Human Cadaveric Lumbar Spines Research Articles

The effects of a new shape-memory alloy interspinous process device on the distribution of intervertebral disc pressures in vitro

This study was designed to measure the pressure distribution of the intervertebral disc under different degrees of distraction of the interspinous process, because of a suspicion that the degree of distraction of the spinous process may have a close relationship with the disc load share. Six human cadaver lumbar spine L2-L5 segments were loaded in flexion, neutral position, and extension. The L3-L4 disc load was measured at each position using pressure measuring films. Shape-memory interspinous process implants (SMID) with different spacer heights, ranging in size from 10 to 20 mm at 2 mm increments, were used. It was found that a SMID with a spacer height equal to the distance of the interspinous process in the neutral position can share the biomechanical disc load without a significant change of load in the anterior annulus. An interspinous process stabilizing device (IPD) would not be appropriate to use in those cases with serious spinal stenosis because the over-distraction of the interspinous process by the SMID would lead to overloading the anterior annulus which is a recognized cause of disc degeneration.

Evaluation of Magnetic Resonance Imaging-Compatible Needles and Interactive Sequences for Musculoskeletal Interventions Using an Open High-Field Magnetic Resonance Imaging Scanner

In this article, we study in vitro evaluation of needle artefacts and image quality for musculoskeletal laser-interventions in an open high-field magnetic resonance imaging (MRI) scanner at 1.0T with vertical field orientation. Five commercially available MRI-compatible puncture needles were assessed based on artefact characteristics in a CuSO4 phantom (0.1%) and in human cadaveric lumbar spines. First, six different interventional sequences were evaluated with varying needle orientation to the main magnetic field B0 (0 degrees to 90 degrees ) in a sequence test. Artefact width, needle-tip error, and contrast-to-noise ratio (CNR) were calculated. Second, a gradient-echo sequence used for thermometric monitoring was assessed and in varying echo times, artefact width, tip error, and signal-to-noise ratio (SNR) were measured. Artefact width and needle-tip error correlated with needle material, instrument orientation to B0, and sequence type. Fast spin-echo sequences produced the smallest needle artefacts for all needles, except for the carbon fibre needle (width <3.5 mm, tip error <2 mm) at 45 degrees to B0. Overall, the proton density-weighted spin-echo sequences had the best CNR (CNR(Muscle/Needle) >16.8). Concerning the thermometric gradient echo sequence, artefacts remained <5 mm, and the SNR reached its maximum at an echo time of 15 ms. If needle materials and sequences are accordingly combined, guidance and monitoring of musculoskeletal laser interventions may be feasible in a vertical magnetic field at 1.0T.

Junction kinematics between proximal mobile and distal fused lumbar segments: biomechanical analysis of pedicle and hook constructs

Background context Biomechanical studies have demonstrated increased motion in motion segments adjacent to instrumentation or arthrodesis. The effects of different configurations of hook and pedicle screw instrumentation on the biomechanical behaviors of adjacent segments have not been well documented. Purpose To compare the effect of three different fusion constructs on adjacent segment motion proximal to lumbar arthrodesis. Methods Seven human cadaver lumbar spines were tested in the following conditions: 1) intact; 2) L4–L5-simulated circumferential fusion (CF); 3) L4–L5-simulated fusion extended to L3 with pedicle screws; and 4) L4–L5-simulated fusion extended to L3 with sublaminar hooks. Rotation data at L2–L3, L3–L4, and L4–L5 were analyzed using both load limit control (±7.5 N·m) and displacement limit control (truncated to the greatest common angular motion of the segments for each specimen). Results Both the L3–L4 and L2–L3 motion segments above the L4–L5-simulated CF had significantly increased motion in all loading planes compared with the intact spine, but no significant differences were found between L3–L4 and L2–L3 motion. When the L3–L4 segment was stabilized with pedicle screws, its motion was significantly smaller in flexion, lateral bending, and axial rotation than when stabilized with sublaminar hooks. At the same time, L2–L3 motion was significantly larger in flexion, lateral bending, and axial rotation in the pedicle screw model compared with the sublaminar hook construct. Conclusions The use of sublaminar hooks to stabilize the motion segment above a circumferential lumbar fusion reduced motion at the next cephalad segment compared with a similar construct using pedicle screws. The semiconstrained hook enhancement may be considered if a patient is at a risk of adjacent segment disorders.

L5 – S1 Segmental Kinematics After Facet Arthroplasty

Background Facet arthroplasty is a motion restoring procedure. It is normally suggested as an alternative to rigid fixation after destabilizing decompression procedures in the posterior lumbar spine. While previous studies have reported successful results in reproducing normal spine kinematics after facet replacement at L4-5 and L3-4, there are no data on the viability of facet replacement at the lumbosacral joint. The anatomy of posterior elements and the resulting kinematics at L5-S1 are distinctly different from those at superior levels, making the task of facet replacement at the lumbosacral level challenging. This study evaluated the kinematics of facet replacement at L5-S1. Methods Six human cadaveric lumbar spines (L1-S1, 46.7 ± 13.0 years) were tested in the following sequence: (1) intact (L1-S1), (2) complete laminectomy and bilateral facetectomy at L5-S1, and (3) implantation of TFAS-LS (Lumbosacral Total Facet Arthroplasty System, Archus Orthopedics, Redmond, Washington) at L5-S1 using pedicle screws. Specimens were tested in flexion (8Nm), extension (6Nm), lateral bending (LB, ± 6Nm), and axial rotation (AR, ± 5Nm). The level of significance was α = .017 after Bonferroni correction for three comparisons: (1) intact vs. destabilized, (2) destabilized vs. reconstructed, and (3) intact vs. reconstructed. Results Laminectomy-facetectomy at L5-S1 increased the L5-S1 angular range of motion (ROM) in all directions. Flexion-extension (F-E) ROM increased from 15.3 ± 2.9 to 18.7 ± 3.5 degrees ( P < .017), LB from 8.2 ± 1.8 to 9.3 ± 1.6 degrees ( P < .017), and AR from 3.7 ± 2.0 to 5.9 ± 1.8 degrees ( P < .017). The facet arthroplasty system decreased ROM compared to the laminectomy-facetectomy condition in all tested directions ( P < .017). The facet arthroplasty system restored the L5-S1 ROM to its intact levels in LB and AR ( P > .017). F-E ROM after the facet arthroplasty system implantation was smaller than the intact value (10.1 ± 2.2 vs. 15.3 ± 2.9 degrees, P < .017). The load-displacement curves after the facet arthroplasty system implantation at L5-S1 were sigmoidal, and quality of motion measures were similar to intact, demonstrating graded resistance to angular motion in F-E, LB and AR. Conclusions The facet arthroplasty system was able to restore stability to the lumbosacral segment after complete laminectomy and bilateral facetectomy, while also allowing near-normal kinematics in all planes. While F-E ROM after the facet arthroplasty system implantation was smaller than the intact value, it was within the physiologic norms for L5-S1. These results are consistent with previous studies of facet arthroplasty at L3-L4 and L4-L5 and demonstrate that TFAS technology can be adapted to the lumbosacral joint with functionality comparable to its application in superior lumbar levels.

A Study on the Structural Properties of the Lumbar Endplate

Histologic experiments and biomechanical tests were performed in human cadaveric lumbar spine models. To determine (1) the anatomic structures of lumbar endplates, (2) the relationship between bone mineral density (BMD) and biomechanical properties of lumbar endplates, and (3) the influence of spinal level on the failure loads of lumbar endplates. Previous works have shown that the posterolateral corners of the lumbar endplates are stronger than the anterior and central regions. Information on the microstructures of lumbar endplates and the effects of both BMD and spinal level on biomechanical properties of lumbar endplates would be valuable for spine surgeons and implant designers to avoid subsidence. Twenty fresh human cadaver lumbar vertebrae specimens were collected for HE staining and the sections through the specimens were examined under light microscope. The areas of the pore structures in the lumbar endplates were measured and analyzed by statistical methods. Sixty-five cadaver lumbar vertebrae were evaluated with dual energy radiograph absorptiometry and according to their BMD, all vertebrae were divided into 3 groups. Indentation tests were performed at 27 standardized test sites in endplates of these vertebrae using a 1.5-mm-diameter, hemispherical indenter with a rate of 12 mm/min. The failure load at each test site was determined using the load-displacement curve. Spearman analysis was used to evaluate the correlation between BMD and failure loads of lumbar endplates. Factorial analysis of variance was performed to reveal the effects of both BMD and spinal level on failure load distribution on the lumbar endplates. (1) The peripheral regions were thicker than the central regions of lumbar endplates. The central regions were porous, as the fused trabeculae and peripheral regions had fewer and smaller pore structures. (2) The tests showed that there were significant differences in failure load between 3 groups (P < 0.01). BMD was positively correlated with the failure load of the lumbar endplate. (3) The strongest position of the lumbar endplate was the posterolateral region closest to the pedicles and the failure loads tended to increase from anterior to posterior regions of the lumbar endplates. (4) The failure load distribution did not change with the BMD decrease. (5) The differences of the failure loads between the lumbar segments were significant (P < 0.05). The failure loads of the lumbar endplates showed an increasing tendency from L1-L5 segments. The differences in the anatomic structures of different regions are the histologic foundation of biomechanical properties of lumbar endplates. It is necessary that BMD should be measured before operation and implants should be placed in posterior-lateral regions of lumbar endplates so that subsidence syndrome can be reduced as much as possible. In addition, the fact that the endplates of the upper lumbar segments with the lower strength have higher risk of subsidence should be concerned about by spine surgeons and implant designers.

Einstichwinkel bei der epidural-perineuralen Injektion an der Lendenwirbelsäule

The aim of this study was to find the correct angle of the needle position for the epidural perineural injection at the lumbar spine without any help by imaging. In 11 human cadaver lumbar spines besides dura, nerve roots and bones all soft tissue had been removed to allow us to look into the anterior lateral epidural spaces between L3 and S1 in different angles with an operation microscope. The area between the dura (medial), facet joint (lateral) and the laminae (cranial and caudal) were photographed and planimetrically measured. This area is called the width of the injection canal. Degenerative lumbar spines show a width of the injection canal of 29.61 mm(2) in L5/S1 with an angle of the needle position of 15 degrees to the midline. The optimal angle position of the needle brought a width of the injection canal in L4/5 only for 7.3 mm(2) and in L3/4 for 3.5 mm(2). In non-degenerative spines the injections canals were much wider. The epidural-perineural injection into the anterolateral epidural space only makes sense in the segment L5/S1. Here the L5 nerve root is reached as well as the S1 root - the main causes of sciatica. In upper segments the injection canal is far smaller even at optimal injection angles. In case of nerve root compression at L4 and upwards other epidural injection techniques should be used such as the epidural dorsal loss of resistance technique or the transforaminal technique. With some training it is possible to perform epidural-perineural injection for sciatica without the help of imaging.

L5 - s1 segmental kinematics after facet arthroplasty.

BackgroundFacet arthroplasty is a motion restoring procedure. It is normally suggested as an alternative to rigid fixation after destabilizing decompression procedures in the posterior lumbar spine. While previous studies have reported successful results in reproducing normal spine kinematics after facet replacement at L4-5 and L3-4, there are no data on the viability of facet replacement at the lumbosacral joint. The anatomy of posterior elements and the resulting kinematics at L5-S1 are distinctly different from those at superior levels, making the task of facet replacement at the lumbosacral level challenging. This study evaluated the kinematics of facet replacement at L5-S1.MethodsSix human cadaveric lumbar spines (L1-S1, 46.7 ± 13.0 years) were tested in the following sequence: (1) intact (L1-S1), (2) complete laminectomy and bilateral facetectomy at L5-S1, and (3) implantation of TFAS-LS (Lumbosacral Total Facet Arthroplasty System, Archus Orthopedics, Redmond, Washington) at L5-S1 using pedicle screws. Specimens were tested in flexion (8Nm), extension (6Nm), lateral bending (LB, ± 6Nm), and axial rotation (AR, ± 5Nm). The level of significance was α = .017 after Bonferroni correction for three comparisons: (1) intact vs. destabilized, (2) destabilized vs. reconstructed, and (3) intact vs. reconstructed.ResultsLaminectomy-facetectomy at L5-S1 increased the L5-S1 angular range of motion (ROM) in all directions. Flexion-extension (F-E) ROM increased from 15.3 ± 2.9 to 18.7 ± 3.5 degrees (P < .017), LB from 8.2 ± 1.8 to 9.3 ± 1.6 degrees (P < .017), and AR from 3.7 ± 2.0 to 5.9 ± 1.8 degrees (P < .017). The facet arthroplasty system decreased ROM compared to the laminectomy-facetectomy condition in all tested directions (P < .017). The facet arthroplasty system restored the L5-S1 ROM to its intact levels in LB and AR (P > .017). F-E ROM after the facet arthroplasty system implantation was smaller than the intact value (10.1 ± 2.2 vs. 15.3 ± 2.9 degrees, P < .017). The load-displacement curves after the facet arthroplasty system implantation at L5-S1 were sigmoidal, and quality of motion measures were similar to intact, demonstrating graded resistance to angular motion in F-E, LB and AR.ConclusionsThe facet arthroplasty system was able to restore stability to the lumbosacral segment after complete laminectomy and bilateral facetectomy, while also allowing near-normal kinematics in all planes. While F-E ROM after the facet arthroplasty system implantation was smaller than the intact value, it was within the physiologic norms for L5-S1. These results are consistent with previous studies of facet arthroplasty at L3-L4 and L4-L5 and demonstrate that TFAS technology can be adapted to the lumbosacral joint with functionality comparable to its application in superior lumbar levels.

Biomechanical comparison of two different concepts for stand alone anterior lumbar interbody fusion

Segmental instability in degenerative disc disease is often treated with anterior lumbar interbody fusion (ALIF). Current techniques require an additional posterior approach to achieve sufficient stability. The test device is an implant which consists of a PEEK-body and an integrated anterior titanium plate hosting four diverging locking screws. The test device avoids posterior fixation by enhancing stability via the locking screws. The test device was compared to an already established stand alone interbody implant in a human cadaveric three-dimensional stiffness test. In the biomechanical test, the L4/5 motion segment of 16 human cadaveric lumbar spines were isolated and divided into two test groups. Tests were performed in flexion, extension, right and left lateral bending, right and left axial rotation. Each specimen was tested in native state first, then a discectomy was performed and either of the test implants was applied. Finite element analysis (FE) was also performed to investigate load and stress distribution within the implant in several loading conditions. The FE models simulated two load cases. These were flexion and extension with a moment of 5 Nm. The biomechanical testing revealed a greater stiffness in lateral bending for the SynFix-LR compared to the established implant. Both implants showed a significantly higher stiffness in all loading directions compared to the native segment. In flexion loading, the PEEK component takes on most of the load, whereas the majority of the extension load is put on the screws and the screw-plate junction. Clinical investigation of the test device seems reasonable based on the good results reported here.

Biomechanical evaluation of different asymmetrical posterior stabilization methods for minimally invasive transforaminal lumbar interbody fusion

Beside several other advantages, the transforaminal approach for lumbar interbody fusion offers the possibility of reducing surgical trauma by limiting the approach to only 1 side. This requires posterior stabilization methods, which are applied without the need to damage contralateral muscles and soft tissues. The goal in this study was to compare different posterior stabilization methods for minimally invasive transforaminal lumbar interbody fusion (TLIF) biomechanically. Stiffness testing was performed in 8 fresh-frozen human cadaveric lumbar spine motion segments, including the following sequentially tested configurations: 1) native motion segment; 2) TLIF and bilateral pedicle screw (PS) construct; 3) TLIF and ipsilateral PS construct; 4) TLIF and ipsilateral PSs plus contralateral translaminar facet screws according to the Magerl technique; and 5) TLIF and ipsilateral PSs plus contralateral lumbar facet interference screw (LFIS). In extension, the unilateral range of motion (uROM) and elastic zone (EZ) were significantly lower than native motion segments for bilateral PS and LFIS. There were no significant differences among the different stabilization methods. In flexion, uROM and EZ were significantly lower than the native segment in the spines treated with bilateral PSs and translaminar facet screws. The LFIS differed from the native segment in EZ only. Again, there were no significant differences between the different posterior stabilization methods. In lateral bending, the EZ of spines treated with uni- and bilateral PS differed significantly. There were no additional significant differences. In rotation, the stiffness values of bilateral PS were significantly higher than native, unilateral PS, and LFIS. The comparison between ipsi- and bilateral PS showed a tendency, but not a significant difference for uROM and EZ. There was no statistically significant evidence that the TLIF method led to an asymmetrical motion behavior in our study. Bilateral PS augmentation offers significantly more stability than unilateral PSs in the majority of the test modes. There was no significant difference between the other tested methods. All tested stabilization methods could achieve at least the stability of the native segment.

Biomechanical Evaluation of an Interspinous Stabilizing Device, Locker

A biomechanical study. To evaluate the biomechanical properties of a novel dynamic interspinous device named Locke There has been no biomechanical study on this device. Five human cadaveric lumbar spine specimens (L2-S1) were tested in the following sequence: (1) intact state; (2) after removal of the interspinous ligaments of L3-L4; (3) after application of the Locker at the interspinous space; (4) after destabilization of the L3-L4 motion segments; and (5) after reapplication of the Locker to the destabilized segments. Range of motion (ROM) and intradiscal pressure were measured by a video-based motion capture system and needle transducers. Applied to the intact spine, the Locker significantly reduced the ROM of the segment in extension and flexion without significant effect on lateral bending and/or axial rotation. When applied to the destabilized segment, it significantly reduced the ROM in all directions of movement except in axial rotation, where it failed to restore the ROM of the segment. The ROM of adjacent segments was not significantly affected by the application of the Locker. Pressures at the posterior anulus and central nucleus were decreased by application of the Locker. The Locker showed a significant stabilizing effect on the spinal motion segment both in the intact and destabilized spine without any significant effect on adjacent segments. It also decreased the pressures of the posterior anulus and central nucleus significantly. However, in the destabilized spine, it showed no stabilizing effect in axial rotation. This biomechanical property should be considered in clinical application.

Biomechanical Testing of a Novel Four-Rod Technique For Lumbo-Pelvic Reconstruction

A biomechanical testing protocol was used to study different lumbo-pelvic fixation techniques in a human cadaveric lumbar spine model. To compare the in vitro biomechanics of a novel four-rod lumbo-pelvic reconstruction technique with and with out cross-links, to that of a conventional cross-linked two-rod technique. Numerous lumbo-pelvic reconstruction methods based on the Galveston two-rod technique have been proposed for cases involving total sacrectomy. Recently a technique that proposes novel use of 4 supporting longitudinal rods across the lumbo-pelvic junction has been reported. No comparative in vitro biomechanical testing has been previously done to evaluate these different reconstruction methods. Five spines were evaluated in flexion, extension, left-right lateral bending and left-right axial rotation in a human total sacrectomy model. The model was comprised of cadaveric lumbar spines (L1-L5) with custom fabricated polyethylene blocks used to simulate pelvic fixation. Three conditions were evaluated: Linked Four-Rod, Linked Two-Rod, and Four-Rod (no cross-links). Flexibility and motion data were compared using a one-way repeated measures analysis of variance and SNK tests. The Linked Four-Rod and Four-Rod conditions significantly decreased flexibility and reduced L5-Pelvic motion over the Linked Two-Rod construct in flexion and extension. The Linked Four-Rod condition significantly decreased flexibility in left-right axial rotation compared with the Four-Rod and Linked Two-Rod conditions. No significant differences occurred in relative lateral movement between left and right pelvic polyethylene blocks. The four-rod technique improved fixation stability over the conventional linked two-rod technique in flexion and extension, and when cross-linked, in left-right axial rotation. The four-rod technique also significantly reduced L5-Pelvic junction movement in flexionand extension, which may have implications for bony fusion. The use of cross-links is recommended.

Mechanical and Biomechanical Characterization of a Polyurethane Nucleus Replacement Device Injected and Cured In Situ Within a Balloon

Background The DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device. Methods A number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the device's compressive, shear properties, and fatigue testing to determine the device's compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress. Results The static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress. Conclusions The results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study. Clinical Relevance Nucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Effect of multilevel lumbar disc arthroplasty on the operative- and adjacent-level kinematics and intradiscal pressures: an in vitro human cadaveric assessment

Background context With lumbar arthroplasty gaining popularity, limited data are available highlighting changes in adjacent-level mechanics after multilevel procedures. Purpose Compare operative– and adjacent-segment range of motion (ROM) and intradiscal pressures (IDPs) after two-level arthroplasty versus circumferential arthrodesis. Study design Cadaveric biomechanical study. Methods Ten human cadaveric lumbar spines were used in this investigation. Biomechanical testing was performed according to a hybrid testing protocol using an unconstrained spine simulator under axial rotation (AR), flexion extension (FE), and lateral-bending (LB) loading. Specimens were tested in the following order: 1) Intact, 2) L3–L5 total disc replacement (TDR), 3) L3–L5 anterior interbody cages+pedicle screws. IDP was recorded at proximal and distal adjacent levels and normalized to controls (%intact). Full ROM was monitored at the operative and adjacent levels and reported in degrees. Results Kinematics assessment revealed L3–L5 ROM reduction after both reconstructions versus intact controls (p<.05). However, global quality of segmental motion distributed over L2–S1 was preserved in the arthroplasty group but was significantly altered after circumferential fixation. Furthermore, adjacent-level ROM was increased for the arthrodesis group under LB at both segments and during AR at L2–L3 relative to controls (p<.05). FE did not reveal any intergroup statistical differences. Nonetheless, after arthrodesis IDPs were increased proximally under all three loading modalities, whereas distally a significant IDP rise was noted during AR and LB (p<.05). No statistical differences in either biomechanical parameter were recorded at the adjacent levels between intact control and TDR groups. Conclusions Our results indicate no significant adjacent-level biomechanical changes between arthroplasty and control groups. In contrast, significant alterations in ROM and IDP were recorded both proximally (ROM=LB & AR; IDP=AR, FE, LB) and distally (ROM=LB; IDP=AR & LB) after circumferential arthrodesis. Therefore, two-level lumbar arthroplasty maintains a more favorable biomechanical environment at the adjacent segments compared with the conventional transpedicular fixation technique. This, in turn, may have a positive effect on the rate of the transition syndrome postoperatively.

Histological Changes and Temperature Distribution Studies of a Novel Bipolar Radiofrequency Heating System in Degenerated and Nondegenerated Human Cadaver Lumbar Discs

The purpose of this experimentation was to investigate the safety of a novel cooled bipolar radiofrequency system by examining histology and monitoring temperature distribution in the disc, epidural space, and adjacent to the nerve roots. In our study we used two human cadaver lumbar spines, one moderately to severely degenerated and the other mildly degenerated. Radiofrequency ablation of the disc posterior annulus is a theoretically plausible technique to ablate the nociceptors and to modify collagen of the annulus fibrosus. A novel cooled bipolar radiofrequency system is used to perform a procedure called intervertebral disc biacuplasty to heat the posterior annulus for the treatment of discogenic pain. Four lumbar intervertebral discs were treated in each spine sample using the bipolar system while two lumbar discs of each spine were used as controls. Temperatures developed in the posterior annulus of the disc were on average 52.35 +/- 5.07 degrees C, while in the intervertebral foramen and in the spinal canal were 38.84 +/- 1.7 degrees C and 38.29 +/- 2.04 degrees C, respectively. There was no histological evidence of damage to any other structures including vertebral end plates, epidural space, or nerve roots. Additionally, there were no histological changes in the posterior annulus that were consistent with heat-induced changes to collagen structure. Temperatures reached in the posterior annulus during transdiscal biacuplasty were greater than required (45 degrees C) for neuroablation. Temperatures reached at the neural foramina and epidural were low enough to avoid neural damage.

Mechanical and biomechanical characterization of a polyurethane nucleus replacement device injected and cured in situ within a balloon.

BackgroundThe DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device.MethodsA number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the device's compressive, shear properties, and fatigue testing to determine the device's compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress.ResultsThe static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress.ConclusionsThe results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study.Clinical RelevanceNucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Intravertebral Pressure During Vertebroplasty and Balloon Kyphoplasty

Intravertebral pressure (IP) measurements were conducted on human cadaveric lumbar spines in a biomechanical study. To assess the pressure that is generated in the center of the vertebral body during the cement fill in vertebroplasty (VP) and balloon kyphoplasty (BKP). High IP during polymethylmethacrylate (PMMA) injection have frequently been raised as a reason for the higher cement leakage rate during VP in contrast to BKP. The IP recorded in the periphery of the vertebral body is much lower than the injection syringe pressure. The pressure ratios in the central region of the vertebrae close to the injection cannula are not known. VP and BKP were performed in 8 lumbar cadaveric spines. A pressure sensor was placed in the center of the vertebral body. In the VP subgroup a total volume of 6 mL of polymethylmethacrylate cement was delivered in 1.5 mL increments. In the BKP subgroup balloon dilation up to a volume of 4 mL was made before cement injection of 6 mL (1.5 mL increments). Room temperature, cement mixing time, and constant volume flow during cement injection were recorded. During the administration of the first 1.5 mL of bone cement the average IP for VP was 18.5 versus 1.2 kPa for BKP. For the second filling an average pressure of 34.9 kPa (VP) and 3.4 kPa (BKP) was recorded. The average IP during the third injection was 53.0 kPa (VP) and 14.8 kPa (BKP). The pressure of the last 1.5 mL averaged in 56.6 kPa (VP) and 25.5 kPa (BKP). The IP measured during cement augmentation in cadaveric spines was lower in BKP than in VP. In the BKP group a relative increase of the IP was registered at the end state of cement delivery when the cavity was overfilled.

The Effect of Dynamic Posterior Stabilization on Facet Joint Contact Forces

Facet contact forces in the lumbar spine were measured during flexibility tests using thin film electroresistive sensors in intact cadaveric spine specimens and in injured specimens stabilized with a dynamic posterior system. The purpose of this study was to investigate the effect of the Dynesys system on the loading in the facet joints. The Dynesys, a posterior nonfusion device, aims to preserve intersegmental kinematics and reduce facet loads. Recent biomechanical evidence showed that overall motion is less with the Dynesys than in the intact spine, but no studies have shown its effect on facet loads. Ten human cadaveric lumbar spine specimens (L2-L5) were tested by applying a pure moment of +/-7.5 N m in 3 directions of loading with and without a follower preload of 600 N. Test conditions included an intact specimen and an injured specimen stabilized with 3 Dynesys spacer lengths. Bilateral facet contact forces were measured during flexibility tests using thin film electroresistive sensors (Tekscan 6900). Implanting the Dynesys significantly increased peak facet contact forces in flexion (from 3 N to 22 N per side) and lateral bending (from 14 N to 24 N per side), but had no significant effect on the magnitude of the peak forces in extension and axial rotation. Peak facet loads were significantly lower with the long spacer compared with the short spacer in flexion and lateral bending. Implantation of the Dynesys did not affect peak facet contact forces in extension or axial rotation compared with an intact specimen, but did alter these loads in flexion and lateral bending. The spacer length affected the compression of the posterior elements, with a shorter spacer typically producing greater facets loads than a longer one.

Immediate Biomechanical Effects of Lumbar Posterior Dynamic Stabilization Above a Circumferential Fusion

Biomechanical in vitro human cadaveric lumbar flexibility testing with 6 sequential treatments. To compare the range of motion (ROM) of dynamic one-level posterior stabilization constructs to one-level rigid rod fixation constructs and to study the effects of extending the posterior construct to the adjacent superior level. Patients experiencing pain and biomechanical instability at one level may also present with radiographic or other indicators of early degeneration at an adjacent level. Clearly, fusion would be warranted at the symptomatic level, but the treatment plan for the adjacent level remains controversial. Additionally, the effects on adjacent motion segments above a fusion level are currently not well understood. Thirteen fresh frozen human cadaveric lumbar spines (L1-L5) were tested in 6 modes of loading: 3 were randomized to dynamic posterior stabilization constructs and 7 to a rigid rod pedicle screw system. Each group was subjected to 6 treatments. When comparing the instrumented treatments, only Treatment 6, two-level hybrid constructs, exhibited a statistically significant effect in flexion-extension bending at L2-L3 between the posterior dynamic system and rigid rod fixation (P = 0.014). ROM at the superior adjacent level (L2-L3) demonstrated no significant difference between intact, destabilized, one-level posterior fixation, and one-level circumferential fusion at the index level (L3-L4) when comparing posterior dynamic stabilization to rigid rod fixation. However, ROM at the superior adjacent level (L2-L3) was significantly greater for lateral bending and axial rotation when both levels (L2-L3 and L3-L4) were stabilized with a dynamic stabilization system. When the functional spinal units were instrumented with a two-level hybrid construct, two-level posterior instrumentation (L2-L3 and L3-L4) with a cage at the index level (L3-L4), all bending modes generated significantly greater ROM for the dynamic stabilization group at L2-L3 compared with rigid rod fixation.

Anatomic and clinical study of spinal osteotomies for traumatic fixed kyphotic deformity of thoracolumbar spine

To investigate the safety and efficiency of spinal osteotomies for traumatic fixed kyphotic deformity of thoracolumbar spine with spinal cord injury. Single-level vertebral osteotomies were performed on 3 groups of fresh-frozen human cadaveric lumbar spines. Group 1 underwent a conventional anterior opening-wedge or posterior closing-wedge osteotomy, Group 2 underwent a conventional decancellation posterior closing-wedge osteotomy, and Group 3 underwent the modified decancellation posterior closing-wedge osteotomy. Sagittal plane angulation as well as anterior height and distance of the spinal column were measured before and after osteotomy. In the clinical study, 26 cases of old thoracolumbar fractures with spinal cord injury, 36 years in average, were recruited in this study. The mean time from injury to this operation was 25 months ranging from 3 months to 11 years. Prior to the index surgery, 9 patients received conservative treatment, and 17 patients underwent surgical treatment. There were complete paraplegia in 10 cases and incomplete paraplegia in 14 cases (Frankel B 2 cases, C 10 and D 2). The patients suffered from the low back pain, the average score of VAS was 4.5 (2.5 - 6.0). The patients were found with remained kyphotic deformity of a mean 35 degrees (20 degrees - 75 degrees ). According to the deformity angles, conventional or modified decancellation posterior closing-wedge osteotomy was performed. On 3 groups of fresh-frozen human cadaveric lumbar spines, the mean correction was (38.0 +/- 2.5) degrees for Group 1, (36.0 +/- 3.6) degrees for Group 2, and (49.0 +/- 2.0) degrees for Group 3. The mean change in anterior height and distance was (13.8 +/- 1.4) mm and (30.2 +/- 2.5) mm respectively for Group 1. For Groups 2 and 3 it was only 2 - 4 mm. In clinical trial, all cases were followed up for 10 months to 6 years, average 12.5 months. Successful decompression and satisfied correction of kyphosis was noticed. The post-operatively mean angle of kyphosis deformity was 10.8 degrees , ranging from 0 degrees to 40 degrees . Neurological functional recovery was noticed in 50% of all cases. For complete spinal cord injury, 30% of cases partially recovered (sensory function), whereas neurological function recovery was noted in 64.3% of cases with incomplete spinal cord injury, a statistical difference was showed between the incomplete and complete spinal cord injury cases (P < 0.01). The score of VAS was 2.3 (1.0 - 3.5) at last follow-up. The traumatic fixed kyphotic deformity of thoracolumbar spine with spinal cord injury could be treated with conventional or modified decancellation posterior closing-wedge osteotomy, neurological function and low back pain were expectably recovered.

Assessment of Human Disc Degeneration and Proteoglycan Content Using T1ρ-weighted Magnetic Resonance Imaging

T1rho relaxation was quantified and correlated with intervertebral disc degeneration and proteoglycan content in cadaveric human lumbar spine tissue. To show the use of T1rho-weighted magnetic resonance imaging (MRI) for the assessment of degeneration and proteoglycan content in the human intervertebral disc. Loss of proteoglycan in the nucleus pulposus occurs during early degeneration. Conventional MRI techniques cannot detect these early changes in the extracellular matrix content of the disc. T1rho MRI is sensitive to changes in proteoglycan content of articular cartilage and may, therefore, be sensitive to proteoglycan content in the intervertebral disc. Intact human cadaveric lumbar spines were imaged on a clinical MR scanner. Average T1rho in the nucleus pulposus was calculated from quantitative T1rho maps. After MRI, the spines were dissected, and proteoglycan content of the nucleus pulposus was measured. Finally, the stage of degeneration was graded using conventional T2 images. T1rho decreased linearly with increasing degeneration (r = -0.76, P < 0.01) and age (r = -0.76, P < 0.01). Biochemical analysis revealed a strong linear correlation between T1rho and sulfated-glycosaminoglycan content. T1rho was moderately correlated with water content. Results from this study suggest that T1rho may provide a tool for the diagnosis of early degenerative changes in the disc. T1rho-weighted MRI is a noninvasive technique that may provide higher dynamic range than T2 and does not require a high static field or exogenous contrast agents.