A Quasi-Linear, Viscoelastic, Structural Model of the Plantar Soft Tissue With Frequency-Sensitive Damping Properties

2004 ◽  
Vol 126 (6) ◽  
pp. 831-837 ◽  
Author(s):  
William R. Ledoux ◽  
David F. Meaney ◽  
Howard J. Hillstrom
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Structural Properties ◽  
Structural Model ◽  
Elastic Behavior ◽  
Damping Properties ◽  
Significant Difference ◽  
Linear Viscoelastic ◽  
Relaxation Experiments ◽  
Plantar Soft Tissue

Little is known about the structural properties of plantar soft-tissue areas other than the heel; nor is it known whether the structural properties vary depending on location. Furthermore, although the quasi-linear viscoelastic (QLV) theory has been used to model many soft-tissue types, it has not been employed to model the plantar soft tissue. The structural properties of the plantar soft tissue were quantified via stress relaxation experiments at seven regions (subcalcaneal, five submetatarsal, and subhallucal) across eight cadaveric feet. The cadaveric feet were 36.9±17.4 (mean±S.D.) years of age, all free from vascular diseases and orthopedics disorders. All tests were performed at a constant environmental temperature of 35°C. Stress relaxation experiments were performed; different loads were employed for different areas based on normative gait data. A modification of the relaxation spectrum employed within the QLV theory allowed for the inclusion of frequency-sensitive relaxation properties in addition to nonlinear elastic behavior. The tissue demonstrated frequency-dependent damping properties that made the QLV theory ill suited to model the relaxation. There was a significant difference between the elastic structural properties (A) of the subcalcaneal tissue and all other areas p=0.004, and a trend p=0.067 for the fifth submetatarsal to have less viscous damping c1 than the subhallucal, or first, second, or third submetatarsal areas. Thus, the data demonstrate that the structural properties of the foot can vary across regions, but careful consideration must be given to the applied loads and the manner in which the loads were applied.

Methods for Quasi-Linear Viscoelastic Modeling of Soft Tissue: Application to Incremental Stress-Relaxation Experiments

2003 ◽  
Vol 125 (5) ◽  
pp. 754-758 ◽  
Author(s):  
Joseph J. Sarver ◽  
Paul S. Robinson ◽  
Dawn M. Elliott
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Normalization Method ◽  
Time Constants ◽  
Future Studies ◽  
Linear Viscoelastic ◽  
Relaxation Experiments ◽  
Different Strains ◽  
Viscoelastic Modeling ◽  
Strain Dependent

The quasi-linear viscoelastic (QLV) model was applied to incremental stress-relaxation tests and an expression for the stress was derived for each step. This expression was used to compare two methods for normalizing stress data prior to estimating QLV parameters. The first and commonly used normalization method was shown to be strain-dependent. Thus, a second normalization method was proposed and shown to be strain-independent and more sensitive to QLV time constants. These analytical results agreed with representative tendon data. Therefore, this method for normalizing stress data was proposed for future studies of incremental stress-relaxation, or whenever comparing stress-relaxation at different strains.

Quasi-Linear Viscoelastic Theory is Insufficient to Comprehensively Describe the Time-Dependent Behavior of Human Cervical Spine Ligaments

2010 ◽  
Author(s):  
Kevin L. Troyer ◽  
Christian M. Puttlitz
Keyword(s):  
Cervical Spine ◽  
Stress Relaxation ◽  
Strain Range ◽  
Relaxation Curve ◽  
Physiological Strain ◽  
Dependent Behavior ◽  
Linear Viscoelastic ◽  
Viscoelastic Theory ◽  
Relaxation Experiments ◽  
Linear Viscoelastic Theory

Stress relaxation experiments were conducted on cervical spine ligaments at multiple strain magnitudes to determine the validity and applicability of the quasi-linear viscoelastic (QLV) theory to model their dynamic behavior. The results indicate that the shape of the stress relaxation curve is dependent upon the magnitude of the applied strain. Thus, a more general, nonlinear formulation is required to model these ligaments within the physiological strain range.

scholarly journals Comparison of Pavement Layers Responses with Considering Different Models for Asphalt Concrete Viscoelastic Properties

2013 ◽  
Vol 21 (2) ◽  
pp. 15-20 ◽  
Author(s):  
Mehdi Koohmishi
Keyword(s):  
Asphalt Concrete ◽  
Structural Model ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Maxwell Model ◽  
Elastic Behavior ◽  
Linear Elastic ◽  
Concrete Layer ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic

Abstract In this paper, a comparison between pavement responses is performed by considering two different models for the linear viscoelastic behavior of an asphalt concrete layer. Two models, the Maxwell model and the Kelvin-Voigt model, are generalized. The former is used in ABAQUS and the latter in KENLAYER. As a preliminary step, an appropriate structural model for a flexible pavement structure is developed in ABAQUS by considering linear elastic behavior for all the layers. According to this model, when the depth of a structural model is equal to 6 meters, there is a good agreement between the ABAQUS and KENLAYER results. In this model, the thickness of the pavement is equal to 30 centimeters, and the thickness of the subgrade is equal to 5.7 meters. Then, the viscoelastic behavior is considered for the asphalt concrete layer, and the results from KENLAYER and ABAQUS are compared with each other. The results indicate that the type of viscoelastic model applied to an asphalt concrete layer has a significant effect on the prediction of pavement responses and, logically, the predicted performance of a pavement.

Study of the Viscoelastic Behavior and Molecular Weight Distribution of Polyisobutylene

1954 ◽  
Vol 27 (2) ◽  
pp. 393-414
Author(s):  
Kensal E. Van Holde ◽  
J. W. Williams
Keyword(s):  
Molecular Weight ◽  
Experimental Investigation ◽  
Stress Relaxation ◽  
Mechanical Behavior ◽  
Weight Distribution ◽  
Viscoelastic Behavior ◽  
Elastic Behavior ◽  
High Polymer ◽  
Relaxation Experiments ◽  
Mechanical Studies

Abstract The viscoelastic behavior of linear high polymers has commanded considerable attention in recent years. The very thorough studies by Fox and Flory of the melt viscosity of polystyrene and polyisobutylene, the stress relaxation experiments of Tobolsky and coworkers, and dynamic-mechanical studies by Ferry have contributed greatly to our knowledge of the mechanical behavior of these interesting substances. However, there are many facets of this subject which have not received thorough experimental investigation. In particular, there has been no detailed study of the effect of molecular weight and polydispersity on the elastic behavior of viscoelastic materials. It was felt, therefore, that a study of the viscoelastic behavior of a series of very carefully characterized samples of a representative linear high polymer would contribute substantially to the understanding of this subject. The polymer chosen was polyisobutylene, which displays both flow and elastic behavior at room temperatures.

The Effect of Overshooting the Target Strain on Estimating Viscoelastic Properties From Stress Relaxation Experiments

2004 ◽  
Vol 126 (6) ◽  
pp. 844-848 ◽  
Author(s):  
Jonathan A. Gimbel ◽  
Joseph J. Sarver ◽  
Louis J. Soslowsky
Keyword(s):  
Stress Relaxation ◽  
Single Step ◽  
Strain History ◽  
Estimation Of Parameters ◽  
Ramp Rate ◽  
Relaxation Experiment ◽  
Curve Fit ◽  
Target Strain ◽  
Linear Viscoelastic ◽  
Relaxation Experiments

Background: Tendon’s mechanical behaviors have frequently been quantified using the quasi-linear viscoelastic (QLV) model. The QLV parameters are typically estimated by fitting the model to a single-step stress relaxation experiment. Unfortunately, overshoot of the target strain occurs to some degree in most experiments. This has never been formally investigated even though failing to measure, minimize, or compensate for overshoot may cause large errors in the estimation of parameters. Therefore, the objective of this study was to investigate the effect of overshoot on the estimation of QLV parameters. Method of approach: A simulated experiment was first performed to quantify the effect of different amounts of overshoot on the estimated QLV parameters. Experimental data from tendon was then used to determine if the errors associated with overshoot could be reduced when a direct fit is used (i.e., the actual strain history was used in the curve fit). Results: We found that both the elastic and viscous QLV parameters were incorrectly estimated if overshoot was not properly accounted for in the fit. Furthermore, the errors associated with overshoot were partially reduced when overshoot was accounted for using a direct fit. Conclusions: A slow ramp rate is recommended to limit the amount of overshoot and a direct fit is recommended to limit the errors associated with overshoot, although other approaches such as adjusting the control system to limit overshoot could also be utilized.

scholarly journals The Effect of Target Strain Error on Plantar Tissue Stress

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Shruti Pai ◽  
William R. Ledoux
Keyword(s):  
Soft Tissue ◽  
Stress Relaxation ◽  
Soft Tissues ◽  
Peak Stress ◽  
Materials Testing ◽  
Small Target ◽  
Tissue Properties ◽  
Target Strain ◽  
Relaxation Experiments ◽  
Tissue Specimens

Accurate quantification of soft tissue properties, specifically the stress relaxation behavior of viscoelastic tissues such as plantar tissue, requires precise testing under physiologically relevant loading. However, limitations of testing equipment often result in target strain errors that can contribute to large stress errors and confound comparative results to an unknown extent. Previous investigations have modeled this artifact, but they have been unable to obtain empirical data to validate their models. Moreover, there are no studies that address this issue for plantar tissue. The purpose of this research was to directly measure the difference in peak force for a series of small target strain errors within the range of our typical stress relaxation experiments for the subcutaneous plantar soft tissue. Five plantar tissue specimens were tested to seven incremental target strain error levels of −0.9%, −0.6%, −0.3%, 0.0%, 0.3%, 0.6%, and 0.9%, so as to undershoot and overshoot the target displacement in 0.3% increments. The imposed strain errors were accurately attained using a special compensation feature of our materials testing software that can drive the actuator to within 0% (1−2 μm) of the target level for cyclic tests. Since stress relaxation tests are not cyclic, we emulated the ramp portion of our stress relaxation tests with 5 Hz triangle waves. The average total stress variation for all specimens was 25±5%, with the highest and lowest stresses corresponding to the largest and smallest strain errors of 0.9% and −0.9%, respectively. A strain overshoot of 0.3%, the target strain error observed in our typical stress relaxation experiments, corresponded to an average stress overshoot of 3±1%. Plantar tissue in compression is sensitive to small target strain errors that can result in stress errors that are several fold larger. The extent to which the overshoot may affect the peak stress will likely differ in magnitude for other soft tissues and loading modes.

scholarly journals Fixation stability and implant-associated complications in periacetabular osteotomy: a comparison of screw and K-wire fixation

2021 ◽  
Author(s):  
Vincent Justus Leopold ◽  
Juana Conrad ◽  
Robert Karl Zahn ◽  
Christian Hipfl ◽  
Carsten Perka ◽  
...  
Keyword(s):  
Soft Tissue ◽  
Screw Fixation ◽  
Periacetabular Osteotomy ◽  
Implant Migration ◽  
Major Complications ◽  
Significant Difference ◽  
Duration Of Surgery ◽  
Wire Fixation ◽  
Fixation Stability ◽  
Screw Group

Abstract Aims The aim of this study was to compare the fixation stability and complications in patients undergoing periacetabular osteotomy (PAO) with either K-wire or screw fixation. Patients and methods We performed a retrospective study to analyze a consecutive series of patients who underwent PAO with either screw or K-wire fixation. Patients who were treated for acetabular retroversion or had previous surgery on the ipsilateral hip joint were excluded. 172 patients (191 hips: 99 K-wire/92 screw fixation) were included. The mean age at the time of PAO was 29.3 years (16–48) in the K-wire group and 27.3 (15–45) in the screw group and 83.9% were female. Clinical parameters including duration of surgery, minor complications (soft tissue irritation and implant migration) and major complications (implant failure and non-union) were evaluated. Radiological parameters including LCE, TA and FHEI were measured preoperatively, postoperatively and at 3-months follow-up. Results Duration of surgery was significantly reduced in the K-wire group with 88.2 min (53–202) compared to the screw group with 119.7 min (50–261) (p < 0.001). Soft tissue irritation occurred significantly more often in the K-wire group (72/99) than in the screw group (36/92) (p < 0.001). No group showed significantly more implant migration than the other. No major complications were observed in either group. Postoperative LCE, TA and FHEI were improved significantly in both groups for all parameters (p = < 0.0001). There was no significant difference for initial or final correction for the respective parameters between the two groups. Furthermore, no significant difference in loss of correction was observed between the two groups for the respective parameters. Conclusion K-wire fixation is a viable and safe option for fragment fixation in PAO with similar stability and complication rates as screw fixation. An advantage of the method is the significantly reduced operative time. A disadvantage is the significantly higher rate of implant-associated soft tissue irritation, necessitating implant removal. Level of evidence III, retrospective trial.

scholarly journals Soft tissue masses: distribution of entities and rate of malignancy in small lesions

BMC Cancer ◽  
2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Felix G. Gassert ◽  
Florian T. Gassert ◽  
Katja Specht ◽  
Carolin Knebel ◽  
Ulrich Lenze ◽  
...  
Keyword(s):  
Soft Tissue ◽  
Benign Lesion ◽  
Maximum Diameter ◽  
Histopathological Diagnosis ◽  
Tumor Diameter ◽  
Mr Images ◽  
Tissue Mass ◽  
Malignancy Rate ◽  
Significant Difference ◽  
Soft Tissue Masses

Abstract Background Small soft tissue masses are often falsely assumed to be benign and resected with failure to achieve tumor-free margins. Therefore, this study retrospectively investigated the distribution of histopathologic diagnosis to be encountered in small soft tissue tumors (≤ 5 cm) in a large series of a tertiary referral center. Methods Patients with a soft tissue mass (STM) with a maximum diameter of 5 cm presenting at our institution over a period of 10 years, who had undergone preoperative Magnetic resonance imaging and consequent biopsy or/and surgical resection, were included in this study. A final histopathological diagnosis was available in all cases. The maximum tumor diameter was determined on MR images by one radiologist. Moreover, tumor localization (head/neck, trunk, upper extremity, lower extremity, hand, foot) and depth (superficial / deep to fascia) were assessed. Results In total, histopathologic results and MR images of 1753 patients were reviewed. Eight hundred seventy patients (49.63%) showed a STM ≤ 5 cm and were therefore included in this study (46.79 +/− 18.08 years, 464 women). Mean maximum diameter of the assessed STMs was 2.88 cm. Of 870 analyzed lesions ≤ 5 cm, 170 (19.54%) were classified as superficial and 700 (80.46%) as deep. The malignancy rate of all lesions ≤ 5 cm was at 22.41% (superficial: 23.53% / deep: 22.14%). The malignancy rate dropped to 16.49% (20.79% / 15.32%) when assessing lesions ≤ 3 cm (p = 0.007) and to 15.0% (18.18% / 13.79%) when assessing lesions ≤ 2 cm (p = 0.006). Overall, lipoma was the most common benign lesion of superficial STMs (29.41%) and tenosynovial giant cell tumor was the most common benign lesion of deep STMs (23.29%). Undifferentiated pleomorphic sarcoma was the most common malignant diagnosis among both, superficial (5.29%) and deep (3.57%) STMs. Conclusions The rate of malignancy decreased significantly with tumor size in both, superficial and deep STMs. The distribution of entities was different between superficial and deep STMs, yet there was no significant difference found in the malignancy rate.

Does soft tissue mobilization assist static stretching to improve hamstring flexibility? A randomized controlled trial

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Shibili Nuhmani
Keyword(s):  
Soft Tissue ◽  
Controlled Trial ◽  
Knee Extension ◽  
Repeated Measure ◽  
Control Group ◽  
Static Stretching ◽  
Significant Difference ◽  
Hamstring Flexibility ◽  
Soft Tissue Mobilization ◽  
Experimental Group

AbstractObjectivesObjective of the study is to investigate whether Soft tissue mobilization (STM) can assist with static stretching to improve hamstring flexibly.MethodsThe design of the study was repeated measure design. The study was conducted at the physical therapy laboratory of Jamia Hamdard University, New Delhi. Participants included 78 healthy males with hamstring tightness, randomly assigned to either the control group (static stretching) or the experimental group (STM and static stretching). The experimental group received five sets of four different STM techniques, followed by two sets of 30-s static stretches 3 days per week over the course of 12 weeks. The control group received 5 min of sham ultrasound with an inactive probe prior to static stretching. Active knee extension test (AKE) was the outcome measure.ResultsBoth groups showed significant improvement in AKE compared with the baseline measurements. With ingroup analysis showed a significant difference in AKE across all measured time periods (weeks 4, 8, and 12) with pre-test in both groups (p<0.05). No significant difference in AKE improvement was found between groups (p>0.05).ConclusionThe results of this study show that STM prior to static stretching does not significantly improve hamstring flexibility among healthy individuals. Although this study cannot be generalized, the results may be useful for evidence-based practice in the management of hamstring tightness.

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