Validation of a freehand 3D ultrasound system for morphological measures of the medial gastrocnemius muscle

Three-dimensional freehand ultrasonography to measure muscle volume of the lumbar multifidus: Reliability of processing technique and validity through comparison to magnetic resonance imaging

There is a growing interest in muscle characteristics of the lumbar multifidus related to low back pain, but findings between studies are inconsistent. One of the issues explaining these conflicting findings might be the use of two-dimensional measures of cross-sectional area and thickness of the lumbar multifidus in most studies, which might be a suboptimal representation of the entire muscle volume. A three-dimensional volumetric assessment, combined with standardized imaging and processing measurement protocols, is highly recommended to quantify spinal muscle morphology. Three-dimensional freehand ultrasonography is a technique with large potential for daily clinical practice. It is achieved by combining conventional two-dimensional ultrasound with a motion-tracking system, recording the position and orientation of the ultrasound transducer during acquisition, resulting in a three-dimensional reconstruction. This study investigates intra- and interprocessor reliability for the quantification of muscle volume of the lumbar multifidus based on three-dimensional freehand ultrasound and its validity, in 31 patients with low back pain and 20 healthy subjects. Two processors manually segmented the lumbar multifidus on three-dimensional freehand ultrasound images using Stradwin software following a well-defined method. We assessed the concurrent validity of the measurement of multifidus muscle volume using three-dimensional freehand ultrasound compared with magnetic resonance imaging in 10 patients with low back pain. Processing reliability and agreement were determined using intraclass correlation coefficients, Bland-Altman plots, and calculation of the standard error of measurement and minimal detectable change, while validity was defined based on correlation analysis. The processing of three-dimensional freehand ultrasound images to measure lumbar multifidus volume was reliable. Good to excellent intraclass correlation coefficients were found for intraprocessor reliability. For interprocessor reliability, the intraclass correlation coefficients were moderate to good, emphasizing the importance of processing guidelines and training. A single processor analysis is preferred in clinical studies or when small differences in muscle volume are expected. The correlation between magnetic resonance imaging and three-dimensional freehand ultrasound measurements of lumbar multifidus volume was moderate to good but with a systematically smaller multifidus volume measured on three-dimensional freehand ultrasound. These results provide opportunities for both researchers and clinicians to reliably assess muscle structure using three-dimensional freehand ultrasound in patients with low back pain and to monitor changes related to pathology or interventions. To allow implementation in both research and clinical settings, guidelines on three-dimensional freehand ultrasound processing and training were provided.

Muscle-Tendon Unit Length Measurement Using 3D Ultrasound in Passive Conditions: OpenSim Validation and Development of Personalized Models

This study investigated the validity of using OpenSim to measure muscle-tendon unit (MTU) length of the bi-articular lower limb muscles in several postures (shortened, lengthened, a combination of shortened and lengthened involving both joints, neutral and standing) using 3D freehand ultrasound (US), and to propose new personalized models. MTU length was measured on 14 participants and 6 bi-articular muscles (semimembranosus SM, semitendinosus ST, biceps femoris BF, rectus femoris RF, gastrocnemius medialis GM and gastrocnemius lateralis GL), considering 5 to 6 postures. MTU length was computed using OpenSim with three different models: OS (the generic OpenSim scaled model), OS + INSER (OS with personalized 3D US MTU insertions), OS + INSER + PATH (OS with personalized 3D US MTU insertions and path obtained from one posture). Significant differences in MTU length were found between OS and 3D US models for RF, GM and GL (from - 6.3 to 10.9%). Non-significant effects were reported for the hamstrings, notably for the ST (- 1.5%) and BF (- 1.9%), while the SM just crossed the alpha level (- 3.4%, p = 0.049). The OS + INSER model reduced the magnitude of bias by an average of 4% for RF, GM and GL. The OS + INSER + PATH model showed the smallest biases in length estimates, which made them negligible and non-significant for all the MTU (i.e. ≤ 2.2%). A 3D US pipeline was developed and validated to estimate the MTU length from a limited number of measurements. This opens up new perspectives for personalizing musculoskeletal models using low-cost user-friendly devices.

3D ultrasound-based determination of skeletal muscle fascicle orientations

Architectural parameters of skeletal muscle such as pennation angle provide valuable information on muscle function, since they can be related to the muscle force generating capacity, fiber packing, and contraction velocity. In this paper, we introduce a 3D ultrasound-based workflow for determining 3D fascicle orientations of skeletal muscles. We used a custom-designed automated motor driven 3D ultrasound scanning system for obtaining 3D ultrasound images. From these, we applied a custom-developed multiscale-vessel enhancement filter-based fascicle detection algorithm and determined muscle volume and pennation angle. We conducted trials on a phantom and on the human tibialis anterior (TA) muscle of 10 healthy subjects in plantarflexion (157 ± 7∘ ), neutral position (109 ± 7∘ , corresponding to neutral standing), and one resting position in between (145 ± 6∘ ). The results of the phantom trials showed a high accuracy with a mean absolute error of 0.92 ± 0.59∘ . TA pennation angles were significantly different between all positions for the deep muscle compartment; for the superficial compartment, angles are significantly increased for neutral position compared to plantarflexion and resting position. Pennation angles were also significantly different between superficial and deep compartment. The results of constant muscle volumes across the 3 ankle joint angles indicate the suitability of the method for capturing 3D muscle geometry. Absolute pennation angles in our study were slightly lower than recent literature. Decreased pennation angles during plantarflexion are consistent with previous studies. The presented method demonstrates the possibility of determining 3D fascicle orientations of the TA muscle in vivo.

Validation of a scanning technique with minimal compression for measuring muscle volume with freehand 3D ultrasound

Freehand 3D ultrasound (3D-US) is a promising technique for measuring muscle volume but it requires gel pads or water tanks to limit probe compression on the skin which makes it hard to use in clinical applications. Our objectives were to measure the effect of different compressions on muscle volume in order to assess the clinical applicability of a minimal compression method for lower limb muscles. 4 muscles of the lower limb on 15 healthy volunteers were scanned with a new commercial freehand 3D-US setup accessible to clinical experimentators. Each muscle was scanned with 3 levels of compression: standard compression, minimal compression and gel pad (method validated against MRI). Volume was calculated using software segmentation tools. Acquisitions and segmentations were done by the same examiner. There was a significant impact of standard compression on volume measurements, but no difference between minimal compression and gel pad. Standard compression underestimated volume with a mean bias of 16 mL. For minimal compression, 75 % of measured differences were below the predefined clinically acceptable limits of 10 mL. Mean bias for this method was 1.1 mL. In conclusion, standard compression in freehand 3D-US induces a systematic bias in volume calculations. But, with a trained examiner and the necessary precautions to minimize compression, this bias could be abolished and become acceptable in clinical applications. When a high accuracy is required, gel pads could still be important to consider.

Tapping Into Skeletal Muscle Biomechanics for Design and Control of Lower Limb Exoskeletons: A Narrative Review

Lower limb exoskeletons and exosuits ("exos") are traditionally designed with a strong focus on mechatronics and actuation, whereas the "human side" is often disregarded or minimally modeled. Muscle biomechanics principles and skeletal muscle response to robot-delivered loads should be incorporated in design/control of exos. In this narrative review, we summarize the advances in literature with respect to the fusion of muscle biomechanics and lower limb exoskeletons. We report methods to measure muscle biomechanics directly and indirectly and summarize the studies that have incorporated muscle measures for improved design and control of intuitive lower limb exos. Finally, we delve into articles that have studied how the human-exo interaction influences muscle biomechanics during locomotion. To support neurorehabilitation and facilitate everyday use of wearable assistive technologies, we believe that future studies should investigate and predict how exoskeleton assistance strategies would structurally remodel skeletal muscle over time. Real-time mapping of the neuromechanical origin and generation of muscle force resulting in joint torques should be combined with musculoskeletal models to address time-varying parameters such as adaptation to exos and fatigue. Development of smarter predictive controllers that steer rather than assist biological components could result in a synchronized human-machine system that optimizes the biological and electromechanical performance of the combined system.

A Narrative Review of Personalized Musculoskeletal Modeling Using the Physiome and Musculoskeletal Atlas Projects

In this narrative review, we explore developments in the field of computational musculoskeletal model personalization using the Physiome and Musculoskeletal Atlas Projects. Model geometry personalization; statistical shape modeling; and its impact on segmentation, classification, and model creation are explored. Examples include the trapeziometacarpal and tibiofemoral joints, Achilles tendon, gastrocnemius muscle, and pediatric lower limb bones. Finally, a more general approach to model personalization is discussed based on the idea of multiscale personalization called scaffolds.

What good is a measure of muscle length? The how and why of direct measurements of skeletal muscle motion

Over the past 50 years our understanding of the central role that muscle motion has in powering movement has accelerated significantly. Fundamental to this progress has been the development of methods for measuring the length of muscles and muscle fibers in vivo. A measurement of muscle fiber length might seem a trivial piece of information on its own. Yet when combined with knowledge of the properties of skeletal muscle it has proven a powerful tool for understanding the mechanics and energetics of locomotion and informing models of motor control. In this perspective we showcase the value of direct measurements of muscle fiber length from four different techniques: sonomicrometry, fluoromicrometry, magnetomicrometry, and ultrasound. For each method, we review its history and provide a high-level user's guide for researchers choosing tools for measuring muscle length in vivo. We highlight key insights that these measurements have provided, including the importance of passive elastic mechanisms and how skeletal muscle properties govern locomotor performance. The diversity of locomotor behaviors revealed across comparative studies has provided an important tool for discovering the rules for muscle function that span vertebrate locomotion more broadly, including in humans.

Validity and Reliability of 3-D Ultrasound Imaging to Measure Hamstring Muscle and Tendon Volumes

OBJECTIVE

The validity and reliability of 3-D ultrasound (US) in estimation of muscle and tendon volume was assessed in a very limited number of muscles that can be easily immersed. The objective of the present study was to assess the validity and reliability of muscle volume measurements for all hamstring muscle heads and gracilis (GR), as well as tendon volume for the semitendinosus (ST) and GR using freehand 3-D US.

METHODS

Three-dimensional US acquisitions were performed for 13 participants in two distinct sessions on separate days, in addition to one session dedicated to magnetic resonance imaging (MRI). Volumes of ST, semimembranosus (SM), biceps femoris short (BFsh) and long (BFlh) heads, and GR muscles and from the tendon from semitendinosus (STtd) and gracilis (GRtd) were collected.

RESULTS

The bias and the 95% confidence intervals of 3-D US compared with MRI ranged from -1.9 mL (-0.8%) to 1.2 mL (1.0%) for muscle volume and from 0.01 mL (0.2%) to -0.03 mL (-2.6%) for tendon volume. For muscle volume assessed using 3-D US, intraclass correlation coefficients (ICCs) ranged from 0.98 (GR) to 1.00, and coefficients of variation (CV) from 1.1% (SM) to 3.4% (BFsh). For tendon volume, ICCs were 0.99, and CVs between 3.2% (STtd) and 3.4% (GRtd).

CONCLUSION

Three-dimensional US can provide a valid and reliable inter-day measurement of hamstrings and GR for both muscle and tendon volumes. In the future, this technique could be used as an outcome for strengthening interventions and potentially in clinical environments.

Advances in imaging for assessing the design and mechanics of skeletal muscle in vivo

Skeletal muscle is the engine that powers what is arguably the most essential and defining feature of human and animal life-locomotion. Muscles function to change length and produce force to enable movement, posture, and balance. Despite this seemingly simple role, skeletal muscle displays a variety of phenomena that still remain poorly understood. These phenomena are complex-the result of interactions between active and passive machinery, as well as mechanical, chemical and electrical processes. The emergence of imaging technologies over the past several decades has led to considerable discoveries regarding how skeletal muscles function in vivo where activation levels are submaximal, and the length and velocity of contracting muscle fibres are transient. However, our knowledge of the mechanisms of muscle behaviour during everyday human movements remains far from complete. In this review, we discuss the principal advancements in imaging technology that have led to discoveries to improve our understanding of in vivo muscle function over the past 50 years. We highlight the knowledge that has emerged from the development and application of various techniques, including ultrasound imaging, magnetic resonance imaging, and elastography to characterise muscle design and mechanical properties. We emphasize that our inability to measure the forces produced by skeletal muscles still poses a significant challenge, and that future developments to accurately and reliably measure individual muscle forces will promote newfrontiers in biomechanics, physiology, motor control, and robotics. Finally, we identify critical gaps in our knowledge and future challenges that we hope can be solved as a biomechanics community in the next 50 years.

Towards modern understanding of the Achilles tendon properties in human movement research

The Achilles tendon (AT) is the strongest tendon in humans, yet it often suffers from injury. The mechanical properties of the AT afford efficient movement, power amplification and power attenuation during locomotor tasks. The properties and the unique structure of the AT as a common tendon for three muscles have been studied frequently in humans using in vivo methods since 1990's. As a part of the celebration of 50 years history of the International Society of Biomechanics, this paper reviews the history of the AT research focusing on its mechanical properties in humans. The questions addressed are: What are the most important mechanical properties of the Achilles tendon, how are they studied, what is their significance to human movement, and how do they adapt? We foresee that the ongoing developments in experimental methods and modeling can provide ways to advance knowledge of the complex three-dimensional structure and properties of the Achilles tendon in vivo, and to enable monitoring of the loading and recovery for optimizing individual adaptations.

Multi-sweep 3-dimensional ultrasound is accurate for in vivo muscle volume quantification, expanding use to larger muscles

Muscle volume is an important parameter in analyzing three-dimensional structure of muscle-tendon units. Three-dimensional ultrasound (3DUS) enables excellent quantification of muscle volume in small muscles; however, when a muscle's cross sectional area is larger than the field of view of the ultrasound transducer at any point along its length, more than one sweep is necessary to reconstruct muscle anatomy. Confounding image registration errors have been reported between multiple sweeps. Here, we detail imaging phantom studies used to (1) define an acquisition protocol that reduces misalignment in 3D reconstruction caused by muscle deformation, and (2) quantify accuracy of 3DUS for measures of volume when phantoms are too large to be fully imaged via a single transducer sweep. Finally, we (3) establish the feasibility of our protocol for in vivo measures by comparing biceps brachii muscle volumes using 3DUS and magnetic resonance imaging (MRI). Phantom studies indicate operator intent to use constant pressure across multiple sweeps effectively mitigates image misalignment, yielding minimal volume error (1.70 ± 1.30%). Intentional application of different pressure between sweeps replicated discontinuity observed previously, leading to larger errors (5.30 ± 0.94%). Based on these findings, we adopted a gel bag standoff and acquired in vivo images of biceps brachii muscles using 3DUS and compared this volume to MRI. We did not observe misalignment errors and there were no significant differences between imaging modalities (-0.71 ± 5.03 %), indicating 3DUS can reliably be used to quantify muscle volume in larger muscles requiring multiple transducer sweeps.

In Vivo 3D Muscle Architecture Quantification Based on 3D Freehand Ultrasound and Magnetic Resonance Imaging

Muscle architecture parameters, such as the fascicle length, pennation angle, and volume, are important muscle morphology characteristics. Accurate in vivo quantification of these parameters allows to detect changes due to pathologies, interventions, and rehabilitation trainings, which ultimately impact on muscles' force-producing capacity. In this study, we compared three-dimensional (3D) muscle architecture parameters of the tibialis anterior and gastrocnemius medialis, which were quantified by 3D freehand ultrasound (3DfUS) and a magnetic resonance imaging (MRI) technique, diffusion tensor imaging (DTI), respectively. Sixteen able-bodied subjects were recruited where seven of them received both 3DfUS and MRI measurement, while the rest underwent 3DfUS measurements twice. Good to excellent intra-rater reliability and inter-session repeatability were found in 3DfUS measurements (intra-class correlation coefficient > 0.81). Overall, the two imaging modalities yielded consistent measurements of the fascicle length, pennation angle, and volume with mean differences smaller than 2.9 mm, 1.8°, and 5.7 cm³, respectively. The only significant difference was found in the pennation angle of the tibialis anterior, although the discrepancy was small. Our study demonstrated, for the first time, that 3DfUS measurement had high reliability and repeatability for measurement of muscle architecture in vivo and could be regarded as an alternative to MRI for 3D evaluation of muscle morphology.

Reliability of 3D freehand ultrasound to assess lower limb muscles in children with spastic cerebral palsy and typical development

This study investigated the reliability of 3-dimensional freehand ultrasound (3DfUS) to quantify the size (muscle volume [MV] and anatomical cross-sectional area [aCSA]), length (muscle length [ML], tendon length [TL], and muscle tendon unit length [MTUL]), and echo-intensity (EI, whole muscle and 50% aCSA), of lower limb muscles in children with spastic cerebral palsy (SCP) and typical development (TD). In total, 13 children with SCP (median age 14.3 (7.3) years) and 13 TD children (median age 11.1 (1.7) years) participated. 3DfUS scans of rectus femoris, semitendinosus, medial gastrocnemius, and tibialis anterior were performed by two raters in two sessions. The intra- and inter-rater and intra- and inter-session reliability were defined with relative and absolute reliability measures, that is, intra-class correlation coefficients (ICCs) and absolute and relative standard error of measurement (SEM and SEM%), respectively. Over all conditions, ICCs for muscle size measures ranged from 0.818 to 0.999 with SEM%s of 12.6%-1.6%. For EI measures, ICCs varied from 0.233 to 0.967 with SEM%s of 15.6%-1.7%. Length measure ICCs ranged from 0.642 to 0.999 with SEM%s of 16.0%-0.5%. In general, reliability did not differ between the TD and SCP cohort but the influence of different muscles, raters, and sessions was not constant for all 3DfUS parameters. Muscle length and muscle tendon unit length were the most reliable length parameters in all conditions. MV and aCSA showed comparable SEM%s over all muscles, where tibialis anterior MV was most reliable. EI had low-relative reliability, but absolute reliability was better, with better reliability for the distal muscles in comparison to the proximal muscles. Combining these results with earlier studies describing muscle morphology assessed in children with SCP, 3DfUS seems sufficiently reliable to determine differences between cohorts and functional levels. The applicability on an individual level, for longitudinal follow-up and after interventions is dependent on the investigated muscle and parameter. Moreover, the semitendinosus, the acquisition, and processing of multiple sweeps, and the definition of EI and TL require further investigation. In general, it is recommended, especially for longitudinal follow-up studies, to keep the rater the same, while standardizing acquisition settings and positioning of the subject.

Short-Term Muscle Power Is Related to Lower Limb Muscle Volume in Young Children

PURPOSE

Muscle power is a component of muscular fitness and is proportional to its volume. Reduced muscular fitness in children is linked to negative health outcomes. Associations between muscle volume (MV) and power have not been examined in young children and could reveal important insights into early neuromuscular development.

METHOD

Forty-four children (2-8 y) completed 3 tests of short-term muscular power: repeated anaerobic sprint test, vertical jump, and horizontal jump. MV was assessed using 3D ultrasound for 3 lower limb muscles (rectus femoris, medial gastrocnemius, and tibialis anterior) and summed for across legs. Associations between muscular power and summed MV were assessed using Pearson correlation (r). Sex-based differences in muscular power and MV were assessed using 1-way analysis of covariance.

RESULTS

Moderate-strong associations (r = .57 - .87) were found between muscular power and summed MV. No differences were found between boys and girls for height, weight, MV, or muscular power.

CONCLUSIONS

Young children who have larger lower limb muscles perform better at tasks dependent on short-term muscular power, such as running and jumping, compared with children with smaller muscles. Sex-based differences in short-term muscular power do not exist in young children and reflect similar anthropometry, including lower limb MV.

Validity of Freehand 3-D Ultrasound System in Measurement of the 3-D Surface Shape of Shoulder Muscles

Freehand 3-D ultrasound (3DUS) system is a promising technique for accurately assessing muscle morphology. However, its accuracy has been validated mainly in terms of volume by examining lower limb muscles. This study was aimed at validating 3DUS in the measurements of 3-D surface shape and volume by comparing them with magnetic resonance imaging (MRI) measurements while ensuring the reproducibility of participant posture by focusing on the shoulder muscles. The supraspinatus, infraspinatus and posterior deltoid muscles of 10 healthy men were scanned using 3DUS and MRI while secured by an immobilization support customized for each participant. A 3-D surface model of each muscle was created from the 3DUS and MRI methods, and the agreement between them was assessed. For the muscle volume, the mean difference between the two models was within -0.51 cm³. For the 3-D surface shape, the distances between the closest points of the two models and the Dice similarity coefficient were calculated. The results indicated that the median surface distance was less than 1.12 mm and the Dice similarity coefficient was larger than 0.85. These results suggest that, given the aforementioned error is permitted, 3DUS can be used as an alternative to MRI in measuring volume and surface shape, even for the shoulder muscles.

Medial gastrocnemius muscle-tendon unit ratios of young females and males

A muscle's contractile element length relative to its muscle-tendon unit (MTU) length is a fundamental design feature affecting MTU function, with high (0.9) or low ratios (0.1) favouring either rapid or economical force production, respectively. Despite the importance for MTU function, little in vivo work has been done to understand contractile element-MTU length ratio variability between individuals and sexes. We therefore compared the medial gastrocnemius (MG) MTU ratios of thirteen females and eighteen males, and explored whether individual ratios could be predicted based on anatomical features. At the presumed tendon slack length ankle joint angle, lengths of MG's MTU, Achilles tendon, muscle belly and its muscle fascicles were measured from B-mode ultrasound images. Contractile element length was represented by the in-series muscle fascicle length (FL) and was calculated by multiplying FL by the cosine of fascicle angle. The mean ± standard deviation in-series FL-MTU length ratio was 0.09 ± 0.02 and ranged from 0.06 to 0.11, whereas the muscle belly length-MTU length ratio was 0.54 ± 0.38 and ranged from 0.47 to 0.60. Neither ratio was significantly different between females and males (p ≥ 0.116). In-series FL was not significantly correlated with MTU length (r = -0.115, p =.538), muscle belly length (r = 0.05, p =.788), or shank length (r = 0.169, p =.364), but MTU length was significantly correlated with muscle belly length (r = 0.641, p <.001), and shank length (r = 0.575, p =.001). A low in-series FL-MTU length ratio suggests that the MG of young, healthy individuals is specialised for energy-efficient stretch-shortening cycles. These findings provide useful inputs for the MTU actuator design of Hill-type models.

From fibre to function: are we accurately representing muscle architecture and performance?

The size and arrangement of fibres play a determinate role in the kinetic and energetic performance of muscles. Extrapolations between fibre architecture and performance underpin our understanding of how muscles function and how they are adapted to power specific motions within and across species. Here we provide a synopsis of how this 'fibre to function' paradigm has been applied to understand muscle design, performance and adaptation in animals. Our review highlights the widespread application of the fibre to function paradigm across a diverse breadth of biological disciplines but also reveals a potential and highly prevalent limitation running through past studies. Specifically, we find that quantification of muscle architectural properties is almost universally based on an extremely small number of fibre measurements. Despite the volume of research into muscle properties, across a diverse breadth of research disciplines, the fundamental assumption that a small proportion of fibre measurements can accurately represent the architectural properties of a muscle has never been quantitatively tested. Subsequently, we use a combination of medical imaging, statistical analysis, and physics-based computer simulation to address this issue for the first time. By combining diffusion tensor imaging (DTI) and deterministic fibre tractography we generated a large number of fibre measurements (>3000) rapidly for individual human lower limb muscles. Through statistical subsampling simulations of these measurements, we demonstrate that analysing a small number of fibres (n < 25) typically used in previous studies may lead to extremely large errors in the characterisation of overall muscle architectural properties such as mean fibre length and physiological cross-sectional area. Through dynamic musculoskeletal simulations of human walking and jumping, we demonstrate that recovered errors in fibre architecture characterisation have significant implications for quantitative predictions of in-vivo dynamics and muscle fibre function within a species. Furthermore, by applying data-subsampling simulations to comparisons of muscle function in humans and chimpanzees, we demonstrate that error magnitudes significantly impact both qualitative and quantitative assessment of muscle specialisation, potentially generating highly erroneous conclusions about the absolute and relative adaption of muscles across species and evolutionary transitions. Our findings have profound implications for how a broad diversity of research fields quantify muscle architecture and interpret muscle function.

Dynamic 3D Ultrasound Imaging of the Tibialis Anterior Muscle

Skeletal muscle volume has been mainly investigated under static conditions, i.e. isometric contractions. The aim of our study is to use ultrasound imaging to determine muscle deformation during movement. We used a custom-designed scanning rig to obtain 3D ultrasound images of a subject moving the foot from plantarflexion to dorsiflexion at constant velocity. Using motion capture, we computed the respective angle of the ankle for each frame and collected them in bins based on the measured angle (rounded on the next normal number). For each degree, we used Stradwin for the 3D reconstruction of the respective volume. We found increasing cross-sectional areas for increasing dorsiflexion angles. The proposed method is a promising approach for determining muscle volume during movement. Future studies aim at collecting more data to compute muscle volume and length during contraction and compare the results to isometric measurements.

Medial gastrocnemius growth in children who are typically developing: Can changes in muscle volume and length be accurately predicted from age?

Muscle size is an important determinant of muscular fitness and health, and so it is important to have accurate estimates of actual muscle growth in children. This study compared actual versus age-predicted growth rates of the medial gastrocnemius (MG) muscle in young children over a 12-month period. Three-dimensional ultrasound was used to measure MG length and volume in 50 children (mean ± standard deviation [SD] age = 70.3 ± 29.9 months) to establish age-predicted muscle growth rates using a least-squares linear regression. Twenty children (mean ± SD age = 78.5 ± 27.2 months) were followed up at 6 and 12 months to establish actual muscle growth of MG volume and length. These data were then compared to their age-predicted muscle growth from the linear regression equation using paired t-tests and Bland-Altman limits of agreement method. Age-predicted MG growth significantly underestimated actual muscle growth for both volume and length at each timepoint. On average, actual muscle volume and length were 11.5% and 21.5% greater than the age-predicted volume and length respectively. Caution is warranted when predicting future muscle size in young children based solely on age.

The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial

The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared with interventions involving a lower level of load duration and intensity. Sixteen healthy participants (12 males, 4 females; age 24.4±9.4 years, body mass 70.9±16.1 kg, height 1.7±0.1 m) performed three isometric interventions of varying levels of load duration (2 s and 8 s) and intensity (35% and 75% maximal voluntary isometric contraction) over a 3 week period. Freehand 3D ultrasound was used to measure free AT volume (at rest) and length (at 35%, 55% and 75% of maximum plantarflexion force) pre- and post-interventions. The slope of the force–elongation curve over these force levels represented individual stiffness (N mm⁻¹). Large reductions in free AT volume and stiffness resulted in response to long-duration high-intensity loading whilst less reduction was produced with a lower load intensity. In contrast, no change in free AT volume and a small increase in AT stiffness occurred with lower load duration. These findings suggest that the applied load on the AT must be heavy and sustained for a long duration to maximize immediate volume reduction, which might be an acute response that enables optimal long-term tendon adaptation via mechanotransduction pathways.

Summary: High levels of load duration and intensity have the greatest acute effect on the free Achilles tendon volume and stiffness.

Human skeletal muscle size with ultrasound imaging: a comprehensive review

Skeletal muscle size is an important factor in assessing adaptation to exercise training and detraining, athletic performance, age-associated atrophy and mobility decline, clinical conditions associated with cachexia, and overall skeletal muscle health. Magnetic resonance (MR) imaging and computed tomography (CT) are widely accepted as the gold standard methods for skeletal muscle size quantification. However, it is not always feasible to use these methods (e.g., field studies, bedside studies, large cohort studies). Ultrasound has been available for skeletal muscle examination for more than 50 years and the development, utility, and validity of ultrasound imaging are underappreciated. It is now possible to use ultrasound in situations where MR and CT imaging are not suitable. This review provides a comprehensive summary of ultrasound imaging and human skeletal muscle size assessment. Since the first study in 1968, more than 600 articles have used ultrasound to examine the cross-sectional area and/or volume of 107 different skeletal muscles in more than 27,500 subjects of various ages, health status, and fitness conditions. Data from these studies, supported by decades of technological developments, collectively show that ultrasonography is a valid tool for skeletal muscle size quantification. Considering the wide-ranging connections between human health and function and skeletal muscle mass, the utility of ultrasound imaging will allow it to be employed in research investigations and clinical practice in ways not previously appreciated or considered.

The reliability and validity of triceps surae muscle volume assessment using freehand three-dimensional ultrasound in typically developing infants

This study assessed the intra-acquirer, intra- and inter-processor reliability, and validity of the in vivo assessment of the medial gastrocnemius (MG), lateral gastrocnemius (LG) and soleus (SOL) muscle volumes using freehand 3D ultrasound (3DUS) in typically developing infants. Reliability assessments of freehand 3DUS were undertaken in infants across three ages groups: three, six and twelve months of age, with validity testing completed against magnetic resonance imaging (MRI) in infants at 3 months of age. Freehand 3DUS scanning was carried out by a single acquirer, with two independent processors manually segmenting images to render volumes. MRI images were segmented independently by a separate processor, with the volumes compared to those obtained via freehand 3DUS. Reliability was assessed using intraclass correlation (ICC), coefficient of variance (CV) and minimal detectable change (MDC) across each assessment time point. Validity was assessed using the limits of agreement. ICCs for intra-acquirer reliability of the acquisition process for freehand 3DUS ranged from 0.91 to 0.99 across all muscles. ICCs for intra-processor and inter-processor reliability for the segmentation process of freehand 3DUS ranged from 0.80 to 0.98 across all muscles. Acceptable levels of agreement between muscle volume obtained by freehand 3DUS and MRI were found for all muscles; however, freehand 3DUS overestimated muscle volume of MG and LG and underestimate the SOL compared with MRI, with average absolute differences of MG = 0.3 ml, LG = 0.3 ml and Sol = 1.2 ml. Freehand 3DUS is a reliable method for measuring in vivo triceps surae muscle volume in typically developing infants. We conclude that freehand 3DUS is a useful tool to assess changes in muscle volume in response to growth and interventions in infants.

3-D Ultrasonographic Quantification of Hand and Calf Muscle Volume: Statistical Shape Modeling Approach

Accurate acquisition and segmentation of muscles are essential in 3-D freehand ultrasonography (US) to estimate in vivo muscle volume, but the source of segmentation inaccuracy in shape variation has never been the focus. This study was aimed at investigating reliability of 3-D US in the acquisition and segmentation for muscle volume of two muscles of different sizes and in identifying a primary source of measurement difference. The lateral gastrocnemius and flexor pollicis brevis of 12 healthy adults were assessed using freehand 3-D US scans. The motion-tracking data of the probe were synchronized with the B-mode ultrasound scan to reconstruct 3-D muscle volume. Statistical shape modeling was used to provide a spatial segmentation volume difference that further explains the variation around segmentation repeatability. The absolute difference of the flexor pollicis brevis was 3.5 percentage points greater than that for the lateral gastrocnemius. The highest measurement differences were observed when for inter-acquirer analysis. Statistical shape modeling revealed that the primary segmentation volume differences were at the muscle ends and edges, where the muscle interfaces with the surrounding muscles. Three-dimensional US is a reliable tool in the clinical setting, but care must be taken to ensure that acquisition and segmentation are consistent, particularly in a small muscle that interfaces with tendons and other soft tissues.

The Dose-Response of the Nordic Hamstring Exercise on Biceps Femoris Architecture and Eccentric Knee Flexor Strength: A Randomized Interventional Trial

PURPOSE

To examine the dose-response of the Nordic hamstring exercise (NHE) on biceps femoris long head (BFlh) architecture and eccentric knee flexor strength.

DESIGN

Randomized interventional trial.

METHODS

Forty recreationally active males completed a 6-week NHE training program consisting of either intermittent low volumes (group 1; n = 10), low volumes (group 2; n = 10), initial high volumes followed by low volumes (group 3; n = 10), or progressively increasing volumes (group 4; n = 10). A 4-week detraining period followed each program. Muscle architecture was assessed weekly during training and after 2 and 4 weeks of detraining. Eccentric knee flexor strength was assessed preintervention and postintervention and after 2 and 4 weeks of detraining.

RESULTS

Following 6 weeks of training, BFlh fascicle length (FL) increased in group 3 (mean difference = 0.83 cm, d = 0.45, P = .027, +7%) and group 4 (mean difference = 1.48 cm, d = 0.94, P = .004, +14%). FL returned to baseline following detraining in groups 3 and 4. Strength increased in group 2 (mean difference = 53.6 N, d = 0.55, P = .002, +14%), group 3 (mean difference = 63.4 N, d = 0.72, P = .027, +17%), and group 4 (mean difference = 74.7, d = 0.83, P = .006, +19%) following training. Strength returned to baseline following detraining in groups 2 and 3 but not in group 4.

CONCLUSIONS

Initial high volumes of the NHE followed by lower volumes, as well as progressively increasing volumes, can elicit increases in BFlh FL and eccentric knee flexor strength. Low volumes of the NHE were insufficient to increase FL, although as few as 48 repetitions in 6 weeks did increase strength.

Validity and reliability of a novel 3D ultrasound approach to assess static lengths and the lengthening behavior of the gastrocnemius medialis muscle and the Achilles tendon in vivo

PURPOSE

Human muscle-tendon units (MTUs) are highly plastic and undergo changes in response to specific diseases and disorders. To investigate the pathological changes and the effects of therapeutic treatments, the use of valid and reliable examination methods is of crucial importance. Therefore, in this study, a simple 3D ultrasound approach was developed and evaluated with regard to: (1) its validity in comparison to magnetic resonance imaging (MRI) for the assessment of the gastrocnemius medialis (GM) MTU, muscle belly, and Achilles tendon lengths; and (2) its reliability for static and dynamic length measurements.

METHODS

Sixteen participants were included in the study. To evaluate the validity and reliability of the novel 3D ultrasound approach, two ultrasound measurement sessions and one MRI assessment were performed. By combining 2D ultrasound and 3D motion capture, the tissue lengths were assessed at a fixed ankle joint position and compared to the MRI measurements using Bland-Altman plots. The intra-rater and inter-rater reliability for the static and dynamic length assessments was determined using the coefficient of variation, standard error of measurement (SEM), minimal detectable change (MDC₉₅), and intraclass correlation coefficient (ICC).

RESULTS

The 3D ultrasound approach slightly underestimated the length when compared with MRI by 0.7%, 1.5%, and 1.1% for the GM muscle belly, Achilles tendon, and MTU, respectively. The approach showed excellent intra-rater as well as inter-rater reliability, with high ICC (≥ 0.94), small SEM (≤ 1.3 mm), and good MDC₉₅ (≤ 3.6 mm) values, with even better reliability found for the static length measurements.

CONCLUSION

The proposed 3D ultrasound approach was found to be valid and reliable for the assessment of the GM MTU, muscle belly, and Achilles tendon lengths, as well as the tissue lengthening behavior, confirming its potential as a useful tool for investigating the effects of training interventions or therapeutic treatments (e.g., surgery or conservative treatments such as stretching and orthotics).

LEVEL OF EVIDENCE

Level II.

Biceps femoris long head sarcomere and fascicle length adaptations after 3 weeks of eccentric exercise training

BACKGROUND

Eccentric exercise increases muscle fascicle lengths; however, the mechanisms behind this adaptation are still unknown. This study aimed to determine whether biceps femoris long head (BFlh) fascicle length increases in response to 3 weeks of eccentric exercise training are the result of an in-series addition of sarcomeres within the muscle fibers.

METHODS

Ten recreationally active participants (age = 27 ± 3 years; mass = 70 ± 14 kg; height = 174 ± 9 cm; mean ± SD) completed 3 weeks of Nordic hamstring exercise (NHE) training on a custom exercise device that was instrumented with load cells. We collected in vivo sarcomere and muscle fascicle images of the BFlh in 2 regions (central and distal) by using microendoscopy and 3 dimension ultrasonography. We then estimated sarcomere length, sarcomere number, and fascicle length before and after the training intervention.

RESULTS

Eccentric knee flexion strength increased after the training (15%; p < 0.001; η_p² = 0.75). Further, we found a significant increase in fascicle length (21%; p < 0.001; η_p² = 0.81) and sarcomere length (17%; p < 0.001; η_p² = 0.90) in the distal but not in the central portion of the muscle. The estimated number of sarcomeres in series did not change in either region.

CONCLUSION

Fascicle length adaptations appear to be heterogeneous in the BFlh in response to 3 weeks of NHE training. An increase in sarcomere length, rather than the addition of sarcomeres in series, appears to underlie increases in fascicle length in the distal region of the BFlh. The mechanism driving regional increases in fascicle and sarcomere length remains unknown, but we speculate that it may be driven by regional changes in the passive tension of muscle or connective tissue adaptations.

Effect of knee joint angle on individual hamstrings morphology quantified using free-hand 3D ultrasonography

Exercise responses and injury rates differ between individual hamstrings and this may be linked with their morphology. The aim of this study was to compare muscle length and tendon dimensions between the individual hamstrings at two knee joint angles using free hand three-dimensional ultrasound (3D US). Muscle-tendon length and distal tendon cross-sectional area (CSA), volume, length and echogenicity of biceps femoris long (BFlh) and short (BFsh) head, semimembranosus (SM) and semitendinosus (ST) of 16 individuals were measured using free-hand 3D US at 0° (full extension) and 45° of knee flexion. ST showed the greatest length than all muscles and BFsh the lowest (p < 0.05). No difference was observed between SM and BFlh length (p > 0.05). Of the four muscles, ST tendon was longer, with less volume and CSA but greater echogenicity than the other tendons. In contrast, SM and BFlh showed shorter tendons and lower echogenicity but a greater volume and CSA than ST (p < 0.05). Muscle and tendon lengthened from 45° to 0° knee flexion angle (p < 0.05) but this change was not statistically different between individual hamstrings (p > 0.05). Freehand 3D US indicated that hamstring muscle length and distal tendon dimensions differ between individual hamstrings. All muscles and tendons lengthened as the knee was extended but this change was similar for all individual hamstrings.

Typical m. triceps surae morphology and architecture measurement from 0 to 18 years: A narrative review

The aim of this review was to report on the imaging modalities used to assess morphological and architectural properties of the m. triceps surae muscle in typically developing children, and the available reliability analyses. Scopus and MEDLINE (Pubmed) were searched systematically for all original articles published up to September 2020 measuring morphological and architectural properties of the m. triceps surae in typically developing children (18 years or under). Thirty eligible studies were included in this analysis, measuring fibre bundle length (FBL) (n = 11), pennation angle (PA) (n = 10), muscle volume (MV) (n = 16) and physiological cross‐sectional area (PCSA) (n = 4). Three primary imaging modalities were utilised to assess these architectural parameters in vivo: two‐dimensional ultrasound (2DUS; n = 12), three‐dimensional ultrasound (3DUS; n = 9) and magnetic resonance imaging (MRI; n = 6). The mean age of participants ranged from 1.4 years to 18 years old. There was an apparent increase in m. gastrocnemius medialis MV and pCSA with age; however, no trend was evident with FBL or PA. Analysis of correlations of muscle variables with age was limited by a lack of longitudinal data and methodological variations between studies affecting outcomes. Only five studies evaluated the reliability of the methods. Imaging methodologies such as MRI and US may provide valuable insight into the development of skeletal muscle from childhood to adulthood; however, variations in methodological approaches can significantly influence outcomes. Researchers wishing to develop a model of typical muscle development should carry out longitudinal architectural assessment of all muscles comprising the m. triceps surae utilising a consistent approach that minimises confounding errors.

Reliability of Processing 3-D Freehand Ultrasound Data to Define Muscle Volume and Echo-intensity in Pediatric Lower Limb Muscles with Typical Development or with Spasticity

This investigation assessed the processer reliability of estimating muscle volume and echo-intensity of the rectus femoris, tibialis anterior and semitendinosus. The muscles of 10 typically developing children (8.15 [1.40] y) and 15 children with spastic cerebral palsy (7.67 [3.80] y; Gross Motor Function Classification System I = 5, II = 5, III = 5) were scanned with 3-D freehand ultrasonography. For the intra-processer analysis, the intra-class correlations coefficients (ICCs) for muscle volume ranged from 0.943-0.997, with relative standard errors of measurement (SEM%) ranging from 1.24%-8.97%. For the inter-processer analysis, these values were 0.853 to 0.988 and 3.47% to 14.02%, respectively. Echo-intensity had ICCs >0.947 and relative SEMs <4% for both analyses. Muscle volume and echo-intensity can be reliably extracted for the rectus femoris, semitendinosus and tibialis anterior in typically developing children and children with cerebral palsy. The need for a single processer to analyze all data is dependent on the size of the expected changes or differences.

Regional Variation in Muscle Echogenicity Is Related to Muscle Thickness in Young Children

Quantitative ultrasound of muscle echogenicity may be influenced by the size of the muscle and, so, corrections may be required when comparing echogenicity between populations with different muscle size. This study examined the relationship between regional muscle echogenicity and geometry in young, typically developing children (n = 49, mean ± standard deviation [SD] age = 70.8 ± 30.0 mo). Three-dimensional ultrasound was used to measure mean echo intensity (EI) and echo variation (EV), together with muscle thickness, cross-sectional area (CSA) and width, over the entire muscle length for the medial gastrocnemius (MG), rectus femoris (RF) and tibialis anterior muscles. Pearson's correlation coefficient (r) was used to assess the strength of the relationship between echogenicity and geometry using all images taken over the entire muscle length. There were moderate-strong correlations (r = 0.67-0.90) between EI and EV and thickness for each muscle, with the strongest correlations evident for the MG and RF. EI and EV were moderately correlated with muscle CSA and weakly correlated with muscle width. Normalisation of echogenicity to muscle thickness may help delineate between regions of contractile and non-contractile tissue and provide a useful measure of muscle echogenicity when comparing muscles of different cross-sectional dimensions. We recommend that researchers consider controlling for muscle size-dependent effects on echogenicity, by normalising EI and EV to muscle thickness, or including the latter as a covariate when comparing between groups.

COpenhagen Neuroplastic TRaining Against Contractures in Toddlers (CONTRACT): protocol of an open-label randomised clinical trial with blinded assessment for prevention of contractures in infants with high risk of cerebral palsy

INTRODUCTION

Contractures are frequent causes of reduced mobility in children with cerebral palsy (CP) already at the age of 2-3 years. Reduced muscle use and muscle growth have been suggested as key factors in the development of contractures, suggesting that effective early prevention may have to involve stimuli that can facilitate muscle growth before the age of 1 year. The present study protocol was developed to assess the effectiveness of an early multicomponent intervention, CONTRACT, involving family-oriented and supervised home-based training, diet and electrical muscle stimulation directed at facilitating muscle growth and thus reduce the risk of contractures in children at high risk of CP compared with standard care.

METHODS AND ANALYSIS

A two-group, parallel, open-label randomised clinical trial with blinded assessment (n=50) will be conducted. Infants diagnosed with CP or designated at high risk of CP based on abnormal neuroimaging or absent fidgety movement determined as part of General Movement Assessment, age 9-17 weeks corrected age (CA) will be recruited. A balanced 1:1 randomisation will be made by a computer. The intervention will last for 6 months aiming to support parents in providing daily individualised, goal-directed activities and primarily in lower legs that may stimulate their child to move more and increase muscle growth. Guidance and education of the parents regarding the nutritional benefits of docosahexaenic acid (DHA) and vitamin D for the developing brain and muscle growth will be provided. Infants will receive DHA drops as nutritional supplements and neuromuscular stimulation to facilitate muscle growth. The control group will receive standard care as offered by their local hospital or community. Outcome measures will be taken at 9, 12, 18, 24, 36 and 48 months CA. Primary and secondary outcome measure will be lower leg muscle volume and stiffness of the triceps surae musculotendinous unit together with infant motor profile, respectively.

ETHICS AND DISSEMINATION

Full approval from the local ethics committee, Danish Committee System on Health Research Ethics, Region H (H-19041562). Experimental procedures conform with the Declaration of Helsinki.

TRIAL REGISTRATION NUMBER

NCT04250454.

EXPECTED RECRUITMENT PERIOD

1 January 2021-1 January 2025.

A Gel Pad Designed to Measure Muscle Volume Using Freehand 3-Dimensional Ultrasonography

We developed an innovative gel pad that covers the entire lower leg to remove artifacts due to the pressure of the transducer in freehand 3-dimensional ultrasonography. In comparison to the reference method in water, this study showed that this new method was valid (bias, 3.4 mL; limit of agreement, 7.7 mL for a volume of ≈220 mL) and reliable (coefficient of variation, <1.1%) for the measurement of gastrocnemius medialis muscle volume. Considering that it is easier to use than the water tank technique, it has much promise for volumetric measurement of many muscles.

Reliability of Human Achilles Tendon Stiffness Measures Using Freehand 3-D Ultrasound

Achilles tendon (AT) stiffness is an important property of both human locomotor performance and injury mechanics. Freehand 3-D ultrasound (3-DUS) is a promising method for measuring stiffness of the Achilles tendon, particularly the free AT (2-6 cm proximal to calcaneus), which is commonly injured. The aim of this study was to investigate the test-retest reliability of freehand 3-DUS in measuring free AT stiffness in humans. The free Achilles tendon length of healthy participants (n = 10) was scanned on the same day on two consecutive occasions (1 h apart) during rest and isometric plantar flexion contractions at 20%, 40% and 60% of maximum force. The slope of the force-elongation curve over these force levels represented individual stiffness (N/mm). Relative reliability was assessed using the intra-class correlation coefficient (ICC), and absolute reliability was estimated with the standard error of measurement (SEM) and smallest detectable change. Systematic bias in stiffness measures was explored by comparing test and retest distributions and Bland-Altman plots. The test-retest reliability of free AT stiffness measured using freehand 3-DUS was excellent [ICC = 0.994, 95% confidence interval [CI]: 0.978-0.999)]. The mean stiffness values at test (361.83 N/mm [170.77]) and retest (364.98 N/mm [168.57]) did not significantly differ (p = 0.72), and the smallest detectable change was 52.14 N/mm. The Bland-Altman plot indicated the absence of systematic bias (95% CI: -22.18 to 15.88). Freehand 3-DUS provides reliable and precise measures of tendon stiffness and can be used to detect small changes in free AT stiffness in response to load or tendon pathology.

3D ultrasound to quantify lateral hip displacement in children with cerebral palsy: a validation study

AIM

To assess the validity of a new index, lateral head coverage (LHC), for describing hip dysplasia in a population of children with cerebral palsy (CP).

METHOD

LHC is derived from 3D ultrasound assessment. Twenty-two children (15 males, seven females; age 4-15y) with CP undergoing routine hip surveillance were recruited prospectively for the study. Each participant had both a planar radiograph acquired as part of their routine care and a 3D ultrasound assessment within 2 months. Reimer's migration percentage (RMP) and LHC were measured by the same assessor, and the correlation between them calculated using Pearson's correlation coefficient. The repeatability of LHC was investigated with three assessors, analysing each of 10 images three times. Inter- and intra-assessor variation was quantified using intraclass correlation coefficients.

RESULTS

LHC was strongly correlated with RMP (Spearman's rank correlation coefficient=-0.86, p<0.001). LHC had similar inter-assessor reliability to that reported for RMP (intraclass correlation coefficient=0.97 and intra-assessor intraclass correlation coefficient=0.98).

INTERPRETATION

This is an initial validation of the use of 3D ultrasound in monitoring hip development in children with CP. LHC is comparable with RMP in estimating hip dysplasia with similar levels of reliability that are reported for RMP.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

In Silico-Enhanced Treatment and Rehabilitation Planning for Patients with Musculoskeletal Disorders: Can Musculoskeletal Modelling and Dynamic Simulations Really Impact Current Clinical Practice?

Over the past decades, the use of computational physics-based models representative of the musculoskeletal (MSK) system has become increasingly popular in many fields of clinically driven research, locomotor rehabilitation in particular. These models have been applied to various functional impairments given their ability to estimate parameters which cannot be readily measured in vivo but are of interest to clinicians. The use of MSK modelling and simulations allows analysis of relevant MSK biomarkers such as muscle and joint contact loading at a number of different stages in the clinical treatment pathway in order to benefit patient functional outcome. Applications of these methods include optimisation of rehabilitation programs, patient stratification, disease characterisation, surgical pre-planning, and assistive device and exoskeleton design and optimisation. This review provides an overview of current approaches, the components of standard MSK models, applications, limitations, and assumptions of these modelling and simulation methods, and finally proposes a future direction.

Morphometric analysis of all 24 hip muscles: A cadaveric study of 18 hip specimens with proposal of a new classification of muscles

PURPOSE

There are few papers investigating the morphometry of hip muscles and reporting either a single muscle or a group of synergistic muscles. With the development of hip joint simulation, hip arthroplasty implants, and gait analysis, a set of biometric data covering all the muscles that act on the hip joint is needed.

METHODS

Using a rigorous dissection process on 18 cadaveric hips, measurements of all 24 hip muscles and bone parameters were conducted. We measured the following: (a) total femur, femoral shaft, and neck lengths, (b) total muscle lengths, (c) intra-muscular and extra-muscular (free) tendon lengths, (d) bone angles, (e) muscle pennation, sagittal, and frontal angles, (f) muscle weight, (g) muscle volume, (h) muscle cross-sectional area, and (i) and bending moment. Data on more than 12,000 morphometric or anatomical parameters were collected. Correlation values between bone variables, muscle variables, and in-between muscle variables were computed. Based on their compliance, muscles were classified using the ratio of belly length over the sum of intra-muscular and free tendons.

RESULTS

Values of the neck, shaft, and total femur lengths were highly correlated in relation to each other. The long muscles and the pelvitrochanteric muscles were highly correlated with femoral bone lengths. The proximal and distal intra-muscular tendon lengths were correlated to the total muscle length for all long muscles, independently of free tendon (extra-muscular) or muscle belly lengths. A very significant correlation was found between muscle weight variations among specimens. Three groups of muscles were identified based on their compliance.

CONCLUSION

This is the first comprehensive anatomical morphometric study which includes all the 24 muscles acting on the hip joint. It generates a unique anatomical dataset comprising all necessary data for musculoskeletal modeling and arthroplasty implants of the hip joint. A new muscle classification was proposed based on compliance where muscles of the same group would exhibit similar compliance and functional anatomy.

Increasing level of neuromusculoskeletal model personalisation to investigate joint contact forces in cerebral palsy: A twin case study

BACKGROUND

Cerebral palsy is a complex neuromuscular disorder that affects the sufferers in multiple different ways. Neuromusculoskeletal models are promising tools that can be used to plan patient-specific treatments for cerebral palsy. However, current neuromusculoskeletal models are typically scaled from generic adult templates that poorly represent paediatric populations. Furthermore, muscle activations are commonly computed via optimisation methods, which may not reproduce co-contraction observed in cerebral palsy. Alternatively, calibrated EMG-informed approaches within OpenSim can capture pathology-related muscle activation abnormalities, possibly enabling more feasible estimations of muscle and joint contact forces.

METHODS

Two identical twin brothers, aged 13, one with unilateral cerebral palsy and the other typically developing, were enrolled in the study. Four neuromusculoskeletal models with increasing subject-specificity were built in OpenSim and CEINMS combining literature findings, experimental motion capture, EMG and MR data for both participants. The physiological and biomechanical validity of each model was assessed by quantifying its ability to track experimental joint moments and muscle excitations.

FINDINGS

All developed models accurately tracked external joint moments; however EMG-informed models better tracked muscle excitations compared to neural solutions generated by static optimisation. Calibrating muscle-tendon unit parameters with EMG data allowed for more physiologically plausible joint contact forces estimates. Further scaling the maximal isometric force of muscles with MR-derived muscle volumes did not affect model predictions.

INTERPRETATION

Given their ability to identify atypical joint contact forces profiles and accurately reproduce experimental data, calibrated EMG-informed models should be preferred over generic models using optimisation methods in informing the management of cerebral palsy.

Effect of increased serum 25(OH)D and calcium on structure and function of post-menopausal women: a pilot study

The purpose was to determine if increasing serum 25(OH)D and calcium in postmenopausal women increased skeletal muscle size, strength, balance, and functional task performance while decreasing muscle fatigue. PCSA of the vastus lateralis increased and ascent of stairs time decreased after 6 months of increased serum 25(OH)D.

PURPOSE

The Institute of Medicine recommends ≥ 20 ng/ml of serum 25-hydroxyvitamin D [25(OH)D] for bone and overall health. Serum 25(OH)D levels have been associated with physical performance, postural sway, and falls. The purpose of this study was to determine if increasing postmenopausal women's serum 25(OH)D levels from 20-30 ng/ml to 40-50 ng/ml improved skeletal muscle size, strength, balance, and functional performance while decreasing skeletal muscle fatigue.

METHODS

Twenty-six post-menopausal women (60-85 years old) with baseline serum 25(OH)D levels between 20 and 30 ng/ml were recruited. Oral over-the-counter (OTC) vitamin D3 and calcium citrate were prescribed to increase subjects' serum 25(OH)D to levels between 40 and 50 ng/ml, serum calcium levels above 9.2 mg/dl, and PTH levels below 60 pg/ml, which were confirmed at 6 and 12 weeks. Outcome measures assessed at baseline and 6 months included muscle physiological cross-sectional area (PCSA), muscle strength, postural balance, time to perform functional tasks, and muscle fatigue. Repeated measures comparisons between baseline and follow-up were performed.

RESULTS

Nineteen subjects completed the study. One individual could not afford the time commitment for the repeated measures. Three individuals did not take their vitamin D as recommended. Two subjects were lost to follow-up (lack of interest), and one did not achieve targeted serum 25(OH)D. Vastus lateralis PCSA increased (p = 0.007) and ascent of stair time decreased (p = 0.042) after 6 months of increasing serum 25(OH)D levels from 20-30 ng/ml to 40-50 ng/ml. Isometric strength was unchanged. Anterior-posterior center of pressure (COP) excursion and COP path length decreased (p < 0.1) albeit non-significantly, suggesting balance may improve from increased serum 25(OH)D and calcium citrate levels.

CONCLUSIONS

Several measures of muscle structure and function were sensitive to elevated serum 25(OH)D and calcium levels indicating that further investigation of this phenomenon in post-menopausal women is warranted.

Fractional Limb Volume in Spina Bifida Fetuses as an Assessment Tool for Postnatal Ambulation

BACKGROUND

Prenatal fractional limb volume (FLV) can be used to assess muscle atrophy in fetuses with myelomeningocele.

OBJECTIVE

We hypothesize that FLV in fetal myelomeningocele (fMMC) repair is different from postnatal repair (PNR). Assessing intrauterine muscle development can predict ambulation.

METHODS

A prospective observational study was performed from July 2012 to April 2016. Demographics, clinical outcomes, and FLV of the fetal thigh were assessed by ultrasound. Ambulation videos were collected from patients over 30 months of age. FLV was compared between the fMMC and PNR groups and between ambulators and non-ambulators. Two-sample t test, ANOVA, Spearman's rho correlation, and Bland-Altman plots were used for analysis. A p value <0.05 was used for statistical significance.

RESULTS

Fifty-nine patients were included, 24 had fMMC and 35 had PNR. Videos were obtained in 47 cases (73%). There was no difference in baseline demographics between the groups. There was no significant change in the fMMC group between the FLV at initial presentation and the repeat at 34 weeks gestation (54.5 ± 28.2 and 62.2% ± 16.4; p = 0.6). In contrast, the FLV in the PNR decreased between the initial evaluation and the repeat at 34 weeks (54.1 ± 27.7 to 35.8 ± 34.1%; p = 0.04). FLV at 34 weeks gestation was higher in the fMMC group as compared to the PNR group (62.2 ± 16.4 vs. 35.8 ± 34.1%; p = 0.02). There was no difference in FLV between ambulators and non-ambulators either at initial evaluation (p = 0.8) or at 34 weeks gestation (p = 0.6).

CONCLUSION

Lower FLV in the PNR group compared to fMMC may suggest in utero muscle atrophy. No correlation was seen between FLV and subsequent ambulation; however, future larger studies may be needed.

Magnetic Resonance Imaging and Freehand 3-D Ultrasound Provide Similar Estimates of Free Achilles Tendon Shape and 3-D Geometry

The purpose of this study was to assess the similarity of free Achilles tendon shape and 3-D geometry between magnetic resonance imaging (MRI) and freehand 3-D ultrasound (3-DUS) imaging methods. Fourteen elite/sub-elite middle-distance runners participated in the study. MRI and 3-DUS scans of the Achilles tendon were acquired on two separate imaging sessions, and all 3-D reconstructions were performed using identical methods. Shape similarity of free Achilles tendon reconstructed from MRI and 3-DUS data was assessed using Jaccard index, Hausdorff distance and root mean square error (RMSE). The Jaccard index, Hausdorff distance and RMSE values were 0.76 ± 0.05, 2.70 ± 0.70 and 0.61 ± 0.10 mm, respectively. The level of agreement between MRI and 3-DUS for free Achilles tendon volume, length and average cross-sectional area (CSA) was assessed using Bland-Altman analysis. Compared to MRI, freehand 3-DUS overestimated volume, length and average CSA by 30.6 ± 15.8 mm³ (1.1% ± 0.6%), 0.3 ± 0.7 mm (0.6% ± 1.9%) and 0.3 ± 1.42 mm² (0.4% ± 2.0%), respectively. The upper and lower limits of agreement between MRI and 3-DUS for volume, length and average CSA were -0.4 to 61.7 mm³ (-0.2% to 2.3%), -1.0 to 1.5 mm (-3.2% to 4.5%) and -2.5 to 3.1 mm² (-3.5% to 4.3%), respectively. There were no significant differences between imaging methods in CSA along the length of the tendon. In conclusion, MRI and freehand 3-DUS may be considered equivalent methods for estimating shape and 3-D geometry of the free Achilles tendon. These findings, together with the practical benefits of being able to assess 3-D Achilles tendon shape and geometry in a laboratory environment and under isometric loading, make 3-DUS an attractive alternative to MRI for assessing 3-D free Achilles tendon macro-structure in future studies.

What is the role of ultrasound in fracture management?: Diagnosis and therapeutic potential for fractures, delayed unions, and fracture-related infection

Objectives

The aim of this study was to review the current evidence and future application for the role of diagnostic and therapeutic ultrasound in fracture management.

Methods

A review of relevant literature was undertaken, including articles indexed in PubMed with keywords "ultrasound" or "sonography" combined with "diagnosis", "fracture healing", "impaired fracture healing", "nonunion", "microbiology", and "fracture-related infection".

Results

The use of ultrasound in musculoskeletal medicine has expanded rapidly over the last two decades, but the diagnostic use in fracture management is not routinely practised. Early studies have shown the potential of ultrasound as a valid alternative to radiographs to diagnose common paediatric fractures, to detect occult injuries in adults, and for rapid detection of long bone fractures in the resuscitation setting. Ultrasound has also been shown to be advantageous in the early identification of impaired fracture healing; with the advent of 3D image processing, there is potential for wider adoption. Detection of implant-related infection can be improved by ultrasound mediated sonication of microbiology samples. The use of therapeutic ultrasound to promote union in the management of acute fractures is currently a controversial topic. However, there is strong in vitro evidence that ultrasound can stimulate a biological effect with potential clinical benefit in established nonunions, which supports the need for further investigation.

Conclusion

Modern ultrasound image processing has the potential to replace traditional imaging modalities in several areas of trauma practice, particularly in the early prediction of impaired fracture healing. Further understanding of the therapeutic application of ultrasound is required to understand and identify the use in promoting fracture healing.Cite this article: J. A. Nicholson, S. T. J. Tsang, T. J. MacGillivray, F. Perks, A. H. R. W. Simpson. What is the role of ultrasound in fracture management? Diagnosis and therapeutic potential for fractures, delayed unions, and fracture-related infection. Bone Joint Res 2019;8:304-312. DOI: 10.1302/2046-3758.87.BJR-2018-0215.R2.

Muscle architecture in children with cerebral palsy and ankle contractures: an investigation using diffusion tensor imaging

BACKGROUND

Children with cerebral palsy frequently have ankle contractures which may be caused by changes in architecture of calf muscles. Here, we compared the architecture of medial gastrocnemius muscles in children with unilateral cerebral palsy and typically developing children using novel imaging techniques.

METHODS AND PROCEDURES

Muscle volumes, fascicle lengths, pennation angles and physiological cross-sectional areas were measured from diffusion tensor images and mDixon scans obtained from 20 ambulant children with unilateral spastic cerebral palsy who had ankle contractures (age 11 ± 3 years; mean ± standard deviation) and 20 typically developing children (11 ± 4 years).

FINDINGS

In children with cerebral palsy, the more-affected side had, on average, 13° less dorsiflexion range and the medial gastrocnemius muscle had 4.9 mm shorter fascicles, 50 cm³ smaller volume and 9.5 cm² smaller physiological cross-sectional area than the less-affected side. Compared to typically developing children, the more-affected side had 10° less dorsiflexion range and the medial gastrocnemius muscle had 4.2 mm shorter fascicles, 51 cm³ smaller volume and 10 cm² smaller physiological cross-sectional area. We did not detect differences between the less-affected and typically developing legs.

INTERPRETATION

Three-dimensional measurement of whole medial gastrocnemius muscles confirmed that the architecture of muscles on the more-affected side of children with cerebral palsy differs from the less-affected side and from muscles of typically developing children. Reductions in fascicle length, muscle volume and physiological cross-sectional area may contribute to muscle contracture.

A Critical Evaluation of the Biological Construct Skeletal Muscle Hypertrophy: Size Matters but So Does the Measurement

Skeletal muscle is highly adaptable and has consistently been shown to morphologically respond to exercise training. Skeletal muscle growth during periods of resistance training has traditionally been referred to as skeletal muscle hypertrophy, and this manifests as increases in muscle mass, muscle thickness, muscle area, muscle volume, and muscle fiber cross-sectional area (fCSA). Delicate electron microscopy and biochemical techniques have also been used to demonstrate that resistance exercise promotes ultrastructural adaptations within muscle fibers. Decades of research in this area of exercise physiology have promulgated a widespread hypothetical model of training-induced skeletal muscle hypertrophy; specifically, fCSA increases are accompanied by proportional increases in myofibrillar protein, leading to an expansion in the number of sarcomeres in parallel and/or an increase in myofibril number. However, there is ample evidence to suggest that myofibrillar protein concentration may be diluted through sarcoplasmic expansion as fCSA increases occur. Furthermore, and perhaps more problematic, are numerous investigations reporting that pre-to-post training change scores in macroscopic, microscopic, and molecular variables supporting this model are often poorly associated with one another. The current review first provides a brief description of skeletal muscle composition and structure. We then provide a historical overview of muscle hypertrophy assessment. Next, current-day methods commonly used to assess skeletal muscle hypertrophy at the biochemical, ultramicroscopic, microscopic, macroscopic, and whole-body levels in response to training are examined. Data from our laboratory, and others, demonstrating correlations (or the lack thereof) between these variables are also presented, and reasons for comparative discrepancies are discussed with particular attention directed to studies reporting ultrastructural and muscle protein concentration alterations. Finally, we critically evaluate the biological construct of skeletal muscle hypertrophy, propose potential operational definitions, and provide suggestions for consideration in hopes of guiding future research in this area.

Muscle volume reconstruction from several short magnetic resonance imaging sequences

The gold standard to determine muscle morphological parameters is magnetic resonance imaging (MRI). To measure large muscles like the vastus lateralis (VL) in one sequence, scanners with a large field of view (FOV) and a high flux density are needed. However, large scanners are expensive and not always available. The purpose of the current study was to develop a marker-based approach to reconstruct the VL from several separate MRI sequences, acquired with a low-field MRI scanner. The VL muscle of 21 volunteers was marked at one-third and two-third of thigh length using fish oil capsules. Three consecutive MRI sequences (i.e. proximal, medial and distal part) of the thigh were captured between the markers and the muscle insertion and origin. After a manual segmentation of the VL the muscle was reconstructed using the developed approach. The muscle volume, maximal anatomical cross-sectional area and length were 715.1 ± 93.4 cm³, 34.0 ± 4.0 cm² and 34.4 ± 2.2 cm respectively. The procedure showed an average error between 0.9% and 2.2% for the reconstructed muscle volume, the averaged RMSD between the cross-sectional areas of two overlapping sequences were between 0.80 ± 0.71 cm² and 0.88 ± 0.78 cm². The proposed approach provides an appropriate accuracy for muscle volume assessment, as the estimated error for muscle volume calculation was quite small. The reconstruction quality depends mainly on the proper marker attachment and identification, as well as the spatial resolution of the image sequences. We are confident that the presented method can be used in most investigations regarding muscle morphology.

Non-invasive Quantitative Assessment of Muscle Force Based on Ultrasonic Shear Wave Elastography

The objective of this study was to investigate the feasibility of using shear wave elastography (SWE) to indirectly measure passive muscle force and to examine the effects of muscle mass and scan angle. We measured the Young's moduli of 24 specimens from six muscles of four swine at different passive muscle loads under different scan angles (0°, 30°, 60° and 90°) using SWE. Highly linear relationships between Young's modulus E and passive muscle force F were found for all 24 muscle specimens at 0^o scan angle with coefficients of determination R² ranging from 0.984 to 0.999. The results indicate that the muscle mass has no significant effect on the muscle E-F relationship, whereas E-F linearity decreases disproportionately with increased scan angle. These findings suggest that SWE, when carefully applied, can provide a highly reliable tool to measure muscle Young's modulus, and could be used to assess the muscle force quantitatively.

Instrumentation of off-the-shelf ultrasound system for measurement of probe forces during freehand imaging

Ultrasound is a popular and affordable imaging modality, but the nature of freehand ultrasound operation leads to unknown applied loads at non-quantifiable angles. The purpose of this paper was to demonstrate an instrumentation strategy for an ultrasound system to measure probe forces and orientation during freehand imaging to characterize the interaction between the probe and soft-tissue as well as enhance repeatability. The instrumentation included a 6-axis load cell, an inertial measurement unit, and an optional sensor for camera-based motion capture. A known method for compensation of the ultrasound probe weight was implemented, and a novel method for temporal synchronization was developed. While load and optical sensing was previously achieved, this paper presents a strategy for potential instrumentation on a variety of ultrasound machines. A key feature was the temporal synchronization, utilizing the electrocardiogram (EKG) feature built-in to the ultrasound. The system was used to perform anatomical imaging of tissue layers of musculoskeletal extremities and imaging during indentation on an in vivo subject and an in vitro specimen. The outcomes of the instrumentation strategy were demonstrated during minimal force and indentation imaging. In short, the system presented robust instrumentation of an existing ultrasound system to fully characterize the probe force, orientation, and optionally its movement during imaging while efficiently synchronizing all data. Researchers may use the instrumentation strategy on any EKG capable ultrasound systems if mechanical characterization of soft tissue or minimization of forces and deformations of tissue during anatomical imaging are desired.