Helene Pavlov, MD #{149}Joseph S. Torg, MD #{149}Bruce Robie, MS #{149}Caren Jahre, MD

Cervical Spinal Stenosis: Determinationwith Vertebral Body Ratio Method’

771

Transient bilateral sensory and mo-tor symptoms after trauma, includ-ing complete paralysis, have beenidentified in patients with cervicalspinal stenosis. Radiographs of 23patient athletes with cervical spinalneurapraxia were used for measure-ment of the cervical spinal canal.Two methods of measurement wereused. In the conventional method,sagittal diameter is measured fromthe posterior surface of the verte-bra! body to the nearest point of thecorresponding laminar line. In theratio method, the sagittal diameterof the spinal canal is divided by thesagittal diameter of the correspond-ing vertebra! body. Results indicatethe ratio method is reliable for de-termining cervical spinal stenosisand is independent of technical fac-tor variables.

Index terms: Spinal canal, stenosis, 31.77

#{149}Spine, abnormalities #{149}Spine. injuries, 31.4

S Spine, radiography, 31.11

Radiology 1987; 164:771-775

1 From the Departments of Radiology (H.P.,C.J.) and Biomechanics (BR.), Hospital for Spe-cial Surgery. 535 E. 70th Street, New York, NYiOO2l, affiliated with New York Hospital-Cor-nell University Medical College. New York;and the Department of Orthopaedic Surgery,University of Pennsylvania. Philadelphia(J.S.T.). Received September 1 1, 1986; revision

requested October 22; revision received April

6, 1987; accepted April 8. Address reprint re-quests to H.P.

e RSNA, 1987

W E have previously reported aclinical and radiographic me-

view of the data on 31 patients with

transient cervical spinal neurapraxia

(1). These patients are young athletes

who experienced sudden sensory

changes that may be associated with

motor symptoms in both arms, both

legs, on all four extremities. Sensory

changes include numbness, burning,

tingling, and paresthesia. Motor

symptoms include weakness and

complete paralysis. These symptoms

are precipitated by sudden hypenex-

tension, hyperflexion, or axial load to

the cervical spine and last a few sec-

onds to 36 hours, with complete me-

covemy. Cervical spine radiogmaphs in

these patients demonstrate congeni-

tal anomalies, disk disease, instabil-

ity, or “normal” findings. Although

cervical spinal stenosis was suspected

clinically, standard radiographic

measurement of the sagittal canal di-

ameten was not always confirmatory.

The purposes of this paper are (a) to

introduce the ratio method of deter-

mining cervical spinal stenosis to the

radiographic literature, (b) to deter-

mine the ratio values in male and fe-

male control groups, and (c) to ex-

plain the radiographic rationale for

the use of this method.

REVIEW OF LITERATURE

Multiple investigators have report-

ed the measurement of the sagittal

diameter of the cervical spinal cord

as a means of diagnosing spinal ste-

nosis. These reports have resulted in

inconsistencies in “normal” and “ab-

normal” values for the sagittal diam-

eten of the cervical spine. Of the van-

ous techniques and measurements

reported, the most commonly em-

ployed method for determining the

sagittal diameter of the spinal canalmakes use of a lateral view of the cer-

vical spine and measures the distance

from the cephalocaudal midpoint

(middle of the posterior surface) of

the vertebral body to the nearest

point of the corresponding spinal

laminar line, which Wilkinson et al.

(2) called the preexisting sagittal di-

ameter (2-8). Using this technique,

Boijsen (3) reported the average non-

mal sagittal diameter for C-4 to C-6 to

be 18.5 mm (range, 14.2-23 mm), andHinck et al. (4) reported the average

measurement for C-3 to C-5 to be 17.0

mm (range, 13.9-20.3 mm); in both

studies, the investigators used a tan-

get distance of 5 feet. Moiel et al. (5),

Payne and Spillane (6), and Wolf et

al. (8) determined the average nor-

mal sagittal diameter of the cervical

spine to be 17.0 mm ± 5; these inves-

tigatons used a target distance of 6

feet. Using this method, Epstein et al.

(9, 10) and Countee and Vijayanathan

(ii) reported severe spinal stenosis at

less than 13 mm and less than 14 mm,

respectively.

Wilkinson et al. (2) reported mea-

sunements from four clinical sub-

groups: one group of patients with

neck and arm pain but without neu-

nologic symptoms and three groups

of patients with neunologic symp-

toms. The cervical sagittal diameter

was largest in those patients without

radiculan pain; the average measure-

ment for C-3 to C-5 was 16.6 mm. A

target distance of 6 feet was used.

Chnispin and Lees (12) found that

on the lateral radiograph, the project-

ed canal area of myelopathic patients

was smaller than the projected verte-

bral body area, but that in nonmyelo-

pathic subjects, the projected canal

and vertebral body areas were ap-

proximately equal. They determined

the actual weights of these areas by

using tracings and cutouts of the ma-

diognaphs. They concluded that in

patients with cervical spondylolysis

and myelopathy, the ratio of the area

of the spinal canal to the area of the

vertebral body was less than 85%.

Ehni (13) simplified their observa-

tion by assuming that since the verti-

cal heights of the spinal canal and

2.0

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Figure 1. The sagittal diameter of the spi-nal canal (a) is measured from the posteriorsurface of the vertebral body to the nearestpoint of the corresponding spinal laminarline. The sagittal diameter of the vertebral

body (b) is measured at the midpoint, fromthe anterior surface to the posterior surface.The spinal canal/vertebral body ratio is de-termined with the formula a/b. The normalratio is approximately 1.00.

the vertebral body are the same, theheight can be eliminated in the for-

mula and, instead of area, the anteno-

posterior diameter of the spinal canal

can be compared directly with that of

the vertebral body. He reported that

in the absence of spondylolytic my-

elopathy, the canal depth is equal to

on greaten than the vertebral body di-

mension, whereas a canal depth of

80%-85% that of the vertebral body

dimension increases the probability

that spondylolytic myelopathy is

present. He also reported that if the

canal depth is only 80% that of the

vertebral body, spondylolytic my-

elopathy is probable, and that if the

canal depth is 50%-75% that of the

body, spondylolytic myelopathy is a

near certainty.

Multiple authors have reported the

association of neunologic symptoms

with spinal stenosis (2, 5-30). Kessler

(14) reported that a diameter of the

cervical spinal canal less than i4 mm

is significant and described two types

of associated symptoms: (a) the sud-

den onset of myelopathy without me-

gression and (b) a brief transient epi-

sode lasting minutes or hours. It was

0 0 0

00 0 ‘-4

0 0 0

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.*

ci

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772 #{149}Radiology September 1987

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MATERIALS AND METHODS

Volume 164 Number 3 Radiology #{149}773

Figure 2. Lateral view of the cervical spine

of a patient with an episode of transient cer-

vical spinal neurapraxia. In this patient withcervical spinal stenosis, the spinal canal/

vertebral body ratio was approximately 0.50.

his observation that either type of

myelopathy could occur with in-

creased physical activity without

trauma or hyperextension of the

neck; he attributed intermittent

symptoms to cord claudication. In

older people, neunologic symptoms

have been attributed to thickening of

the ligamentum flavum on hypentro-

phic proliferative spurs; in younger

people, to developmental stenosis.

Countee and Vijayanathan (11) have

reported the cases of young patients

with quadniplegia after trauma on

falls who had cervical spinal canal di-

ametens of 14 mm or less. Moiel et al.

(5) reported the case of a young pa-

tient with congenital narrowing of

13 mm at C-4 to C-6. Specific case me-

ports of quadnipanesis in football

players have also been reported:

Grant and Puffer (24) reported the

case of an 18-year-old man with de-

velopmental stenosis; Stratford (25)

reported that of a 23-year-old man

with a sagittal diameter of 12 mm;

Funk and Wells (26) reported the

cases of two players with quadnipane-

sis, one that occurred after hyperfiex-

ion and one after hypenextension;

and Maroon (27) reported the symp-

toms in a patient with “normal” ma-

diognaphs.

To obtain a control population, radio-graphs of the lateral cervical spine ob-tainted in the emergency room were col-lected consecutively over several months.Patients with cervical spinal abnormali-ties, fractures, disclocations, or a historyof previous or current neurologic symp-toms related to the cervical spine wereeliminated. Only radiographs of patientsaged 15-38 years were included. The re-sultant control group consisted of 49 maleand 25 female patients.

For comparison, nadiographs of the lat-enal cervical spine of 23 of 31 patientswith documented transient cervical spi-nal neurapraxia occurring in athletes

were examined. These patients are thoseof one of the authors (J.S.T.) or of the Na-tional Football Head and Neck InjuryRegistry and are the same populationused in an extensive clinical and radio-graphic review (1). The patients were allmale and ranged in age from 15 to 32years (mean, 20.2 years). The primary ath-letic involvement was football; 29 pa-tients were involved in football (ninehigh school, 16 university, and four pro-fessional), one was a professional boxer,and one was a university hockey player.

The radiographic measurements wereperformed at C-3 through C-6 on the rou-tine lateral view of the cervical spine.Cervical spinal measurements were deter-mined with two different methods. Thefirst method, designated for this report asthe “conventional method,” is the onemost often referred to in the literature.With this method, the sagittal spinal Ca-nal diameter is measured from the middleof the posterior surface of the vertebralbody to the nearest point of the come-sponding spinal laminar line (Fig. 1) (2-8). The second method, designated as the

“ratio method,” compares the sagittal spi-nal canal diameter, measured as just de-scnibed, with the sagittal diameter of thecorresponding vertebral body, measured

at its midpoint (Fig. 1).Statistical analysis was performed on

the conventional and ratio values withuse of the Mann-Whitney U test and rela-tive operating characteristic (ROC)curves. The Mann-Whitney nonparamet-nc test does not assume normal distnibu-tion of the data. The conventional and ma-tio measurements of the symptomaticpatients were compared with those of themale control group. Measurements of themale control group were also comparedwith those of the female control group.ROC curves (31) were used to analyzeboth the conventional and the ratio meth-

ods of evaluating cervical spinal stenosis.An ROC curve is a graphic method of ex-pressing the effectiveness of a decisionfor different values of the decision van-able. The decision variables in this in-stance are the measurement of sagittal ca-nal diameter (conventional methodvalue) and the sagittal spinal canal-verte-bral body ratio (ratio method value). TheROC curves were determined with use ofall the measurements made on the control

male subjects (195 vertebrae) and thesymptomatic patients (91 vertebrae).

RESULTS

Measurements of the sagittal diam-

eter of the cervical spinal canal of C-3

through C-6 in the control groups are

detailed in Table 1 . For the male con-

trol group, the mean sagittal diame-

ten was 18.9 mm (13.7-23.5 mm), and

the mean sagittal ratio was 0.98 (0.69-

1 .27). For the female control group,

the mean sagittal diameter was 17.2

mm (13.3-20.4 mm), and the mean

sagittal ratio was 1.02 (0.81-1.26). The

overall mean sagittal diameter for the

entire control group was 18.2 mm,

and the mean sagittal ratio was 0.99

(Fig. 1).

Review of the radiognaphs avail-able for the 23 symptomatic patients

demonstrated no obvious radio-

graphic anomalies in 12 patients

(subgroup 1); of the 11 patients in

subgroup 2, four had congenital

anomalies, two had instability, and

five had intervertebral disk disease.

Of the four patients with congenitalanomalies, three patients had failure

of segmentation at C2-3, C3-4, and

C2-3 and C3-4, respectively, and onepatient had extensive bony prolifera-

tion at the anterior aspect of the yen-

tebral bodies. Measurements of the

sagittal diameter of the vertebral

bodies in the latter patient did not

include the proliferative bony mass.

The cervical sagittal canal diameter

measurements of C-3 through C-6 in

the symptomatic patients are also de-

tailed in Table 1. In subgroup 1, the

mean sagittal diameter was 14.0 mm

(8.5-17.0 mm), and the mean sagittal

ratio was 0.646 (0.31-0.81). For sub-

group 2, the mean sagittal diameter

was 16.6 mm (12.0-23.5 mm), and the

mean sagittal ratio was 0.745 (0.55-

1.18). For the overall symptomatic

patient population, the mean sagittal

diameter was 15.2 mm, and the mean

sagittal ratio was 0.69 (Fig. 2).

With both the conventional and

the ratio methods, there was statisti-

cally significant (P < .000i) spinalstenosis at each level from C-3

through C-6 in each subgroup and in

the entire symptomatic patient group

compared with the male control

group.

Statistical analysis performed to

compare the spinal canal sagittal di-

ameters of male and female control

subjects as measured with the con-

ventional method indicated a statisti-

cal difference (Table 1). It was alsodetermined that the sagittal diameter

of the canal was proportional to the

1 .0-

.9 -

.7 -

.5 -

.3 -

+r�’;.���4”-

,‘

HIT

RATE

I �

.5 .7 .9

774 #{149}Radiology September 1987

sagittal diameter of the vertebral

body and that the vertebral bodies

enlarge proportionally with the ca-

nals. No statistical difference was

identified in the spinal canal/verte-

bra! body ratios between the male

and female control groups.

ROC curves were determined forboth the conventional and the ratio

values (Fig. 3). The conventional val-

ue and the ratio value were the deci-

sion variables. For a given cutoff val-

ue of a decision variable, there are a

certain number of correct choices

whereby a stenotic spine is diag-

nosed as a stenotic spine; these are

called hits. Additionally, theme are a

number of incorrect choices whereby

a normal spine is diagnosed as a ste-

notic spine; these are called false

alarms. The ratio of hits to the num-

ben of stenotic vertebrae is called the

hit rate. The ratio of false alarms to

the number of normal vertebrae is

called the false-alarm rate. Each

change in the cutoff value produces a

new hit rate and an associated false-

alarm rate. Selection of a series of

cutoff values yields a set of hit rates

and false-alarm rates. An ROC curve

is a plot of these sets of pairs with the

hit mate plotted on the ordinate axis

and the false-alarm rate plotted on

the abscissa. The points on the curves

were generated by varying the cutoff

value for the decision variables such

that each change in the cutoff value

increased the hit rate, false-alarm

rate, or both, by the smallest amount

possible; this produced the maximal

number of points to plot the curves.

A perfect decision would have a hitrate of i and a false-alarm rate of 0.

Therefore, as the curve shifts toward

the upper left corner of the graph,

the more sensitive and specific the

test (32).

With use of an operating point of a

sagittal canal diameter of less than 14

mm to indicate stenosis, the hit rate

was 0.35 and the false-alarm rate was

0.01. Hence, 65% of all stenotic canals

would have been misinterpreted as

normal, and i% of the normal canals

would have been interpreted as ste-

notic. With use as an operating point

a spinal canal/vertebral body ratio of

less than 0.82 to indicate stenosis, the

hit rate was 0.92 and the false-alarm

rate was 0.06. Hence, 8% of all stenot-

ic canals would have been misintem-

preted as normal and 6% of all nor-

ma! canals would have been inter-

preted as stenotic. Based on the cu-

mulative data (195 normal vertebrae,

91 abnormal vertebrae), a ratio value

of less than 0.76 represented a stenot-

ic canal 98.5% of the time, and a ratio

value of less than 0.80 represented a

stenotic canal 96.3% of the time.

DISCUSSION

Spinal stenosis of the lumbar spine

is best determined with computed to-

mogmaphy; in the cervical spine,

however, lordosis may create a false

appearance of spinal stenosis, and

measurement of the sagittal dimen-

sion of the cervical spine on a con-

ventional radiograph is more reliable

(33). Use of the actual measure-

ment in millimeters on the lateral

view of the cervical spine to docu-

ment spinal stenosis, however, is

misleading, and the dimensions con-

sidened to be significant as reported

in the literature vary. Boijsen (3) in-

vestigated the cause of variation in

the reported radiographic measure-

ments of the sagittal diameter of the

cervical spinal canal and evaluated

the effects of the following two fac-

tons: (a) the focus-to-film (i.e., the tan-

get) distance and (b) the object-to-

film (i.e., the cervical spine to the

cassette) distance. He reported that

the effect of a difference between a 1-

and 1 .5-m focus-to-film distance on

the resultant sagittal canal measure-

ment is 0.5 mm. To evaluate the ef-

fect of the object-to-film distance, he

calculated that the average difference

in shoulder breadth between men

and women is 10 cm (approximately

a 5-cm difference in the object-to-

film distance). The effect of a 5-cmdifference in the object-to-film dis-

tance on the resultant sagittal canal

measurement is 1.2 mm at a focus-to-

film distance of 1 m, and 0.7 mm at a

focus-to-film distance of 1.5 m.

In our series, the average sagittal

dimension of the vertebral body in

the symptomatic patient group was

22 mm, compared with 19.2 mm in

the control group. This increased di-

mension of the vertebral body may

be actual, projected, on a combina-

tion: actual because the symptomatic

subjects were athletically active,

well-developed football players who

may have had increased skeletal size;

projected, because the patients in the

symptomatic group may have had an

increased shoulder girth compared

with that of the average population,

which increases the object-to-film

distance and thereby the magnifica-

tion. Despite the effect of magnifica-

tion on the sagittal dimension of the

vertebral body, however, the average

sagittal spinal canal dimension was

14 mm in the symptomatic patients,

compared with 18.9 mm in the con-

trol group. Therefore, even with the

0.0-0.0

.1 .3

FALSE ALARM RATE

Figure 3. ROC curve for all data. Solid lineand + indicate value obtained with ratiomethod. Broken line and 0 indicate valueobtained with conventional method.

contributing effects of magnification,

the canal measurement was signifi-

cantly smaller in the symptomatic pa-

tient group compared with the con-

trol group. It would be interesting to

obtain lateral radiographs of the cer-

vical spine of asymptomatic high

school, university, and professional

football players of the same size and

weight as our symptomatic patient

group to determine if the sagittal di-

mensions of the vertebra! bodies and

the spinal canal are proportinally en-

larged compared with those of our

control group; however, in this liti-

gious age, radiation exposure of

young, healthy, asymptomatic adults

is difficult to justify. The size of the

spinal cord was not evaluated as pant

of this study, and it is unknown if

the spinal cord size increases propon-

tionally with that of the vertebral

bodies, although there have been re-

ports indicating that the sagittal di-

mension of the spinal cord is rela-

tively constant from the cervical

level to the midthonacic level (34-38).

In our series, statistically signifi-

cant cervical spinal stenosis was de-

tected with both the conventional

and the ratio methods in the symp-

tomatic patients compared with the

male control group. However, the ac-

tual measurement of the sagittal di-

ameten of the cervical spinal canal

was within normal limits, that is, 14

mm or more at two on more levels, in

2i of the 23 symptomatic patients. By

comparison, the ratio value was with-

in normal limits (i.e., greater than

0.82 at two on more levels) in only

two of the 23 symptomatic patients,

both of whom were in subgroup 2

and one of whom had obvious con-

genital anomalies. Comparison of the

conventional and ratio methods for

determining cervical spinal stenosis

with use of ROC curves shows that

the ratio method is more than 21/2

times as sensitive as the conventional

Volume 164 Number 3 Radiology #{149}775

method with use of a cutoff value of

0.82. Also, the ratio method is more

specific than the conventional meth-

od for determining spinal stenosis.

At a ratio of 0.82, the ROC curveyields a 92% accuracy with only a 6%

false-alarm rate. With use of 6% as

the maximal false-alarm rate, the con-

ventional method (at 14 mm) yields

only a 62% accuracy.

CONCLUSION

The ratio method of diagnosing

cervical spinal stenosis is indepen-

dent of magnification factors caused

by differences in target distance, ob-

ject-to-film distance, or body type,

because the sagittal diameter of the

spinal canal and that of the vertebral

body are in the same anatomic plane

and are similarly affected by magnifi-

cation. There is normally a one-to-

one relationship between the sagittal

diameter of the spinal canal and that

of the vertebral body, regardless of

sex. A spinal canal/vertebral body ma-

tio of less than 0.82 indicates signifi-

cant cervical spinal stenosis. U

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