FOURTEENTH ANNUAL EUROPEAN PRESSURE ULCER ...

Thursday September 1st
Proceedings of the 14th Annual European Pressure Ulcer Meeting
Oporto, Portugal
Relationship Between “Tilt in Space” Wheelchair Function and Risk of Pressure Ulcer
Development
Introduction
Olesen, C.G. 1* , Siefert, A. 2 , de Zee, M 3 , Pankoke, S. 2 , Rasmussen, J. 1
1* M-Tech, Aalborg University, Denmark, (cgo@m-tech.aau.dk)
2 Wölfel Beratende Ingenieure GmbH + Co.KG, Würzburg, Germany
3 Department of Health Science and Technology, Aalborg University, Denmark,
It is well acknowledged that sustained mechanical
loading of soft tissues causes pressure ulcers [1].
The wheelchair adjustments affect the tissue loading in
the sense that the tissue stresses, and thereby the risk
of ulceration, change when the seated posture is
adapted [2]. This study focuses on a basic wheelchair
adjustment called the “Tilt-in-Space” function, with
which many wheelchairs are equipped. The tilt-inspace
function enables the cushion and backrest to
incline while the angle between the cushion and
backrest is kept constant [3]. When the tilt-in-space
function is used, the cushion and the backrest reaction
forces change, which causes a change in tissue
deformation under the buttocks. This study focuses on
investigating how much the reaction forces between
the body and the chair change when tilted in space;
this information will then be used to estimate how the
buttock tissue is deformed.
Methods
The Seated Human computational model from the
AnyBody Modeling System was used to calculate
reaction forces acting between the seat and the
human for different postures. The model has been
validated with respect to the calculated forces by
experimental data.
Figure 1 show the seated AnyBody model not tilted, and
tilted
The “Tilt-in-Space” function was modeled by fixing the
cushion and backrest at a 90° angle relative to each
other. The chair was then rotated backwards with 5°
increments to a maximal inclination of 45° and the
reaction forces for each increment were computed.
The calculated reaction forces were then applied as
boundary conditions to the human body model
CASIMIR. In the interest of limiting computational time,
the finite element model only comprises the buttocks.
Finally the tissue deformation changes caused by the
“Tilt-in-Space” function were evaluated. The FE-model
83
used was a commercially available model developed
by Wölfel, Würzburg, Germany [4].
Figure 2 Human body model CASIMIR used for
calculating tissue deformation
Results
Preliminary results show that the reaction forces
between the seat and the buttocks change, and this
leads to a change in buttocks tissue deformation.
Discussion
The preliminary results found in this study indicate that
the “Tilt-in-Space” function found on many wheelchairs
is not optimal, with respect to risk of developing
pressure ulcers.
Clinical relevance
This work is clinical relevant for wheelchair designers
who aim to enhance wheelchair design with respect to
prevention of pressure ulcers.
Acknowledgements
This work was supported by the project Minimizing the
risk of developing a pressure ulcer (ERDFN-09-0070),
supported by Growth Fund North Denmark and
European Regional Development Fund.
Conflict of Interest
There were no conflict of interests
References
[1] Romanelli M. et.al. Science and Practice of
Pressure Ulcer Management, Springer, 2005
[2] Bush TR. et.al. J.Biomech.Eng. 129: 1: 58-65,
2007.
[3] Michael SM et.al. Clin.Rehabil. 21: 12: 1063-1074,
2007
[4] Siefert A. et.al. Int.J.Ind.Ergonomics 38: 5-6: 410,
2008.
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