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Research Papers

Multisegment Kinematics of the Spinal Column: Soft Tissue Artifacts Assessment

[+] Author and Article Information
Sara Mahallati

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

Hossein Rouhani

Department of Mechanical Engineering,
10-368 Donadeo Innovation Centre for Engineering,
University of Alberta,
Edmonton, AB T6G 1H9, Canada

Richard Preuss

School of Physical
and Occupational Therapy,
McGill University,
3630 Promenade Sir-William-Osler,
Montreal, QC H3G 1Y5, Canada;
The Constance Lethbridge Rehabilitation Centre
site of the Centre de Recherche
Interdisciplinaire en Réadaptation (CRIR),
7005 Boulevard de Maisonneuve Ouest,
Montreal, QC H4B 1T3, Canada

Kei Masani, Milos R. Popovic

Institute of Biomaterials
and Biomedical Engineering,
University of Toronto,
164 College Street,
Toronto, ON M5S 3G9, Canada;
Rehabilitation Engineering Laboratory,
Lyndhurst Centre,
Toronto Rehabilitation Institute—University
Health Network,
520 Sutherland Drive,
Toronto, ON M4G 3V9, Canada

1Corresponding author.

Manuscript received September 8, 2015; final manuscript received February 16, 2016; published online June 7, 2016. Assoc. Editor: Pasquale Vena.

J Biomech Eng 138(7), 071003 (Jun 07, 2016) (8 pages) Paper No: BIO-15-1443; doi: 10.1115/1.4033545 History: Received September 08, 2015; Revised February 16, 2016

A major challenge in the assessment of intersegmental spinal column angles during trunk motion is the inherent error in recording the movement of bony anatomical landmarks caused by soft tissue artifacts (STAs). This study aims to perform an uncertainty analysis and estimate the typical errors induced by STA into the intersegmental angles of a multisegment spinal column model during trunk bending in different directions by modeling the relative displacement between skin-mounted markers and actual bony landmarks during trunk bending. First, we modeled the maximum displacement of markers relative to the bony landmarks with a multivariate Gaussian distribution. In order to estimate the distribution parameters, we measured these relative displacements on five subjects at maximum trunk bending posture. Then, in order to model the error depending on trunk bending angle, we assumed that the error grows linearly as a function of the bending angle. Second, we applied our error model to the trunk motion measurement of 11 subjects to estimate the corrected trajectories of the bony landmarks and investigate the errors induced into the intersegmental angles of a multisegment spinal column model. For this purpose, the trunk was modeled as a seven-segment rigid-body system described using 23 reflective markers placed on various bony landmarks of the spinal column. Eleven seated subjects performed trunk bending in five directions and the three-dimensional (3D) intersegmental angles during trunk bending were calculated before and after error correction. While STA minimally affected the intersegmental angles in the sagittal plane (<16%), it considerably corrupted the intersegmental angles in the coronal (error ranged from 59% to 551%) and transverse (up to 161%) planes. Therefore, we recommend using the proposed error suppression technique for STA-induced error compensation as a tool to achieve more accurate spinal column kinematics measurements. Particularly, for intersegmental rotations in the coronal and transverse planes that have small range and are highly sensitive to measurement errors, the proposed technique makes the measurement more appropriate for use in clinical decision-making processes.

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Figures

Grahic Jump Location
Fig. 1

Double-static bony landmark calibration procedure: A representative triad of bony landmarks (denoted by  b1,2,3) for each segment was palpated. These locations were marked (denoted by  m1,2,3) in both upright sitting and maximum bending posture. The skin-mounted marker displacement with respect to the underlying bony landmark (denoted by MaxDb−m), hence, would be the difference in the two marked locations. This procedure is repeated for all bony landmarks.

Grahic Jump Location
Fig. 2

Flowchart diagram of modeling the relative movement between skin-mounted markers and the underlying bony landmarks and applying it to the recorded marker trajectories to compensate for errors due to STAs

Grahic Jump Location
Fig. 3

The multisegment model of the spinal column (a) placement of five targets for bending in five directions: Left (L), AL, anterior (A), AR, right (R). (b) The bending task to reach each target was such that the trunk made a 45 deg angle with respect to the upright sitting posture.

Grahic Jump Location
Fig. 4

Kinematic model of the seven-segment spinal column model. Segments superior (rostral) to inferior (caudal): UT, MUT, MLT, LT, UL, LL, and SC segments. The bony anatomical landmarks in each segment were: (i) seventh cervical vertebra (C7), (ii) third thoracic vertebra (T3), (iii) sixth thoracic vertebra (T6), (iv) ninth thoracic vertebra (T9), (v) 12th thoracic vertebra (T12), (vi) third lumbar vertebra (L3), (vii) first sacral vertebra (S1) which is approximately the midpoint between and the left and right IC, and (viii) the midpoint between the left and right PSISs.

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