The application of ultrasound elastography in the shoulder

Sonographic Characterization of the Pericruciate Fat Pad with the Use of Compression Elastography-A Cross-Sectional Study among Healthy and Post-Injured Patients

Background: The pericruciate fat pad (PCFP) in the knee joint is still insufficiently studied despite its potential role in knee pathologies. This is the first reported study which aimed to clarify the characteristics of the PCFP in healthy individuals and contrast them with cases of post-traumatic injuries. Methods: Conducted as a retrospective cross-sectional study (n = 110 knees each) following STROBE guidelines, it employed grayscale ultrasound with echogenicity measurement, compression elastography with elasticity measurement, and Color Doppler for blood flow assessment. Results: PCFP showed a homogenic and hyperechoic echostructure. The echogenicity of the PCFP was higher than that of the posterior cruciate ligament (PCL) (p < 0.001, z-score = 8.97) and of the medial head of gastrocnemius (MHG) (p = 0.007, z-score = 2.72) in healthy knees, but lower than subcutaneous fat (SCF) (p < 0.001, z-score = -6.52). Post-injury/surgery, PCFP echogenicity surpassed other structures (p < 0.001; z-score for PCL 12.2; for MHG 11.65 and for SCF 12.36) and notably exceeded the control group (p < 0.001, z-score = 8.78). PCFP elasticity was lower than MHG and SCF in both groups, with significantly reduced elasticity in post-traumatic knees (ratio SCF/PCFP 15.52 ± 17.87 in case group vs. 2.26 ± 2.4 in control group; p < 0.001; z-score = 9.65). Blood flow was detected in 71% of healthy PCFPs with three main patterns. Conclusions: The main findings, indicating increased echogenicity and reduced elasticity of PCFP post-trauma, potentially related to fat pad fibrosis, suggest potential applications of echogenicity and elasticity measurements in detecting and monitoring diverse knee pathologies. The description of vascularity variations supplying the PCFP adds additional value to the study by emphasizing the clinically important role of PCFP as a bridge for the middle genicular artery on its way to the inside of the knee joint.

Deltoid Muscle Tension Alterations Post Reverse Shoulder Arthroplasty: An Investigation Using Shear Wave Elastography

INTRODUCTION

This study aimed to evaluate the utility of shear wave elastography (SWE) in assessing changes in deltoid muscle properties following reverse shoulder arthroplasty (RSA).

METHODS

Our cohort consisted of 18 patients who underwent RSA due to various conditions, including osteoarthritis, cuff arthropathy, and irreducible proximal humeral fractures. Pre- and postoperative muscle elasticity and stiffness were measured using SWE and were compared with functional outcomes and radiological parameters.

RESULTS

Our results showed significant changes in deltoid muscle elasticity after RSA, particularly in the anterior and middle portions. However, these alterations were not correlated with postoperative functional outcomes or specific radiological parameters. The study also underscored the potential of SWE for future applications, including the preoperative assessment of deltoid function, postoperative monitoring, and intraoperative use for optimal component positioning during RSA.

CONCLUSION

Further research, involving larger, more homogeneous patient cohorts is needed to confirm these findings and to explore the potential influence of these changes on the biomechanical design of implants and prosthesis positioning in RSA.

Effect of durations and pressures of cupping therapy on muscle stiffness of triceps

Cupping therapy has been used for the alleviation of muscle soreness in athletes. However, clinical studies of cupping therapy show conflicting results. Lack of standardized guidelines of the dose-response relationship of cupping therapy, such as appropriate cupping duration and negative pressure, limits the adoption of cupping therapy in clinical practice. The objectives of this study were to investigate the effect of various pressures and durations of cupping therapy on reducing muscle stiffness. The 2 × 2 factorial design with the repeated measures and counterbalanced design was used to test four cupping protocols, including two negative pressures at -225 and -300 mmHg and two durations at 5 and 10 min, in 12 healthy young people. B-mode and elastographic ultrasound was used to assess muscle stiffness of the triceps before and after cupping therapy. The region of interest of elastographic image was divided into the superficial and deep layers for assessing the effect of cupping therapy on stiffness of various depths of the triceps. Normalized stiffness was calculated as a ratio of pre-cupping stiffness divided by post-cupping stiffness of each participant. The two-way analysis of variance (ANOVA) was used to examine the main effects of the pressure and duration factors and the interaction effect between the pressure and duration factors. The results showed that there were no interactions between the pressure and duration factors (overall layer p = 0.149, superficial layer p = 0.632, and deep layer p = 0.491). The main effects of duration of the overall, superficial and deep layers were p = 0.538, p = 0.097 and p = 0.018, respectively. The results showed that 10-min cupping at -300 mmHg is more effective on reducing stiffness of the deep layer of the triceps compared to 5-min cupping (p = 0.031). This study provides the first evidence that the dose of cupping therapy could significantly affect changes of triceps stiffness and the deep layer of the muscle is more sensitive to cupping therapy compared to the superficial and overall layers.

Ultrasound shear wave elastography-derived tissue stiffness is positively correlated with rotator cuff tear size and muscular degeneration

PURPOSE

The purpose of this study is to describe rotator cuff muscle stiffness in patients with different degrees of rotator cuff tear (RCT) severity and to assess its predictive ability for RCT reparability.

METHODS

One hundred and thirty-three consecutive patients who were scheduled to undergo arthroscopic shoulder surgery were prospectively enrolled. Tendon retraction, fatty infiltration, and muscle atrophy were evaluated using magnetic resonance imaging. Shear modulus of supraspinatus (SSP) and infraspinatus (ISP) muscles were measured by ultrasound shear wave elastography (SWE). The tear size and reparability were determined intraoperatively.

RESULTS

There were 97 patients in RCT group and 36 patients in control group. Bilateral shear modulus discrepancy (Δshear modulus) was used to represent rotator cuff stiffness. Severely fatty-infiltrated rotator cuff muscles possessed a significantly higher stiffness compared with their counterparts (SSP: CI 27.8-31.8 vs. 13.5-15.6 kPa, ISP: CI 33.2-38.1 vs. 8.8-11.2 kPa, p < 0.001). The same trend applied to muscles with distinct tendon retraction (SSP: CI 27.7-32.3 vs. 10.9-14.9 kPa, ISP: CI 33.2-38.6 vs. 6.5-11.0 kPa, p < 0.001) and obvious muscle atrophy (SSP: CI 27.9-32.1 vs. 13.6-15.8 kPa, ISP: CI 32.9-38.2 vs. 9.0-11.7 kPa, p < 0.001). Irreparable massive RCT (MRCT) patients had significantly stiffer SSP (CI 27.7-31.9 vs. 13.5-16.5 kPa, p < 0.001) and ISP (CI 33.5-37.8 vs. 10.3-14.8 kPa, p < 0.001) than reparable MRCT. The Δshear modulus of the ISP was a highly accurate predictor of RCT reparability. A cutoff value of 18.0 kPa had a sensitivity of 100% and specificity of 98.8% for irreparable MRCT.

CONCLUSION

Ultrasound SWE-derived rotator cuff muscle stiffness is closely correlated with RCT size and severity.

LEVEL OF EVIDENCE

I.

A novel measurement to evaluate supraspinatus tendinopathies with strain elastography

BACKGROUND

In addition to the traditional strain ratio (STR), a novel measurement termed hard percent of the whole tendon, provided by the device's software and resembling shear-wave elastography, was included in the study.

PURPOSE

To evaluate the correlation between magnetic resonance imaging (MRI) and strain elastography findings in cases with rotator cuff tendinopathy, including tears.

MATERIAL AND METHODS

As a prospective study, cases suggestive of rotator cuff tendinopathy were included. After MRI evaluation by two observers, grading of the elastography examination was performed by a third radiologist. For the first measurement, the region of interest (ROI) was chosen from the gray-scale evaluation corresponding to the area showing a MRI pathological signal. Stiffness was assessed with the STR. For the second measurement, the whole visible tendon was measured as the ROI. The hard percent (unaffected areas as a percent) was measured. Correlation coefficients between MRI grade and the two strain value measurements were calculated.

RESULTS

There were 93 cases (31 men, 62 women) with 112 involved tendons. The correlation coefficient between MRI grade and age was calculated as 0.56, between MRI grade and STR it was -0.51, and with the novel measurement the correlation coefficient was -0.53.

CONCLUSION

This study showed a good association of findings of tendon stiffness with those of tendinopathy on MRI. Using the hard ratio as a novel measurement, its correlation with MRI grade was as reliable as the STR. We also experienced that the benefit of elastography is a challenging issue for defining small ruptures.

Is early diagnosis of myofascial pain syndrome possible with the detection of latent trigger points by shear wave elastography?

Purpose

The aim of the study was to investigate the contribution of shear wave elastography to the diagnosis of myo-fascial pain syndrome (MPS) of the upper part of the trapezius.

Material and methods

Ethical committee approval was obtained for the study. Thirty volunteer women with trigger points in the upper part of the trapezius muscle and 30 healthy women with a similar age distribution were included in the study. The patient group performed a self-stretching exercise program for 4 weeks. No intervention was applied to the control group. Muscle stiffness values of both groups were evaluated with shear wave elastography (SWE), and pain levels of all volunteers were evaluated by the Visual Analogue Scale at the beginning and the end of the study. The statistical analyses were performed using SPSS version 18.0.

Results

There was a significant decrease after the treatment in terms of upper trapezius muscle stiffness and the pain levels in the patient group (p < 0.001 and p < 0.001). In the patient group, there was a moderate correlation between the decrease in the pain level and the reductions in muscle stiffness (r = 0.595). In control group, there was no significant difference in terms of both muscle stiffness and pain levels before and after treatment (p > 0.05).

Conclusions

SWE is a reliable method for detecting latent trigger points in MPS, and it can be used for evaluating the response to treatment.

Muscle elasticity in patients with neonatal brachial plexus palsy using shear-wave ultrasound elastography. Preliminary results

Ultrasound shear wave elastography (SWE) is a noninvasive, reliable and reproducible method, used for the qualitative and quantitative evaluation of tissues. The aim of this study was to compare muscle elasticity between the healthy and the involved sides in children with neonatal brachial plexus palsy (NBPP) using the elastography tool and to assess whether the difference was correlated with the Mallet grading system. We repeatedly measured the shear modulus coefficient of several muscles around the shoulder in stretched or passively relaxed positions on 14 patients. We evaluated the abductor muscles (supraspinatus and deltoid), the infraspinatus, the pectoralis major and the latissimus dorsi. We found a mean shear modulus significantly higher in most studied muscles in the pathologic side (P < 0.001), especially in the stretched position (P < 0.001). Moreover, the shear modulus increases with the degradation of the Mallet score for the abduction and external rotation tasks. SWE seems to be a reliable and reproducible tool to assess muscle elasticity in NBPP.

Return to Play After a Hamstring Strain Injury: It is Time to Consider Natural Healing

Return to play (RTP) criteria after hamstring strain injuries (HSIs) help clinicians in deciding whether an athlete is ready to safely resume previous sport activities. Today, functional and sport-specific training tests are the gold standard in the decision-making process. These criteria lead to an average RTP time between 11 and 25 days after a grade 1 or 2 HSI. However, the high re-injury rates indicate a possible inadequacy of the current RTP criteria. A possible explanation for this could be the neglect of biological healing time. The present review shows that studies indicating time as a possible factor within the RTP-decision are very scarce. However, studies on biological muscle healing showed immature scar tissue and incomplete muscle healing at the average moment of RTP. Twenty-five percent of the re-injuries occur in the first week after RTP and at the exact same location as the index injury. This review supports the statement that functional recovery precedes the biological healing of the muscle. Based on basic science studies on biological muscle healing, we recommend a minimum period of 4 weeks before RTP after a grade 1 or 2 HSI. In conclusion, we advise a comprehensive RTP functional test battery with respect for the natural healing process. Before deciding RTP readiness, clinicians should reflect whether or not it is biologically possible for the injured tissue to have regained enough strength to withstand the sport-specific forces. In an attempt to reduce the detrimental injury-reinjury cycle, it is time to start considering (biological healing) time.

Quantitative assessment of normal middle deltoid muscle elasticity at various arm abduction using ultrasound shear wave elastography

The objective of this study is to assess the change in the normal MD elasticity using shear wave elastography (SWE) through measuring the middle deltoid (MD) elasticity in healthy participants at various arm abduction (with bilateral arms at 0 degrees abduction and 90 degrees active abduction) and analyzing the factors affecting normal MD elasticity. Mean shear wave velocity (SWV) of the MD in healthy right-handed participants were evaluated using SWE at different arm abduction, and potential factors (gender, MD thickness, age, body mass index) affecting MD elasticity were analyzed. Different arm abduction positions of each participant were as follows: (i) 0° abduction of bilateral arm (L0° and R0°), (ii) 90° active abduction of bilateral arm (L90° and R90°). Mean SWV was significantly higher at L90° than L0°, higher at R90° than R0°, higher at R0° than L0°, and higher at R90° than L90° (all P < 0.0001). SWV was significantly higher in males at both L0° (P < 0.05) and R0° (P < 0.01) than in females. Neither MD thickness, age nor body mass index influenced MD elasticity. Reference ranges of normal MD elasticity were 2.4–3.1 m/s in males and 2.2–2.9 m/s in females at L0° and 2.5–3.3 m/s in males and 2.4–3.2 m/s in females at R0°, and were 4.9–6.7 m/s at L90°, 5.2–7.1 m/s at R90° for both males and females. SWE is a feasible technique to assess normal MD elasticity at various arm abduction. Our results suggest that normal MD elasticity at L0°, R0°, L90°, and R90° with SWE are different. Moreover, these reference ranges may serve as quantitative baseline measurements for assessment of normal MD elasticity in the future.

Shoulder ultrasound: current concepts and future perspectives

Ultrasonography is an established and effective imaging technique that can be used to evaluate articular and periarticular structures around the shoulder. It has been shown to be useful in a wide range of rotator cuff diseases (e.g. tendon tears, rotator cuff calcific tendinopathy and bursitis) as well as non-rotator cuff abnormalities (instability, synovial joint diseases and nerve entrapment syndrome). A scanning protocol is highly recommended to reduce the rate of operators’ errors by following a standardized scheme including a list of main structures. Shoulder ultrasound has several advantages: it is a relatively cheap and widely available technique, free from ionizing radiation, that can reach excellent diagnostic accuracy even compared to magnetic resonance imaging. Moreover, it is the only imaging technique that allows dynamic evaluation of musculoskeletal structures, which is important for the evaluation of impingement. Also, due to the shoulder’s superficial anatomical position, ultrasound can also be helpful in guiding interventional percutaneous procedures, both for diagnostic (e.g. magnetic resonance arthrography) and therapeutic purposes (e.g. percutaneous treatment of calcific tendonitis). Contrast-enhanced ultrasound and speckle tracking offer complimentary evaluations of shoulder anatomy and biomechanics. Moreover, the advent of ultra-high-frequency US, with probes up to 70 MHz allowing for a resolution as low as 30 μm, is a promising tool for further evaluation of the shoulder anatomy, and diagnostic and therapeutic strategies.

Anterior deltoid muscle tension quantified with shear wave ultrasound elastography correlates with pain level after reverse shoulder arthroplasty

INTRODUCTION

Reverse shoulder arthroplasty (RSA) leads to medialization and distalization of the centre of rotation of the shoulder joint resulting in lengthening of the deltoid muscle. Shear wave ultrasound elastography (SWE) is a reliable method for quantifying tissue stiffness. The purpose of this study was to analyse if deltoid muscle tension after RSA correlates with the patients' pain level. We hypothesized that higher deltoid muscle tension would be associated with increased pain.

MATERIAL AND METHODS

Eighteen patients treated with RSA were included. Constant score (CS) and pain level on the visual analogue scale (VAS) were analysed and SWE was performed on both shoulders. All three regions of the deltoid muscle were examined in resting position and under standardized isometric loading.

RESULTS

Average patient age was 76 (range 64-84) years and average follow-up was 15 months (range 4-48). The average CS was 66 points (range 35-89) and the average pain level on the VAS was 1.8 (range 0.5-4.7). SWE revealed statistically significant higher muscle tension in the anterior and middle deltoid muscle region in patients after RSA compared to the contralateral non-operated side. There was a statistically significant correlation between pain level and anterior deltoid muscle tension.

CONCLUSION

SWE revealed increased tension in the anterior and middle portion of the deltoid muscle after RSA in a clinical setting. Increased tension of the anterior deltoid muscle portion significantly correlated with an increased pain level. SWE is a powerful, cost-effective, quick, dynamic, non-invasive, and radiation-free imaging technique to evaluate tissue elasticity in the shoulder with a wide range of applications.

LEVEL OF EVIDENCE

Diagnostic study, Level III.

Analysis of Three-Dimensional Ultrasound in Diagnosis of Shoulder and Neck Inflammation and Surrounding Tissue Lesions

Ultrasound imaging technology can not only show neck tear the degree and extent of disease, to help make the correct diagnosis, can also be used to assess shoulder neck inflammation after surgery to repair a shoulder muscle neck tissue integrity and healing. Ultrasound imaging with high-resolution, real-time operation, low cost, etc. gradually become shoulder neck inflammatory disease preferred imaging modality. The sensitivity and specificity for three-dimensional ultrasound imaging of shoulder neck inflammation were 78% and 93% in this study. The full-thickness inflammation sensitivity and specificity were 50% and 95%. The sensitivity and specificity of inflammation were 57% and 87%, respectively. This study shows that the diagnostic accuracy of 3D ultrasound imaging in shoulder and neck inflammation and surrounding tissue lesions is close to that of MRI. Three-dimensional appearance of new technologies such as ultrasound imaging will further improve ultrasound imaging techniques in shoulder neck inflammation application in the diagnosis and treatment assessment.

Efficacy of foam rolling with additional vibration stimulation on the mobility of the thoracolumbar fascia. An observational study

INTRODUCTION

Observations show that foam rolling improves joint movements. Likewise, it can be stated that a vibration stimulation of the tissue leads to improved joint mobility.

METHOD

This study investigates whether the combination of foam rolling and vibrations (31 Hz) can influence the sliding of the thoracolumbar fascia more effectively than normal foam rolling. 45 subjects participated in the study and were divided into a foam roll with additional vibration group (FRV), a foam roll group (FR) and a control group (CG). The intervention groups rolled out the gluteal muscles, the lateral trunk and the upper and lower back. Mobility measures were taken pre and post the respective intervention. Subsequent cross correlation software analysis quantified the sliding of the fascia and calculated its shear strain mobility (SSM).

RESULTS

The sliding of the thoracolumbar fascia improved significantly within the FRV by 2.83 mm (SD ± 1.08/p < .001), in the FR by 0.96 mm (SD ± 0.43/p < .001) and in the CG decreased the sliding by 0.1401 mm (SD ± 0.28/p = .076). The fascia/fascia SSM increased in the FRV by 22.61% (SD ± 15.64/p < .001), in the FR by 11.41% (SD ± 20.38/p = .056) and in the CG decreased the SSM by 0.9473% (SD ± 11.35/p < .751). The lumbar movement increased in both intervention groups, but showed no significant result.

CONCLUSION

The use of a foam roll with additional vibration and standard intervention have increased thoracolumbar fascia sliding and lumbar movements. The improved shear strain mobility can be attributed to the multi-activity of mechanoreceptors, such as Pacini- and Ruffini-Bodies.

Proximal humeral fracture morphology in patients with advanced cuff tear arthropathy: an observational study in a surgically treated cohort

BACKGROUND

In the presence of cuff tear arthropathy (CTA), joint kinematics is alternated and fracture configuration might be different. The purpose of this study was to identify fracture patterns in patients with advanced CTA to facilitate recognition and treatment.

METHODS

Radiographs and computed tomography scans of all patients undergoing surgical treatment for a proximal humeral fracture (PHF) in our institution during a 5-year period were retrospectively analyzed. Fracture pattern according to the AO-OTA and Resch classification and the presence of CTA were evaluated. Glenoid configuration according to Walch, fatty atrophy of the supraspinatus muscle and the centrum-collum-diaphyseal (CCD) angle were analyzed.

RESULTS

A total of 574 out of 713 patients were included. Twenty-three patients (4%) with a mean age of 82 ± 8 years showed advanced CTA with acetabularization of the acromion (≥ stage 3 according to Hamada/Fukuda). There were exclusively valgus fractures with a mean CCD angle of 158° ± 18°. Patients with CTA ≥ grade 3 had a nearly twofold greater risk (risk ratio: 1.8; confidence interval (CI): 95% 1.6-1.9; p < 0.0001) of sustaining a valgus fracture compared to patients without or with CTA < grade 3. The risk for a tuberosity fracture was nearly twofold greater in patients without or with mild CTA (risk ratio: 1.68; confidence interval (CI): 95% 1.17-2.40; p = 0.0046) compared to those with advanced CTA.

CONCLUSION

In advanced CTA, a predominantly valgus fracture pattern can be observed. In addition, fractures of the greater tuberosity were significantly less frequent and were rarely displaced. Up to date, no classification system for PHF has been developed in the setting of CTA although it might indicate a different treatment, and therefore, recognition is crucial. However, when present, this changes the fracture pattern and ability to treat the fracture as the rotator cuff can no longer be utilized as a means of reducing the fragments.

Shear-Wave and Strain Ultrasound Elastography of the Supraspinatus and Infraspinatus Tendons in Patients with Idiopathic Adhesive Capsulitis of the Shoulder: A Prospective Case-Control Study

Objective

To compare the elasticity of the supraspinatus tendon (SST) and infraspinatus tendon (IST) in patients with idiopathic adhesive capsulitis of the shoulder (ACS) with those in the control groups and to evaluate the relationship between age and tendon elasticity.

Materials and Methods

The Institutional Review Board approved this prospective, case-control study, which was conducted between November 2017 and March 2018, and informed consent was obtained from all participants. Control groups comprised healthy individuals or those with asymptomatic contralateral shoulders. Twenty-five shoulders in 20 participants in the ACS group (14 women; 53.5 ± 7.9 years) and 24 shoulders in 18 participants in the control group (6 women; 52.6 ± 10.5 years) were included. Elastography was performed in the oblique coronal plane at the neutral shoulder position. Mean/maximum/minimum velocity and stiffness from the shear-wave ultrasound elastography (SWE) and strain ratio (subcutaneous fat/target-tendon) from the strain ultrasound elastography (SE) of the SST and IST were evaluated. Statistical analyses were performed using the Mann-Whitney U test, receiver operating characteristic (ROC) curve, and Spearman correlation.

Results

Both velocity and stiffness in SWE were higher, and the strain ratio in SE was lower in participants with symptomatic shoulders than in those with normal shoulders (p < 0.001). SST- and IST-mean velocity, mean stiffness, and strain ratios showed excellent area under the ROC curve (> 0.970). The elastic modulus was little correlated with age (ρ = −0.340–0.239).

Conclusion

SWE and SE indicated that SST and IST were stiffer in patients with ACS than in those with normal shoulders regardless of aging.

Pitching shoulder passive flexibility: torque-angle analysis for external rotation and internal rotation

In this study, a custom device was developed to analyse the pitching shoulder's external rotation (ER) and internal rotation (IR) passive flexibility. We analysed three novel measures: the resistance onset angle (ROA = angle where the shoulder begins stretching), rotational stiffness, and torque at the end range of motion (ROM). The purpose was to conduct a bilateral analysis to determine if there are significant differences between the throwing and non-throwing shoulder. Participants were 30 upper level pitchers (13 division I, 17 minor league). During testing, pitchers laid supine on a treatment table and the arm was secured to a rotational wheel with the shoulder abducted 90° and elbow flexed 90°. Dependent t-tests revealed significant (p < 0.01) and relatively extreme bilateral differences for all three variables. The throwing shoulder had: increased ER ROA (9°), decreased IR ROA (5.3°), increased ER stiffness (17%), increased IR stiffness (34%), increased ER torque (21%), and increased IR torque (30%). Secondary correlation analysis was completed to determine if the torque-angle variables were good predictors of the end ROM. Stiffness correlations were weak for ER (r = 0.35, p = 0.048) and IR (r = 0.42, p = 0.017) but ROA correlations were strong for ER (r = 0.85, p < 0.001) and IR (r = 0.86, p < 0.001).

Musculoskeletal application and validation of speckle-tracking ultrasonography

Background

Diseased, injured, or dysfunctional skeletal muscles may demonstrate abnormal function and contractility. Currently, only few in vivo imaging techniques are able to characterize the contractile properties of muscle tissue. This study aimed to test the hypothesis that muscle strain can be tracked in two upper extremity skeletal muscles by speckle-tracking ultrasonography (STU) and correlates with isometric muscle contractions.

Methods

A convenience sample of 10 healthy, adult volunteers with normal shoulder function were tested. The 5 women and 5 men had a mean age of 45 years (range: 39–59 years) and BMI < 30. STU was applied to the supraspinatus (SS) and biceps brachii (BB) muscles using a M11 L-MHz linear transducer (frequency 8–15 MHz) hooked to a Vivid E 9TM ultrasound machine. Strain validation was performed by correlating peak strain against standardized sub-maximal, isometric load conditions of the two muscles (20–80% of maximal voluntary contraction) using a custom-built muscle dynamometer based on strain-gauge technique. Data were analyzed offline using the EchoPac speckle-tracking software and were blinded to the examiner.

Results

Intramuscular strain measured by STU in the SS and BB muscles showed moderate to strong correlations with external muscle load (SS: r = − 0.76, p < 0.0001 and BB: r = − 0.60, p < 0.0001). We found strain to vary from approximately 10–20% during increasing submaximal, isometric conditions.

Conclusions

We demonstrate that STU can be applied on healthy skeletal musculature (SS and BB muscles). The observed correlations between strain and isometric contractions suggest a valid technique. However, the concept of measuring muscle strain non-invasively needs further investigation for validity, accuracy, responsiveness, and reliability before its therapeutic and research potential can be realized.