Sitting Biomechanics Laboratory

Part of the
Sensory Motor Performance Program
Room 1340, Rehabilitation Institute of Chicago

Soft Tissue Stiffness using an Ultrasound Indentation System

Nearly 40% of individuals who use wheelchairs develop serious tissue breakdown at pressure points due to prolonged sitting or bed rest without proper pressure relief Treatment of established pressure ulcers is extremely difficult, often necessitating expensive, invasive surgeries and postoperative care. A targeted preventive approach is likely to prove less costly and more effective than one focused on treating established pressure ulcers. Improved pressure ulcer detection requires a consistent assessment of tissue health. Current diagnostic imaging techniques such as radiography, CT scanning, magnetic resonance imaging and B-mode ultrasound mapping can be used to assess tissue health. However, these methods are more expensive and time consuming, and some of them pose potential health risks related to the use of dyes and radiation. Therefore, there is a need for an effective and clinically practical diagnostic tool capable of obtaining an indication of tissue stiffness in pressure-ulcer prone areas to quantitatively detect, in an early stage, the pressure ulcer and possibly the deep-tissue injury formation below intact skin.


	Application of Tissue Stiffness in Detecting Pressure Ulcers in the Earliest Stage The Tissue Ultrasound Palpation System (TUPS) (http://tups.org) is a lightweight and portable device that permits the measurement of the stiffness and thickness (in millimeters) of soft tissues with a pen-size probe, as shown in Figure 1. Participants were asked to lie supine, with the probe placed on the skin of the targeted testing location. Tissue was then palpated with alternating loading and unloading cycles to identify a clear echo or signal from the relevant anatomical site. For each trial, the recorded loading force and the induced change of soft-tissue thickness from the loading/unloading cycles were used to establish a force-deformation relationship. .
A soft tissue model of tissue elasticity based on a system composed of two parallel springs (K1 and K2 denoted the stiffness of the springs)	A soft tissue model of tissue elasticity based on a system composed of two parallel springs (K1 and K2 denoted the stiffness of the springs) Objectives of his project are to investigate the relationship between post pressure injury macroscopicchanges in stiffness and microscopic changes in muscle tissue structure, and to evaluate a non-invasive tissue ultrasound palpations system (TUPS) probe that measures tissue stiffness as predictor of early PU formation in SCI patients.
	B Mode Ultrasound: It was used to record thickness and maximum deformation under compression from bilateral ischial tuberosities(IT), bilateral greater trochanters (GT), posterior mid thighs (MT), and the bulk of right biceps brachii (BIC). By collecting the tissue image, the orientation of tissues, and tissue thickness can be measured and the a mode results validated. .

Results:

In both able-bodied persons and individuals with chronic SCI, we found that the soft tissue over the IT was significantly less stiff than at the other 3 locations (GT, MT, and BIC). However, with respect to StiffnessLD values, the BIC was the least stiff among the SCI group. Soft tissue over the GT was among the stiffer ones, especially with respect to StiffnessLD. This finding confirmed our hypothesis about the differential stiffness among body locations

For both groups, the IT site experienced significantly larger deformation than the other 3 recording sites, except when compared with the BIC in control group. At the same time, the maximal compressive force applied to the IT site was the smallest among all the recording sites. This was significant in control group when compared with all the other 3 locations, but significant in the SCI group only when compared with the BIC.

When comparing the 2 groups, StiffnessBasic at the IT and MT was significantly lower for individuals with SCI (IT: P ¼ 0.035; MT: P ¼ 0.001). StiffnessLD at the BIC was also significantly lower for the SCI group (P¼0.001). The xs value was significantly lower at the GT (P ¼ 0.002) for the SCI group than that for the able-bodied subjects.

Continuing research:

The ability of the tups probe to detect presence and evaluate the stiffness of a pressure sore as it develops The ability of the tups probe to assesss wound condition based on the stiffenss of adjacent tissues

Last updated May 25, 2008 by Makhsous.
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