally than C3 and C4, which need removal of the C4 and C5 inferior articular process. Facet joint violation and removal of the C4 and C5 inferior articular process may cause instability or arthritic change. This might not be of great concern if we consider fusion. However, the exact effect of removal of the inferior articular process has to be evaluated. To insert the screw along the pedicle, not only oblique axial image but also oblique sagittal image should be understood thoroughly before operation. We suggest that the C3 and C4 pedicle screw should be inserted through the one third point from the posterior border of the superior articular process at the posterolateral border of the lateral mass. The entry point at C5 is the near posterolateral border of the superior articular process and that at C6 is superior to the posterior border of the superior articular process at a line medial to the
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posterolateral border of the C5 lateral mass. CA and SA should be considered carefully when inserting the screw. With regard to SA and MI, the C3 and C4 screw size should be measured carefully to avoid penetration of the upper end plate, and the C4 and C5 inferior articular process should be removed to find the C5 and C6 entry point. Our study only gives an idea that during pedicle screw insertion at the cervical vertebra, sagittal orientation has to be taken into consideration, which means that the surgical method and its outcome has to be studied more. If we put screws as we planned, CPS fixation in the Korean population is feasible. However, the surgical method of inserting the screw exactly as we planned is another big issue that needs to be solved. With the aid of fluoroscopy, sagittal orientation can be checked during surgery. The upper end plate of each vertebral body in lateral view can be a guide to inserting the screw correctly in the sagittal plane. However, further studies are needed to evaluate this surgical method and its outcome. REFERENCES 1. Canale ST, Beaty JH, Campbell WC. Campbell’s Operative Orthopaedics. St Louis: Mosby Elsevier; 2008. 2. Abumi K, Itoh H, Taneichi H, et al. Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord. 1994;7:19–28. 3. Abumi K, Kaneda K, Shono Y, et al. One-stage posterior decompression and reconstruction of the cervical spine by using pedicle screw fixation systems. J Neurosurg. 1999;90(suppl): 19–26. 4. Jones EL, Heller JG, Silcox DH, et al. Cervical pedicle screws versus lateral mass screws. Anatomic feasibility and biomechanical comparison. Spine. 1997;22:977–982. 5. Kotani Y, Abumi K, Ito M, et al. Cervical spine injuries associated with lateral mass and facet joint fractures: new classification and surgical treatment with pedicle screw fixation. Eur Spine J. 2005; 14:69–77. 6. Karaikovic EE, Kunakornsawat S, Daubs MD, et al. Surgical anatomy of the cervical pedicles: landmarks for posterior cervical pedicle entrance localization. J Spinal Disord. 2000;13:63–72. 7. Panjabi MM, Shin EK, Chen NC, et al. Internal morphology of human cervical pedicles. Spine. 2000;25:1197–1205. 8. Xu R, Kang A, Ebraheim NA, et al. Anatomic relation between the cervical pedicle and the adjacent neural structures. Spine. 1999;24:451–454. 9. Abumi K, Shono Y, Ito M, et al. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25:962–969. 10. Kotil K, Akcetin MA, Savas Y. Neurovascular complications of cervical pedicle screw fixation. J Clin Neurosci. 2012;19:546–551. r
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11. Hacker AG, Molloy S, Bernard J. The contralateral lamina: a reliable guide in subaxial, cervical pedicle screw placement. Eur Spine J. 2008;17:1457–1461. 12. Abumi K, Kaneda K. Pedicle screw fixation for nontraumatic lesions of the cervical spine. Spine. 1997;22:1853–1863. 13. Nakashima H, Yukawa Y, Imagama S. Complications of cervical pedicle screw fixation for nontraumatic lesions: a multicenter study of 84 patients. J Neurosurg Spine. 2012;16:238–247. 14. Jeanneret B, Gebhard JS, Magerl F. Transpedicular screw fixation of articular mass fracture separation: results of an anatomical study and operative technique. J Spinal Disord. 1994;7:222–229. 15. Sakamoto T, Neo M, Nakamura T. Transpedicular screw placement evaluated by axial computed tomography of the cervical pedicle. Spine. 2004;29:2510–2515. 16. Shin EK, Panjabi MM, Chen NC, et al. The anatomic variability of human cervical pedicles: considerations for transpedicular screw
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17. 18.
19.
20.
fixation in the middle and lower cervical spine. Eur Spine J. 2000;9:61–66. Tan SH, Teo EC, Chua HC. Quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae of Chinese Singaporeans. Eur Spine J. 2004;13:137–146. Yusof MI, Ming LK, Abdullah MS, et al. Computerized tomographic measurement of the cervical pedicles diameter in a Malaysian population and the feasibility for transpedicular fixation. Spine. 2006;31:E221–E224. Reinhold M, Bach C, Audige L, et al. Comparison of two novel fluoroscopy-based stereotactic methods for cervical pedicle screw placement and review of the literature. Eur Spine J. 2008;17: 564–575. Su P, Ma R, Li C, et al. Pedicle screw fixation of the cervical spine: guidance by computed tomography. Clin Orthop Relat Res. 2007; 462:99–104.
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ARTICLE
Analysis of Cervical Pedicle With Reconstructed Computed Tomography Imaging in Korean Population Feasibility and Surgical Anatomy Soo-Hoon Oh, MD and Woo-Kie Min, MD, PhD
Study Design: We analyzed the anatomy of C3–C6 cervical pedicles with reconstructed computed tomography images. Objectives: The objective of the study was to estimate the feasibility and to understand the surgical anatomy in order to reduce pedicle penetration. Summary of Background Data: It is necessary to minimize pedicle penetration by anatomic analysis of cervical pedicles. Many studies have been conducted on cervical pedicle anatomy and cervical pedicle screw fixation, yet there are debates about the feasibility and surgical anatomy. Methods: Oblique axial and oblique sagittal images were reconstructed from a 1 mm cut computed tomography image. The pedicle transverse diameter, pedicle length, pedicle convergence angle (CA), and pedicle distance were measured on the oblique axial images. The pedicle sagittal diameter, pedicle sagittal angle (SA), and lateral mass index were measured on the oblique sagittal images. The multiple t test was used for statistical analysis. Results: The averages of the pedicle transverse diameter ranged from 5.79 to 6.19 mm, the pedicle length ranged from 16.24 to 17.56 mm, the CA ranged from 47.49 to 48.86 degrees, the pedicle distance ranged from 22.67 to 24.93 mm, the SA ranged from 15.43 to 19.98 degrees, and the lateral mass index ranged from 0.64 to 1.25. Conclusions: Because of a tight safe margin, to reduce pedicle penetration the screw should be inserted along the pedicle. With regard to SA, C3 and C4 have a risk of upper end plate penetration. However, C5 and C6 have a risk of facet joint violation, which needs C4 and C5 inferior articular process removal for screw placement. The entry point at C3 and C4 is near one third of the lateral mass height from the posterior border of the superior articular process at the posterolateral border of the lateral mass. The entry point at C5 is near the posterolateral border of the superior articular process and that at C6 is superior to the Received for publication September 23, 2012; accepted March 11, 2013. From the Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, Korea. The authors declare no conflict of interest. Reprints: Woo-Kie Min, MD, PhD, Department of Orthopedic Surgery, Kyungpook National University Graduate School of Medicine, PO Box 700-721, 130 Dongduk-ro, Jung-gu, Daegu, Korea (e-mail: [email protected]). Copyright r 2013 by Lippincott Williams & Wilkins
J Spinal Disord Tech
Volume 27, Number 3, May 2014
posterior border of the superior articular process at a line medial to the posterolateral border of the C5 lateral mass. During insertion, not only CA but even SA should be considered carefully to reduce pedicle penetration. Key Words: pedicle screw, cervical, penetration, entry point, feasibility (J Spinal Disord Tech 2014;27:E99–E103)
S
urgical options for stabilization of the cervical vertebrae are the anterior cervical plate fixation, posterior wiring, lateral mass screw fixation, and cervical pedicle screw (CPS) fixation. The anterior cervical plate fixation allows immediate rigid fixation, but in a vertebral fracture with incompetent posterior elements and ligamentous structures or in a multilevel disease, the anterior cervical plate fixation alone usually is insufficient. Moreover, in a patient who needs posterior decompression, the anterior cervical plate fixation demands another posterior approach.1 The wiring technique may be sufficient for cervical vertebra fixation, but in case of a deficient spinous process due to a trauma or disease and in case of a multilevel instability, the wiring technique is inadequate.1–3 The lateral mass screw fixation provides firm fixation and is safer than the CPS screw fixation, but if the lateral mass is small or if the lateral mass or facet joint has been fractured, the lateral mass screw fixation may face the problem of screw loosening.2,4,5 The CPS screw fixation is most stable when compared with others. However, the CPS screw fixation has a risk of causing neurovascular injury due to the anatomy around the pedicle. The nerve root passes the upper and lower surface of the pedicle, the spinal cord passes the inner surface of the pedicle, and the vertebral artery passes the outer surface of the pedicle.6–8 Some surgeons who have performed the CPS fixation reported that screw penetration did not cause serious neurovascular complications.9–11 Abumi et al3,9,12 reported a screw penetration rate of 1%–10% with few cases having neurovascular injury. However, in recent study, Nakashima et al13 reported that screw misplacement occurred in 76 of 390 screws placed, and 5 screws caused neurovascular injury. Although some report that the CPS is safe, possible disastrous complications lead most surgeons to hesitate using the CPS. To date many www.jspinaldisorders.com |
E99
J Spinal Disord Tech
Oh and Min
Volume 27, Number 3, May 2014
studies have been performed, yet there are debates about the feasibility and surgical anatomy.2,3,6–9,11,12,14–20 This study was conducted to estimate the feasibility of the CPS fixation in Korean population and to study pedicle orientation for minimizing pedicle screw penetration, by analyzing the anatomy of the cervical vertebrae (C3–C6) using reconstructed computed tomography (CT) imaging.
MATERIALS AND METHODS Among 4173 patients, who underwent CT of the cervical vertebrae in the Kyungpook National University Hospital (Daegu, Korea) from April 2004 to March 2008, 2589 patients were excluded from the study because of age (age restriction was over 20 y and under 65 y) and diagnosis (patients with diagnosis of tumor, infection, congenital deformity, and C3–C6 level fracture were excluded). The included 2589 patients were divided into 2 groups on the basis of sex. From each group, 100 male and 100 female patients were selected to perform the measurements. Only chart numbers were given to the observer when selecting patients. From these 200 patients, 800 right pedicles (C3–C6) were evaluated. From 1 mm axial cut CT images, oblique axial and oblique sagittal images were reconstructed. Oblique axial images were reconstructed parallel to the superior and inferior border of each pedicle. Among the reconstructed oblique axial images, those in which the pedicle diameters were the largest were used to perform the measurements. The pedicle transverse diameter (PTD), pedicle length (PL), pedicle convergence angle (CA), and pedicle distance (PD) were measured on the oblique axial images. The PTD was defined as the width of the pedicle. A pedicle longitudinal axis was defined as the line parallel to and in the middle of the lateral and medial border of the pedicle. The point where the pedicle longitudinal axis and lateral mass posterior cortex meet was termed projection point. The area where the pedicle and the vertebral body meet was termed contact area. The PL was defined as a length of the longitudinal axis of the pedicle from the projection point to the contact area. The CA was defined as the angle between the midline and the longitudinal axis of the pedicle. The PD was defined as the shortest distance from the midline to the projection point (Fig. 1). Oblique sagittal images for measurement were made along with the longitudinal axis of the pedicle. The pedicle sagittal diameter (PSD), pedicle sagittal angle (SA), and lateral mass index (MI) were measured on the oblique sagittal images. The PSD was defined as the width of the pedicle. The SA was defined as the angle between the upper end plate of the vertebral body and the longitudinal axis of the pedicle. The MI was calculated as the ratio (the length of the posterior border of the inferior articular process to the projection point divided by the posterior height of the lateral mass) (Fig. 2). All measurements were made twice in an interval of 2 weeks by 1 observer with picture archiving and communication system; the average values of the 2
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FIGURE 1. Oblique axial image of the C4 vertebra from a 57year-old man who had C2 fracture. P indicates the projection point; a, pedicle transverse diameter (PTD); b, pedicle length (PL); c, pedicle distance (PD); d, pedicle convergence angle (CA).
measurements were used. The multiple t test was used for statistical analysis.
RESULTS The average age of the study participants was 46.3 years (range, 23–64 y). The average and SD of the body mass index was 26.3 ± 4.4 kg/m2. The averages and SDs of each parameter on the oblique axial images (Table 1) and the oblique sagittal images (Table 2) were calculated. Statistical results of the PTD showed significant difference between C3 and C5, C3 and C6, and C4 and C6 (P < 0.05). Statistical results of the PL showed significant difference between all levels from C3 to C6 except C3 and C4 (P < 0.05). Statistical results of the CA showed significant difference between C3 and C4, C3 and C5, C4 and C6, and C5 and C6 (P < 0.05). Statistical results of the PD showed significant difference between all levels from C3 to C6 (P < 0.05). Statistical results of the PSD
FIGURE 2. Oblique sagittal image of the C4 vertebra from a 57-year-old man who had C2 fracture. a indicates pedicle sagittal diameter (PSD); b, pedicle sagittal angle (SA); c, posterior height of lateral mass; and d/c, lateral mass index (MI). The entry point is near one third of the lateral mass height from the posterior border of the superior articular process. r
2013 Lippincott Williams & Wilkins
J Spinal Disord Tech
Volume 27, Number 3, May 2014
Reconstructed CT in Analysis of Cervical Pedicle
TABLE 1. Averages and SDs of Measured Parameters at the Oblique Axial Images Cervical Level
PTD (mm)
PL (mm)
CA (deg.)
PD (mm)
C3 C4 C5 C6
5.76 ± 0.83 5.86 ± 0.73 6.07 ± 0.69 6.19 ± 0.76
17.31 ± 1.15 17.56 ± 0.91 16.71 ± 0.97 16.24 ± 1.01
48.86 ± 3.56 50.90 ± 3.51 50.49 ± 3.35 47.49 ± 3.67
22.67 ± 1.70 23.44 ± 1.61 24.93 ± 1.70 24.25 ± 1.59
CA indicates pedicle convergence angle; PD, pedicle distance; PL, pedicle length; PTD, pedicle transverse diameter.
showed significant difference between all levels from C3 to C6 except C3 and C6 (P < 0.05). Statistical results of the SA showed significant difference between all levels from C3 to C6 (P > 0.05). Statistical results of the MI showed significant difference between all levels from C3 to C6 except C3 and C4 (P < 0.05). The PSD was significantly larger than the PTD from C3 to C6 (P < 0.05).
DISCUSSION Because PTD is larger than PSD, PTD is more important than PSD when evaluating the feasibility of screw insertion. From our result and other previous studies, the cervical pedicle size has a tight safe margin when considering 3.5 mm CPS. Tan et al,17 in a study of a Singaporean Chinese population, reported that averages of PTD (C3– C7) ranged from 4.4 to 5.7 mm, with the smallest diameter at C3 and the largest at C7. Yusof et al,18 in a study of a Malaysian population, reported that averages of PTD (C2–C7) ranged from 5.1 to 6.5 mm in the male population and from 4.6 to 5.6 mm in the female population, with the smallest diameter at C3 and the largest at C7. Hacker et al,11 in a study of a British population, reported that averages of PTD (C3–C7) ranged from 4.9 to 6.6 mm. Sakamoto et al,15 in a study of a Japanese population, reported that averages of PTD (C3–C7) ranged from 5.5 to 7.4 mm, with the smallest diameter at C3 and the largest at C7. Su et al,20 in a study of a South Chinese population, reported that averages of PTD (C3–C7) ranged from 5.2 to 6.6 mm, with the smallest diameter at C3 and the largest at C7. Our result showed that averages of PTD (C3–C6) ranged from 5.76 to 6.19 mm, with the smallest diameter at C3 and the largest at C6. Owing to the tight safe margin and the surrounding neurovascular structure, if CPS fixation is needed, the TABLE 2. Averages and SDs of Measured Parameters at the Oblique Sagittal Images Cervical Level
PSD (mm)
SA (deg.)
C3 C4 C5 C6
7.21 ± 0.71 8.08 ± 0.69 7.67 ± 0.61 7.02 ± 0.63
19.98 ± 6.84 8.59 ± 6.47 2.04 ± 6.71* 15.43 ± 7.81*
MI 0.66 ± 0.03 0.64 ± 0.03 0.91 ± 0.02 1.25 ± 0.07
*Negative value of SA; caudal tilt of pedicle. MI indicates lateral mass index; PSD, pedicle sagittal diameter; SA, pedicle sagittal angle.
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FIGURE 3. Three-dimensional reconstruction image of the cervical vertebrae. White dot is the entry point, and the white arrow is insertion angle of each vertebra. The entry point at C6 is on the inferior articular process of the C5 lateral mass.
screw has to be inserted more precisely. To fulfill this criterion, pedicle orientation and the entry point should be thoroughly understood. There are several studies on pedicle orientation and entry point. Jeanneret et al14 suggested that the entry point is 3 mm beneath the facet joint on a vertical line in the middle of the articular mass, and the insertion angle is close to 45 degrees. Abumi et al2 suggested that the entry point is slightly lateral to the center of the lateral mass and close to the posterior margin of the superior articular surface, and the insertion angle is 25–45 degrees toward the midline. Meanwhile, Sakamoto et al15 suggested, by analyzing the axial CT of cervical pedicles, that the entry point is located as laterally as possible on the posterior surface of the lateral mass, and the insertion angle is close to 50 degrees in the transverse plane. Authors of these previous studies focused mostly on pedicle orientation and the entry point in a horizontal plane. In addition, they regarded the entry point in the sagittal plane as slightly inferior to the posterior border of the facet joint and inserted screws along the upper end plate of each vertebral body. Although PSD is larger than PTD, this roughly measured entry point and screw insertion angle in the sagittal plane may cause root injury. According to our result of CA and PD, the entry point in the horizontal plane is close to the posterolateral border of the lateral mass, and the insertion angle in the horizontal plane is close to 50 degrees, which is somewhat similar to the previous studies.2,14,15 However, according www.jspinaldisorders.com |
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FIGURE 4. Oblique sagittal image of C3 (left) and C6 (right) from a 40-year-old man who had C7–T1 fracture dislocation. Screw insertion along the pedicle hazards the upper end plate of the vertebral body at C3 (left) and the facet joint at C6 (right).
to our result of SA and MI, the entry point and screw insertion angle in the sagittal plane is different from those reported in previous studies. From our SA result, C3 and C4 pedicles and C5 and C6 pedicles have different orientations. C3 and C4 pedicles are in the posteroinferior to anterosuperior direction, whereas the C5 pedicle is almost parallel to the upper end plate of the vertebral body, and the C6 pedicle is in the posterosuperior to anteroinferior direction. From our MI result, the entry point in the sagittal plane is near one third of the lateral mass height from the posterior border of the superior articular process at C3 and C4, near the posterior border of the superior articular process at C5, and superior to the posterior border of the superior articular process at C6 (Fig. 3). This result implicates that C3 and C4 have a risk of penetration of the upper end plate, and C5 and C6 have a risk of facet joint violation when the screw is inserted along the pedicle (Fig. 4). Therefore, at C3 and C4, consideration of the screw length is important when the screw is inserted along the pedicle. Jones et al4 reported that, in a mechanical study, the amount of cortical purchase in the pedicle canal is important for screw pull-out strength, whereas the amount of cancellous purchase in the vertebral body has little relation to the screw pull-out strength. If this experiment is right, the screw size should be carefully checked to have full cortical purchase and to not penetrate the upper end plate for C3 and C4. The average screw length for C3 and C4 might be 18–20 mm from our PL measurement result. At C5 and C6, to insert along the pedicle, the screw should be inserted more caudally than C3 and C4, which need removal of the C4 and C5 inferior articular process. Facet joint violation and removal of the C4 and C5 inferior articular process may cause instability or arthritic change. This might not be of great concern if we consider fusion. However, the exact effect of removal of the inferior articular process has to be evaluated. To insert the screw along the pedicle, not only oblique axial image but also oblique sagittal image should be understood thoroughly before operation. We suggest that the C3 and C4 pedicle screw should be inserted through the one third point from the posterior border of the superior articular process at the posterolateral border of the lateral mass. The entry point at C5 is the near posterolateral border of the superior articular process and that at C6 is superior to the posterior border of the superior articular process at a line medial to the
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posterolateral border of the C5 lateral mass. CA and SA should be considered carefully when inserting the screw. With regard to SA and MI, the C3 and C4 screw size should be measured carefully to avoid penetration of the upper end plate, and the C4 and C5 inferior articular process should be removed to find the C5 and C6 entry point. Our study only gives an idea that during pedicle screw insertion at the cervical vertebra, sagittal orientation has to be taken into consideration, which means that the surgical method and its outcome has to be studied more. If we put screws as we planned, CPS fixation in the Korean population is feasible. However, the surgical method of inserting the screw exactly as we planned is another big issue that needs to be solved. With the aid of fluoroscopy, sagittal orientation can be checked during surgery. The upper end plate of each vertebral body in lateral view can be a guide to inserting the screw correctly in the sagittal plane. However, further studies are needed to evaluate this surgical method and its outcome. REFERENCES 1. Canale ST, Beaty JH, Campbell WC. Campbell’s Operative Orthopaedics. St Louis: Mosby Elsevier; 2008. 2. Abumi K, Itoh H, Taneichi H, et al. Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord. 1994;7:19–28. 3. Abumi K, Kaneda K, Shono Y, et al. One-stage posterior decompression and reconstruction of the cervical spine by using pedicle screw fixation systems. J Neurosurg. 1999;90(suppl): 19–26. 4. Jones EL, Heller JG, Silcox DH, et al. Cervical pedicle screws versus lateral mass screws. Anatomic feasibility and biomechanical comparison. Spine. 1997;22:977–982. 5. Kotani Y, Abumi K, Ito M, et al. Cervical spine injuries associated with lateral mass and facet joint fractures: new classification and surgical treatment with pedicle screw fixation. Eur Spine J. 2005; 14:69–77. 6. Karaikovic EE, Kunakornsawat S, Daubs MD, et al. Surgical anatomy of the cervical pedicles: landmarks for posterior cervical pedicle entrance localization. J Spinal Disord. 2000;13:63–72. 7. Panjabi MM, Shin EK, Chen NC, et al. Internal morphology of human cervical pedicles. Spine. 2000;25:1197–1205. 8. Xu R, Kang A, Ebraheim NA, et al. Anatomic relation between the cervical pedicle and the adjacent neural structures. Spine. 1999;24:451–454. 9. Abumi K, Shono Y, Ito M, et al. Complications of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine. 2000; 25:962–969. 10. Kotil K, Akcetin MA, Savas Y. Neurovascular complications of cervical pedicle screw fixation. J Clin Neurosci. 2012;19:546–551. r
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11. Hacker AG, Molloy S, Bernard J. The contralateral lamina: a reliable guide in subaxial, cervical pedicle screw placement. Eur Spine J. 2008;17:1457–1461. 12. Abumi K, Kaneda K. Pedicle screw fixation for nontraumatic lesions of the cervical spine. Spine. 1997;22:1853–1863. 13. Nakashima H, Yukawa Y, Imagama S. Complications of cervical pedicle screw fixation for nontraumatic lesions: a multicenter study of 84 patients. J Neurosurg Spine. 2012;16:238–247. 14. Jeanneret B, Gebhard JS, Magerl F. Transpedicular screw fixation of articular mass fracture separation: results of an anatomical study and operative technique. J Spinal Disord. 1994;7:222–229. 15. Sakamoto T, Neo M, Nakamura T. Transpedicular screw placement evaluated by axial computed tomography of the cervical pedicle. Spine. 2004;29:2510–2515. 16. Shin EK, Panjabi MM, Chen NC, et al. The anatomic variability of human cervical pedicles: considerations for transpedicular screw
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fixation in the middle and lower cervical spine. Eur Spine J. 2000;9:61–66. Tan SH, Teo EC, Chua HC. Quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae of Chinese Singaporeans. Eur Spine J. 2004;13:137–146. Yusof MI, Ming LK, Abdullah MS, et al. Computerized tomographic measurement of the cervical pedicles diameter in a Malaysian population and the feasibility for transpedicular fixation. Spine. 2006;31:E221–E224. Reinhold M, Bach C, Audige L, et al. Comparison of two novel fluoroscopy-based stereotactic methods for cervical pedicle screw placement and review of the literature. Eur Spine J. 2008;17: 564–575. Su P, Ma R, Li C, et al. Pedicle screw fixation of the cervical spine: guidance by computed tomography. Clin Orthop Relat Res. 2007; 462:99–104.
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