Regardless of the way of treatment, persistent deficits in calf muscles in recovered patients from Achilles tendon rupture (ATR) exist long-term postinjury. Studies on calf muscle changes mostly highlight morphological changes in the calf muscles and Achilles tendon. However, limited attention has been given to fascicular changes. Diffusion tensor imaging (DTI) can provide a better understanding of the characteristics and properties of tissues with organized microstructure. In the current study, we used DTI-derived indices (mean diffusivity (MD), fractional anisotropy (FA), and eigenvalues-λ 1, λ 2, and λ 3) and fiber tractography to better understand the soleus muscle after recovery from ATR by comparing the results of injured legs with healthy ones. Our findings suggest that the standard deviations of measured parameters (FA, MD, and eigenvalues) within the soleus muscle are better predictors of the changes associated with the ATR as compared to the control counterpart for the volumetric region of interest (ROI). Additionally, in four out of five participants, smaller tracts were observed in the injured leg compared to the healthy one, as evidenced by the fiber length distribution of the tracts. Altogether, this study demonstrates the feasibility of the DTI and fiber tractography approaches to quantify the fascicular changes in the individuals recovered from ATR.

Graft site morbidities after bone-patellar tendon-bone (BPTB) autograft harvest for anterior cruciate ligament reconstruction (ACLR) negatively impacts rehabilitation. The purpose of this study was to establish tendon structural properties 1-month after BPTB autograft harvest compared to the uninvolved patellar tendon, and subsequently to quantify the healing trajectory of the patellar tendon over the course of rehabilitation. Patellar tendon morphology (ultrasound) and mechanical properties (continuous shear wave elastography) from 3 regions of the tendon (medial, lateral, central) were measured in 34 participants at 1 month, 3-4 months, and 6-9 months after ACLR. Mixed models were used to compare tendon structure between limbs at 1 month, and quantify healing over 3 timepoints. The involved patellar tendon had increased cross-sectional area and thickness in all regions 1-month after ACLR. Thickness reduced uniformly over time. Possible tendon elongation was observed and remained stable over time. Tendon viscosity was uniform across the three regions in the involved limb while the medial region had higher viscosity in the uninvolved limb, and shear modulus was elevated in all three regions at 1 month. Viscosity and shear modulus in only the central region reduced over time. Statement of Clinical Significance: The entire patellar tendon, and not just the central third, is altered after graft harvest. Tendon structure starts to normalize over time, but alterations remain especially in the central third at the time athletes are returning to sport. Early rehabilitation consisting of tendon loading protocols may be necessary to optimize biologic healing at the graft site tendon.

Abstract Radio frequency ablation (RFA) of the medial branch nerve is a widely used therapeutic intervention for back pain originating from the facet joint. However, multifidus denervation is a well-known adverse effect of this RFA procedure. Computational simulations of RFA can be used to design a new multifidus-sparing RFA procedure for facet joint pain. Unfortunately, there is not a computational model available for RFA of porcine spines (a common animal model for the translation of spinal treatments). The objective of this study is to develop and verify a computational model for bipolar radio frequency ablation of porcine spine muscle. To do this, the electrical and thermal conductivity properties were measured over a temperature range of 20–90 °C in ex vivo porcine spinal. A proportional, integral, and derivative (PID) controlled finite element (FE) model was developed and tuned to simulate the ablation process. Finally, tissue temperatures from simulations and experimental ablations were compared. Thermal conductivity values of spinal muscle ranged from 0.33 W/mK to 0.57 W/mK. Similarly, electrical conductivity varied from 0.36 S/m to 1.28 S/m. The tuned PID parameters for temperature-controlled model were KP=40, Ki=0.01, and Kd=0. A close agreement between experimental measurements of tissue temperature and simulations were observed in the uncertainty range with R-squared values between 0.88 and 0.98. The model developed in this study is a valuable tool for preclinical studies exploring new RFA methods of spinal nerves.

Patellar tendons are assumed to be uniform in morphology and mechanical properties despite a higher prevalence of tendinopathies observed in the medial region. The purpose of this study was to compare the thickness, length, viscosity, and shear modulus of the medial, central, and lateral regions of healthy patellar tendons of young males and females in vivo. B-mode ultrasound and continuous shear wave elastography were performed on 35 patellar tendons (17 females, 18 males) over three regions of interest. A linear mixed-effects model (α = 0.05) was used to determine differences between the three regions and sexes followed by pairwise comparisons for significant findings. The lateral region (mean [95% confidence interval] = 0.34 [0.31-0.37] cm) was thinner compared with the medial (0.41 [0.39-0.44] cm, p < 0.001), and central (0.41 [0.39-0.44] cm, p < 0.001) regions regardless of sex. Viscosity was lower in the lateral (19.8 [16.9-22.7] Pa-s) versus medial region (27.4 [24.7-30.2] Pa-s, p = 0.001). Length had a region-by-sex interaction (p = 0.003) characterized by a longer lateral (4.83 [4.54-5.13] cm) versus medial (4.42 [4.12-4.72] cm) region in males (p < 0.001), but not females (p = 0.992). Shear modulus was uniform between regions and sexes. The thinner, and less viscous lateral patellar tendon may reflect the lower load the tendon experiences explaining the differences in regional prevalence of developing tendon pathology. Statement of Clinical Significance: Healthy patellar tendons are not uniform in morphology or mechanical properties. Considering regional tendon properties may help guide targeted interventions for patellar tendon pathologies.

Numerical simulation of spine mechanics relies on anatomical features of the vertebrae. Statistical shape models aid in these simulations by including shape variability and differences between groups, facilitating finite element simulations for medical procedures. This study aims to develop a statistical shape model of the lumbar vertebrae and to determine shape differences between genders. This study used CT images and 3D segmentations from the Vertebrae Segmentation challenge (VerSe) with a total of 138 vertebrae from 46 patients consisting of L3, L4, and L5 vertebrae. From these segmentations, statistical shape models were created, using ShapeWorks software, for the overall and gender-specific means. Moreover, gender differences, principal component analysis and modes of variations were illustrated. Major differences in posterior elements between overall, male, and female means were identified. Regarding the principal component analysis, the first principal component accounted for 39.4% of the variation, which was distributed between the vertebrae in dissimilar patterns. The second principal component, accounting for 20.4% of the variation, was concentrated in L5. In conclusion, this study specifies locations in the lumbar vertebrae with significant differences between genders and identifies modes of variations in the sample using principal component analysis.

Radiofrequency ablation (RFA) of the medial branch nerve is a widely used therapeutic intervention for facet joint pain. However, denervation of the multifidus muscle is an inevitable consequence of RFA. New ablation techniques with the potential to prevent muscle denervation can be designed using computational simulations. However, depending on the complexity of the model, they could be computationally expensive. As an alternative approach, deep neural networks (DNNs) can be used to predict tissue temperature during RFA procedure. The objective of this paper is to predict the tissue spatial and temporal temperature distributions during RFA using DNNs. First, finite element (FE) models with a range of distances between the probes were run to obtain the temperature readings. The measured temperatures were then used to train the DNNs that predict the spatio-temporal temperature distribution within the tissue. Finally, a separate data obtained from FE simulations were used to test the efficacy of the network. The results presented in this paper demonstrate that the network can achieve an error rate as low as 0.05%, accompanied by a 92% reduction in time compared to FE simulations. The approach proposed in this study will play a major role in the design of new RFA treatments for facet joint pain.

Radiofrequency ablation of the medial branch is commonly used to treat chronic low back pain involving facet joints, which accounts for 12% to 37% of the total cases of chronic low back pain. An adverse effect of this procedure is the denervation of the multifidus muscle, which may lead to its atrophy which can affect the spine and possibly disc degeneration. This study aims to quantify changes in joint angles and loading caused by multifidus denervation after radiofrequency ablation. AnyBody model of the torso was used to evaluate intervertebral joints in flexion, lateral bending, and torsion. Force-dependent kinematics was used to calculate joint angles and forces. These dependent variables were investigated in intact multifidus, unilateral, and bilateral ablations of L3L4, L4L5, and L5S1 joints. The results showed pronounced angular joint changes, especially in bilateral ablations in flexion, when compared with other cases. The same changes' trend from intact to unilaterally then bilaterally ablated multifidus occurred in joint angles of lateral bending. Meanwhile, joint forces were not adversely affected. These results suggest that multifidus denervation after radiofrequency ablation affects spinal mechanics. Such changes may be associated with abnormal tissue deformations and stresses that can potentially alter their mechanobiology and homeostasis, thereby possibly affecting the health of the spine.

The clinical relevance of altered tendon structure in patellar tendinopathy is contested since structural change persists after symptom resolution. The purpose of this study was to explore the relationships between tendon structure and clinical impairments in patellar tendinopathy. In this retrospective, secondary analysis of individuals with patellar tendinopathy (n = 41), tendon structure (thickness, cross-sectional area [CSA], shear modulus, and viscosity), symptom severity, lower extremity function (counter-movement jump [CMJ] height), and quadriceps muscle performance (knee extension force and central activation ratio [CAR]) were recorded for the symptomatic limb. Relationships among structure, symptom severity, lower extremity function, and quadriceps muscle performance were examined using sequential regression models. Adjusting for age, sex, body mass index, and pain levels, there were significant positive relationships for thickness (p < 0.001, β = 0.718) and viscosity (p = 0.006, β = 0.496) with CMJ height. There were significant negative relationships between CSA with both CMJ height (p = 0.001, β = -0.538) and CAR (p = 0.04, β = -0.517). This is the first study to demonstrate relationships between tendon structure and lower extremity function or quadriceps muscle performance in patients with patellar tendinopathy. Clinical significance: Since structural changes persist after symptom resolution, addressing these changes may assist in restoring lower extremity function and quadriceps muscle performance.

We aimed to (1) compare pain, tendon structure, lower limb function, and Achilles tendon loads while running between limbs in runners with Achilles tendinopathy, and (2) explore the relations of pain, tendon structure, and lower limb function to Achilles tendon loads while running. Twenty runners with Achilles tendinopathy participated in this pilot study. Pain was assessed with questionnaires, quantitative sensory testing, and functional testing. Tendon morphology and mechanical properties were evaluated with ultrasound imaging, continuous shear wave elastography, and ultrasound imaging combined with dynamometry. Lower limb function was assessed with an established test battery. Achilles tendon loads were estimated from biomechanical data acquired during running. Compared to the least symptomatic limb, the most symptomatic limb had lower scores on the Victorian Institute of Sports Assessment - Achilles questionnaire and worse pain during drop countermovement jumping, hopping, and running. Tendon thickness and cross-sectional area were greater, and Young's modulus, drop countermovement jump height, and plyometric quotient during hopping were lower on the most symptomatic limb. Side-to-side differences in drop countermovement jump height were significantly associated with side-to-side differences in Achilles tendon peak forces and average loading rates during running. Various measures of pain, structure, and function differ between limbs in runners with Achilles tendinopathy during return-to-sport. Tendon forces, however, do not differ between limbs during comfortable running. In addition to measures that differ between limbs, measures of performance during drop countermovement jumping may aid in clinical decision-making during return-to-sport because they are associated with tendon forces while running.

OBJECTIVES:Patellar tendon injuries occur via various mechanisms such as overuse, or due to surgical graft harvest for anterior cruciate ligament reconstruction (ACLR). Quantified patellar tendon stiffness after injury may help guide clinical care. Continuous shear wave elastography (cSWE) allows for the assessment of viscosity and shear modulus in tendons. The reliability of the measure, however, has not been established in the patellar tendon. The purpose of this study was to investigate the interrater reliability, intrarater reliability, and between-day stability of cSWE in both healthy and pathological patellar tendons.METHODS:Participants with patellar tendinopathy (n = 13), history of ACLR using bone-patellar tendon-bone autograft (n = 9), and with no history of patellar tendon injury (n = 13) were recruited. cSWE was performed 4 times by multiple raters over 2 days. Intraclass correlations (ICC) and minimum detectable change (MDC95% ) were calculated.RESULTS:Good to excellent between-day stability were found for viscosity (ICC = 0.905, MDC95%  = 8.3 Pa seconds) and shear modulus (ICC = 0.805, MDC95%  = 27.4 kPa). The interrater reliability measures, however, were not as reliable (ICC = 0.591 and 0.532).CONCLUSIONS:cSWE is a reliable assessment tool for quantifying patellar tendon viscoelastic properties over time. It is recommended, however, that a single rater performs the measure as the interrater reliability was less than ideal.

This Work-in-Process paper summarizes our current effort to re-design our ME curriculum to adjust the issue of lacking critical thinking practice in traditional laboratory courses. Five 1-credit topic-based laboratory courses are consolidated into a single 3-credit problem-based laboratory course. This new course aims to improve student cognitive skills and prepare them to plan and conduct investigations on complex system-level problems. Students will revise engineering principles through solving 21st-century engineering problems surrounded the topics, Sustainability, Big Data, Advanced Manufacturing, Autonomy and Robotics, and Energy. The engineering principles being focused in this course are Heat Transfer, Fluid Mechanics, Solid Mechanics, Materials, and Chemistry, five-core fundamental ME knowledge identified by our faculty and Industrial and Professional Advisory Council (IPAC) members. To gradually enhance students' higher-order thinking, this course is structured in multiple levels, follows the six levels of Bloom's taxonomy, Remember, Understand, Apply, Analyze, Evaluate, and Create. In each level, a real-world engineering problem will be used to initiate thinking, connect multi-week hands-on activities, and facilitate group discussion. Students apply prior knowledge from ME core curriculum courses to solve the problem, at the same time, utilize essential practical skills for the future workplace. Skills included Data Analysis, Data Acquisition, Critical Thinking, Numerical Simulation, Problem Solving, and Design of Experiment. In this work, we summarize a total of nine multiple-weeks lab activities, which designed to prepare students to work in both thermal and mechanical systems. Here we include three examples, 1. Apply statistics knowledge to solve the problem - How can smartwatch measure and classify our activity? Students have to remember statistics knowledge in junior-level courses, identify and select the proper method and equation to analyze the data, then apply them to extract valuable information. 2. Analyze dependent parameters in heat transfer to solve the problem - What are the best heating strategies for Lithium-ion batteries in cold weather? Students will apply heat transfer knowledge, e.g., conduction, convection, and insulation, to perform numerical simulations and hands-on experiments to study the effect of parametric variation in heat transfer rate. 3. Create and design control logic to solve the problem - How to drive an autonomous vehicle along a planned route? Students will apply basic kinematic, control, and mechatronics knowledge to program ground robotics to perform different tasks in an autonomous vehicle town. Lastly, following the new ABET student outcome (3), an ability to communicate effectively with a range of audiences, students will practice preparing different written and oral deliverables for a variety of audiences in this course. Students' submissions will alternate between homework, tradition project report, email, presentation, and video journal. Each format will explore the communication styles necessary to reach specific audiences, e.g., peers, coworkers, supervisors, and the general public. We anticipate this new course will be pilot in FA 2021 after the new lab space construction is going to be completed in SP 2021.

Objective.Calf strain occurs frequently in tennis players and has been termed "tennis leg".To date, there is a lack of information showing how injury history, age, gender, or level of play, may predispose tennis players to injury (1, 2).The purpose of this study was to investigate the elastographic properties of the gastrocnemius-soleus complex in a group of club-level tennis players.We hypothesized that elastographic properties of the gastrocnemius-complex are affected by age and sport specificity (tennis only vs multi-sport).Methods.Participants were recruited through contact personnel of a local tennis club.At the club's annual summer tournament, each participant voluntarily consented and completed a survey to obtain information about age, level of play, length of play, participation in other sports, relevant injuries, and relevant surgeries.Participants underwent ultrasonography that included visualization of the medial gastrocnemius musculotendinous junction, soleus muscle, and Achilles tendons, bilaterally.Shear wave speed (SWS) was gathered from ultrasonography for all tissues to provide a comparative standard unit of measurement.The data was analyzed with a mixed effects model.Results.20 participants with mean age 33.5 years old (range, 14-61) were evaluated.There was a statistically significant trend in medial gastrocnemius SWS depending on age, participation in sports other than tennis, and two different metrics for skill level (highest level of competitive play and USTA NTRP rating).There was a statistically significant trend between Achilles tendon SWS and highest level of competitive play.Results showed no significant trends for any of the tissues and serving hand, whether the ultrasound was conducted before or after a match, or for any of the four metrics for tennis experience (times playing tennis per week, overall tennis experience, years playing > 3 times per week, and whether a player had > 10 or < 10 years of experience).No statistically significant trends were observed for the soleus muscle when compared to any of the demographics.Conclusions.Age, exclusively playing tennis as opposed to other sports, and two metrics of skill level (highest level of competitive play and USTA NTRP rating) significantly affected gastrocnemius SWS.Highest level of competitive play was the only metric found to affect Achilles tendon SWS.Soleus SWS exhibited no significant changes with any of the variables, despite following similar trends with gastrocnemius SWS.

The multifidus is an important muscle for the active stabilization of the spine. Unfortunately, clinical procedures such as posterior lumbar fusion (PLF) and radio frequency neurotomy (RFN) cause injury to these muscles affecting their function. However, evaluating multifidus function using traditional biomechanical methods is challenging due to its unique anatomical features. The change in muscle shear modulus during contraction has been corrected to force generation for several skeletal muscles. Therefore, the change in shear modulus can be used to quantify muscle contraction. The objective of this study was to evaluate multifidus dysfunction by comparing changes in shear modulus during muscle contraction in healthy individuals and patients who received RFN and PLF in the lumbar spine. We used our recently developed protocol which consists of measuring changes of multifidus shear modulus at lying prone, sitting up, and sitting up with the arms lifted. In healthy individuals, the median multifidus shear modulus increased progressively from prone, sitting, and sitting with arms raised: 18.55 kPa, 27.14 kPa, and 38.45 kPa, respectively. A moderate increase in shear modulus for these body positions was observed in PLF patients: 9.81 kPa, 17.26 kPa, and 21.85 kPa. In RFN patients, the shear modulus remained relatively constant: 14.44 kPa, 16.57 kPa, and 17.26 kPa. Overall, RFN and PLF caused a reduction in the contraction of multifidus muscles. However, the contraction of multifidus muscle slightly increased during multifidus activation in PLF patients, while it did not change in RFN patients. These preliminary measurements suggest that the proposed protocol using SWE can provide important information about the function of individual spine muscles to guide the design and evaluation of postsurgical rehabilitation protocols.

Tendon mechanical properties have been proposed as a biomarker of tendon health to track response to injury and treatment. Prior to utilizing these properties in an injured population, it is critical to understand how these are influenced by age and sex in an uninjured population. A retrospective analysis was conducted of 118 uninjured Achilles tendons to evaluate the relationship between tendon mechanical properties, age and sex. Mechanical properties (shear modulus and viscosity) were assessed using continuous shear wave elastography. A moderator regression analysis was completed to examine the relationship between tendon mechanical properties, age and sex, after adjusting for body mass index and physical activity level. There was an interaction between age and sex for shear modulus (p=0.049, R2 change=0.034). Females had a negative relationship between age and shear modulus (p=0.030, β=-0.350) but no relationship was observed for males (p=0.78, β=0.031). A positive relationship was found between age and viscosity (p=0.034, β=0.214). Increased viscosity was related to increased age with no difference between sexes. The effect of aging on shear modulus differed between men and women and may help explain sex specific injury risks and their differing response to mechanical load.

BACKGROUND:Achilles tendinopathy is a debilitating overuse injury characterized by pain, altered Achilles tendon structure, and impaired functional performance. Evaluating tendon structure as part of the physical examination may help establish a well-defined prognosis. However, the usefulness of measuring tendon structure for developing a prognosis has been questioned since structural abnormalities can exist without symptoms. PURPOSE:To determine whether initial measures of tendon morphology and mechanical properties were associated with patient-reported symptoms and calf muscle endurance at baseline, 6-month follow-up, and 1-year follow-up by prospectively following a cohort of individuals with Achilles tendinopathy. STUDY DESIGN:Cohort study; Level of evidence, 2. METHODS:A total of 59 participants with midportion or insertional Achilles tendinopathy completed an initial assessment and follow-up assessments at 6 months and 1 year. At the initial assessment, patient-reported symptoms, calf muscle endurance, and Achilles tendon thickening were evaluated, and Achilles tendon mechanical properties were estimated. At the 6-month and 1-year follow-up assessments, patient-reported symptoms and calf muscle endurance were reevaluated. RESULTS:Greater Achilles tendon thickening at the initial assessment was consistently associated with worse patient-reported symptoms and calf muscle endurance at each assessment. Changes in symptoms over the year were moderated by the initial shear modulus of the tendon, with a lower shear modulus associated with less improvement in symptoms. Lower viscosity at the initial assessment was also associated with worse calf muscle endurance at each assessment. CONCLUSION:Measures of tendon morphology and mechanical properties appear to be associated with patient-reported symptoms and calf muscle function for patients with Achilles tendinopathy.

Measurement of mechanical properties of thin-layered tissues has broad applications in the diagnosis of several pathologies. Ultrasound shear wave elastography (SWE) measures the shear wave speed as a means of estimating the mechanical properties of tissues. However, the wave speed in thin-layered tissues is affected by their thickness and the properties of surrounding tissues. The objective of this study is to introduce a method that combines numerical simulations and SWE measurements to provide a more accurate calculation of shear modulus in layered tissues. In the proposed method, the spatial distribution of the acoustic radiation force (ARF) emitted by the transducer was first computed. The ARF was then used as input for simulating the guided wave propagation in the thin layer with its surroundings. The simulations were repeated for several values of the shear modulus of the layer to obtain the corresponding simulated wave speed. By comparing the measured and simulated wave speeds, a more accurate (corrected) shear modulus can be obtained. The proposed method was validated using experiments in agarose gels. In-vivo SWE measurements were also performed for the fascia of the tibialis anterior (TA) muscle and the aponeurosis of musculotendinous junction (MTJ) in medial gastrocnemius (MG) head in a group of healthy individuals. The simulated and measured wave speed in gel constructs were in good agreement with a maximum error of 7.22%. The average of measured wave speed of fascia and aponeurosis was 3.90 ± 0.16 m/s and 2.33 ± 0.60 m/s, while the corresponding corrected shear modulus was 95.63 ± 17.89 kPa and 6.36 ± 8.98 kPa, respectively. Thickness had a substantial effect on the wave speed in thin-layered tissues with decreasing speed for thinner tissues. The SWE-based simulation method presented in this study has the potential of enhancing clinical assessment for several musculoskeletal conditions involving thin-layered tissues.

An epithermal neutron time-of-flight (TOF) facility is being developed at the Penn State Breazeale Reactor (PSBR). Various novel designs of a mechanical neutron chopper are being explored to produce nearly monoenergetic pulses of neutrons up to 40 eV. These neutrons will be used for epithermal neutron activation analysis (ENAA) for material samples from various stages of nuclear fuel cycle, as well for epithermal-neutron imaging (ENI). Specifically, four different mechanical chopper designs are currently being investigated and each design is intended to act as a mechanical shutter to pulse a continuous neutron beam at PSBR. Fermi choppers and disc choppers are compared to two novel design approaches; pistons and rings. The piston chopper offers the ability to carry a sufficient amount of absorbing material at the expense of a small slit width. The ring chopper is able to act as a monochromator due to its inherent geometry; however, the inertial stresses of a rotating ring impose theoretical limits for pulse intensity and energy resolution.

Objectives Evaluate the immediate (within 4 hours) effects of laser-induced photobiomodulation (PBM) therapy on Achilles tendon morphology and mechanical properties in healthy and pathologic tendons. Materials and methods Twenty people with healthy Achilles tendons and twelve people with Achilles tendinopathy participated. One Achilles tendon received PBM treatment following an established protocol, and the contralateral side received a placebo treatment. Achilles tendon morphology and mechanical properties were evaluated bilaterally with ultrasound imaging and continuous shear wave elastography immediately before treatment, immediately after treatment, then 2 and 4 hours after treatment. Results There were no immediate effects of PBM on tendon morphology or mechanical properties when comparing the PBM-treated side and placebo-treated side within each cohort. Additionally, the effects of PBM did not differ between healthy and pathologic Achilles tendons. Conclusion When treated with a laser-induced PBM treatment, healthy and pathologic Achilles tendons do not have immediate (within 4 hours) changes in tendon morphology or mechanical properties. These findings suggest that PBM therapy can be administered before other clinical treatments or high-load activities.

Multifidus function is important for active stabilization of the spine, but it can be compromised in patients with chronic low back pain and other spine pathologies. Force production and strength of back muscles are often evaluated using isometric or isokinetic tests, which lack the ability to quantify multifidi contribution independent of the erector spinae and adjacent hip musculature. The objective of this study is to evaluate localized force production capability in multifidus muscle using ultrasound shear wave elastography (SWE) in healthy individuals. Three different body positions were considered: lying prone, sitting up, and sitting up with the right arm lifted. These positions were chosen to progressively increase multifidus contraction and to minimize body motion during measurements. Shear modulus was measured at the superficial and deeper layers of the multifidus. Repeatability and possible sources of error of the shear modulus measurements were analyzed. Multifidus shear modulus (median (interquartile range)) increased from prone, i.e., 16.15 (6.69) kPa, to sitting up, i.e., 27.28 (15.72) kPa, to sitting up with the right arm lifted position, i.e., 45.02 (25.27) kPa. Multifidi shear modulus in the deeper layer of the multifidi was lower than the superficial layer, suggesting lower muscle contraction. Intraclass correlation coefficients (ICCs) for evaluation of shear modulus by muscle layer were found to be excellent (ICC = 0.76-0.80). Results suggest that the proposed protocol could quantify local changes in spinal muscle function in healthy adults; further research in patients with spine pathology is warranted.

Chronic exertional compartment syndrome (CECS) is an exercise-induced condition, in which high pressure develops in one or several lower leg compartments, resulting in pain, numbness, and temporary muscle paresis. Diagnosis of CECS is assisted by measurements of intracompartment pressures (ICP) at rest, 1-min and 5-min after cessation of running exercise (Pedowitz criteria). ICP is measured via needle manometry, which is an invasive procedure. We have recently shown that intramuscular pressure is correlated to shear modulus measured via shear wave elastography (SWE) (Spearman's correlation coefficient = 0.99). The objectives of this study were to quantify temporal changes in shear modulus of muscle in lower leg compartments of healthy individuals before and after running exercise, and to evaluate a Pedowitz-like criterion for diagnosis of CECS using muscle shear modulus as biomarker. Specifically, the shear modulus of the tibialis anterior (TA) and peroneus longus (PL) was measured at time intervals of 1 min for 10 min after cessation of exercise. The shear modulus of the TA, PL, Soleus and Tibialis posterior were also measured bilaterally before, and at 1- and 5-min after exercise in a procedure that resembles the Pedowitz test for ICP. The shear modulus of all compartments increased significantly in both legs 1-min postexercise and gradually decreased to prerunning values. 50% of such decrease occurred at between 3 and 5 min after cessation of exercise. Additionally, the change in shear modulus followed a similar pattern than ICP in the Pedowitz-like protocol. Therefore, SWE has the potential to diagnose CECS noninvasively.