JBJS | Growth and Development of the Pediatric Cervical Spine Documented Radiographically

The Journal of Bone & Joint Surgery, Volume 83, Issue 8

Articles | August 01, 2001

Growth and Development of the Pediatric Cervical Spine Documented Radiographically

Jeffrey C. Wang, MD; Stephen L. Nuccion, MD; John E. Feighan, MD; Brad Cohen, MD; Frederick J. Dorey, PhD; Peter V. Scoles, MD

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Investigation performed at the Department of Orthopaedic Surgery, University of California at Los Angeles School of Medicine, Los Angeles, California, and the Department of Orthopaedic Surgery, Case Western Reserve University, Cleveland, Ohio
Jeffrey C. Wang, MD
Stephen L. Nuccion, MD
Frederick J. Dorey, PhD
Department of Orthopaedic Surgery, University of California at Los Angeles School of Medicine, Box 956902, Los Angeles, CA 90095-6902

John E. Feighan, MD
Brad Cohen, MD
Department of Orthopaedic Surgery, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106

Peter V. Scoles, MD
National Board of Medical Examiners, 3750 Market Street, Philadelphia, PA 19104-3190

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

The Journal of Bone & Joint Surgery. 2001; 83:1212-1218

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Abstract

Background: The radiographic anatomy of the cervical spine in children is complex and can be difficult to interpret. The present study was undertaken to document radiographically the growth and development of the cervical spine in a prospective, longitudinal manner and to establish standard radiographic measurements on the basis of findings in patients who were followed serially from the age of three months until skeletal maturity.

Methods: The radiographic resources of the Cleveland Study of Normal Growth and Development (Bolton-Brush Collection, Cleveland, Ohio) were reviewed. From this large database, we identified fifty boys and forty-six girls who had a sufficient number of radiographs of the cervical spine for inclusion in our study. With use of a computerized image analyzer, the growth and development of the atlantodens interval, the diameter of the spinal canal, the Torg ratio, the height and width of the second through fifth cervical vertebral bodies, the height of the dens, and the ossification of the first cervical vertebra were assessed on serial radiographs made from the age of three months until skeletal maturity.

Results: Serial measurements of the atlantodens interval, the anteroposterior diameter of the cervical canal, the height and anteroposterior width of the cervical vertebral bodies, and the height of the dens, made in normal, healthy children from the age of three months to fifteen years, are presented in tabular and graphic forms. The median Torg ratio was 1.47 for both males and females primarily, and it reached values of 1.06 for males and 1.10 for females by maturity. The anterior arch of the first cervical vertebra had ossified in 33% of the children by the age of three months and in 81% of the children by the age of one year. Closure of the synchondroses was completed in all children by the age of three years.

Conclusions: The measurements presented in the current study are important because they are the first, as far as we know, to document the radiographic parameters of the cervical spine in children who were followed longitudinally from before the age of three years through the course of growth and development until skeletal maturity.

Figures in this Article

Introduction

The radiographic appearance of the pediatric cervical spine is an important tool for the detection of congenital malformations, neoplasms, and injuries^1-7. The potentially devastating consequences of undiagnosed abnormalities have prompted clinicians in a number of disciplines to develop guidelines to aid in the interpretation of pediatric cervical radiographs.

Proper interpretation of radiographs of the immature cervical spine requires accurate normal standards. Many investigators have calculated norms for the cephalad portion of the cervical spine in adults with use of radiographic and anatomical techniques^8-10. The relationship of the spinal cord to the osseous structures of the cervical spine is of critical importance. Fractures, dislocations, and subluxations of the neck may encroach upon the cervical canal and impinge upon the cord. Although spinal injuries in infants and children are uncommon, they tend to involve the cervical spine more than the thoracic or lumbar spine and tend to affect the cephalad portion of the cervical spine more than the caudad portion¹¹.

It is clear from previous studies that the diameter of the cervical spinal canal and the size of the cervical vertebral bodies change differentially with growth. Other investigators have proposed broad standards for normal canal size in childhood. Simril and Thurston proposed standards for the thoracic and lumbar interpedicular spaces in children, but they did not study the cervical spine because of the difficulty in differentiating the junction of the lamina and the pedicle¹². The studies by Hinck et al.¹³, Markuske¹⁴, and Naik¹⁵ have been used as references for the evaluation of patients with developmental, neoplastic, and traumatic lesions of the cervical spine. Although useful, none of these studies were truly longitudinal. The advantage of a longitudinal study is that the values are obtained from the same patients as they grow rather than from different patients at various ages and then averaged. Longitudinal studies result in a more accurate method of assessing changes in anatomy with growth and development.

The present radiographic standards for children and adolescents have been established from studies of small groups of patients^1,10,12,13. We are not aware of any previous longitudinal study in which the growth and development of the cervical spine has been followed from birth to maturity. The purpose of our study was to document radiographically the growth and development of the cervical spine in a highly controlled, longitudinal manner and to establish standard radiographic measurements for the pediatric cervical spine. We assessed the atlantodens interval, the canal diameter, the Torg ratio, the height and width of the second through fifth cervical vertebral bodies, the height of the dens, and the ossification of the anterior arch of the first cervical vertebra in patients from the age of three months until skeletal maturity¹⁶.

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Fig. 1:: Diagram of the method that was used to measure the variables that were examined. The diagram on the left shows the tracing of the cephalad part of the cervical spine. The diagram on the right demonstrates some, but not all, of the variables that were measured. A = width of the dens, B = sagittal diameter of the canal at the first cervical level, C = width of the second cervical vertebra, D = sagittal diameter of the canal at the second cervical level, E = sagittal diameter of the third cervical vertebral body, F = sagittal diameter of the canal at the third cervical level, and G = height of the fourth cervical vertebra.

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Fig. 2:: Values (in millimeters) for the tenth percentile, the median, and the ninetieth percentile for the atlantodens interval (ADI), graphed continuously over time.

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Fig. 3:: Values (in millimeters) for the tenth percentile, the median, and the ninetieth percentile for the sagittal diameter of the canal at the second cervical level, graphed continuously over time.

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Fig. 4:: Values for the tenth percentile, the median, and the ninetieth percentile for the Torg ratio, graphed continuously over time.

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Fig. 5:: Values (in millimeters) for the tenth percentile, the median, and the ninetieth percentile for the height of the body of the second cervical vertebra, graphed continuously over time.

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: TABLE I Data on the Atlantodens Interval and the Canal Diameters According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Atlantodens interval (mm)	?2.02 (0.40)	?2.16 (0.57)	?2.19 (0.67)	?2.16 (0.96)	?1.91 (0.51)	?1.83 (0.64)
Diameter of canal (mm)
Second cervical level	15.63 (1.01)	17.89 (1.19)	18.22 (1.35)	14.73 (1.21)	17.02 (1.39)	17.42 (1.63)
Third cervical level	13.92 (0.88)	15.55 (1.19)	15.76 (1.34)	13.30 (0.98)	14.93 (1.08)	15.44 (1.20)
Fourth cervical level	13.51 (0.84)	15.06 (1.09)	15.37 (1.28)	13.00 (0.92)	14.64 (0.99)	14.93 (1.35)
Fifth cervical level	13.79 (0.89)	14.98 (1.03)	15.22 (1.41)	13.41 (1.21)	14.79 (1.00)	14.82 (1.29)

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: TABLE I Data on the Atlantodens Interval and the Canal Diameters According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Atlantodens interval (mm)	?2.02 (0.40)	?2.16 (0.57)	?2.19 (0.67)	?2.16 (0.96)	?1.91 (0.51)	?1.83 (0.64)
Diameter of canal (mm)
Second cervical level	15.63 (1.01)	17.89 (1.19)	18.22 (1.35)	14.73 (1.21)	17.02 (1.39)	17.42 (1.63)
Third cervical level	13.92 (0.88)	15.55 (1.19)	15.76 (1.34)	13.30 (0.98)	14.93 (1.08)	15.44 (1.20)
Fourth cervical level	13.51 (0.84)	15.06 (1.09)	15.37 (1.28)	13.00 (0.92)	14.64 (0.99)	14.93 (1.35)
Fifth cervical level	13.79 (0.89)	14.98 (1.03)	15.22 (1.41)	13.41 (1.21)	14.79 (1.00)	14.82 (1.29)

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: TABLE II Data on the Width and Height of the Cervical Vertebrae According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Width (mm)
Second cervical vertebra	10.41 (0.61)	12.88 (0.82)	14.52 (0.98)	?9.79 (0.70)	12.49 (0.84)	14.30 (1.02)
Third cervical vertebra	10.36 (0.62)	12.93 (0.84)	14.53 (0.97)	?9.74 (0.65)	12.26 (0.91)	13.86 (0.95)
Fourth cervical vertebra	10.37 (0.62)	12.76 (1.18)	14.10 (1.18)	?9.68 (0.69)	12.11 (0.92)	13.38 (1.08)
Fifth cervical vertebra	10.57 (0.66)	12.57 (0.95)	13.94 (1.60)	10.05 (0.74)	12.03 (1.24)	13.64 (1.17)
Height (mm)
Second cervical vertebra	18.79 (5.03)	27.54 (3.26)	33.65 (3.71)	18.92 (5.49)	27.48 (3.09)	34.28 (3.75)
Third cervical vertebra	?5.52 (1.18)	?7.82 (1.29)	11.51 (2.45)	?5.84 (1.18)	?8.09 (1.20)	11.56 (2.69)
Fourth cervical vertebra	?5.41 (1.24)	?7.77 (1.15)	10.98 (2.12)	?5.70 (1.17)	?8.01 (1.24)	11.27 (2.43)
Fifth cervical vertebra	?5.47 (1.19)	?7.53 (0.99)	10.51 (2.10)	?5.74 (1.12)	?7.69 (1.10)	10.79 (2.16)

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: TABLE II Data on the Width and Height of the Cervical Vertebrae According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Width (mm)
Second cervical vertebra	10.41 (0.61)	12.88 (0.82)	14.52 (0.98)	?9.79 (0.70)	12.49 (0.84)	14.30 (1.02)
Third cervical vertebra	10.36 (0.62)	12.93 (0.84)	14.53 (0.97)	?9.74 (0.65)	12.26 (0.91)	13.86 (0.95)
Fourth cervical vertebra	10.37 (0.62)	12.76 (1.18)	14.10 (1.18)	?9.68 (0.69)	12.11 (0.92)	13.38 (1.08)
Fifth cervical vertebra	10.57 (0.66)	12.57 (0.95)	13.94 (1.60)	10.05 (0.74)	12.03 (1.24)	13.64 (1.17)
Height (mm)
Second cervical vertebra	18.79 (5.03)	27.54 (3.26)	33.65 (3.71)	18.92 (5.49)	27.48 (3.09)	34.28 (3.75)
Third cervical vertebra	?5.52 (1.18)	?7.82 (1.29)	11.51 (2.45)	?5.84 (1.18)	?8.09 (1.20)	11.56 (2.69)
Fourth cervical vertebra	?5.41 (1.24)	?7.77 (1.15)	10.98 (2.12)	?5.70 (1.17)	?8.01 (1.24)	11.27 (2.43)
Fifth cervical vertebra	?5.47 (1.19)	?7.53 (0.99)	10.51 (2.10)	?5.74 (1.12)	?7.69 (1.10)	10.79 (2.16)

Materials and Methods

The radiographic resources of the Cleveland Study of Normal Growth and Development (Bolton-Brush Collection, Cleveland, Ohio) were reviewed. The collection was compiled from 1927 to 1942 and includes data only from healthy children with no evidence of congenital, neurological, or developmental disease who were evaluated at regular intervals from the age of three months until skeletal maturity^17,18. Approximately 3000 children participated in the overall study. The Gruelich and Pyle atlases of skeletal maturation of the hand, wrist, and knee were developed from this database¹⁹.

Approximately 200 children participated in the radiographic evaluation of the cervical spine. Each subject was to have a plain lateral radiograph of the cranium and the cervical spine made at the ages of three, six, nine, twelve, eighteen, twenty-four, thirty, thirty-six, forty-two, forty-eight, fifty-four, and sixty months and then annually until the age of seventeen years. A standard tube-to-film distance was used with a film-to-focal spot distance of approximately 72 in (183 cm). The head was immobilized in a rigid frame during the exposures. Fifty boys and forty-six girls had a sufficient number of radiographs of the cervical spine for inclusion in the present study. This group was considered to be eligible for our study on the basis of the clarity of the radiographs and the availability of studies that had been made until skeletal maturity. Radiographs were considered to be suboptimal if they were blurred by motion or if any of the osseous structures were obscured by the head-holder; suboptimal studies were not included in the analysis. Additionally, not every child had each scheduled radiograph. However, radiographs were available for a total of more than seventy-five subjects at each time-point before the age of twelve years. More than one-half of the subjects had radiographs made until the age of fourteen years, and approximately one-third of the subjects had radiographs made until the age of seventeen years.

The outline of the cervical spine on each radiograph was traced onto a transparent sheet. Examples of some of the measured variables are shown in Figure 1. As the radiographs frequently did not include the sixth and seventh cervical vertebrae, these levels were not included in the measurements. Vertical lines were placed along the most anterior and posterior points of the vertebral bodies and along the most anterior point of the posterior arches, along the posterior portion of the anterior aspect of the atlas, and along the anterior portion of the dens. Horizontal lines were placed along the most superior and inferior portions of the vertebral bodies. Images were entered into a computer with use of a SummaSketch Plus digitizing pad (SummaGraphics, GTCO CalComp, Scottsdale, Arizona). The images were analyzed with use of a custom-designed software program written in Turbo Basic.

The atlantodens interval was measured as the distance between the posterior aspect of the anterior arch of the first cervical vertebra and the anterior aspect of the dens in the anteroposterior direction. The sagittal diameter of the canal at the second cervical level was measured from the most anterior aspect of the posterior arch of that vertebra to the posterior aspect of the dens at the same level on a horizontal line in the anteroposterior direction on the lateral radiograph. For the third, fourth, and fifth cervical vertebrae, the sagittal diameter of the canal was measured from the most anterior portion of the posterior arch to the center of the posterior aspect of the corresponding vertebral body along the anteroposterior plane. The Torg ratio was also calculated, in the fashion originally described by Torg, by dividing the value for the sagittal diameter of the canal at the fifth cervical level by the anteroposterior diameter of the vertebral body¹⁶. The width of the second, third, fourth, and fifth cervical vertebral bodies was measured at the midpoint of the posterior aspect of each vertebral body. The vertical height was measured at both the anterior and posterior portions of these vertebral bodies. The average of the anterior and posterior heights for each vertebral body was used to calculate the height of the individual vertebra. The height of the second cervical vertebra was measured from the inferior aspect of the vertebral body to the tip of the dens. The height of the dens itself was measured from the tip of the dens to the synchondrosis. All measurements were recorded in millimeters, and individual plots were made for each subject.

Once all of the measurements had been made, they were analyzed in the following statistical fashion. For each variable x, a quadratic polynomial equation with the formula y = a + bx + cx² was solved with use of linear regression for each individual. The predicted value at each time-point for each individual was used to calculate the distribution of measurements for each time-period. The tenth percentile, median, and ninetieth percentile values were subsequently calculated at each time-point and graphed over time. The data were also summarized by calculating, separately for males and females, the median value and the standard deviation for three different age-groups (zero to sixty months, sixty-one to 120 months, and 121 to 180 months).

Results

The study began with forty-six female subjects and fifty male subjects. Some radiographs could not be included in the study for technical reasons, and some subjects were lost to follow-up as the study progressed. The sample size for the male and female subjects who had radiographs that could be measured remained fairly constant until a gradual attrition of subjects began at the age of ten years and continued until the age of seventeen years. Forty-four (96%) of the original forty-six female subjects and forty-seven (94%) of the original fifty male subjects had radiographs made until the age of ten years. Only twenty-one female subjects and seventeen male subjects were followed for more than fifteen years. There was equal representation of both boys and girls at all time-points. The results are presented in Tables I and II.

The Atlantodens Interval

At six months, the median atlantodens interval was 1.97 mm for boys and 2.01 mm for girls. By 180 months, the median value had reached 2.45 mm for both boys and girls. A graph of the results is shown in Figure 2.

Canal Diameter

In male subjects, the median canal diameter at the second cervical level increased from 12.79 mm at six months to 16.00 mm by 156 months and remained constant thereafter. In female subjects, the median canal diameter at the second cervical level increased from 12.27 mm at six months to 15.75 mm by 168 months. A graph of the results is shown in Figure 3. The canal diameters at the third and fourth cervical levels were nearly identical in terms of both dimension and rate of change. In male subjects, the median canal diameter increased from 12.33 mm initially to 15.54 mm by maturity. In female subjects, the median canal diameter at these levels increased from 11.76 mm to 15.31 mm. In male subjects, the median canal diameter at the fifth cervical level increased from 12.74 mm to 15.67 mm, and in female subjects, it increased from 12.26 mm to 15.22 mm.

Torg Ratio

The median Torg ratio (the ratio of the canal diameter to the vertebral body diameter) at the fifth cervical level was 1.47 (tenth to ninetieth percentile, 1.26 to 1.64) at three months and 1.06 (0.81 to 1.33) by maturity for male subjects and 1.47 (1.04 to 1.75) and 1.10 (0.88 to 1.20), respectively, for female subjects. A graph of the results is shown in Figure 4.

Width of the Cervical Vertebral Bodies

The median width of the second cervical vertebral body increased from 9.13 mm initially to 15.15 mm by maturity for male subjects and from 8.40 mm to 14.90 mm for female subjects. The median width of the third cervical vertebral body increased from 9.04 mm to 14.64 mm for males and from 8.38 mm to 14.12 mm for females. The median width of the fourth cervical vertebral body increased from 9.28 mm to 14.60 mm for males and from 8.48 mm to 13.87 mm for females. The median width of the fifth cervical vertebral body increased from 9.47 mm to 14.44 mm for males and from 8.96 mm to 13.81 mm for females.

Height of the Cervical Vertebral Bodies

The median height of the second cervical vertebral body was 14.51 mm initially and 35.54 mm by maturity for males and 14.05 mm and 34.29 mm, respectively, for females. A graph of the results is shown in Figure 5. The median height of the third cervical vertebra increased from 4.68 mm to 13.94 mm for males and from 5.10 mm to 12.23 mm for females. The median height of the fourth cervical vertebra increased from 4.45 mm to 12.89 mm for males and from 4.69 mm to 11.69 mm for females. The median height of the fifth cervical vertebra increased from 4.47 mm to 12.47 mm for males and from 4.89 mm to 11.17 mm for females.

Height of the Dens

The initial median height of the dens was 5.78 mm (tenth to ninetieth percentile, 5.21 to 6.85) for males and 5.66 mm (4.96 to 6.68) for females. By maturity, the dens had attained a median height of 10.35 mm (9.33 to 11.77) for males and 10.61 mm (9.21 to 12.23) for females.

Ossification of the First Cervical Vertebra

The anterior arch had ossified in 33% of the children by three months and in 81% of the children by one year. Ossification was complete in all children by three years of age.

Discussion

Standard values have been proposed in the literature for the atlantodens interval, the contour of the odontoid process, the width of the spinal canal at each cervical level, the proportion of the canal occupied by the dens at the first cervical level, and the ratio of the cervical canal to the width of the vertebral body (the Torg ratio)^{1,2,4,8-11,13-15,20}. The standard values were based on studies involving a review of the radiographs of the cervical spine of neurologically normal adults or on small studies of cadavera.

The studies by Markuske¹⁴, Hinck et al.¹³, and Naik¹⁵ in particular have been used as references for the evaluation of patients with developmental, neoplastic, and traumatic lesions of the cervical spine. Although useful, these studies were not truly longitudinal and provide only limited information about the growth of the pediatric cervical spine.

Markuske measured the sagittal diameter of the cervical canal in three groups of forty patients each who were stratified according to age (three to six years old, seven to ten years old, or eleven to fourteen years old)¹⁴. In addition to providing the mean diameter (and standard deviation) of the canal for each group, he standardized the relationship between the diameter of the canal and the height of the patient (in 10-cm increments) for the entire sample population. His findings showed a slight increase in sagittal diameter at each vertebral level as the patients increased in both height and age. Markuske’s study, however, was not longitudinal. Furthermore, the increase in the diameter of the cervical canal from the three to six-year-old age-group to the eleven to fourteen-year-old age-group was within the standard deviation for both groups. Markuske did not investigate the diameter of the canal in infants, and his findings cannot be used as standards for children who are less than three years old, a group that is characterized by substantial growth and development.

Hinck et al. attempted to study the longitudinal development of the cervical canal over a ten-year period in patients who were three years of age and older¹³. They proposed reference standards for the first through the fifth cervical vertebra. Unfortunately, none of the patients were followed for the full ten-year period. In addition, the study only included patients who had reached the age of three years, by which time the majority of changes in the cervical spine have already occurred.

Naik proposed a method for calculating the sagittal diameter of the cervical spinal canal in infants, which can be difficult because of the cartilaginous nature of the lamina posteriorly¹⁵. Measurements on twenty-five radiographs were compared with findings on eleven postmortem dissections of the cervical spine. The measurements were found to be within 2 mm of each other. However, neither standard deviations nor the ages of the subjects were noted in that study. Additionally, the sample size was quite small.

Locke et al. studied 200 children of various ages to construct standards for the atlantodens interval in the asymptomatic child²⁰. Although Locke et al. contributed valuable information, their study differs from the present study in several regards. They studied children of various ages at a single time-point, whereas we examined children on a longitudinal basis. Their patients were at least three years old, whereas our patients were followed beginning at the age of three months. Additionally, Locke et al. measured only the atlantodens interval, whereas we evaluated a wide variety of radiographic dimensions of the cervical spine in the growing child. The atlantodens interval is a radiographic representation of the relationship between the posterior aspect of the anterior arch of the first cervical vertebra and the anterior aspect of the odontoid process. The normal value suggests that the transverse ligament and the other check ligaments are still functional.

A standard set of normal values for the cervical vertebral bodies has not been published in the literature. Very few, if any, investigators have even attempted to examine the growth and development of the pediatric cervical vertebral body¹. Most investigators have concentrated on depicting standard values for the cervical canal^14,15. Swischuk et al. examined the lateral radiographs of the cervical spine of 481 pediatric patients to assess the configuration of the vertebral bodies²¹. Their findings demonstrated that cervical vertebral bodies are oval early in infancy and become more rectangular as maturation proceeds. That study was not longitudinal. The authors also did not attempt to provide numerical values for the vertebrae as they developed.

It is important to note that the current study is an examination of radiographic manifestations and measurements of development and applies only to the portion of the skeleton that has transformed into bone.

To our knowledge, the present investigation is the first prospective, highly controlled study in which the growth and development of the cervical spine was assessed in a longitudinal manner from the age of three months to skeletal maturity. We found that the cervical canal grows rapidly during the first three years of life, by which time it has reached nearly 95% of its mature diameter. The increase in the height of the third, fourth, and fifth vertebral bodies was linear from the age of six months to maturity, but the growth of the second cervical vertebra was most rapid in the first five years of life and became linear thereafter. This appears to be a function of the increasing height of the dens, and it may be an artifact of the ossification of the superior portion of the dens. Our findings indicate that the vertebral bodies grow rapidly during the first five years of life and then continue to grow at a slower rate until maturity. The normal dimensions of the developing spine that are documented in the present study can be used as reliable growth standards for female and male children. Clinical comparisons can be made to assess a patient with regard to age, the potential further development of the cervical spine, and the radiographic standards for the anatomical structures.

Appendix

The present study was performed in an attempt to establish normal values for the cervical canal, atlantodens interval, Torg ratio, and height and width of the cervical vertebral bodies in the pediatric population. Although the growth patterns and development of the cervical spine are reported, complete presentation of all of the data demonstrating all of the values, norms, and percentiles for the all of the measurements according to the ages of the patients is beyond the scope of this single article. These data have been calculated and sorted into multiple graphs according to gender and age and are available with the electronic versions of this article, on our web site (www.jbjs.org) and on our CD-ROM (call 781-449-9780, ext. 140, to order).

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Fig. 2:: Values (in millimeters) for the tenth percentile, the median, and the ninetieth percentile for the atlantodens interval (ADI), graphed continuously over time.

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Fig. 4:: Values for the tenth percentile, the median, and the ninetieth percentile for the Torg ratio, graphed continuously over time.

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Fig. 5:: Values (in millimeters) for the tenth percentile, the median, and the ninetieth percentile for the height of the body of the second cervical vertebra, graphed continuously over time.

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: TABLE I Data on the Atlantodens Interval and the Canal Diameters According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Atlantodens interval (mm)	?2.02 (0.40)	?2.16 (0.57)	?2.19 (0.67)	?2.16 (0.96)	?1.91 (0.51)	?1.83 (0.64)
Diameter of canal (mm)
Second cervical level	15.63 (1.01)	17.89 (1.19)	18.22 (1.35)	14.73 (1.21)	17.02 (1.39)	17.42 (1.63)
Third cervical level	13.92 (0.88)	15.55 (1.19)	15.76 (1.34)	13.30 (0.98)	14.93 (1.08)	15.44 (1.20)
Fourth cervical level	13.51 (0.84)	15.06 (1.09)	15.37 (1.28)	13.00 (0.92)	14.64 (0.99)	14.93 (1.35)
Fifth cervical level	13.79 (0.89)	14.98 (1.03)	15.22 (1.41)	13.41 (1.21)	14.79 (1.00)	14.82 (1.29)

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: TABLE I Data on the Atlantodens Interval and the Canal Diameters According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Atlantodens interval (mm)	?2.02 (0.40)	?2.16 (0.57)	?2.19 (0.67)	?2.16 (0.96)	?1.91 (0.51)	?1.83 (0.64)
Diameter of canal (mm)
Second cervical level	15.63 (1.01)	17.89 (1.19)	18.22 (1.35)	14.73 (1.21)	17.02 (1.39)	17.42 (1.63)
Third cervical level	13.92 (0.88)	15.55 (1.19)	15.76 (1.34)	13.30 (0.98)	14.93 (1.08)	15.44 (1.20)
Fourth cervical level	13.51 (0.84)	15.06 (1.09)	15.37 (1.28)	13.00 (0.92)	14.64 (0.99)	14.93 (1.35)
Fifth cervical level	13.79 (0.89)	14.98 (1.03)	15.22 (1.41)	13.41 (1.21)	14.79 (1.00)	14.82 (1.29)

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: TABLE II Data on the Width and Height of the Cervical Vertebrae According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Width (mm)
Second cervical vertebra	10.41 (0.61)	12.88 (0.82)	14.52 (0.98)	?9.79 (0.70)	12.49 (0.84)	14.30 (1.02)
Third cervical vertebra	10.36 (0.62)	12.93 (0.84)	14.53 (0.97)	?9.74 (0.65)	12.26 (0.91)	13.86 (0.95)
Fourth cervical vertebra	10.37 (0.62)	12.76 (1.18)	14.10 (1.18)	?9.68 (0.69)	12.11 (0.92)	13.38 (1.08)
Fifth cervical vertebra	10.57 (0.66)	12.57 (0.95)	13.94 (1.60)	10.05 (0.74)	12.03 (1.24)	13.64 (1.17)
Height (mm)
Second cervical vertebra	18.79 (5.03)	27.54 (3.26)	33.65 (3.71)	18.92 (5.49)	27.48 (3.09)	34.28 (3.75)
Third cervical vertebra	?5.52 (1.18)	?7.82 (1.29)	11.51 (2.45)	?5.84 (1.18)	?8.09 (1.20)	11.56 (2.69)
Fourth cervical vertebra	?5.41 (1.24)	?7.77 (1.15)	10.98 (2.12)	?5.70 (1.17)	?8.01 (1.24)	11.27 (2.43)
Fifth cervical vertebra	?5.47 (1.19)	?7.53 (0.99)	10.51 (2.10)	?5.74 (1.12)	?7.69 (1.10)	10.79 (2.16)

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: TABLE II Data on the Width and Height of the Cervical Vertebrae According to Gender and Age*

*The values are given as the median, with the standard deviation in parentheses.

Variable	Male			Female
0-60 mo	61-120 mo	121-180 mo	0-60 mo	61-120 mo	121-180 mo
Width (mm)
Second cervical vertebra	10.41 (0.61)	12.88 (0.82)	14.52 (0.98)	?9.79 (0.70)	12.49 (0.84)	14.30 (1.02)
Third cervical vertebra	10.36 (0.62)	12.93 (0.84)	14.53 (0.97)	?9.74 (0.65)	12.26 (0.91)	13.86 (0.95)
Fourth cervical vertebra	10.37 (0.62)	12.76 (1.18)	14.10 (1.18)	?9.68 (0.69)	12.11 (0.92)	13.38 (1.08)
Fifth cervical vertebra	10.57 (0.66)	12.57 (0.95)	13.94 (1.60)	10.05 (0.74)	12.03 (1.24)	13.64 (1.17)
Height (mm)
Second cervical vertebra	18.79 (5.03)	27.54 (3.26)	33.65 (3.71)	18.92 (5.49)	27.48 (3.09)	34.28 (3.75)
Third cervical vertebra	?5.52 (1.18)	?7.82 (1.29)	11.51 (2.45)	?5.84 (1.18)	?8.09 (1.20)	11.56 (2.69)
Fourth cervical vertebra	?5.41 (1.24)	?7.77 (1.15)	10.98 (2.12)	?5.70 (1.17)	?8.01 (1.24)	11.27 (2.43)
Fifth cervical vertebra	?5.47 (1.19)	?7.53 (0.99)	10.51 (2.10)	?5.74 (1.12)	?7.69 (1.10)	10.79 (2.16)