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Technical Brief

Sensitivity of Intersegmental Angles of the Spinal Column to Errors Due to Marker Misplacement

[+] Author and Article Information
Hossein Rouhani

Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
164 College Street,
Toronto, Ontario M5S 3G9, Canada
Lyndhurst Centre,
Toronto Rehabilitation Institute—University Health Network,
520 Sutherland Drive,
Toronto, Ontario M4G 3V9, Canada
e-mail: hossein.rouhani@utoronto.ca

Sara Mahallati

Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
164 College Street,
Toronto, Ontario M5S 3G9, Canada
Lyndhurst Centre,
Toronto Rehabilitation Institute—University Health Network,
520 Sutherland Drive,
Toronto, Ontario M4G 3V9, Canada
e-mail: sara.mahallati@mail.utoronto.ca

Richard Preuss

School of Physical & Occupational Therapy,
McGill University,
3630 Promenade Sir-William-Osler,
Montreal, Quebec H3G 1Y5, Canada
The Constance Lethbridge Rehabilitation Centre site of the
Centre de Recherche Interdisciplinaire en Réadaptation (CRIR),
7005 Boul. de Maisonneuve Ouest,
Montreal, Quebec H4B 1T3, Canada
e-mail: richard.preuss@mcgill.ca

Kei Masani

Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
164 College Street,
Toronto, Ontario M5S 3G9, Canada
Lyndhurst Centre,
Toronto Rehabilitation Institute—University Health Network,
520 Sutherland Drive,
Toronto, Ontario M4G 3V9, Canada
e-mail: k.masani@utoronto.ca

Milos R. Popovic

Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
164 College Street,
Toronto, Ontario M5S 3G9, Canada
Lyndhurst Centre,
Toronto Rehabilitation Institute—University Health Network,
520 Sutherland Drive,
Toronto, Ontario M4G 3V9, Canada
e-mail: milos.popovic@utoronto.ca

1Corresponding author.

Manuscript received September 18, 2014; final manuscript received April 9, 2015; published online June 3, 2015. Assoc. Editor: Brian D. Stemper.

J Biomech Eng 137(7), 074502 (Jul 01, 2015) (6 pages) Paper No: BIO-14-1467; doi: 10.1115/1.4030406 History: Received September 18, 2014; Revised April 09, 2015; Online June 03, 2015

The ranges of angular motion measured using multisegmented spinal column models are typically small, meaning that minor experimental errors can potentially affect the reliability of these measures. This study aimed to investigate the sensitivity of the 3D intersegmental angles, measured using a multisegmented spinal column model, to errors due to marker misplacement. Eleven healthy subjects performed trunk bending in five directions. Six cameras recorded the trajectory of 22 markers, representing seven spinal column segments. Misplacement error for each marker was modeled as a Gaussian function with a standard deviation of 6 mm, and constrained to a maximum value of 12 mm in each coordinate across the skin. The sensitivity of 3D intersegmental angles to these marker misplacement errors, added to the measured data, was evaluated. The errors in sagittal plane motions resulting from marker misplacement were small (RMS error less than 3.2 deg and relative error in the angular range less than 15%) during the five trunk bending direction. The errors in the frontal and transverse plane motions, induced by marker misplacement, however, were large (RMS error up to 10.2 deg and relative error in the range up to 58%), especially during trunk bending in anterior, anterior-left, and anterior-right directions, and were often comparable in size to the intersubject variability for those motions. The induced errors in the frontal and transverse plane motions tended to be the greatest at the intersegmental levels in the lower lumbar region. These observations questioned reliability of angle measures in the frontal and transverse planes particularly in the lower lumbar region during trunk bending in anterior direction, and thus did not recommend interpreting these measures for clinical evaluation and decision-making.

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Copyright © 2015 by ASME
Topics: Errors , Human spine
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Figures

Grahic Jump Location
Fig. 1

Experimental setup and marker placement: (a) the seated subject was asked to bend his/her trunk toward a target (five directions), and to touch it with his/her head. Target distance was based on seated trunk height, so that trunk bending would reach a 45 deg angle. (b) Markers were placed over targeted geometrical locations, as shown in the figure, forming seven segments. According to ISB recommendation, for each segment, the X-axis was anterior and Y-axis was upward.

Grahic Jump Location
Fig. 2

Angular curves (in degrees) for six intersegmental levels of the multisegmented spinal column, in the sagittal, frontal, and transverse planes during trunk bending in (a) anterior and (b) left directions (as representatives of the five directions). The original (error-free: black) angular curves obtained for one trial of one subject and erroneous (gray) angular curves for the same trial and obtained with one run out of 1000 runs of the simulation are depicted in the time period (in second) of bending and returning to the upright sitting position.

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