Intervertebral disc degeneration greatly affects daily life. Suitable mechanical stress is important for intervertebral disc health as it affects disc cells. Research shows it helps disc cell proliferation and collagen synthesis. However, the influences of forces in diverse directions on the intervertebral disc remain ambiguous. Our study aimed to investigate the impact of stress in various directions on intervertebral discs in New Zealand rabbits. The rabbit model was used because our team previously had established and validated it,which providing an effective platform for researching disc degeneration and treatment methods. We resected the spinal L3/4 and L5/6 motion segments and categorized them into 5 groups. Apart from the control group, distinct mechanical loads (pressure, traction, rotation, rotational traction) were applied to the remaining groups. After mechanical intervention, in contrast to the other groups except for the control group, it was found that the creep displacement in the rotational traction force group was the lowest (0.90 ± 0.06), the fatigue resistance was enhanced, and the tensile strength was increased, showing advantages over the other groups (p < 0.05). Histological examination revealed that the rotational traction force group had a protective effect on the intervertebral disc structure, while the cell damage in the rotational force group was the most severe. This study will help understand the unique effects of stresses in different directions on the intervertebral disc. The general public should avoid direct rotational movements in daily life. Physicians can explore the therapeutic effect of rotational movements under traction on lumbar degenerative changes.

Finite element analysis (FEA) is the leading numerical technique for studying joint biomechanics related to the onset and progression of osteoarthritis. However, subject-specific FEA of joint mechanics is a time- and compute-intensive process limiting its clinical applicability. We introduce and evaluate a novel hybrid modelling framework combining discrete element analysis (DEA) and FEA for computationally efficient evaluation of cartilage mechanics in the hip joint. In our approach, the hip joint contact mechanics are first estimated using DEA and subsequently used as input for matching FEA models, substantially reducing model complexity. The cartilage mechanical responses obtained using the hybrid DEA-FEA method were evaluated for subject-specific hip joint geometries from five asymptomatic individuals under loading conditions typical to normal walking gait and compared to conventional FEA in terms of peak intra-tissue mechanical stresses and model run-times. The hybrid DEA-FEA method had a median run-time of 3.6 min per subject (64-core processor, 512 GB RAM) and produced minimum principal (compressive) stress estimates comparable to stresses obtained using conventional FEA models with a median run-time of 96.2 min. On average, the peak compressive stresses obtained using the hybrid DEA-FEA approach were 0.06 MPa (95 % confidence interval: -0.86-0.99) lower than the stresses estimated with conventional FEA. Despite up to 1.4 MPa differences at individual gait time-points, the results indicate that the proposed hybrid DEA-FEA method enables estimation of hip cartilage mechanics in a fraction of time compared to conventional FEA, facilitating implementation in large cohort studies and clinical applications.

Motor control impairments post-stroke significantly limit walking ability, with residual gait impairments often persisting despite rehabilitation efforts. Integrating motor control-based assessments in post-stroke gait evaluations is essential for monitoring the underlying causes of the limited functionality and enhancing recovery outcomes. This study aimed to develop motor control-based post-stroke gait evaluation techniques using common gait measures to inform and guide rehabilitation decisions. Subject-specific, forward-dynamic simulations of eight individuals with post-stroke gait undergoing a 12-weeks FastFES gait retraining program were created pre- and post-treatment to determine muscle activation patterns for muscle module analysis. The motor control complexity index was defined by the variance not accounted for by one module (VNAF) as a summary measure of the analysis. Twenty-eight gait measures were investigated, and the relevant measures were selected using feature selection methods and fed into a multiple linear regression model to estimate the motor control complexity index. The motor control complexity of 182 gait cycles were quantified (0.164 ± 0.047). No strong relationship (quantified using Pearson correlation coefficients) was found between gait measures and the motor control complexity index. However, a combination of four gait measures from the paretic side (maximum hip abduction and knee flexion angle during swing, knee range of motion, and maximum paretic ankle power) explained most of the variation (R = 0.66) in motor control complexity.

Non-uniform displacement is a well-documented phenomenon of healthy tendons that has shown to be reduced among injured and aging populations. Non-uniformity is considered a biomarker of tendon health, yet immediate response to physical exercise is unknown. This study examined acute changes in Achilles tendon (AT) non-uniform displacement in response to high strain magnitude isometric plantarflexion exercise. The reliability of the method was also examined. Fourteen healthy participants (7 men, 7 women, mean ± SD age: 26.4 ± 4.8 years) performed unilateral isometric plantarflexion exercise at 90 % of maximal voluntary isometric contractions (MVIC) with 5 sets of 4 repetitions, each lasting 3 s. The contralateral leg served as control. AT displacement was measured during ramp contractions to a constant torque level (30 % of MVIC) before the exercise, between the loading sets, and six times during 72-h recovery period. AT nonuniformity (difference between maximum and minimum displacement) was analyzed from sagittal B-mode ultrasound videos using speckle tracking. Two-way repeated measures ANOVA was used to compare the values across different timepoints. Non-uniformity did not change in response to exercise and was 2.99 ± 1.52 mm before and 3.19 ± 1.42 mm immediately after exercise. The reliability of non-uniformity between trials within a single measurement session varied from moderate to excellent (ICC: 0.680-0.920). While the isometric high strain plantarflexion exercise did not acutely alter the non-uniform displacement of the AT in young healthy adults, strenuous exercises containing knee and ankle joint angle changes should be investigated to confirm adaptability of AT non-uniform displacement.

Flow patterns and classification within Spontaneous Isolated Superior Mesenteric Artery Dissection (SISMAD) are crucial for selecting subsequent treatment options. This study aims to propose a new classification of SISMAD and to propose two corresponding treatment plans based on this new classification. The 3D models of 70 patients with SISMAD were reconstructed and classified into Li types I-V based on morphology, followed by computational fluid dynamics analysis. The results show significant differences in blood flow patterns among patients with the same Li-type SISMAD, suggesting that the same treatment plan should not be applied universally. Based on the different blood flow conditions, a new classification of SISMAD is proposed (HX classification): Type I (dual-lumen flow type), subdivided into Ia and Ib; and Type II (single-lumen flow type). The simulation reveals that the rupture area of Type I SISMAD is related to the pressure difference between its true and false lumens, while the maximum-to-minimum diameter ratio of Type II SISMAD is associated with insufficient true lumen blood supply and lumen dilation. Furthermore, based on patient follow-up data and hemodynamic simulation results, corresponding treatment plans were proposed for the new classification: Type I was judged based on the ratio of rupture area to entrance area as a risk factor, and intervention treatment was recommended if the value was greater than 0.44; Type II can be judged as a risk factor based on the ratio of minimum diameter to maximum diameter, and if the value is less than 0.38, intervention treatment is recommended.

Bone-anchored limbs (BALs) are a transformative alternative for patients with lower-limb amputation who suffer from debilitating socket problems by eliminating the need for skin-to-prosthetic contact. Despite its successes, some individuals continue to face challenges with BALs, experiencing a loss of implant integration resulting in prosthetic loosening. A thorough understanding of biomechanical behavior at the residual limb and bone-implant interface is necessary to fully understand mechanical failure mechanisms. In addition, a deeper understanding of BAL biomechanical behavior would allow clinicians and researchers to predict and test different implant geometries, inform patient eligibility, rehabilitation strategies, and implantation methods in a safe and low-cost way. Thus, this study designed an innovative simulation method to quantify the temporal mechanical behavior of the residual limb in transfemoral and transtibial BALs by using subject-specific kinematics, musculoskeletal loads, and bone geometry and health. Our novel method was applied to two patients (one transtibial, one transfemoral) with similar BMI and age during level ground walking. Our results demonstrated a pattern of higher residual limb stresses in the transtibial model (26.80 MPa vs. 23.69 MPa). This study not only furthers our understanding of BAL biomechanics but introduces a versatile subject-specific methodology with direct applications in clinical practice. As we navigate the complexities of BAL implantation, this modeling platform lays the groundwork for more informed decision-making.

Muscle forces are difficult to measure in vivo, so the force-generating capacity of muscles is commonly inferred from muscle architecture. It is often assumed, implicitly or explicity, that a muscle's maximum force-generating capacity is proportional to physiological cross-sectional area (PCSA), and that a muscle's operating range is proportional to mean optimal fascicle length. Here, we examined the effect of muscle architecture (PCSA and fascicle length) on muscle function (maximal isometric force and operating range) using a three-dimensional finite element model which accounts in a mechanically consistent way for muscle deformation and other complexities of muscle contraction. By varying architectural properties independently, it was shown that muscle force-generating capacity does not scale by the same factor as PCSA, and that operating range does not scale by the same factor as optimal fascicle length. For instance, 3-fold independent variation of mean optimal fascicle length caused the maximum isometric force-generating capacity of the muscle to vary from 83% to 105% of the force predicted by PCSA alone. Non-uniformities in fascicle length that develop as the muscle deforms during contraction reduce muscle force and operating range. Thus, a three-dimensional finite element model that satisfies fundamental physical constraints predicts that the maximum force-generating capacity of skeletal muscle depends on factors other than PCSA, and that operating range depends on factors other than optimal fascicle length. These findings have implications for how the force-generating properties of animal muscles are scaled to human muscles, and for how the functional capacity of muscles is predicted from muscle architecture.

Cycling is a popular competitive and recreational exercise and is recommended as safe to perform following hip or knee surgery. During cycling, joint contact forces (JCF) have been recorded in-vivo and estimated via neuromusculoskeletal models, but model estimates are yet to be validated. In this study, motion data, crank force, and electromyograms for a range of cadences (40 and 60 revolutions per minute (rpm)) and power outputs (25, 35, 50, 60, 79, 75, 85, 95, 120 W) were collected from 7 healthy people cycling on a powered stationary ergometer. A (1) calibrated electromyogram-informed neuromusculoskeletal model and an (2) uncalibrated model that utilised static optimisation were used to estimate hip and knee JCF. Hip and knee JCF estimates were compared against in-vivo measurements of hip and knee JCF from literature. Peak hip and knee JCF were overestimated by both electromyogram-informed and static optimisation solutions, however, the magnitude and gradients of JCF as a function of cadence and power estimated by the electromyogram-informed solution more closely matched in-vivo measurement than those computed by static optimisation. Similarly, the profile of knee JCF as a function of crank angle estimated by the electromyogram-informed solution more closely matched in-vivo knee JCF than the static optimisation solution. Results indicate electromyogram-informed modelling is a valid computational approach to estimate knee and hip biomechanics during standard seated ergometer cycling.

Diverse marker sets and validation techniques have previously been utilized, posing challenges in comparing studies when assessing soft tissue artefacts in knee joint kinematics from motion analysis. This study aimed to analyse the data obtained from three different marker sets with the results derived from radiostereometric analysis (RSA) in measuring angular movements of the knee joint. Twelve post-knee replacement participants performed a one-leg step-down movement. Knee joint angular movements were analysed in flexion-extension, adduction-abduction, and internal-external rotation across all marker sets. The results were subsequently compared with those obtained from the RSA system using simple linear regression, a linear mixed-effects model, mean values and mean differences. All marker sets were found to systematically underestimate flexion-extension compared to RSA, with differences intensifying at higher knee flexion angles. The mean differences in the sagittal plane between RSA and the IOR marker set, progressively increased from approximately 5° (95% CI 4.3-4.9) to 15° (95% CI 11.6-17.9), reaching a maximum difference of 20° (95% CI 13.8-25.7) at 40° of knee flexion. Transverse and frontal plane data from all marker sets exhibited erratic errors compared to RSA. In summary, knee flexion-extension motions were consistent between marker sets, indicating minimal impact on results based on the marker set choice. However, all marker sets systematically underestimated skeletal motions in knee flexion-extension compared to RSA measurements. Data from the transverse and frontal planes were too inconsistent and therefore not reliable for use.

Fascia sliding mobility and deformation magnitude are potential biomarkers for musculoskeletal disorders, particularly in the thoracolumbar fascia over the erector spinae muscles, which are associated with low back pain. The use of speckle tracking analysis of ultrasound images through open-source software has been proposed for assessing fascia sliding mobility and deformation of the fascia. However, little is known about the validity and reliability of speckle tracking analysis. Since open-source projects for speckle tracking analysis have made great progress, an assessment of validity and reliability is required. Therefore, this study aimed to test the metric quality of speckle tracking analysis using an open-source software program. A custom-made tissue sliding device was developed to slide two gel pad phantoms over each other at a constant speed. The shear displacement was documented in real-time as the ground truth, while ultrasound videos were recorded. The ground truth data were then compared with the speckle tracking analysis data extracted from the ultrasound videos. Speckle tracking analysis for assessing tissue displacement using free and open-source software achieved excellent test-retest reliability and showed very high validity and reliability with low measurement errors. The presented open-source ultrasound-based speckle tracking analysis method can be recommended for research and clinical use in various environments.

Understanding function and dysfunction of the shoulder may be best addressed by capturing the motion of the shoulder in the unstructured, free-living environment where the magnitudes and frequencies of required daily motion can be quantified. Miniaturized wearable inertial measurement units (IMUs) enable measurement of shoulder motion in the free-living environment; however, there are challenges in using IMU-based data to estimate traditionally used measures of shoulder motion from lab-based motion capture. There are limited options for IMU placement/fixation that minimize soft tissue effects and there are significant challenges in developing the algorithms that can accurately estimate shoulder joint angles from IMU measurements of acceleration and angular velocity. In an effort to collate current knowledge and highlight solutions to addressable challenges, in this paper, we report the results of a focused search of research articles using IMUS for kinematic measurements of the shoulder in the free-living environment, discuss the basic steps required for quantifying shoulder motion in the non-laboratory field-based setting using wearable IMUs, and we discuss the challenges that must be overcome in the context of the shoulder joint and the literature review. Finally, we suggest some IMU-based measures that are less sensitive to experimental design and algorithm choices, make recommendations for the information documented in manuscripts describing studies that use IMUs to quantify shoulder motion, and propose directions for future research.

Creep in the viscoelastic tissues of the lumbar spine reduces the force-producing capability of these tissues. This study aimed to explore the impact of passive tissue creep on lumbar biomechanics. Sixteen participants performed controlled sagittally symmetric trunk flexion motions after a 30-minute protocol consisting of 12 min of full trunk flexion and 18 min of upright standing. Trunk kinematics and EMG activities of trunk muscles were captured as input variables in three biomechanical models: a) EMG-assisted model with no passive tissue (Active), b) EMG-assisted model with time-invariant passive tissue (No-Creep), and c) EMG-assisted model with time-variant passive tissue components (Creep). The mean absolute error (MAE) between the external moment and the estimated internal moment was calculated as a function of model type and trunk flexion. Results revealed no significant difference in MAE between the three models at 0-30° trunk flexion but as the angle exceeded 30°, the MAE of the No-Creep and Creep models were significantly smaller than that of the Active model. Beyond thetrunk flexion angle of flexion-relaxation of erector spinae muscles, the MAE of the Creep model was significantly smaller than that of the No-Creep model (21.8 Nm vs. 40.3 Nm), leading to reduced compression and shear forces of the L4/L5 disc by 784.7 N (31.7 %) and 280.6 N (21.6 %) at full flexion. These results indicate the modulation of the time-dependent stiffness of passive tissues led to amore accurate prediction of the net internal moment at near full flexion postures, preventing overestimation of spinal loads.

When discrepancies between planned and actual movements arise due to environmental changes, humans adjust movement parameters to achieve task goals. While motor adaptation has been extensively studied, the mechanisms involved in redundant movement parameters remain unclear. Split-belt treadmill adaptation, where each belt moves at a different speed, is an example of this phenomenon. Such adaptation initially induces gait asymmetry, which diminishes over time. Previous studies have postulated step length asymmetry as the target function; however, recent evidence challenges this assumption, leaving the target function undefined. This study investigates the target function by analyzing step parameter asymmetry using the goal-equivalent manifold and generalization predictability. The goal-equivalent manifold assesses whether adaptation is close to optimal in minimizing step parameter asymmetry, while generalization predictability reflects adaptation effects across different contexts, indicating potential target functions. We propose that step velocity asymmetry, rather than step length asymmetry, serves as the target function in split-belt treadmill adaptation. This framework facilitates the prediction and interpretation of both the learning process and the transfer of learning effects from trained to untrained conditions. In addition, it explains the overadaptation of step length asymmetry and the achievement of energy-efficient gait after adaptation. Therefore, we propose that step velocity asymmetry is the primary target function in split-belt treadmill adaptation.

Thumb motion is a key outcome metric for assessing disease progression or treatment efficacy. A literature review found nearly 25 % of recent papers incorrectly described their motion measurements as those of the first carpometacarpal (CMC) joint, when in fact their technology was only capable of measuring thumb motion. The aim of this manuscript is to clarify the importance of the accurate terminology and to rigorously examine the potential error by comparing thumb motion and CMC joint motion. Computed tomography (CT) images from 46 healthy subjects were analyzed using 3D markerless bone registration techniques to compute thumb rotation (first metacarpal (MC1) relative to the radius) and CMC joint rotation (MC1 relative to trapezium). We found thumb rotation was a poor measure of CMC joint rotation. For example, at thumb rotations of 20°, the true CMC joint rotations ranged from 3° to 30°. On average, thumb rotation over predicted CMC rotation by approximately 10°, with 95 % Limits of Agreement ranging from 30° (over estimating CMC joint motion) to -11° (underestimating CMC joint motion). Importantly, the character of the data demonstrated that CMC motion cannot be predicted from thumb motion. 3D CMC joint motion can only be assessed with skeletal imaging technologies; goniometers and skin-based markers can, at best, only measure thumb motion. Referring to goniometer and skin marker measurements as CMC joint motion is incorrect. It is critical that investigators be precise in their reporting of thumb motion versus CMC joint motion, especially when reporting interventions for thumb pathologies.

Mechanical stimulation is a widely used technique in the development of tissue engineered cartilage. While various regimes can enhance tissue growth and improve construct mechanical properties, existing outcome measures predominantly assess the anabolic effect of mechanical stimuli. Catabolic responses are generally overlooked, and a critical gap remains in how mechanical loading simultaneously affects both anabolic and catabolic processes. In this study, full-thickness articular cartilage was aseptically harvested from the metacarpal-phalangeal joints of skeletally mature bovine. Isolated chondrocytes were encapsulated in agarose gels and subjected to dynamic compressive strains from 0 % to 15 % for either 20 or 60 min using a custom-built mechanical stimulation device. Anabolism was assessed by [H]-proline and [S]-sulfate incorporation, while catabolism was evaluated by MMP-13 enzymatic activity. Long-term effects of dynamic loading were assessed through biochemical analyses and histological evaluation. Results showed that low-to-moderate strains (2.5 % and 5 %) induced high anabolic activity relative to control with minimal catabolic response. In contrast, high strains (15 %) resulted in elevated catabolic and reduced anabolic activity relative to control. The application of mechanical stimuli over the long-term elicited comparable responses with lower compressive stains leading to improved cartilaginous extracellular matrix accumulation. This study provides valuable insights into the complex interplay between anabolic and catabolic metabolism in chondrocyte-seeded agarose constructs subjected to dynamic compression. This research underscores the necessity of evaluating both responses to optimize the growth and properties of tissue-engineered cartilage.

Biomechanically, falling after a walking perturbation may be influenced by: (1) the pre-perturbation state of mechanical stability (e.g., stability margins) and (2) the response to a perturbation (i.e., recovery skill). Walking stability margins must be modifiable to serve as a target for fall-prevention interventions. We investigated if neurotypical adults could proactively modulate pre-perturbation anteroposterior stability margins while walking. Eleven adults walked on a treadmill at three speeds with and without anterior and posterior perturbations. We measured stability margins anteriorly at mid-swing and posteriorly at foot strike for pre-perturbation steps. A repeated-measures factorial ANOVA evaluated main effects and interactions of walking speed (0.6, 0.8, 1.0 stats/s) and perturbation type (anterior, none, posterior). With posterior perturbation threats, the posterior stability margins were more positive at foot strike (p < 0.01) compared to trials without perturbations. With anterior perturbation threats, the anterior stability margins were not different at mid-swing compared to trials without perturbations (p > 0.05). With any perturbation threat, step lengths shortened (p < 0.01) and step rates increased (p < 0.01). Step width was not different (p > 0.11). At slow speeds with posterior perturbation threats, double-support time decreased (p = 0.04). Proactive modifications to stability margins are indeed possible in a neurotypical population. Consequently, anteroposterior stability margins may be a feasible target for fall-prevention interventions by targeting decreased step lengths or increased step rates within a given walking speed. We do not know the extent to which the observed effects have a meaningful effect on perturbation recovery.

Electromyography (EMG)-assisted biomechanical models of the lumbar spine have been developed to estimate spinal loading, but these models often have limited representation of passive tissue contributions to the trunk extension moment. Recent evidence suggests that sustained near full trunk flexion can lead to increased contribution of the passive tissues to resist the external moment due to increased lumbar flexion as the extensor muscle fatigue. This leads to our hypothesis that spinal loading might be increased due to load transfers between active and passive tissues. Sixteen participants maintained a trunk flexion posture that was ten degrees less than the trunk flexion angle inducing flexion-relaxation of erector spinae muscles for 12 min with breaks every three minutes. Trunk kinematic and EMG measures were collected. A muscle fatigue-modified EMG-assisted model with passive tissue components was employed to estimate the time-dependent force and moment profiles at the L4/L5 level. Results revealed that these postures led to a time-dependent increase in the proportion of passive tissues to resist the external moment (39.9 % to 49.5 %) during each 3-minute time block, thereby resulting in the time-dependent increase in the compression and anterior-posterior shear forces of the L4/L5 disc by 181.7 N and 125.2 N, respectively (all p-value < 0.001). These results indicate that the load transfer from active to passive tissues can lead to increased compression and anterior-posterior shear forces of the L4/L5 disc at a constant external moment. This study suggests that a time-dependent approach to an EMG-assisted model with passive tissue components can provide more accurate estimates of tissue stresses.

The heart's developed pressure (DP) in Langendorff heart experiments increases with preload via the Frank-Starling mechanism up to a critical transition point at which DP starts to decrease with preload. A similar behavior is found at the cellular level, where the tension developed by skinned cardiac fibers or myocytes in isometric tension test increases with sarcomere length up to a transition point beyond which, the tension decreases. This cellular-level behavior is termed myofilament length dependent activation. While these two behaviors are similar, they occur at vastly different scales. Specifically, the DP - preload and sarcomere length - tension relationships occur, respectively, at the organ and cellular scales. Correspondingly, it remains unclear how much these behaviors are related. To address this issue, we use computer modeling that connects cellular to organ mechanics found in the ex-vivo beating rat heart experiments to determine whether the DP - preload relationship at the organ level can be explained solely by the sarcomere length - tension relationship at the cellular level. We found that the non-monotonic behavior of the DP with preload is consistent with a model predicted feature of myocardial contractility. The LV sarcomere length at the transition where DP and myocardial contractility start to reduce is 2.12 ± 0.03 μm. This transition sarcomere length is outside the range of 2.2 - 2.4 μm that is associated with the peak tension found in skinned rat cardiac fibers or myocytes with isometric tension test. This disparity suggests the presence of other factors affecting the DP - preload relationship found in Langendorff heart experiments such as the prescribed initial length of sarcomere that vary between different rat species.

While several biomechanical investigations have measured acromion and scapular spine strains for various pathological conditions to better understand the risk factors for fracture, no study has measured strains in the native shoulder. The objective of this study was to use an ex-vivo shoulder motion simulator to measure principal strain during continuous, unconstrained, muscle-driven motion of the native shoulder. Eight cadaveric specimens (57 ± 6 years) were used to simulate scapular plane abduction (27.5 to 80° of humerothoracic elevation), forward flexion (27.5 to 72.5° of humerothoracic elevation), external rotation (0 to 40° of external rotation), and circumduction (elliptical path) with glenohumeral rotation speeds of 10°/s. Principal strain was measured throughout motion in four clinically relevant regions of the scapular spine and acromion according to the Levy classification using tri-axial strain gauge rosettes. Increases in humeral elevation during scapular plane abduction and forward flexion were associated with increases in deltoid force and scapula strain. However, above approximately 60° of humerothoracic elevation, strains plateaued while deltoid forces continued to increase indicating that scapula strain patterns are influenced by deltoid force magnitude and direction. Scapula strain was higher during scapular plane abduction than forward flexion in all regions but was only significantly higher in Levy 3B (p = 0.038). The highest strains were observed in Levy regions 2 and 3A (p ≤ 0.01) which correspond to regions with the highest clinically observed fracture rates demonstrating that the shape of the acromion and scapular spine may influence strain distribution irrespective of the joint condition.

The aim of this study was to analyze the morphology of the median nerve (MN) in the carpal tunnel during hand motion and palmar load in healthy participants using ultrasound. Twenty healthy participants (10 men and 10 women) were enrolled in the study. Wrist flexion angle is negatively correlated with cross-sectional area (CSA) and perimeter, and positively correlated with circularity, whereas wrist extension angle is negatively correlated with MNCSA and circularity. At 15°, 45°, and 60° wrist flexion and extension, both MNCSA and perimeter were significantly smaller than at neutral (all P < 0.05). MN circularity was significantly greater at 30°, 45°, and 60° wrist flexion than at neutral (all P < 0.05). At 30° ulnar deviation of the wrist, MNCSA and perimeter were significantly smaller than the neutral position, while circularity was significantly larger (all P < 0.05). At 15° of wrist radial deviation, MNCSA and perimeter were significantly smaller than at the neutral position (all P < 0.05). Compared to the 40 % maximum voluntary effort (MVE), thumb-ring finger pinch (10 %MVE) resulted in significantly higher MNCSA and perimeter, while circularity was noticeably smaller (all P < 0.05). In the neutral position, no differences were observed in MNCSA, perimeter and circularity unloaded at 100 g, 200 g, 300 g, 400 g and 500 g palmar loads (all P > 0.05). The results indicate that wrist positions involving flexion, extension, and deviations, as well as finger pinch, can significantly impact the morphology of the MN. This is an important step in understanding the biomechanics of MN compression within the carpal tunnel.

The zygapophyseal (facet) joint plays a critical role in load transmission and stability of the spine, and facet degeneration is a common consequence of aging and osteoarthritis. The ability to accurately measure facet space is important, as decreased facet space is associated with facet degeneration and lower back pain. Although grading systems exist for assessing facet joint space narrowing, static imaging fails to characterize changes in the facet gap under load that play a role in segmental stability. Current methods for estimating the dynamic behavior of the facet joint are either inaccurate, radiation costly, or clinically impractical. In the current study, we demonstrate the feasibility of a novel method for 3D measurement of facet joint space using digital tomosynthesis (DTS) imaging in supine and standing positions. Facet gap measurements were found to be strongly correlated with (r to 0.98) and accurate (<20 µm error for median facet gap) relative to microcomputed tomography reference values. In a pilot in vivo demonstration with seven participants, the effect of physiological loading was detectable, with median facet joint space being larger in standing as compared to supine images (p < 0.0001). The presented approach may be useful in directly characterizing changes in the facet joint relevant to segmental stability that are not readily assessed via current clinical imaging methods.