A numerical study to determine the effect of ligament stiffness on kinematics of the lumbar spine during flexion

Abstract

BackgroundThere is a wide range of mechanical properties of spinal ligaments documented in literature. Due to the fact that ligaments contribute in stabilizing the spine by limiting excessive intersegmental motion, those properties are of particular interest for the implementation in musculoskeletal models. The aim of this study was to investigate the effect of varying ligament stiffness on the kinematic behaviour of the lumbar spine.MethodsA musculoskeletal model with a detailed lumbar spine was modified according to fluoroscopic recordings and corresponding data files of three different subjects. For flexion, inverse dynamics analysis with a variation of the ligament stiffness matrix were conducted. The influence of several degrees of ligament stiffness on the lumbar spine model were investigated by tracking ligament forces, disc forces and resulting moments generated by the ligaments. Additionally, the kinematics of the motion segments were evaluated.ResultsAn increase of ligament stiffness resulted in an increase of ligament and disc forces, whereas the relative change of disc force increased at a higher rate at the L4/L5 level (19 %) than at the L3/L4 (10 %) level in a fully flexed posture. The same behaviour applied to measured moments with 67 % and 45 %. As a consequence, the motion deflected to the lower levels of the lumbar spine and the lower discs had to resist an increase in loading.ConclusionsHigher values of ligament stiffness over all lumbar levels could lead to a shift of the loading and the motion between segments to the lower lumbar levels. This could lead to an increased risk for the lower lumbar parts.

Experimental platform to facilitate novel back brace development for the improvement of spine stability

“…The elastic modulus of vertebrae ranges from 1.5 to 3 GPa (Swamy, 2014), and so ABS1400 with an Young's modulus of 1.68 GPa (Ultimaker, 2017) was selected to represent bone within the spine structure. Ligaments were modelled as tension-only springs and defined through a particular stiffness (Pitzer, et al, 2016). Compressive testing of flexible polyurethane foam samples yielded an elastic modulus of 0.128 MPa, within the limits stated by Bonnaire et al (Bonnaire, et al, 2014) for the human abdomen (0.01 to 1 MPa).…”

Sensitivity of muscle and intervertebral disc force computations to variations in muscle attachment sites

“…Thirdly, we did not incorporate spinal ligaments but implemented their collective rotational stiffnesses linearly in the intervertebral and rib cage joints. Thus, excluding the ligaments or simplifying their non-linear mechanical behaviors could alter the load sharing mechanism between the muscles and affect our findings (Putzer, Auer, et al 2016;Ghezelbash et al 2018). For example, Putzer, Auer, et al (2016) found that implementing stiffer ligaments could cause a shift of the loads to the lower lumbar disc levels.…”

“…Previously, several authors investigated the sensitivity of their models against the locations of intervertebral center of rotation (Zander et al 2016), spine rhythms and abdominal pressure (Arshad et al 2016), ligament stiffness (Putzer, Auer, et al 2016), and vertebral morphology (Putzer, Ehrlich, et al 2016). Muscle recruitment during trunk exertions is dependent on muscle lines-of-action, however, there is only one study which aimed to investigate the sensitivity of muscle and intervertebral disc force computations against muscle attachment sites in the spine.…”

Diffuse idiopathic skeletal hyperostosis is associated with lumbar spinal stenosis requiring surgery

“…In the present study, there are a few patients required decompression at just distal level of fused segment by DISH. The most affected stenotic level were lower lumbar segment which were generally exposed highest stress during postural change [17,18], even patients with DISH. However, higher occurrence of stenosis at upper lumbar levels, and multi-level stenosis were observed in patients with DISH required surgery than without DISH in patients with LSS required surgery.…”