A biomechanical model to simulate the effect of a high vertical loading on trunk flexural stiffness

A human trunk model was developed to simulate the effect of a high vertical loading on trunk flexural stiffness. A force–length relationship is attributed to each muscle of the multi-body model. Trunk stiffness and muscle forces were evaluated experimentally and numerically for various applied loads. Experimental evaluation of trunk stiffness was carried out by measuring changes in reaction force following a sudden horizontal displacement at the T10 level prior to paraspinal reflexes induction. Results showed that the trunk stiffness increases under small applied loads, peaks when the loads were further increased and decreases when higher loads are applied. A sensitivity analysis to muscle force–length relationship is provided to determine the model's limitations. This model pointed out the importance of taking into account the changes in muscle length to evaluate the effect of spinal loads beyond the safe limit that cannot be evaluated experimentally and to predict the trunk instability under vertical load.     

Method and computer-aided system of intensive health recovery for estimation and correction of the psychophysical condition of an individual

A method for evaluating psychophysical condition and behavioral optimization of lifestyle, including selection of training loads, was developed on the basis of questionnaire data and simple physiological parameters such as muscle strength, load intensity, blood pressure, heart rate, and expiratory breath holding time at rest, during graded exercises, and during recovery. For evaluating the functional condition, an original variant of the bicycle ergometric test or step test was used as the basic method and standard tests with training equipment and routine exercises were used as additional methods. The method was implemented as a computer program, Health Regulator.     

Effect of load position on muscle forces, internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.     

Validation of a personalized curved muscle model of the lumbar spine during complex dynamic exertions

Previous curved muscle models have typically examined their robustness only under simple, single-plane static exertions. In addition, the empirical validation of curved muscle models through an entire lumbar spine has not been fully realized. The objective of this study was to empirically validate a personalized biologically-assisted curved muscle model during complex dynamic exertions. Twelve subjects performed a variety of complex lifting tasks as a function of load weight, load origin, and load height. Both a personalized curved muscle model as well as a straight-line muscle model were used to evaluate the model’s fidelity and prediction of three-dimensional spine tissue loads under different lifting conditions. The curved muscle model showed better model performance and different spinal loading patterns through an entire lumbar spine compared to the straight-line muscle model. The curved muscle model generally showed good fidelity regardless of lifting condition. The majority of the 600 lifting tasks resulted in a coefficient of determination (R²) greater than 0.8 with an average of 0.83, and the average absolute error less than 15% between measured and predicted dynamic spinal moments. As expected, increased load and asymmetry were generally found to significantly increase spinal loads, demonstrating the ability of the model to differentiate between experimental conditions. A curved muscle model would be useful to estimate precise spine tissue loads under realistic circumstances. This precise assessment tool could aid in understanding biomechanical causal pathways for low back pain.     

Effect of load position on muscle forces,internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.     

Low-back loading in lifting two loads beside the body compared to lifting one load in front of the body

Low-back load during manual lifting is considered an important risk factor for the occurrence of low-back pain. Splitting a load, so it can be lifted beside the body (one load in each hand), instead of in front of the body, can be expected to reduce low-back load. Twelve healthy young men lifted 10 and 20-kg wide and narrow loads in front of the body (the single-load lifts). These single-load lifts were compared to a lifting condition in which two 10-kg loads (a total of 20 kg) were lifted beside the body (the split-load lift). Lifts were performed from an initial hand height of 29 cm with four different lifting techniques (stoop, squat, straddle and kneeling techniques). Using measured kinematics, ground reaction forces, and electromyography, low-back loading (3D net moments and spinal forces at the L5/S1 joint) was estimated. Lifting a 20-kg split-load instead of a 20-kg single-load resulted in most cases in a reduction (8–32%) of peak L5/S1 compression forces. The magnitude of the reduction was roughly comparable to halving the load mass and depended on lifting technique and load width. The effects of load-splitting could largely be explained by changes in horizontal distance between the load and L5/S1.     

Biomechanical implications of lumbar spinal ligament transection

Many lumbar spine surgeries either intentionally or inadvertently damage or transect spinal ligaments. The purpose of this work was to quantify the previously unknown biomechanical consequences of isolated spinal ligament transection on the remaining spinal ligaments (stress transfer), vertebrae (bone remodelling stimulus) and intervertebral discs (disc pressure) of the lumbar spine. A finite element model of the full lumbar spine was developed and validated against experimental data and tested in the primary modes of spinal motion in the intact condition. Once a ligament was removed, stress increased in the remaining spinal ligaments and changes occurred in vertebral strain energy, but disc pressure remained similar. All major biomechanical changes occurred at the same spinal level as the transected ligament, with minor changes at adjacent levels. This work demonstrates that iatrogenic damage to spinal ligaments disturbs the load sharing within the spinal ligament network and may induce significant clinically relevant changes in the spinal motion segment.     

Spinal stability and role of passive stiffness in dynamic squat and stoop lifts

The spinal stability and passive-active load partitioning under dynamic squat and stoop lifts were investigated as the ligamentous stiffness in flexion was altered. Measured in vivo kinematics of subjects lifting 180 N at either squat or stoop technique was prescribed in a nonlinear transient finite element model of the spine. The Kinematics-driven approach was utilized for temporal estimation of muscle forces, internal spinal loads and system stability. The finite element model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles and trunk dynamic characteristics while subject to measured kinematics and gravity/external loads. Alterations in passive properties of spine substantially influenced muscle forces, spinal loads and system stability in both lifting techniques, though more so in stoop than in squat. The squat technique is advocated for resulting in smaller spinal loads. Stability of spine in the sagittal plane substantially improved with greater passive properties, trunk flexion and load. Simulation of global extensor muscles with curved rather than straight courses considerably diminished loads on spine and increased stability throughout the task.     

Response of trunk muscle coactivation to changes in spinal stability

The goal of this effort was to assess the neuromuscular response to changes in spinal stability. Biomechanical models suggest that antagonistic co-contraction may be related to stability constraints during lifting exertions. A two-dimensional biomechanical model of spinal equilibrium and stability was developed to predict trunk muscle co-contraction as a function of lifting height and external load. The model predicted antagonistic co-contraction must increase with potential energy of the system even when the external moment was maintained at a constant value. Predicted trends were compared with measured electromyographic (EMG) data recorded during static trunk extension exertions wherein subjects held weighted barbells at specific horizontal and vertical locations relative to the lumbo-sacral spine junction. The task was designed to assure the applied moment was identical during each height condition, thereby changing potential energy without influencing moment. Measured EMG activity in the trunk flexors increased with height of the external load as predicted by the model. Gender difference in spinal stability were also noted. Results empirically demonstrate that the neuromuscular system responds to changes in spinal stability and provide insight into the recruitment of trunk muscle activity.     

The onset and progression of spinal injury: a demonstration of neutral zone sensitivity.

Spinal injuries are a great cost to society and the afflicted individuals. It is well known that most spinal injuries are not bony fractures but rather soft tissue lesions falling in the 'subfailure' region. For the clinical diagnosis of spinal injuries, abnormal motion patterns under physiological loads are considered an important factor. The purpose of the present study was to determine the onset and progression of spinal injury, and compare the sensitivity of three motion parameters: neutral zone (NZ), elastic zone (EZ), and range of motion (ROM). Spinal injury was defined as a significant increase in any of the three motion parameters. A repeatable high-speed flexion-compression load vector was applied individually to six porcine cervical spine specimens. Several impacts of increasing severity were applied to each specimen. After each impact, flexion-extension motion was measured. Neutral zone was the residual deformation from the neutral position to the position under zero load at the start of the final load cycle. Elastic zone was the displacement from zero load to the maximum load on the final load cycle. Range of motion was the sum of the neutral and elastic zones. The first significant increase in motion was determined by the neutral zone parameter with few observable anatomic lesions on the specimens. This was the onset of spinal injury. The next significant motion increase was also determined by the neutral zone parameter. After this motion increase, termed the progression of injury, ligament ruptures were observed in some specimens. It was concluded that the neutral zone was the most sensitive motion parameter in defining the onset and progression of spinal injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spinal stiffness in asymptomatic subjects

The objective of the study was to measure postero-anterior stiffness of thoracolumbar spine from normal asymptomatic subjects at T₄, T₉, and L₂ levels using a standardized device and protocol. Sixteen volunteer subjects (eight males and eight females) meeting the inclusion and exclusion criteria were recruited for the study. Their T₄, T₉, and L₂ spinous processes were identified and marked. These spinous processes were cyclically loaded with 22.5 N, 45 N, 90 N, and 135 N fixed forces at 0.1 Hz in postero-anterior direction by a computer controlled and operated Therapeutic Spinal Mobilizer (TSM) for five cycles to the level of subject’s acceptance of the load magnitude. The magnitude of the force and displacement experienced at the spinal level were recorded using a load cell and linear variable differential transducer. The stiffness was obtained from the slope of the load/deformation curve. The stiffness values were subjected to analysis of variance to determine the effect of independent variables. The stiffness at different levels was significantly different (p < 0.0001) and it was significantly affected by the testing load (p < 0.0001). The age, sex, height and weight were not significantly associated with the stiffness, neither were the cycles at the same load. The postero-anterior stiffness of the thoracolumbar spine is different at different spinal levels and varies with testing loads.     

Passive and dynamic muscle architecture during transverse loading for gastrocnemius medialis in man

External forces from our environment impose transverse loads on our muscles. Studies in rats have shown that transverse loads result in a decrease in the longitudinal muscle force. Changes in muscle architecture during contraction may contribute to the observed force decrease. The aim of this study was to quantify changes in pennation angle, fascicle dimensions, and muscle thickness during contraction under external transverse load.Electrical stimuli were elicited to evoke maximal force twitches in the right calf muscles of humans. Trials were conducted with transverse loads of 2, 4.5, and 10 kg. An ultrasound probe was placed on the medial gastrocnemius in line with the transverse load to quantify muscle characteristics during muscle twitches.Maximum twitch force decreased with increased transverse muscle loading. The 2, 4.5, and 10 kg of transverse load showed a 9, 13, and 16% decrease in longitudinal force, respectively. Within the field of view of the ultrasound images, and thus directly beneath the external load, loading of the muscle resulted in a decrease in the muscle thickness and pennation angle, with higher loads causing greater decreases. During twitches the muscle transiently increased in thickness and pennation angle, as did fascicle thickness. Higher transverse loads showed a reduced increase in muscle thickness. Smaller increases in pennation angle and fascicle thickness strain also occurred with higher transverse loads.This study shows that increased transverse loading caused a decrease in ankle moment, muscle thickness, and pennation angle, as well as transverse deformation of the fascicles.     

A frontal plane model of the lumbar spine subjected to a follower load: implications for the role of muscles

Compression on the lumbar spine is 1000 N for standing and walking and is higher during lifting. Ex vivo experiments show it buckles under a vertical load of 80-100 N. Conversely, the whole lumbar spine can support physiologic compressive loads without large displacements when the load is applied along a follower path that approximates the tangent to the curve of the lumbar spine. This study utilized a two-dimensional beam-column model of the lumbar spine in the frontal plane under gravitational and active muscle loads to address the following question: Can trunk muscle activation cause the path of the internal force resultant to approximate the tangent to the spinal curve and allow the lumbar spine to support compressive loads of physiologic magnitudes? The study identified muscle activation patterns that maintained the lumbar spine model under compressive follower load, resulting in the minimization of internal shear forces and bending moments simultaneously at all lumbar levels. The internal force resultant was compressive, and the lumbar spine model, loaded in compression along the follower load path, supported compressive loads of physiologic magnitudes with minimal change in curvature in the frontal plane. Trunk muscles may coactivate to generate a follower load path and allow the ligamentous lumbar spine to support physiologic compressive loads.     

In situ chondrocyte deformation with physiological compression of the feline patellofemoral joint

The mechanical environment is an important factor affecting the maintenance and adaptation of articular cartilage, and thus the function of the joint and the progression of joint degeneration. Recent evidence suggests that cartilage deformation caused by mechanical loading is directly associated with deformation and volume changes of chondrocytes. Furthermore, in vitro experiments have shown that these changes in the mechanical states of chondrocytes correlate with a change in the biosynthetic activity of cartilage cells. The purpose of this study was to apply our knowledge of contact forces within the feline patellofemoral joint to quantify chondrocyte deformation in situ under loads of physiological magnitude. A uniform, static load of physiological magnitude was applied to healthy articular cartilage still fully intact and attached to its native bone. The compressed cartilage was then chemically fixed to enable the evaluation of cartilage strain, chondrocyte deformation and chondrocyte volumetric fraction. Patella and femoral groove articular cartilages differ in thickness, chondrocyte aspect ratio, and chondrocyte volumetric fraction in both magnitude and depth distribution. Furthermore, when subjected to the same compressive loads, changes to all of these parameters differ in magnitude and depth distribution between patellar and femoral groove articular cartilage. This evidence suggests that significant chondrocyte deformation likely occurs during in vivo joint loading, and may influence chondrocyte biosynthetic activity. Furthermore, we hypothesise that the contrasts between patella and femoral groove cartilages may explain, in part, the site-specific progression of osteoarthritis in the patellofemoral joint of the feline anterior cruciate ligament transected knee.     

Altered tissue properties induce changes in cancellous bone architecture in aging and diseases

The mechanical properties of cancellous bone depend on its architecture and the tissue properties of the mineralized matrix. The architecture is continuously adapted to external loads. In this paper, it was assumed that changes in tissue properties leading to changes in tissue deformation can induce adaptation of the architecture. We asked whether changes in cancellous bone architecture with aging and in e.g. early osteoarthrosis can be explained from changes in tissue properties.This was investigated using computer models in which the cancellous architecture was adapted to external loads. Bone tissue with deformations below a certain threshold was resorbed, deformations above another threshold induced formation. Deformations between these two boundaries, in the 'lazy zone', did not induce bone adaptation. The effects of changes in bone tissue stiffness on bone mass, global stiffness and architecture were investigated. The bone gain (40-60%) resulting from a 50% decrease in tissue stiffness (simulating diseased tissue) was much larger than the bone loss (2-30%) resulting from a 50% increase in tissue stiffness (simulating highly mineralized, old tissue). The adaptation induced by a decrease in tissue stiffness resulted in an almost constant stiffness in the main load bearing direction, but the transversal stiffness decreased. An increased tissue stiffness resulted in a higher stiffness in the main direction and overcompensation in the transversal directions: the global stiffness could become even smaller than the stiffness of the original model. Concluding, we showed that changes in trabecular bone in aging and diseases can be partly explained from changes in tissue properties.     

数据记忆动物游泳测试仪的研制

目的研制一种用于检测动物负载游泳状况及过程的仪器,用于动物疲劳游泳试验。方法采用不同直径的可调换加载钢球、恒温水池、接近传感器信号转换、51系列单片微机控制和记忆信号。结果研制出一台可同时做六路平行实验的动物游泳测试仪,自动记忆动物在加载的情况下抗疲劳游泳的全过程。结论经36例小鼠实验证明,效果良好,该仪器为动物负载游泳实验提供了一种全新的测试方法。     

Titanium as an implant material for rods of transpedicular instrumentation of the lumbar spine]

BACKGROUND AND AIM: Titanium alloys are increasingly being used as an implant material in orthopaedics and for spinal instrumentation. In this study a metallographic analysis and mechanical testing were performed to evaluate the resistance of rods of Ti-A16-V4 in particular to tensile forces. METHOD: The surface texture of unprepared Ti-A16-V4 and a rod of the same material for spinal instrumentation were evaluated in a metallographic analysis using light microscopy and electron microscopy. Tensile strength measurements were performed on 2 rods, and the strength of the connection between rod and pedicle screws was tested in 9 cases. An electron microscopic analysis of surface changes of the connections between rod and pedicle screws after loading was performed. RESULTS: The titanium alloy Ti-A16-V4 has a mill-annealed appearance, which has a high resistance to tearing under stress. Titanium rods show high tensile strength before failure under loading. The connection between rod and pedicle screws also as high resistance to tensile loads (> 27 kN) with only little deformation of the connecting surface and no tearing. CONCLUSION: The titanium alloy Ti-A16-V4 is an appropriate material for dorsal spinal instrumentation rods because of its low weight, high biocompability and high tensile strength.     

Effects of elastic loading on porcine trachealis muscle mechanics

To shorten in vivo, airway smooth muscle must overcome an elastic load provided by cartilage and lung parenchyma. We examined the effects of linear elastic loads (0.2-80 g/cm) on the active changes in porcine trachealis muscle length and tension in response to electrical field stimulation in vitro. Increasing elastic loads produced an exponential decrease in the shortening and velocity of shortening while causing an increase in tension generation of muscle strips stimulated by electrical field stimulation. Shortening was decreased by 50% at a load of 8 g/cm. At small elastic loads (less than or equal to 1 g/cm) contractile responses approximated isotonic responses (shortening approximately 60% of starting length), whereas at large loads (20 g/cm) responses approximated isometric responses with minimal shortening (20%). We conclude that elastic loading significantly alters the mechanical properties of airway smooth muscle in vitro, effects that are likely relevant to the loads against which the smooth muscle must contract in vivo.     

Stretch along the craniocaudal axis improves shape recoverability of the spinal cord

The spinal cord is physiologically stretched along the craniocaudal axis, and is subjected to tensile stress. The purpose of this study was to examine the effect of the tensile stress on morphological plasticity of the spinal cord under compression and decompression condition. The C1-T2 spinal column was excised from 4 rabbits. The laminae and lateral masses were removed. After excision of surrounding structures, a small rod was placed on the spinal cord. The rod was connected with a pan of the scale balance. Varying the weight between 0 and 20g on the other scalepan, the indentation of the rod was measured. Then, the spinal cord was cut transversely to remove longitudinal tensile stress. The samples were measured again with the same protocol at point 10mm caudal to each pre-measured point on the spinal cord. The shape recovery rate was calculated. The length of the spinal cord decreased by 9.7% after the separation. The maximum indentation was 2.1mm (mean) at 20g, and did not differ between the separated and un-separated cords. The recovery rate was not significantly different between the separated and un-separated cords until 3g. At the load under 3g, the recovery rate after the separation was significantly lower than that before the separation. The tensile stress along the craniocaudal axis in the spinal cord did not affect the spinal cord deformation in response to the compression, but it did affect the shape recoverability after the decompression.     

Under how wide a set of conditions will nonrandom mating occur in Raphanus sativus (Brassicaceae)?

Studies of the weedy annual Raphanus sativus have demonstrated that nonrandom mating, a prerequisite for sexual selection, can occur in greenhouse plants. To determine whether this nonrandom mating pattern can occur under a wide range of conditions, including conditions that might occur in the field, we considered variation in both maternal condition and pollen load size. Maternal condition was varied by altering the watering regime. Pollen load size was varied from approximately 26 to 343 pollen grains per stigma. At the smallest pollen load size, patterns of seed paternity were altered in two of the three pollen donor pairs; seed paternity became more equal among donors. For one of three pollen donor pairs, seed paternity was more divergent among donors on stressed maternal plants. Finally, for one pollen donor pair, rank order of pollen donor performance changed from the medium to the small pollen loads on stressed vs. control maternal plants. Thus, some field conditions may alter patterns of nonrandom mating in wild radish.