Estimating lumbar passive stiffness behaviour from subject-specific finite element models and in vivo 6DOF kinematics

• Published in: Journal of biomechanics Vol. 102; p. 109681
• Main Authors: Affolter, Christian, Kedzierska, Joanna, Vielma, Thomas, Weisse, Bernhard, Aiyangar, Ameet
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 26-03-2020; Elsevier Limited
• Subjects: Behavior; Biomechanical Phenomena; Cadavers; Computed tomography; Computer simulation; Data acquisition; Datasets; Estimation; Feasibility studies; Finite Element Analysis; Finite element method; Humans; In vivo methods and tests; Kinematics; Ligaments; Load; Lumbar spinal loading; Lumbar Vertebrae - diagnostic imaging; Lumbar Vertebrae - physiology; Male; Mathematical models; Neutral position; Parameter estimation; Passive stiffness; Pressure; Radiography; Range of Motion, Articular; Rigid-body musculoskeletal modelling; Rotation; Spine (lumbar); Stiffness; Subject-specific kinematics; Supine position; Translation; Vertebrae; Weight; Weight-Bearing; X ray imagery; Lumbar spinal loading; Rigid-body musculoskeletal modelling; Neutral position; Subject-specific kinematics; Passive stiffness
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2020.109681

Passive rotational stiffness of the osseo-ligamentous spine is an important input parameter for estimating in-vivo spinal loading using musculoskeletal models. These data are typically acquired from cadaveric testing. Increasingly, they are also estimated from subject-specific imaging-based finite element (FE) models, which are typically built from CT/MR data obtained in supine position and employ pure rotation kinematics. We explored the sensitivity of FE-based lumbar passive rotational stiffness to two aspects of functional in-vivo kinematics: (a) passive strain changes from supine to upright standing position, and (b) in-vivo coupled translation-rotation kinematics. We developed subject-specific FE models of four subjects’ L4L5 segments from supine CT images. Sagittally symmetric flexion was simulated in two ways: (i) pure flexion up to 12° under a 500 N follower load directly from the supine pose. (ii) First, a displacement-based approach was implemented to attain the upright pose, as measured using Dynamic Stereo X-ray (DSX) imaging. We then simulated in-vivo flexion using DSX imaging-derived kinematics. Datasets from weight-bearing motion with three different external weights [(4.5 kg), (9.1 kg), (13.6 kg)] were used. Accounting for supine-upright motion generated compressive pre-loads ≈ 468 N (±188 N) and a “pre-torque” ≈2.5 Nm (±2.2 Nm), corresponding to 25% of the reaction moment at 10° flexion (case (i)). Rotational stiffness estimates from DSX-based coupled translation-rotation kinematics were substantially higher compared to pure flexion. Reaction Moments were almost 90% and 60% higher at 5° and 10° of L4L5 flexion, respectively. Within-subject differences in rotational stiffness based on external weight were small, although between-subject variations were large.