escoliose e fotogrametria

8/9/2019 Escoliose e Fotogrametria

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Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

Spine Publish Ahead of Print

DOI: 10.1097/BRS.0b013e3181f7cfaa

New Method of Scoliosis Assessment:

Preliminary Results using Computerized Photogrammetry

Rozilene Maria Cota Aroeira, MSc

Jefferson Soares Leal, MD

Antônio Eustáquio de Melo Pertence, PhD

From the Federal University of the State of Minas Gerais, Belo Horizonte, Brazil.

The manuscript submitted does not contain information about medical device(s)/ drug(s). No

funds were received in support of this work. No benefits in any form have been or will bereceived from a commercial party related directly or indirectly to the subject of this manuscript.

This research was approved by Research Ethics Committee of Federal University of the State of

Minas Gerais on the 14th of February, 2008 (ETIC 579/07).

Address correspondence and reprint requests to Jefferson Soares Leal, MD, rua Padre Rolim,

815/ 107, Vertebra Clinic, Santa Efigênia, Belo Horizonte, Minas Gerais, Brazil. Zip Code:

30130-090.

E-mail: [email protected]


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Study Design. A new method for non-radiographic evaluation of scoliosis was independently

compared with the Cobb radiographic method, for the quantification of scoliotic curvature.

Objectives. To develop a protocol for computerized photogrammetry, as a non-radiographicmethod, for the quantification of scoliosis, and to mathematically relate this proposed method

with the Cobb radiographic method.

Summary of Background Data. Repeated exposure to radiation of children can be harmful to

their health. Nevertheless, no non-radiographic method until now proposed has gained

popularity as a routine method for evaluation, mainly due to a low correspondence to the Cobb

radiographic method.

Methods. Patients undergoing standing posteroanterior full length spine radiographs, who were

willing to participate in this study, were submitted to dorsal digital photography in the orthostatic

position with special surface markers over the spinous process, specifically the vertebrae C7 to

L5. The radiographic and photographic images were sent separately for independent analysis to

two examiners, trained in quantification of scoliosis for the types of images received. The

scoliosis curvature angles obtained through computerized photogrammetry (the new method)

were compared to those obtained through the Cobb radiographic method.

Results. Sixteen individuals were evaluated (14 female and 2 male). All presented idiopathic

scoliosis, and were between 21.4± 6.1 years of age; 52.9 ± 5.8Kg in weight; 1.63 ± 0.05m in

height, with a body mass index (BMI) of 19.8 ± 0.2. There was no statistically significant

difference between the scoliosis angle measurements obtained in the comparative analysis of

both methods, and a mathematical relationship was formulated between both methods.


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Conclusion. The preliminary results presented demonstrate equivalence between the two

methods. More studies are needed to firmly assess the potential of this new method as a co-

adjuvant tool in the routine following of scoliosis treatment.

MINI ABSTRACT

A new method of non-radiographic evaluation of scoliotic curve using computerized

photogrammetry is described. The new method was easy to apply, with low cost of

implementation and results similar to those of the Cobb method.

KEY POINTS

• Computerized photogrammetry is presented as a new method in the non-radiographic

evaluation of scoliotic curves.

• The proposed method is described in detail.

•

In the presented sample, the values of the curves determined through computerized photogrammetry method were similar to those determined through the Cobb radiographic

method.

Introduction

Scoliosis has been defined as a lateral curvature of the spinal column superior to 10°

Cobb, generally associated to vertebral rotation1. Monitoring of this angle has been one of the

principal parameters used in defining the type of treatment to be instituted in young patients who

are still growing 2. The most trustworthy method to accompany the evolution of the curvature


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has been the standing posteroanterior full length spine radiograph, with curvature measurement

using the Cobb method 3. However, over the course of follow-up, this can result in taking more

than 25 radiographs 4. Nearly 15% of patients in one study had undergone 50 or more

radiographic examinations, and approximately 17% had received an estimated cumulativeradiation dose of 20 cGy or greater 4. This high number of radiographs can expose patients to

relatively high doses of ionizing radiation. Various studies have shown that repeated exposure to

radiation in children can be harmful to their health 4-10.

Many non-radiographic methods of scoliosis accompaniment have been proposed as an

alternative to radiographic evaluation 11-15. Nevertheless, the majority have not demonstrated a

good correlation with the Cobb method 16.

Photogrammetry can be regarded as the science and technology of obtaining spatial

measurements, and other geometrically reliable information, derived from photographs 17. The

computerized photogrammetry method proposed in this study can be considered one of many

uses of photogrammetry. It has been used in different fields, such as: cartography, architecture,

engineering, quality control, and 3-D modeling. However, its use in the evaluation of scoliosis

has not been well studied. To the authors’ knowledge, no data is presently available in the

literature which proposes a protocol for photogrammetric measurement of scoliosis which is

applicable to clinical practice.

The goals of this investigation were to develop a protocol for computerized

photogrammetry method for the quantification of scoliosis curvature as well as to compare the

results with those from the Cobb radiographic method in the group of volunteers. Our hypothesis

is that both methods yield similar results in obtaining the scoliosis curvature angle.

Materials and Methods


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Field Studies

After approval from the Research Ethics Committee of our hospital, all patients who were

undergoing conservative treatment for idiopathic scoliosis in the spine unit between March andOctober of 2008, and who had received the medical requisition for radiological monitoring of

their deformity, were invited to participate in this study. The only exclusion criteria adopted for

this phase was the refusal of the patient or of his parents. All accepted the invitation and gave

their formal informed consent.

Radiological Exam

Full-length standing posteroanterior spine radiographs were obtained using an X-ray

generator TOSHIBA KXO 15R ® (Tokyo, Japan) and a digital radiography Agfa Health System ©

(Mortsel, Belgium). The images were acquired in a single exposure for each incidence, and then

digitally obtained images were printed on a single sheet of 35.6 x 43.2 cm film. Only the

posteroanterior incidence for each patient was chosen for radiographic analysis. The scoliotic

curvature and the apical vertebra were determined for each patient by one examiner. Five

separate measurements were made at different times for each exam, and the average of these five

values was utilized for statistical analysis.

Computerized Photogrammetry Exam

Immediately after the radiological exam, a single trained, experienced examiner initiated

palpation and marking on the spinous process with surface markers, for all vertebrae localized

between C7 and L5. An Anatomical Landmarks Type Vector (ALTV), 45mm in length with a


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metallic base of 8mm, was developed and standardized as a surface marker specifically for this

study. Following this, each patient was photographed in standing, dorsal, lateral (right side

visualization 90º) and oblique (left side 45º) positions, utilizing a digital camera, Sony® 7.1

megapixel (Manaus, Amazonas, Brazil), at definition 3072 x 2304, mounted on a Greika

®

WT3750 (São Paulo, SP, Brazil) tripod, set to a height of 1.10m, with a focal distance of 1.30m.

A Carci® Simetograph (Americanópolis, SP, Brazil), 2.02m in height and 0.72m in width, was

used to provide a base metric reference. The images were imported and analyzed using

CorelDraw13® software (Corel Corporation, Canada), and the angle of deviation of scoliotic

curvature was calculated. The protocol for the deviation calculation consisted, initially, of the

identification of the apical vertebra and the superior limit vertebra of the upper curve. This

procedure was done by tracing two vertical lines (using the “ free hand” tool in the software

toolbar), one line tangential to the convex face of the curve, and the other crossing through the

vertical axis of the C7 vertebra (Figure 1). The apical vertebra was defined as that furthest from

the vertical axis of C7 and touching the tangential line.

The second step of the calculation consisted of measurement of the angle of deviation of

each segment between the superior limit vertebra and the apical vertebra marked with the ALTV,

using the “dimension” tool located in CorelDraw13® (Corel Corporation, Canada). The sum of

the angles of deviation of the previous segments determined the final angle calculated through

computerized photogrammetry, which is called angle MR (Figure 2).

Definition of Angle MR

Angle MR was defined as the angular quantification calculated for a specific scoliotic

curve obtained through computerized photogrammetry in the frontal plane. It was calculated

through the sum of the lateral deviation of each segment between the superior limit vertebra and


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the apical vertebra. Its radiological correspondent is the Cobb angle as obtained through the

radiographic method.

Calculation of Angle MR

The deviation of each segment was denominated as angle Rn (R1, R2, R3, etc). Angle Rn

was that formed between the lines traced between the centers of the MASV in two vertebrae of

the segment (adjacent vertebrae) with the line of the vertical axis Y (Figure 2). The sum of these

angle Rn measurements for each segment between the superior limit vertebra and the apical

vertebra determined the Angle MR.

For each volunteer in this study, five measurements were taken of each angle Rn, at

distinct intervals, by the same examiner. The average of the sum of these angle measurements

was considered to be the angular value of the deformity.

Analysis of Data

The radiographic and photogrammetric measurements were performed separately by an

orthopedic spine surgeon, and a physiotherapist experienced in photogrammetry of the spine,

respectively.

To determine the profile of the study participants, a frequency distribution was performed

for the variables ‘gender’ and ‘type of curvature’, along with calculation of the central tendency

for the variables of ‘age’ and ‘body mass index’ (BMI).

In order to verify the differences in measurements of thoracic and lumbar scoliosis

curvatures between the Cobb and computerized photogrammetry methods, the Wilcoxon test was

realized.


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The localization of the apical vertebra was compared between the two methods through

concordance calculation using Kappa statistics. The non-parametric test was used, considering

the size and the characteristics of the sample. Concordance in the localization of the apical

vertebra in this study was defined as the identification of the same vertebra, or at most, oneadjacent vertebra. This definition was established considering that the computerized

photogrammetry method actually detects the tip of the spinous process rather than the vertebral

body of the apical vertebra, and also considering that the real apex curve detected through

radiographic method could be localized in the intervertebral space. The significance level

adopted for all tests was 5%.

Results

Sixteen volunteers were evaluated using the two methods. All presented idiopathic

scoliosis. The average age was 21.4 years. For weight, height and body mass index, the averages

were 52.9kg, 1.63m and 19.8kg/m2, respectively. There was predominance of females (87.5%),

and with a female to male ratio of 7:1. In relation to curvature type, a double thoracic/lumbar

curve was the most frequent, with 12 cases observed (75%), followed by a single lumbar curve

(18.7%), and a single thoracic curve (6.2%). The general characteristics and the measurements

using Cobb and computerized photogrammetry methods of each individual included in the study

are presented in table 1.

The values of the thoracic curve measurements obtained using the Cobb method varied

between 17.8º and 73.0º, with an average of 36.1º, while the values of the curve measurements

obtained using the computerized photogrammetry method varied between 19.6º and 74.2º, with

and average of 36.4º, with no significant difference noted between the two groups (Table 2 and

Figure 3).


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The average difference between the angle values obtained through the Cobb method and

the computerized photogrammetry method was 2.9º for thoracic curves.

In the lumbar region, the average of the curvature evaluated through the Cobb method

was 27.2º, with a variation of 14º to 48.6º, while the average through the computerized photogrammetry method was 25.7º, with a variation of 10º to 55.0º (Table 2 and Figure 3). The

average difference between the two methods in the lumbar region was 5.1º.

There was no significant difference between the average curve measurement values

obtained through the Cobb and computerized photogrammetry methods for all curves analyzed

together. The average of the differences between the methods for all curves was 4.1º.

The average Kappa index for evaluation of intensity of concordance in the localization of

the apical vertebra between the methods for the thoracic region was 0.92. For the lumbar region

the Kappa index was 0.82.

Discussion

Various non-radiographic methods for the quantification of scoliosis have been proposed

in the last thirty years 11-15. Unfortunately, they have not survived the test of time, due to a

variety of possible reasons, notably: 1) non-radiographic techniques cannot entirely replace

radiographs; 2) there are important direct costs in the implementation of new technology as well

as recurrent costs with training, salary of the technician and others; 3) theses techniques take

more time than the radiological exam; and 4) finally, the majority have demonstrated low

correlation to the Cobb method 16.

The radiological exam with frontal plane measurement of the Cobb angle has been

considered to be the gold-standard for the quantification and monitoring of scoliosis1, 2. In

addition to the determination of the Cobb angle, it provides information as to skeletal maturity,


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the flexibility of the curve, the presence of congenital bone malformations, and the general

balance of the spine, which is all indispensable to good clinical practice in scoliotic patients.

However, once these data have been established, further monitoring of the Cobb angle may be

considered the main reason for the repetition of radiological examination

3

. Along with theimportant benefits of X-rays, there are risks that need to be considered as well. Brenner et al 18,

in a study conducted by a large group of epidemiologists and radiation scientists, concluded that

there is good epidemiological evidence for an increased cancer risk for some doses of radiograph

exposition. Doody et al 4, analyzing breast cancer mortality in 5573 women, reported a 69%

excess in breast cancer mortality among women with scoliosis. And consistent with radiation as

a causative factor, they showed that the risk of dying of breast cancer increased significantly with

number of radiograph exposures and with cumulative radiation dose. Sadetzki and Mandelzweig

19, in a recent paper, stated that children constitute a subgroup at greater risk from exposure to

develop radiation-induced cancer. Uncomfortably, patients with scoliosis continue to be exposed

to ionizing radiation, practically the same as they were thirty years ago. Although the risks

involved may be relatively small, the ancient concept expressed by Hippocrates of ‘ Primum non

nocere’ (First, do no harm) should serve as a guide when assessing the appropriateness of

radiation-based imaging procedures in pediatric patients.

Mathematical relationship between the Cobb and the photogrammetry methods

The scoliotic curve obtained through the Cobb method (MC), is measured by the arc,

defined by the superior plateau of the uppermost inclined vertebra, and by the inferior plateau of

the lowermost inclined vertebra (Figure 4). The angular measurement of the scoliosis curve

obtained through computerized photogrammetry method (MR) was calculated by the sum of the

deviation angles of axis Y, denominated R1, R2, R3 and R4 (the sum of the deviation angles of


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each segment between the superior limit vertebra and the apical vertebra). Thus, the deviation

angle is considered to be that encountered between the secant lines drawn from two consecutive

spinous processes, and the Y axis. Additionally, considering the interval used in the Cobb

method and the interval used in computerized photogrammetry method, a similarity between MCand MR angles can be shown (Figure 4).

In our study, it was possible to establish a mathematical correlation between curve

measurements obtained through the methods taking into account some conditions. Defining the

scoliotic curve as being constituted of perfect segments of a circular arc, as indicated in figure 4,

then the MC measurement is equal to the sum of the angles C1, C2, C3 and C4 obtained between

the consecutive spinous processes found at the same interval of this measurement. Thus, if

angles C1, C2, C3 and C4 are all equal, and equal to C, we will find that the sum of these angles

obtained at the same interval through the Cobb method will be equal to 4C.

Naturally, the scoliotic curve is not a perfect segment of an arc, so a perfect extrapolation

between the curve measurements through the Cobb method and the computerized

photogrammetry method should not easily be made. However, the failure of complete adherence

to mathematical premises for the establishment of a relationship between the two methods did

not result in significant differences in measurements, and appeared to be valid for practical use

within acceptable margins.

Equations

Further considering that the scoliotic curvature is constituted of segments of circular arcs,

the triangles BÂD, DÂE, GFH, and HFJ (Figure 5) will be isosceles triangles.

Therefore, angle X will be indicated by equation (1):

X= (180- C) / 2 (1)


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In addition, there is a relationship between the angles of deviation of axis Y (R1, R2, R3

e R4) obtained through computerized photogrammetry, with the angles (C) of each vertebral

segment as obtained using the Cobb method, as indicated in equations (2), (3), (4), (5):

R1=90 - X = 90 - (180- C)/2 = C/2 (2)R2= R1 + C = C/2 + C = 3C/2 (3)

R3= R4 + C = C/2 + C = 3C/2 (4)

R4= 90 – X = 90 - (180- C)/2 = C/2 (5)

Thus, the MR measurement will be indicated by equation (6):

MR= R1 + R2 +R3 + R4 = C/2 + 3C/2 + 3C/2 + C/2 = 4C (6)

As a result, mathematically, the value of the measurement obtained through computerized

photogrammetry will be equal to that obtained through the Cobb method.

The mathematical proof proposal considered the scoliotic curve as a polynomial arc of

degree 2. It is important to bear in mind that the prior demonstration does not represent a general

solution. However, it makes it easier to understand, as observed in clinical practice, that there is

equivalence between the measurements obtained in this study and those obtained through the

Cobb method.

Results

The curvature values obtained using the computerized photogrammetry method were

similar to the values obtained using the Cobb radiographic method. The proposed method

showed less difference in the thoracic region than in the lumbar region. The total average of

difference of 4.1º between the methods, which includes all thoracic and lumbar curves, was

compatible with the intrinsic error of the Cobb method in inter- and intraobserver analysis 20-22.

Measurements of the Cobb angle bear both an inter- and intraobserver variability of


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approximately 4º to 8º 21, 23-29. The average for the individual measurement differences between

the methods in the thoracic region was 2.9º, while in the lumbar region the average difference

was 5.1º, influenced by the differences observed in two volunteers. Unfortunately, the limited

number of cases in this initial study did not allow for inferences to be made about the possiblecauses involved.

The identification of the apical vertebra was an important step of the computerized

photogrammetry method, and the use of ALTV marks helped in this task. The vertebra with the

largest variation in the analysis of the three-dimensional coordinates from the base to the tip of

the ALTV coincided, generally, with the identified apical vertebra. The concordance in the

localization of the apical vertebra between the computerized photogrammetry method and the

Cobb method , as estimated through Kappa index, was excellent, according to criteria based on

the interpretation of Landis and Koch (Kappa > 0.80 = excellent concordance) 30. Besides, with

the use of these marks, virtual images of the spatial behavior of the spinal column could be

generated using SolidWorks® software (Santa Monica, CA, USA)(Figure 6).

Döhnert and Tomasi attempted, without success, to detect mild scoliosis using

photogrammetric principles31. The protocol used by them was different from the protocol applied

in this study. They chose an analysis protocol using surface marks only in C7, T9 and L5. Saad

et al32 also did not find a linear relationship between the photogrammetric and radiographic

methods using a similar protocol to that used by Döhnert and Tomasi. We believe that the

protocol used in both studies does not allow adequate angular quantification of scoliotic

curvature, because a mathematical relation of similarity is not possible with the Cobb method

using their methodology and parameters.

Although this study did not have as an objective the evaluation of costs, a few

considerations on the topic are pertinent. The total cost of the photogrammetric equipment

(computer, software license, simetograph, digital camera, tripod, surface markers) was US$


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1,826. Strictly for use as a comparison, the cost of installed radiographic equipment used in this

study was US$ 216,238. Basic skills needed for the use of this method were: primary knowledge

on spinal anatomy, photography and imaging software. The time spent with the radiographic

method on a typical patient was 13 minutes (positioning, photographic exposure, and one curvemeasurement), while the time spent using the manual photogrammetric measurement was 28

minutes (surface marking, photographic exposure and one curve measurement). We considered

this longer time period the principal drawback of the photogrammetric method. On the other

hand, we believe that the automation of the photogrammetric curve measurement with the

development of software specific to this task is feasible and, hypothetically, may reduce the time

necessary to obtain the curvature angle.

This study presents limitations. In this consecutive series, the majority of volunteers

presented a BMI below or within normal variation (18.5 – 25 kg/m2), which may have facilitated

a more precise localization of the spinous process and, presumably, have positively influenced

the performance of this method, having the Cobb method as a reference. Beyond body weight,

factors such as lumbar curves, previous spine surgery, and the ability of the examiner, may

constitute obstacles which could restrict the application of the method.

Radiography currently is and probably will remain the principal examination method for

children with spinal deformities. The method presented in this study does not seek or intend to

replace the radiological exam. It introduces a new approach in the non-radiographic evaluation

of scoliosis, with potential application in monitoring the curvature. Further studies are needed to

firmly assess the potential of this method as a co-adjuvant tool in the routine following of

scoliosis treatment. Important points arising from this preliminary evaluation, such as refinement

of the photogrammetric technique, costs, and validation of a new diagnostic test are now under

current investigation in our institution.


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Figure 1. The left line (white) identifies the apical vertebra through the tangent of the vertical

line and convexity of the curve (T10). The right line (grey) identifies the first vertebra to

interrupt the vertical alignment (T4) as the superior limit vertebra.

Figure 2. Measurement of angle Rn for each segment localized between the superior limit

vertebra (T4) and the apical vertebra (T10): R 1 = 10º, R 2 = 4º, R 3 = 8º, R 4 = 12º, R 5 = 10º, R 6 = 9º

and R 7 = 4º. Angle MR = sum Rn = 57 degrees.


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Figure 3. Comparison between the curve measurements obtained through the Cobb method and

the computerized photogrammetry method for thoracic and lumbar curves.

Figure 4. Angle of scoliosis curvature obtained through the Cobb method (MC=C1+C2+C3+C4),

and obtained through the computerized photogrammetry method (MR=R 1+R 2+R 3+R 4).


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Figure 5. Demonstration of the isosceles triangles formed by the circular arcs of each vertebral

segment (BÂD, DÂE, GFH and HFJ) and their relationship with angles R1, R2, R3 and R4.

Figure 6. The figures represent the spatial behavior of a scoliotic curve of a volunteer, using

anatomical landmark type vector (ALTV) processed in three distinct planes.


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Table1. General characteristics of each individual included in the study and their measurements using

Cobb method and computerized photogrammetry method for thoracic and lumbar regions.

COBB COMPUTERIZED

PHOTOGRAMMETRY

S u b j e c t s

A g e ( y e a r s )

G e n d e r

B M I

S c o l i o s i s l e v e l

Thoracic Lumbar TAV LAV Thoracic Lumbar TAV

LAV

1 39 F 20.8 T and L 59.8º 26.0º T10 L4 57.4º 17.6º

T10

L3

2 15 M 17.1 T and L 32.0º 15.0º T9-T10 L2-L3 34.4º 17.2º T9 L3

3 22 F 18.3 Thoracic 27.0º - T9-T10 - 25.8º - T9 -

4 13 F 25.5 T and L 30.4º 32.0º T7-T8 L2 22.6º 24.0º T8 L2

5 12 F 21.7 T and L 39.6º 33.8º T8 L2 40.8º 10.0º T7 L2

6 19 F 22.9 T and L 28.2º 38.4º T8 L1 22.4º 35.4º T8 L2

7 16 F 22.2 T and L 42.2º 22.8º T9 47.0º 22.8º T7 L2

8 14 F 17.4 T and L 22.4º 27.0º T9 L2-L3 23.0º 30.0º T9 L3

9 11 F 19 T and L 50.4º 48.6º T7 L2 51.0º 55.0º T7 L2

10 25 F 19.8 T and L 21.4º 18.8º T8 L2 26.4º 16.8º T9 L3

11 45 F 23.4 T and L 25.6º 26.4º T7 L2 29.0º 27.8º T7 L3

12 46 F 18.9 T and L 73.0º 41.8º T6-T7 L2 74.2º 39.4º T7 L2

13 14 F 17.8 L - 19.8º - L2-L3 - 22.0º - L3

14 13 F 15.9 L - 14.0º - L1 - 26.0º

T12

-

15 15 M 16.9 L - 18.4º - L1 - 17.8º - L1

16 25 F 23.1 T and L 17.8º 25.5º T5 L2 19.6º 23.8º T5 L1

F= Female; M=Male; BMI= Body Mass Index; T= Thoracic; L= Lumbar. TAV= Thoracic Apical

Vertebra;


22/22

A

C C E P T E

D

LAV= Lumbar Apical Vertebra.

Table 2. Comparison between the curve measurements obtained through the Cobb

method and the computerized photogrammetry method for thoracic and lumbar

curves.

N minimum maximum average

standard

deviation p-value

Thoracic Cobb 13 17.80º 73.00º 36.14º 16.38º

Thoracic Photogrammetry 13 19.60º 74.20º 36.43º 16.67º 0.529

Lumbar Photogrammetry 15 10.00º 55.00º 25.71º 11.04º

Lumbar Cobb 15 14.00º 48.60º 27.20º 10.05º 0.615

escoliose e fotogrametria

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