Radial Bulge Research Articles

Insights into the role of water concentrations on nanomechanical behavior of type I collagen-hyaluronan interfaces in annulus fibrosus: A molecular dynamics investigation.

Multi-faceted deformation capabilities of Annulus Fibrosus (AF) results from an intricate mechanical design by nature. Wherein, organization and interactions between the constituents, collagen type I (CI), collagen type II (C2), hyaluronan, aggrecan, and water are instrumental. However, mechanisms by which such interactions influence AF mechanics at tissue-scale is not well understood. This work investigates nanoscale interfacial interactions between CI and hyaluronan (CI-H) and presents insights into their influence on tissue-scale mechanics of AF. For this, three-dimensional molecular dynamics (MD) simulations of tensile and compressive deformation are conducted on atomistic model of CI-H interface at 0%, 65%, and 75% water concentrations (WC). Results show hyaluronan lowers local hydration around CI component of interface, owing to its hydrophilic nature. Analyses show that increase in WC from 65% to 75% leads to increased interchain sliding in hyaluronan, which further lowers tensile modulus of the interface from 2.1 GPa to 660 MPa, contributing to softening observed from outer to inner AF. Furthermore, increase in WC from 65% to 75%, shifts compressive deformation from buckling-dominant to non-buckling-dominant which contributes towards lower radial bulge at inner AF. Findings provide deeper insights into mechanistic interactions and mechanisms at fundamental length-scale which influence the AF structure-mechanics at tissue-scale.

The Evolution of the Star-Forming Interstellar Medium Across Cosmic Time

Over the past decade, increasingly robust estimates of the dense molecular gas content in galaxy populations between redshift z = 0 and the peak of cosmic galaxy/star formation ( z ∼ 1–3) have become available. This rapid progress has been possible due to the advent of powerful ground- and space-based telescopes for the combined study of several millimeter to far-IR, line or continuum tracers of the molecular gas and dust components. The main conclusions of this review are as follows: ▪ Star-forming galaxies contained much more molecular gas at earlier cosmic epochs than at the present time. ▪ The galaxy-integrated depletion timescale for converting the gas into stars depends primarily on z or Hubble time and, at a given z, on the vertical location of a galaxy along the star-formation rate versus stellar mass main sequence (MS) correlation. ▪ Global rates of galaxy gas accretion primarily control the evolution of the cold molecular gas content and star-formation rates of the dominant MS galaxy population, which in turn vary with cosmological expansion. Another key driver may be global disk fragmentation in high- z, gas-rich galaxies, which ties local free-fall timescales to galactic orbital times and leads to rapid radial matter transport and bulge growth. The low star-formation efficiency inside molecular clouds is plausibly set by supersonic streaming motions and internal turbulence, which in turn may be driven by conversion of gravitational energy at high z and/or by local feedback from massive stars at low z. ▪ A simple gas regulator model is remarkably successful in predicting the combined evolution of molecular gas fractions, star-formation rates, galactic winds, and gas-phase metallicities.

Testing a theoretical prediction for bar formation in galaxies with bulges

Earlier studies have shown that massive bulges impede bar formation in disk galaxies. Recent N-body simulations have derived a bar formation criterion that depends on the radial bulge force in a galaxy disk. We use those simulations to show that bars can form only when the force constant FB < 0.13, where FB depends on the ratio of the bulge force to the total force of the galaxy at twice the disk scale length 2Rd. In this article, we test this theoretical prediction using observational data obtained from the literature. Our sample consists of 63 barred galaxies with a wide range of Hubble classes taken from the S4G catalog; for the galaxies that we include, bulge, disk, and bar decomposition has been carried out. We find that 92% of our sample galaxies satisfy the condition FB < 0.13 for bar formation in galaxies and hence agree with the bar formation criterion given by the simulations.

A Study on the Shape deviation rate of Hydroforming of Seamed tubes Based on Two Different Velocity

Due to the low price, the seamed tubes are used more and more widely in various industrial fields in recent years. The difference in material properties between the weld zone of the parent metal zone of the thin-walled seamed tubes, the deformation of the hydraulic bulging under the same conditions will also be different, thus resulting in an inconsistency in the overall bulging of the seamed tubes. In this paper, the hydraulic bulging experiment of the seamed tubes at low and medium velocity, and the shape deviation law of the seamed tubes at different velocity are obtained. In the first half of the bulging, the seamed tubes at the medium velocity drops faster than the low velocity shape deviation rate, and the medium velocity is closer to circle; in the second half of the bulging, the medium velocity is go up faster than the low velocity. The shape deviation rate is higher before the tubes are burst, but the medium velocity’s radial average bulge height is smaller than the low velocity.

Development of Design Charts for Installation of Granular Piles in Soft Clays

The vertical loads on the soil reinforced with Granular Pile results in axial compression of both the soil and the Granular Pile material. The imposed stresses result in radial bulge of the pile material against the surrounding soil though it is restricted to the upper portion of pile length. Considering this nature of the Granular Pile, analytically solution for the strength of the composite ground reinforced with Granular Piles is discussed herein. The radial bulge extends up to the depth equal to the four times the diameter of the Granular Pile. Various factors such as undrained shear strength of the soil and the internal friction angle of the pile material are used to derive the capacity of the Granular Pile. The proposed solution is used to calculate the capacity of Granular Pile varying the properties of surrounding soil and Granular Pile material. Values of undrained shear strength (cu) were varied from 10 to 50 k Pa. Bulk density (γ) of the clay soil is assumed as 20 k N/m3. Angle of internal friction for Granular Pile material (ϕc) is varied from 380 to 420. The design charts between safe bearing pressure and the angle of internal friction for Granular Pile material are drawn. The diameter of Granular Pile is kept from 0.3 m to 1.05 m and the spacing between them is varied from 2D to 3.5D. The triangular pattern of Granular Pile arrangement is considered. For different spacing of the Granular Pile and undrained shear strength, the design charts explained and illustrated through an example.

Effect of collagen fibre orientation on intervertebral disc torsion mechanics.

The intervertebral disc is a complex fibro-cartilaginous material, consisting of a pressurized nucleus pulposus surrounded by the annulus fibrosus, which has an angle-ply structure. Disc injury and degeneration are noted by significant changes in tissue structure and function, which significantly alters stress distribution and disc joint stiffness. Differences in fibre orientation are thought to contribute to changes in disc torsion mechanics. Therefore, the objective of this study was to evaluate the effect of collagen fibre orientation on internal disc mechanics under compression combined with axial rotation. We developed and validated a finite element model (FEM) to delineate changes in disc mechanics due to fibre orientation from differences in material properties. FEM simulations were performed with fibres oriented at [Formula: see text] throughout the disc (uniform by region and fibre layer). The initial model was validated by published experimental results for two load conditions, including [Formula: see text] axial compression and [Formula: see text] axial rotation. Once validated, fibre orientation was rotated by [Formula: see text] or [Formula: see text] towards the horizontal plane, resulting in a decrease in disc joint torsional stiffness. Furthermore, we observed that axial rotation caused a sinusoidal change in disc height and radial bulge, which may be beneficial for nutrient transport. In conclusion, including anatomically relevant fibre angles in disc joint FEMs is important for understanding stress distribution throughout the disc and will be important for understanding potential causes for disc injury. Future models will include regional differences in fibre orientation to better represent the fibre architecture of the native disc.

New record of Durania cornupastoris (rudist) from the Campanian of the Aruma Formation, Riyadh, Saudi Arabia: Description and biogeographic remarks

A Radiolitidae (rudist, bivalvia), Durania cornupastoris (Des Moulins) is a well-known species defined as an index fossil from the Turonian (mostly middle-upper) deposits in the Mediterranean Tethys and also in the USA. This study includes new rudist materials and well-preserved samples of the species from the Campanian Khanasir Limestone Member of the Aruma Formation outcropping around the Riyadh (Saudi Arabia) region. Durania cornupastoris is characterized by the many finely ribbed, generally flat, sometimes slightly or pronounced concave posterior and ventral radial bands and bulge interband with thick costae similar to the external ornament of the rest of the right valve surface. The width of the radial bands are variable. A comparison of the species with the well-known Durania species such as Durania arnaudi (Choffat), Durania gaensis (Dacqué) and Durania apula Parona is considered. The broadening of the stratigraphic range up to the Campanian and biogeographic distribution into the eastern part of the Arabo-African plate of the species are also emphasized.

Effect of Coking Size on the Thermal Diffusion and Stress Distribution of Cr25Ni35Nb and Cr35Ni45Nb Austenitic Steels

Cr25Ni35Nb and Cr35Ni45Nb austenitic steels, used as furnace tube material in the ethylene pyrolysis furnace, generally suffer from coking during the long operation period. In the present paper, for coked Cr25Ni35Nb and Cr35Ni45Nb austenitic steel, using the finite element ABAQUS code, a sequentially coupled thermal stress procedure was developed to calculate distribution of the temperature and thermal stress field. The results show that thermal diffusion property of Cr25Ni35Nb and Cr35Ni45Nb steel deteriorates obviously with coking layer increasing. Radial bulge and rupture at local field would generate due to excess temperature for applied subsequent measurement. Maximum stress distribute along the cross-section of coking layer and metal matrix. Finally, the critical depth of coking layer of Cr25Ni35Nb and Cr35Ni45Nb austenitic steel are predicted when decoking measurement must be executed.

Height and torsional stiffness are most sensitive to annular injury in large animal intervertebral discs

Acute annulus fibrosus injury has been identified as a contributing factor to intervertebral disc (IVD) degeneration. Injuries as small as those resulting from needle injection result in localized mechanical disruption via fiber breakage, but it is unknown whether these injuries initiate degeneration locally or through changes in the mechanical behavior of the entire disc. However, in vitro biomechanical studies of injury are limited to a single type of injury or measurements in only one or two degrees of freedom. The aim of this study is to provide a comprehensive assessment of the joint level mechanical response to IVD injuries of various sizes in a large animal model. We hypothesize that annular injuries will affect disc mechanics differently depending on size, location, and mode of loading. We further hypothesize that a large injury to one side of the disc will induce a bending moment reaction under axial compression, which may decrease spinal column stability. A comprehensive biomechanical study investigating effects of small and large injuries on IVD pressurization and six-degree-of-freedom stiffness behaviors using bovine motion segments. Bovine caudal motion segments were subjected to a series of annular injuries ranging from 21-gauge needle puncture to 10-mm scalpel incisions and evaluated before and after injury with both mechanical testing under multiple degrees of freedom (axial compression, flexion-extension, lateral bending, and torsion) and nucleus pulposus (NP) fluid pressurization tests. Mechanical tests showed that axial torsional stiffness and disc height under resting compressive load were the parameters most sensitive to large annular injury. Bending and compressive stiffnesses, as well as bending moments induced by axial compression, were not significantly changed by scalpel incisions. Additionally, large injuries resulted in altered relaxation behavior after NP pressurization indicative of increases in both radial bulge compliance and fluid flow rates. These findings suggest that loss of disc height, torsional stiffness, and NP fluid pressurization are the immediate results of acute annular injury and are therefore those properties that IVD repair strategies must strive to restore or maintain. The lack of change in bending stiffness and moment under compression suggests that acute annular tears alone are not sufficient to induce off-axis motion and instability.

The Effect of Nucleotomy and the Dependence of Degeneration of Human Intervertebral Disc Strain in Axial Compression

Biomechanics of human intervertebral discs before and after nucleotomy. To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration. Herniation and nucleotomy may accelerate the progression of disc degeneration. Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI). Degeneration was quantitatively assessed by the T1ρ relaxation time in the NP. Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include axial deformation, AF radial bulge, and strains. RESULTS.: The axial deformation was more compressive after nucleotomy. In the neutral position, the axial deformation after nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy. Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.

Restoration of compressive loading properties of lumbar discs with a nucleus implant—a finite element analysis study

Background Context Discectomy is a common procedure for treating sciatica. However, both the operation and preceding herniated disc alter the biomechanical properties of the spinal segment. The disc mechanics are also altered in patients with chronic contained herniation. The biomechanical properties of the disc can potentially be restored with an elastomeric nucleus replacement implanted via minimally invasive surgery. Purpose The purpose of this study was to determine whether the compressive characteristics of the intervertebral disc after a nucleotomy can be restored with an elastomeric nucleus replacement. Study Design A finite element model of the L4–L5 intervertebral disc was created to investigate the effect of the implantation of an elastomeric nucleus replacement on the biomechanical properties of the disc under axial loading. Method A L4–L5 physiologic intervertebral disc model was constructed and then modified to contain a range by volume of nucleotomies and nucleus replacements. The material properties of the nucleus replacement were based on experimental data for an elastomeric implant. The compressive stiffness, radial annular bulge, and stress distribution of the nucleotomy and nucleus replacement models were investigated under displacement-controlled loading. Results Removal of nucleus pulposus from the physiologic disc reduced the force necessary to compress the disc 2 mm by 50%, altered the von Mises stress distribution, and reduced the outward radial annular bulge. Replacing the natural nucleus pulposus of the physiologic disc with an artificial nucleus reduced the force required to compress the disc 2 mm by 10%, indicating a restoration of disc compressive stiffness. The von Mises stress distribution and annular bulge observed in the disc with an artificial nucleus were similar to that observed in the physiologic disc. Conclusion This study demonstrates that despite having different material properties, a nucleus replacement implant can restore the axial compressive mechanical properties of a disc after a discectomy. The implant carries compressive load and transfers the load into annular hoop stress.

A biochemical/biophysical 3D FE intervertebral disc model

Present research focuses on different strategies to preserve the degenerated disc. To assure long-term success of novel approaches, favorable mechanical conditions in the disc tissue are essential. To evaluate these, a model is required that can determine internal mechanical conditions which cannot be directly measured as a function of assessable biophysical characteristics. Therefore, the objective is to evaluate if constitutive and material laws acquired on isolated samples of nucleus and annulus tissue can be used directly in a whole-organ 3D FE model to describe intervertebral disc behavior. The 3D osmo-poro-visco-hyper-elastic disc (OVED) model describes disc behavior as a function of annulus and nucleus tissue biochemical composition, organization and specific constituent properties. The description of the 3D collagen network was enhanced to account for smaller fibril structures. Tissue mechanical behavior tests on isolated nucleus and annulus samples were simulated with models incorporating tissue composition to calculate the constituent parameter values. The obtained constitutive laws were incorporated into the whole-organ model. The overall behavior and disc properties of the model were corroborated against in vitro creep experiments of human L4/L5 discs. The OVED model simulated isolated tissue experiments on confined compression and uniaxial tensile test and whole-organ disc behavior. This was possible, provided that secondary fiber structures were accounted for. The fair agreement (radial bulge, axial creep deformation and intradiscal pressure) between model and experiment was obtained using constitutive properties that are the same for annulus and nucleus. Both tissue models differed in the 3D OVED model only by composition. The composition-based modeling presents the advantage of reducing the numbers of material parameters to a minimum and to use tissue composition directly as input. Hence, this approach provides the possibility to describe internal mechanical conditions of the disc as a function of assessable biophysical characteristics.

CHEMICAL COMPOSITION OF FAINT (I∼ 21 mag) MICROLENSED BULGE DWARF OGLE-2007-BLG-514S

We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff = 5600 +/- 180 K. This I~21 mag star was magnified by a factor ranging from 1160 to 1300 at the time of observation. Its high metallicity ([Fe/H] = 0.33 +/- 0.15) places this star at the upper end of the bulge giant metallicity distribution. Using a K-S test, we find a 1.6% probability that the published microlensed bulge dwarfs share an underlying distribution with bulge giants, properly accounting for a radial bulge metallicity gradient. We obtain abundance measurements for 15 elements and perform a rigorous error analysis that includes covariances between parameters. This star, like bulge giants with the same metallicity, shows no alpha enhancement. It confirms the chemical abundance trends observed in previously analyzed bulge dwarfs. At supersolar metallicities, we observe a discrepancy between bulge giant and bulge dwarf Na abundances.

Changes in the lumbar intervertebral disk following use of the Holmium-Yag laser--a biomechanical study

For a biomechanical study 10 specimen of the lumbar spine (L1-S1) were scanned with MRI. After that 18 normal motion segments were prepared for the experiments. The paraspinal musculature as well as the posterior elements were removed. Under an axial load of 500 N, in each disc 500 J and 1000 J of energy were applicated with a Holmium-Yag laser (2060 nm, fiber thickness 600 microns) into the nucleus pulposus. In nine of the 18 discs also 1500 J and 2000 J were applicated. At the beginning of every standardized experiment of a motion segment, as well as after every 500 J, the height of the disc, intradiscal pressure, the contour of the disc and the size of the transversal plane of the disc were determined with an axial load on the motion segment of 1000 N. The change in radial bulging of the disc was measured using the computer-assisted recordings of each disc contour. All the data were statistically analyzed using the Friedman-/Wilcoxon-test. After every application of 500 J energy, in the 18 discs as well as in the 9 discs, the height and the intradiscal pressure reduced. The differences per 500 J were for all measurements not significant (p < 0.05). Up till the application of 1500 J the radial bulge and the size of the transversal plane of the disc increased, although the differences per 500 J were not significant. From 1500 J to 2000 J the radial bulge and size of transversal plane of the disc decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

The Structure of Tornadoes near Attica, Kansas, on 12 May 2004: High-Resolution, Mobile, Doppler Radar Observations

Abstract The University of Massachusetts W- and X-band, mobile, Doppler radars scanned several tornadoes at close range in south-central Kansas on 12 May 2004. The detailed vertical structure of the Doppler wind and radar reflectivity fields of one of the tornadoes is described with the aid of boresighted video. The inside wall of a weak-echo hole inside the tornado was terminated at the bottom as a bowl-shaped boundary within several tens of meters of the ground. Doppler signatures of horizontal vortices were noted along one edge in the lowest 500 m of the tornado. The vertical structure of Doppler velocity displayed significant variations on the 100-m scale. Near the center of the tornado, a quasi-horizontal, radial bulge of the weak-echo hole at ∼500–600 m AGL dropped to about 400 m above the ground and was evident as a weak-echo band to the south of the tornado. It is suggested that this feature represents echo-weak material transported radially outward by a vertical circulation. Significant vertical variations of Doppler velocity were found in the surface friction layer both inside and outside the tornado core. The shape of a weak-echo notch that was associated with a hook echo wrapped around the tornado is described. Highest Doppler velocities were located outside the condensation funnel. The structure of the other tornadoes is also described, but with much less detail. Some of the analyses are compared with numerical simulations of tornado-like vortices done elsewhere.

Equilibrium Disk‐Bulge‐Halo Models for the Milky Way and Andromeda Galaxies

We describe a new set of self-consistent, equilibrium disk galaxy models that incorporate an exponential disk, a Hernquist model bulge, an NFW halo, and a central supermassive black hole. The models are derived from explicit distribution functions for each component, and the large number of parameters permit detailed modeling of actual galaxies. We present techniques that use structural and kinematic data such as radial surface brightness profiles, rotation curves, and bulge velocity dispersion profiles to find the best-fit models for the Milky Way and M31. Through N-body realizations of these models we explore their stability against the formation of bars. The models permit the study of a wide range of dynamical phenomenon with a high degree of realism.

4:41 Metastatic burst fracture risk prediction

Purpose of study: The clinical validity and utility of three biomechanically based predictive models for burst fracture risk in metastatically involved vertebrae were assessed. This study determines the ability of these models to accurately predict vertebral stability and yield clear clinical threshold values for burst fracture risk.Methods used: Digital computed tomography scan images of lytic thoracic and lumbar spinal metastases were categorized as burst fractured, wedge fractured or intact. Stability was analyzed using three predictive models of vertebral load carrying capacity: 1) VBN (maximum radial vertebral bulge under load), 2) VHN (maximum axial vertebral displacement under load), and 3) TS, (percentage volume of tumor). VBN and VHN were previously developed from an experimentally validated finite element model reflecting the biphasic mechanism of burst fracture while incorporating semiautomated estimates of tumor volume, bone mineral density, disc quality and pedicle involvement. Receiver-operator curves (ROC) and Hosmer-Lemeshow tests (HLT) were used to determine goodness of fit.of findings: Lytic metastases were identified in 72 patients, yielding a total of 92 vertebrae (maximum 2 per patient): 21 were fractured (23%, 4 wedge,17 burst) and 71 were intact (77%). Burst fracture prediction using VBN was found to have a specificity, sensitivity and confidence interval of 1 (ROC and HLT) at a threshold of 5.22 (Fig. 1). Burst fracture prediction using VHN and TS were also strong with ROC/HLT values of 0.992/0.873 and 0.988/0.749, respectively. Because the model is based on the mechanics of burst fracture, it is not predictive of wedge fracture risk.Relationship between findings and existing knowledge: Previous biomechanical analyses of metastatic spinal stability have not modeled the mechanism of burst fracture, thus limiting their predictive ability. Retrospective radiographic studies have shown tumor size and pedicle involvement to increase the risk of fracture in the metastatic spine. However, such methods based on the maximum cross-sectional area of the tumor have not yielded good specificity or clear threshold values as compared with the three-dimensional quantifications used in this study.Overall significance of findings: The VBN model exhibited excellent (100%) predictive ability for burst fractures in metastatically involved vertebrae providing useful clinical information for prophylactic decision making. Although more extensive prospective study is needed, these retrospective study results support the wider implementation of biomechanically based fracture risk prediction tools for use in clinically assessing patients with skeletal metastases.Disclosures: No disclosures.Conflict of interest: No conflict.

Nonhomogeneous permeability of canine anulus fibrosus.

This report examines the permeability coefficient and aggregate modulus of slices of anulus cut from canine lumbar intervertebral discs. To examine the influence of radial position on the properties of these materials, including outer samples with intact anulus edge. The outer edge of anulus fibrosus shows radial bulge during axial compression of motion segments. The radial bulge increases monotonically when the axial compression is sustained for several hours, until a plateau is reached. Triphasic modeling of axial compression shows that this time course of radial bulge can not be obtained using a uniform permeability coefficient according to values in the literature. Confined consolidation experiments (controlled load) were designed to measure the time course of uniaxial deformation of samples of anulus that were 4 mm in diameter and 1 mm tall. The rotation symmetry axis of the samples was defined in the radial direction of the disc. The radial permeability coefficient and the aggregate modulus were determined using the consolidation data and the linear biphasic theory. The permeability coefficient was lower at the periphery than in deeper layers of the anulus. Outer samples with outer surfaces that were 0.0-0.5 mm from the anulus edge had an average permeability coefficient of (1.02 +/- 0.57) x 10(-16) m4/Ns (n = 24). Inner samples that were 2.0-2.5 mm from the anulus edge had an average permeability coefficient of (2.81 +/- 0.98) x 10(-16) m4/Ns (n = 13). The aggregate modulus HA of outer samples was significantly higher (HA = 1.56 +/- 0.34 MPa) than that of inner samples (HA = 1.31 +/- 0.47 MPa). The fact that the outer anulus is less permeable than the inner anulus may explain why radial bulge of anulus fibrosus increases monotonically in time to an equilibrium value during sustained axial compression of a motion segment.

Biomechanical changes of the lumbar intervertebral disc after automated and nonautomated percutaneous discectomy: an in vitro investigation

A total of 40 human lumbar motion segments were prepared and tested in an electromechanical materials testing machine to investigate the biomechanical changes, i.e., intradiscal pressure, radial extension, and height of the intervertebral disc, after percutaneous discectomy. In 20 discs (group A) the nuclear material was excised using the nonautomated percutaneous lumbar discectomy technique (NAPLD). In the other 20 (group B) the material was removed with the automated percutaneous lumbar discectomy method (APLD). The results of the two groups were analyzed statistically and compared to each other. In the NAPLD group the removal of 0.1 g freeze-dried nucleus pulposus material reduced the height of the disc an average of 0.32 mm, versus 0.47mm in the APLD group. The radial bulge increased in both groups after the removal of 0.1 g freeze-dried nucleus pulposus material, on average 0.10 mm versus 0.15 mm. The intradiscal pressure also decreased in both groups after the removal of 0.1 g freeze-dried nucleus pulposus material, on average 0.94 bar versus 1.88 bar. The differences between the biomechanical data of the two groups were statistically significant for all three parameters (P < 0.05). Our results show that the mechanism for improving radicular pain in patients with herniated disc after treatment with percutaneous discectomy is still in question. We postulate that loss of height of the disc and, as a consequence, reduction of tension in the affected nerve root, plays a major role with regard to this improvement.

Change of Disc Height, Radial Disc Bulge, and Intradiscal Pressure From Discectomy An in Vitro Investigation on Human Lumbar Discs

Partial discectomy was done in vitro on 15 human lumbar discs from donors 20-40 years of age. The change of disc height, radial disc bulge, and intradiscal pressure was measured in relation to the mass of central disc tissue excised. Disc height decreases and radial disc bulge increases approximately in proportion with the mass of the tissue excised. At the same time, intradiscal pressure decreases. On average, removal of 1 g of disc tissue results in a height decrease of 0.8 mm and a radial bulge increase of 0.2 mm. Removal of 3 g of central disc tissue lowers the intradiscal pressure to approximately 40% of its initial value. A mechanical model is presented which explains the observed relation between the volume of material removed and the subsequent change of height, bulge, and pressure. The experimental results and the model provide insight into the rationale of disc pressurization. A high intradiscal pressure is a prerequisite for the mechanical function of the disc under physiologic conditions.