Geometrical dimensions and morphological study of the lumbar spinal canal, in
Egyptian populations
O Amin, MD. Kamal Hafez, M.D., Tarek Ali, M.D. and M El-Sayad, M.Sc
Faculty of Medicine, Tanta University, Egypt
Correspondence
Osama Amin
Faculty of Medicine
Tanta University
Fax: 020-40-3407734
Telephone: 020-40-3319735
E-mail: osamin16@hotmail.com
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Abstract:
This study was carried out on 300 patients to present data on the dimensions of the
mid-sagittal diameter, and inter-pedicular distance from digitised CT images of the lumbar
spine in Egyptian population. There were, 162 men (54%) ranging in age from 18 to 74 years
(mean = 44.3 years), and 138 women (46%) ranging in age from 22 to 78 years (mean = 51.6
years) were studied. CT was done and the mid-sagittal diameter, inter-pedicular distance, and
lateral recess were measured to determine the normal values of these measurements in normal
Egyptians populations. Results: L3 was the narrowest level. The range of the mid-sagittal
diameter at all levels was 11.07-26.07 mm and the mean values had an hourglass shape. The
range of the inter-pedicular distance at all levels was 17.00-43.41 mm. There was an increase
in the inter-pedicular diameter from L1 to L5 vertebra. In all cases at all levels the range of
depth of lateral recess was
4-14 mm and the mean was 6.7 mm No significant difference
between right and left sides was found. L5 had the narrowest lateral recess. The incidence of
the trefoil shape of the canal at L5 was 20%. There were a significant correlation between our
subjects and the Korean and white population concerning the mid-sagittal diameter while it
was insignificant with black population. There were a small group of subjects, 3.3%, who’s
the measurement of their mid-sagittal diameter (MSD) can be said to be statistically stenotic
(bony stenosis). The interpedicular distance (IPD) was correlated with Korean population.
Trifoils canals were seen mainly in the lower lumbar vertebrae mainly at fifth lumbar vertebra
followed by the fourth lumbar vertebra. Conclusion: These data from a large number of CT
scans, coupled with accurate measurement, provide the bases not only for anatomical studies
and clinical research, but also for sensible rational implants development for a restricted
inventory to promote a solution in the vast majority of cases.
Key words: lumbar spine, anatomy, CT scanning
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Introduction
Accurate and comprehensive data for the spinal canal measurements, in the lumbar
vertebrae are incomplete at present. Several methods have been used to image the lumbar
spine including routine radiographs, myelography, CT and MRI (1). Information on the
precise dimensions of the lumber vertebrae is, however essential, for the spinal surgery, and
instrumentation such as pedicle screws. Previous studies have depended on direct
measurements from plain X-ray films (2-5), or from computed tomography (CT) scans (6). A
few reports have involved the analysis of cadaver specimens (7-11). The value of the data has
depended on the number of samples and the accuracy of measurement. Panjabi, et al (9)
reported comprehensive studied of human cadaver lumbar vertebrae, but because of the
extreme difficulty in obtaining such specimens, the study was limited to only 12 specimens.
Fang et al (6) published an important study in 1994 providing data applicable to the Asian
lumbar spine, also obtained from CT scans, but these are not necessarily applicable to the
Egyptian spine.
The purpose of this study is to present data on the dimensions of the mid-sagittal
diameter, and inter-pedicular distance from digitised CT images of the lumbar spine in a
series of 300 Patients in Egyptian population.
Patient and method
Study population:
This study was carried out on 300 patients, attended in Tanta university hospital,
radiology department during the period of 1999 to 2000. They were selected for this study
from individuals undergoing computed tomographic studies of the abdomen and ethical
approval was obtained.
All chosen cases met the following criteria:
1. The CT study was done including images from L1 to S1.
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2.
The subject age was 18 years or older.
3.
The lumbar spine appeared normal on CT images, although minor degenerative
changes were allowed if there was no evident encroachment upon the spinal canal.
There were, 162 men (54%) ranging in age from 18 to 74 years (mean = 44.3 years),
and 138 women (46%) ranging in age from 22 to 78 years (mean = 51.6 years) were studied.
Patients who had accompanied symptoms such as low back pain and lower
extremity pain were excluded from this group. Patients who had vertebral abnormalities,
gross spinal pathology (including spondylolisthesis, retrolithesis, and disc space collapse)
and those who had undergone spinal surgery were excluded.
Measuring method
CT was done using a GX-Vision (Toshiba), in the Department of Diagnostic Radiology.
Sequential 3-mm continuous axial images were made parallel to both upper and lower end
plates for each vertebra, and were studied from the first lumbar vertebra to the upper sacrum.
1500 lumbar vertebrae from L1 to L5 of the above 300 subjects were examined. The midsagittal diameter, inter-pedicular distance, and lateral recess were measured to determine the
normal values of these measurements in normal Egyptians populations. The images were
stored in a computerised system, allowing enhancement, magnification, and rotational
facilities. It also incorporates a measuring tool. To measure the distance between two points, a
cursor is positioned using the mouse over an initial reference point. The cursor is then moved
to the second reference point by dragging the mouse. When the mouse button is released, the
distance between the two points is automatically displayed in the information box, reflecting
not only a measurement from the CT film, but also the actual size of the lumbar vertebral
canal in the plane of the slice. Two parameters were measured from the cross-sectional
images, in each lumbar vertebra. (Figs. 1, 2). The spinal canal width (Interpedicular Diameter)
(IPD) was measured at the pedicular level as the distance between the inner borders of both
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pedicles of one vertebral body of the all five lumbar. Spinal canal depth (Mid Sagittal
Diameter) (MSD) was defined as the distance from the posterior border of the vertebra to the
lamina posteriorly at the midline. The depth of the lateral recess was measured from the
dorsal surface of the vertebral body to the most ventral segment of the superior articular facet.
Reliability of measurements
All parameters were measured twice by the same observer, in the same day.
Statistical Analysis
Statistical presentation and analysis of our present study was conducted using the
mean, standard deviation, standard error and Student t test. A significance level of P<0.05 was
used.
The value obtained from measuring the mid-sagittal, inter-pedicular diameters and
lateral recess depth, were all arranged in tables representing the measurement obtained in each
lumbar level from L1 to L5 in different age groups and the mean value was calculated, and
then tabulated.
Results
The total number of 300 patients was examined by computed tomography in this
study.
1. Mid-sagittal diameter (Table 1). It was measured and analysed. At L3 it was the narrowest
level. The range at all levels was 11.07-26.07 mm. The mean values of the mid-sagittal
diameter of the lumbar vertebra had an hourglass shape.
2. Interpedicular diameter (Table 2): The range at all levels was 17.00-43.41 mm. The
measurement of the lumbar vertebra shows steady increase in the inter-pedicular diameter
from L1 to L5 vertebra.
3. Depth of lateral recess: In all cases at all levels the range of depth of lateral recess was 4-
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14 mm and the mean was 6.7 mm No significant difference between right and left sides was
found. L5 had the narrowest lateral recess.
4. Shape of the canal: It was not simply uniform shape along the five lumbar vertebrae, as the
shape of the canal was ranging from circular or rounded shape in upper lumber vertebrae,
triangular in the mid lumbar vertebrae, or trefoil in the lower lumbar vertebrae especially at
L5 vertebra. The incidence of the trefoil shape of the canal at L5 was 20%.
Discussion
Computed tomography (CT) is a validated simple standardised method for making
precise measurements of the spinal canal directly from the display of a computed tomography
(CT). It is used to measure normal values for antero-posterior diameter and interpedicular
distance of the lumbar spinal canal. A careful study of canal configuration should allow the
computed tomography (CT) to diagnose lumbar spinal stenosis with a high level of confidence (12).
Measurements of human vertebra have been performed by a number of authors (4,614). The significance of their data has depended on the number of samples they had in their
study, and the accuracy of their measurement. Assessment of a small number of samples
cannot provide adequate and representative information, and a larger series such as that in our
present study is required.
In our study, the range for each parameter between the minimum and maximum was
substantial. In addition, the methods used in the past affect the accuracy of the information. It
is, for example, difficult to obtain large number of cadaver’s specimens, and also to provide
appropriate information concerning dimensions from these specimens, which will have
undergone post-mortal changes. Early studies were carried out on plain x-ray films, but it is
difficult to include an appropriate reference object in the focal plane, and errors are frequently
introduced due to an inability to allow for the magnification factor.
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The introduction of computed tomography (CT) provided the first real opportunity for
appropriate assessment of cross-section, including vertebral body dimensions in living
subjects. Computed tomography (CT) combined with the available measuring facilities will
provide more accurate measurement, obtained with comparative ease, allowing a thorough
assessment of a wide range of vertebral measurements in larger number of subjects. Accurate
measurement is also allowed on computed tomography (CT) by availability of adjustment of
contrast for optimisation of image quality, and measurement of distance. Nevertheless,
potential source of error due to the inter-observer error, which was 5 % in the study of Zhou,
et al (15) was excluded in our study, because a single investigator performed all
measurements.
As the axial plane is ideal, for the assessment of the size and configuration of the spinal
canal; the entire bony circumference of the spinal canal can be directly visualised, which is
present and available by computed tomography (CT) (16). Thus bony encroachment on the
spinal canal was well demonstrated. Computed tomography (CT) has an advantage that it is
superior in obese and de-mineralised patients.
Akl (17) had performed morphologic study of the lumbar spinal canal on post-mortal
lumbar vertebrae of Egyptians (table 3). It is obvious that, in the study of Akl (17), L1 had the
largest mid-sagittal diameter in all measured lumbar vertebrae, which matched the results in
our study. There is also reduction in the value of the mid-sagittal diameter of the lumbar
vertebrae from L1 to L3, then it increases again till L5 lumbar vertebra, this also was present
in our study. In correlation between our study and study of Akle (17), concerning the midsagittal diameter values, significant P value was found. This can be explained due to the
difference in the instrument used for measurement, and that our measurements was done in
living human using computed tomography, while in the study of Akl (17), the measurements
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were done on the lumbar vertebrae in non living lumbar spines, which may undergo postmortal changes.
Many morphologic studies of the lumbar spinal canal have been conducted according to
race (tables 4-7). In comparison with the studies of Lee (18), Eisenstein (8), and AmonoKuofi (19). They all showed that L1 has the largest mid-sagittal diameter, and showed also
the reduction of the mid-sagittal diameter till L3, followed by increase again till L5 vertebra.
In correlation with our study and the study of Lee (18) on Korean subject, P values were
significant. While the study performed by Eisenstein (8), which was performed on South
African Negroes and Caucasian showed significant P value with White population. The
difference in this outcome may be due to racial and environmental factors, or due to different
method of measurements. The P values were insignificant with Black in the study of AmonoKuofi (19) in Nigerian population.
The mid-sagittal diameter of the lumbar spinal canal through L1 to L5, series, had an
“hour-glass” pattern. This was also seen in the Korean subjects, in whom the narrowest
diameter was found at L3 and L4. These findings are consistent with the data reported by
Hinck, et al (20). In our study, and others (8,18,19) the largest mid-sagittal (MSD) was
detected at the first lumbar vertebra. This phenomenon was explained by Davis (21) as he
stated the fact that the lower end of lumbar enlargement of the spinal cord is located at the
first lumbar vertebra level and this is the transitional area from the thoracic spine to thin
lumbar spine. The first lumbar level coincides with the region of functional transition between
the relatively immobile thoracic spine and the mobile lumbar segment.
Therefore, the diameter of the spinal canal at this level may not only be a reflection of
the size of its contents, but also an adaptation to ensure protection of those contents during
complex movements of this transitional region (19).
Together with the above outcome normal measurements in our study, there were a
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small group of subjects, 3.3%, who’s the measurement of their mid-sagittal diameter (MSD)
can be said to be statistically stenotic (bony stenosis) (8).. It is important to recognise that
even those stenotic vertebra were only marginally below the lower limit of normal midsagittal diameter (MSD) of the scanned lumbar vertebra at each level. As the shortest midsagittal diameter in our study was 11.01 mm, while the lower limit of normal is 12 mm (8).
Eisenstein (8) stated that, this marginal skeletal stenosis might well predispose to cauda
equina compression, which may be caused by minimal degenerative changes, in either bony
and/or soft tissue structures bordering the spinal canal. He found a slight lower incidence (1.3
%) in his study.
The interpedicular distance (IPD) ranged in all lumbar vertebrae L1 to L5 from 17.03 to
43.41 mm, the interpedicular diameters showed a steady increase from L1 to L5. This
coincides with the findings of Lee (18). The range of inter pedicular distance coincides with
the study of Zhou, et al (15). The minimum normal inter-pedicular diameter (IPD) values in
our study were slightly lower than those given by Lee, et aI (18).
The shape of the spinal canal in our study was not uniform through out the five lumbar
vertebrae; it was not simply a truncated cylinder. In the first lumbar vertebrae it was found to
be rounded or oval in cross section. When it was transverse oval, the transverse diameter is
greater than the antero-posterior diameter. In the mid and lower lumbar regions, the spinal
canal was triangular with the apex directed posteriorly with a large transverse dimension than
the antero-posterior dimension. In the lower lumbar region the lamina bowed inside with
some indentation towards the canal. This finding coincides with Naheedy (22). In our study
trefoils canals were seen mainly in the lower lumbar vertebrae mainly at fifth lumbar vertebra
followed by the fourth lumbar vertebra. This coincides with Dorwart (23).
The alteration of the shape of the lumbar spinal canal can be due to anatomical
variation, and not due to pathological conditions. This view was also shared with Eisenstein
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(8), who had referred this alteration in the usual triangular shape of the lower lumbar vertebral
canal, mostly at the fifth lumbar level as mentioned above, as a variation of normal anatomy
and not a pathological state causing compression. The lumbar canal at this level has to
accommodate only the fifth lumbar and the sacral nerve roots.
These data from a large number of CT scans, coupled with accurate measurement,
provide the bases not only for anatomical studies and clinical research, but also for sensible
rational implants development for a restricted inventory to promote a solution in the vast
majority of cases.
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Figure legend
Figure 1,2: Methods of measuring the MSD, IPD, and Depth of the lateral recess.
AB= Aantero-posterior distance= Sagittal diameter.
IPD= Interpedicular distance.
R= Lateral recess distanse.
Table (1): Mid sagittal diameter in mm at L1, L2, L3, L4, and L5 vertebral bodies.
Table (2): Inter-pedicular diameter in mm at L1, L2, L3, L4, and L5 vertebral bodies.
Table (3): Comparison of outcome measurement of the mid-sagittal diameter in Egyptians,
between our study and the study of Akl (17).
Table (4): Racial comparison of mid-sagittal diameter in the lumbar vertebrae in our present
study and Korean population by Lee (18).
Table (5): Racial comparison of mid-sagittal diameter in the lumbar vertebrae in our present
study and White population by Eisenstein (8).
Table (6): Racial comparison of mid-sagittal diameter in the lumbar vertebrae in our present
study and Black population by Amono-Kuofi (19).
Table (7): Racial comparison of Mid-sagittal diameter in the lumbar vertebrae in our present
study and in study of Zhou, et al (15).