Soft Tissue Stiffness Research Articles

Scaling of Dynamics in the Earliest Stages of Walking

Although the description of mature walking is fairly well established, less is known about what is being learned in the process. Such knowledge is critical to the physical therapist who wants to teach children with developmental delays. The purpose of this experiment was to test the notion that learning to walk efficiently involves fine-tuning the body's controllable stiffness (by co-contraction and isometric muscle contractions against gravity) to match (at a 1:1 scaling) the gravitational (pendular) stiffness of the swing leg. The study participants were 7 children with typical development and the newly emerged ability to walk 6 steps without falling (ages 11 months to 1 year 5 months at the onset of walking). Pendular stiffness and spring stiffness were estimated from the equations of motion for a hybrid model with kinematic data as children walked over ground. Testing occurred once per month for the first 7 months of walking. After the first month of walking, children walked with greater spring stiffness than would be predicted by the model. The ratio began to approach the predicted value (1:1) as the months progressed. The results of this and a previous study of the pendular dynamics of gait suggest that learning to walk is a 2-stage process. The first stage involves the child's discovery of how to conserve energy by inputting a particular muscular force at the correct moment in the cycle. The second stage involves the fine-tuning of the soft-tissue stiffness that takes advantage of the resonance characteristics of tissues. In order to address developmental delays, investigators must discover the dynamic resources used for the activity and attempt to foster their development. A number of interventions that probe this approach are discussed.

Passive in vivo elastography from skeletal muscle noise

Measuring the in vivo elastic properties of muscles (e.g., stiffness) provides a means for diagnosing and monitoring muscular activity: muscles typically become ‘‘harder’’ during contraction occurring through physiological changes. Standard elastography imaging techniques estimate soft tissue (e.g., skeletal muscle, breast) stiffness using propagating shear waves in the human body generated by an external active source (e.g., indentation techniques, ultrasonic radiation force). We demonstrated a passive in vivo elastography technique without an active external radiation source. This technique instead uses cross-correlations of contracting skeletal muscle noise recorded with skin-mounted sensors. The coherent arrivals emerge from a correlation process that accumulates contributions over time from noise sources whose propagation paths pass through both sensors successively. Each passive sensor becomes a virtual in vivo shear wave source. The results point to a low-cost, noninvasive technique for monitoring biomechanical in vivo muscle properties. The efficacy of the passive elastography technique originates from the high density of cross paths between all sensor pairs potentially achieving the same sensitivity obtained from active elastography methods. The application of this passive elastography technique for constructing biomechanical models of in vivo muscle properties will be discussed.

High Frequency Ultrasound Assessment of Skin Fibrosis: Clinical Results

Fibrosis is a common late effect of radiotherapy treatment for cancer patients. Current clinical assessment of radiation-induced fibrosis is generally limited to clinician-based rating scales, which are usually not sufficient for quantitative and objective evaluations. Ultrasonic propagation properties of tissues are widely reported to be sensitive to the alterations of tissue compositions and structures. Based on our previous feasibility study, we used four parameters including skin thickness and three ultrasonic parameters of dermal tissues (attenuation slope [β], integrated attenuation [IA] and integrated backscatter [IBS]) in the frequency range of 10 to 25 MHz for the assessment of skin fibrosis. Experiments were conducted on the forearm and neck skin in patients with postirradiation fibrosis in the neck region. The palpation score and stiffness of the neck soft tissue were also measured as an indication of fibrotic severity. Comparisons of the results between 38 patients and 20 control subjects showed a significantly smaller β ( p = 0.005) and a significantly larger skin thickness ( p < 0.004) and IA ( p = 0.04) in the neck skins of the patients. However, age-matched comparisons showed there were neither significant differences among patient subgroups with different fibrotic levels assessed using manual palpation or significant correlations between the four parameters and the overall stiffness of the neck soft tissues ( p > 0.05). In conclusion, ultrasound tissue characterization may provide additional information for the assessment of postirradiation skin fibrosis in the neck region. Further studies are necessary to investigate the feasibility of applying the current measurement for differentiating the severity of skin fibrosis. (E-mail: ypzheng@ieee.org)

Protein Nutrition in Fibromyalgia

AbstractBackground: Fibromyalgia (FM) is a soft-tissue disease of unknown origin. It causes soft-tissue pain and stiffness, often with chronic fatigue, disrupted sleep, headaches and irritable bowel. Fibromyalgia affects an estimated six million Americans of which 80 to 90 percent are female.Objective: To determine whether dietary intake of protein, Tryptophan, and Branched Chain Amino Acids (BCAA) meet Dietary Reference Intake (DRI) recommendations, and whether there is a difference in animal and vegetable protein intake in subjects with FM compared to healthy controls.Methods: Thirty subjects with FM and an equal number of controls completed a Food Frequency Questionnaire (FFQ) regarding dietary intake over the previous month. The FFQs were then computer analyzed to determine dietary intake.Results: Protein intake of all subjects was more than adequate to meet DRI recommendations and there was no significant difference in intake of protein, BCAA, Tryptophan, animal or vegetable protein. Subjects with FM...

Guidance of engineered tissue collagen orientation by large-scale scaffold microstructures

The tensile strength and stiffness of load-bearing soft tissues are dominated by their collagen fiber orientation. While microgrooved substrates have demonstrated a capacity to orient cells and collagen in monolayer tissue culture, tissue engineering (TE) scaffolds are structurally distinct in that they consist of a three-dimensional (3-D) open pore network. It is thus unclear how the geometry of these open pores might influence cell and collagen orientation. In the current study we developed an in vitro model system for quantifying the capacity of large scale (∼200 μm), geometrically well-defined open pores to guide cell and collagen orientation in engineered tissues. Non-degradable scaffolds exhibiting a grid of 200 μm wide rectangular pores (1:1, 2:1, 5:1, and 10:1 aspect ratios) were fabricated from a transparent epoxy resin via high-resolution stereolithography. The scaffolds ( n = 6 per aspect ratio) were surface modified to support cell adhesion by covalently grafting GRGDS peptides, sterilized, and seeded with neonatal rat skin fibroblasts. Following 4 weeks of static incubation, the resultant collagen orientation was assessed quantitatively by small angle light scattering (SALS), and cell orientation was evaluated by laser confocal and scanning electron microscopy. Cells adhered to the struts of the pores and proceeded to span the pores in a generally circumferential pattern. While the cell and collagen orientations within 1:1 aspect ratio pores were effectively random, higher aspect ratio rectangular pores exhibited a significant capacity to guide global cell and collagen orientation. Preferential alignment parallel to the long strut axis and decreased spatial variability were observed to occur with increasing pore aspect ratio. Intra-pore variability depended in part on the spatial uniformity of cell attachment around the perimeter of each pore achieved during seeding. Evaluation of diamond-shaped pores [Sacks, M.S. et al., 1997. J. Biomech. Eng. 119(1), 124–127] suggests that they are less sensitive to initial conditions of cell attachment than rectangular pores, and thus more effective in guiding engineered tissue cell and collagen orientation.

Feasibility of the use of a novel soft tissue stiffness meter

Simple but objective measurement of soft tissue consistency would be advantageous in the assessment of many neurological, lymphostatic and venous disorders. The aim of the present study was to evaluate the feasibility of using a novel hand-held computerized soft tissue stiffness meter (STSM). The STSM describes the soft tissue stiffness (STS) in the form of the instantaneous force (N) by which the tissue resists the constant deformation produced by a cylindrical intender. Firstly, the STSM was used to test elastomer samples with known mechanical properties. In the in vivo assessment, 12 healthy, nondisabled adults (age range, 24–57 years) and 16 subjects with chronic myofascial neck pain syndrome (age range, 27–55 years) were studied. To study the reproducibility (coefficient of variation (CV(%))) of the method, the measurement sites were either marked with a marker pen (marked points) or localized anatomically (unmarked points). Measurements were made from the dorsal forearm (Arm), trapezius (Tra), levator scapulae (Lev), infraspinatus (Inf) and deltoideus (Del) muscle areas. STS in the forearm was studied during different types of short-term relative isometric loading of the muscle as well as during venous occlusion. STS values of the myofascial trigger points in the Lev muscles were evaluated bilaterally. A linear, positive relationship was found between the indenter force (N) and the dynamic compressive modulus (MPa) of elastomer stiffness (r2 = 0.90, n = 9). Intra- and interrater CVs of marked and unmarked sites varied between 4.31% and 12.06%. STS increased linearly along the relative muscle load (r2 = 0.96) and nonlinearly during the venous occlusion (r2 = 0.97). Statistically significant regional variation of STS was found between the different measurement sites (p < 0.05). In conclusion, STSM can evaluate tissue stiffness quantitatively and yield reproducible data.

Microsurgical latissimus dorsi flap in a case of breast aplasia caused by radiation therapy

The use of ionizing radiation in the breast region while a patient is at developmental age is still responsible for most monolateral hypoplasias and iatrogenic-based breast asymmetries. These alterations often involve several anatomical structures, thus causing severe hypoplasia of the breast and muscle tissues and stiffness of soft tissues, with atrophic and cicatricial skin. Reconstruction methods vary from case to case, but most of the time reconstruction with a homolateral latissimus dorsi with or without a breast implant seems most suitable. In some cases, however, this is not a viable alternative due to particular general and local conditions, making it necessary to consider other solutions. We present the case of a young prepubertal patient who came under our observation due to a radiotherapy outcome in the right breast and thoracic region; she had been previously subjected to breast reconstruction elsewhere, with the fitting of a subcutaneous prosthesis. Due to the patient's particular general and local conditions and the pathological involvement of the homolateral thoracic musculature, to improve the clinical picture, we deemed it appropriate to use the microsurgical reinnervated contralateral latissimus dorsi muscle, which so far has enabled us to obtain considerable and lasting results.

Three-dimensional finite element analysis of the foot during standing—a material sensitivity study

Information on the internal stresses/strains in the human foot and the pressure distribution at the plantar support interface under loading is useful in enhancing knowledge on the biomechanics of the ankle–foot complex. While techniques for plantar pressure measurements are well established, direct measurement of the internal stresses/strains is difficult. A three-dimensional (3D) finite element model of the human foot and ankle was developed using the actual geometry of the foot skeleton and soft tissues, which were obtained from 3D reconstruction of MR images. Except the phalanges that were fused, the interaction among the metatarsals, cuneiforms, cuboid, navicular, talus, calcaneus, tibia and fibula were defined as contact surfaces, which allow relative articulating movement. The plantar fascia and 72 major ligaments were simulated using tension-only truss elements by connecting the corresponding attachment points on the bone surfaces. The bony and ligamentous structures were embedded in a volume of soft tissues. The encapsulated soft tissue was defined as hyperelastic, while the bony and ligamentous structures were assumed to be linearly elastic. The effects of soft tissue stiffening on the stress distribution of the plantar surface and bony structures during balanced standing were investigated. Increases of soft tissue stiffness from 2 and up to 5 times the normal values were used to approximate the pathologically stiffened tissue behaviour with increasing stages of diabetic neuropathy. The results showed that a five-fold increase in soft tissue stiffness led to about 35% and 33% increase in the peak plantar pressure at the forefoot and rearfoot regions, respectively. This corresponded to about 47% decrease in the total contact area between the plantar foot and the horizontal support surface. Peak bone stress was found at the third metatarsal in all calculated cases with a minimal increase of about 7% with soft tissue stiffening.

Place des orthèses en pathologie ligamentaire du genou. Revue de la littérature

Objective. – To review the literature for the benefits of the three different knee braces (prophylactic, rehabilitation, functional) that can be used to treat ligament injuries of the knee. What is their influence on stability? Do they have adverse effects? Is their use justified? Methods. – We searched the Medline and Embase databases with use of the keywords knee, orthoses, brace, proprioception, stability, rehabilitation, physical therapy, and anterior cruciate ligament for reports published between 1980 and 2003 and selected 93 articles, expert reports or literature reviews. Results. – Anterior tibial displacement can be controlled with mechanical strains (150 N), which are lower than physiological restraints? (400 N). The control of joint position is improved by increasing proprioception. Soft tissue stiffness influences the control of anterior tibial displacement. The beneficial effects observed are mainly subjective. Our analysis of the literature showed limitations and variations in study methodologies. Conclusion. – We did not find any justification for use of either prophylactic or rehabilitation braces. Functional braces can improve stability, as reported by the patient, and may be used in some situations.

Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy

Klaesner JW, Hastings MK, Zou D, Lewis C, Mueller MJ. Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy. Arch Phys Med Rehabil 2002;83:1796-801. Objective: To determine if a difference exists in the plantar soft tissue of patients with diabetes mellitus (DM) and peripheral neuropathy (PN) compared with age-matched controls. Design: Case-control study with a parallel 3-element 1-dimensional viscoelastic model developed to characterize indentation data. Setting: Data collection performed in an academic physical therapy laboratory. Participants: Forty subjects were recruited into 2 groups (20 subjects with DM, PN, and history of plantar ulcers; 20 control subjects), matched for age (DM: 55.22±9.39y; control: 55.91±10.97y), gender (DM: 14 men, 6 women; control: 14 men, 6 women), and body mass index (DM: 32.96±8.39kg/m2; control: 32.58±7.69kg/m2). Interventions: The plantar soft tissue stiffness was measured over the first, third, and fifth metatarsals, and heel of each subject using an indentor system that accurately measures force/displacement (F/D) data. A parallel 3-element viscoelastic mechanical model was then used to transform the F/D data into values that were used to make stiffness assessments. Main Outcome Measures: The element coefficients of our model indicated the stiffness of the plantar tissue. Results: The plantar tissue of the subjects with DM over the metatarsal heads was stiffer than the control population as indicated by one of the spring constants in the parallel 3-element model (first: 1.13±0.55N/mm vs .72±.32N/mm; third: .96±.32 N/mm vs .79±.17N/mm; fifth: .90±.31N/mm vs .69±.28N/mm; P<.05). Conclusions: The plantar tissue of subjects with DM, PN, and a history of ulcers was stiffer than control subjects. However, additional research is needed to determine the relationship among increased soft tissue stiffness, plantar pressures, and skin breakdown. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

2431 超音波パルス法による軟組織の硬さ測定

2431 超音波パルス法による軟組織の硬さ測定

Integration of plantar soft tissue stiffness measurements in routine MRI of the diabetic foot

Objective. A method of measuring mechanical properties of plantar soft tissues in vivo by integrating a photoelastic technique into an MRI system is presented. Background. Plantar tissue stiffening in the diabetic foot is associated with development of ulcers at the highest-pressure sites. MRI is used as an effective means of demonstrating tissue damage caused by diabetic ulceration. Design. The new measurement method uses the indentation of a sphere into the plantar tissue, which is simultaneously scanned by MRI. The indentation force is obtained using the photoelastic technique while tissue deflection is measured on the MRI scans, to yield a characteristic load–displacement curve. Methods. Applicability of the proposed method in characterizing the plantar tissue stiffness and indentation patterns of two young normal subjects and two older diabetic patients was tested. Results. Significantly higher effective shear and elastic moduli were measured for the diabetic plantar tissue compared with that of normal. For the diabetic patients, local stiffness in proximity of the 1st metatarsal head was substantially larger than in other sites, and this could be associated with initial tissue ulceration at this location. Relevance The present method seems applicable as a practical means of identifying regions in the diabetic plantar tissue that are vulnerable to ulceration, and can be easily integrated into routine MRI scans for assessing tissue damage in these patients.

A model of a snorer's upper airway

In snorers, the physiologic decrease of postural muscle tone during sleep results in increased collapsibility of the upper airway. Measurement of nasal pressure changes with prongs is increasingly used to monitor flow kinetics through a collapsing upper airway. This report presents a mathematical model to predict nasal flow profile from three critical components that control upper airway patency during sleep. The model includes the respiratory pump drive, the stiffness of the pharyngeal soft tissues, and the dynamic support of the muscles surrounding the upper airway. Depending on these three components, the proposed model is able to reproduce the characteristic changes in flow profile that are clinically observed in snorers and non-snorers during sleep.

A mechanical arthrometer to measure knee joint contracture in rats.

Animal models for joint diseases are necessary for in vivo studies. Joint contractures are characterized by lack of the normal range of motion of a joint most often due to increased soft tissue stiffness. Biological and biochemical data have been obtained but biomechanical data on small animals are rare. An instrument was developed to measure rat knee angular displacement at various soft tissue loads in normal and pathological circumstances. This article describes the instrument and reports its reproducibility and accuracy. The reproducibility and accuracy of this instrument was found to be acceptable thereby validating its use for research purposes with adult rat knees.

A rate-controlled indentor for in vivo analysis of residual limb tissues.

A tissue tester was designed to enable rate-controlled indentation of the bulk soft tissues of lower extremity residual limbs. The tissue tester employs a digital linear actuator that implements rate-controlled indentation, and a load cell that measures the reaction force resulting from tissue indentation. Viscoelastic phenomena such as preconditioning, hysteresis and force relaxation can be assessed, and the effect of varying indentation rates on soft tissue stiffness can be investigated. The device accommodates indentor excursions up to 30 mm, indentation at rates of 0 to 10 mm/s, reaction forces up to 44 N, and multiple loading/unloading cycles. The tissue tester is controlled via a notebook personal computer with a PCMCIA data acquisition card. The tissue testing trials are automated and the entire test system is portable and amenable for use in a clinical or research environment. System output consists of force-displacement curves from cyclic loading, and force-time curves following ramped-step indentation. The mean indentor positioning error was 0.071 (+/-0.75)% of the desired displacement. This error varied as a function of indentation and was approximately independent of the indentation rate. Indentation rates were accurate to within 0.94(+/-0.68)% of the desired value and also varied with indentation. Indentation of a viscoelastic foam yielded force-displacement curves that were consistent with that obtained from an Instron universal testing machine.

A tactile sensor for detection of physical properties of human skin in vivo

A spring loaded tactile sensor with displacement sensing has been evaluated for non-invasive assessment of physical properties, stiffness and elasticity, of human skin in vivo. The tactile sensor consists of a piezoelectric vibrator (61 kHz) with a vibration pickup, electronics and PC with software for measurement of the change in frequency when the sensor is attached to an object. Integrated with the tactile sensor is a displacement sensor that shows the compression of the spring that loads the sensor element against the object during measurement. Under certain conditions (e.g. fixed contact pressure) this change in frequency monitors the acoustic impedance of the object and is related to the stiffness of soft tissue. The experimental results on silicone gum and on healthy Japanese and Swedish women indicated that the instrument was able to detect changes in stiffness and elastic related properties of human skin, related to age, day-to-day variations and application of cosmetics. The instrument was concluded to be easy to handle and suitable for field work.

Reconstruction of elastic modulus distribution from envelope detected B-mode data

A variety of ultrasonic methods have been shown to be capable of imaging the stiffness of soft tissue but most require specialised equipment and non-standard approaches to ultrasonic examination. In breast imaging by Elastography, for example, the elastic modulus distribution (EMD) is estimated by using 1-D cross correlation tracking of radiofrequency (RF) echo signals to image the distribution of strain induced by a controlled static deformation. Our work aims to explore the possibilities for employing standard ultrasound scanning methods and equipment, and simple processing techniques, to image the EMD of soft tissues. A simple reconstruction algorithm was developed and its convergence was studied at different elastic contrasts (EC) using 'ideal' strain data that was derived using the finite element method. EMD reconstruction of hard inclusions improved substantially according to a Chi-squared statistic, but soft inclusions showed little change after the first iteration. For example Chi-squared for a +20 dB EC inclusion reduced from 10 at the start to 0.0001 after 5 iterations, whilst it improved from 3 to only 1.6 for a -20 dB inclusion. The performance of a 1-D cross correlation tracking algorithm was studied with RF and envelope detected data when external strains of 2% and 5% were applied to the surface of simulated phantom. The algorithm accurately estimated displacement /spl les/1.5/spl lambda/ with both RF and ED data when the applied strain was 2%. However better precision and signal to noise ratio (SNR) was obtained using RF as oppose to ED. At an applied strain of 5% more accurate estimates, better precision and SNR was obtain using ED. We conclude that there is no great disadvantage to using the envelope detected signal for estimating internal tissue displacements that are likely to be encountered in standard clinical scanning practice.

What role does plantar soft tissue stiffness play in determining peak pressure under the heel?

What role does plantar soft tissue stiffness play in determining peak pressure under the heel?

Analytical and Experimental Studies on the Measurement of Soft Biological Tissue Elasticity using a Pipette with Rectangular Cross Section.

A pipette aspiration technique has been developed to clarify the local anisotropic stiffness of soft biological tissues. This technique provides a simple and practical method of measuring an initial elastic modulus by comparing the slope of the pressure-deformation curve obtained from a finite element analysis with that obtained by experiment using a pipette to aspirate the tissue surface. In previous studies, linear numerical simulations were performed for circular cross-sectional pipettes using an axisymmetric model that is assumed to be isotropic and homogeneous. In this paper, the use of rectangular cross-sectional pipettes was proposed to parametrically evaluate the effects of anisotropic properties of living tissues on the measurement of their stiffness. The calculated results indicated that rectangular pipettes eliminated the effect of the modulus parallel to the pipette major axis. The aspiration technique with a rectangular cross-sectional pipette should be effective for clarifying the anisotropy of biological tissues. Experimental verification of this technique was performed for the canine ligamentum nuchae.

Seat cushion design for elderly wheelchair users based on minimization of soft tissue deformation using stiffness and pressure measurements.

A method for designing seat support surfaces using interface pressure and soft tissue stiffness criteria was evaluated. An algorithm designed to drive a rigid support surface on a programmable seating system to a shape for which the externally applied pressure is inversely related to the measured stiffness of adjacent soft tissue was evaluated on 30 elderly subjects (age 65 years or older). The resulting support surface shapes were transferred to compliant foam cushions and evaluated using interface pressure measurements. Pressure and stiffness measurements on the seating system indicated the surface shape control algorithm met the desired programmed criteria by achieving an inverse relationship between pressure and stiffness, as it converged to an "optimal" support surface shape. Evaluation of interface pressures on the compliant foam cushions showed that the pressure distributions on the cushions contoured to the optimal surface shapes were more uniform and had lower values than distributions on flat foam cushions and foam cushions contoured to shapes measured using state-of-the-art load-deflection devices. The results suggest that support surfaces designed using tissue stiffness as a criteria can provide loading conditions intended to minimize relative deformation and, thus, stress in load-bearing soft tissue.