DEVELOPMENT OF A MECHANICAL INSTRUMENT

TO EVALUATE BIOMECHANICALLY THE SPINAL COLUMN

IN PREGNANT WOMEN

Cláudia Quaresma, Mário Forjaz Secca

CEFITEC, Dep. of Physics, Faculdade de Ciências e Tecnologia, UNL

Quinta da Torre, P-2829-516, Caparica, Portugal

João O’Neill

Faculdade de Ciências Médicas, UNL , Quinta da Torre, P-2829-516, Caparica, Portugal

Jorge Branco

Maternidade Dr. Alfredo da Costa, Lisboa, Portugal

Keywords: Biomechanics, Vertebral column, Non-invasive instrument, Evaluation, Biomechanical, Standing position.

Abstract: The incidence of problems related to rachialgiae is so frequent and usual that it must be studied as if it were

an epidemic and social disease (Knoplich, 2003). Instruments that evaluate the spinal column in a standing

position, in a global way, are needed to attain a better insight into this problem. This work presents a

completely safe instrument to assess the evolution of all the vertebra locations throughout time, in order to

study the biomechanical changes in women during pregnancy. A mechanical system, registered as Vertebral

Metrics, with the objective of evaluating the curvatures and lateral deviations of the spinal column in the

standing position was built. A measuring part, which is the body of the instrument, and a supporting part,

where the previous part is mounted, constitute the new non-invasive instrument. The measuring part

consists of 17 identical adjustable mechanical blocks that allow us to reproduce the position of each vertebra

of the spinal column, from the first cervical vertebra to the first sacral vertebra. Vertebral Metrics was

originally planned and built to be applied to pregnant women. However, after redefining dimensions of the

different parts it can be applied to any type of population, in the future.

1 INTRODUCTION

Rachialgiae constitute a relevant problem in modern

society (Alexandre & Moraes, 2001). In many

women this problem appears for the first time during

pregnancy and remains for the rest of their lives,

causing serious problems of absenteeism and

consequently a great loss under the point of view of

the economy of the country. It is necessary to have

instruments that evaluate, in a global way, the spinal

column in standing position, in order to understand

better the behaviour of the spinal column during the

gestational period.

There are many instruments to evaluate the

spinal column. However, most use ionizing radiation

and very few allow us to analyse the spinal column

in a standing position.

The instrument that is most used to evaluate the

spinal column in the standing position is the

radiograph. However, since it uses ionizing

radiation, it should not be used on pregnant women

(Harlick e al, 2007; Pinel-Giroux e tal, 2006) and,

besides, it would only give a collapsed two-

dimensional view.

The study presented here is part of a broader

analysis where we intend to identify and describe the

biomechanical alterations of the spinal column that

occur throughout pregnancy. We found it was

necessary to build a non-invasive instrument that

would allow the reproduction of the position of each

of the vertebrae, through the identification of each of

the vertebral apophyses of the spinal column, from

310

Quaresma C., Forjaz Secca M., O’Neill J. and Branco J. (2009).

DEVELOPMENT OF A MECHANICAL INSTRUMENT TO EVALUATE BIOMECHANICALLY THE SPINAL COLUMN IN PREGNANT WOMEN.

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 310-313

DOI: 10.5220/0001779903100313

 SciTePress

the first cervical vertebra to the first sacral vertebra.

In a global way Vertebral Metrics evaluates the

curvatures and lateral deviations of the spinal

column in the standing position.

After an exhaustive search of existing

instruments we found the inexistence of an apparatus

with the required characteristics, which led us to

prepare and elaborate an equipment to measure the

lateral deviations and curvatures of the spinal

column.

The elaboration started with the conceptual

design of the apparatus, based on some existing

instruments. Measurements on 134 women were

carried out in order to define its dimensions,

including the height of the body, the support, the

size of horizontal pieces and the stand of Vertebral

Metric. The experimental procedure of the

previously mentioned study was performed as

follows:

1- The length between various points of reference

was measured in each woman.

2 - The Normality test for each of the variables was

applied.

3 - Significance> 0.05 was found.

4 - The confidence intervals for 99% were calculated

The details of the mechanisms of each of the pieces

and the choice of the convenient materials to use

(polycarbonate, brass, steel and duralumin) to build

the instrument were defined afterwards.

Finally, Vertebral Metrics was built (Figure 1)

and the necessary adjustments were performed.

2 VERTEBRAL METRICS:

DESCRIPTION

AND FUNCTIONING

The objective of Vertebral Metrics, a non-invasive

mechanical instrument, is to identify the x, y and z

positions of each vertebra, from the first cervical

vertebra to the first sacral vertebra. After entering

these data into a mathematical model of the spine,

the curvatures and lateral deviations of that segment

in the standing position can be calculated.

The components of the apparatus (Figure 2) are

the “body” (1) and the “support” (2).

The “body” has a vertical piece (5), mounted in

the support (2), with 18 horizontal pieces (4) called

“2D Positioner”. Two pieces, one vertical, where

the body of the instrument fits, and a stand where the

person to be evaluated stands up, constitute the

“support”.

Figure 1: Image of Vertebral Metrics.

Figure 2: Diagram of Vertebral Metrics.

Figure 2 presents two views of the whole

instrument, with (a) and (b) showing the frontal view

and the left lateral view, respectively.

The Vertical piece of the body (Figure 3)

consists of a rectangular profile with two plates at

the ends, which provide rigidity and the fixation to

the system.

Figure 3: Vertical piece of the body of Vertebral Metrics.

A detail of the instrument, is presented in Figure

4. The “2D Positioner” (4) slides along the scaled

ruler attached on the vertical piece (3).

DEVELOPMENT OF A MECHANICAL INSTRUMENT TO EVALUATE BIOMECHANICALLY THE SPINAL

COLUMN IN PREGNANT WOMEN

311

Figure 4: One of the “2D Positioner” and the vertical

piece of the body of the instrument.

Figure 5 shows components, 6, 7, 8, 9 and 10 of

the “2D Positioner. The component 7 is a square

sectioned rod, with a cone shaped tip, which is

where it makes contact with each vertebra apophysis

contact point. This rod is manoeuvred by two

pinions, (6), placed horizontally and touching the

rod via a neoprene O-ring surrounding the pinions. It

fixes the y position of the vertebral apophysis. This

coordinate is calculated through the distance from

the conical end, (5), to each “2D Positioner”, (4), of

the body of the instrument.

The pieces 6 and 7, moved by the horizontal

threaded rod (8), are fixed at the top by a plate and

two bolts. These bolts are inserted in two vertical

threaded holes, passing through the rotational axis of

the pinions 6.

At the fixed end of the rod 8 there is a small handle

which rotation enabling rotational movement of the

rod, which, in turn, allows movement of piece 7.

Measurements of the x position (see Figure 4) of the

vertebral apophysis of each of the vertebrae are then

possible.

Figure 5: Top view of “2D Positioner”.

The component 9 is a piece that fixes the “2D

Positioner” which moves upwards/downwards on

the vertical piece (3), as component 10 rotates.

Finally, coordinate z is obtained from the

measurement of the position of the horizontal part in

piece 4 (see Figure 1).

The support of Vertebral Metrics has two pieces:

one horizontal plate supported on four feet, where

the person to be evaluated stands, and one vertical

piece, shown in Figure 6, where the vertical part of

the body of the instrument (see Figure 2) fits.

Figure 6: The support of Vertebral Metrics.

After marking the vertebral apophyses (Figure 7),

with a washable pen, each pregnant woman stands

up on the stand of the support of the instrument with

the posterior face of the trunk facing the body of

Vertebral Metrics.

Figure 7: Marking the vertebral apophyses with a

washable pen.

All the 18 “2D Positioners” of the body of

Vertebral Metrics are identical and adjustable,

allowing the identification of the x, y and z positions

of the vertebral apophyses, from the first cervical

vertebra to the first sacral vertebra.

Three of the “2D Positioner” pieces are used

distinctively. The first is placed in the occipital

region and is used, during the data collection, as a

reference point. The second piece collects the data of

the cervical vertebra and the piece number fifteen

collects the data from the first, second and third

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lumbar vertebra. The remaining horizontal pieces

will identify the position of all other vertebral

apophyses of the spinal column (Fig 8).

The x, y and z positions of each “2D Positioner” are

then obtained.

Figure 8: Example of application of Vertebral Metrics.

Each data collection lasts seven minutes. Figure 9

shows the position of the “2D Positioner” after

application of Vertebral Metrics.

Figure 9: After the application of Vertebral Metrics.

The collected data are then recorded and

transferred to a specific data basis with correction

factors associated with the instrument included. The

final data will then be inserted into the previously

mentioned mathematical model.

3 CONCLUSIONS

Vertebral Metrics is a non-invasive mechanical

instrument, which assesses the curvatures and lateral

deviations of the spine in a standing position. The

patent was registered and the study with pregnant

women was accepted by the Ethics Committees of

the Maternidade Dr Alfredo da Costa and Regional

Health Administration of Lisbon and Vale do Tejo.

The validation process for the instrument,

including the calculation of the correction factors

and uncertainties associated with it was

accomplished.

This instrument allows a global assessment of the

spine. Thus, identification of dysfunctions and / or

diseases of the spinal column in pregnant women,

will be shown on a thorough diagnosis. Intervention

programs, directly connected to specific problems of

each person, may then be elaborated and

implemented.

Vertebral Metrics was originally planned and

built to be applied to pregnant women. However, it

can be applied to any type of population after

redefining the dimensions of the different parts.

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