Under Construction and Updating
Sitting Biomechanics Laboratory
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Molecular Biomarkers for Detecting Deep Tissue Injury in Individuals with SCI
Serious tissue breakdown such as pressure ulcers (PU) is the leading complication in individuals with SCI. Deep tissue injury (DTI) is a serious PU which initiates in deep tissue, mainly in muscle, and progresses rapidly to a full-thickness wound even with treatment. Currently, the diagnosis of DTI is still vague at best with only subjective visual inspection and palpation. We are researching on using molecules that sensitive to muscle injury to use as indicators of DTI formation. Several of these molecules, including myoglobin, heart-type fatty acid binding protein (H-FABP), creatine kinase (CK), myosin, and Troponin-I (TnI), are being assessed in our lab using a SCI-DTI rat model. It is expected that knowledge gained from this study may lead to a promising new methodology to sense the visually invisible DTI.
FINDINGS
- All the tested molecules showed apparent response to created DTI. Most of the molecules were elevated substantially in serum within 48 hours of DTI formation.
- Similar elevation was seen in urine with a delay from that in serum.
- Some of the researched molecules were able to show differential response for DTI and superficial tissue injury (shown is differential response of serum myoglobin for DTI and skin-deep tissue injury)
- Initial analysis suggested a high correlation between the elevation of some of the molecules and the tissue injury volume within the induced DTI. This finding provides clue to quantification of tissue damage using these molecules.
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SCI-PU Model
It has long been the understanding that PUs occur at tissue pressure points around a bony prominence. Many animal PU models have been developed to test different hypotheses related to DTI. However, none of the existing PU rat models, especially those for DTI research, has a bony prominence component that prevents those models from yielding more clinically relevant data. Moreover, none of the DTI rodent models was established on animals with SCI, which presents an intrinsic weakness for these models to represent SCI condition.
We have developed a SCI-PU rat model and examined the effect of SCI condition and the presence of a bony prominence.
Components of this rat model include a chronic SCI, by surgical transection of the spinal cord, and a simulated bony prominence, by surgical placement of an implant on the interface of tibia bone and tibialis anterior (TA) muscle (shown below).
An axis MRI image of left leg showing muscle, bone and implant A longitudinal B-mode ultrasound image of right leg showing muscle, bone and implant
FINDINGS
- Rats with chronic SCI (8 weeks post SCI) weighed significantly less than their age- and sex- matched controls. TA muscle of the chronic SCI rats was significantly smaller in volume.
- When comparable pressure loading was delivered to the TA muscle to create DTI, rats with chronic SCI had significantly greater volume of tissue injury.
- When comparable pressure loading was delivered to bilateral TA muscles, the side with implanted “bony” prominence had significantly greater volume of tissue injury
Results from the experiment and subsequent histological analysis observation confirmed that the developed model is successful in simulating the said clinical conditions of DTI and SCI. Our current model combines chronic SCI condition with the component of “bony” prominence. Not only the shape of the implant resembles that of the ischial tuberosity, but the subsequent compression on top of the implant simulates the natural loading scenario of sitting. We believe that this rat SCI-DTI model can simulate well the clinical conditions of chronic SCI and tissue load onto an embedded bony prominence. It is a unique research tool that can be used in SCI-PU related research.
RELATED PUBLICATIONS
Clinical Trial (RIC and Schwab Rehabilitation Hospital at Chicago): Promoting Pressure Ulcer Healing Process using an Individualized Cyclic Pressure-Relief Protocol (iPUPc wheelchair)
Individuals with SCI and with existing pressure ulcers in sitting area were enrolled to test the effectiveness of an individualized cyclic pressure-relief protocol in helping their wound healing.
It was found that using this pressure-relief protocol significantly promoted the healing of existing pressure ulcers. Patients in iPUPc group had significantly faster healing of their PU than that from a control group who used the regular wheelchair.
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Finite Element (FE) Model for Evaluating Buttock-Thigh Mechanical Response to Sitting Load
3 dimensional finite-element (FE) models were developed and validated for able-bodied and SCI individuals to investigate mechanical response within buttock-thigh structure under the sitting load. Model geometry was based on high-resolution MRI images collected from a simulated sitting posture. These models have been used to evaluate different seating devices and the influence of material properties on FE simulation.
FINDINGS
- Highest stress was found in the vicinity of bony prominence such as ischial tuberosity (IT)
- Highest stress was found mainly in the deep muscle tissue, which may suggest the initiation of deep tissue injury under pressure load
- A seating device which can shift sitting load towards the thighs can substantially decrease the stress in deep tissues around the IT
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Sitting & Trunk Control in Hemiparetic Stroke
Balance impairment is common in stroke survivors. Maintaining a stable seated position requires good trunk control and is essential for many activities of daily living (ADL). The biomechanical parameters related to postural balance and control include quantifying the sway of the Center of Pressure (COP) and the asymmetry of forces and moments in static and dynamic tasks. The purpose of this study is to introduce such quantitative measurements into evaluation of postural balance and trunk control in sitting posture in subjects who have suffered a stroke.
Representative data are from 1 healthy control and one stroke patient.
FINDINGS (COP data)
- Stroke subjects had significantly larger sway area and an asymmetrical sway area distribution during upright sitting than that of the healthy controls.
- There was a significantly larger maximal coronal displacement in stroke subjects. It implies that the impaired sitting balance may be mainly in the postural control of side-wise body movement.
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