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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 a
clinical 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), and
Hinck 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, from
the 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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5-.-, �.� -H�H41-H -H-H-H44(5 G’ (‘I ‘C LI) in c’ � C’.
a, � � m ‘.o 0 ‘.0 c’�
b:’.o’.oIf� �---- 0000
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 ratio
method. 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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