Original article Morphometric analysis of the cervical spine of Indian population by using computerized tomography

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1 J M e d A l l i e d S c i ; 2 ( 2 ) : w w w. j m a s. i n P r i n t I S S N : O n l i n e I S S N : X Journal of Medical & Allied Sciences Original article Morphometric analysis of the cervical spine of Indian population by using computerized tomography Partha Sarathi Banerjee 1, Amit Roychoudhury 2, Santanu Kumar Karmakar 3 1 Product Design and Simulation Division, Central Mechanical Engineering Research Institute, Durgapur, Bardhaman , West Bengal, India. 2 Department of Aerospace Engineering and Applied Mechanics; 3 Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, , West Bengal, India. Article history: Abstract Received 18 July 2012 Revised 29 August 2012 Accepted 29 August 2012 Early online 25 August 2012 Print 31 August 2012 Corresponding author Partha Sarathi Banerjee Principal Scientist and Head, Product Design and Simulation Division, Central Mechanical Engineering Research Institute (CMERI), P.O. Durgapur, Bardhaman West Bengal, India. Phone: Fax: partho_cmeri@yahoo.com The purpose of the present study was to measure the surgically important morphological parameters of cervical spine region of a representative sample of Indian population from the images obtained through computerized tomography (CT). Another purpose has been to compare the computed statistical mean, standard deviation and range of variation of these data with those of other Asian population and also European/American populations. With that aim, ninety five (95) CT scan data of Indian people (73 for male patients and 22 for female patients) pertaining to undeformed normal cervical spine has been collected from an Indian hospital. From these, 15 important morphological parameters have been measured. These values have been tabulated and their mean, standard deviation and range of variation have been computed. It has been found that pedicle dimensions of Indian people are smaller at almost all vertebra levels as compared to Caucasian people. Pedicle axis length for Indian people are found to be smaller at C3, C4 and C5 levels than those for other Asian people including Chinese people, but it is bigger at C6 and C7 levels. Indian people have longer measurements of pedicle length + lateral mass on an average than their other Asian counterparts at C5, C6 and C7 levels, but shorter measurements at C3 and C4 levels. The results of the present work may help in better understanding of morphological parameters of cervical spine region of Indian population. It may be further useful in designing spinal implants which would be biomechanically compatible to the anatomy of Indian people. Key words: Anatomy, cervical spine, Indian population, morphological data, pedicle, vertebra 2012 Deccan College of Medical Sciences. All rights reserved. Human spine is quite an interesting mechanical assembly complex in structure and function. Its purpose is to protect the spinal cord and nerve roots and also to provide flexibility and mobility to the main body. While transmitting weight of the upper body to the pelvis, it is subjected to internal stresses which may exceed many times the entire body weight of the person. For this 66

2 reason, spine is often associated with various problems like back pains and injuries. In addition, neck pain has become a very common health problem now, especially in urban societies, which is caused mainly due to worn-out inter-vertebral discs in cervical spine. Such kind of degeneration is thought to be a consequence of changed lifestyle, which often involves watching TV or working on computer for long durations without changing the sitting posture. Biomechanical remedies to such spinal problems often involve surgical intervention and implantation. In the conventional surgical procedure known as arthrodesis or surgical fusion, upper and lower adjacent vertebrae of the degenerated region are joined with plates and screws. Thus motion of the damaged or defective vertebral portion is eliminated and further manifestation of wear and tear is prevented. The most common form of arthrodesis is anterior cervical plate fixation. In other cases, where this kind of surgical intervention is not possible, owing to unavailability of bone mass from anterior side, another method, known as posterior lateral mass screw fixation, is employed. A further improved version of arthrodesis, introduced a few years back, is known as transpedicular screw fixation. This method does not involve any plates and pedicles of adjacent vertebrae are held together with screws. The more advanced kind of surgery, known as arthroplasty, involves replacement of damaged inter-vertebral disc(s) by implantation of artificial discs. However, this is a newer concept and is still in development stage. But for all these methods of surgery, few metric inputs are required to be studied and understood clearly, for designing such spinal implants which can solve the spinal malfunction satisfactorily after their implantation surgery. First of all, shape and geometrical dimensions of bone vertebrae are to be studied. In this regard, computerized tomography (CT) scan data provide a clear picture about the internal anatomical structures i.e. bones and cartilages. Using specialized CT scan data processing software like Materialise Interactive Medical Image Control System (MIMICS), the CT data in DICOM format can be extracted layer after layer and important anatomical dimensions can be conveniently measured from it. In this connection, it may be pertinent to mention here that there is no significant difference in anatomical dimensions whether measured via radiography (CT) or directly, as reported earlier 1. Human cervical spine consists of seven vertebrae, with the two upper vertebrae; atlas (C1) and axis (C2), as shown in figure 1 and 2, being atypical vertebrae. The remaining five vertebrae (C3 to C7) being typical vertebrae. C7 is shown in figure 3. The vertebral bodies of atlas and axis have unique anatomical appearances. In the lower cervical spine (C3 to C7) osseous elements, called pedicles, extend posteriorly from the vertebral bodies; transverse processes and spinous processes extend laterally and posteriorly from the lamina. Fig 1. Atlas (C1 vertebra). Fig 2. Axis (C2 vertebra). Fig 3. C7 vertebra. Many researchers investigated different important aspects of human cervical spine, e.g. anatomy, kinematics, in vivo loads and mechanical properties of vertebra as well as of inter-vertebral discs. The first such extensive compilation of articles on 67

3 the cervical spine was published by Van Eck et al. 2 and their work remains an important reference manual on cervical injuries and range of motion. The book written by White and Punjabi 3 presented a comprehensive review and analysis of the clinically relevant scientific data on the mechanics of the human spine. It served as a guiding literature for researchers in this field. The anatomical dimensions of cervical vertebra, which have been measured, are in accordance with the discussions on functional biomechanics of spine as found in the chapter 2 of the aforesaid book. In this connection, one investigation which deserves a mention here has been conducted by Duray et al. 4, who studied the importance of morphological data in cervical spine region for identifying human races. Their study reveals that anatomical characteristics, especially in amount of bifidity, within C3 C6 region of cervical spine can be taken as an important parameter for distinguishing White-American people from Black-American people from the viewpoint of a forensic scientist. In a very important study, Yoganandan et al. 5 investigated geometrical properties of the facet joints including cartilage thickness and gap using human cadaver cervical spinal columns and cryomicrotomy techniques for determining the existence of level or gender dependency on facet joint morphology in the human cervical spine. They found that facet joint morphology varies with the regions of the cervical spine, gender and location. They also find that the lack of adequate cartilage in females may expose the underlying adjacent sub-chondral bone to direct stresses during normal physiologic and traumatic loads. Kettler et al. 6 conducted a study to determine the degree of cartilage degeneration of cervical facet joints with respect to spinal level and age, to investigate whether any region of the joint surface is more often affected by degeneration, and to determine the localization of osteophytes. They inspected a total of 128 left-sided facet surfaces from 15 fresh frozen cervical spine specimens (59 92 years). They found that the prevalence of cervical facet joint degeneration is very high in individuals, aged 50 years and more, with a tendency to increase in severity with age. Also, in the cervical spine in most cases the cartilage has been found to be evenly degenerated all over the joint surface while in the lumbar spine certain regions have been reported to be affected predominantly. Kayalioglu et al. 7 measured pedicle dimensions (length, width, height) and inter-pedicular distances for Turkish population and compared their measured values with those of previously published papers in refereed journals Ruofu et al. 15 measured pedicle dimensions and also other important anatomic dimensions in cervical spine area of Chinese population (30 males and 30 females) from their CT scan data. They computed the mean, standard deviation and range of variation of all these parameters. Senoglu et al. 16 investigated the variation of morphological dimensions in the C2 vertebra region of 86 cadaverous specimens of all Caucasian people with an aim to determine maximum permissible screw length for C2 anterior plate fixation. Their report provides some guidelines for operating on the anterior C2 spine region. They also compared the measured data with similar previous studies viz. Schaffler et al. 17, Xu, Nadaud et al. 18 and Naderi et al. 19. Liu et al. 20 conducted a systematic review and analysis of 33 previous studies with the measurements of 1311 partial and complete cervical spines. They found that there are more significant differences comparing the cervical pedicles of males and females in the European/American population than exists in the Asian population, specifically in pedicle width and height. They found significant differences at C3 and C4 cervical pedicle between the Asian and European/American population, specifically in the pedicle axis length and transverse angle. All these investigations on measurement of morphological dimensions in cervical spine area are focused on the anatomy of Caucasian population only, sans one study, which dealt with Chinese population 15. Other than these, a recent report of Singh et al. 21 focuses on Indian population and their morphological parameters. They studied the morphometric data obtained from direct measurements of 100 cadaveric thoracic spines (T1 to T12) of Indian population. Their study reveals that the smallest diameter screw and shortest available screw for adults may not be safe in majority of the Indian population in mid-thoracic region. However, most of the previous reports including the report of Singh et al. 21 have focused primarily on the morphological parameters of lumber region and no significant study on measurement and analysis of morphological parameters of the cervical spine region of Indian people has been carried out so far. Materials and Methods To ensure dimensional compatibility of the designed implants with the bone anatomy, a detailed understanding of the important morphological parameters as well as their nature of variations is imperative. In the present study, 95 CT scan data of cervical spine of Indian population have been collected for measuring those anatomical dimensions which are considered to be significant for designing spinal implants. Their mean, standard 68

4 deviation and range of variation also have been calculated. All the CT scan data have been obtained from a hospital, where patients have reported for problems other than cervical spine deformity. Therefore, the CT scan data of undeformed cervical spine only have been collected. Out of the 95 patients, 73 were males and 22 were females. Mean age for male patients was 54.8 years (range 38 to 68 years) and mean age for female patients was 45.9 years (range of 37 to 60 years). Most of the patients were from southern part of India and the remaining from Eastern India. As shown in figure 4 and 5 and also described below, fifteen important anatomic dimensions have been identified, which are significant from viewpoint of spinal surgery. PL L = Pedicle length (Left) PL R = Pedicle length (Right) PDW L = Pedicle width (Left) PDW R = Pedicle width (Right) PDH L = Pedicle height (Left) PDH R = Pedicle height (Right) PAL L = Pedicle axis length (Left) PAL R = Pedicle axis length (Right) PL&LM L = Pedicle length + lateral mass (Left) PL&LM R = Pedicle length + lateral mass (Right) PTA L = Pedicle transverse angle (Left) PTA R = Pedicle transverse angle (Right) IPD = Inter pedicular distance LPD L = Lateral pedicle distance (Left) LPD R = Lateral pedicle distance (Right) Fig 4. Important morphological parameters (on transverse plane). Fig 5. Important morphological parameters (on coronal plane). These parameters have been measured (for each of five cervical vertebrae, C3 to C7) from the CT scan data of the patients, by using MIMICS software. Degenerative problem is very rare at C1 and C2 level and it is prevalent at the lower cervical spine i.e. from C3 to C7 level. The mean, standard deviation and range of variation of all these parameters have been calculated and tabulated. Also, the nature of variation of mean values of the parameters with respect to vertebra levels (C3 to C7) has been plotted and is shown in figures 6 to 13. The calculated values of mean, standard deviation, etc. have been also compared with those of previous studies and are shown in Tables 1 to 7. Results and Discussion As shown in figure 6, the mean values of pedicle lengths have been found to be progressively increasing for both males and females from C3 to C6 vertebrae level and then slightly decreasing at C7 level. Also, it can be seen that the mean values for females are smaller than those for males, for both left and right side. Figure 7 shows the variation of mean values of pedicle widths through vertebrae levels from C3 to C7. The same progressively increasing trend is noticed here too, which continues upto C7. Like pedicle length values, in this case pedicle widths also are found to be smaller for women than for men, at all vertebrae levels, but the difference between left side and right side is very little for both men and women. The variation of mean values of pedicle height is shown in figure 8. A little fluctuating nature is observed for women though the values are smaller than those for men. For this parameter, very little difference is observed between left side values 69

5 Fig 6. Nature of variation of pedicle length (PL). Fig 10. Nature of variation of pedicle length + lateral mass (PL & LM). Fig 7. Nature of variation of pedicle width (PDW). Fig 11. Nature of variation of pedicle transverse angle (PTA). Fig 8. Nature of variation of pedicle height (PDH). Fig 12. Nature of variation of inter pedicular distance (IPD). Fig 9. Nature of variation of pedicle axis length (PAL). and right side values for men. But, for women, some appreciable difference is noted. Fig 13. Nature of variation of lateral pedicle distance (LPD). The nature of variation of mean values of five other important morphological parameters for left and 70

6 Vertebra level Orientation Banerjee PS et al. right side of both men and women viz. PAL, PL&LM, PTA, IPD and LPD are shown in figures 9 to 13. PAL shows a continuously increasing trend from C3 to C7 for both men and women. But, PL&LM for men increases upto C6 level, and then it decreases almost upto its initial value at C3 level. For women, decrease in mean value of PL&LM starts from C5 level. The mean value of PTA (in degrees) displays similar trend of variation for men and women with respect to both left and right sides. The highest value of PTA occurs at C4 and lowest is found at C7 for both men and women. Also, the mean values for men and women at all vertebrae levels are almost same. As shown in figure 12, the nature of variation of IPD for both men and women, increases upto C6 level and then decreases slightly at C7 level. The values for women are smaller than those for men, except at C3 level where it is reverse. Table 1: Comparison of morphological parameters of male population, measured from CT scan data (with Asian people, from previous studies) Morphological parameters measured Ruofu et al. (2008) 15 Liu et al. (2010) 20 Present study Mean SD Max Min Mean SD Max Min Mean SD Max Min Pedicle axis length (PAL) (in mm) Pedicle length + lateral mass (PL + LM) (in mm) Pedicle transverse angle (PTA) (in degree) Inter pedicular distance (IPD) (in mm) Lateral pedicle distance (LPD) (in mm) C L R C L R C L R C L R C L R C3 NA NA NA NA L R C4 NA NA NA NA L R C5 NA NA NA NA L R C6 NA NA NA NA L R C7 NA NA NA NA L R C L R C L R C L R C L R C L R C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R

7 Vertebra level Orientation Banerjee PS et al. Figure 13 shows the nature of variation for LPD, which also displays similar trend for both men and women including right and left sides. But, values are smaller for women upto C6 level beyond which it is almost equal. The calculated mean values, standard deviations and also ranges of variation of these five morphological parameters viz. PAL, PL&LM, PTA, IPD and LPD (for male population) are tabulated and compared with those of two previous reports 15,20. For Indian male population, table 1 shows such comparative scenario with Asian people and Chinese people, while table 3 shows it with European/American population. It may be noted here that in the report of Liu et al. 20, Asian population means combination of Chinese, Japanese, Malaysian and Singaporean people while European/American population means combination of American, Turkish, Austrian, English, German and Brazilian people. Similar comparisons for females are represented in table 2 and table 4. Table 2: Comparison of morphological parameters of female population, measured from CT scan data (with Asian people, from previous studies) Morphological parameters measured Ruofu et al. (2008) 15 Liu et al. (2010) 20 Present study Mean SD Max Min Mean SD Max Min Mean SD Max Min Pedicle axis length (PAL) (in mm) Pedicle length + lateral mass (PL + LM) (in mm) Pedicle transverse angle (PTA) (in degree) Inter pedicular distance (IPD) (in mm) Lateral pedicle distance (LPD) (in mm) C L R C L R C L R C L R C L R C3 NA NA NA NA L R C4 NA NA NA NA L R C5 NA NA NA NA L R C6 NA NA NA NA L R C7 NA NA NA NA L R C L R C L R C L R C L R C L R C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R C NA NA NA NA L R

8 It may be observed from table 1 that the PAL values for Indian males are found to be smaller at C3, C4 and C5 levels than those for other Asian male population including Chinese people, but it is bigger at C6 and C7 levels. Same trend is observed for females also, as revealed in table 2. As for PL&LM, Indian men have longer measurements on an average than their other Asian counterparts at C5, C6 and C7 levels, but shorter measurements at C3 and C4 levels, as observed and shown in table 1. Almost similar trend is found for Indian women too as shown in table 2. PTA values are also found to be smaller for Indian men and women in comparison with other Asian people at C3 and C4 levels. But it is bigger at C5, C6 and C7 levels. As for IPD, Indian males have been found to possess smaller values than other Asian males at C3 to C5 levels, but larger values below that level. The trend for Indian females is found to be different in this case. Except at C5 level, the IPD values are all larger in comparison to other Asian females. Lastly, LPD values for Indian males are found to be larger than other Asian males at C3 to C5 level, but smaller at levels below that. For Indian females, this parameter is found to be smaller at almost all levels from C3 to C7 than their other Asian counterparts. Tables 5, 6 and 7 show the comparative measures of mean pedicle length, width and height of Indian males and females with those already reported in eleven previous studies all of which dealt with European and American people. From these three tables, it can be seen that the pedicle dimensions of Indian people are smaller at almost all vertebra levels as compared to Caucasian people. Since pedicle dimensions are important for transpedicular screw fixation and similar surgeries, this smaller size of pedicle in Indian population needs to be taken into account while planning such a surgical procedure. Conclusions From the calculated mean and standard deviation of the measured values of PDW-L and PDW-R for both Indian males and females, it may be concluded that the safe length of screw for surgery for Indian male patients may be taken within 4 mm to 7 mm whereas for Indian female patients, the safe length can be between 3.5 mm to 6.5 mm. Table 3: Comparison of morphological parameters of male population, measured from CT scan data (with European people, from previous studies) Morphological parameters measured Pedicle axis length (PAL) (in mm) Pedicle length + lateral mass (PL + LM) (in mm) Pedicle transverse angle (PTA) (in degree) Vertebra level Liu et al. (2010) 20 Present study Mean SD Max Min Orientation Mean SD Max Min C C C C C C C C C C NA NA NA C C C C C L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R

9 Table 4: Comparison of morphological parameters of female population, measured from CT scan data (with European people, from previous studies) Morphological parameters measured Pedicle axis length (PAL) (in mm) Pedicle length + lateral mass (PL + LM) (in mm) Pedicle transverse angle (PTA) (in degree) Vertebra Liu et al. (2010) 20 Present study level Mean SD Max Min Orientation Mean SD Max Min C L R C L R C L R C L R C L R C L R C L R C L R C L R C NA NA NA L R C L R C L R C L R C L R C L R Table 5: Comparison of present and previous measurements of pedicle length of cervical vertebrae Author (year) Pedicle length (mean ± standard deviation, in mm) C3 level C4 level C5 level C6 level C7 level Panjabi et al. (1991) 11 NA NA NA NA NA Stanescu et al. (1994) 14 NA NA 4.7± ±0.7 NA Ebraheim et al. (1997) 9 NA NA NA 6.1±0.8 NA Jones et al. (1997) 10 NA NA NA NA NA Karaikovic et al. (1997) 1 NA NA NA NA NA Xu, Kang et al. (1999) 22 NA NA NA NA NA Ugur et al. (2000) 13 NA NA NA NA NA Panjabi et al. (2000) 12 NA NA NA NA NA Bozbuga et al. (2004) 8 5.3± ± ± ±0.8 NA Kayalioglu et al. (2007) ± ± ± ±1.05 NA Liu J et al. (2010) 20 NA NA NA NA NA Present Study Left side 4.51± ± ±1 5.04± ±1.12 Right side 5.03± ± ± ± ±1.08 Regarding inclinations of pedicles or pedicle transverse angle (PTA), which are supposed to determine the direction of screw advancement, it is found from the present study that the angle is varying from to with mean value of for Indian males, while the corresponding values are from 31.6 to with mean value of for Indian females. For posterior lateral mass screw fixation type of surgery, screw lengths to be used are determined by lateral pedicle distance (LPD). From the computed values of LPD in the present study, it is found that screw lengths from 1.91 mm 2.72 mm may be used for Indian males while for Indian females, the corresponding range is from 1.3 mm to 2.5 mm. Acknowledgments The authors wish to express their sincere thanks to 74

10 Table 6: Comparison of present and previous measurements of pedicle width of cervical vertebrae Author (year) Pedicle width (mean ± standard deviation, in mm) C3 level C4 level C5 level C6 level C7 level Panjabi et al. (1991) ± ± ± ±0.5 NA Stanescu et al. (1994) 14 NA NA 5.2± ±0.8 NA Ebraheim et al. (1997) 9 4.7± ± ± ±0.7 NA Jones et al. (1997) NA Karaikovic et al. (1997) 1 4.9± ± ± ±0.9 NA Xu, Kang et al. (1999) ± ± ± ±0.5 NA Ugur et al. (2000) ± ± ± ±0.4 NA Panjabi et al. (2000) ± ± ± ±0.9 NA Bozbuga et al. (2004) 8 4.5± ± ± ±0.5 NA Kayalioglu et al. (2007) ± ± ± ±0.93 NA Liu J et al. (2010) ± ± ± ± ±0.49 Present Study Left side 4.89± ± ± ± ±1.01 Right side 4.71± ± ± ± ±1.03 Table 7: Comparison of present and previous measurements of pedicle height of cervical vertebrae Author (year) Pedicle height (mean ± standard deviation, in mm) C3 level C4 level C5 level C6 level C7 level Panjabi et al. (1991) ± ± ± ±0.4 NA Stanescu et al. (1994) 14 ND ND 6.7± ±0.9 NA Ebraheim et al. (1997) 9 5.8± ± ±0.8 ND NA Jones et al. (1997) NA Karaikovic et al. (1997) 1 6.8± ± ± ±1.0 NA Xu, Kang et al. (1999) ± ± ± ±1.1 NA Ugur et al. (2000) ± ± ± ±0.6 NA Panjabi et al. (2000) ± ± ± ±0.5 NA Bozbuga et al. (2004) 8 6.9± ± ± ±0.6 NA Kayalioglu et al. (2007) ± ± ± ±0.97 NA Liu J et al. (2010) ± ± ± ± ±0.81 Present Study Left side 6.66± ± ± ± ±1.09 Right side 6.15± ± ± ± ±1.02 the authorities of Central Mechanical Engineering Research Institute, Durgapur and Bengal Engineering and Science University, Shibpur for permitting to take up this study. Also, the authors are thankful to Council of Scientific and Industrial Research (CSIR), Government of India for sponsoring the research project. Conflict of interest The authors declare that they have no conflict of interest. References 1. Karaikovic EE, Daubs MD, Madsen RW, Gaines RW Jr: Morphologic characteristics of human cervical pedicle. Spine 1997; 22: Van Eck PJ, Chaffin DB, Foust DR, Baum JK, Snyder RG: A bibliography of whiplash and cervical kinematic measurement. Ann Arbor, University of Michigan, UM-HSRI- B1-73-6, White AA III and Panjabi MM. Clinical Biomechanics of the Spine. J.B. Lippincott Company, Philadelphia, Duray SM, Morter HB, Smith FJ. Morphological variation in cervical spinous processes: potential applications in the forensic identification of race from the skeleton. J Forensic Science 1999; 44(5): Yoganandan N, Knowles SA, Maiman DJ, Pintar FA. Anatomic study of the morphology of human cervical facet joint. Spine 2003; 28: Kettler A, Werner K, Wilke HJ. Morphological changes of cervical facet joints in elderly individuals. Eur Spine J 2007; 16: Kayalioglu G, Erturk M, Varol T, Cezayirli E. Morphometry of the cervical vertebral pedicles as a guide for transpedicular screw fixation. Neurol Med Chir (Tokyo) 2007; 47: Bozbuga M, Ozturk A, Ari Z, Sahinoglu K, Bayraktar B, Cecen A. Morphometric evaluation of subaxial cervical vertebrae for surgical application of transpedicular screw fixation. Spine 2004; 29: Ebraheim NA, Xu R, Knight T, Yeasting RA. Morphometric evaluation of lower cervical pedicle and its projection. Spine 1997; 22: Jones EL, Heller JG, Silcox DH, Hutton WC. Cervical pedicle screws versus lateral mass screws: anatomic feasibility and biomechanical comparison. Spine 1997; 22: Panjabi MM, Duranceau J, Goel V, Oxland T, Takata K. Cervical human vertebrae: quantitative three-dimensional anatomy of the middle and lower regions. Spine 1991; 16: Panjabi MM, Shin EK, Chen NC, Wang JL. Internal morphology of human cervical pedicles. Spine 2000; 25: Ugur HC, Attar A, Uz A, Tekdemir I, Egemen N, Caglar S, Genc Y. Surgical anatomic evaluation of the cervical pedicle and adjacent neural structures. Neurosurgery 2000; 47: Stanescu S, Ebraheim NA, Yeasting R, Bailey AS, Jackson WT. Morphometric evaluation of the cervico-thoracic junction. Spine 1994; 19: Ruofu Z, Huilin Y, Xiaoyun H, Xishun H, Tiansi T, Liang C, 75

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