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FRI0476-HPR Accuracy of a new three dimension postural analysis system based on low cost infrared sensors and emmiters
  1. T.N. Burke,
  2. F.R. França,
  3. A.D. Neto,
  4. L.V. Ramos,
  5. R.R. Caffaro,
  6. A.P. Marques
  1. Department of Physical Therapy, University of São Paulo, São Paulo, Brazil


Background Postural assessment is regarded as the initial physical examination basic procedure to be conducted on patients [1]. However, most existing systems for postural assessment do not use the methodology of real-time scanning of anatomical markers, which could increase the error during the process and analyze posture only in two dimensions. Other systems such as computed tomography, infrared cameras, electrogioniometers or the use of ultrasound, assess posture in three dimensions but are not easily accessible [2,3].

Objectives Develop and verify the accuracy of a low cost 3D postural analysis system based on the automatic scanning of anatomical points by infrared sensors.

Methods The System was developed using the Nintendo Wii videogame controller as a infrared sensor and infrared LEDs as body markers. The sensor tracks each spatial marker coordinates and send them to the computer by bluetooth connection. To calculate distances, the System uses the Pythagorean Theorem d2=(xb-xa)2 + (yb-ya)2 and to calculate angles, the Law of cosines a2 =b2+c2-2bc.cosθ.

To the accuracy evaluation, the markers were positioned at a distance of 2.5 meters of the Wiimote, at the same plane, and the system was calibrated with two markers, positioned at 50 cm between them (distance measured by a digital precision caliper). After the calibration, the LEDs distance was modified to 56 cm and the system tracked the new markers position. Another marker was added, randomly, generating an unknown triangle. The three inner angles were measured and the values summed. The value found was compared with the expected sum (180o), according to the interior angle sum theorem. The differences between the known values and those found were considered as system error.

Results The system error for distances was 4 mm and for angles was zero degrees.

Conclusions The system showed good accuracy in measuring angles and distances, with erros of 0% and 0,7%, respectively and can be useful for clinical use and for scientific research. The next step is to develop an algorithm to calculate the sagittal and coronal curvatures of the spine in real time. The system can be useful for clinicians because of the low cost and the good applicability.

  1. Cocchiarella L, Anderson GBJ. Guides to the evaluation of permanent impairment. AMA Press; 2001.p.375–422.

  2. Christensen HW, Nilsson N. The ability to reproduce the neutral zero position of the head. J Manipulative Physiol Ther 1999, 22: 26-28.

  3. Strimpakos N, Sakellari V, Gioftsos G, Papathanasiou M, Brountzos E, Kelekis D, Kapreli E, Oldham J. Cervical spine ROM measurements: optimizing the testing protocol by using a 3D ultrasound-based motion analysis system. Cephalgia 2005, 25: 1133-45.

Disclosure of Interest None Declared

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