Method of measuring plantar pressure with resistive sensors.

Dobra, Andreea

1. INTRODUCTION

The means of measurement are as diverse and feet as they measured, how each system offers a number of advantages, and comes with a number of limitations, so will not find a system that is suitable for all types of measurements.

Plantar pressure may be measure static and / or dynamic through several ways. All require expensive equipment and complex software. The methods of investigation of plantar pressure began in 1881 and evolved along with technology development.

The papers propose a measurement method for plantar pressure with resistive sensors. The device consists of a platform with 8 sensors, an acquisition board (Labjack U12 National Instrument) and a connection by USB with a PC.

Special software made in Visual Basic environment, allow viewing value measured, date & time of measurement and save this in a database.

For future development to this device it can multiply number of sensors and putting them in a specific area. The device is made for general use to preliminary trace or forewarns any problems of feet (heel, shank, etc.) in any place where is necessary.

2. GENERAL PROBLEMS OF DISEASES LEGS

Legs are very complex structures, composed of bones, joints, muscles, tendons, nerves, blood vessels and skin. They may develop some problems (with origins in other parts of the body) or may suffer injuries, traumas. The most obvious symptoms are pain at shank and dysfunction such as over a foot, inability to bear pressure on heel or fingers, etc. The pain can be caused by inappropriate footwear, injury or stretch the tendon and ligaments.

What are the most common problems?

2.1 General problems

--Fingered "hammer" (fig.1.1a)

--Bursitis hallux: (Hallux Abducto Valgus) (fig. 1.1b).

--Flat feet (fig. 1.1c)--Arch plantar develops between the ages of 3 and 10 years. At birth, and after a few years, all children have flat feet. Many people, although they have a small arc plantar not suffer of flat feet. Causes of this disease can be atrophying of muscles and ligaments submission by older, or years of standing in inappropriate footwear.

--Pes cavus (fig. 1.1d) is a medical term for a cavus deformity of the foot due to a fixed plantar flexion of the foot. There is a high arched foot--it is the opposite of flat feet. It is much less common than flat feet and the cause may be neurological, orthopedic or neuromuscular. Unlike most cases of flat feet, pes cavus can be painful because of metatarsal compression.

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2.2 Problems due to sports activities

* Tendonitis Achilles

* Calcaneus's fracture is the most common cause of heels pain

* Dysfunction of posterior tibiae tendons

2.3 Problems caused by diabetes

High level of glucose in the blood of diabetes patients can cause major problems on two legs:

--Termination nerve damage: if nerves are deteriorating, it may not realize pain, heat or cold to the legs.

--Blood circulation deficit: this makes it very difficult wound healing and infections.

3. METHODS OF DETECTION OF DISEASES LEGS

3.1 Plantar Pressure measurement in footwear (static or dynamic)

There are complex systems that allow a very high degree of mobility patient, allowing play under normal pressure from the soles. They even allow recording of movies with patients, and real-time play map pressure from the soles. (Actis et al., 2005) The system is composed of a receiver, fixed around the waist, which is connected to the inner soles that sit in footwear. The receiver stores all information relating force / pressure from the soles. Mobile Unit attached to the PC may transfer parameters and test data collected, allowing a view real-time data (Tekscan, 2006). This interface makes it possible to view 2-D and 3-D data recorded, showing curves of dependency pressure and force depending on time, allows comparison of data obtained pre-and post-treatment and isolation of specific areas of the soles.

3.2 Carpet sensory elements to measure the pressure / static forces static conditions

This system allows the evaluation, registration, documentation and data collected from the soles.

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It can be used to prescribe orthotic inner soles, and educate patients (Fig.2.)(Kirby, 2007).

3.3 Carpet sensory elements to measure the pressure / force in the dynamic conditions

This system allows measurements in both static and dynamic. It can do an analysis of normal or perturbed walking along several steps (Fig. 3.)(Urry, 1999)

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3.4 Assessing the plantar pressure by photographic methods

It is a method low cost viewing pressure plantar, which consists in a photocopier to support the weight of the human body. By this method can distinguish healthy feet, with flat feet or feet with plantar arch too high (Fig. 4).

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3.5 Plantar pressure measurement through fiber-optic network

This method is based on the modification of light transmitted through an optical fiber network. By applying a force on it, is hereby-amended section fiber, which leads to diminishing light in this area (Fig. 5.).

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4. EQUIPMENT DESCRIPTION

The proposed system as a platform consists of acquisition board Labjack U12 and a PC (Fig.6.). The link between the platform and measuring acquisition board is achieved through two connectors for each plantar platform individual.

Multiplexing board is a printed circuit board, which takes over the role-multiplexing signal from the eight sensors. Multiplexer is an electronic switch, which carried out the operation of interruption, the ordering of input signals, namely the selection of an entry. The application is used two of the eight entries of the measuring, making it possible acquisition of six other types of signals, which can contribute to the diversification of the application, depending on the customer's requirements (Dobra & Albert, 2006). The used sensors are CZN--CP6 type (Membrane compression sensors). Software to measure a plantar pressure--is made in Visual Basic 6.0 environment. The user interface is shown in Fig. 7. is compose from 4 areas: patient's identification--name, gender, date of birth--(text boxes), pressure points visualization--sensors distribution picture (picture box), values tables and action area (command buttons: delete, read value, save & history, and end).In the picture box, the date on which the investigation is automatically generated based on the data system. Database can be view whenever with or without measuring step.

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5. CONCLUSION

With equipment were made measurements (in different dates and times) and was created a database. By increasing the number of resistive sensors and putting, them in specific areas such increase measurement sensitivity and equipment performance. Improved equipment will allow to measure preventive and periodical, a static plantar pressure for everyone (children or adults), by placing the device in school or workplace.

6. REFERENCES

Actis, R. L.; Ventura, L. B.; Szabo, B. A. (2005). Plantar Pressure Distribution In The Diabetic Foot During Push-Off: Numerical Simulation Using The P-Version Of The Finite Element Method, proceeding of XXth Congress of the International Society of Biomechanics And 29th Annual Meeting of the American Society of Biomechanics July 31-August 5, 2005, Cleveland, Ohio

Dobra, A. & Albert, E. (2006). Measurement methods of plantar pressure, Work License, POLITEHNICA University of Timisoara, Mechatronic Department (June 2006)

Kevin A., Kirby. (2007). Emerging Concepts in Podiatric Biomechanics--Available from: http://www.podiatrytoday.com/article/6436 Accessed: 2007-03-10

Tekscan, (2006), Medical page, Available from: http://www.tekscan.com, Accessed: 2006-01-27

Urry, S. (1999). Plantar pressure measurement sensor, Measurement. Science and. Technology, Volume 10, No.1, (1999) R16-R32, Available from: http://www.iop.org/EJ/abstract/0957-0233/10/1/017, Accessed: 2006-02-12