DataSheet2_Biomechanical consequences of cement discoplasty: An in vitro study on thoraco-lumbar human spines.PDF

With the ageing of the population, there is an increasing need for minimally invasive spine surgeries to relieve pain and improve quality of life. Percutaneous Cement Discoplasty is a minimally invasive technique to treat advanced disc degeneration, including vacuum phenomenon. The present study aimed to develop an in vitro model of percutaneous cement discoplasty to investigate its consequences on the spine biomechanics in comparison with the degenerated condition. Human spinal segments (n = 27) were tested at 50% body weight in flexion and extension. Posterior disc height, range of motion, segment stiffness, and strains were measured using Digital Image Correlation. The cement distribution was also studied on CT scans. As main result, percutaneous cement discoplasty restored the posterior disc height by 41% for flexion and 35% for extension. Range of motion was significantly reduced only in flexion by 27%, and stiffness increased accordingly. The injected cement volume was 4.56 ± 1.78 ml (mean ± SD). Some specimens (n = 7) exhibited cement perforation of one endplate. The thickness of the cement mass moderately correlated with the posterior disc height and range of motion with different trends for flexions vs. extension. Finally, extreme strains on the discs were reduced by percutaneous cement discoplasty, with modified patterns of the distribution. To conclude, this study supported clinical observations in term of recovered disc height close to the foramen, while percutaneous cement discoplasty helped stabilize the spine in flexion and did not increase the risk of tissue damage in the annulus.</p

DataSheet1_Biomechanical consequences of cement discoplasty: An in vitro study on thoraco-lumbar human spines.PDF

With the ageing of the population, there is an increasing need for minimally invasive spine surgeries to relieve pain and improve quality of life. Percutaneous Cement Discoplasty is a minimally invasive technique to treat advanced disc degeneration, including vacuum phenomenon. The present study aimed to develop an in vitro model of percutaneous cement discoplasty to investigate its consequences on the spine biomechanics in comparison with the degenerated condition. Human spinal segments (n = 27) were tested at 50% body weight in flexion and extension. Posterior disc height, range of motion, segment stiffness, and strains were measured using Digital Image Correlation. The cement distribution was also studied on CT scans. As main result, percutaneous cement discoplasty restored the posterior disc height by 41% for flexion and 35% for extension. Range of motion was significantly reduced only in flexion by 27%, and stiffness increased accordingly. The injected cement volume was 4.56 ± 1.78 ml (mean ± SD). Some specimens (n = 7) exhibited cement perforation of one endplate. The thickness of the cement mass moderately correlated with the posterior disc height and range of motion with different trends for flexions vs. extension. Finally, extreme strains on the discs were reduced by percutaneous cement discoplasty, with modified patterns of the distribution. To conclude, this study supported clinical observations in term of recovered disc height close to the foramen, while percutaneous cement discoplasty helped stabilize the spine in flexion and did not increase the risk of tissue damage in the annulus.</p

DataSheet3_Variability of intervertebral joint stiffness between specimens and spine levels.pdf

Introduction: Musculoskeletal multibody models of the spine can be used to investigate the biomechanical behaviour of the spine. In this context, a correct characterisation of the passive mechanical properties of the intervertebral joint is crucial. The intervertebral joint stiffness, in particular, is typically derived from the literature, and the differences between individuals and spine levels are often disregarded.Methods: This study tested if an optimisation method of personalising the intervertebral joint stiffnesses was able to capture expected stiffness variation between specimens and between spine levels and if the variation between spine levels could be accurately captured using a generic scaling ratio. Multibody models of six T12 to sacrum spine specimens were created from computed tomography data. For each specimen, two models were created: one with uniform stiffnesses across spine levels, and one accounting for level dependency. Three loading conditions were simulated. The initial stiffness values were optimised to minimize the kinematic error.Results: There was a range of optimised stiffnesses across the specimens and the models with level dependent stiffnesses were less accurate than the models without. Using an optimised stiffness substantially reduced prediction errors.Discussion: The optimisation captured the expected variation between specimens, and the prediction errors demonstrated the importance of accounting for level dependency. The inaccuracy of the predicted kinematics for the level-dependent models indicated that a generic scaling ratio is not a suitable method to account for the level dependency. The variation in the optimised stiffnesses for the different loading conditions indicates personalised stiffnesses should also be considered load-specific.</p

Workflow used to compare predicted and experimental local displacements and axial forces predicted.

<p>An example of the step-wise load displacement curve is reported on the top highlighting the Preloaded (1) and Loaded (5% apparent strain, 2) conditions. A picture of the loading jig and a scheme of the sample fixation are reported on the top-right corner. The Digital Volume Correlation (DVC) algorithm was applied to the Preloaded and Loaded images to calculate the map of displacement in the whole vertebral body. MicroFE models of the vertebral body between the PMMA pots were generated from the preloaded image after the application of a single level threshold chosen from the analyses of the frequency plot of the grey-values and visual inspection. The displacement values at the top and bottom layer of the microFE models were assigned by interpolation of the DVC measurements in those planes. Displacements along the axial (Z) and transverse (X, Y) directions were compared between microFE predictions and DVC measurements at the nodes of the DVC grid that lay within microFE elements. Predicted axial forces were compared to those measured from the experimental load-displacement curves (ΔF).</p

Values of axial forces predicted by the microFE models for E_t = 12.0GPa and E_t = 4.6GPa and experimentally measured, for all specimens.

<p>The absolute percentage differences (%diff_AF) between numerical and experimental values are reported.</p

Linear regression analysis between experimental and predicted local displacements for a tissue modulus E_t = 12.0GPa.

<p>Data are reported for predictions along the three Cartesian directions (X and Y in a transverse plane, Z in the axial direction) for the individual specimens and for pooled data.</p

Overview of the elastic modulus of human vertebral bone tissue reported in the literature from wet microindentation tests performed at the BSU level, or from back-calculation procedures in combination with microFE models.

<p>Overview of the elastic modulus of human vertebral bone tissue reported in the literature from wet microindentation tests performed at the BSU level, or from back-calculation procedures in combination with microFE models.</p

Relationship between numerical (AF_Z_microFE) and experimental (AF_Z_Exp) measurements of axial force for each specimen.

<p>Predictive results obtained from models generated with a tissue modulus (Et) equal to 12.0GPa (black) or 4.6GPa (grey).</p

Regression analysis of microFE models predictions of local displacements per specimen and bone type.

<p>MicroFE models predictions and DVC measurements computed along the transverse (X, Y) and axial (Z) directions for each specimen within cortical (red circles) and trabecular (black crosses) bone regions.</p

DataSheet2_Variability of intervertebral joint stiffness between specimens and spine levels.pdf

Introduction: Musculoskeletal multibody models of the spine can be used to investigate the biomechanical behaviour of the spine. In this context, a correct characterisation of the passive mechanical properties of the intervertebral joint is crucial. The intervertebral joint stiffness, in particular, is typically derived from the literature, and the differences between individuals and spine levels are often disregarded.Methods: This study tested if an optimisation method of personalising the intervertebral joint stiffnesses was able to capture expected stiffness variation between specimens and between spine levels and if the variation between spine levels could be accurately captured using a generic scaling ratio. Multibody models of six T12 to sacrum spine specimens were created from computed tomography data. For each specimen, two models were created: one with uniform stiffnesses across spine levels, and one accounting for level dependency. Three loading conditions were simulated. The initial stiffness values were optimised to minimize the kinematic error.Results: There was a range of optimised stiffnesses across the specimens and the models with level dependent stiffnesses were less accurate than the models without. Using an optimised stiffness substantially reduced prediction errors.Discussion: The optimisation captured the expected variation between specimens, and the prediction errors demonstrated the importance of accounting for level dependency. The inaccuracy of the predicted kinematics for the level-dependent models indicated that a generic scaling ratio is not a suitable method to account for the level dependency. The variation in the optimised stiffnesses for the different loading conditions indicates personalised stiffnesses should also be considered load-specific.</p