Longitudinal assessment of the effect of alkali burns on corneal biomechanical properties using optical coherence elastography.

Eye injury due to alkali burn is a severe ocular trauma that can profoundly affect corneal structure and function, including its biomechanical properties. Here, we assess the changes in the mechanical behavior of mouse corneas in response to alkali-induced injury by conducting longitudinal measurements using optical coherence elastography (OCE). A non-contact air-coupled ultrasound transducer was used to induce elastic waves in control and alkali-injured mouse corneas in vivo, which were imaged with phase-sensitive optical coherence tomography. Corneal mechanical properties were estimated using a modified Rayleigh-Lamb wave model, and results show that Young's modulus of alkali-burned corneas were significantly greater than that of their healthy counterparts on days 7 (p = 0.029) and 14 (p = 0.026) after injury. These findings, together with the changes in the shear viscosity coefficient postburn, indicate that the mechanical properties of the alkali-burned cornea are significantly modulated during the wound healing process.

Shear-wave elastography for assessment of trapezius muscle stiffness: Reliability and association with low-level muscle activity.

PURPOSE: Shear-wave elastography has been recognized a useful tool for quantifying muscle stiffness, commonly reported as shear modulus, however the reports on reliability are often limited to test-retest correlations. In this study, we explored the reliability of shear-wave elastography for assessment of the trapezius muscle stiffness and its relationship with low-level muscle activity. METHODS: Twenty participants were included in a two-session experiment. Measurements of shear modulus and muscle activity were performed at rest and during low-level activity, induced by shoulder abduction without additional external resistance. RESULTS: Good to excellent intra-session repeatability (ICC > 0.80) and moderate inter-rater and inter-session reproducibility (ICC = 0.66-0.74) were observed. Typical errors were acceptable (7.6% of the mean value) only for intra-session measurements in resting conditions, but not acceptable for all conditions with low-level muscle activity (10.2-16.6% of the mean value). Inverse relationships between shear modulus and muscle activity at 40° and 60° of shoulder abduction (r = -0.53 and -0.57) were observed on a group level. We also found higher shear modulus in males compared to females, for the parallel probe position compared to the perpendicular position (in relation to muscle fiber orientation), and for the dominant side of the body compared to the non-dominant side. CONCLUSIONS: This study showed an inverse relationship between muscle activity in low-level range and shear modulus on a group level, suggesting inherent passive stiffness could account for a larger portion of the variance (compared to muscle activity) in shear modulus when the muscle activity is low. Our results imply that shear-wave elastography can be used in research exploring muscle stiffness, however, caution is needed since only intra-session examination in resting conditions showed acceptable within-participant typical errors. The secondary analyses of the study showed higher shear modulus for males, for the non-dominant side of the body and for the parallel orientation of the ultrasound probe.

Bidirectional Ultrasound Elastographic Imaging Framework for Non-invasive Assessment of the Non-linear Behavior of a Physiologically Pressurized Artery.

Studies of non-destructive bidirectional ultrasound assessment of non-linear mechanical behavior of the artery are scarce in the literature. We hereby propose derivation of a strain-shear modulus relationship as a new graphical diagnostic index using an ultrasound elastographic imaging framework, which encompasses our in-house bidirectional vascular guided wave imaging (VGWI) and ultrasound strain imaging (USI). This framework is used to assess arterial non-linearity in two orthogonal (i.e., longitudinal and circumferential) directions in the absence of non-invasive pressure measurement. Bidirectional VGWI estimates longitudinal (µL) and transverse (µT) shear moduli, whereas USI estimates radial strain (ɛr). Vessel-mimicking phantoms (with and without longitudinal pre-stretch) and in vitro porcine aortas under static and/or dynamic physiologic intraluminal pressure loads were examined. ɛr was found to be a suitable alternative to intraluminal pressure for representation of cyclic loading on the artery wall. Results revealed that µT values of all samples examined increased non-linearly with εr magnitude and more drastically than µL, whereas µL values of only the pre-stretched phantoms and aortas increased with ɛr magnitude. As a new graphical representation of arterial non-linearity and function, strain-shear modulus loops derived by the proposed framework over two consecutive dynamic loading cycles differentiated sample pre-conditions and corroborated direction-dependent non-linear mechanical behaviors of the aorta with high estimation repeatability.

Mechanical Anisotropy Assessment in Kidney Cortex Using ARFI Peak Displacement: Preclinical Validation and Pilot In Vivo Clinical Results in Kidney Allografts.

The kidney is an anisotropic organ, with higher elasticity along versus across nephrons. The degree of mechanical anisotropy in the kidney may be diagnostically relevant if properly exploited; however, if improperly controlled, anisotropy may confound stiffness measurements. The purpose of this study is to demonstrate the clinical feasibility of acoustic radiation force (ARF)-induced peak displacement (PD) measures for both exploiting and obviating mechanical anisotropy in the cortex of human kidney allografts, in vivo. Validation of the imaging methods is provided by preclinical studies in pig kidneys, in which ARF-induced PD values were significantly higher ( , Wilcoxon) when the transducer executing asymmetric ARF was oriented across versus along the nephrons. The ratio of these PD values obtained with the transducer oriented across versus along the nephrons strongly linearly correlated ( R2 = 0.95 ) to the ratio of shear moduli measured by shear wave elasticity imaging. On the contrary, when a symmetric ARF was implemented, no significant difference in PD was observed ( p > 0.01 ). Similar results were demonstrated in vivo in the kidney allografts of 14 patients. The symmetric ARF produced PD measures with no significant difference ( p > 0.01 ) between along versus across alignments, but the asymmetric ARF yielded PD ratios that remained constant over a six-month observation period post-transplantation, consistent with stable serum creatinine level and urine protein-to-creatinine ratio in the same patient population ( p > 0.01 ). The results of this pilot in vivo clinical study suggest the feasibility of 1) implementing symmetrical ARF to obviate mechanical anisotropy in the kidney cortex when anisotropy is a confounding factor and 2) implementing asymmetric ARF to exploit mechanical anisotropy when mechanical anisotropy is a potentially relevant biomarker.

Shear wave elastography of the cervical arteries: A novel approach to the assessment of cervical arterial wall stiffness. An investigation of psychometric properties and intra-rater reliability.

BACKGROUND: Cervical arterial dissection, can occur spontaneously and is a rare but catastrophic adverse event associated with neck manipulation. Pathophysiology involves altered integrity of the arterial wall increasing its vulnerability to minor trauma. Those at risk are difficult to detect. Previous screening investigated blood flow but altered mechanical properties as stiffness of cervical arterial wall could provide a more valid indication of arterial integrity or even early dissection. OBJECTIVES: To investigate suitability and intra-rater reliability of shear wave ultrasound elastography to measure mechanical properties of the cervical arterial wall. Suitability was assessed by ability to track arteries along their length and measurement accuracy. DESIGN: Observational and intra-rater reliability study. METHODS: Internal carotid (ICA) and vertebral arteries (VA) of healthy participants were examined with shear wave elastography. Shear wave velocity (m/s) indicative of wall stiffness was measured with the head in the neutral position: proximally (C3-4) and distally (C1-2) where injuries have been more commonly reported. Proximal measures were repeated to assess intra-rater reliability. RESULTS: Thirty healthy participants (13 female), mean age of 29 (±12.8) years were imaged. Mean VA wall stiffness (3.4 m/s) was greater than ICA (2.3 m/s) (p < 0.000). Intra-rater reliability for ICA was ICC 0.81 (CI 0.52 to 0.92) and for VA ICC 0.76 (CI 0.38 to 0.9). Standard error of measurement was 0.16 for ICA and 0.34 for VA. CONCLUSIONS: Shear wave ultrasound elastography appears a suitable and reliable method to measure cervical arterial wall stiffness, justifying further research into its use for screening arterial integrity.

Trans-abdominal ultrasound shear wave elastographyfor quantitative assessment of female bladder neck elasticity.

INTRODUCTION AND HYPOTHESIS: Disorders of micturition result from a wide variety of conditions and evaluation often involves multiple diagnostic modalities. However, the sensitivity and specificity of these techniques are highly variable and may not always yield a diagnosis. Novel imaging techniques such as ultrasound shear wave elastography may help to improve diagnostic accuracy. METHODS: Continent women were recruited from outpatient gynecology offices from a tertiary medical system. Participants underwent ultrasound evaluation with measurement of the shear wave velocity (SWV) of the bladder neck (BN). SWV was used to determine the Young's modulus of the bladder neck. The median bladder neck stiffness was calculated and univariate and step-wise and backward multivariate logistic regression analyses were used to identify significant patient characteristics associated with bladder neck stiffness above or below the median. RESULTS: Fifty-seven women underwent SWE of the bladder; 12 were excluded, and 45 were included in the analysis. The median bladder neck stiffness of the study population was 22 (17.1-28.2) kPa. Age greater than 45 years was associated with a bladder neck stiffness above the median, OR 8.39, p < 0.001. Having no vaginal deliveries was also associated with a bladder neck stiffness greater than 22 kPa, unadjusted OR 4.76 (95 % CI 1.41-20.0, p = 0.012). Bladder volume and bladder neck thickness were not significantly associated with bladder neck stiffness above or below the median. CONCLUSION: Trans-abdominal shear wave elastography can be used to quantitatively assess bladder neck stiffness. This technique may potentially be useful for evaluating chronic urinary retention.

Assessment of the arterial stiffness in patients with acute ischemic stroke using longitudinal elasticity modulus measurements obtained with Shear Wave Elastography.

AIM: Arterial wall elasticity including the circumferential and longitudinal modulus is a measure of sub-clinical cardiovascular disease; the circumferential modulus is increased in acute ischemic stroke (AIS). There are still no reports of non-invasive measurement of longitudinal elastic modulus of arterial wall and its prospect of clinical application. In this study, the longitudinal elastic modulus of the arterial wall was assessed using real-time shear wave elastography in patients with AIS. The technique's feasibility and its related factors were studied initially. MATERIALS AND METHODS: In this study 179 patients with AIS and 168 age- and sex-matched controls were examined. The pulse wave velocity (PWV) of the bilateral carotid arteries was measured using radio frequency ultrasound technology. The 20 areas of superficial walls of bilateral carotid artery were analyzed by real-time shear wave elastography (SWE), and the average values of longitudinal average elastic modulus (ME-mean), maximum elastic modulus (ME-max), minimum elastic modulus (ME-min), and elastic modulus standard deviation (MESD) were measured. RESULTS: The PWV, ME-mean, ME-max and ME-sp of the carotid artery in patients with AIS were greater than those in the control group. Age, systolic blood pressure, PWV, and low-density lipoprotein were positively related to ME-mean and ME-max (r=0.221and r=0.248, r=0.174 and r=0.176, r=0.776 and r=0.716, r=0.173 and r=0.200, p<0.05) and were independent risk factors for ME-mean and ME-max ROC curves for detection of ischemic stroke as decided by PWV, ME-mean and ME-max. The area under the curves were 0.55+/-0.03 (p

In vivo assessment of wall strain in embryonic chick heart by spectral domain optical coherence tomography.

The ability to measure in vivo wall strain in embryonic hearts is important for fully understanding the mechanisms of cardiac development. Optical coherence tomography (OCT) is a powerful tool for the three-dimensional imaging of complex myocardial activities in early-stage embryonic hearts with high spatial and temporal resolutions. We describe a method to analyze periodic deformations of myocardial walls and evaluate in vivo myocardial wall strains with a high-speed spectral domain OCT system. We perform four-dimensional scanning on the outflow tract (OFT) of chick embryonic hearts and determine a special cross-section in which the OFT can be approximated as an annulus by analyzing Doppler blood-flow velocities. For each image acquired at the special cross-section, the annular myocardial wall is segmented with a semiautomatic boundary-detection algorithm, and the fluctuation myocardial wall thickness is calculated from the area and mean circumference of the myocardial wall. The experimental results shown with the embryonic chick hearts demonstrate that the proposed method is a useful tool for studying the biomechanical characteristics of embryonic hearts.

On the energetics of quadrupedal running: predicting the metabolic cost of transport via a flexible-torso model.

In this paper, the effect of torso flexibility on the energetics of quadrupedal bounding is examined in a template setting. Two reductive sagittal-plane models, one with a rigid, non-deformable torso and one with a flexible, unactuated torso are proposed. Both models feature non-trivial leg mass and inertia to capture the energy associated with repositioning the legs after liftoff as well as the energy lost due to impacts. Bounding motions that minimize the cost of transport are generated for both models via a simple controller that coordinates leg recirculation. Comparisons reveal that torso compliance promotes locomotion efficiency by facilitating leg recirculation in anticipation of touchdown at speeds that are sufficiently high. Furthermore, by considering non-ideal torque generating and compliant elements with biologically reasonable efficiency values, it is shown that the flexible-torso model can predict the metabolic cost of transport for different animals, estimated using measurements of oxygen consumption. This way, the proposed model offers a means for approximating the energetic cost of transport of running quadrupeds in a simple and direct fashion.

Utility of Real-Time Shear Wave Elastography in the Assessment of Testicular Torsion.

Real-time shear-wave elastography (SWE) is a newly developed method which can obtain the stiffness of tissues and organs based on tracking of shear wave propagation through a structure. Several studies have demonstrated its potential in the differentiation between diseased and normal tissue in clinical practices, however the applicability to testicular disease has not been well elucidated. We investigated the feasibility and reproducibility of SWE in the detection of testicular torsion. This prospective study comprised 15 patients with complete testicular torsion. Results obtained from SWE along with conventional gray-scale and color Doppler sonography and post-operative pathology were compared. The results revealed that (i) the size of injured testis was increased and the twisted testis parenchyma was heterogeneous. The blood flow signals in injured testis were barely visible or absent; (ii) The Young's modulus, including Emean, Emax, Emin and SD values in the border area of torsional testis were higher than those of normal testis (Emean, 78.07±9.01 kPa vs 22.0±5.10 kPa; Emax, 94.07±6.53 kPa vs 27.87±5.78 kPa; Emin, 60.73±7.84 kPa vs 18.90±4.39 kPa; SD, 7.67±0.60 kPa vs 2.30±0.36 kPa, [P<0.05]); The Emax and SD values in the central area of the torsional testis were higher than the corresponding area of the normal testis (Emax, 8.23±0.30 kPa vs 3.97±0.95 kPa; SD, 1.5±0.26 kPa vs 0.67±0.35 kPa,[P<0.05]) and Emin values was lower than those of normal testicles (0.93±0.51 kPa vs 1.6±0.36 kPa; [P<0.05]); (iii) The Young's modulus measurement between two physicians showed good agreement. The pathological findings were accordance with SWE measurement. SWE is a non-invasive, convenient and high reproducible method and may serve as an important alternative tool in the diagnosis and monitoring the progression of the acute scrotums, in additional to conventional Doppler sonography.

Reduced Patellar Tendon Elasticity with Aging: In Vivo Assessment by Shear Wave Elastography.

How aging affects the elasticity of tendons has long been debated, partly because of the limited methods for in vivo evaluation, which differ vastly from those for in vitro animal studies. In this study, we tested the reliability of shear wave elastography (SWE) in the evaluation of patellar tendons and their change in elasticity with age. We recruited 62 healthy participants in three age groups: 20-30 years (group 1), 40-50 years (group 2) and 60-70 years (group 3). Shear wave velocity and elastic modulus were measured at the proximal, middle and distal areas of the patellar tendon. Reliability was excellent at the middle area and fair to good at both ends. Compared with the other groups, group 3 had significantly decreased elastic modulus and shear wave velocity values (p ≤ 0.001 vs. group 1 or 2), with significant increased side-to-side differences. SWE may be valuable in detecting aging tendons before visible abnormalities are observed on B-mode ultrasonography.

The use of strain, strain rate, and displacement by 2D speckle tracking for assessment of systolic left ventricular function in goats: applicability and influence of general anesthesia.

BACKGROUND: Assessment of left ventricular (LV) systolic function can be achieved by conventional echocardiographic methods, but quantification of contractility, regional myocardial function, and ventricular synchrony is challenging. The goal of this study was to investigate the applicability of two-dimensional speckle tracking (2DST) to characterize segmental and global wall motion for assessment of LV function and LV synchrony in healthy goats. We aimed to describe the techniques, report normal values of a variety of 2DST indices, and determine the influence of general anesthesia. METHODS: Prospective study on 22 healthy female Saanen goats (3.7 ± 1.1 y, 60.2 ± 10.5 kg [mean ± SD]). All goats underwent two transthoracic echocardiographic examinations, the first standing and unsedated and the second 7.4 ± 3.5 days later during isoflurane anesthesia and positioned in sternal recumbency. Data analyses were performed offline, blinded, and in random order. Left ventricular longitudinal, radial and circumferential strain and strain rate as well as longitudinal and radial displacement were measured using 2DST methods. Summary statistics were generated and differences of 2DST variables between myocardial segments and treatments (i.e., awake vs. anesthetized) were assessed statistically (alpha level=0.05). RESULTS: Echocardiographic analyses by 2DST were feasible in all goats and at both time points. Longitudinal systolic strain, strain rate and displacement followed a gradient from apex to base. Absolute systolic strain was generally lower and strain rate was higher in awake goats compared to anesthetized goats. Circumferential and radial indices did not consistently follow a segmental pattern. Generally, peak strain occurred later in anesthetized goats compared to awake goats. General anesthesia did not significantly influence LV synchrony. CONCLUSIONS: 2SDT is a valid method for non-invasive characterization of LV wall motion in awake and anesthetized goats. The results of this study add to the understanding of LV mechanical function, aid in the diagnosis of global and segmental LV systolic dysfunction, and will be useful for future cardiovascular studies in this species. However, effects of anesthesia and species-specific characteristics should be considered when goats are used as animal models for human disease.

Sonoelastographic assessment of the age-related changes of the Achilles tendon.

AIMS: Tendons are crucial for optimal muscle force transfer and subject to changes with aging which may impair functional ability of elderly individuals. Achilles is the largest and the strongest tendon in the body; therefore it is an excellent site for the radiologic investigation of aging of tendons. Sonoelastography (SE) is a new ultrasound-based imaging technique that provides information on elastic properties and stiffness of tissues. The aim of our study was to investigate the age-related alterations in Achilles tendons using SE. MATERIAL AND METHODS: Forty five geriatric (age ≥ 65 years) and 42 young (age 18-40 years) healthy consecutive subjects were enrolled. Subjects with known history of metabolic or endocrine diseases, sports or traumatic injuries, peripheral vascular disorders were excluded. Both Achilles tendons were scanned with a real-time SE probe at a frequency of 6-15 MHz. Strains of Achilles tendons' proximal, middle and distal parts were assessed semi-quantitatively with comparing a reference tissue. RESULTS: Both SE methods -color coded evaluation and strain measurement- showed a remarkably stiffer tendon in the elderly subjects compared to young subjects in all thirds of Achilles tendons. In young subjects 84.9 % tendon thirds were blue, and 15.1% were green whereas, in elders 93.7% were blue and 6.3% were green (p=0.024). There was a significant correlation between age and stiffness of tendons assessed with strain indices. CONCLUSION: Our result showed increased tendon stiffness in elderly subjects which might be responsible for the high prevalence of Achilles tendinopathies observed in elderly subjects.

Quantitative assessment of corneal viscoelasticity using optical coherence elastography and a modified Rayleigh-Lamb equation.

We demonstrate the use of a modified Rayleigh­Lamb frequency equation in conjunction with noncontact optical coherence elastography to quantify the viscoelastic properties of the cornea. Phase velocities of air-pulse-induced elastic waves were extracted by spectral analysis and used for calculating the Young's moduli of the samples using the Rayleigh­Lamb frequency equation (RLFE). Validation experiments were performed on 2% agar phantoms (n » 3) and then applied to porcine corneas (n » 3) in situ. The Young's moduli of the porcine corneas were estimated to be ∼60 kPa with a shear viscosity ∼0.33 Pa · s. The results demonstrate that the RLFE is a promising method for noninvasive quantification of the corneal biomechanical properties and may potentially be useful for clinical ophthalmological applications.

Non-invasive, energy-based assessment of patient-specific material properties of arterial tissue.

The mechanical properties of human biological tissue vary greatly. The determination of arterial material properties should be based on experimental data, i.e. diameter, length, intramural pressure, axial force and stress-free geometry. Currently, clinical data provide only non-invasively measured pressure-diameter data for superficial arteries (e.g. common carotid and femoral artery). The lack of information forces us to take into account certain assumptions regarding the in situ configuration to estimate material properties in vivo. This paper proposes a new, non-invasive, energy-based approach for arterial material property estimation. This approach is compared with an approach proposed in the literature. For this purpose, a simplified finite element model of an artery was used as a mock experimental situation. This method enables exact knowledge of the actual material properties, thereby allowing a quantitative evaluation of material property estimation approaches. The results show that imposing conditions on strain energy can provide a good estimation of the material properties from the non-invasively measured pressure and diameter data.

Progressive attenuation of the longitudinal kinetics in the common carotid artery: preliminary in vivo assessment.

Longitudinal kinetics (LOKI) of the arterial wall consists of the shearing motion of the intima-media complex over the adventitia layer in the direction parallel to the blood flow during the cardiac cycle. The aim of this study was to investigate the local variability of LOKI amplitude along the length of the vessel. By use of a previously validated motion-estimation framework, 35 in vivo longitudinal B-mode ultrasound cine loops of healthy common carotid arteries were analyzed. Results indicated that LOKI amplitude is progressively attenuated along the length of the artery, as it is larger in regions located on the proximal side of the image (i.e., toward the heart) and smaller in regions located on the distal side of the image (i.e., toward the head), with an average attenuation coefficient of -2.5 ± 2.0%/mm. Reported for the first time in this study, this phenomenon is likely to be of great importance in improving understanding of atherosclerosis mechanisms, and has the potential to be a novel index of arterial stiffness.

Performance assessment of bio-inspired systems: flow sensing MEMS hairs.

Despite vigorous growth in biomimetic design, the performance of man-made devices relative to their natural templates is still seldom quantified, a procedure which would however significantly increase the rigour of the biomimetic approach. We applied the ubiquitous engineering concept of a figure of merit (FoM) to MEMS flow sensors inspired by cricket filiform hairs. A well known mechanical model of a hair is refined and tailored to this task. Five criteria of varying importance in the biological and engineering fields are computed: responsivity, power transfer, power efficiency, response time and detection threshold. We selected the metrics response time and detection threshold for building the FoM to capture the performance in a single number. Crickets outperform actual MEMS on all criteria for a large range of flow frequencies. Our approach enables us to propose several improvements for MEMS hair-sensor design.

Ex vivo and in vivo assessment of the non-linearity of elasticity properties of breast tissues for quantitative strain elastography.

The aim of this study was to reveal the background to the image variations in strain elastography (strain imaging [SI]) depending on the manner of manipulation (compression magnitude) during elasticity image (EI) acquisition. Thirty patients with 33 breast lesions who had undergone surgery followed by SI assessment in vivo were analyzed. An analytical approach to tissue elasticity based on the stress-elastic modulus (Young's modulus) relationship was adopted. Young's moduli were directly measured ex vivo in surgical specimens ranging from 2.60 kPa (fat) to 16.08 kPa (invasive carcinoma) under the weak-stress condition (<0.2-0.4 kPa, which corresponds to the appropriate "light touch" technique in SI investigation. The contrast (ratio) of lesion to fat in elasticity ex vivo gradually decreased as the stress applied increased (around 1.0 kPa) on the background of significant non-linearity of the breast tissue. Our results indicate that the differences in non-linearity in elasticity between the different tissues within the breast under minimal stress conditions are closely related to the variation in EI quality. The significance of the "pre-load compression" concept in tissue elasticity evaluation is recognized. Non-linearity of elasticity is an essential attribute of living subjects and could provide useful information having a considerable impact on clinical diagnosis in quantitative ultrasound elastography.

Automated, objective and expert-independent assessment of the analyzability of strain and strain rate in tissue Doppler images in term neonates by analysis of beat-to-beat variation.

The variation in longitudinal strain and strain rate (SR) between two consecutive heartbeats (beat-to-beat-variation, BBV) was used to evaluate the analyzability of longitudinal strain and SR in tissue Doppler images in term neonates. Strain and SR BBV analysis and visual evaluation of analyzability were performed in 2394 segments; 1739 segments (73%) were deemed to be analyzable by visual evaluation, with an intra-rater κ score of 0.87 and inter-rater κ score of 0.61 (p < 0.001). Compared against visual evaluation, the κ scores for identification of analyzable segments were 0.57 based on SR BBV and 0.58 based on strain BBV (p < 0.001). The areas under the receiver operating characteristic curves for identification of analyzable segments were 0.87 (0.85-0.88) for strain BBV and 0.87 (0.85-0.89) for SR BBV (p < 0.001). For both BBVs, the sensitivity for identification of analyzable segments was 77% at a specificity of 80%. Analysis of BBV can be used for automated, objective and expert-independent assessment of analyzability.

Transverse ultrasound assessment of median nerve deformation and displacement in the human carpal tunnel during wrist movements.

The symptoms of carpal tunnel syndrome, a compression neuropathy of the median nerve at the wrist, are aggravated by wrist motion, but the effect of these motions on median nerve motion are unknown. To better understand the biomechanics of the abnormal nerve, it is first necessary to understand normal nerve movement. The purpose of this study was to evaluate the deformation and displacement of the normal median nerve at the proximal carpal tunnel level on transverse ultrasound images during different wrist movements, to have a baseline for comparison with abnormal movements. Dynamic ultrasound images of both wrists of 10 asymptomatic volunteers were obtained during wrist maximal flexion, extension and ulnar deviation. To simplify the analysis, the initial and final shape and position of the median nerve were measured and analyzed. The circularity of the median nerve was significantly increased and the aspect ratio and perimeter were significantly decreased in the final image compared with the first image during wrist flexion with finger extension, wrist flexion with finger flexion and wrist ulnar deviation with finger extension (p < 0.01). There were significant differences in median nerve displacement vector between finger flexion, wrist flexion with finger extension and wrist ulnar deviation with finger extension (all p's < 0.001). The mean amplitudes of median nerve motion in wrist flexion with finger extension (2.36 ± 0.79 normalized units [NU]), wrist flexion with finger flexion (2.46 ± 0.84 NU) and wrist ulnar deviation with finger extension (2.86 ± 0.51 NU) were higher than those in finger flexion (0.82 ± 0.33 NU), wrist extension with finger extension (0.77 ± 0.46 NU) and wrist extension with finger flexion (0.81 ± 0.58 NU) (p < 0.0001). In the normal carpal tunnel, wrist flexion and ulnar deviation could induce significant transverse displacement and deformation of the median nerve.