TY - JOUR
T1 - Load-sharing in the lumbosacral spine in neutral standing & flexed postures – A combined finite element and inverse static study
AU - Liu, Tao
AU - Khalaf, Kinda
AU - Naserkhaki, Sadegh
AU - El-Rich, Marwan
N1 - Funding Information:
This study is financially supported by the China Scholarship Council and NSERC Discovery Grant ( 402046-2013 ), Canada.
Publisher Copyright:
© 2017 Elsevier Ltd
PY - 2018/3/21
Y1 - 2018/3/21
N2 - Understanding load-sharing in the spine during in-vivo conditions is critical for better spinal implant design and testing. Previous studies of load-sharing that considered actual spinal geometry applied compressive follower load, with or without moment, to simulate muscle forces. Other studies used musculoskeletal models, which include muscle forces, but model the discs by simple beams or spherical joints and ignore the articular facet joints. This study investigated load-sharing in neutral standing and flexed postures using a detailed Finite Element (FE) model of the ligamentous lumbosacral spine, where muscle forces, gravity loads and intra-abdominal pressure, as predicted by a musculoskeletal model of the upper body, are input into the FE model. Flexion was simulated by applying vertebral rotations following spine rhythm measured in a previous in-vivo study, to the musculoskeletal model. The FE model predicted intradiscal pressure (IDP), strains in the annular fibers, contact forces in the facet joints, and forces in the ligaments. The disc forces and moments were determined using equilibrium equations, which considered the applied loads, including muscle forces and IDP, as well as forces in the ligaments and facet joints predicted by the FE model. Load-sharing was calculated as the portion of the total spinal load carried along the spine by each individual spinal structure. The results revealed that spinal loads which increased substantially from the upright to the flexed posture were mainly supported by the discs in the upright posture, whereas the ligaments’ contribution in resisting shear, compression, and moment was more significant in the flexed posture.
AB - Understanding load-sharing in the spine during in-vivo conditions is critical for better spinal implant design and testing. Previous studies of load-sharing that considered actual spinal geometry applied compressive follower load, with or without moment, to simulate muscle forces. Other studies used musculoskeletal models, which include muscle forces, but model the discs by simple beams or spherical joints and ignore the articular facet joints. This study investigated load-sharing in neutral standing and flexed postures using a detailed Finite Element (FE) model of the ligamentous lumbosacral spine, where muscle forces, gravity loads and intra-abdominal pressure, as predicted by a musculoskeletal model of the upper body, are input into the FE model. Flexion was simulated by applying vertebral rotations following spine rhythm measured in a previous in-vivo study, to the musculoskeletal model. The FE model predicted intradiscal pressure (IDP), strains in the annular fibers, contact forces in the facet joints, and forces in the ligaments. The disc forces and moments were determined using equilibrium equations, which considered the applied loads, including muscle forces and IDP, as well as forces in the ligaments and facet joints predicted by the FE model. Load-sharing was calculated as the portion of the total spinal load carried along the spine by each individual spinal structure. The results revealed that spinal loads which increased substantially from the upright to the flexed posture were mainly supported by the discs in the upright posture, whereas the ligaments’ contribution in resisting shear, compression, and moment was more significant in the flexed posture.
KW - Finite element analysis
KW - Forward flexion
KW - In-vivo loading conditions
KW - Inverse static analysis
KW - Load-sharing
KW - Musculoskeletal model
KW - Neutral standing
UR - http://www.scopus.com/inward/record.url?scp=85034425084&partnerID=8YFLogxK
U2 - 10.1016/j.jbiomech.2017.10.033
DO - 10.1016/j.jbiomech.2017.10.033
M3 - Article
C2 - 29153706
AN - SCOPUS:85034425084
SN - 0021-9290
VL - 70
SP - 43
EP - 50
JO - Journal of Biomechanics
JF - Journal of Biomechanics
ER -