Biomechanical implications of lumbar spinal ligament transection

Abstract

Many lumbar spine surgeries either intentionally or inadvertently damage or transect spinal ligaments. The purpose of this work was to quantify the previously unknown biomechanical consequences of isolated spinal ligament transection on the remaining spinal ligaments (stress transfer), vertebrae (bone remodelling stimulus) and intervertebral discs (disc pressure) of the lumbar spine. A finite element model of the full lumbar spine was developed and validated against experimental data and tested in the primary modes of spinal motion in the intact condition. Once a ligament was removed, stress increased in the remaining spinal ligaments and changes occurred in vertebral strain energy, but disc pressure remained similar. All major biomechanical changes occurred at the same spinal level as the transected ligament, with minor changes at adjacent levels. This work demonstrates that iatrogenic damage to spinal ligaments disturbs the load sharing within the spinal ligament network and may induce significant clinically relevant changes in the spinal motion segment.

Low Back Pain

“…26 However, a brief description of the model development is included here for reference. A hexahedral fi nite element model of the lumbar spine (T12-S1) was developed corresponding to the geometry of a 65-year-old female based on quantitative computed tomography data of a lumbar cadaver spine.…”

“…26 The constitutive model implementation of intervertebral disc degeneration was validated by comparing the changes in disc height between the nondegenerated and degenerated models while under a 444 N follower load designed to simulate body weight and muscle tension. The loaded disc height in the degenerated model was reduced by 16.5% as compared with that of the nondegenerated model, which correlated well with the measured disc height reduction for a disc that exhibits mild but observable degeneration.…”

Changes in Vertebral Strain Energy Correlate With Increased Presence of Schmorl's Nodes in Multi-Level Lumbar Disk Degeneration

“…A previously validated and published nonlinear finite element model of a lumbar spine [19] here for reference. The geometry for the model (T12-S1) was obtained using quantitative computed tomography (QCT) data of a 65-year-old female (Fig.…”

“…The finite element model (234,380 elements) was previously evaluated for stressconvergence and validated against experimental and published data for instantaneous axes of rotation, quality of motion, range of motion, cortical strains, and disk pressure [19]. Material response of the degenerated intervertebral disks was further validated by comparing changes in disk height between degenerated and nondegenerated disks when compressed with a 444 N follower load.…”

“…Applied rotations, rather than applied moments were applied in order to determine adjacent level effects. The magnitudes of these applied rotations were chosen as those corresponding to applied moments of 8 Nm Flexion, 6 Nm extension, 6 Nm lateral bending, 6 Nm axial rotation for a healthy spine, and were based on our previously published validation work [19]. Rotational displacements were applied via a rigid plate attached to the inferior endplate of the T12 vertebrae, while the superior endplate of the S1 vertebrae was held in a fixed position.…”