Biomechanical Loading Research Articles

Effects of passive exoskeleton support on EMG measures of the neck, shoulder and trunk muscles while holding simulated surgical postures and performing a simulated surgical procedure

Exoskeletons have shown significant impact at reducing the biomechanical demand on muscles during repetitive lifting and overhead tasks in non-healthcare industries. However, the benefits of exoskeletons are yet to be realized in the operating room, particularly as work-related musculoskeletal disorders continue to be a concern for surgeons. This study quantified the effect of using neck, arm, and trunk exoskeletons on muscle activity while assuming typical postures held in the operating room. Fourteen participants were recruited to participate in this study. In this two-part experiment participants were asked to 1) hold a series of neck flexion, arm abduction and trunk flexion postures seen in surgical procedures, and 2) perform a simulated surgical task requiring five different trunk flexion posture levels. Participants were required to complete these tasks with and without passive exoskeleton(s). This study showed that even for postures held short time periods, exoskeletons are beneficial at reducing the demand on muscles; however, the reduction in muscle demand depends on body segment and postural angle, as intended with these passive exoskeletons. Furthermore, for the simulated surgical task with awkward trunk flexion postures (10–65°), the trunk exoskeletons showed a significant reduction in the rate of rise in back muscle sEMG (+1.365%MVC/min vs. +0.769%MVC/min for non-dominant lumbar extensor muscles, p = 0.0108; +1.377%MVC/min vs. +0.770%MVC/min for the dominant lumbar extensor muscles, p = 0.0196) over 25 min, consequently resulting in improved trunk subjective discomfort scores (7.34 vs. 4.30, p < 0.05), with no impact on the neck and shoulder biomechanical demand. The results from this study indicate that exoskeletons may be a potential intervention to reduce biomechanical loading during surgery.

Biomechanical In Vitro and Finite Element Study on Different Sagittal Alignment Postures of the Lumbar Spine During Multiaxial Daily Motion.

Lumbar lordotic correction (LLC), the gold standard treatment for sagittal spinal malalignment (SMA), and its effect on sagittal balance have been critically discussed in recent studies. This paper assesses the biomechanical response of the spinal components to LLC as an additional factor for the evaluation of LLC. Human lumbar spines (L2L5) were loaded with combined bending moments in flexion (Flex)/extension (Ex) or lateral bending (LatBend) and axial rotation (AxRot) in a physiological environment. We examined the dependency of AxRot range of motion (RoM) on the applied bending moment. The results were used to validate a finite element (FE) model of the lumbar spine. With this model, the biomechanical response of the intervertebral discs (IVD) and facet joints under daily motion was studied for different sagittal alignment postures, simulated by a motion in Flex/Ex direction. Applied bending moments decreased AxRot RoM significantly (all P < 0.001). A stronger decline of AxRot RoM for Ex than for Flex direction was observed (all P < 0.0001). Our simulated results largely agreed with the experimental data (all R2 > 0.79). During the daily motion, the IVD was loaded higher with increasing lumbar lordosis (LL) for all evaluated values at L2L3 and L3L4 and posterior annulus stress (AS) at L4L5 (all P < 0.0476). The results of this study indicate that LLC with large extensions of LL may not always be advantageous regarding the biomechanical loading of the IVD. This finding may be used to improve the planning process of LLC treatments.

Novice Female Exercisers Exhibited Different Biomechanical Loading Profiles during Full-Squat and Half-Squat Practice.

Simple SummaryThis study adapted a customized OpenSim model aiming to analyze the loadings difference between full-squat and half-squat in novice females. The joint moment and joint angle of the hip, knee, and ankle increase significantly in the full-squat, which might increase the risks of potential injury. In the case of training, the cohort of young females could perform half-squat practice when muscle strength is insufficient. This study may present implications for the design of novice strength training programs and the formulation of rehabilitation plans.Background: Females with different practice experience may show different body postures and movement patterns while squatting in different depths, which may lead to changes of biomechanical loadings and increase the risks of injuries. Methods: Sixteen novice female participants without squat training experience participated in this study. A 3D motion capture system was used to collect the marker trajectory and ground reaction force data during bodyweight squatting in different depths. The participants’ kinematic data and joint moment were calculated using OpenSim’s inverse kinematics and inverse dynamics algorithm. In this study, authors adapted a model especially developed for squatting and customized the knee joint with extra Degree-of-Freedom (DoF) in the coronal and horizontal plane with adduction/abduction and internal/external rotation. A paired-sample t-test was used to analyze the difference of joint range of motions (ROM) and peak moments between full-squat (F-SQ) and half-squat (H-SQ). One-Dimensional Statistical Parametric Mapping (SPM1D) is used to analyze the difference of joint angle and moment between the process of squatting F-SQ and H-SQ. Results: (1) Compared with H-SQ, F-SQ showed larger ROM in sagittal, coronal, and transverse planes (p < 0.05). (2) SPM1D found that the difference in joint angles and joint moments between F-SQ and H-SQ was mainly concentrated in the mid-stance during squatting, which suggested the difference is greatly pronounced during deeper squat. (3) Peak hip extension moment, knee extension moment, hip adduction moment, and plantar flexion moment of F-SQ were significantly higher than H-SQ (p < 0.05). (4) Difference of hip and knee extension moments and rotation moments between the F-SQ and H-SQ were exhibited during descending and ascending. Conclusions: The study found that novice women had larger range of joint motion during the F-SQ than H-SQ group, and knee valgus was observed during squatting to the deepest point. Greater joint moment was found during F-SQ and reached a peak during ascending after squatting to the deepest point. Novice women may have better movement control during H-SQ. The findings may provide implications for the selection of lower limb strength training programs, assist the scientific development of training movements, and provide reference for squat movement correction, thus reducing the risk of injury for novice women in squatting practice.

A computer-vision method to estimate joint angles and L5/S1 moments during lifting tasks through a single camera

Weight lifting is a risk factor of work-related low-back musculoskeletal disorders (MSD). From the ergonomics perspective, it is important to measure workers’ body motion during a lifting task and estimate low-back joint moments to ensure the low-back biomechanical loadings are within the failure tolerance. With the recent development of advanced deep neural networks, an increasing number of computer vision algorithms have been presented to estimate 3D human poses through videos. In this study, we first performed a 3D pose estimation of lifting tasks using a single RGB camera and VideoPose3D, an open-source library with a fully convolutional model. Joint angle trajectories and L5/S1 joint moment were then calculated following a top-down inverse dynamic biomechanical model. To evaluate the accuracy of the computer-vision-based angular trajectories and L5/S1 joint moments, we conducted an experiment in which participants performed a variety of lifting tasks. The body motions of the participants were concurrently captured by an RGB camera and a laboratory-grade motion tracking system. The body joint angles and L5/S1 joint moments obtained from the camera were compared with those obtained from the motion tracking system. The results showed a strong correlation (r > 0.9, RMSE < 10°) between the two methods for shoulder flexion, trunk flexion, trunk rotation, and elbow flexion. The computer-vision-based method also yielded a good estimate for the total L5/S1 moment and the L5/S1 moment in the sagittal plane (r > 0.9, RMSE < 20 N·m). This study showed computer vision could facilitate safety practitioners to quickly identify the jobs with high MSD risks through field survey videos.

Towards ergonomics working - machine learning algorithms and musculoskeletal modeling

Ergonomic workplaces lead to fewer work-related musculoskeletal disorders and thus fewer sick days. There are various guidelines to help avoid harmful situations. However, these recommendations are often rather crude and often neglect the complex interaction of biomechanical loading and psychological stress. This study investigates whether machine learning algorithms can be used to predict mechanical and stress-related muscle activity for a standardized motion. For this purpose, experimental data were collected for trunk movement with and without additional psychological stress. Two different algorithms (XGBoost and TensorFlow) were used to model the experimental data. XGBoost in particular predicted the results very well. By combining it with musculoskeletal models, the method shown here can be used for workplace analysis but also for the development of real-time feedback systems in real workplace environments.

Design and Pilot Evaluation of a Prototype Sensorized Trunk Exoskeleton.

Trunk exoskeletons are wearable devices that support wearers during physically demanding tasks by reducing biomechanical loads and increasing stability. In this paper, we present a prototype sensorized passive trunk exoskeleton, which includes five motion processing units (3-axis accelerometers and gyroscopes with onboard digital processing), four one-axis flex sensors along the exoskeletal spinal column, and two one-axis force sensors for measuring the interaction force between the wearer and exoskeleton. A pilot evaluation of the exoskeleton was conducted with two wearers, who performed multiple everyday tasks (sitting on a chair and standing up, walking in a straight line, picking up a box with a straight back, picking up a box with a bent back, bending forward while standing, bending laterally while standing) while wearing the exoskeleton. Illustrative examples of the results are presented as graphs. Finally, potential applications of the sensorized exoskeleton as the basis for a semi-active exoskeleton design or for audio/haptic feedback to guide the wearer are discussed.

Biomechanical Analysis of the Joint and Muscle Forces of the Lower Extremities in Walking of Rheumatoid Arthritis Patient

Summary. Rheumatoid arthritis (RA) is an immunomodulated, chronic inflammatory disease, accompanied by the proliferation of the inflamed synovium and destruction of the articular cartilage, which leads to the formation of contracture of lower extremities joints and disability. Understanding the values of biomechanical loads on the articular surfaces with contracture of the joints of the lower extremities in patients with RA and the muscle forces (MF) participation in this process with the formation of adaptation and compensation mechanisms can contribute to the development of new views and approaches to the tactics of therapeutic measures specific to each stage of the disease.&#x0D; Objective: to analyze the behavior of the musculoskeletal system of an RA patient in his walking pattern by calculating the forces acting in the main muscle groups and joints of the lower extremities.&#x0D; Materials and Methods. Initial data were obtained from the examination of a female patient K., who was diagnosed with stage 2 phase 3 RA with a predominant lesion of the hip and knee joints and severe pain in the left hip joint. A video system of 6 cameras, reflective markers and a force platform were used for motion capture of the walking. A simulation musculoskeletal model of the gait of the RA patient using the AnyBody Modeling System 6.0 software (Denmark) was created. Joint reaction forces (JRF) and MF were calculated.&#x0D; Results. Normal mode of loading of the lower extremities was altered to compensate for structural disorders in joints of RA patients. The peaks of vertical component of the ground reaction force (GRF) are lower compared to the normal population; the gait is static and asymmetric, sparing. MF increase in m. gluteus (maximus, medius, minimus) with increasing amplitude of movements in the frontal plane. JRF of both hips increase in all planes.&#x0D; Conclusions. Walking of RA patients with limitation of active extensions in the hip and knee joints occurs due to an increase in the amplitude of the frontal plane compensatory movements. Postural muscle imbalance increases the m. gluteus, m. biceps femoris, m. semitendinosus and m. semimembranosus MF. Other lower extremities muscles decrease their MF. The MF redistribution is compensatory and aimed to keep the RA patient in the upright position and optimize the biomechanics of walking due to less painful movements. Biomechanical overloading of the hip and knee articular surfaces can serve as a factor in maintaining the inflammatory response, the development of degenerative processes, or the further progression of arthrosis and stiffness of the joints of the lower extremities in this category of patients.

Increased trunk flexion may underlie elevated knee flexor activity in people with knee osteoarthritis

BackgroundPrevious research has demonstrated elevated activation of the knee flexor muscles in people with knee osteoarthritis. People with this condition have also been observed to walk with increased trunk flexion; this may alter biomechanical loading patterns and change muscle activation profiles. Therefore, the aim of this study was to understand the biomechanical effect of increasing trunk flexion during walking. MethodsKinetic and EMG data were collected from a sample of 20 people with knee osteoarthritis and a sample of 20 healthy matched controls during normal walking. Using a biofeedback protocol, participants were subsequently instructed to walk with a 5° increase in trunk flexion. Sagittal moments, muscle activations and co-contractions were then compared across a window in early stance with a two-way ANOVA test. ResultsWhen trunk flexion was increased, there was a corresponding increase in activity of the medial and lateral hamstrings and gastrocnemius muscles as well as a rise in medial co-contraction. This effect was consistent across the two groups. The most pronounced effect was observed for semitendinosus, which showed a dramatic change in activation profile in the healthy group and a 127% increase in activation during early stance. ConclusionsThis is the first study to demonstrate that increased trunk flexion in people with knee osteoarthritis may explain, to some degree, the elevated knee flexor activity and medial co-contraction which is associated with this disease. These findings motivate further work to understand the therapeutic potential of interventions designed to improve postural alignment.

Impact of calcific aortic valve disease on valve mechanics.

The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of forward and reverse flow patterns. Calcific aortic valve disease (CAVD) resulting in compromised valve function and increased pressure overload on the ventricle potentially leading to heart failure if untreated, is the most predominant valve disease. CAVD is a multi-factorial disease involving molecular, tissue and mechanical interactions. In this review, we aim at recapitulating the biomechanical loads on the aortic valve, summarizing the current and most recent research in the field in vitro, in-silico, and in vivo, and offering a clinical perspective on current strategies adopted to mitigate or approach CAVD.

Retrieval analysis of neck fracture on uni-modular total hip arthroplasty stems: The contributions of material processing and stem design.

Total hip arthroplasty stem fracture is an important contributor to morbidity rate and increases the cost of revision surgery. Failure is usually caused by issues related to overload, inadequate stem support, inappropriate stem design or dimensions and material processing. In this study, the role of the relationship between material characterization and biomechanical performance in the fracture of retrieved stems was explored. The stems were manufactured with forged stainless steel, had the same length, 12/14 trunnion, and 28-mm head. These stems were evaluated by macroscopic and microscopic examination to identify the causes of premature failure. Each stem was sectioned into four regions, and the cross-sections were used for the microhardness and grain size analysis. Finite element analysis (FEA) was carried out, considering the stem positioned at the femur, a musculoskeletal model, and biomechanical loading. All stems had fractured through a fatigue mechanism, mainly a unidirectional bending loading condition, with crack nucleation on the lateral side and propagation on the medial side. The numerical analysis revealed maximum mechanical stress on the lateral side of the stem neck, but this was below the yield stress calculated via the hardness. The use of a shorter head neck length could reduce the maximum mechanical stress at the neck. At a cross-section near the plane of the stem fracture, the hardness was lower than that normally reported by the ASM, and there were heterogonous and coarse grain sizes on the lateral side. The main cause of failure of the two stems analyzed was a combination of low hardness and coarse grain size, due to inappropriate materials processing, worsen by a high level of stress on the lateral side of the neck due to the large stem-head offset selected by the orthopedic surgeon.

Biomechanical Analysis of Single Interference Screw vs Interference Screw With Cortical Button for Flexor Hallucis Longus Transfer.

Background:Flexor hallucis longus tendon transfer (FHL) with a cortical button tension slide is an innovative addition that has not been measured against traditional methods.Methods:12 pairs (n=24) of fresh-frozen cadaveric tibia-to-toe samples were used and randomized to receive one of the operative FHL techniques. Specimens underwent bone density analysis. Biomechanical loading was applied between 20 and 60 N at 1 Hz for 100 cycles. Post–cyclic load to failure occurred at 1.25 mm/s. Cyclic displacement, structural stiffness, and ultimate load were derived from load-displacement curves. Student t tests evaluated significant effects between both FHL techniques. Linear regression analysis assessed interactions between bone density and strength of FHL technique.Results:Average tendon diameter was 5.44±0.46 mm. Average bone density was 1.06±0.08 g/cm2. Addition of a cortical button to FHL transfer did not significantly affect cyclic displacement (0.78±0.52 mm vs 0.87±0.80 mm) or structural stiffness (162.11±43.34 N/mm vs 167.57±49.19 N/mm). Cortical button addition to FHL transfer resulted in significantly increased ultimate load (343.72±68.93 N) compared with interference screw alone (255.62±77.17 N) (P = .0002). Linear regression analyses did not reveal any significant interactions between bone density and FHL tendon transfer technique.Conclusion:Enhanced strength can be achieved with FHL tendon transfer to calcaneus using an interference screw and cortical button tension slide technique as compared to an interference screw alone. Cortical buttons in the setting of FHL tendon transfer to the calcaneus offers an additional level of support.Clinical Relevance:Operative cases presenting with poor bone quality due to osteoporosis or osteopenia could benefit from cortical button fixation during FHL transfer. Clinical studies are needed to determine if the increased construct stability conferred from the additional use of a flip button results in fewer FHL transfer failures or better clinical outcomes.Level of Evidence:Level V, Controlled Laboratory Study.

Mechanical Characterization of Dental Implant Due to Biomechanical Loading

The presence of dental implant has totally altered the force transfer from crown to the surrounding bone and the oral mechanical environment. This leads to abnormal bone remodelling. The high stiffness of the implant decreased the physiologic loading of the surrounding bone. This situation is described as stress shielding. Stress shielding is the common cause of failure in the fixture of dental implant. There are various implant geometries that have different impacts on the stress shielding effect. The aim of this study is to analyse the effects of implant length to stress shielding by using finite element method. 3 different lengths of dental implant models (6mm, 8mm and 10mm) are drawn using ANSYS APDL 2019 and a shear force of 30N is applied to the implant to examine the stress distribution of the implant and surrounding bone. Stress transfer parameter (STP) is computed and compared for each dental implant. This study found that by increasing the length of the dental implant, the maximum Von Mises stress decreases. The stress shielding effect also decreases when the length of dental implant increases.

Influence of Lumbar Lordosis on Posterior Rod Strain in Long-Segment Construct During Biomechanical Loading: A Cadaveric Study.

ObjectiveThe lordotic shape of the lumbar spine differs substantially between individuals. Measuring and recording strain during spinal biomechanical tests is an effective method to infer stresses on spinal implants and predict failure mechanisms. The geometry of the spine may have a significant effect on the resultant force distribution, thereby directly affecting rod strain. MethodsSeven fresh-frozen cadaveric specimens (T12-sacrum) underwent standard (7.5 Nm) nondestructive sagittal plane tests: flexion and extension. The conditions tested were intact and pedicle screws and rods (PSR) at L1-sacrum. The posterior right rod was instrumented with strain gauges between L3–4 (index level) and the L5–S1 pedicle screw. All specimens underwent lateral radiographs before testing. Lordotic angles encompassing different levels (L5–S1, L4–S1, L3–S1, L2–S1, and L1–S1) were measured and compared with rod strain. Data were analyzed using Pearson correlation analyses. ResultsStrong positive correlations were observed between lordosis and posterior rod strain across different conditions. The L3–S1 lordotic angle in the unloaded intact condition correlated with peak rod strain at L3–4 with PSR during flexion (R=0.76, p=0.04). The same angle in the unloaded PSR condition correlated with peak strain in the PSR condition during extension (R=-0.79, p=0.04). The unloaded intact L2–S1 lordotic angle was significantly correlated with rod strain at L3–4 in the PSR condition during flexion (R=0.85, p=0.02) and extension (R=-0.85, p=0.02) and with rod strain at L5–S1 in the PSR condition during flexion (R=0.84, p=0.04). ConclusionLordosis measured on intact and instrumented conditions has strong positive correlations with posterior rod strain in cadaveric testing.

Toughening of Bioceramic Composites for Bone Regeneration

Bioceramics are widely considered as elective materials for the regeneration of bone tissue, due to their compositional mimicry with bone inorganic components. However, they are intrinsically brittle, which limits their capability to sustain multiple biomechanical loads, especially in the case of load-bearing bone districts. In the last decades, intense research has been dedicated to combining processes to enhance both the strength and toughness of bioceramics, leading to bioceramic composite scaffolds. This review summarizes the recent approaches to this purpose, particularly those addressed to limiting the propagation of cracks to prevent the sudden mechanical failure of bioceramic composites.

Reversible changes in the 3D collagen fibril architecture during cyclic loading of healthy and degraded cartilage

Biomechanical changes to the collagen fibrillar architecture in articular cartilage are believed to play a crucial role in enabling normal joint function. However, experimentally there is little quantitative knowledge about the structural response of the Type II collagen fibrils in cartilage to cyclic loading in situ, and the mechanisms that drive the ability of cartilage to withstand long-term repetitive loading. Here we utilize synchrotron small-angle X-ray scattering (SAXS) combined with in-situ cyclic loading of bovine articular cartilage explants to measure the fibrillar response in deep zone articular cartilage, in terms of orientation, fibrillar strain and inter-fibrillar variability in healthy cartilage and cartilage degraded by exposure to the pro-inflammatory cytokine IL-1β. We demonstrate that under repeated cyclic loading the fibrils reversibly change the width of the fibrillar orientation distribution whilst maintaining a largely consistent average direction of orientation. Specifically, the effect on the fibrillar network is a 3-dimensional conical orientation broadening around the normal to the joint surface, inferred by 3D reconstruction of X-ray scattering peak intensity distributions from the 2D pattern. Further, at the intrafibrillar level, this effect is coupled with reversible reduction in fibrillar pre-strain under compression, alongside increase in the variability of fibrillar pre-strain. In IL-1β degraded cartilage, the collagen rearrangement under cyclic loading is disrupted and associated with reduced tissue stiffness. These finding have implications as to how changes in local collagen nanomechanics might drive disease progression or vice versa in conditions such as osteoarthritis and provides a pathway to a mechanistic understanding of such diseases. Statement of significanceStructural deterioration in biomechanically loaded musculoskeletal organs, e.g., joint osteoarthritis and back pain, are linked to breakdown and changes in their collagen-rich cartilaginous tissue matrix. A critical component enabling cartilage biomechanics is the ultrastructural collagen fibrillar network in cartilage. However, experimental probes of the dynamic structural response of cartilage collagen to biomechanical loads are limited. Here, we use X-ray scattering during cyclic loading (as during walking) on joint tissue to show that cartilage fibrils resist loading by a reversible, three-dimensional orientation broadening and disordering mechanism at the molecular level, and that inflammation reduces this functionality. Our results will help understand how changes to small-scale tissue mechanisms are linked to ageing and osteoarthritic progression, and development of biomaterials for joint replacements.

Prophylactic Efficacy of Tibial Plateau Levelling Osteotomy for a Canine Model with Experimentally Induced Degeneration of the Cranial Cruciate Ligament

The aim of this study was to clarify the histological effects of tibial plateau levelling osteotomy on cranial cruciate ligament degeneration induced by excessive tibial plateau angle. Five female Beagles were used to bilaterally create excessive tibial plateau angle models surgically. A second tibial plateau levelling osteotomy was performed 11 months after the first surgery on the right stifle (tibial plateau levelling osteotomy group), and a sham operation that did not change the tibial plateau angle was performed on the left stifle (excessive tibial plateau angle group). At 6 months after the second surgery, the dogs were euthanatized. The cranial cruciate ligament was stained with haematoxylin-eosin to assess the cell density, Alcian-Blue to assess proteoglycans and Elastica-Eosin to assess elastic fibres, and immunohistochemically stained to assess type I (COL1) and type II collagen and SRY-type HMG box 9 (SOX9) expression. In each group, the cranial cruciate ligament degeneration, especially on the tibial side, including the presence of Alcian-Blue- and Elastica-Eosin-positive regions, decreased in COL1-positive regions, and enhancement of SOX9 expression was observed. Besides, compared with the tibial plateau levelling osteotomy group, the excessive tibial plateau angle group showed increases in Alcian-Blue- and Elastica-Eosin-positive regions and a decrease in the COL1-positive regions. The results suggested that excessive tibial plateau angle-induced cranial cruciate ligament degeneration can be suppressed by reducing the biomechanical load on the cranial cruciate ligament by performing tibial plateau levelling osteotomy.

Podoplanin is dispensable for mineralized tissue formation and maintenance in the Swiss outbred mouse background

Podoplanin, PDPN, is a mucin-type transmembrane glycoprotein widely expressed in many tissues, including lung, kidney, lymph nodes, and mineralized tissues. Its function is critical for lymphatic formation, differentiation of type I alveolar epithelial lung cells, and for bone response to biomechanical loading. It has previously been shown that Pdpn null mice die at birth due to respiratory failure emphasizing the importance of Pdpn in alveolar lung development. During the course of generation of Pdpn mutant mice, we found that most Pdpn null mice in the 129S6 and C57BL6/J mixed genetic background die at the perinatal stage, similar to previously published studies with Pdpn null mice, while all Pdpn null mice bred with Swiss outbred mice survived. Surviving mutant mice in the 129S6 and C57BL6/J mixed genetic background showed alterations in the osteocyte lacunocanalicular network, especially reduced osteocyte canaliculi in the tibial cortex with increased tibial trabecular bone. However, adult Pdpn null mice in the Swiss outbred background showed no overt differences in their osteocyte lacunocnalicular network, bone density, and no overt differences when challenged with exercise. Together, these data suggest that genetic variations present in the Swiss outbred mice compensate for the loss of function of PDPN in lung, kidney, and bone.

Inter-individual variability in a repetitive lifting task

Trunk kinematics directly impact the biomechanical loading of the tissues of the low back. Quantifying the variability in trunk kinematics may provide deeper insights into biomechanical loading and low back injury risk. Inter-lifter variability in trunk kinematics was assessed as twenty participants performed a repetitive lifting task at three levels of the NIOSH Lifting Index. Trunk kinematics were captured and Levene’s test of homogeneity of variance was used to test the hypothesis that variance in kinematic parameters increased as a function of level of lifting index. Results showed considerable levels of variability in all kinematics parameters, and for sagittal range of motion, mean sagittal velocity, transverse range of motion, and mean transverse velocity the variance was significantly affected (p&lt;0.05) by level of lifting index. The results of this study demonstrate that variability (both inter- and intra-lifter) should be considered as one considers the relative risk of a lifting task.

The biomechanical disadvantage of dysplastic hips.

Developmental dysplasia of the hip (DDH) is strongly associated with an increased risk for hip osteoarthritis. Skeletal deformities undeniably contribute to detrimental biomechanical loading in dysplastic hips, but cannot explain all types of damage and symptoms that patients with DDH experience. Characterizing the geometry and function of the muscles spanning the hip is a logical next step in our progression of knowledge about DDH pathomechanics. In this study, we compared skeletal geometry, muscle volumes, intramuscular fatty infiltration, moment arms, and isometric strength in patients with DDH (N = 20) to healthy controls (N = 15). Femoral coverage was significantly less in patients (p < 0.001, Cohen's d effect size = 2.2), femoral neck-shaft angles were larger (p = 0.001, d = 1.3), and hip joint centers (HJCs) were more lateral (p = 0.001, d = 1.3). These skeletal abnormalities were associated with smaller abductor muscle moment arms in patients with DDH (e.g., gluteus medius [GMED]: p = 0.001, d = 1.2). Patients with DDH also had larger GMED volumes (p = 0.02, d = 0.83), but no differences in fatty infiltration, compared to controls. Isometric strength of the hip abductors, extensors, and flexors was lower in patients, but not significantly different from controls. The abnormal skeletal geometry, lateralized HJC, and reduced muscle moment arms represent a chronic biomechanical disadvantage under which patients with DDH operate. This phenomenon causes increased demand on the abductor muscles and results in high medially and superiorly directed joint reaction forces, which can explain reports of superomedial femoral cartilage damage in patients. The abnormal muscle geometry and function, in context with abnormal skeletal structure, are likely strong, but underappreciated, contributors to damaging loads in DDH.

Fibroblast Derived Human Engineered Connective Tissue for Screening Applications.

Fibroblasts are phenotypically highly dynamic cells, which quickly transdifferentiate into myofibroblasts in response to biochemical and biomechanical stimuli. The current understanding of fibrotic processes, including cardiac fibrosis, remains poor, which hampers the development of new anti-fibrotic therapies. Controllable and reliable human model systems are crucial for a better understanding of fibrosis pathology. This is a highly reproducible and scalable protocol to generate engineered connective tissues (ECT) in a 48-well casting plate to facilitate studies of fibroblasts and the pathophysiology of fibrotic tissue in a 3-dimensional (3D) environment. ECT are generated around the poles with tunable stiffness, allowing for studies under a defined biomechanical load. Under the defined loading conditions, phenotypic adaptations controlled by cell-matrix interactions can be studied. Parallel testing is feasible in the 48-well format with the opportunity for the time-course analysis of multiple parameters, such as tissue compaction and contraction against the load. From these parameters, biomechanical properties such as tissue stiffness and elasticity can be studied.