Quantitative anatomy of the lumbar musculature

Stokes, Ian A. F.; Gardner‐Morse, Mack

doi:10.1016/s0021-9290(98)00164-x

Cited by 142 publications

(98 citation statements)

References 19 publications

(25 reference statements)

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“…A previously reported mathematical model of the lumbar spine and its musculature 5,6 was used as the basis for this study. The spinal geometry was modified to represent five different magnitudes of scoliosis deformity (Figure 1 six motion segments of the lumbar spine (T12-L1 through L5-S1), and the muscles that cross those levels.…”

Section: Methodsmentioning

confidence: 99%

Muscle Activation Strategies and Symmetry of Spinal Loading in the Lumbar Spine With Scoliosis

Stokes

Gardner‐Morse

2004

Spine

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Study Design. Biomechanical analysis of muscle and spinal forces in a lumbar spine with scoliosis.Objectives. To calculate spinal loading asymmetry and its dependence on muscle activation strategy.Summary of Background Data. It is commonly assumed that a spine with scoliosis experiences greater loading on the concave side and that this asymmetric loading causes asymmetric growth and progression of deformity. However, neither the magnitude of the asymmetric loading imposed on the spine as a function of the scoliosis curve nor the resulting mechanically altered vertebral growth and disc remodeling have been quantified.Methods. Spinal loading was estimated in a lumbar spine model with increasing degrees of scoliosis. External loading was each of three pure moments or forces acting at T12, with magnitudes of either 50% or 75% of maximum effort. For each external loading, the muscle activation patterns were determined with each of three different muscle activation strategies in an optimization model: 1) minimize the sum of cubed muscle stresses; 2) minimize spinal asymmetric load (i.e., "follower load"); and 3) reverse the spinal load asymmetry (increased compression on convex side) at the level of the apex.Results. The first strategy produced loading that tended to increase the curve magnitude, with the resultant force acting at up to 15 mm lateral to the intervertebral disc center. Both Strategies 2 and 3 had increased muscle stress averaging between 42% and 75%.Conclusions. We speculate that individuals with scoliosis can adopt different muscle activation strategies and that these strategies may determine whether or not the spinal loading causes scoliosis progression during growth. Muscle activation patterns generating spinal loading that does not promote curve progression during growth have greater physiologic cost.Key words: scoliosis, biomechanics, muscles, deformity. Spine 2004;29:2103-2107Progression of scoliosis deformity during growth is thought to be associated with asymmetric loading of the spine that produces asymmetric growth. It is assumed that a spine that is straight in the coronal plane is habitually loaded symmetrically, whereas a spine with scoliosis is asymmetrically loaded. Further, there is speculation that the asymmetric loading causes progressive deformity, especially while the spine continues to grow. The "vicious cycle" theory of scoliosis progression 1-3 proposes that scoliosis causes loading of the spine that is asymmetric in the coronal plane, and that vertebral growth and disc remodeling respond to the chronic presence of these asymmetric forces. Progression of scoliosis is observed to occur when there is rapid growth of the spine. 4 This notion that progression of spinal deformity results from mechanical modulation of growth that in turn produces asymmetrically wedged vertebrae and discs is intuitively attractive, and it provides a supposed rationale for scoliosis management with braces.While qualitatively plausible, the vicious cycle theory lacks quantification of two crucial componen...

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Section: Methodsmentioning

confidence: 99%

Muscle Activation Strategies and Symmetry of Spinal Loading in the Lumbar Spine With Scoliosis

Stokes

Gardner‐Morse

2004

Spine

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“…1) [6,8,10,94]. In order to accurately simulate the curved path of global muscles (i.e., longissimus thoracis pars thoracic and iliocostalis lumborum pars thoracic) at flexion angles considered in this study, these muscles were constrained to follow a curved path whenever their distances from T12 to L5 vertebral centers at undeformed configuration diminished beyond~10% (i.e., to reach the limit values of 53, 53, 55, 56, 54 and 48 mm for the global longissimus and 58, 56, 56, 55, 52 and 45 mm for the global iliocostalis at T12-L5 vertebrae, respectively).…”

Section: Muscle Model and Muscle Force Calculationmentioning

confidence: 99%

Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads

2006

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Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/ external loads. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting~2 s, the effect of inertia and damping was not, in general, important. Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force).

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“…The cost function proposed by Crowninshield and Brand [9] to predict muscle activation with the aim of minimising muscle fatigue was used in the current model, and has been validated for this purpose previously [10,11]. Skeletal and muscular trunk anatomy input data were derived from a previous study describing 180 muscles [48]. Optimization calculations were performed using the constrained optimization function ('fmincon') in the Matlab 6.5 (The Mathworks Inc., Natick, MA, USA) optimization toolbox, to determine a vector of muscle activation minimising the cost function described above.…”

Section: Load Estimationsmentioning

confidence: 99%

The effect of osteoporotic vertebral fracture on predicted spinal loads in vivo

et al. 2006

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The aetiology of osteoporotic vertebral fractures is multi-factorial, and cannot be explained solely by low bone mass. After sustaining an initial vertebral fracture, the risk of subsequent fracture increases greatly. Examination of physiologic loads imposed on vertebral bodies may help to explain a mechanism underlying this fracture cascade. This study tested the hypothesis that model-derived segmental vertebral loading is greater in individuals who have sustained an osteoporotic vertebral fracture compared to those with osteoporosis and no history of fracture. Flexion moments, and compression and shear loads were calculated from T2 to L5 in 12 participants with fractures (66.4 ± 6.4 years, 162.2 ± 5.1 cm, 69.1 ± 11.2 kg) and 19 without fractures (62.9 ± 7.9 years, 158.3 ± 4.4 cm, 59.3 ± 8.9 kg) while standing. Static analysis was used to solve gravitational loads while muscle-derived forces were calculated using a detailed trunk muscle model driven by optimization with a cost function set to minimise muscle fatigue. Least squares regression was used to derive polynomial functions to describe normalised load profiles. Regression co-efficients were compared between groups to examine differences in loading profiles. Loading at the fractured level, and at one level above and below, were also compared between groups. The fracture group had significantly greater normalised compression (p = 0.0008) and shear force (p < 0.0001) profiles and a trend for a greater flexion moment profile. At the level of fracture, a significantly greater flexion moment (p = 0.001) and shear force (p < 0.001) was observed in the fracture group. A greater flexion moment (p = 0.003) and compression force (p = 0.007) one level below the fracture, and a greater flexion moment (p = 0.002) and shear force (p = 0.002) one level above the fracture was observed in the fracture group. The differences observed in multi-level spinal loading between the groups may explain a mechanism for increased risk of subsequent vertebral fractures. Interventions aimed at restoring vertebral morphology or reduce thoracic curvature may assist in normalising spine load profiles.

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Quantitative anatomy of the lumbar musculature

Cited by 142 publications

References 19 publications

Muscle Activation Strategies and Symmetry of Spinal Loading in the Lumbar Spine With Scoliosis

Muscle Activation Strategies and Symmetry of Spinal Loading in the Lumbar Spine With Scoliosis

Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads

The effect of osteoporotic vertebral fracture on predicted spinal loads in vivo

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