Biomechanical Properties of Paraspinal Muscles Influence Spinal Loading—A Musculoskeletal Simulation Study

Abstract

Paraspinal muscles are vital to the functioning of the spine. Changes in muscle physiological cross-sectional area significantly affect spinal loading, but the importance of other muscle biomechanical properties remains unclear. This study explored the changes in spinal loading due to variation in five muscle biomechanical properties: passive stiffness, slack sarcomere length (SSL), in situ sarcomere length, specific tension, and pennation angle. An enhanced version of a musculoskeletal simulation model of the thoracolumbar spine with 210 muscle fascicles was used for this study and its predictions were validated for several tasks and multiple postures. Ranges of physiologically realistic values were selected for all five muscle parameters and their influence on L4-L5 intradiscal pressure (IDP) was investigated in standing and 36° flexion. We observed large changes in IDP due to changes in passive stiffness, SSL, in situ sarcomere length, and specific tension, often with interesting interplays between the parameters. For example, for upright standing, a change in stiffness value from one tenth to 10 times the baseline value increased the IDP only by 91% for the baseline model but by 945% when SSL was 0.4 μm shorter. Shorter SSL values and higher stiffnesses led to the largest increases in IDP. More changes were evident in flexion, as sarcomere lengths were longer in that posture and thus the passive curve is more influential. Our results highlight the importance of the muscle force-length curve and the parameters associated with it and motivate further experimental studies on in vivo measurement of those properties.

Dysfunctional paraspinal muscles in adult spinal deformity patients lead to increased spinal loading

“…To explore the influence of measured biomechanical properties on spinal loading, an enhanced validated musculoskeletal model of the lumbar spine with 210 muscles was employed [ 32 ]. Briefly, the model consisted of the sacrum and pelvis (both fixed to the ground), five mobile lumbar vertebrae connected through 6-DOF springs (representing the stiffness of each pair of adjacent vertebrae with their connecting ligaments, facet joints, and intervertebral disc along three translational and three rotational degrees of freedom); and the thoracic spine that was rigidly fixed to the L1.…”

“…Briefly, the model consisted of the sacrum and pelvis (both fixed to the ground), five mobile lumbar vertebrae connected through 6-DOF springs (representing the stiffness of each pair of adjacent vertebrae with their connecting ligaments, facet joints, and intervertebral disc along three translational and three rotational degrees of freedom); and the thoracic spine that was rigidly fixed to the L1. Muscles were modeled as Hill-type musculotendon actuators, whose active and passive forces were determined using the force–length and force–velocity curves parametrized by Millard et al [ 33 ] (see [ 32 ] for further details on muscle properties and calculation of its forces).…”

Muscle-driven forward dynamic active hybrid model of the lumbosacral spine: combined FEM and multibody simulation

“…The parameters for pennation angle, passive stiffness, sarcomere length, and specific muscle tension were constant for most of the muscle groups. However, a recent simulation study ( Malakoutian et al, 2022 ) showed the relevance of these paraspinal muscle parameters on the predicted spinal loads. To use reference material parameters, we scaled these linearly based on muscle cross-sections and body weight.…”

“…Reported values for K vary between 10 and 100 N/cm 2 ( Daggfeldt and Thorstensson, 2003 ; Hansen et al, 2006 ). In models of the lower back, most commonly values of 46 ( Bogduk et al, 1992 ; Stokes and Gardner-Morse, 1995 ; Christophy et al, 2012 ), 60 ( Arjmand and Shirazi-Adl, 2006a ), 90 ( Arshad et al, 2016 ), or 100 N/cm 2 ( Bruno et al, 2015 ; Bayoglu et al, 2019 ; Favier et al, 2021a ; Lerchl et al, 2022 ; Malakoutian et al, 2022 ) were assumed. Thus, we tested values of 46, 73, and 100 N/cm 2 for K , expected ≤ 1.0°, and that no muscle was fully activated by the TC.…”

Multibody Models of the Thoracolumbar Spine: A Review on Applications, Limitations, and Challenges

“…The stabilizing influence of intra-abdominal pressure (IAP) on the spine has been widely studied [124,125]. However, only a few MBS models consider its effects [38,60,63,70,77]. In consequence, spinal loads in lifting tasks or the inclination of the upper body are assumed to be overestimated in the MBS modeling of the spine.…”