In vitro human cadaveric biomechanical study.The objectives were to determine the effect of total disc replacement (TDR) on kinematics, especially range of motion (ROM), helical axis of motion (HAM), and facet joint contact force.Ball-and-socket type artificial discs are designed to mimic normal motion, but the biomechanical effect on kinematics has not been thoroughly clarified.Fourteen human cadaveric L4-L5 units were tested before and after TDR. In 7 specimens, facet contact forces were directly measured with thin-film piezoresistive load transducers inserted in the facet joints. In the other 7 specimens, the facet joint capsules were kept intact. Moments (±7.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation motion, with and without an axial compressive preload of 400 N. Three-dimensional motion was recorded, and each angular ROM and HAM were calculated.Without axial compressive preload, the TDR did not produce significant differences in ROMs in all cases. However, under compressive preload, the TDR produced significantly larger ROMs for flexion (4.0° and 8.7°) and lateral bending (2.4° and 5.6°) (intact state and TDR, respectively). The TDR did not alter the HAM significantly except the location in lateral bending without compressive preload and the orientation in flexion/extension against horizontal plane. The location of HAM was slightly shifted caudally by the compressive preload in intact and TDR states. Despite the increased ROMs, the facet contact forces were not significantly altered by the TDR either with or without compressive preload (26 N and 27 N in extension, 41 N and 41 N in lateral bending, 117 N and 126 N in axial rotation).TDR using a ball-and-socket type artificial disc significantly increased ROM under axial load and maintained the HAM with similar facet contact forces to the intact state.
Despite the significant impairment associated with degenerative disc disease, a clear understanding of pathogenesis of disc degeneration is still lacking. In order to clarify the relationship between degenerative disc disease and morphological and biomechanical properties, an accurate measurement method is needed. Recent advancement of medical imaging has allowed us to create an in vivo three dimensional (3D) computer model with high accuracy. The purpose of the current study was to evaluate the disc height distribution and changes in stress distribution under compression loading of the rabbit lumbar intervertebral disc using a 3D computer model created from micro computer tomography images. The results of the study showed the contribution of 3D geometry of the endplate to stress concentration which may cause disc degeneration.
The purpose of this study was to establish a finite element stress analysis method of intervertebral discs in a rheumatoid arthritis (RA) patient with cervical involvement using a three dimensional (3D) computer model reconstructed from computer tomography (CT) and magnetic resonance (MR) images. Intervertebral disc 3D finite element models were created using point cloud data of endplates of cervical spine (C2-C7) vertebral bodies in three different positions; neutral, flexion, and extension positions. Transformations of each endplate in flexion and extension positions were determined using a volume merge method. Changes in stress/strain distribution during flexion and extension were analyzed using displacement data of the endplate as input data. Stress concentration was noted at both lateral regions in C2/3 and C3/4 intervertebral discs. However, no significant changes in stress distribution during motion were observed at C4/5, C5/6, and C6/7 intervertebral discs.
Disc herniation and low back pain constitute widespread problems in modern society, although a direct relationship between both conditions has not been established. Proper quantification of intervertebral disc bulging is important for studies on pathogenesis and pathological conditions of disc related disease such as herniations. Intervertebral disc disorders are related to the mechanical failure of the annulus fibrosus [1] and annulus failure is caused by high tensile stresses produced by the high intervertebral disc pressure [2]. To the best of the authors’ knowledge, there has been no study on the simultaneous measurement of disc bulging and the disc pressure under physiological loading conditions. The objective of this study was to describe the radial displacement of the outer annulus wall under a variety of loading schemes. Moreover, this data could also be used to assist in the validation process for finite element models.
