Pressure sores (PS) in deep muscles are potentially fatal and are considered one of the most costly complications in spinal cord injury patients. We hypothesize that continuous compression of the longissimus and gluteus muscles by the sacral and ischial bones during wheelchair sitting increases muscle stiffness around the bone-muscle interface over time, thereby causing muscles to bear intensified stresses in relentlessly widening regions, in a positive-feedback injury spiral. In this study, we measured long-term shear moduli of muscle tissue in vivo in rats after applying compression (35 KPa or 70 KPa for –2 h, ), and evaluated tissue viability in matched groups (using phosphotungstic acid hematoxylin histology, ). We found significant (1.8-fold to 3.3-fold, ) stiffening of muscle tissue in vivo in muscles subjected to 35 KPa for 30 min or over, and in muscles subjected to 70 KPa for 15 min or over. By incorporating this effect into a finite element (FE) model of the buttocks of a wheelchair user we identified a mechanical stress wave which spreads from the bone-muscle interface outward through longissimus muscle tissue. After 4 h of FE simulated motionlessness, 50%–60% of the cross section of the longissimus was exposed to compressive stresses of 35 KPa or over (shown to induce cell death in rat muscle within 15 min). During these 4 h, the mean compressive stress across the transverse cross section of the longissimus increased by 30%–40%. The identification of the stiffening-stress-cell-death injury spiral developing during the initial 30 min of motionless sitting provides new mechanistic insight into deep PS formation and calls for reevaluation of the 1 h repositioning cycle recommended by the U.S. Department of Health.
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June 2005
Technical Papers
In Vivo Muscle Stiffening Under Bone Compression Promotes Deep Pressure Sores
A. Gefen,
A. Gefen
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
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N. Gefen,
N. Gefen
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
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E. Linder-Ganz,
E. Linder-Ganz
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
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S. S. Margulies
S. S. Margulies
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, Pennsylvania
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A. Gefen
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
N. Gefen
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
E. Linder-Ganz
Department of Biomedical Engineering, Faculty of Engineering,
Tel Aviv University
, Tel Aviv, Israel
S. S. Margulies
Department of Bioengineering,
University of Pennsylvania
, Philadelphia, PennsylvaniaJ Biomech Eng. Jun 2005, 127(3): 512-524 (13 pages)
Published Online: January 31, 2005
Article history
Received:
August 12, 2004
Revised:
December 23, 2004
Accepted:
January 31, 2005
Citation
Gefen, A., Gefen, N., Linder-Ganz, E., and Margulies, S. S. (January 31, 2005). "In Vivo Muscle Stiffening Under Bone Compression Promotes Deep Pressure Sores." ASME. J Biomech Eng. June 2005; 127(3): 512–524. https://doi.org/10.1115/1.1894386
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