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The functional renormalization group (FRG) provides a flexible tool to study correlations in low-dimensional electronic systems. In this paper, we present a novel FRG approach to the steady-state of quantum wires out of thermal equilibrium. Our method is correct up to second order in the two-particle interaction and accounts for inelastic scattering. We combine semi-analytic solutions of the flow equations with MPI parallelization techniques, which allows us to treat systems of up to 60 lattice sites. The equilibrium limit is well-understood and serves as a benchmark. We compute effective distribution functions, the local density of states, and the steady-state current and demonstrate that all of these quantities depend strongly on the choice of the cutoff employed within the FRG. Non-equilibrium is plagued by the lack of physical arguments in favor of a certain cutoff as well as by the appearance of secular higher-order terms which are only partly included in our approach. This demonstrates the inadequacy of a straightforward second-order FRG scheme to study interacting quantum wires out of equilibrium in the absence of a natural cutoff choice.

We employ a novel, unbiased renormalization-group approach to investigate non-equilibrium phase transitions in infinite lattice models. This allows us to address the delicate interplay of fluctuations and ordering tendencies in low dimensions out of equilibrium. We study a prototypical model for the metal to insulator transition of spinless interacting fermions coupled to electronic baths and driven out of equilibrium by a longitudinal static electric field. The closed system features a Berezinskii-Kosterlitz-Thouless transition between a metallic and a charge-ordered phase in the equilibrium limit. We compute the non-equilibrium phase diagram and illustrate a highly non-monotonic dependence of the phase boundary on the strength of the electric field: For small fields, the induced currents destroy the charge order, while at higher electric fields it reemerges due to many-body Wannier-Stark localization physics. Finally, we show that the current in such an interacting non-equilibrium system can counter-intuitively flow opposite to the direction of the electric field. This non-equilibrium steady-state is reminiscent of an equilibrium distribution function with an effective negative temperature.

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction1-3, light emission4, thermoelectric energy conversion5,6, quantum interference7,8, heat dissipation9,10 and electronic noise11 at atomic and molecular scales. But a quantity of considerable current interest-the thermal conductance of a single-molecule junction-has eluded direct experimental determination, reflecting the considerable challenge of detecting minute heat currents at the picowatt level. Here we show that, when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, the custom-developed probes that enabled thermal conductance measurements of single-metal-atom junctions12 can also quantify the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au-alkanedithiol-Au junctions, where the number of carbon atoms was varied from two to ten, confirm that thermal conductance is to a first approximation independent of molecular length, consistent with detailed ab initio simulations. We anticipate that our approach will enable systematic exploration of thermal transport in many other one-dimensional systems, such as short molecules and polymer chains, for which computational predictions of thermal conductance13-16 have remained experimentally inaccessible. published

We present a procedure to determine transmission eigenchannels for coherent phonon transport in nanoscale devices using the framework of nonequilibrium Green's functions. We illustrate our procedure by analyzing a one-dimensional chain, where all steps can be carried out analytically. More importantly, we show how the procedure can be combined with ab initio calculations to provide a better understanding of phonon heat transport in realistic atomic-scale junctions. In particular, we study the phonon eigenchannels in a gold metallic atomic-size contact and different single-molecule junctions based on molecules such as an alkane chain, a brominated benzene-diamine, where destructive phonon interference effects take place, and a C60 junction. published

Calorimetry reaches an atomic junction Electrical and thermal conductivity in metals are linked at the macroscopic length scale because electrons carry both heat and current. Cui et al. found that this relationship, the Wiedemann-Franz law, holds down to the atomic scale in gold and platinum (see the Perspective by Segal). They made thermal and electrical conductance measurements through a point contact only one atom thick. In gold, the thermal and electrical conductance was quantized, owing to the electronic band structure of the metal. The experiments pave the way for high-resolution calorimetry and other thermal measurements at the nanoscale. Science , this issue p. 1192 ; see also p. 1125

Motivated by recent experiments [Science 355, 1192 (2017); Nat. Nanotechnol. 12, 430 (2017)], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The main goal of this work is to elucidate the role of phonons in the thermal transport through these atomic contacts as well as to study the validity of the Wiedemann-Franz law, which relates the electrical and the thermal conductance. For this purpose, we have employed two different custom-developed theoretical approaches. The first one is a transport method based on density functional theory (DFT) that allows one to accurately compute the contributions of both electrons and phonons to the thermal transport in few-atom-thick contacts. The second technique is based on a combination of classical molecular dynamics (MD) simulations and a tight-binding model that enables the efficient calculation of the electronic contribution to the thermal conductance of atomic contacts of larger size. Our DFT-based calculations show that the thermal conductance of few-atom contacts of Au and Pt is dominated by electrons, with phonons giving a contribution typically below 10% of the total thermal conductance, depending on the contact geometry. For these two metals we find that the small deviations from the Wiedemann-Franz law, reported experimentally, largely stem from phonons. In the case of Al contacts we predict that the phononic contribution can be considerably larger with up to 40% of the total thermal conductance. We show that these differences in the phononic contribution across metals originate mainly from their distinct Debye energies. On the other hand, our MD-based calculations demonstrate that the electronic contribution to the thermal conductance follows very closely the Wiedemann-Franz law, irrespective of the material and the contact size. Finally, the ensemble of our results consistently shows that the reported observation of quantized thermal transport at room temperature is restricted to few-atom contacts of Au, a monovalent metal in which the transport is dominated by the s valence orbitals. In the case of multivalent metals like Pt and Al this quantization is statistically absent due to the fact that additional orbitals contribute to the transport with conduction channels that have intermediate transmissions between 0 and 1, even in the case of single-atom contacts. published

We investigate the thermodynamics and transient dynamics of the (unbiased) Ohmic two-state system by exploiting the equivalence of this model to the interacting resonant level model. For the thermodynamics, we show, by using the numerical renormalization group (NRG) method, how the universal specific heat and susceptibility curves evolve with increasing dissipation strength, $\alpha$, from those of an isolated two-level system at vanishingly small dissipation strength, with the characteristic activated-like behavior in this limit, to those of the isotropic Kondo model in the limit $\alpha\to 1^{-}$. For the transient dynamics of the two-level system, $P(t)=\langle \sigma_{z}(t)\rangle$, with initial-state preparation $P(t\leq0)=+1$, we apply the time-dependent extension of the NRG (TDNRG) to the interacting resonant level model, and compare the results obtained with those from the noninteracting-blip approximation (NIBA), the functional renormalization group (FRG), and the time-dependent density matrix renormalization group (TD-DMRG). We demonstrate excellent agreement on short to intermediate time scales between TDNRG and TD-DMRG for $0\lesssim\alpha \lesssim 0.9$ for $P(t)$, and between TDNRG and FRG in the vicinity of $\alpha=1/2$. Furthermore, we quantify the error in the NIBA for a range of $\alpha$, finding significant errors in the latter even for $0.1\leq \alpha\leq 0.4$. We also briefly discuss why the long-time errors in the present formulation of the TDNRG prevents an investigation of the crossover between coherent and incoherent dynamics. Our results for $P(t)$ at short to intermediate times could act as useful benchmarks for the development of new techniques to simulate the transient dynamics of spin-boson problems., Comment: 27 pages, 22 figures; published version

Die unspezifische destruierende Spondylodiszitis ist eine schwerwiegende Erkrankung, welche mit einer hohen Letalitat einhergeht. Weitestgehende Einigkeit besteht, wann die Indikation zum operativen Vorgehen vorliegt. Bei der operativen Therapie ist die Wiederherstellung des sagittalen Profils mit zu berucksichtigen. So ist das operative Vorgehen auf die Fehlstellung, das Destruktionsausmas, die Klinik des Patienten und die Ausbreitung der Erkrankung abzustimmen.

Die Nichtberucksichtigung des sagittalen Profils bei primaren stabilisierenden Wirbelsaulenoperationen ist ein haufiger Grund fur Revisionsoperationen. Dementsprechend ist bei der Notwendigkeit einer Revision eine Berucksichtigung bzw. Wiederherstellung des sagittalen Profils der Wirbelsaule zu beachten. Die physiologische Einstellung des fusionierten Bereichs sollte auch den nichtinstrumentierten Abschnitten der Wirbelsaule kranial und kaudal der Spondylodese eine segmentale physiologische Profilierung ermoglichen. Bei Patienten mit einer physiologischen Schwerpunktlinie und einer normalen sakralen Inklination ist die Inzidenz einer Anschlussinstabilitat am geringsten. Eine sagittale Imbalance nach durchgefuhrter Revision ist ein Risikofaktor fur das Wiederauftreten einer Pseudarthrose nach einer Revisionschirurgie. Vor allem bei Pseudarthrosen fuhrt ein kombiniertes Vorgehen zu einer hoheren Effektivitat bei der Wiederherstellung der sagittalen Balance und zu einer verbesserten Fusionsrate.

Als vermeintliche Vorteile der Dynesys-Instrumentation werden die suffiziente und auch langstreckige Augmentation der dorsalen Strukturen unter Erhaltung einer Restbeweglichkeit angegeben. In dieser Untersuchung wurden bei 20 nicht voroperierten Patienten mit einer polysegmentalen Wirbelsaulenpathologie eine polysegmentale Dekompression und eine Dynesys-Instrumentation durchgefuhrt. Bei allen Patienten wurde praoperativ eine Knochendichtemessung vorgenommen. Alle 20 Patienten wurden durchschnittlich 11,8 Monate postoperativ nachuntersucht. Durch die Operation wurde eine Verlangerung der Gehstrecke von 581,5 auf 1640,0 m erreicht. Als perioperative Komplikationen wurden ein revisionbedurftiges Duraleck und eine hypertensive Krise im Verlauf beobachtet. Eine Implantatlockerung wurde bei einer Patientin beobachtet, diese wurde revidiert und dorsoventral fusioniert. Die Anwendung des Dynesys-Verfahren ist bei Patienten mit mehrsegmentalen Wirbelsaulenpathologien durchaus sinnvoll. Die Reprofilierung ausgepragter Fehlstellungen oder Deformitaten ist jedoch damit nicht moglich.

This article aims at shedding light on the role of physician and patient gender in the medical consultation. Because of the scarce amount of studies concentrating on gender aspects of the physician-patient interaction in rehabilitation or chronic disease, mostly results from general medicine are reported. Female physicians have a more emotional and less dominant communication style. Female patients bring up more psychosocial topics and disclose more information about themselves in general. Both female and male physicians give more information and apply a more partnership-oriented communication style when seeing a female patient. Female and male patients communicate more partnership-oriented with female physicians and share more psychosocial and medical information with them. Same-gender dyads seem beneficial most of the time for physician-patient communication. Mixed-gender dyads are more difficult, especially when a younger female physician sees a male patient. There is no single good communication style recommendable for all physicians. Rather, the research results presented should be applied to communication trainings for physicians. This could provide physicians with a flexible choice of communication styles to apply according to different situations.

Die dynamische Dynesys®-Stabilisierung wurde 1994 als eine bewegungserhaltende Erfindung eingefuhrt, in dem Versuch, die Nachteile der Fusion zu uberwinden, eine ausreichende Stabilitat und die Restauration der segmentalen Gelenkkinematik zu gewahrleisten, der Instabilitat vorzubeugen und die Degeneration der angrenzenden Segmente zu vermeiden. Die Ergebnisse sind, insbesondere fur Spinalkanalstenosen mit und ohne degenerative Spondylolisthese bis Grad I nach Meyerding, als gut zu bezeichnen. Eine Dekompression erscheint in den meisten Fallen ein wichtiger Bestandteil fur ein gutes Ergebnis der Operation zu sein. Die Degeneration der Bandscheibe im verbundenen und angrenzenden Segment scheint trotz der Dynesys®-Stabilisierung fortzuschreiten. Diese zunehmende Degeneration konnte durch die naturliche Zunahme der Krankheit verursacht sein. Es ist wahrscheinlich, dass diese zunehmende Bandscheibendegeneration eher durch die naturliche Krankheitszunahme bedingt ist, als ein Effekt der Stabilisation ist.

A number of factors need to be borne in mind in the planning and performance of instrumental fixation of the spine in patients with osteoporosis. Improved implant anchoring using special screws and cement augmentation can help to avoid implant dislocations. Nevertheless, particular attention should be paid to spinal balance in these patients.

Motivated by recent experiments, we present here a systematic ab-initio study of the length dependence of the thermal conductance of single-molecule junctions. We make use of a combination of density functional theory with non-equilibrium Green's function techniques to investigate the length dependence of the phonon transport in single alkane chains, contacted with gold electrodes via both thiol and amine anchoring groups. Additionally, we study the effect of the substitution of the hydrogen atoms in the alkane chains by heavier fluorine atoms to form polytetrafluoroethylenes. Our results demonstrate that (i) the room-temperature thermal conductance is fairly length-independent for chains with more than 5 methylene units and (ii) the efficiency of the thermal transport is strongly influenced by the strength of the phononic metal-molecule coupling. Our study sheds new light onto the phonon transport in molecular junctions, and it provides clear guidelines for the design of molecular junctions for thermal management., Comment: 9 pages, 7 figures

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.

Study design A retrospective clinical study investigated patients undergoing surgery for destructive pyogenic and tuberculous spondylodiscitis. Objective To compare anterior debridement and bone grafting with a combined anterior and posterior procedure in terms of the physiologic alignment of the segmental sagittal spinal profile. Summary of background data There is considerable agreement in the literature on the indications for surgical treatment of destructive spondylodiscitis. An anterior approach usually is recommended for debridement and bone grafting. Additional posterior instrumentation is applied to reduce kyphotic deformities and to prevent a correction loss. No comparison has been made so far in the literature between repositioning results obtained after surgery for destructive spondylodiscitis and physiologic segmental sagittal angles. Methods The surgical results of 49 patients treated by anterior debridement and bone grafting were compared with those of 22 patients who received additional posterior instrumentation. A comparison between the segmental kyphotic angles obtained and the standard values reported in the literature enabled an assessment of the segmental spinal alignment in the sagittal plane. Data were obtained from medical record review, imaging procedures, and patient follow-up examinations. Results All the subgroups submitted to a combined procedure had a greater preoperative segmental kyphosis angle than those undergoing anterior fusion alone. In marked segmental kyphotic false positioning, good postoperative repositioning was achieved by the combined procedure, and an increase in segmental kyphosis was permanently prevented. Conclusions In single-level spondylodiscitis with no major substance loss, anterior debridement and bone grafting alone seem to be adequate, especially in the lumbar spine. Additional posterior instrumentation is indicated in multiple-level spondylodiscitis, extensive kyphotic deformity, or both.

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.

Es wurde ein detailliertes Computermodell der Lendenwirbelsaule erstellt. In das Rechenmodell wurden ein bisegmentales Wirbel-Fixateur-interne-System sowie nacheinander 2 unterschiedliche Implantate zum Ersatz eines Wirbelkorpers eingebaut. Belastet wurde das Modell mit Momenten in den 3 anatomischen Hauptebenen, sowie mit Kraften wie beim Stehen. Durch einen Wirbelkorperersatz wird die Beweglichkeit im betreffenden Bereich drastisch reduziert. In den benachbarten Segmenten hat ein Implantat bei den gewahlten Belastungen nur einen minimalen Einfluss auf die Beweglichkeit und Spannungen. Eine Vorlast, wie sie beispielsweise durch die zusatzliche Distraktion eines passgenau eingebrachten ventralen Implantats aufgebracht wird, hat einen starken Einfluss auf die Spannungen in den implantatnahen Endplatten. Unterschiedliche Grosen der Kontaktflachen zwischen Implantat und Wirbelkorper haben nur einen lokalen Effekt auf die Spannungsverteilung.

Objective Restoration of a normal profile of spinal column by complete or almost complete reduction, stabilization achieved by instrumentation and fusion of the lumbosacral intervertebral segment. Alleviation or at least marked reduction of pain and neurologic deficits present before surgery.

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.

Kyphosis is a dorsally convex curvature of the spine in the sagittal plane. A pathological kyphosis of the thoracic spine has a Cobb angle greater than 50 degrees. It occurs when the anterior and/or posterior load-transferring elements of the spine are overloaded or damaged. Wedge-shaped vertebral bodies may be found at one or several levels. A wedge-shaped vertebral body increases the curvature of the spine and moves the centre of gravity of the body parts above of the corresponding vertebral body in a ventral direction. This increases the flexion-bending moment acting on the spine. In the case of a wedge-shaped deformation of a vertebral body, the relative increase of the flexion moment is a function of the wedge angle and of the original position of the centre of gravity of the upper body.

Assessing the initial post-traumatic situation is of imminent importance in choosing the most suitable approach for primary treatment of thoracic and lumbar spine fractures. Misjudging the static situation of the injured spine is a common reason for selecting an inadequate therapeutic procedure. The consequence is a defective spinal position with the corresponding symptoms, which usually requires a complicated surgical procedure. Our experience is based on 34 patients with a post-traumatic defective position of the thoracic and lumbar spine: 12 patients underwent primary surgical and 22 primary conservative treatment. The aim of our study was to demonstrate the initial situation and primary management as well as subsequent problems and the respective surgical procedure applied in our department for correcting and stabilizing the areas involved and to present intermediate results.

Von 1989–1998 wurden 129 Patienten in der Orthopadischen Universitatsklinik der Freien Universitat Berlin wegen einer unspezifischen Spondylodiszitis operativ behandelt. In der vorliegenden Studie konnten 56 dieser Patienten nachuntersucht und klinische sowie radiologische Ergebnisse ausgewertet werden. Das Operationsergebnis von 40 mit alleiniger ventraler Herdausraumung und Defektuberbruckung durch Beckenkammspan behandelten Patienten wurde mit dem von 16 mit zusatzlich durchgefuhrter dorsaler uberbruckender Instrumentation durch Fixateur interne behandelten Patienten verglichen. Im Mittel wurden bei der ventralen Spanspondylodese 2,3 Wirbelkorper fusioniert, die mittlere dorsale Instrumentationstrecke durch Fixateur interne lag bei 3,8 Wirbelkorpern. Zum Zeitpunkt der Nachuntersuchung lag die Operation durchschnittlich 5,1 Jahre zuruck, das Durchschnittsalter der Patienten zum Zeitpunkt der Operation lag bei 57,1 Jahren. Die postoperative Mobilisierung der Patienten erfolgte nach ventrodorsaler Fusion im Mittel bereits nach 5 Tagen, ein rein ventrales Vorgehen erforderte eine postoperative Immobilisationszeit von durchschnittlich 3,6 Wochen und die Anpassung eines Stutzkorsetts fur durchschnittlich 8,2 Monate. In einem Fall war es 25 Monate postoperativ zu einem Rezidiv der Spondylodiszitis gekommen, wodurch eine operative Revision des Herdes erforderlich wurde. Die Durchbauungsraten der Spanspondylodese in den verschiedenen Untergruppen lagen bei 84–100%. Bei der Darstellung der Ergebnisse erfolgte eine differenzierte Betrachtung der Wirbelsaulenbereiche sowie der Fusionsstrecken der ventralen Fusion, um eine Aussage uber die Entwicklung insbesondere des sagittalen Wirbelsaulenprofils treffen zu konnen. Ein Vergleich der gemessenen segmentalen Kyphosewinkel mit in der Literatur angegebenen Normalwerten ermoglichte eine Beurteilung der segmentalen Einstellung der Wirbelsaule in der Sagittalebene. Bei Durchfuhrung einer kombinierten ventrodorsalen Fusion hatte praoperativ in allen Untergruppen ein hoherer segmentaler Kyphosewinkel bestanden als bei alleiniger ventraler Fusion. Bei ausgepragter segmentaler kyphotischer Fehlstellung konnte durch das kombinierte ventrodorsale Vorgehen ein gutes postoperatives Repositionsergebnis erreicht und eine Zunahme der segmentalen Kyphosierung dauerhaft verhindert werden. Eine alleinige ventrale Herdausraumung und Spanspondylodese erscheint bei einetagiger Spondylodiszitis besonders im Bereich der Lendenwirbelsaule ausreichend, im Falle einer langerstreckigen ventralen Fusion sollte jedoch eine zusatzliche dorsale Instrumentation erfolgen.

In the presence of a vertebral injury or disease, manifest osteoporosis affects preoperative planning. Thus, if surgery is indicated, bone density should be determined in cases of suspected or diagnosed osteoporosis. Instrumentation of the spine is frequently not required in surgical interventions. However, if indicated, instrumentation should be fixed multifocally and the deformity should be corrected with special care. It is absolutely necessary to avoid ending instrumentation within a kyphosis.

It is generally accepted that the progression of an idiopathic scoliotic deformity with a Cobb angle of between 25 degrees and 40 degrees can be stopped by brace treatment alone provided that the generally acknowledged criteria for the treatment concerning skeletal growth of the individual are respected. In Europe, the Cheneau brace, which was originally designed as an active derotation orthosis, is widely in use and is constantly being improved. The biomechanical principle of this orthosis consists of a pressure vector that is applied laterally (with regard to the 3-point principle) to exert pressure on the peak of the curvature in the frontal and transversal planes. Thus, the thoracic, lumbar and pelvic body mass that was rotated out of normal body symmetry is transferred back to its original position via pressure and derotation. Therefore, an active back like the Cheneau orthosis must provide pressure surfaces and sufficient expansion spaces. Subtle insights into the actual effect of braces have furthered ongoing development to take into consideration the changes to the trunk in the sagittal plain and have respected the different states of expansion of the two halves of the trunk in the craniocaudal direction. The thoracic flat back and cyphosis of the lumbal spine, which were formerly ignored, actually provide a real challenge for the technical realization of the brace. The new generation of Cheneau braces potentially provides an effective means for the active correction of scoliotic spinal deformity in all three dimensions and thus fulfills the requirements of modern conservative scoliosis treatment.

A number of different procedures are used for the surgical treatment of King II scoliosis. One reason for the controversial discussion in this context is that the term King II scoliosis is usually inadequate, because there are partly marked clinical and radiological differences in this type of curvature. From January 1996 to December 1997, a total of 26 patients with rigid King II scoliosis were submitted to a ventrodorsal procedure. Twenty-three patients were included in the study. The indication for this procedure was established in cases with a secondary lumbar curvature of at least 50 degrees as well as unsatisfactory straightening of the primary and secondary curvature in the bendings and inadequate horizontal positioning of the caudal end vertebra of not less than 10 degrees. Ventral Derotation-Spondylodesis (VDS) and Dorsal correction-Spondylodesis (DKS) led to a thoracic and lumbar straightening from 68.4 degrees to 13.2 degrees and from 61.4 degrees to 17.8 degrees, respectively. The tilt of the vertebra instrumented farthest caudally was corrected from 21.2 degrees to 4.9 degrees. The thoracic hypokyphosis was improved from 16.6 degrees to 25.1 degrees. In 11 patients, the dorsal instrumentation was extended to the caudal end vertebra, in another 11 patients, instrumentation was achieved up to a vertebra cranial from the end vertebra. The correction loss and complication rate was extremely low. Based on the surgical goals discussed further down, combined application of VDS and DKS is efficient and suitable in conjunction with the indication described. The complication rate is quite low. The different types of King II scoliosis have to be differentiated preoperatively.

Besides the microsurgical ventral decompression for treatment of cervical disc prolapses, combined with an intercorporal fusion using an autologous bone graft from the iliac crest and a plate osteosynthesis, the microsurgical, transoral approach to the craniocervical junction has proven to be an effective procedure for adequate indications. Even for surgical treatment of diseases and injuries of the craniocervical junction ventral, anterolateral, lateral and dorsal approaches are applicable alone or in combination. The special anatomic and functional conditions of this region, however, obviously require that the indicational criteria for the various approaches differ from those selected for the other cervical segments. The postoperative complication risk requires that particulary critical consideration be given to the question of isolated transoral interventions. The same holds true for the question as the necessity for additional ventral stabilisation in combined dorsoventral interventions. This report is about 20 patients who underwent transoral decompression, about the indications and the procedure typical problems.

We show that the single-particle spectral properties of gapless one-dimensional Fermi systems in the Luttinger liquid state reached at intermediate times after an abrupt quench of the two-particle interaction are highly indicative of the unusual nonequilibrium nature of this state. The line shapes of the momentum integrated and resolved spectral functions strongly differ from their ground state as well as finite temperature equilibrium counterparts. Using an energy resolution improved version of radio-frequency spectroscopy of quasi one-dimensional cold Fermi gases it should be possible to experimentally identify this nonequilibrium state by its pronounced spectral signatures., Comment: 5 pages, 3 figures

Nonspecific destructive spondylodiscitis is a severe illness which is accompanied by a high mortality rate. There is agreement in the literature on the indications for surgical treatment of destructive spondylodiscitis and sagittal alignment has to be considered for the operative procedure. Therefore, the operative procedure has to make considerations for the deformity, the extent of destruction, the clinical characteristics of the patient and the extent of spondylodiscitis.

The operative therapy management of vertebral osteomyelitis including debridement and stabilization is well established. Autologous bone is the preferred graft material but is limited due to availability, failure of consolidation in large defects and donor morbidity. Titanium mesh cages are alternatively equally well evaluated and other materials are also mentioned. Immobilization of affected segments is the fundamental requirement for healing of osteomyelitis. The operative therapy of choice is meticulous debridement and internal stabilization of the defect. Autologous bone seems to provide the best conditions to bridge and consolidate defects. Bone marrow aspirate, reaming irrigator aspiration (RIA) and bone marrow protein (BMP) in combination with cages have the same qualities considering bone healing but they are not yet sufficiently evaluated for management of vertebral osteomyelitis. Autologous bone graft remains the gold standard, nevertheless, its disadvantages point out the need for alternative grafts. Titanium is well proven to provide stability but bone substitutes are not sufficiently evaluated but seem to be promising.

Ignoring the sagittal profile in primary spinal fusion surgery is a common reason for revision surgery. Therefore, it is important that in cases of spinal revision surgery the sagittal alignment is realized. The physiological alignment of the instrumented spine should also indirectly influence the profile of the non-stabilized spine cranial and caudal to the fusion. Patients with normal C7 plumb-line and a physiological sacral inclination have a lower incidence of adjacent segment degeneration. Sagittal imbalance after revision surgery is a risk factor for recurrent pseudarthrosis. In cases of pseudarthrosis a combined approach may be more effective in realizing sagittal balance und enhancing rates of fusion.

The advantages of using the Dynesys System are claimed to be sufficient and polysegmental dorsal stabilization of the spine while preserving a certain amount of motion.In this study 20 patients with a polysegmental spinal pathology were treated with polysegmental decompression and using the Dynesys Dynamic Stabilization system. None of the patients had had spinal surgery previously. Bone density was measured in all patients preoperatively.All 20 patients were followed up for an average of 11.8 months postoperatively. The ability to walk was improved from 581.5 m to 1640.0 m after surgery. Complications observed were one leakage of the dura and one hypertensive crisis. Implant loosening was observed in one female patient, which was revised and dorso-ventral fusion was carried out.The use of the Dynesys Dynamic Stabilization system is a reasonable treatment in patients with polysegmental pathology of the spine. However, the system does not allow restoration of extensive malalignments or deformities of the spine.

Dynamic stabilization was introduced in 1994 as a motion preserving device in an attempt to overcome the disadvantages of fusion and to provide sufficient stability, to restore normal segmental kinematics, to prevent instability, and to avoid adjacent segmental degeneration. The results in patients with spinal stenosis with or without degenerative spondylolisthesis can be considered good. Decompression should be performed in the most cases. Disc degeneration of the bridged and the adjacent segment seems to continue despite Dynesys stabilization. It is likely that this continuing degeneration is due to natural disease progression rather than an effect of stabilization.

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.

Facetectomy and laminectomy are techniques for decompressing lumbosacral spinal stenosis. Resections of posterior bony or ligamentous parts normally lead to a decrease in stability. The degree of instability depends on the extent of resection, the loading situation and the condition of the intervertebral discs. The correlation between these parameters is not well understood. In order to investigate how these parameters relate to one another, a three-dimensional, non-linear finite element model of the lumbosacral spine was created. Intersegmental rotations, intradiscal pressures, stresses, strains and forces in the facet joints were calculated while simulating an intact spine as well as different extents of resection (left and bilateral hemifacetectomy, hemilaminectomy and bilateral laminectomy, two-level laminectomy), disc conditions (intact and degenerated) and loading situations (pure moment loads, standing and forward bending). The results of the modelling showed that a unilateral hemifacetectomy increases intersegmental rotation for the loading situation of axial rotation. Expanding the resection to bilateral hemifacetectomy increases intersegmental rotation even more, while further resection up to a bilateral laminectomy has only a minor additional effect. Hemilaminectomy and laminectomy only differ in their effect for ventriflexion and muscle-supported forward bending. Two-level laminectomy increases the intersegmental rotation only for standing. Degenerated discs result in smaller intersegmental rotations and higher disc stresses at the respective levels. Decompression procedures affect the examined biomechanical parameters less markedly in degenerated than in intact discs. Resection of posterior bony or ligamentous elements has a stronger influence on the amount than on the distribution of stresses and deformations in a disc. It has only a minor effect on the biomechanical behaviour of the adjacent region. Spinal stability is decreased after a laminectomy for forward bending, and after a two-level laminectomy for standing. For axial rotation, spinal stability is decreased even after a hemifacetectomy. Patients should therefore avoid excessive axial rotation after such a treatment.

Pull-out of the cranial end-vertebra screw following a correction of a scoliosis with the VDS implant is a common complication, especially in the thoracic region. It requires an extension of the fusion length or at least reduces the outcome of the correction.We therefore looked for a new approach to solve the problem of end-vertebra screw pull-out. It was postulated that the axial pull-out force at the end-vertebra screw is reduced by a screw with a hinge between the head and threaded part. The aim of our study was to calculate theoretically and then determine experimentally the screw pull-out force of regular and modified VDS screws with a hinge during lateral shifting of the screw heads in the frontal plane.The use of a modified end-vertebra screw with a hinge on the cranial end vertebra of the correction region changes the shape of the threaded rod between the last two screws. Theoretically estimated, this leads to a reduction of the pull-out force to one-fourth of the value for the original VDS screw. Experimentally, the mean pull-out force for the modified end-vertebra screw was 110+/-8.6 N in comparison with the original screw, where the pull-out force was 214+/-7.2 N.A reduction of screw pull-out can be expected when a screw with a hinge is used for the cranial end vertebra.

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.

A three-dimensional, nonlinear finite element model of the lumbar spine was created. A bisegmental internal spinal fixation device and successively two kinds of vertebral body replacements were integrated into the computer model. The model was loaded with pure moments in the three anatomical main planes as well as with forces that are expected during standing. A vertebral body replacement drastically reduces the mobility in the implant region. An implant has only a minor influence on the mobility and stresses in the adjacent regions for the loading cases chosen. A preload, for example, caused by additional distraction from the precisely fitted ventral implant, exerts a very strong effect on the stresses in the end plates that are in contact with the implant. Different sizes of the contact area between implant and vertebral body have only a local effect on stress distribution.

There is little information about the influence of bone graft size, position and elasticity on the mechanical behavior of the lumbar spine. Intersegmental motion, intradiscal pressure and stresses in the lumbar spine were calculated using a three-dimensional, nonlinear finite element model which included an internal spinal fixation device and a bone graft. Cross-sectional area, position, and elastic modulus of the graft were varied in this study. Bone grafts, especially very stiff ones, increase stresses on adjacent endplates. Though larger grafts lead to less contact pressure, it is difficult to judge the quality of different bone graft positions. In general, ventral flexion results in lower maximum contact pressure than lateral bending. There is always little intersegmental rotation in the bridged region compared with that of an intact spine. A larger graft with low stiffness should be favored from a mechanical point of view. Patients should avoid lateral bending of the upper body shortly after surgery.

Primary bone tumors and tumor-like lesions of the vertebral column are rare in children. After operative tumor resection, 25 children under the age of 17 could be reviewed in a retrospective analysis. Malignant bone tumors occurred only twice in the region of the vertebral body. No deformity was registered in 9 of 16 cases after local tumor resection with and without laminectomy on one level. In contrast, after resection of one or both facets in combination with laminectomy cranial to L4 or thoracal, progressive kyphosis was found within 6-22 months postoperatively in four cases. This required a secondary fusion. After primary fusion and instrumentation, no deformity was registered. In nine cases with a location of the tumor in the vertebral body, only two patients developed a secondary instability of the spine. Both cases had no primary fusion. The other seven patients with initial fusion and instrumentation showed no deformity within 24 up to 127 months postoperatively. These results are compared with data from the current literature.

Assessing the initial post-traumatic situation is of imminent importance in choosing the most suitable approach for primary treatment of thoracic and lumbar spine fractures. Misjudging the static situation of the injured spine is a common reason for selecting an inadequate therapeutic procedure. The consequence is a defective spinal position with the corresponding symptoms, which usually requires a complicated surgical procedure. Our experience is based on 34 patients with a post-traumatic defective position of the thoracic and lumbar spine: 12 patients underwent primary surgical and 22 primary conservative treatment. The aim of our study was to demonstrate the initial situation and primary management as well as subsequent problems and the respective surgical procedure applied in our department for correcting and stabilizing the areas involved and to present intermediate results.

From 1989 to 1998, 129 patients underwent surgery for unspecific spondylodiscitis in the Department of Orthopedics of the Free University of Berlin. Fifty-six of them were followed up, and their clinical and radiological results were evaluated in this study. The surgical results of 40 patients with only ventral removal of a focus and defect coverage with an iliac crest graft were compared to those of 16 with additional dorsal bridging instrumentation by internal fixation. A mean of 2.3 vertebrae were fused in ventral spondylodesis; the mean length of dorsal instrumentation by internal fixation was 3.8 vertebrae. Patients were followed up a mean of 5.1 years after surgery. The mean age of patients was 57.1 years at the time of surgery. Patients were postoperatively mobilized a mean of 5 days after ventrodorsal fusion. A purely ventral procedure required a mean postoperative immobilization period of 3.6 weeks and brace fitting of a mean 8.2 months. There was one case of recurrent spondylodiscitis 25 months postoperatively, which made a revision of the focus necessary. The consolidation rate of the ventral spondylodesis was 84-100% in the different subgroups. A differential view of the spinal areas and ventral fusion segments was used to make a statement about the development of the sagittal spine profile. The segmental position of the spine in the sagittal plane was assessed by comparing the segmental kyphosis angles to normal values in the literature. All subgroups submitted to combined ventrodorsal fusion had a greater preoperative segmental kyphosis angle than those undergoing ventral fusion alone. In marked segmental kyphotic false positioning, the combined ventrodorsal procedure achieved good postoperative repositioning results, and an increase in segmental kyphosis was prevented. Ventral removal of a focus and bone graft spondylodesis seem to be adequate in single-level spondylodiskitis especially in the lumbar spine, but additional dorsal instrumentation should be performed in the case of long ventral fusion.

Spondyloptosen, aber auch hochgradige Spondylolisthesen kommen nahezu ausschlieslich am lumbosakralen Ubergang vor und sind atiopathogenetisch mit wenigen Ausnahmen den dysplastischen Spondylolisthesen zuzuordnen. Da es durch die kyphotische Einstellung des lumbosakralen Ubergangs zu einer lokalen Fehlbeanspruchung, zu Spinalkanal- und Foraminalstenose und zu Kompensationsmechanismen mit Verstarkung der Lendenlordose und Aufrichtung der Beckenkippung unter Einbeziehung der Huft- und Kniegelenke kommt, hat bei der operativen Versorgung der hochgradigen Spondylolisthese und der Spondyloptose die Wiederherstellung eines physiologischen sagittalen Profils, durch moglichst vollstandige Reposition, unter dauerhafter Fusionierung nur des lumbosakralen Bewegungssegments, eine vorrangige Bedeutung. Diese Zielsetzung hat zu folgendem Behandlungsweg gefuhrt: dorsale Reposition nach vorheriger Sakraldomresektion, entsprechend einer tatsachlichen Ruckfuhrung des pathophysiologischen Gleitvorgangs und anschliesende intersomatische Fusion in PLIF-Technik. Das vorbeschriebene Verfahren wurde von Januar 1995 bis Januar 1998 bei insgesamt 11 Patienten praktiziert. Darunter waren 6 viertgradige Spondylolisthesen und 5 Spondyloptosen; 4 Patienten waren voroperiert. Zur Verlaufskontrolle als auch zur Kontrolle der postoperativen Ergebnisse wurden der Gleitwinkel (Boxall), der Gleitgrad (Taillard), die sakrale Inklination (Boxall) und die sagittale Rotation (Wiltse u. Winter) gemessen. Eine Einteilung sowohl des pra- und postoperativen Beschwerdestatus als auch des der letzten Untersuchung erfolgte in Anlehnung an die Schmerzskala von Denis. Bei einem voroperierten Patient kam es zu einer unzureichenden Reposition, wobei in diesem Fall wegen einer ausgerissenen Pedikelschraube bei L5 von L4 bis S1 instrumentiert werden musste. Intraoperativ wurde bei einem weiteren voroperierten Patient die Dura verletzt und entsprechend versorgt. Derselbe Patient zeigte postoperativ ein neu aufgetretenes einseitiges Wurzelsyndrom, welches im weiteren Verlauf keine wesentliche Besserung zeigte. Ein weiterer Patient entwickelte im Nachuntersuchungszeitraum eine Dekompensation des kranialen Nachbarsegments. Die Reposition gelang in 10 Fallen bei Durchfuhrung einer monosegmentalen Fusion vollstandig oder zumindest nahezu vollstandig. Eine feste knocherne Konsolidierung trat bei allen Patienten ein. Die Beschwerden waren bei allen Patienten im Vergleich zum praoperativen Status deutlich reduziert.

Kyphosis is a dorsally convex curvature of the spine in the sagittal plane. A pathological kyphosis of the thoracic spine has a Cobb angle greater than 50 degrees. It occurs when the anterior and/or posterior load-transferring elements of the spine are overloaded or damaged. Wedge-shaped vertebral bodies may be found at one or several levels. A wedge-shaped vertebral body increases the curvature of the spine and moves the centre of gravity of the body parts above of the corresponding vertebral body in a ventral direction. This increases the flexion-bending moment acting on the spine. In the case of a wedge-shaped deformation of a vertebral body, the relative increase of the flexion moment is a function of the wedge angle and of the original position of the centre of gravity of the upper body.

In the presence of a vertebral injury or disease, manifest osteoporosis affects preoperative planning. Thus, if surgery is indicated, bone density should be determined in cases of suspected or diagnosed osteoporosis. Instrumentation of the spine is frequently not required in surgical interventions. However, if indicated, instrumentation should be fixed multifocally and the deformity should be corrected with special care. It is absolutely necessary to avoid ending instrumentation within a kyphosis.