Exploring the geometric and mechanical characteristics of the spine musculature to provide rotational stiffness to two spine joints in the neutral posture (original) (raw)
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Medical Engineering & Physics, 2017
Inverse dynamic musculoskeletal human body models are commonly used to predict the spinal loads and trunk muscle forces. These models include rigid body segments, mechanical joints, active and passive structural components such as muscles, tendons and ligaments. Several studies used simple definition of lumbar spinal discs idealized as spherical joints with infinite translational stiffness. The aim of the current sensitivity study was to investigate the influence of disc translational stiffness (shear and compressive stiffness) on the joint kinematics and forces in intervertebral discs (L1 −L5), trunk muscles and ligaments for an intermediately flexed position (55 °). Based on in vitro data, a range of disc shear stiffness (10 0 −20 0 N/mm) and compressive stiffness (190 0 −270 0 N/mm) was considered in the model using the technique of force dependent kinematics (FDK). Range of variation in spinal loads, trunk muscle forces and ligaments forces were calculated (with & without load in hands) and compared with the results of reference model (RM) having infinite translational stiffness. The discs' centers of rotation (CoR) were computed for L3 −L4 and L4 −L5 motion segments. Between RM and FDK models, maximum differences in com pressive forces were 7% (L1 −L2 & L2 −L3), 8% (L3 −L4) and 6% (L4 −L5) whereas in shear forces 35% (L1 −L2), 47% (L2 −L3), 45% (L3 −L4) and more than 100% in L4 −L5. Maximum differences in the sum of global and local muscle forces were approximately 10%, whereas in ligament forces were 27% (supraspinous), 40% (interspinous), 56% (intertransverse), 58% (lig. flavum) and 100% (lig. posterior). The CoRs were predicted posteriorly, below (L3 −L4) and in the disc (L4 −L5). FDK model predicted lower spinal loads, ligament forces and varied distribution of global and local muscle forces. Consideration of translational stiffnesses influenced the model results and showed increased differences with lower stiffness values.
Spinal stiffness increases with axial load: another stabilizing consequence of muscle action
Journal of Electromyography and Kinesiology, 2003
This paper addresses the role of lumbar spinal motion segment stiffness in spinal stability. The stability of the lumbar spine was modelled with loadings of 30 Nm or 60 Nm efforts about each of the three principal axes, together with the partial body weight above the lumbar spine. Two assumptions about motion segment stiffness were made: First the stiffness was represented by an 'equivalent beam' with constant stiffness properties; secondly the stiffness was updated based on the motion segment axial loading using a relationship determined experimentally from human lumbar spinal specimens tested with 0, 250 and 500 N of axial compressive preload. Two physiologically plausible muscle activation strategies were used in turn for calculating the muscle forces required for equilibrium. Stability analyses provided estimates of the minimum muscle stiffness required for stability. These critical muscle stiffness values decreased when preload effects were used in estimating spinal stiffness in all cases of loadings and muscle activation strategies, indicating that stability increased. These analytical findings emphasize that the spinal stiffness as well as muscular stiffness is important in maintaining spinal stability, and that the stiffness-increasing effect of 'preloading' should be taken into account in stability analyses.
Majlesi Journal of Mechatronic Systems, 2017
Many spinal problems which could lead to pain are associated with the instability of spine. Experiments have shown that the ligamentous spine is inherently unstable, because the isolated lumbar spine buckles under approximately 90N load. Spinal deformities can originate instability of spine, but studies have shown that in normal state, combination of the various mechanisms, such as muscle forces and intra-abdominal pressure render the spine stable. In this research, we try to find out the relationship between spinal deformity and lumbar muscles activity. According to the biomechanical and geometrical complexity of the spine, it’s crucial to use biomechanical models in order to study the stability of the spine. Granata and Wilson presented a simple two-links model of lumbar spine considering twelve muscles, and by satisfying the mechanical stability conditions, they calculated the muscular forces for different physical activities. Through experiments conducted using Electromyography ...
Musculoskeletal support of lumbar spine stability
Pathophysiology, 2005
Using a biomechanical model and experimental data the self-stabilising behaviour of antagonistic trunk muscles was analyzed. The biomechanical model is constituted of a pair of antagonistic Hill-type muscles, their geometric arrangement with respect to the spine, and the instantaneous centre of rotation in frontal plane. Using Ljapunov's theory, the stability of certain motion and loading situations was analyzed. Applying a sensitivity analysis, the influence of different muscle properties and the geometric arrangement on stability was investigated.
Journal of Morphological Sciences
Background Changes in the load-displacement relationship in spine segments suggesting alterations in biomechanical stiffness may not yield significant clinical information. Changes in Spine stiffness may arise secondary to neuro-muscular adjustments in the para-spinal muscles and may not be associated with physical anatomical laxity or motion restrictions at segmental articulations. Segmental stiffness may vary dynamically at different zones within the range-of-motion, suggesting a non-linear load-displacement relationship during motion. There is no linear, mechanistic relationship between spine pain and biomechanical markers of spine instability. Objective To review diagnostic assessment approaches of spine instability based on palpatory techniques, end-of-range radiography and imaging in light of our current understanding of biomechanical spine stability. Method The Medline and PubMed databases were screened for primary medical and engineering research articles and reviews on spin...
Structural behavior of human lumbar spinal motion segments
Journal of Biomechanics, 2004
The objectives of this study were to obtain linearized stiffness matrices, and assess the linearity and hysteresis of the motion segments of the human lumbar spine under physiological conditions of axial preload and fluid environment. Also, the stiffness matrices were expressed in the form of an 'equivalent' structure that would give insights into the structural behavior of the spine. Mechanical properties of human cadaveric lumbar L2-3 and L4-5 spinal motion segments were measured in six degrees of freedom by recording forces when each of six principal displacements was applied. Each specimen was tested with axial compressive preloads of 0, 250 and 500 N. The displacements were four slow cycles of 70.5 mm in anterior-posterior and lateral displacements, 70.35 mm axial displacement, 71.5 lateral rotation and 71 flexion-extension and torsional rotations. There were significant increases with magnitude of preload in the stiffness, hysteresis area (but not loss coefficient) and the linearity of the loaddisplacement relationship. The mean values of the diagonal and primary off-diagonal stiffness terms for intact motion segments increased significantly relative to values with no preload by an average factor of 1.71 and 2.11 with 250 and 500 N preload, respectively (all eight tests po0:01). Half of the stiffness terms were greater at L4-5 than L2-3 at higher preloads. The linearized stiffness matrices at each preload magnitude were expressed as an equivalent structure consisting of a truss and a beam with a rigid posterior offset, whose geometrical properties varied with preload. These stiffness properties can be used in structural analyses of the lumbar spine. r
Muscle force evaluation and the role of posture in human lumbar spine under compression
European Spine Journal, 2002
Changes in the sagittal curvature of the human lumbar spine (i.e. lordosis) and pelvic orientation have been recorded during various recreational and occupational activities of daily living. Such alterations affect the distribution of gravity and external loads among passive and active sub-systems of the human trunk, thus influencing the stability margin of the system and stress/strain values in comprising tissues. Previous in vivo studies have demonstrated the compensatory changes in the lumbar posture in a variety of conditions: in micro-gravity, under load, in supine position, sitting on chairs with different back inclinations, wearing high-heeled shoes, and in groups of normal and low-back pain populations in standing position . In vivo measurements of normal volunteers, with no instruction on the posture, carrying up to 445 N loads symmetrically in the hands while standing have shown that the pelvis rotates posteriorly and the lumbar spine flattens as the loads increase . There was, however, negligible surface electromyographic (EMG) activity in back superficial muscles, with or without loads in the hands . Although, in general, squat lifting (i.e. knees bent) is considered to be safer than the stoop lifting (i.e. knees straight) in reducing the net moment on the spine, the respective benefits of preserving or changing lordosis during lifting remains less understood.