Assessment of the mechanical properties of the muscle-tendon unit by supersonic shear wave imaging elastography: a review

Evaluation of the Mechanical Behavior of the Patellar and Semitendinosus Tendons Using Supersonic Shear-wave Imaging (SSI) Elastography and Tensile Tests

Objective  To analyze the mechanical properties of the patellar (PT) and semitendinosus (ST) tendons from fresh-frozen human cadavers from a tissue bank using supersonic shear-wave imaging (SSI) elastography and tensile tests. Methods  We tested seven PT and five ST samples on a traction machine and performed their simultaneous assessment through SSI. The measurements enabled the comparison of the mechanical behavior of the tendons using the stress x strain curve and shear modulus (μ) at rest. In addition, we analyzed the stress x μ relationship under tension and tested the relationship between these parameters. The statistical analysis of the results used unpaired t -tests with Welch correction, the Pearson correlation, and linear regression for the Young modulus (E) estimation. Results  The μ values for the PT and ST at rest were of 58.86 ± 5.226 kPa and 124.3 ± 7.231 kPa respectively, and this difference was statistically significant. The correlation coefficient between stress and μ for the PT and ST was very strong. The calculated E for the PT and ST was of 19.97 kPa and 124.8 kPa respectively, with a statistically significant difference. Conclusion  The ST was stiffer than the PT in the traction tests and SSI evaluations. The μ value was directly related to the stress imposed on the tendon. Clinical relevance  The present is an evaluation of the mechanical properties of the tendons most used as grafts in knee ligament reconstruction surgeries.

Matrix mechanics regulates muscle regeneration by modulating kinesin-1 activity

Sarcopenia, a prevalent muscle disease characterized by muscle mass and strength reduction, is associated with impaired skeletal muscle regeneration. However, the influence of the biomechanical properties of sarcopenic skeletal muscle on the efficiency of the myogenic program remains unclear. Herein, we established a mouse model of sarcopenia and observed a reduction in stiffness within the sarcopenic skeletal muscle in vivo. To investigate whether the biomechanical properties of skeletal muscle directly impact the myogenic program, we established an in vitro system to explore the intrinsic mechanism involving matrix stiffness control of myogenic differentiation. Our findings identify the microtubule motor protein, kinesin-1, as a mechano-transduction hub that senses and responds to matrix stiffness, crucial for myogenic differentiation and muscle regeneration. Specifically, kinesin-1 activity is positively regulated by stiff matrices, facilitating its role in transporting mitochondria and enhancing translocation of the glucose transporter GLUT4 to the cell surface for glucose uptake. Conversely, the softer matrices significantly suppress kinesin-1 activity, leading to the accumulation of mitochondria around nuclei and hindering glucose uptake by inhibiting GLUT4 membrane translocation, consequently impairing myogenic differentiation. The insights gained from the in-vitro system highlight the mechano-transduction significance of kinesin-1 motor proteins in myogenic differentiation. Furthermore, our study confirms that enhancing kinesin-1 activity in the sarcopenic mouse model restores satellite cell expansion, myogenic differentiation, and muscle regeneration. Taken together, our findings provide a potential target for improving muscle regeneration in sarcopenia.

Is musculoskeletal pain associated with increased muscle stiffness? Evidence map and critical appraisal of muscle measurements using shear wave elastography

INTRODUCTION AND AIMS

Approximately 21% of the world's population suffers from musculoskeletal conditions, often associated with sensations of stiff muscles. Targeted therapy requires knowing whether typically involved muscles are objectively stiffer compared to asymptomatic individuals. Muscle stiffness is quantified using ultrasound shear wave elastography (SWE). Publications on SWE-based comparisons of muscle stiffness between individuals with and without musculoskeletal pain are increasing rapidly. This work reviewed and mapped the existing evidence regarding objectively measured muscle stiffness in musculoskeletal pain conditions and surveyed current methods of applying SWE to measure muscle stiffness.

METHODS

A systematic search was conducted in PubMed and CINAHL using the keywords "muscle stiffness", "shear wave elastography", "pain", "asymptomatic controls" and synonyms. The search was supplemented by a hand search using Google Scholar. Included articles were critically appraised with the AXIS tool, supplemented by items related to SWE methods. Results were visually mapped and narratively described.

RESULTS

Thirty of 137 identified articles were included. High-quality evidence was missing. The results comprise studies reporting lower stiffness in symptomatic participants, no differences between groups and higher stiffness in symptomatic individuals. Results differed between pain conditions and muscles, and also between studies that examined the same muscle(s) and pathology. The methods of the application of SWE were inconsistent and the reporting was often incomplete.

CONCLUSIONS

Existing evidence regarding the objective stiffness of muscles in musculoskeletal pain conditions is conflicting. Methodological differences may explain most of the inconsistencies between findings. Methodological standards for SWE measurements of muscles are urgently required.

Chinese Ultrasound Doctors Association Guideline on Operational Standards for 2-D Shear Wave Elastography Examination of Musculoskeletal Tissues

The Ultrasound Physician Branch of the Chinese Medical Doctor Association sought to develop evidence-based recommendations on the operational standards for 2-D shear wave elastography examination of musculoskeletal tissues. A consensus panel of 22 Chinese musculoskeletal ultrasound experts reviewed current scientific evidence and proposed a set of 12 recommendations for 13 key issues, including instruments, operating methods, influencing factors and image interpretation. A final consensus was reached through discussion and voting. On the basis of research evidence and expert opinions, the strength of recommendation for each proposition was assessed using a visual analog scale, while further emphasizing the best available evidence during the question-and-answer session. These expert consensus guidelines encourage facilitation of the standardization of clinical practices for collecting and reporting shear wave elastography data.

The long head of the biceps tendon undergoes multiaxial deformation during shoulder motion

The long head biceps tendon (LHBT) is presumed a common source of shoulder joint pain and injury. Despite common LHBT pathologies, diagnosis and preferred treatment remain frequently debated. This Short Communication reports the development of a subject-specific finite element model of the shoulder joint based on one subject's 3D reconstructed anatomy and 3D in vivo kinematics recorded from bone-fixed electromagnetic sensors. The primary purpose of this study was to use the developed finite element model to investigate the LHBT mechanical environment during a typical shoulder motion of arm raising. Furthermore, this study aimed to assess the viability of material models derived from uniaxial tensile tests for accurate simulation of in vivo motion. The findings of our simulations indicate that the LHBT undergoes complex multidimensional deformations. As such, uniaxial material properties reported in the existing body of literature are not sufficient to simulate accurately the in vivo mechanical behavior of the LHBT. Further experimental tests on cadaveric specimens, such as biaxial tension and combinations of tension and torsion, are needed to describe fully the mechanical behavior of the LHBT and investigate its mechanisms of injury.

Biomechanical assessment of gastrocnemii and Achilles tendon using MyotonPRO: in vivo measurements, and preliminary in situ measurements using formalin-fixed tissues

PURPOSE

This study aims to evaluate the reliability and validity of using MyotonPRO to quantify the mechanical properties of the muscle-tendon unit through in vivo measurements and preliminary in situ measurements using formalin-fixed tissues.

MATERIALS AND METHODS

The mechanical properties of gastrocnemii and the Achilles tendon of 12 healthy adults (six males and six females, 34.9 ± 5.8 years) were examined for in vivo test twice within a day and once post-24 hours using MyotonPRO, while nine human cadavers (formalin-fixed, 3 males and 6 females, 89.9 ± 5.1 years) were assessed for preliminary in situ test with identical time schedule to evaluate the within-day and inter-day reliability and validity.

RESULTS

In vivo tests had very high within-day (ICC: 0.96-0.99) and inter-day reliability (ICC: 0.83-0.96), while in situ tests (formalin-fixed tissues) showed high within-day (ICC: 0.87-0.99) and inter-day reliability (ICC: 0.76-0.98) for the results of tone and stiffness. There was no significant difference in the stiffness of the free part of the Achilles tendon between in vivo and in situ conditions. The stiffness of the lateral gastrocnemius (r = 0.55, p = 0.018), proximal part of the Achilles tendon (r = 0.56, p = 0.015), and free part of the Achilles tendon (r = 0.47, p = 0.048) before removing the skin was significantly correlated with that after removing the skin condition.

CONCLUSIONS

The findings of the current study suggest that MyotonPRO is reliable and valid for evaluating tendon stiffness both in vivo and in situ (formalin-fixed tissues).

Correlation between the shear modulus measured by elastography (SSI) and tangent modulus from tensile tests of in vitro fresh-frozen human tendons

Assessing the mechanical properties of tendons in vivo allows for quantifying the degree of pathology and tracking functional improvements. The Supersonic Shearwave Imaging (SSI) technique is a state-of-the-art method for analyzing musculoskeletal tissues in vivo. This technique estimates tissue stiffness as the shear elastic modulus µ [kPa]. However, only a few studies have validated the accuracy of SSI-estimated shear modulus against the gold standard for in vitro material testing, the tensile test. This study compared the SSI-measured shear elastic modulus (µ) with the tangent modulus (Etan) obtained from mechanical tensile tests for human Achilles (AT) and patellar tendons (PT). The sample comprised eleven fresh-frozen human Achilles tendons and five fresh-frozen human patellar tendons from cadavers that were not degraded by formalin or ionizing radiation. The tendons were tested in a tensile machine, and elastography videos were collected and segmented every 5% of the total experiment time. The absolute µ values estimated from both instruments presented an up to 20-fold difference. However, a strong significant positive correlation was found between µ and Etan for both tendons (range AT: R = 0.9765-0.9972 and PT: R = 0.8719-0.9782). The two resulting curves (µ and Etan) as a function of strain (ε) were normalized by their maxima for visually comparing stiffness × strain profiles. In conclusion, despite the inaccurate absolute values, SSI has been shown to measure relative changes in human Achilles and patellar tendon stiffness. This study endorses future clinical use of SSI to provide in vivo estimations of human tendons' mechanical properties.

To What Extent Implanting Single vs Pairs of Magnets Per Muscle Affect the Localization Accuracy of the Myokinetic Control Interface? Evidence From a Simulated Environment

OBJECTIVE

We recently proposed a new concept of human-machine interface to control hand prostheses which we dubbed the myokinetic control interface. Such interface detects muscle displacement during contraction by localizing permanent magnets implanted in the residual muscles. So far, we evaluated the feasibility of implanting one magnet per muscle and monitoring its displacement relative to its initial position. However, multiple magnets could actually be implanted in each muscle, as using their relative distance as a measure of muscle contraction could improve the system robustness against environmental disturbances.

METHODS

Here, we simulated the implant of pairs of magnets in each muscle and we compared the localization accuracy of such system with the one magnet per muscle approach, considering first a planar and then an anatomically appropriate configuration. Such comparison was also performed when simulating different grades of mechanical disturbances applied to the system (i.e., shift of the sensor grid).

RESULTS

We found that implanting one magnet per muscle always led to lower localization errors under ideal conditions (i.e., no external disturbances). Differently, when mechanical disturbances were applied, magnet pairs outperformed the single magnet approach, confirming that differential measurements are able to reject common mode disturbances.

CONCLUSION

We identified important factors affecting the choice of the number of magnets to implant in a muscle.

SIGNIFICANCE

Our results provide important guidelines for the design of disturbance rejection strategies and for the development of the myokinetic control interface, as well as for a whole range of biomedical applications involving magnetic tracking.

Mechanosensitive traction force generation is regulated by the neutrophil activation state

The generation of traction forces by neutrophils regulates many crucial effector functions responsible for host defense, such as attachment, spreading, migration, phagocytosis, and NETosis. The activation state of the cell is a strong determinant of the functional efficacy of the neutrophil; however, the effect of activation on traction force production has not yet been determined experimentally. Previously, the mapping of cellular-generated forces produced by human neutrophils via a Traction Force Microscopy (TFM) method has required a three-dimensional imaging modality to capture out-of-plane forces, such as confocal or multiphoton techniques. A method newly developed in our laboratories can capture out-of-plane forces using only a two-dimensional imaging modality. This novel technique-combined with a topology-based single particle tracking algorithm and finite element method calculations-can construct high spatial frequency three-dimensional traction fields, allowing for traction forces in-plane and out-of-plane to the substrate to now be differentially visualized and quantified with a standard epifluorescence microscope. Here we apply this technology to determine the effect of neutrophil activation on force generation. Sepsis is a systemic inflammatory response that causes dysregulated neutrophil activation in vivo. We found that neutrophils from septic patients produced greater total forces than neutrophils from healthy donors and that the majority of this dysregulation occurred in-plane to the substrate. Ex vivo activation of neutrophils from healthy donors showed differential consequences depending on activation stimuli with mechanosensitive force decreases observed in some cases. These findings demonstrate the feasibility of epifluorescence-based microscopy in mapping traction forces to ask biologically significant questions regarding neutrophil function.

Force transmission and interactions between synergistic muscles

The classical view of muscles as independent motors has been challenged over the past decades. An alternative view has emerged in which muscles are not isolated but embedded in a three-dimensional connective tissue network that links them to adjacent muscles and other non-muscular structures in the body. Animal studies showing that the forces measured at the distal and proximal ends of a muscle are not equal have provided undisputable evidence that these connective tissue linkages are strong enough to serve as an extra pathway for muscular force transmission. In this historical review, we first introduce the terminology and anatomy related to these pathways of muscle force transmission and provide a definition for the term epimuscular force transmission. We then focus on important experimental evidence indicating mechanical interactions between synergistic muscles that may affect force transmission and/or influence the muscles' force generating capacity. We illustrate that there may exist different expressions of the highly relevant force-length properties depending on whether the force is measured at the proximal or distal tendon and depending on the dynamics of surrounding structures. Changes in length, activation level or disruption of the connective tissue of neighboring muscles, can affect how muscles interact and produce force on the skeleton. While most direct evidence is from animal experiments, studies on humans also suggest functional implications of the connective tissues surrounding muscles. These implications may explain how distant segments, which are not part of the same joint system, affect force generation at a given joint, and, in clinical conditions, explain observations from tendon transfer surgeries, where a muscle transferred to act as an antagonist continues to produce agonistic moments.

A finite element analysis of load distribution during donning and orthostatic posture in the ITOP hybrid subischial socket

INTRODUCTION

Pressure and shear stresses applied to the stump of a transfemoral amputee wearing a newly designed prosthetic socket have been analyzed by a finite element modeling approach.

METHODS

The new socket was developed by the Istituto Tecnico Ortopedico Preneste, and it was named the "hybrid subischial socket." This work aimed at understanding the loads' distribution on the stump surface in 2 operative conditions: at the end of the wearing phase and during the orthostatic posture. The model of the stump was composed of 4 different materials: the femoral bone, the muscle tissue, the fat, and the skin layers. Except for the bone (rigid), the biological tissues were modeled as Neo-Hookean, and their mechanical properties were taken from the literature. The socket was composed of a containment frame, made of carbon fiber composite material, a shell made of flexible silicone, and a liner made of hyperelastic silicone.

RESULTS

The results of our simulation show that the main support areas are located in a proper position, in agreement with the ideal principles of this prosthetic design, and the maximum pressures are well below the pain threshold reported in the literature for the same contact areas.

CONCLUSIONS

We can conclude that although the upper rim of the socket is well below the ischiatic area, the new socket design allows for a safe and comfortable support of the body weight. This is in agreement with the evidence of a good functionality and acceptance of this prosthetics gathered in the many real applications.

Quantitative assessment of biceps brachii muscle stiffness by using Young’s modulus–Angle curve during passive stretching in stroke patients

Purpose: This study aims to use shear wave elastography (SWE) to dynamically describe the characteristics of biceps brachii muscle stiffness during passive stretching in healthy participants, investigate changes in the Young’s modulus–angle curve under various states of muscle tone in stroke patients, and develop a new method for measuring muscle tone quantitatively.

Methods: In total, 30 healthy volunteers and 54 stroke patients were evaluated for elbow flexor muscle tone on both sides using passive motion examination and were divided into groups based on their muscle tone status. The real-time SWE video of the biceps brachii and the Young’s modulus data were recorded during the passive straightening of the elbow. The Young’s modulus–elbow angle curves were created and fitted using an exponential model. The parameters yielded from the model were subjected to further intergroup analysis.

Results: The repeatability of the Young’s modulus measurement was generally good. During passive elbow extension, the Young’s modulus of the biceps brachii steadily increased as muscle tone increased, and it increased faster when the modified Ashworth scale (MAS) score got higher. The exponential model’s fitness was generally good. The curvature coefficient was significantly different between the MAS 0 group and the hypertonia groups (MAS 1, 1+, and 2 groups).

Conclusion: The passive elastic characteristics of the biceps brachii are consistent with the exponential model. The Young’s modulus–elbow angle curve of the biceps brachii changes in distinct ways depending on the muscle tone status. SWE can be used to quantify muscular stiffness during passive stretching as a new way of muscle tone evaluation, allowing for quantitative muscle tone evaluation and mathematical assessment of muscle mechanical properties in stroke patients.

Repeatability of Rotational 3-D Shear Wave Elasticity Imaging Measurements in Skeletal Muscle

Shear wave elasticity imaging (SWEI) usually assumes an isotropic material; however, skeletal muscle is typically modeled as a transversely isotropic material with independent shear wave speeds in the directions along and across the muscle fibers. To capture these direction-dependent properties, we implemented a rotational 3-D SWEI system that measures the shear wave speed both along and across the fibers in a single 3-D acquisition, with automatic detection of the muscle fiber orientation. We tested and examined the repeatability of this system's measurements in the vastus lateralis of 10 healthy volunteers. The average coefficient of variation of the measurements from this 3-D SWEI system was 5.3% along the fibers and 8.1% across the fibers. When compared with estimated respective 2-D SWEI values of 16.0% and 83.4%, these results suggest using 3-D SWEI has the potential to improve the precision of SWEI measurements in muscle. Additionally, we observed no significant difference in shear wave speed between the dominant and non-dominant legs along (p = 0.26) or across (p = 0.65) the muscle fibers.

Passive muscle stiffness is correlated with the intramuscular adipose tissue in young individuals

PURPOSE

We investigated the relationship between intramuscular adipose tissue (IntraMAT) and muscle stiffness (passive and mechanical) and lengthening in young individuals, hypothesizing that (1) passive muscle stiffness is negatively correlated with the IntraMAT content, and (2) the IntraMAT content is negatively correlated with mechanical changes in muscle stiffness and fascicle length during passive dorsiflexion.

METHODS

Twenty men and women (20.3 ± 1.3 years) participated in this study. Axial T1-weighted magnetic resonance imaging was performed at the thickest point of the medial gastrocnemius (MG) to measure the IntraMAT cross-sectional area (CSA) and muscle tissue CSA (units; cm²). The shear wave velocity (SWV) and fascicle length at the three ankle joint angles, namely 15° with plantarflexion (PF15), 0° with neutral position (NP), and 15° with dorsiflexion (DF15), were measured as parameters of muscle stiffness (unit; m/s) and lengthening (unit; cm) using ultrasound shear wave elastography and B-mode imaging. We further calculated the changes in SWV and fascicle length from PF15 to NP and from NP to DF15 as mechanical muscle stiffness and lengthening, respectively.

RESULTS

There was a relationship between IntraMAT CSA and absolute SWV at DF15 (r = - 0.47, P < 0.05). Further, a relationship was observed between IntraMAT CSA and change in SWV and fascicle length from NP to DF15 (r = - 0.47 and r = 0.59, P < 0.05); whereas no relationship was observed between changes in fascicle length and muscle SWV (r = - 0.23, P = 0.33).

CONCLUSION

These results may indicate biomechanical and/or physiological associations between IntraMAT CSA and passive muscle stiffness.

Leukocyte and Platelet-Rich Plasma (L-PRP) in Tendon Models: A Systematic Review and Meta-Analysis of in vivo/in vitro Studies

Purpose

To perform a systematic review on the application of leukocyte- and platelet-rich plasma (L-PRP) in tendon models by reviewing in vivo/in vitro studies.

Methods

The searches were performed via electronic databases including PubMed, Embase, and Cochrane Library up to September 2022 using the following keywords: ((tenocytes OR tendon OR tendinitis OR tendinosis OR tendinopathy OR tendon injury) AND (platelet-rich plasma OR PRP OR autologous conditioned plasma OR leukocyte- and platelet-rich plasma OR L-PRP OR leukocyte-richplatelet-rich plasma Lr-PRP)). Only in vitro and in vivo studies that assessed the potential effects of L-PRP on tendons and/or tenocytes are included in this study. Description of PRP, study design and methods, outcomes measured, and results are extracted from the data.

Results

A total of 17 studies (8 in vitro studies and 9 in vivo studies) are included. Thirteen studies (76%) reported leukocyte concentrations of L-PRP. Four studies (24%) reported the commercial kits. In in vitro studies, L-PRP demonstrated increased cell proliferation, cell migration, collagen synthesis, accelerated inflammation, and catabolic response in the short term. In addition, most in vivo studies indicated increased collagen type I content. According to in vivo studies reporting data, L-PRP reduced inflammation response in 71.0% of studies, while it enhanced the histological quality of tendons in 67.0% of studies. All 3 studies reporting data found increased biomechanical properties with L-PRP treatment.

Conclusions

Most evidence indicates that L-PRP has some potential effects on tendon healing compared to control. However, it appears that L-PRP works depending on the biological status of the damaged tendon. At an early stage, L-PRP may accelerate tendon healing, but at a later stage, it could be detrimental.

Parametric Analysis of SV Mode Shear Waves in Transversely Isotropic Materials Using Ultrasonic Rotational 3-D SWEI

Ultrasonic rotational 3-D shear wave elasticity imaging (SWEI) has been used to induce and evaluate multiple shear wave modes, including both the shear horizontal (SH) and shear vertical (SV) modes in in vivo muscle. Observations of both the SH and SV modes allow the muscle to be characterized as an elastic, incompressible, transversely isotropic (ITI) material with three parameters: the longitudinal shear modulus μL , the transverse shear modulus μT , and the tensile anisotropy χE . Measurement of the SV wave is necessary to characterize χE , but the factors that influence SV mode generation and characterization with ultrasonic SWEI are complicated. This work uses Green's function (GF) simulations to perform a parametric analysis to determine the optimal interrogation parameters to facilitate visualization and quantification of SV mode shear waves in muscle. We evaluate the impact of five factors: μL , μT , χE , fiber tilt angle [Formula: see text], and F-number of the push geometry on SV mode speed, amplitude, and rotational distribution. These analyses demonstrate that the following hold: 1) as μL increases, SV waves decrease in amplitude so are more difficult to measure in SWEI imaging; 2) as μT increases, the SV wave speeds increase; 3) as χE increases, the SV waves increase in speed and separate from the SH waves; 4) as fiber tilt angle [Formula: see text] increases, the measurable SV waves remain approximately the same speed, but change in strength and in rotational distribution; and 5) as the push beam geometry changes with F-number, the measurable SV waves remain approximately the same speed, but change in strength and rotational distribution. While specific SV mode speeds depend on the combinations of all parameters considered, measurable SV waves can be generated and characterized across the range of parameters considered. To maximize measurable SV waves separate from the SH waves, it is recommended to use an F/1 push geometry and [Formula: see text].

Structural and passive mechanical properties of the medial gastrocnemius muscle in ambulatory individuals with chronic stroke

BACKGROUND

This study aimed to investigate the structural, morphological and passive mechanical properties of the medial gastrocnemius muscle among ambulating chronic stroke survivors using a computational model previously established in healthy individuals without stroke.

METHODS

Individuals with chronic stroke (n = 14, age = 63.4 ± 6.0 years) and healthy controls (n = 15, age = 59.6 ± 8.4 years) participated in the study. The mechanical properties of the medial gastrocnemius were measured during continuous passive ankle motion using ultrasound elastography and a corresponding muscle mechanical property-angle curve was estimated where slack angle and elasticity were determined. Muscle thickness, fascicle length, pennation angle, and echo intensity were also assessed using B-mode ultrasound.

FINDINGS

No significant differences in slack angle (paretic: -16.2° ± 6.13°, non-paretic: -16.93° ± 6.80°, p = 0.82), or slack elasticity (paretic: 4.36 ± 1.94 kPa, non-paretic: 4.54 ± 1.24 kPa, p = 0.64) were found between sides or groups. Lower muscle pennation angle (paretic: 13.6 ± 2.9°, non-paretic: 15.9 ± 2.0°, p = 0.019) and higher echo intensity (paretic: 80.5 ± 13.6, non-paretic: 63.4 ± 17.1, p = 0.003) were observed for paretic muscles. No significant between-sides differences were found for muscle thickness (paretic: 1.5 ± 0.3 cm, non-paretic: 1.6 ± 0.2 cm, p = 0.255) or fascicle length (paretic: 6.6 ± 1.9 cm, non-paretic: 7.1 ± 2.2 cm, p = 0.216). Significant between-groups difference was also observed for fascicle length [non-dominant side (control): 6.2 ± 0.8 cm, paretic side (stroke): 6.6 ± 1.9 cm, p = 0.017].

INTERPRETATION

Although muscle mechanical properties increased exponentially over the slack ankle, measures between paretic and non-paretic sides were similar in ambulating participants with chronic stroke. Side-to-side differences in structural and morphological measures suggest the impact of stroke was relatively more pronounced for these muscle parameters than for passive mechanical properties.

A scoping review of methods used in musculoskeletal soft tissue and nerve shear wave elastography studies

This scoping review of shear wave elastography (SWE) articles in musculoskeletal soft tissue and nerve research demonstrates methodological heterogeneity resulting from a lack of standardized data collection and reporting requirements. Seven literature databases were searched for original articles published in English from 2004-2020 that examine human skeletal muscles, tendons, and nerves in vivo. Although 5,868 records were initially identified, only 375 reports met inclusion criteria. Of the 375 articles, 260 examined 89 unique muscles, 94 examined 14 unique tendons, and 43 examined 8 unique nerves. Cohorts were often small (n = 11-20) and young (mean = 20-29 years), and participants were typically tested in the prone position. Regarding equipment, a variety of ultrasound systems (n = 11), ultrasound models (n = 18), and transducers (n = 19) were identified. Only 11% of articles contained information on the use of electromyography to confirm absence of muscle activity, and only 8% reported measurement depth. Since musculoskeletal soft tissue and nerve stiffness can vary significantly based on data collection methods, it is essential to standardize SWE collection and reporting procedures. This will allow SWE to serve as a valid and reproducible tool for assessing tissue pathology, disease progression, and response to intervention within a variety of musculoskeletal and nerve-related disorders.

Study of the kinetics of the determinants of performance during a mountain ultra marathon: Multidisciplinary protocol of the first Trail Scientifique de Clécy 2021 (Preprint)

Background

The growing interest of the scientific community in trail running has highlighted the acute effects of practice at the time of these races on isolated aspects of physiological and structural systems; biological, physiological, cognitive, and muscular functions; and the psychological state of athletes. However, no integrative study has been conducted under these conditions with so many participants and monitoring of pre-, per-, and postrace variables for up to 10 days over a distance close to 100 miles.

Objective

The aim of this study was to evaluate the kinetics of the performance parameters during a 156 km trail run and 6000 m of elevation gain in pre-, per-, and postrace conditions. The general hypothesis is based on significant alterations in the psychological, physiological, mechanical, biological, and cognitive parameters.

Methods

The Trail Scientifique de Clécy took place on November 11, 2021. This prospective experimental study provides a comprehensive exploration of the constraints and adaptations of psychophysiological and sociological variables assessed in real race conditions during a trail running of 156 km on hilly ground and 6000 m of elevation gain (D+). The study protocol allowed for repeatability of study measurements under the same experimental conditions during the race, with the race being divided into 6 identical loops of 26 km and 1000 m D+. Measurements were conducted the day before and the morning of the race, at the end of each lap, after a pit stop, and up to 10 days after the race. A total of 55 participants were included, 43 (78%) men and 12 (22%) women, who were experienced in ultra–trail-running events and with no contraindications to the practice of this sport.

Results

The launch of the study was authorized on October 26, 2021, under the trial number 21-0166 after a favorable opinion from the Comité de Protection des Personnes Ouest III (21.09.61/SIRIPH 2G 21.01586.000009). Of the 55 runners enrolled, 41 (75%) completed the race and 14 (25%) dropped out for various reasons, including gastric problems, hypothermia, fatigue, and musculoskeletal injuries. All the measurements for each team were completed in full. The race times (ie, excluding the measurements) ranged from 17.8206 hours for the first runner to 35.9225 hours for the last runner. The average time to complete all measurements for each lap was 64 (SD 3) minutes.

Conclusions

The Trail Scientifique de Clécy, by its protocol, allowed for a multidisciplinary approach to the discipline. This approach will allow for the explanation of the studied parameters in relation to each other and observation of the systems of dependence and independence. The initial results are expected in June 2022.

International Registered Report Identifier (IRRID)

RR1-10.2196/38027

Visualization of Human Skeletal Muscle Anisotropy by Using Dual-Direction Shear Wave Imaging

OBJECTIVE

Ultrasound (US) shear wave elasticity imaging (SWEI) is a mature technique for diagnosing the elasticity of isotropic tissues. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be diagnosed correctly using SWEI because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, SWEI has been studied for measuring the anisotropic properties of muscles by rotating the transducer; however, this is difficult for clinical practice.

METHODS

In this study, a novel dual-direction shear wave imaging (DDSWI) technique was proposed for visualizing the mechanical anisotropy of muscles without rotation. Longitudinal and transverse shear waves were created by a specially designed external vibrator and supersonic pushing beam, respectively; the SWVs were then tracked using ultrafast US imaging. Subsequently, the SWV maps of two directions were obtained at the same scanning cross section, and the mechanical anisotropy was represented as the ratio between them at each pixel.

RESULTS

The performance of DDSWI was verified using a standard phantom, and human experiments were performed on the gastrocnemius and biceps brachii. Experimental results of phantom revealed DDSWI exhibited a high precision of <0.81 % and a low bias of <3.88 % in SWV measurements. The distribution of anisotropic properties in muscle was visualized with the anisotropic ratios of 1.54 and 2.27 for the gastrocnemius and biceps brachii, respectively.

CONCLUSION

The results highlight the potential of this novel anisotropic imaging in clinical applications because the conditions of musculoskeletal fiber orientation can be easily and accurately evaluated in real time by DDSWI.

Supersonic shear wave imaging of the tibial nerve for diagnosis of diabetic peripheral neuropathy: A meta-analysis

BACKGROUND

Diabetic peripheral neuropathy (DPN) is the most common diabetes-associated complication and imposes a significant burden to healthcare systems. Thus, early diagnosis of DPN is extremely critical for management and outcome of diabetic patients. Supersonic Shear Wave Imaging (SSI) enables the noninvasive measurement of nerve stiffness. However, previous studies on SSI in the diagnosis of DPN were limited in sample sizes and reported various results. In this meta-analysis, we aimed to obtain comprehensive evidence on the value of tibial nerve stiffness measurement by SSI in the diagnosis of DPN.

METHODS

A comprehensive literature search in English and Chinese electronic database was conducted for studies (published until January 25, 2022) that investigated the diagnostic performance of tibial nerve stiffness measurement by SSI for detecting DPN. Summary receiver operating characteristics (SROC) modelling was constructed to conduct the meta-analysis of diagnostic accuracy of SSI for detecting DPN.

RESULTS

Finally, a total of 12 eligible studies with 1325 subjects were included for evaluation, and a meta-analysis was conducted to evaluate the diagnostic performance of tibial nerve stiffness measurement by SSI for detecting DPN. For tibial nerve stiffness measurement by SSI, the summary sensitivity and specificity for the diagnosis of DPN were 80% (95% confidence interval [CI]: 73%-86%) and 86% (95% CI: 82%-89%), respectively. The summary area under the ROC curve (AUROC) value of the SROC was 0.90 (95% CI: 0.87-0.92), for diagnosing DPN. A subgroup analysis of 11 SSI studies from China revealed similar diagnostic performance, with a summary sensitivity of 79% (95% CI: 72%-85%), specificity of 86% (95% CI: 82%-89%) and summary AUROC value of the SROC of 0.90 (95% CI: 0.87-0.92) for diagnosing DPN.

CONCLUSIONS

Our meta-analysis suggests that a tibial nerve stiffness measurement by SSI shows good performance in diagnosing DPN and has considerable potential as a noninvasive tool for detecting DPN.

Full Characterization of in vivo Muscle as an Elastic, Incompressible, Transversely Isotropic Material Using Ultrasonic Rotational 3D Shear Wave Elasticity Imaging

Using a 3D rotational shear wave elasticity imaging (SWEI) setup, 3D shear wave data were acquired in the vastus lateralis of a healthy volunteer. The innate tilt between the transducer face and the muscle fibers results in the excitation of multiple shear wave modes, allowing for more complete characterization of muscle as an elastic, incompressible, transversely isotropic (ITI) material. The ability to measure both the shear vertical (SV) and shear horizontal (SH) wave speed allows for measurement of three independent parameters needed for full ITI material characterization: the longitudinal shear modulus μL , the transverse shear modulus μT , and the tensile anisotropy χE . Herein we develop and validate methodology to estimate these parameters and measure them in vivo, with μL = 5.77±1.00 kPa, μT = 1.93±0.41 kPa (giving shear anisotropy χμ = 2.11±0.92 ), and χE = 4.67±1.40 in a relaxed vastus lateralis muscle. We also demonstrate that 3D SWEI can be used to more accurately characterize muscle mechanical properties as compared to 2D SWEI.

Influence of the Amount of Change in Quadriceps Tendon Young’s Modulus on Amount of Change in Walking Speed before and after Total Knee Arthroplasty

Background and Objectives: Walking speed after total knee arthroplasty (TKA) is an important outcome. However, the effect of quadriceps tendon stiffness on walking speed remains unclear. This study aimed to clarify the influence of the amount of change in quadriceps tendon stiffness on the degree of change in walking speed before and after TKA. Materials and Methods: Sixteen patients who underwent TKA for knee osteoarthritis participated in this study (median age: 74.0 years (interquartile range: 64.5–75.8)). Shear-wave elastography was deployed to measure quadriceps tendon stiffness using Young’s modulus. A motion analysis system was used to assess kinematic parameters and walking speed. Participants’ knee circumference, range of motion, extension strength, one-leg standing time, walking pain level, and activity level were measured preoperatively and one year after TKA, and changes in values were calculated. We used path analysis to clarify the influence of the amount of change in the quadriceps tendon Young’s modulus on the change in walking speed. Results: The quadriceps tendon Young’s modulus negatively affected the knee flexion angle during swing (standardized partial regression coefficients (β) = −0.513, p = 0.042). The knee flexion angle during swing positively affected step length (β = 0.586, p = 0.017). Step length positively affected cadence (β = 0.733, p = 0.001). Step length and cadence positively affected walking speed (β = 0.563, p < 0.001, β = 0.502, p < 0.001, respectively). Conclusions: The amount of change in the quadriceps tendon Young’s modulus may affect the degree of change in walking speed after TKA through the amount of change in the knee flexion angle during swing, step length, and cadence. Clinically, reducing quadriceps tendon stiffness can be addressed in rehabilitation programs to increase walking speed after TKA.

Acute Effects of Dermal Suction on Passive Muscle and Joint Stiffness

The aim of the present study was to examine the acute effects of dermal suction on the passive mechanical properties of specific muscles and joints. Dermal suction was applied to the calves of 24 subjects. Passive plantar flexion torque was measured with the right knee fully extended and the right ankle positioned at 20°, 10°, 0°, and −10° angles, where 0° represents the ankle neutral position, and positive values correspond to the plantar flexion angle. The shear wave velocity (SWV) (m/s) of the medial gastrocnemius was measured in the same position using ultrasound shear wave elastography. The relationship between the joint angle and passive torque at each 10° angle was defined as passive joint stiffness (Nm/°). Passive muscle and joint stiffness were measured immediately before and after the dermal suction protocol. When the ankle joint was positioned at 20° (r = 0.53, P = 0.006), 10° (r = 0.43, P = 0.030), and −10° (r = 0.60, P = 0.001), the SWV was significantly higher after dermal suction than that before dermal suction. Regarding joint stiffness, we found no significant difference between the pre- and post-dermal suction values (partial η² = 0.093, P > 0.05). These findings suggest that dermal suction increases passive muscle stiffness and has a limited impact on passive joint stiffness.

Convergent Validity and Test-Retest Reliability of Multimodal Ultrasonography and Related Clinical Measures in People With Chronic Stroke

OBJECTIVE

To assess the test-retest reliability of diagnostic ultrasonography measurements of the bilateral biceps brachii (BB), brachial artery, medial gastrocnemius (MG), and popliteal artery in survivors of stroke and their convergent validity with related clinical comparators.

DESIGN

Cross-sectional study.

SETTING

All procedures were conducted in a university laboratory.

PARTICIPANTS

Sixty-five community dwelling adults (N=65; 26 women, 39 men) with an average age of 60.9±7.7 years and stroke duration of 5.7±3.9 years participated in this study.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Measures of muscle structure (ie, thickness, cross-sectional area, fascicle length, pennation angle), stiffness, and intramuscular blood perfusion were conducted using B-mode, elastography and color flow Doppler ultrasonography modes, respectively. Convergent validity was assessed by examining correlations between ultrasonography measures and assessments of related constructs (ie, dynamic stiffness, isometric peak torque, spasticity, and systemic vascular function using myotonometry, dynamometry, the Composite Spasticity Scale, and the Ankle-Brachial Index, respectively). A 2-way random-effects intraclass correlation coefficient (ICC) model (ICC_2,3) was used to determine agreement between intersession measures among a smaller cohort of participants with stroke (n=20).

RESULTS

ICC estimates ranged from moderate to excellent for muscle stiffness (paretic: ICC=0.74-0.89; nonparetic: ICC=0.66-0.88), structure (paretic: ICC=0.87-0.99; nonparetic: ICC=0.81-0.98), and blood perfusion measures (paretic: ICC=0.74-0.84; nonparetic: ICC=0.73-0.88). Weak to moderate associations were found between myotonometry and elastography measures of the bilateral BB (r=0.29-0.52, P≤.05) and MG muscles (r=0.31-0.69, P≤.05). The correlations between elastography measures and spasticity scores for the paretic upper (r=0.35-0.63, P≤.05) and lower limbs (r=0.25-0.37, P≤.05) were also weak to moderate.

CONCLUSIONS

Elastography demonstrated mostly weak to moderate correlation with measures of stiffness using myotonometry as well as scores of paretic upper and lower limb spasticity. The results also indicate acceptable intersession reliability for muscle and vascular measures using several ultrasonography modalities among individuals with chronic stroke.

Muscle stiffness of the rectus femoris and vastus lateralis in children with Osgood-Schlatter disease

BACKGROUND

The relevance of the mechanical properties of muscles in relation to Osgood-Schlatter disease (OSD) remains unclear. The present study aimed to examine rectus femoris (RF) and vastus lateralis (VL) muscle stiffness in children with OSD.

METHODS

A total of 28 legs affected by OSD and 26 legs without OSD were assessed. The shear-wave velocity (SWV) of the RF and VL (in m/s) during passive knee flexion (0° (i.e., fully extended position), 45°, and 90° knee joint flexion) and isometric contraction (50% of maximal voluntary contraction) was measured using shear-wave elastography.

RESULTS

The SWV of the RF was higher in subjects with OSD than in those without OSD at 45° and 90° flexion (P = 0.033 and P = 0.035, respectively); however, the SWV of the RF did not significantly differ at 0° flexion (P = 0.469). Similarly, the SWV of the VL exhibited no significant difference between the tested groups (P > 0.05). No significant difference in the SWV of both muscles during isometric contraction was observed between the two groups (P > 0.05).

CONCLUSIONS

The results suggest that a stiffer RF under stretched conditions (45° and 90° flexion) is related to the presence of OSD. Furthermore, both muscles under unstretched and contracted conditions and the VL under stretched conditions have limited association with the presence of OSD. These results have important implications for understanding the association between the mechanical properties of muscles and OSD.

Muscle elasticity is different in individuals with diastasis recti abdominis than healthy volunteers

Objective

To determine the value of shear wave elastography (SWE) in assessing abdominal wall muscles, including rectus abdominis (RA), external oblique muscle (EO), internal oblique muscle, and transversus abdominis (TrA) in patients with diastasis recti abdominis (DRA) and healthy controls.

Methods

From October 2018 to December 2019, 36 postpartum DRA patients and 24 nulliparous healthy women were identified. Inter-rectus distance (IRD) measurements were taken by B-mode ultrasound. Shear wave speed (SWS) values were acquired by one operator at ten specific locations. Clinical and ultrasound variables, including demographics, IRD, muscle thickness, and muscle SWS, were compared between the two groups using Student’s t test or Fisher's exact test. Pearson correlation analyses were conducted for the variables of IRD, muscle thickness, and SWS in the 36 DRA patients.

Results

The maximum diameter of recti abdominus separation was located at the umbilicus in DRA patients (4.59 ± 1.14 cm). The SWS value was significantly lower in the RA (p = 0.003) and higher in the TrA muscle (p < 0.001) in DRA patients compared with the age-matched controls. However, SWS in both muscles (RA and TrA) showed a statistically positive correlation with IRD (p < 0.05). In addition, the SWS value in EO statistically decreased in DRA patients compared with the healthy controls (1.65 ± 0.15 vs. 1.79 ± 0.14, p = 0.001).

Conclusions

The application of SWE to abdominal wall muscles in DRA patients is feasible. The correlation between SWS value and IRD in RA should be interpreted with caution.

In-vivoviscoelastic properties estimation in subcutaneous adipose tissue by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT)

In-vivoviscoelastic properties have been estimated in human subcutaneous adipose tissue (SAT) by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT) under the influence of external compressive pressure-P.Thepve-MTM predicts the ion concentration distributioncmod(t)by coupling the poroviscoelastic and mass transport model to describe the hydrodynamics, rheology, and transport phenomena inside SAT. Thew-EIT measures the time-difference conductivity distribution∆γ(t)in SAT resulted from the ion transport. Based on the integration, the two viscoelastic properties which are viscoelastic shear modulus of SATGvand relaxation time of SATτvare estimated by applying an iterative curve-fitting between the normalized average ion concentration distributioncˆmod(t)predicted frompve-MTM and the experimental normalized average ion concentration distributioncˆexp(t)derived fromw-EIT. Thein-vivoexperiments were conducted by applying external compressive pressure-Pon human calf boundary to induce interstitial fluid flow and ion movement in SAT. As a result, the value ofGvwas range from 4.9-6.3 kPa and the value ofτvwas range from 27.50-38.5 s with the value of average goodness-of-fit curve fittingR² > 0.76. These values ofGvandτvwere compared to the human and animal tissue from the literature in order to verify this method. The results frompve-MTM provide evidence thatGvandτvplay a role in the predicted value ofcˆmod.

Implementing Ultrasound Imaging for the Assessment of Muscle and Tendon Properties in Elite Sports: Practical Aspects, Methodological Considerations and Future Directions

Ultrasound (US) imaging has been widely used in both research and clinical settings to evaluate the morphological and mechanical properties of muscle and tendon. In elite sports scenarios, a regular assessment of such properties has great potential, namely for testing the response to training, detecting athletes at higher risks of injury, screening athletes for structural abnormalities related to current or future musculoskeletal complaints, and monitoring their return to sport after a musculoskeletal injury. However, several practical and methodological aspects of US techniques should be considered when applying this technology in the elite sports context. Therefore, this narrative review aims to (1) present the principal US measures and field of applications in the context of elite sports; (2) to discuss, from a methodological perspective, the strengths and shortcomings of US imaging for the assessment of muscle and tendon properties; and (3) to provide future directions for research and application.

Hamstrings load bearing in different contraction types and intensities: A shear-wave and B-mode ultrasonographic study

The main aim was to examine the load bearing of individual hamstring muscles in different contraction types and intensities, through local stiffness measurement by shear wave elastography (SWE). A secondary aim was to examine the relationship between the SWE stiffness measure and hamstrings morphology. Ten healthy males (age 22.1±4.1 years; height 173.7±5.9 cm; body mass 68.6±12.4 kg; mean ± SD) performed knee flexions on an isokinetic dynamometer at different intensities (20–70%MVC, random order) in three separate, randomized conditions: isometric (ISO), concentric (CON) and eccentric (ECC). SWE was used to measure muscle shear wave velocity (SWV) in biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) during contraction. Muscle anatomical cross-sectional area (ACSA) was measured with magnetic resonance imaging and muscle architecture with B-mode ultrasonography. Muscle SWV increased linearly with contraction intensity, but at a varying rate among muscles and contraction types. ST exhibited greater SWV than BFlh and SM in all contraction types, however, there was an upward shift in the SM SWV–torque relationship in ECC compared to ISO and CON. Strong negative correlations were found between peak ISO SWV and ST ACSA (r = -0.81, p = 0.005) and BFlh pennation angle (r = -0.75, p = 0.012). These results suggest that ST has a primary role in hamstrings load bearing in all contraction types, likely due to its morphology; however, there is evidence of increased contribution from SM in eccentric muscle actions.

Objective Assessment of Regional Stiffness in Vastus Lateralis with Different Measurement Methods: A Reliability Study

The objective of this study was to evaluate the reliability of four methods of assessing vastus lateralis (VL) stiffness, and to describe the influence of structural characteristics on them. The stiffness of the dominant lower-limb’s VL was evaluated in 53 healthy participants (28.4 ± 9.1 years) with shear wave elastography (SWE), strain elastography (SE), myotonometry and tensiomyography (TMG). The SWE, SE and myotonometry were performed at 50%, and TMG was assessed at 30%, of the length from the upper pole of the patella to the greater trochanter. The thickness of the VL, adipose tissue and superficial connective tissue was also measured with ultrasound. Three repeated measurements were acquired to assess reliability, using intraclass correlation coefficients (ICC). Pearson’s correlation coefficients were calculated to determine the relationships between methodologic assessments and between structural characteristics and stiffness assessments of the VL. Myotonometry (ICC = 0.93; 95%-CI = 0.89,0.96) and TMG (ICC = 0.89; 95%-CI = 0.82,0.94) showed excellent inter-day reliability whereas with SWE (ICC = 0.62; 95%-CI = 0.41,0.77) and SE (ICC = 0.71; 95%-CI = 0.57,0.81) reliability was moderate. Significant correlations were found between myotonometry and VL thickness (r = 0.361; p = 0.008), adipose tissue thickness (r = −0.459; p = 0.001) and superficial connective tissue thickness (r = 0.340; p = 0.013). Myotonometry and TMG showed the best reliability values, although myotonometry stiffness values were influenced by the structural variables of the supra-adjacent tissue.

Reliability of Sonoelastography Measurement of Tongue Muscles and Its Application on Obstructive Sleep Apnea

Few studies have explored the feasibility of shear-wave ultrasound elastography (SWUE) for evaluating the upper airways of patients with obstructive sleep apnea (OSA). This study aimed to establish a reliable SWUE protocol for evaluating tongue muscle elasticity and its feasibility and utility in differentiating patients with OSA. Inter-rater and intra-rater reliability of SWUE measurements were tested using the intraclass correlation coefficients. Submental ultrasound was used to measure tongue thickness and stiffness. Association between the ultrasound measurements and presence of OSA was analyzed using multivariate logistic regression. One-way analysis of variance was used to examine if the values of the ultrasound parameters varied among patients with different severities of OSA. Overall, 37 healthy subjects and 32 patients with OSA were recruited. The intraclass correlation coefficients of intra‐ and inter-rater reliability for SWUE for tongue stiffness ranged from 0.84 to 0.90. After adjusting for age, sex, neck circumference, and body mass index, the risk for OSA was positively associated with tongue thickness [odds ratio 1.16 (95% confidence interval 1.01–1.32)] and negatively associated with coronal imaging of tongue muscle stiffness [odds ratio 0.72 (95% confidence interval 0.54–0.95)]. There were no significant differences in tongue stiffness among OSA patients with varying disease severity. SWUE provided a reliable evaluation of tongue muscle stiffness, which appeared to be softer in patients with OSA. Future longitudinal studies are necessary to investigate the relationship between tongue softening and OSA, as well as response to treatment.

The Measurement of Stiffness for Major Muscles with Shear Wave Elastography and Myoton: A Quantitative Analysis Study

The present study was performed to assess the relationship between hand-held myotonometer MyotonPRO and shear wave elastography (SWE) measurements of lower limb muscle stiffness during resting and active voluntary contraction. Forty healthy young adults, (20 males and 20 females) participated in the study. The stiffness of each subject’s rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and medial gastrocnemius (MG) was measured repeatedly by MyotonPRO and SWE. Moderate to strong correlations between the two methods’ measurements were found for both resting and active voluntary contraction. (r = 0.416–0.669, p < 0.05; r = 0.398–0.594, p < 0.05, respectively). Muscle stiffness at rest was significantly lower compared contraction in all four muscles measured by both methods (p < 0.05). Intra-rater reliabilities were generally lower when measurements were taken during contraction. Additionally, when compared by gender, muscle stiffness measured by MyotonPRO was significantly higher at rest in men compared to women, except for the TA. However, a significant difference was found in TA muscle stiffness by gender when measured with SWE. When muscles were contracted, all muscles showed significantly higher stiffness in men compared to women. There were moderate to good correlations in muscle stiffness between measurements of SWE and MyotonPRO at rest and during active voluntary contraction. Additionally, both instruments showed good intra-rater reliability.

Measurement of Shear Wave Speed and Normalized Elastic Modulus of Human Skin with and without Dermal Striae Using Shear Wave Elastography

Supersonic shear imaging is a non-invasive technique used for detecting physiologic and pathologic changes in biological tissues. In this study, supersonic shear imaging was used to measure and compare shear wave speed (c_s) and normalized elastic modulus (E_N) values of skin with and skin without dermal striae (DS) in vivo. The values were measured at angles of 0°, 45°, 90° and 315° to the skin tension lines. In the presence of DS, a statistically significant reduction in the elasticity dermis was observed (p value <0.05). The mean values of c_s and E_N for STLs were higher in normal skin at 45° (4.26 ± 1.05 m/s and 56.23 ± 25.31 kPa) and 90° (4.26 ± 0.55 m/s and 54.91 ± 14.22 kPa), and those for DS were also higher at 45° (3.59 ± 0.72 m/s and 42.71 ± 27.97 kPa) and 90° (3.52 ± 0.65 m/s and 42.34 ± 31.68 kPa) than at other angles. Supersonic shear imaging was found to be a promising technique in the study of skin with DS. The data obtained in this study are expected to be relevant for future studies using shear wave elastography for the aforementioned purpose.

Developing a Quantifying Device for Soft Tissue Material Prop-Erties around Lumbar Spines

Knowing the material properties of the musculoskeletal soft tissue could be important to develop rehabilitation therapy and surgical procedures. However, there is a lack of devices and information on the viscoelastic properties of soft tissues around the lumbar spine. The goal of this study was to develop a portable quantifying device for providing strain and stress curves of muscles and ligaments around the lumbar spine at various stretching speeds. Each sample was conditioned and applied for 20 repeatable cyclic 5 mm stretch-and-relax trials in the direction and perpendicular direction of the fiber at 2, 3 and 5 mm/s. Our device successfully provided the stress and strain curve of the samples and our results showed that there were significant effects of speed on the young's modulus of the samples (p < 0.05). Compared to the expensive commercial device, our lower-cost device provided comparable stress and strain curves of the sample. Based on our device and findings, various sizes of samples can be measured and viscoelastic properties of the soft tissues can be obtained. Our portable device and approach can help to investigate young's modulus of musculoskeletal soft tissues conveniently, and can be a basis for developing a material testing device in a surgical room or various lab environments.

Individual variation in Achilles tendon morphology and geometry changes susceptibility to injury

The unique structure of the Achilles tendon, combining three smaller sub-tendons, enhances movement efficiency by allowing individual control from connected muscles. This requires compliant interfaces between sub-tendons, but compliance decreases with age and may account for increased injury frequency. Current understanding of sub-tendon sliding and its role in the whole Achilles tendon function is limited. Here we show changing the degree of sliding greatly affects the tendon mechanical behaviour. Our in vitro testing discovered distinct sub-tendon mechanical properties in keeping with their mechanical demands. In silico study based on measured properties, subject-specific tendon geometry, and modified sliding capacity demonstrated age-related displacement reduction similar to our in vivo ultrasonography measurements. Peak stress magnitude and distribution within the whole Achilles tendon are affected by individual tendon geometries, the sliding capacity between sub-tendons, and different muscle loading conditions. These results suggest clinical possibilities to identify patients at risk and design personalised rehabilitation protocols.

Sonographic measures and sensory threshold of the normal sciatic nerve and hamstring muscles

PURPOSE

The sciatic nerve innervates the hamstring muscles. Occasionally, the sciatic nerve is injured along with a hamstring muscle. Detailed biomechanical and sensory thresholds of these structures are not well-characterized. Therefore, we designed a prospective study that explored high-resolution ultrasound (US) at multiple sites to evaluate properties of the sciatic nerve, including cross-sectional area (CSA) and shear-wave elastography (SWE). We also assessed SWE of each hamstring muscle at multiple sites. Mechanical algometry was obtained from the sciatic nerve and hamstring muscles to assess multi-site pressure pain threshold (PPT).

METHODS

Seventy-nine asymptomatic sciatic nerves and 147 hamstring muscles (25 males, 24 females) aged 18-50 years were evaluated. One chiropractic radiologist with 4.5 years of US experience performed the evaluations. Sciatic nerves were sampled along the posterior thigh at four sites obtaining CSA, SWE, and algometry. All three hamstring muscles were sampled at two sites utilizing SWE and algometry. Descriptive statistics, two-way ANOVA, and rater reliability were assessed for data analysis with p ≤ 0.05.

RESULTS

A significant decrease in sciatic CSA from proximal to distal was correlated with increasing BMI (p < 0.001). Intra-rater and inter-rater reliability for CSA was moderate and poor, respectively. Elastographic values significantly increased from proximal to distal with significant differences in gender and BMI (p = 0.002). Sciatic PPT significantly decreased between sites 1 and 2, 1 and 3, and 1 and 4. Significant correlation between gender and PPT was noted as well as BMI (p < 0.001). Hamstring muscle elastographic values significantly differed between biceps femoris and semitendinosus (p < 0.001) and biceps femoris and semimembranosus (p < 0.001). All three hamstring muscles demonstrated increased PPT in males compared to females (p < 0.001). In addition, PPT of the biceps femoris correlated with BMI (p = 0.02).

CONCLUSION

High-resolution US provided useful metrics of sciatic nerve size and biomechanical properties. PPT for the normal sciatic nerve and hamstring muscles was obtained for future clinical application.

Reliability and Validity of Ultrasound Elastography for Evaluating Muscle Stiffness in Neurological Populations: A Systematic Review and Meta-Analysis

OBJECTIVE

Ultrasound elastography is an emerging diagnostic technology used to investigate the biomechanical properties of the musculoskeletal system. The purpose of this study was to systematically review the psychometric properties of ultrasound elastography techniques for evaluating muscle stiffness in people with neurological conditions.

METHODS

A systematic search of MEDLINE, EMBASE, CINAHL, and Cochrane Library databases was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Using software, reviewers independently screened citations for inclusion. Peer-reviewed studies that evaluated in vivo muscle stiffness in people with neurological conditions and reported relevant psychometric properties were considered for inclusion. Twenty-one articles were included for final review. Data relevant to measurement technique, site, and neurological condition were extracted. The Consensus-Based Standards for the Selection of Health Measurement Instruments checklist was used to rate the methodological quality of included studies. The level of evidence for specific measurement outcomes was determined using a best-evidence synthesis approach.

RESULTS

Reliability varied across populations, ultrasound systems, and assessment conditions (ie, joint/body positions, active/passive muscle conditions, probe orientation), with most studies indicating moderate to good reliability (ICC = 0.5-0.9, n = 13). Meta-analysis results showed a good overall correlation across studies (r = 0.78, 95% confidence interval = 0.64-0.86), with no between-group difference based on population (Q1 = 0.00). Convergent validity was demonstrated by strong correlations between stiffness values and measures of spasticity (n = 5), functional motor recovery or impairment (n = 5), and grayscale or color histogram pixel intensities (n = 3). Discriminant or known-groups validity was also established for multiple studies and indicated either significant between-group differences in stiffness values (n = 12) or within-group differences between more and less affected limbs (n = 6). Responsiveness was observed in all intervention studies reporting posttreatment stiffness changes (n = 6).

CONCLUSIONS

Overall, ultrasound elastography techniques showed moderate reliability in evaluating in vivo muscle stiffness, good convergent validity with relevant clinical assessments, and good divergent validity in discriminating tissue changes within and between groups.

IMPACT

Ultrasound elastography has clinical utility in assessing muscle stiffness, monitoring its temporal changes, and measuring the response to intervention in people with neurological conditions.

Usability and Pitfalls of Shear-Wave Elastography for Evaluation of Muscle Quality and Its Potential in Assessing Sarcopenia: A Review

Sarcopenia is age-related progressive and generalized loss of skeletal muscle mass and strength. Its prevalence is rising, which poses a burden for society because it increases disability and dependency and therefore raises health care costs. Muscle mass quality, however-an essential part of sarcopenia-is not easily diagnosable yet. Recent interest has risen for ultrasonographic evaluation of muscle. This review introduces muscle elastography as a possible, easy and cheap tool to evaluate qualitative muscle parameters. Basic principles of muscle elastography are described, as well as different elastography techniques and some technical considerations. Furthermore, a proposal for practical guidelines is offered and factors influencing muscle stiffness are highlighted.

Shear Wave Elastographic Study of the Myotendinous Junction of the Medial Gastrocnemius: Normal Patterns and Dynamic Evaluation

OBJECTIVES

The myotendinous junction (MTJ) represents a specialized anatomic region through which the contractile strength is transmitted from the muscle to the tendon. The integrity of this region is essential to permit force transmission and to optimize energy expenditure during walking, running, and globally for human movement. We evaluated the MTJ with shear wave elastography to assess its elasticity variation during a functional test.

METHODS

Forty professional soccer players were enrolled in the study. Shear wave elastography was performed at the level of the medial gastrocnemius MTJ both in a resting position and during a standing calf rise position to assess functional contraction.

RESULTS

All 40 participants were male, aged between 18 and 38 years (mean age, 25 years). The results of the elastographic study showed mean stiffness values ± SD of 4.19 ± 0.86 m/s for the right medial gastrocnemius and 4.20 ± 0.87 m/s for the left medial gastrocnemius with the muscle relaxed. During contraction, the stiffness values were 8.33 ± 0.5 m/s for the right medial gastrocnemius and 8.30 ± 0.48 m/s for the left medial gastrocnemius.

CONCLUSIONS

Our study showed an increase of stiffness at the level of the MTJ during muscle contraction. This result is in line with the physiologic stiffening of the MTJ to resist the high level of force applied during muscle contraction. Shear wave elastography could be a useful method to assess the characteristics of the MTJ under both physiologic and pathologic conditions.

Evaluation of the ulnar nerve with shear-wave elastography: a potential sonographic method for the diagnosis of ulnar neuropathy

PURPOSE

This study was designed to verify whether shear-wave elastography (SWE) can be used to differentiate ulnar neuropathy at the cubital tunnel from asymptomatic ulnar nerve or medial epicondylitis. An additional aim was to determine a cut-off value to identify patients with ulnar neuropathy.

METHODS

This study included 10 patients with ulnar neuropathy at the cubital tunnel as confirmed with electromyography (three women and seven men; mean age, 51.9 years), 10 patients with medial epicondylitis (nine women and one man; mean age, 56.1 years), and 37 patients with asymptomatic ulnar nerve and lateral epicondylitis (21 women and 16 men; mean age, 54.0 years). Each patient underwent SWE of the ulnar nerve at the cubital tunnel, distal upper arm, and proximal forearm.

RESULTS

Patients with ulnar neuropathy at the cubital tunnel exhibited significantly greater mean ulnar nerve stiffness at the cubital tunnel (66.8 kPa) than controls with medial epicondylitis (21.2 kPa, P=0.015) or lateral epicondylitis (33.9 kPa, P=0.040). No significant differences were observed between patients and controls with regard to ulnar nerve stiffness at the distal upper arm or the proximal forearm. A stiffness of 31.0 kPa provided 100% specificity, 80.0% sensitivity, 100% positive predictive value, and 83.3% negative predictive value for the differentiation between ulnar neuropathy and medial epicondylitis.

CONCLUSION

Cubital tunnel syndrome is associated with a stiffer ulnar nerve than lateral or medial epicondylitis. SWE seems to be a new, reliable, and simple quantitative diagnostic technique to aid in the precise diagnosis of ulnar neuropathy at the cubital tunnel.

Systematic Review of Instrumented Measures of Skeletal Muscle Mechanical Properties: Evidence for the Application of Shear Wave Elastography with Children

The aim of this review was to identify instrumented devices that quantify skeletal muscle mechanical properties and to evaluate their potential clinical utility and clinimetric evidence with respect to children. Four databases were searched to identify articles reporting original clinimetric data for devices measuring muscle stiffness or elastic modulus, along a muscle's main fibre direction. Clinimetric evidence was rated using the Consensus-Based Standard for the Selection of Measurement Instruments (COSMIN) checklist. Sixty-five articles provided clinimetric data for two devices meeting our criteria: the Aixplorer and the Acuson. Both are shear wave elastography devices that determine the shear modulus of muscle tissue. The Aixplorer had strong construct validity and reliability, and the Acuson, moderate construct validity and reliability. Both devices have sound clinical utility with non-invasive application at various joint positions and data acquisition in real time, minimizing fatigue. Further research is warranted to evaluate utility for children with specific disorders of abnormal muscle structure or function.

Hip position influences shear wave elastography measurements of the hamstring muscles in healthy subjects

Ultrasound shear wave elastography (SWE) has recently emerged as a non-invasive tool for assessing muscle stiffness. The majority of studies utilizing SWE have focused primarily on upper-extremity muscles, with little attention attributed to lower-extremity muscles. In addition, of the studies that have been published, various joint and muscle positions have been examined, rendering it difficult to compare results across studies. Thus, the purpose of this investigation was to examine lower extremity medial hamstring muscles (semitendinosus and semimembranosus) and to determine how hip position (0° versus 90°) and muscle position (knee flexed versus extended) impacted resulting shear modulus values. Ten subjects varying widely in age participated in this study, and their hamstring stiffness was assessed in four separate positions: seated with the knee flexed and extended, and lying prone with the knee flexed and extended. Higher shear modulus values were found at the group-level when participants were seated compared to prone (hip placed at 90° compared to 0°). In addition, higher values were also found when the knee was extended compared to flexed, but only when the hip was placed at 90° (not 0°). These results demonstrate that joint and muscle position, particularly when assessing the hamstrings, largely impact resulting shear modulus values. Therefore, joint and muscle position need to be systematically controlled for and reported when establishing normative ranges for shear modulus values across specific age groups. This will enable physicians to more precisely determine whether patients' shear modulus values indicate clinically meaningful differences in comparison to normative data.

Detecting muscle activation using ultrasound speed of sound inversion with deep learning

Functional muscle imaging is essential for diagnostics of a multitude of musculoskeletal afflictions such as degenerative muscle diseases, muscle injuries, muscle atrophy, and neurological related issues such as spasticity. However, there is currently no solution, imaging or otherwise, capable of providing a map of active muscles over a large field of view in dynamic scenarios.In this work, we look at the feasibility of applying longitudinal sound speed measurements to the task of dynamic muscle imaging of contraction or activation. We perform the assessment using a deep learning network applied to prebeamformed ultrasound channel data for sound speed inversion.Preliminary results show that dynamic muscle contraction can be detected in the calf and that this contraction can be positively assigned to the operating muscles. Potential frame rates in the hundreds to thousands of frames per second are necessary to accomplish this.

The Structure and Role of Intramuscular Connective Tissue in Muscle Function

Extracellular matrix (ECM) structures within skeletal muscle play an important, but under-appreciated, role in muscle development, function and adaptation. Each individual muscle is surrounded by epimysial connective tissue and within the muscle there are two distinct extracellular matrix (ECM) structures, the perimysium and endomysium. Together, these three ECM structures make up the intramuscular connective tissue (IMCT). There are large variations in the amount and composition of IMCT between functionally different muscles. Although IMCT acts as a scaffold for muscle fiber development and growth and acts as a carrier for blood vessels and nerves to the muscle cells, the variability in IMCT between different muscles points to a role in the variations in active and passive mechanical properties of muscles. Some traditional measures of the contribution of endomysial IMCT to passive muscle elasticity relied upon tensile measurements on single fiber preparations. These types of measurements may now be thought to be missing the important point that endomysial IMCT networks within a muscle fascicle coordinate forces and displacements between adjacent muscle cells by shear and that active contractile forces can be transmitted by this route (myofascial force transmission). The amount and geometry of the perimysial ECM network separating muscle fascicles varies more between different muscle than does the amount of endomysium. While there is some evidence for myofascial force transmission between fascicles via the perimysium, the variations in this ECM network appears to be linked to the amount of shear displacements between fascicles that must necessarily occur when the whole muscle contracts and changes shape. Fast growth of muscle by fiber hypertrophy is not always associated with a high turnover of ECM components, but slower rates of growth and muscle wasting may be associated with IMCT remodeling. A hypothesis arising from this observation is that the level of cell signaling via shear between integrin and dystroglycan linkages on the surface of the muscle cells and the overlying endomysium may be the controlling factor for IMCT turnover, although this idea is yet to be tested.

Modulation in the elastic properties of gastrocnemius muscle heads in individuals with plantar fasciitis and its relationship with pain

The objectives of this study were (1) to investigate the passive stiffness of the medial gastrocnemius (MG) and lateral gastrocnemius (LG) in patients with and without plantar fasciitis (PF), (2) to explore the correlation between gastrocnemius stiffness and plantar fascia thickness (PFT) as well as the intensity of pain in patients with PF, (3) to detect optimal cut-off points for stiffness of the MG and LG for identifying patients with PF. Forty patients (mean age = 51.1 years ± 12.9) participated in this study. The elastic properties of the MG and LG were quantified using shear wave elastography ultrasound. The thickness of the plantar fascia was measured by B-mode imaging. The intensity of pain was assessed using a visual analogue scale. The results showed that when the ankle was in the relaxed position, patients with PF had increased passive stiffness in the MG (P < 0.05) but not in the LG. Significant correlations were found between pain and the stiffness of the MG (middle, distal; all P-values < 0.05) and no correlation was observed between pain and PFT (P = 0.416). The initial cut-off point for the stiffness of the MG was 29.08 kPa when the ankle was in the relaxed position. The findings from the present study show that an increase in muscle stiffness is not the same in the individual muscles of the gastrocnemius muscle. Traditional treatment of the whole gastrocnemius muscle might not be targeted at the tight muscle.

Meniscus Stiffness Measured with Shear Wave Elastography is Correlated with Meniscus Degeneration

The aim of this study was to evaluate the diagnostic performance of shear wave elastography (SWE) in human meniscus degeneration, with histology serving as the standard of reference. This comparative in vivo and ex vivo study was performed in 15 medial and 15 lateral menisci from 13 patients undergoing total knee arthroplasty (TKA) for primary osteoarthritis with varus deformity. Patients underwent in vivo coronal measurement with SWE for meniscus before surgery. Then, ex vivo assessment of meniscus stiffness with SWE was performed with the tissue obtained after TKA. SWE measurements were made in coronal and sagittal views with respect to the meniscus. Samples were analyzed histologically on a 0-18 scale according to the level of degeneration based on surface integrity, cellularity, fiber organization, collagen alignment and Safranin O staining intensity. The correlation between SWE measurement scale and histology was analyzed using Spearman's correlation. The area under the receiver operating characteristic curve (AUROC) was used to calculate the diagnostic performance of SWE in evaluating meniscus degeneration. Significant increases in stiffness were observed with increasing histologic degeneration in both in vivo and ex vivo coronal SWE. AUROCs were 0.79 (95% confidence interval [CI]: 0.49-1.00) for in vivo coronal SWE, 0.73 (95% CI: 0.53-0.95) for ex vivo coronal SWE and 0.56 (95% CI: 0.27-0.84) for ex vivo sagittal SWE. The medial meniscus, which exhibited more degeneration on histologic analysis, had greater stiffness than the lateral meniscus on ex vivo coronal SWE. The values of meniscus stiffness measured with SWE are correlated with the degree of meniscus degeneration. Further large-scale prospective studies may confirm the diagnostic performance of SWE as a non-invasive tool to assess meniscus degeneration.

Tensiomyography Derived Parameters Reflect Skeletal Muscle Architectural Adaptations Following 6-Weeks of Lower Body Resistance Training

Measurement of muscle specific contractile properties in response to resistance training (RT) can provide practitioners valuable information regarding physiological status of individuals. Field based measurements of such contractile properties within specific muscle groups, could be beneficial when monitoring efficacy of training or rehabilitation interventions. Tensiomyography (TMG) quantifies contractile properties of individual muscles via an electrically stimulated twitch contraction and may serve as a viable option in the aforementioned applications. Thus, aims of this study were; (i) to investigate the potential use of TMG to quantify training adaptations and differences, in response to exercise specific lower limb RT; and (ii) investigate any associations between TMG parameters and accompanying muscle architectural measures. Non-resistance trained male participants (n = 33) were randomly assigned to 1 of 3 single-exercise intervention groups (n = 11 per group); back squat (BS), deadlift (DL), or hip thrust (HT). Participants completed a 6-week linearized training program (2× per week), where the assigned exercise was the sole method of lower body training. Pre- and post-intervention testing of maximal dynamic strength was assessed by one repetition maximum (1RM) of BS, DL, and HT. Radial muscle belly displacement (Dm) and contraction time (Tc) were obtained via TMG from the rectus femoris (RF) and vastus lateralis (VL) pre- and post-intervention, alongside muscle architectural measures (pennation angle and muscle thickness). All three groups displayed significant increases all 1RM strength tests (p < 0.001; pη2 = 0.677-0.753). Strength increases were accompanied by significant overall increases in RF muscle thickness (p < 0.001, pη2 = 0.969), and pennation angle (p = 0.007, pη2 = 0.220). Additionally, an overall reduction in RF Dm (p < 0.001, pη2 = 0.427) was observed. Significant negative relationships were observed between RF Dm and pennation angle (p = 0.003, r = -0.36), and with RF Dm and muscle thickness (p < 0.001, r = -0.50). These findings indicate that TMG is able to detect improved contractile properties, alongside improvements in muscle function within an untrained population. Furthermore, the observed associations between Dm and muscle architecture suggest that TMG contractile property assessments could be used to obtain information on muscle geometry.

Regional Elastic Properties of the Achilles Tendon Is Heterogeneously Influenced by Individual Muscle of the Gastrocnemius

Background

Anatomical studies and the mechanical property studies showed that there is a strong correlation between Achilles tendon (AT) elasticity and individual gastrocnemius muscle (the medial head of gastrocnemius (MG) and the lateral head of gastrocnemius (LG)) elasticity. Limited ankle dorsiflexion range of motion has been correlated with decreased flexibility of the MG/LG/AT complex. However, no studies have been conducted to examine the exact correlation between the Achilles tendon and the individual muscle of the gastrocnemius.

Purposes

The purposes of the present study were (1) to evaluate intra- and interoperator reliabilities of elastic property measurements in the gastrocnemius muscle-Achilles tendon complex by using the shear wave elastography (SWE) and (2) to examine the correlation between the regional elastic properties of the AT and the individual muscle of the gastrocnemius.

Methods

Twenty healthy subjects (mean age: 22.50 (3.02) years) were recruited in this study. The elastic properties of the AT and the individual muscle of the gastrocnemius were quantified using the SWE.

Findings

The SWE has comparatively high reliability in quantifying the elastic properties of the muscle-tendon range from good to excellent. The intraoperator ICC of the gastrocnemius muscle-Achilles tendon complex was 0.77 to 0.95, while the interoperator ICC was 0.76 to 0.94. The minimal detectable change (MDC) of the muscle was 1.72 kPa, while the AT was 32.90 kPa. A significant correlation was found between the elastic modulus of AT and the elastic modulus of the MG (r = 0.668 and p = 0.001 at the relaxing position and r = 0.481 and p = 0.032 at the neutral position).

Conclusions

The SWE has the potential to assess localized changes in muscle-tendon elastic properties, provide more intuitive relations between elastic properties of the muscle tendon and function, and evaluate the therapeutic effect of the muscle tendon. A significant correlation between the AT and the MG was found, and it may provide a new treatment idea (targeted to the tight muscle heads) for the clinical setting to treat subjects with AT disorders.