Comparison of Roentgenography and Moire
Topography for Quantifying Spinal Curvature
MOHSEN M. EL-SAYYAD
The purpose of this study was to compare roentgenography and moire topography
for identification, treatment, and prevention of scoliosis at an early age. Moire
topography was used as an assessment tool for the quantitative examination of
12 children with mild-to-moderate scoliosis receiving physical therapy during a
three-month period. Each child's roentgenogram also was analyzed independently by orthopedic physicians and radiologists using the Cobb method of measuring spinal curvature. Rho correlations of Cobb angles and the spinal curvature
angles based on moire photographs taken at weeks 4, 8, and 12 were found to
be +.94, +.96, and +.93, respectively. The moire method, thus, may be used as
an available, inexpensive, and easily interpreted diagnostic and treatment tool in
physical therapy.
Key Words: Physical therapy, Radiography, Scoliosis, Spine.
Both the initial examination of
patients with scoliosis and their followup assessment during treatment present
a considerable challenge to health care
professionals. The lack of accurate and
scientifically acceptable assessment
tools previously made the quantification
of the degree of deformity and of improvement of scoliosis difficult to document.
In 1982, the faculties of the School of
Physical Therapy and the Department
of Orthopedics in the School of Medicine of Cairo University jointly participated in the examination of children
enrolled in a preschool and in an elementary school to detect, treat, and prevent scoliosis at an early age. In this
study, moire topography was chosen as
one of the tools for examination of the
school children and for the follow-up
assessment of those children who subsequently were assigned to physical therapy for the treatment of scoliosis. Other
methods of assessment used were independent clinical examinations conducted by orthopedic physicians and
roentgenographic examinations conducted by radiologists. In this article,
Dr. El-Sayyad was Associate Professor of Physical
Therapy, School of Medicine, Cairo University,
Cairo, Egypt, when this study was conducted. He is
currently Associate Professor of Physical Therapy,
King Abdulaziz University, Medinah Munawwara,
PO Box 344, Saudi Arabia.
This paper was presented at the Ninth Congress
of the International Society of Biomechanics, Waterloo, Ontario, Canada, August 7-12, 1983.
This article was submitted March 4, 1985; was
with the author for revision 19 weeks; and was
accepted November 20, 1985.
1078
moire topography is described as a
method of obtaining quantified data
used to analyze changes in spinal curvature. The results of a correlational
study comparing moire and roentgenogram data are presented.
Moire topography is a simple biostereometric method of analysis of spatial
characteristics by means of three-dimensional mapping of the body. It involves
the illumination of the subject with a
spotlight through a special screen to
highlight contour surfaces of the body
that will appear as "fringes" or separate
bands that can be observed or photographed. The technique is not new, having been described as long ago as the
late 19th century.1,2 Its applicability to
body surface shape was introduced first
by Takasaki in 1970.3 In a moire study
of scoliosis conducted by Adair et al, the
authors compared the results of three
independent diagnostic methods: roentgenogram analysis, moire topography,
and orthopedic clinical examination.4
They reported that 94% of the diagnoses
of scoliosis made using roentgenography
also were detected using moire topography, but that only 46% of those diagnoses also were made through clinical
examination. The authors, therefore,
concluded that the moire method essentially is as effective as roentgenography
in the diagnosis of scoliosis and that it
is superior to clinical examination. The
moire method may be used both to obtain a graphical representation of the
back for the qualitative evaluation of
scoliosis and to obtain mathematical
measurements for a quantitative assess-
ment of scoliosis as described by ElSayyad and Kamal in 1981.5
A review of the literature reveals that
the reliability of quantitative measurements of the Cobb angle5"7 using the
roentgenograms of patients with scoliosis have not been reported. Cobb's
method of measuring spinal curvature,
also called the "end-of-curve method,"8
is used widely today. Cobb suggested
measuring the angle of spinal curvature
by drawing lines parallel to the upper
border of the upper vertebral body and
to the lower border of the lowest vertebral body of the primary curve. The
angle between perpendiculars erected
from these lines is the angle of curvature. A literature search also revealed
that the reliability of the moire topographic technique used in this study was
not known previously.9 Tredwell and
Bannon, however, cite an unpublished
report of a study conducted by Tredwell
at Shaughnessy Hospital in Vancouver,
Canada, August 1983, in which an interrater variance of ±3 degrees for measurements of the Cobb angle in scoliosis
was reported.9
METHOD
Subjects
Four hundred children were examined by the orthopedic physicians. Of
that total, seven boys and five girls ranging in age from 4 to 7 years ( age 5.5
years, s = .98) were diagnosed and classified according to the angle of spinal
curvature as either mildly scoliotic (515°) or moderately scoliotic (15-40°).
PHYSICAL THERAPY
RESEARCH
Roentgenograms and moiré photographs were taken for each child at the
beginning and at monthly intervals of
the three-month physical therapy program. Roentgenographic data of the
subjects were not made available either
to me as I conducted the moire examinations or to the physical therapists who
treated the children. Informed consent
was obtained from a parent of each subject before the study.
Equipment
For standardized positioning of each
subject, two laser beams were aimed at
an angle of 45 degrees to the midline of
the body and focused on the center of
the mirror installed on a belt worn at
the subject's waist (Fig. 1). For the photograph of the back, the mirror's center
was marked with a dot and aligned as
precisely as possible with the umbilicus
of the subject, who stood facing the lasers with his back to the screen.
For this study, a special 100-cm × 50cm moiré screen was constructed at
Cairo University. The screen was composed of a simple frame and of a grid of
horizontally placed nylon wires that
were separated by a distance equal to
their thickness (Fig. 2). The subjects
stood behind the screen and were photographed with a sonar-focusing, instant-processing camera and with a 35mm single-lens reflex camera located
170 cm from the screen. A 1,000 W
tungsten light source was positioned 50
cm above the cameras.
Fig. 1.
Positioning of the subject.
Procedures
The positioning of the subjects is the
most important element in taking a
good photograph for moiré analysis. A
moiré topogram taken with the subject
misaligned would appear blurred or unclear and cannot be used for quantitative analysis.10-13 In this study, the subjects were instructed to stand looking
straight ahead, arms down in a relaxed
position and back parallel to the screen,
and as close as possible to the grid without actually touching it. If required, the
subject's position was adjusted until the
fringe patterns demonstrated by the buttocks were symmetrical. No attempt was
made to position the upper trunk, except that the subjects were instructed to
relax.
A standard projection system involves
a grid screen, a light source, and a camVolume 66 / Number 7, July 1986
Fig. 2. Arrangement of equipment.
era arranged in a geometric relationship
according to Takasaki's equation3:
(1)
where h is the height of the n-th fringe
from the grating plane, L is the distance
from the camera to the screen, w is the
distance from the light source to the
camera, d is the pitch of the fringe
screen, and n is the fringe plane number.
The screen-length measurement (70
cm) was photographed and used to calculate the ratio of real screen length to
projected screen length. Two reflective
dots, one located at the seventh cervical
vertebra (C7) and the other at the first
sacral vertebra (Sl), were used as reference points. All photographs were scaled
1079
malities of the structural and functional
relationships between the right and left
sides of the body.
The spine is symmetrical if all corresponding points (eg, points H and E in
Fig. 4) that are located equidistant from
a central axis (PQ) are mirror images. A
scoliotic spine, however, will show a lack
of symmetry that is associated with lateral deviation.
Disturbances in the surface contours
are produced readily by scoliosis in the
thoracic region because the rib cage
magnifies the rotational component of
the scoliosis. In the left lower thoracic
curve shown in Figure 4, the asymmetry
involves primarily both the scapular pattern and the W pattern. In this particular
pattern disturbance, a greater number
of scapular contours are shown in the
involved right side compared with the
uninvolved left side, and one limb of
the W pattern descends along the upper
thoracolumbar region of the involved
side indicating elevation in this area.
Fig. 3. Moiré pattern of a normal spine.
to a factor of 1:3 at the level of the grid
screen for topographic analysis.
The moiré topography procedure described in this article varies from that
used by other investigators. It provides
anatomical points of reference (C7 and
Sl) for the examination of spinal curvature, rather than of the shape of the
back, either by using an arbitrary vertical line on the moiré screen or drawing
a line on the moiré photograph dividing
the body into right and left segments.3,14
The subjects' alignment also was improved by instructing them to relax with
their arms hanging naturally.
As the lower base points of the W
pattern descend along the paravertebral
thoracolumbar region into the upper
lumbar region, they are replaced by vertically oriented contour levels descending on either side of the waist (Fife. 4).
The nearest visible moiré fringes to the
central axis (PQ) corresponding to
points E and H represent the level of
maximum asymmetry. The point 0 is
the midpoint of the line segment HE,
and point C is the origin. The distance
between points E and H was determined
using the following formula:
Normal Back Topography
The surface of the normal back (Fig.
3) reflects the expected elevations in the
scapular and middle thoracic regions,
the depression through the middle lumbar region, and subsequent elevation in
the sacral region. Because the contour
lines formed by the moiré fringe represent lines of uniform height, they tend
to be continuous O patterns around the
elevated areas of each scapula and the
gluteal region. In the upper thoracic region, as the contour lines rise cephalad
from these elevated scapular regions toward the base of the neck, the contour
lines become discontinuous laterally in
the shoulder region to form the contours
of the shoulder. Similarly, the contour
lines descending caudally from the scapular region usually form a W pattern in
the thoracic region. The lower base
points of the W pattern descend along
the paravertebral thoracolumbar ridges
into the upper lumbar regions where
they are replaced by vertically oriented
contour levels descending on either side
1080
Fig. 4. Measurement of the angle of spinal
curvature by moiré topographs.
of the waist, which are designated lateral
V left andright.The pattern of the upper
back begins to repeat itself, proceeding
caudally in the lumbar region.13
In the normal back, the number of
fringes are equal on both sides of the
back to within one fringe interval of
difference (Fig. 3). The actual number
of fringe lines occurring symmetrically
on both sides is, in part, determined by
the size of the subject and the amount
of deformity. Because the generator of
the curved surface is a straight line, the
curves of the oblique section of the spine
are symmetric if the spine is symmetric
and parallel to the screen. This distinctive feature of an instrument composed
of a horizontal grid is used to detect
asymmetries that may indicate abnor-
d1 = ½ (CH + CE)
(2)
where line segment CE (positive) is the
distance on theright,and line segment
CH (negative) is the distance on the left.
In the upper thoracic region, as the
contour lines rise cephalad from these
elevated scapular regions toward the
base of the neck, the contour lines become discontinuous laterally in the
shoulder region to form the minimum
asymmetry level. The nearest visible
moiré fringes to the central axis (PQ)
corresponding to points G and D represent the level of minimum asymmetry. At point A above point C, the
distance d2 was determined using the
following formula:
d2 = ½ (AD + AG)
(3)
At point B below point C, where the
moiré fringes also show minimum
PHYSICAL THERAPY
RESEARCH
asymmetry, the distance d3 was determined using the following formula:
d3 = ½ (BF + BI)
(4)
The angle of spinal curvature at point
O, thus, was calculated using the equation:
Q = tan-1 (d, - d2/AC)
TABLE
Correlation of the Angles of Scoliosis Curvature Based on Roentgenogram and Moiré
Methods (N = 12)
First Measurements
(after 4 wk)
Subjects
-1
+ tan (d1 - d3/BC) (5)
The data were processed at Indiana University using a Fortran digital computer
program and the formula for determining the angle of spinal curvature. To
obtain the angle of spinal curvature
from the roentgenograms, the radiologists used the Cobb method.
Data Analysis
Spearman's rho correlation coefficients, appropriate for small sample
sizes, were determined using the data
obtained after the 4th, 8th, and 12th
weeks of the treatment program.
RESULTS
The Table shows the angles of spinal
curvature for each examination period,
as calculated from the roentgenograms
using the Cobb method and from the
moiré photographs using the formula
described earlier. The statistical correlation of the two sets of measurement
for each examination period were calculated using Spearman's method of rho
correlation. The rho correlation coefficients were found to be +.94, +.96, and
+.93 for weeks 4,8, and 12, respectively.
DISCUSSION
The calculation of the moiré angle
provides a method for the objective
measurement of symmetry because the
calculation is based on a single midline
axis between C7 and the gluteal fold.
Unlike profile-type analysis, it is not
dependent on locating other landmarks
on a subject's back to be repeatable over
a period of time, such as during the
course of treatment for the subject's scoliosis.
Moiré topography involves the examination of the outside of the body,
rather than of the skeleton. The objective of moiré topography, therefore, is
to align the subject's skeleton according
to fixed reference points that will facilitate the analysis of contour changes. I
believe that it is important to align the
subject's skeleton so that repeated moiré
Volume 66 / Number 7, July 1986
1
2
3
4
5
6
7
8
9
10
11
12
Rho correlation
coefficient
Second
Measurements
(after 8 wk)
Third Measurements
(after 12 wk)
Cobb
Angle (°)
Moire
Angle (°)
Cobb
Angle (°)
Moiré
Angle (°)
Cobb
Angle (°)
Moiré
Angle (°)
11.50
20.00
15.50
31.50
8.00
11.00
36.00
25.00
22.50
34.00
16.50
28.50
11.26
22.50
16.08
31.44
9.38
11.96
36.74
23.00
22.25
31.80
16.75
28.24
9.00
16.50
15.00
28.00
4.50
11.00
34.50
23.50
22.00
31.00
9.50
21.00
10.75
16.58
16.52
29.90
6.00
11.25
33.88
23.70
23.10
30.74
10.15
19.62
8.50
17.00
14.50
25.00
5.00
9.00
27.50
20.00
17.50
31.50
7.50
20.00
8.94
16.75
14.22
24.88
8.30
10.74
29.70
19.96
16.95
32.15
8.24
22.60
+.94
photographs will show that contour
changes are caused by skeletal changes.
Other methods of moiré topography
used in the diagnosis and treatment of
scoliosis also have been reported.15-19
Drerup et al demonstrated the changes
resulting from treatment of spinal curvature using a longitudinal cross-sectional contour graph.2 This method is
simple and graphically demonstrates the
changes in the back produced by an
operation. Roger analyzed the digital
data of moiré topograms and developed
a transverse cross-sectional contour
graph based on five different reference
points on the back.10 He then calculated
rotation, from the reference plane, of
the time tangent of both humps of the
contour line. This method is useful to
reveal rotational deformities of the scoliotic back. The method of moiré topography that I used in my study is more
comprehensive than the methods used
in these previous studies because the
method that I used enables the clinician
to determine the location and the angle
of spinal curvature.
The correlation coefficients in the Table indicate that the moiré method of
quantifying mild and moderate scoliosis
and of analyzing changes in the subject's
spinal curvature is a simple and convenient physical therapy technique. Such
results should be interpreted with caution, however, because of the following
potential sources of error:
1. Changes in the patient's positioning
during roentgenography or moiré
+.96
+.93
photography may alter the shape of
the spinal curvature, thereby affecting
measurements based on the Cobb angle or the moiré topography formula.
2. The growth of the child generally results in changes in the measurements
obtained by either method of examination and may be misinterpreted as
changes attributed to treatment.
3. Studies of the interrater reliability of
the Cobb method of measuring topographic values have not been reported
in the literature and are needed.
4. Studies of the intrarater reliability of
measurements based on the Cobb angle or on moiré topography and obtained from the same subjects during
the same examination period have
not been reported.
CONCLUSIONS
In this study of mild and moderate
scoliosis using both roentgenography
and moiré fringe topography, I found
that distinct patterns could be identified
that correlated with the anatomical regions of the scoliosis. The measurements of the moire angles and of the
Cobb angles were closely correlated.
Moiré analysis can reduce the risk of
radiation to children who presently
must undergo repeated roentgenographical examinations. Moiré topography is
economical (about 40 cents an examination), noninvasive, and relatively fast
and easy to use and interpret. It is an
assessment tool that is available to physical therapy clinics without requiring
1081
much space or training. The topographs
may be maintained as permanent records of patients in physical therapy and
allow the therapist to review and compare curve changes in a quantified manner. The topographs also provide a basis
for the clear identification of the region
of spinal involvement if anatomical regions are used as points of reference, as
described in this study.
Further research of the reliability of
the methods of measurement used in
this preliminary study based on a larger
sample is needed. The experimental design of future studies should include a
control group of healthy subjects to
counterbalance the effects of growth
change and other possible sources of
invalidity. The development of a positioning protocol is essential to further
studies of moiré topography, as well as
to its clinical use in physical therapy.
Acknowledgment. I thank Dr. Tali
Conine, Professor and Director, School
of Rehabilitation Medicine, University
of British Columbia, for her continuing
advice and support.
1082
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PHYSICAL THERAPY