Vertebral Metrics

Application of a Non-invasive System to Analyse Vertebrae Position using Two

Seating Platforms

Ana Teresa Gabriel

, Cláudia Quaresma

, Mário Forjaz Secca

1,2

and Pedro Vieira

LIBPhys-UNL, Departamento de Física, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Caparica,

Portugal

Ressonância Magnética – Caselas, Lisboa, Portugal

Keywords: Spine, Medical Device, Non-invasive, Vertebrae Position.

Abstract: The study of the biomechanical changes in the spinal column is particularly important in modern society since

they are considered the main responsible for back pain. Vertebral Metrics is an instrument that aims the global

evaluation of the spinal column. Noninvasively and semi-automatically, this image processing based system

allows the identification of X, Y and Z position of each spinal process on standing position. The analysis of

vertebraes position using two different seating platforms through the application of Vertebral Metrics is the

aim of this work. Along the paper the main stages concerning to the study will be described. Nine volunteers

were recruited and an ergonomic chair and a bench were used to perform the study. Results show that

differences in vertebrae position are not relevant when sitting in the ergonomic sit or in the lab. Also, spinal

curvatures as well as lateral deviations of the spine were properly represented from data collected with

Vertebral Metrics. The study proved that Vertebral Metrics has a huge potential to perform the analysis of

the spinal curvatures.

1 INTRODUCTION

Spinal column is an essential component of human

body promoting support and protection functions.

Also, trunk and limbs movements are provided by the

spine (Seeley et al., 2003).

Back pain has long been a relevant problem in

modern society. The number of people affected by

this symptom increases every year (Manek and

MacGregor, 2005). Previous studies pointed out that

50% to 80% of the individuals experience at least one

episode of back pain during their lifetime (Rubin,

2007). From those 80% to 90% are caused by

mechanical spinal disorders (Najm et al., 2003;

Quaresma et al., 2010). Congenital malformations,

sedentary lifestyle, posture and incorrect physical

exercise have a great contribution for the mechanical

disorders (Jordão et al., 2011).

An important tool to identify the spinal problem

and delineate the appropriate methodologies is the

study of the spinal curvatures. Radiological

techniques are the most widely used methods for

assessing the spinal column however they use

ionizing radiation. Thus, these techniques must be

carefully applied (Harlick et al., 2007; Pinel-Giroux

et al., 2006).

Ionizing radiation free devices are needed to

evaluate, in a global way, the spinal column.

Although many non-invasive devices have been

developed to assess the spinal column most of them

does not allow the three-dimensional evaluation of

the spine. In addition, those who allow a 3D analysis

are extremely expensive as the methods that use

infrared cameras (Hinman, 2004).

Vertebral Metrics – National patent PT/103990,

European patent PCT/IB2009/005018 and American

patent US20110004125 - is a non-invasive system

designed to identify the spatial position of the spinal

apophysis from the first cervical to the first sacral

vertebrae in the standing position. Using a fluorescent

marker to identify the skin projection above the spinal

processes, recognition is achieved with software

capable of distinguish the marks (Gabriel et al.,

2015a; Gabriel et al., 2015b). Due to its versatility the

equipment can have several applications from

screening and prevention to monitoring the

intervention methodologies for each clinical case.

Gabriel, A., Quaresma, C., Secca, M. and Vieira, P.

Vertebral Metrics - Application of a Non-invasive System to Analyse Vertebrae Position using Two Seating Platforms.

DOI: 10.5220/0005790202350240

In Proceedings of the 9th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2016) - Volume 1: BIODEVICES, pages 235-240

ISBN: 978-989-758-170-0

 2016 by SCITEPRESS – Science and Technology Publications, Lda. All rights reser ved

235

The aim of this paper is to present a study

concerning to the application of Vertebral Metrics in

the sitting position. Sedentary lifestyle is a significant

concern of modern society and seating position is one

of the most adopted positions. In addition, the

majority of the occupational activities are carried out

in that position.

According to studies performed by Chen et al.

(Chen et al., 2006), a significant change in spinal

curvature is found in a sitting position, causing a

forward displacement of the lumbar spine, increased

thoracic kyphosis and a decrease in pelvic angle. It

contributes to a posterior pelvic tilt. They concluded

that the pressure on the intervertebral discs is larger

in this position than in the standing position, which is

explained by the pelvis rotation. This causes a change

in the biomechanics of the spinal column, leading to

a pressure increasing in the lumbar intervertebral

discs. The sitting posture is highly stressful because it

requires large static work of the muscles involved.

During the study nine volunteers were recruited

and vertebrae’s configuration was analysed in the

sitting position using two seating platforms - an

ergonomic seat and a lab seat. The ergonomic seat is

prescribed by physicians as a good posture promoter

in sitting position. Lab seats are widely used however

as they do not have a lumbar support they stimulate

bad postures. The main goal of the study is to quantify

postural differences between the two sitting

platforms.

2 MATERIALS AND METHODS

2.1 Vertebral Metrics

For a better understanding of the object of this study

the considered axis system will be defined as follows:

the transversal distance is X coordinate, the antero-

posterior distance is Y coordinate and the height is the

Z coordinate (Figure 1).

Figure 1: Mechanical apparatus of Vertebral Metrics and

axis system.

Vertebral Metrics system consists of a vertical

positioner – Z positioner - and a horizontal positioner

– X positioner – with a bracket coupled. A stereo

vision system and two ultraviolet lights are fixed on

the bracket in specific positions. A resolution better

than 1 mm in each direction is provided by the stereo

vision system. Therefore two monochromatic video

cameras are fixed side by side in the horizontal

support. The cameras (model UI-3480ML from

IDS™) are 47 mm from each other. They have

2560x1920 pixels resolution and a lens with 12 mm

of focal distance (Optica Goyo from IDS™).

Hardware is controlled by software that was specially

developed for that purpose. Communication

functions as well as the user interface were defined in

Visual Studio™ (Gabriel, 2015b).

A fluorescent marker is used to identify the spinal

processes above the skin. When excited by ultraviolet

light this dye emits a well-known wavelength – 635 –

whereas the ultraviolet light emits at 400 nm. Image

processing algorithms were implemented in Matlab™

to recognize the fluorescent marker and determine the

spatial coordinates of each point. To simplify the

definition of the image processing algorithms an

optical filter (BP635 from MedOpt™) was coupled to

each camera. The optical filters selectively transmit

light in a particular range of wavelengths - from 600

nm to 700 nm - while blocking the remainder.

Therefore the fluorescent marks stand out in the

pictures acquired by the cameras which allowed the

definition of less demanding image processing

algorithms (Gabriel, 2015b).

In the beginning of each scan, the mechanical

structure must be positioned under the point that

identifies the first sacral vertebrae. This step is

performed by a physician using the user interface.

When the previous condition is accomplished the

physician should press the Start Button to initialize

data collection. Thereby an automatic cyclical

process is carried out by software. During that process

a pair of images is acquired simultaneously by the

cameras and then the mechanical structure moves

upwards. After 50 mm the equipment stops and

another pair of images is acquired by the cameras.

Sequential images are recorded in a folder to be

posteriorly analysed by image processing algorithms.

The algorithms will identify the fluorescent marks

and determine its tridimensional coordinates. It is

noteworthy that data acquisition is completed in such

a short period of time – between 30 and 40 seconds -

because image processing is performed after a

complete full scan of the spine (Gabriel et al., 2015b).

Data collection with Vertebral Metrics becomes

available a table with the 3D coordinates of each

BIODEVICES 2016 - 9th International Conference on Biomedical Electronics and Devices

236

spinal process as well as a 3D representation of these

points. By definition, first sacral vertebrae is always

considered the reference – its coordinates are (0,0,0)

– and the other vertebraes coordinates represent

relative positions comparing with the reference.

2.2 Application Protocol

The application of Vertebral Metrics to analyse

vertebrae position using two seating platforms is the

main goal of this work. Thus an ergonomic sit and a

lab sit were used consecutively to perform the study

(

Figure 2). Nine volunteers – eight male and one

female - aged between 18 and 27 years old and with

no associated pathology were recruited. Letters from

A to I were used to identify the volunteers.

Procedures, purposes and risks associated with the

study were explained and informed consent was

obtained from each volunteer before participation.

Tests were performed in the Instrumentation for

Medicine Laboratory under a project lead by

FCT/UNL.

Figure 2: Seating platforms: a) ergonomic sit; b) lab sit.

Before data collection, the spinal processes were

identified by the physician. In each individual twenty

spinal processes were identified – from the sixth

cervical vertebrae to the first sacral vertebrae – and

five consecutive scans were performed using the

ergonomic sit followed by five consecutive scans

using the lab sit. The first five cervical vertebraes

were not identified because their skin projection was

covered by hair. The fluorescent marker spreads

when applied above hair. Thus, the marks are not

identified by the image processing algorithms as they

are optimized to recognize circular shapes only. This

problem will be addressed in the future with a better

method to place the markers.

Figure 3 shows volunteer

C during the data acquisition process with both

seating platforms.

It is noteworthy that he number of subjects (nine

volunteers) as well as the number of consecutive

scans (five for each subject in each sitting platform)

was set based on what was considered correct given

the data acquisition time and the reasonable number

of measurements.

Figure 3: Data collection: a) ergonomic sit; b) lab sit.

3 RESULTS

Collected data was carefully analysed in order to

evaluate vertebrae position differences between the

two seating platforms used along the study.

As five scans were performed to each platform,

the first approach included the determination of

means and standard deviations. Spinal processes are

represented by 3 coordinates – X, Y and Z – and we

performed five scans with each seating platform so

mean value and standard deviation were calculated

for each coordinate of each vertebrae. Several

standard deviation values obtained are bigger than

system resolution – 1 mm in each spatial direction. As

the sound of the repositioning movement of the

mechanical apparatus was identified by the

volunteers, postural adjustments performed during

this periods are the main responsible for the

unexpected values. Furthermore, the standard

deviation increases in the upward region which is

explained by the larger spinal mobility in the thoracic

and cervical area. Besides the previous constraints the

3D coordinates obtained in each independent scan of

the spine are not affected by the movement artefacts.

Postural adjustments are insignificant during the 30

seconds required for a complete scan. In these

circumstances, a comparison of vertebrae coordinates

mean values does not make any sense. An alternative

approach involved the analysis of the first scan for

both situations. First scan was chosen because

volunteers were extremely focused in stay perfectly

still in the begging of each test. Nevertheless any

other scan could have been analysed. Spinal process

position observed from the coronal and sagittal planes

are shown in Figure 4 and Figure 5, respectively.

Vertebral Metrics - Application of a Non-invasive System to Analyse Vertebrae Position using Two Seating Platforms

237

Figure 4: Vertebrae position observed from the coronal

plane: a) volunteer A; b) volunteer B; c) volunteer C; d)

volunteer D; e) volunteer E; f) volunteer F; g) volunteer G;

h) volunteer H; i) volunteer I.

Spinal curvatures information is not

comprehensive by observing vertebrae position from

the coronal plane – x0z. Nevertheless this view is

useful to analyse lateral deviations of the spine.

Although Figure 4 b, c, d, e, f and g present an

identical shape regarding to lateral deviations

between both seating platforms, there is no link on

Figure 5: Vertebrae position observed from the sagittal

plane: a) volunteer A; b) volunteer B; c) volunteer C; d)

volunteer D; e) volunteer E; f) volunteer F; g) volunteer G;

h) volunteer H; i) volunteer I.

which platform contributes to a bigger deviation.

Lateral deviation differences as well as the absence of

a standard may be explained by movement artefacts.

Changing the seat implies up and sit down which

leads to postural changes.

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238

Figure 5 allows the analysis of spinal curvatures

by observing vertebrae position form the sagittal

plane – y0z. Similar to what was found in the analysis

of lateral deviations there is no standard on the

results. Once again movement artefacts have

contributed to the unexpected results. However spinal

curvatures have an identical shape in both cases.

At last another type of analysis was performed. To

the X and Y coordinates separately, distances between

vertebrae position in lab seat and the ergonomic seat

were calculated. In Figure 6 a scheme of the referred

distance in X direction just to one vertebrae is

presented in order to understand which distance - ∆

- we are determining. The same method was used to

calculate distances in Y direction.

Figure 6: Scheme of the calculated distance in X direction.

Mean and standard deviation were determined for

the X and Y coordinate each vertebrae considering the

five acquisitions performed with both seats in each

volunteer. Moreover mean and standard deviation

were determined for each vertebrae considering all

the acquisition performed in all volunteers. Table 1

presents the results obtained for the second condition.

In both cases mean values are smaller than the

deviation so it is not possible to conclude the

adjustment carried out by each seating platform.

By observing the aforementioned table it is found

that

∆

increases along the spinal column, namely

from S1 until C6 vertebraes. As ∆ represents the

difference between the lab seat and ergonomic seat

(



−



), negative values indicate

that, in general, the lateral deviation of the spine is

greater to the ergonomic chair. The same correlation

is identified to the standard deviation. High values of

this parameters are explained by interpersonal

differences. Regarding to the Y coordinate, there is no

standard in ∆ and it was found an increase in the

standard deviation. Again this is explained by

interpersonal differences.

Table 1: Mean and standard deviation of distance between

X vertebrae position in the lab sit and the ergonomic sit and

distance between Y vertebrae position in the lab sit and the

ergonomic sit for all acquisitions in all volunteers.

∆



(mm)



∆





(mm)

∆



(mm)



∆



(mm)

0.00 0.00 0.00 0.00

-0.35 0.79 -1.44 2.84

-0.48 1.45 -2.07 3.81

-0.54 2.47 -3.07 5.62

-0.82 3.17 -3.12 6.93

-1.09 3.88 -1.78 8.31

T12

-1.48 4.61 -0.96 9.44

T11

-1.83 5.37 -0.03 9.73

T10

-1.82 5.89 0.40 11.18

-2.25 6.65 2.37 12.62

-2.49 7.30 3.22 13.20

-2.75 7.77 4.20 14.73

-3.06 8.05 5.41 15.80

-3.10 8.16 5.49 17.29

-3.40 9.12 3.57 15.93

-3.40 9.80 6.76 20.45

-4.38 10.46 -0.64 22.17

-4.91 11.06 6.85 21.95

-5.81 11.64 5.73 22.30

-6.28 12.10 6.73 23.33

4 CONCLUSIONS

Vertebral Metrics is a non-invasive equipment

developed by our research group. It was primarily

designed to identify the spatial position of the spinal

processes from the first cervical to the first sacral

vertebrae in the standing position.

Present another application of the equipment - the

analysis of vertebrae position using two seating

platforms - is the object of this study. Nine volunteers

were recruited and five acquisitions with the

ergonomic sit followed by five acquisitions using the

lab sit were performed. Collected data was carefully

analysed and results show that there are no significant

differences in vertebrae position when sitting on the

ergonomic sit or in the lab sit. Also a standard was not

found regarding to the use of the two platforms.

Postural adjustments when the seat was changed

contributed to the lack of uniformity.

A complete scan of the spine takes about 30

seconds while the automatic repositioning of the

Vertebral Metrics - Application of a Non-invasive System to Analyse Vertebrae Position using Two Seating Platforms

239

mechanical structure to return to the initial position

takes 15 seconds approximately. Thus the time

required to perform five consecutive acquisitions is

about 4 minutes which is too long for any person

stand perfectly still. Although Vertebral Metrics not

touch the volunteer’s backs, motion artefacts were

identified between scans. Postural adjustments

performed during the repositioning of the mechanical

structure are the cause of the artefacts.

Overall, remarkable differences were not found in

vertebrae position regarding to the use of an

ergonomic seating or a lab seating. Also results does

not allow to conclude the adjustment performed by

each seat. However, spinal curvatures as well as

lateral deviations are properly viewed from data

collected with Vertebral Metrics.

The study proved that Vertebral Metrics has a

strong potential to become a powerful tool to evaluate

the spinal column curvatures in standing or sitting

position. This unique and already patented device will

avoid unnecessary invasive methodologies as well as

qualified staff for screening and prevention of spinal

disorders because it will allow repeated scans without

causing damage to the individuals. Vertebral Metrics

will also became available the definition of the most

appropriate intervention methodologies to each

particular clinical case.

ACKNOWLEDGEMENTS

The authors express gratitude for the precious

collaboration of the ten volunteers recruited to

perform this study. Also the author would like to

acknowledge NGNS – Ingenious Solutions for the

support provided during the development of

Vertebral Metrics.

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