Longitudinal Rods Research Articles

Flexible non-fusion scoliosis correction systems reduce intervertebral rotation less than rigid implants and allow growth of the spine: a finite element analysis of different features of orthobiom™

The orthobiom non-fusion scoliosis correction system consists of two longitudinal rods, polyaxial pedicle screws, mobile and fixed connectors and a cross-connector. The mobile connectors can move along and around the rod, thus allowing length adaptation during growth. The aim of this study was to determine the effects of different features of this novel implant on intervertebral rotations, to calculate the movement of the mobile connectors along the rods for different loading cases and to compare the results with those of a rigid implant construct. A finite element analysis was performed using six versions (M1-M6) of a three-dimensional, nonlinear model of a spine ranging from T3 to L2. The models were loaded with pure moments of 7.5 N m in the three main anatomical planes. First, the validated intact model (M1) was studied. Then, the orthobiom implant system was inserted, bridging the segments between T4 and L1 (M2). The effect of pedicle screws only in every second vertebrae was investigated (M3). For comparison, three connection variations of screws and rods were investigated: (1) an implant with rigid screws and mobile connectors (M4), (2) an implant with non-locking polyaxial screws and fixed connectors (M5) and (3) a completely rigid implant construct (M6). For flexion, extension and lateral bending, intervertebral rotation was reduced at all implant levels due to the implants. A rigid implant construct (M6) and an implant with non-locking polyaxial screws and fixed connectors (M5) led to the strongest reduction of intervertebral rotation. The orthobiom non-fusion implant system (M2, M3) allowed much more intervertebral rotation than a rigid implant (M6). Differences in intervertebral rotations were small when polyaxial screws were placed at every second level only (M3) instead of at every level (M2). For axial rotation, intervertebral rotation was strongly reduced by a rigid implant construct (M6) and by an implant with rigid screws and mobile connectors (M4). For rotation, an implant with non-locking polyaxial screws (M2, M3, M5) led to nearly the same intervertebral rotations as in an intact spine without an implant (M1). The predicted maximum translation of the mobile connectors along the rod was 4.2 mm for extension, 3.1 mm for lateral bending, 1.6 mm for flexion and 0.8 mm for axial rotation. The movement of the connectors was highest for those closest to the ends of the rods. With rigid screws, the maximum translation was significantly reduced. This study, conducted under a load-controlled loading protocol, showed that intervertebral rotation was reduced much less by the non-fusion orthobiom system than by a rigid implant. The mobile connectors moved considerably along the rod when the spine was bent. It can be expected that the connectors also move along the rod as the adolescent grows, possibly leaving the discs intact until the patient is fully grown.

Mechanical Performance of PRIMA OCT System under Interconnection Testing and Corpectomy Testing

The fixation of the vertebral column using transpedicular screws is a well-establish technique. Multi-axial pedicle screw designs allow deviation of the screw away from the perpendicular to the longitudinal rod, which facilitates application of a screw-rod system such as PRIMA OCT into the curved spine. This study was performed a static (compression bending and torsion) and dynamic (compression bending fatigue) empirical analysis of PRIMA OCT component such as pedicle screw, rod and set screw based on the guideline of ASTM F136-98 using Ultra-high Molecular Weight Polyethylene (UHMWPE) blocks as test vertebral bodies.

Syntheon Endoguide: A Novel Overtube to Assist Colonoscopy

Background: Patient comfort and safety during routine colonoscopy continue to be of primary concern. Passage of the endoscope through the lower left colon can be a rate-limiting step for many endoscopists, and the source of discomfort for many patients. Overtubes have been used in the past as colonoscopy assist devices for difficult bowel anatomy. A novel overtube was recently designed (EndoGuide, Syntheon, LLC, Miami, FL) to address this situation. This new technology should permit the endoscopist to advance the colonoscope with minimal stretching of the bowel and less air insufflation, and may allow for procedures to be done with minimal or no sedation. The EndoGuide is designed to fit over a pediatric colonoscope and can be converted from a flexible to a rigid configuration, on demand, using a vacuum source. The EndoGuide will conform to the anatomy it is in, even when stiffened to the rigid configuration. It consists of an outer jacket and an inner liner. Between these inner and outer layers is a body tube supported by rings and longitudinal rods. The body tube is responsible for the column strength exhibited by the entire device. A sliding switch controls the application of suction to stiffen the overtube into a rigid configuration. Aim: To develop and assess the function and safety of the EndoGuide system in a pre-clinical animal model and in a small pilot human clinical study. Methods: Two anesthetized 30 kg farm-raised pigs received a bowel cleansing. The instrument was mounted on a standard pediatric colonoscope and advanced under fluoroscopic guidance from the anus to the more proximal colon. Human volunteers undergoing routine sedated colonoscopy were recruited and consented to an observational descriptive study in which the overtube was employed during their scheduled procedure. The endoscopist completed an written evaluation rating the function of the EndoGuide and the colonoscope following the procedure. Results: In the porcine model, the EndoGuide was fluoroscopically observed to inhibit excessive movement of bowel loops when it was stiffened during proximal advancement of the colonoscope. In three patients (one male and two female), the overtube was deployed. Routine colonoscope function was preserved when it was encompassed by the overtube in both the flexible and rigid states. No adverse events and no mucosal trauma was observed. Conclusions: The EndoGuide can be easily and safely inserted into the colon and manipulated using a vacuum source to change its flexibility without any deleterious effect to the mucosal lining. Further studies are needed to determine which patients may benefit from this colonoscopy assist device.

A Novel “Four-Rod Technique” for Lumbo-Pelvic Reconstruction: Theory and Technical Considerations

Surgical technique with case example. To report on a novel technique that allows for the placement of 4 separate longitudinal rods across the lumbo-pelvic junction. Despite advances in surgical techniques and instrumentation, lumbo-pelvic fixation remains a significant challenge. Fusions to the pelvis create long lever arms and generate high forces across the lumbosacral junction, resulting in high rates of screw pullout and implant fracture. In the attempt to achieve better bony fixation, techniques described include the use of bone cement, hydroxyapatite, and expandable screws. Although this process has decreased the incidence of screw pullout, it has not addressed the problem of rod fracture at the lumbo-pelvic junction. There are 4 separate longitudinal rods placed across the lumbo-pelvic junction that couples proximal lumbar screw anchors to 4 separate pelvic fixation points. Proximal lumbar fixation anchors are based on alternating Roy-Camille "straight ahead" screws and Magerl "lateral to medial converging" pedicle screws. There are 4 distal pelvic fixation anchors used based on 1 pair of Galveston-like screws and 1 pair of proximal iliac wing screws. Early results of both ex vivo and in vivo reconstruction show that careful insertion of the lumbar and pelvic screws allows for divergent placement of the pedicle screw heads in a manner that 2 longitudinal rods can be placed per side, resulting in a total of 4 longitudinal rods across the lumbo-pelvic junction. Selection of cross-links in various combinations allows for additional axial and torsional stability, depending on the desired reconstruction. Longer follow-up is necessary, and biomechanical and finite element studies are needed to show long-term efficacy of this technique, however, early results indicate that such a construct is feasible. Furthermore, depending on the general medical condition of the patient, immediate postoperative weight bearing is possible and reasonable.

Posterior Instrumentation of the Cervical Spine Using the Neon Occipito-Cervical System

Posterior cervical and cervicothoracic stabilization, if necessary, in combination with posterior spondylodesis, after closed or open reduction as well as with or without neural decompression as clinically indicated. Instabilities and deformities of rheumatoid, traumatic, neoplastic, infectious, iatrogenic or congenital origin. Multilevel cervical spinal stenosis with degenerative instability or kyphosis of the affected spinal segment. Corrective spondylodesis for posttraumatic or postinfectious kyphosis. Infection in the operative field. Inability to undergo anesthesia. Prone position, rigid head fixation, e. g., with Mayfield tongs. If appropriate, closed reduction under lateral image intensification. Midline posterior surgical approach at the level of the segment to be instrumented. If necessary, open reduction. Insertion of the cervical/upper thoracic screws. If necessary, posterior decompression. Instrumentation with prebent longitudinal rods. If a fusion is to be obtained, decortication of the posterior bone elements with a burr and onlay of cancellous bone. 44 patients, 13 women and 31 men, with an average age of 57 years were operated on between August 2000 and August 2003. All patients underwent a follow-up examination 4-39 months (average 15.7 months) after the initial surgery. Fusion was achieved in all patients who had undergone a posterior spondylodesis: no implant failure, no implant removal or reoperation. The preoperatively planned instrumentation could be implemented intraoperatively in all patients.

COMPARATIVE STUDY OF ROTATIONAL STABILITY PARAMETERS OF TRANSPEDICULAR SPINAL FUSION IN EXPERIMENT

Objectives. To estimate macroscopically the strength, rigidity and limit of elasticity in the “spinal segments – transpedicular fixator” system. versus similar characteristics of the intact spine under dislocating rotational loads. Material and Methods. Еxperiments with anatomic specimens of Th12–L2 segments were performed. Unstable damages of L1 and transpedicular fixation with 4 screw transpedicular spinal system were imitated. All specimens were exposed to the testing rotational load in universal test machine Zwick 1464. Results. It is established that under rotational load general strength of the injured Th12–L1–L2 spinal segments fused with transpedicular fixator is 20 % lower than that in a corresponding intact spine segment. Rigidity parameters of fused segments are 17.5 % lower than those of intact segments. Destabilization of «spinal segments – transpedicular fixator» system under rotational loads is caused by the compression of a bone substance in Th12 and L2 bodies with screws and a turn of screws around longitudinal rods due to a rod slip in anchoring elements. Conclusion. The performed study may serve a basis for following data analysis from a viewpoint of metal resistance and for development of optimal rehabilitation loads to the injured spine during postoperative period.

Constructs Incorporating Intralaminar C2 Screws Provide Rigid Stability for Atlantoaxial Fixation

An in vitro biomechanical study of C1-C2 posterior fusion techniques using a cadaveric model. To investigate the acute stability afforded across the atlantoaxial segment by a novel technique that uses intralaminar screws in C2, and to compare these results to the stability obtained using a C2 pedicle fixation technique. There are numerous techniques available for rigidly coupling C1 and C2. It has been shown that screw techniques provide higher acute stability than wiring practices. However, many of these methods that use screw fixation in C2 can be technically difficult, especially in cases in which there is an aberrant vertebral artery course or if the C2 pedicle is not large enough to accommodate the instrumentation. A novel technique that uses intralaminar screws in C2 with C1 pedicle screws and bilateral longitudinal rods has been recently developed in an effort to overcome many of these issues. To date, there are no published reports as to whether this new technique provides equivalent (or better) fixation to the currently accepted methods. Six fresh-frozen human cadaveric cervical spines (C0-C4) were used in this study. Specimens were tested in their intact condition after destabilization via odontoidectomy, and after implantation of 3 different fixation constructs: (1) the Harms technique, 2 pedicle screws in C2, (2) a single C2 pedicle screw and a single C2 intralaminar screw, and (3) a construct having bilateral intralaminar C2 screws. Pure moment loading in flexion/extension, lateral bending, and axial rotation was applied to the occiput. Subsequent relative intervertebral rotations were determined using a 3 camera system. Range of motion for the intact, destabilized, and 3 fixation scenarios was determined, and statistical analysis was performed using one-way analysis of variance Fisher least-significant-difference post hoc test for multiple comparisons. The data indicate that odontoidectomy significantly increased C1-C2 motion in flexion/extension and lateral bending. All 3 fixation techniques significantly reduced motion compared to the intact and destabilized cases. There were no statistically significant differences between the C2 intralaminar and pedicle screw techniques. The results clearly indicate the potential of the intralaminar screw technique to provide stability that is equivalent to methods currently used. Given the serious complications that can follow vertebral artery injury and the decreased likelihood of injury by avoiding placement of C2 pedicle screw(s) and C1-C2 transarticular screw(s), strong consideration should be given to using a construct that incorporates C2 intralaminar screw(s).

Effect of different surgical strategies on screw forces after correction of scoliosis with a VDS implant

Pullout of the cranial end-vertebra screw following the correction of a scoliosis with the VDS implant is a common complication. Very little is known about the forces acting on the screws during ventral derotation spondylodesis (VDS) in ventral scoliosis surgery. These forces determine the risk of screw-loosening. The purpose of this study was to identify implant properties and to determine surgical correction strategies that reduce the risk of cranial end-vertebra screw pullout. For this aim, a three-dimensional nonlinear finite element model of a scoliotic thoracic spine was created with a Cobb angle of 61 degrees and 32 degrees rotation. The VDS implant was inserted between T5 and T9. The longitudinal rod diameter, the implant material and seven surgical correction strategies were examined to determine their influence on the Cobb angle as well as on derotation and on axial and transverse forces in the screws. A stiffer implant achieves a better correction but causes higher axial and transverse screw forces. Axial tensile forces act on the screws fixed to the cranial end vertebra and the middle vertebra, while axial compressive forces act on the other screws. A strong correction at the cranial segment leads to high axial and transverse screw forces in the farthest cranial screw and thus to a high risk of screw pullout. The resultant transverse force is often much higher than the axial force component. Simulation of local trunk muscle forces has only a minor effect on the results. The axial tensile forces and thus the risk of screw pullout are highest at the cranial end vertebra. A strategy in which surgical correction is strong in the middle segments and moderate in the outer ones leads to a good reduction of the Cobb angle, a wide derotation angle, and relatively low axial tensile forces at the cranial end vertebra screw.

Nonrounded dielectric rectangular rods in helix traveling-wave tubes

Longitudinal dielectric rods in helix traveling-wave tubes (TWTs) contribute to the determination of the performance. A study on nonrounded rectangular rods that exhibit improved dielectric loading with respect to typical rectangular rods is proposed. The expressions for computing the effective dielectric constants for the inhomogeneous dielectric loading model are proposed. Simulated dispersion characteristics are compared with measured data from literature. An analysis method based on rigorous solutions of the field equations is adopted. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 101–103, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21093

Possibilities of Transpedicular Osteosynthesis in Treatment of Thoracic and Lumbar Spine Injuries

Results of surgical treatment of 84 patients with thoracic and lumbar spine injuries using transpedicular osteosynthesis are presented. The patients were operated on within the terms from 2 days to 3.5 years after trauma. Different types of surgical reposition were used depending on the terms after injury and value of deformity. In 51 patients anterior corporodesis was performed. Average correction of local kyphosis was from 7.4° to 17.7° in different groups of patients. Vertical size of inured segments was restored up to 63.8-92%. Suggested method of intraoperative spine reposition enabled to increase the correction volume 1.7-2 times in late terms after injury. In severe deformities preliminary stage, i.e. transpedicular osteosynthesis using external fixation device with gradual correction over 35° was used. Complications - fracture of longitudinal rod (3 cases), partial destabilization of spine column in osteoporosis (2 cases), as well as loss of correction by 2-3° (9 cases) and 6-15° (3 cases) did not influence the outcomes significantly. In 48 patients the follow-up period was over 1 year. In 44 patients good results were achieved and satisfactory result was noted in 4 patients.

Sperm structure and spermiogenesis in Coletinia sp. (Nicoletiidae, Zygentoma, Insecta) with a comparative analysis of sperm structure in Zygentoma

The spermatozoon of Coletinia sp. has a bilayered acrosome, a short nucleus (4μm) and a relatively short sperm tail with two mitochondrial derivatives. The chromatin is uniformly dense except for several electron-lucid channels or strands which permeate the nucleus and which originate in the spermatid as invaginations of the nuclear envelope. The invaginations occur mostly or exclusively along two meridians of the spermatid that are also characterized by the presence of a longitudinal rod of medium electron density. The two rods (designated as ‘mid-spermatid rods’) evidently are instrumental in the formation of the electron-lucid channels. The significance of this elaborate system of intranuclear channels is not understood. The sperm tail has a 9+9+2 axoneme with each of the nine microtubular doublets accompanied by an accessory microtubule; scant intertubular material can also be distinguished. Hence, the tail axoneme resembles that of many pterygote insects. Each of the two mitochondrial derivatives contains a crystalline inclusion that has periodically spaced layers going in different directions on either side of the midline. Two synapomorphic traits appear to be shared by Ateluridae and Nicoletiidae, namely the invaginations of the nuclear membrane along two meridians of the nucleus and the shape of the crystalline inclusions of the mitochondrial derivatives. Four species from the family Lepismatidae were also examined as to their sperm ultrastructure. Three of them, Allacrotelsa kraepelini, Ctenolepisma longicaudata and Ctenolepisma sp., were found to be very similar to the two previously examined lepismatids, Thermobia domestica and Lepisma saccharina. On the other hand, spermatozoa of Tricholepisma aurea were aggregated in small groups rather than pairwise joined as seen in the other lepismatids. Sperm characters are also used to reconstruct a phylogenetic hypothesis which suggests a close relationship between Ateluridae and Nicoletiidae.

Sperm structure and spermiogenesis in Coletinia sp. (Nicoletiidae, Zygentoma, Insecta) with a comparative analysis of sperm structure in Zygentoma

The spermatozoon of Coletinia sp. has a bilayered acrosome, a short nucleus (4 μm) and a relatively short sperm tail with two mitochondrial derivatives. The chromatin is uniformly dense except for several electron-lucid channels or strands which permeate the nucleus and which originate in the spermatid as invaginations of the nuclear envelope. The invaginations occur mostly or exclusively along two meridians of the spermatid that are also characterized by the presence of a longitudinal rod of medium electron density. The two rods (designated as ‘mid-spermatid rods’) evidently are instrumental in the formation of the electron-lucid channels. The significance of this elaborate system of intranuclear channels is not understood. The sperm tail has a 9+9+2 axoneme with each of the nine microtubular doublets accompanied by an accessory microtubule; scant intertubular material can also be distinguished. Hence, the tail axoneme resembles that of many pterygote insects. Each of the two mitochondrial derivatives contains a crystalline inclusion that has periodically spaced layers going in different directions on either side of the midline. Two synapomorphic traits appear to be shared by Ateluridae and Nicoletiidae, namely the invaginations of the nuclear membrane along two meridians of the nucleus and the shape of the crystalline inclusions of the mitochondrial derivatives. Four species from the family Lepismatidae were also examined as to their sperm ultrastructure. Three of them, Allacrotelsa kraepelini , Ctenolepisma longicaudata and Ctenolepisma sp., were found to be very similar to the two previously examined lepismatids, Thermobia domestica and Lepisma saccharina . On the other hand, spermatozoa of Tricholepisma aurea were aggregated in small groups rather than pairwise joined as seen in the other lepismatids. Sperm characters are also used to reconstruct a phylogenetic hypothesis which suggests a close relationship between Ateluridae and Nicoletiidae.

The effect of posterior cervical distraction on foraminal dimensions utilizing a screw-rod system.

Cadaveric human cervical spine anatomic study using posterior lateral mass screw-rod instrumentation to assess foraminal enlargement via distraction techniques. To determine the role of posterior cervical distraction on foraminal dimensions and to ascertain the impact of this technique on segmental kyphosis. Management of cervical spondylotic radiculopathy includes removal of offending compressive structures and enlarging the neuroforamen via anterior discectomy with interbody fusion or posterior laminoforaminotomy. Six human cervical spines were prepared and posterior exposure performed. Lateral mass screws were inserted from C5 to C7 and a longitudinal rod attached. Distraction was applied between the screw heads at 2 mm intervals and accuracy confirmed with digitized calipers. Pre- and postdistraction computed tomography was performed including axial and reformatted images. Foraminal area, height, and width and sagittal alignment and disc heights were evaluated. The results suggest that minimal posterior distraction of 4 to 6 mm at C5-C6 and C6-C7 may enlarge the neuroforamen by 10 to 18 mm. Foraminal height and width increased minimally from baseline to maximum distraction; however, these measurements did not reach statistical significance at either level. A decrease of segmental lordosis at C5-C6 was noted from baseline to 8 mm of distraction. Statistically significant kyphosis from baseline was present at 6 mm of distraction leading to overall 5.2 +/- 1.4degrees change in alignment. At C6-C7, statistically significant kyphosis was not present until 8 mm of distraction (4.62 +/- 2.23degrees). This study suggests that posterior cervical instrumented distraction in the setting of foraminal stenosis is a reasonable supplement to direct laminoforaminotomy and nerve root decompression. Distraction leads to minimal segmental kyphosis, allowing this technique to serve as an adjunct for additional foraminal enlargement.

Sperm structure of Mecoptera and Siphonaptera (Insecta) and the phylogenetic position of Boreus hyemalis

Sperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemalis has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera.

Instrumented forceps for measuring tensile forces in the rod of the VDS implant during correction of scoliosis.

Ventral derotation spondylodesis (VDS) is the standard in ventral scoliosis surgery. Especially in the thoracic spine, there are no alternatives to VDS with compression and derotation as its correction forces. However, pull-out of the end-vertebra screw during correction of scoliosis with the VDS implant is a common complication involving particularly the cranial end-vertebra screw in the thoracic region. This complication requires an extension of the fusion length or reduces at least the outcome of the correction. There are no in vivo data on correction forces in ventral scoliosis surgery. Thus the correction depends on the skill and experience of the surgeon. An instrumented forceps developed and built to measure forces in the longitudinal rod allows axial tensile forces to be determined in the longitudinal rod during surgery. The instrumented forceps has the advantage of reducing the risk of screw pull-out. Furthermore, viscoelastic behavior of the spine can be measured during ventral correction. In addition, knowledge of the correction forces improves our biomechanical understanding of the spine, especially during correction of scoliosis. Intraoperative force measurement is in no way detrimental to the patient.

Comparison of the mechanical behavior of the lumbar spine following mono- and bisegmental stabilization

Objective. To determine whether the mechanical behavior of the entire lumbar spine differs following mono- and bisegmental stabilization. Design. The mechanical behavior of the lumbar spine was studied using the finite element method. Background. Nonunion is somewhat more frequent after bi- than after monosegmental stabilization of the spine. Little is known about differences between the mechanical behavior associated with these procedures. Methods. A three-dimensional nonlinear finite element model of the lumbar spine with internal spinal fixators and bone grafts was used to study mechanical behavior after mono- and bisegmental fixation with and without stabilization of the bridged vertebra. Finite element analyses were performed to determine the influence of four different graft positions, five loading conditions, and six different pretensions in the longitudinal fixator rod. The following parameters were considered: the maximum contact pressure at the interface between the bone graft and vertebral body, the force transmitted by the bone graft, and the size of the contact area between the graft and the vertebral body. Results. Our model shows no clear differences between mono- and bisegmental fixation. Additional stabilization of the bridged vertebra exerts a partly adverse influence on the parameters studied. Pretension in the bridged region has a strong effect on the mechanical behavior. Conclusions. The mechanical behavior of the lumbar spine after mono- and bisegmental stabilization is similar. Thus biological factors and the surgical procedure are probably decisive in determining the fusion rate. Relevance Knowledge of the mechanical behavior after stabilization of the spine may help to improve the fusion rate. Our results suggest that the mechanical factors studied have only a minor influence on fusion rate and that other factors, such as incomplete resection of cartilage plate and poor local blood supply, are more decisive.

Preparation of single-walled nanotubes with the help of a Ni/Cr-based catalyst

The high-yield synthesis of single-walled carbon nanotubes (SWNTs) is carried out in an electric-arc discharge using the Ni-Cr alloy as a catalyst. A new method of introducing the catalyst into the plasma hot region is used in the synthesis. In this method, the anode with a sandwich structure consists of two longitudinal graphite rods of a rectangular cross section, between which the Ni-Cr alloy in the form of a foil having a thickness approximately equal to 0.2 mm is placed. The obtained samples are investigated using transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetry. According to the results of TEM observations, SWNTs are tied into bundles with a length of several micrometers and a diameter of about 10 nm. The Raman spectra indicate that the diameter distribution of SWNTs lies between 1.2 and 1.5 nm with a peak at approximately 1.24 nm. The SWNT content in the obtained samples is approximately 20%. Heat treatment at various temperatures with a dosed air supply leads to a noticeable mass loss of the sample and to a change in its composition. For example, thus heating to 600 K causes a mass loss of about 40%, leading to an increase in the content of SWNTs up to 35% without their noticeable destruction. Further heating above 600 K leads to a virtually complete thermal decomposition of SWNTs.

The use of interbody cage devices for spinal deformity: a biomechanical perspective.

Spinal instrumentation has revolutionized the treatment of spinal deformities and offers a plethora of techniques and designs to surgically treat deformity conditions. The authors address the biomechanical properties afforded by various posterior and anterior spinal instrumentation mechanisms, with and without intervertebral reconstruction, and the principles associated with optimal reconstruction techniques. The integration of multiple strategies can improve anterior and posterior construct stiffness in the treatment of spinal deformities. Structural interbody support probably is the best method to minimize longitudinal rod and screw-bone interface strain. Moreover, anterior load-bearing structural grafts and interbody devices have been shown to increase construct stiffness, decrease the incidence posterior implant failure, permit the use of smaller diameter longitudinal rods, and may enhance the rate of successful spinal arthrodesis. From a biomechanical standpoint, treatment of medium to high-grade spondylolisthesis with stand-alone interbody or transvertebral cages, in the absence of supplemental posterior fixation, is contraindicated. Collectively, the included studies reinforce the principles of load sharing between the anterior and posterior spinal columns and affirm the biomechanical dominance of anterior column support in circumferential spinal arthrodesis.

Similarity Relations for the Impact Penetration of an Elastic Rod into a Brittle Target

Similarity factors for the kinetic parameters of the rod (impact velocity or energy) in case of geometric and energy similarities of target fracture patterns are determined from the analysis of the penetration equation and experimental results. The geometric and energy similarities of the target fracture upon the rod penetration over the investigated range of impact velocities (up to 10 m/s) and penetration depths (h >> d) are shown to be attained on linear variations of longitudinal and transverse rod dimensions, with impact velocities remaining unchanged.

Effect of a double intervertebral cage on the mechanical behavior of the lumbar spine

A three-dimensional nonlinear finite element model of the lumbar spine was developed. Paired threaded cages and a monosegmental internal spinal fixation device were integrated into the computer model. The model was loaded with such forces as apply during standing, as well as with pure moments in the three main anatomical planes, plus an additional preload. The latter was generated by shortening the distance between the pedicle screws on the longitudinal rod of the fixator. With the exception of torsional loading, an implant appreciably reduces the mobility in the segment concerned. At the loads studied, cages had only a minor impact on the movements and stresses in the adjacent regions, but a strong influence on the stresses in the endplates in contact with them. A preload increases these stresses dramatically. Contact conditions between vertebral body and cages also have a marked effect on the stress distribution in the corresponding vertebral endplate, especially in the case of extension loading. Owing to the preload, maximum stresses were higher for the rigid bond than when contact elements were used.