M. Arand

Stability increase of the lumbar spine with different muscle groups. A biomechanical in vitro study.

Study design This study investigated the influence of five different muscle groups on the monosegmental motion (L4–L5) during pure flexion/extension, lateral bending, and axial rotation moments. Objectives. The results showed and compared the effect of different muscle groups acting in different directions on the stability of a single motion segment to find loading conditions of in vitro experiments that simulate more physiologically reasonable loads. Summary of Background Data. In spine biomechanics research, most in vitro experiments have been carried out without applying muscle forces, even though these forces stabilize the spinal column in vivo. Methods. Seven human lumbosacral spines were tested in a spine tester that allows simulation of up to five symmetrical muscle forces. Changing pure flexion/extention, lateral binding, and axial rotation moments up to ±3.75 Nm were applied without muscle forces, with different muscle groups and combinations. The three-dimensional monosegmental motion was determined using an instrumented spatial linkage system. Results. Simulated muscle forces were found to strongly influence load-deformation characteristics. Muscle action generally increased the range of motion and the natural zone of the motion segments. This was most evident for flexion and extension. After five pairs of symmetrical, constant muscle forces were applied (80 N per pair) the range of motion decreased about 93% in flexion and 85% in extension. The total natural zone for flexion and extension was decreased by 83% muscle action. The multifluids muscle group had the strongest influence. Conclusion. This experiment showed the important of including at least some of the most important muscle groups in invitro experiments in lumbar spine specimens.

Human osteoblasts from younger normal and osteoporotic donors show differences in proliferation and TGFβ-release in response to cyclic strain

Mechanical stimulation of bone tissue by physical activity stimulates bone formation in normal bone and may attenuate bone loss of osteoporotic patients. However, altered responsiveness of osteoblasts in osteoporotic bone to mechanical stimuli may contribute to osteoporotic bone involution. The purpose of the present study was to investigate whether osteoblasts from osteoporotic patients and normal donors show differences in proliferation and TGF beta production in responses to cyclic strain. Human osteoblasts isolated from collagenase-treated bone explants of 10 osteoporotic patients (average age 70 +/- 6 yr) and 8 normal donors (average age 54 +/- 10 yr) were plated into elastic rectangular silicone dishes. Subconfluent cultures were stimulated by cyclic strain (1%, 1 Hz) in electromechanical cell stretching apparatus at three consecutive days for each 30 min. The cultures were assayed for proliferation, alkaline phosphatase activity and TGF beta release in each three parallel cultures. In all experiments, osteoblasts grown in the same elastic dishes but without mechanical stimulation served as controls. Significant differences between stimulated cultures and unstimulated controls were determined by a paired two-tailed Wilcoxon test. In comparison to the unstimulated controls, osteoblasts from normal donors significantly increased proliferation (p = 0.025) and TGF beta secretion (p = 0.009) into the conditioned culture medium. In contrast, osteoblasts from osteoporotic donors failed to increase both proliferation (p > 0.05) and TGF beta release (p > 0.05) in response to cyclic strain. Alkaline phosphatase activity was not significantly affected (p > 0.05) in normal as well as osteoporotic bone derived osteoblasts. These findings suggest a different responsiveness to 1% cyclic strain of osteoblasts isolated from normal and osteoporotic bone that could be influenced by both the disease of osteoporosis and the higher average age of the osteoporotic patient group. While osteoblasts from osteoporotic donors failed to increase proliferation and TGF beta release under the chosen mechanical strain regimen that stimulated both parameters in normal osteoblasts, it is possible that some other strain regimen would provide more effective stimulation of osteoporotic cells.

Does Computer-Assisted Spine Surgery Reduce Intraoperative Radiation Doses?

Study Design. Prospective clinical study. Objective. Computer-assisted surgery (CAS) means improved accuracy in inserting screws. Usually the required time of the intraoperative use of a C-arm device is reduced. The aim of the study was to quantify the radiation doses during spine surgery in different types of computer-assisted surgical procedures (i.e., computerized tomography [CT] based and C-arm) compared to standard methods and, as a new technique, the Iso-C3D C-arm (Siemens, GER). Summary of Background Data. A total of 38 individuals were enrolled in the study, including 8 who underwent standard spine surgery, 10 with CT-based, 9 with C-arm based, and 11 with Iso-C3D C-arm based. The thermoluminescence dosimetry measurements were 2 at the radiation source, 2 at the patient, and 2 at the receiver. Methods. This study is based on the thermoluminescence method. A total of 38 individuals were enrolled in the study. Despite the small number of patients, the existing results up until now showed a clear reduction of the duration of radiation time using CAS compared to standard methods in spine surgery. Much more important is the fact that the radiation doses were clearly reduced from a median of 1091 mGy using the standard procedure versus 432 mGy in CT-based and 664 mGy in C-arm based guided surgery. The Iso-C3D C-arm showed a median of 152 mGy. Results. The duration of radiation was reduced from 177 seconds in the standard spine procedure to 75 seconds in CT-based CAS spine intervention. Comparing the different types of CAS application at the spine, the Iso-C3D C-arm based surgery is the method with the lowest duration of radiation. The radiation doses at the C-arm tube (source) are reduced from a median of 1091 mGy in the standard procedure versus 432 mGy in CT-based and 664 mGy in C-arm based guided surgery. In this study, the median dose of an Iso-C3D C-arm was 152 mGy. Conclusion. These findings are important for the operating room personnel, which is exposed daily to radiation intraoperatively, as well as the patients, when using CAS procedures.

Präzisionsanalyse navigationsgestützt implantierter thorakaler und lumbaler Pedikelschrauben : Eine prospektive klinische Studie

ZusammenfassungZiel der vorliegenden prospektiven Studie war die Überprüfung der Präzision navigiert und konventionell eingebrachter Pedikelschrauben. Die Anwendung des Navigationssystems bedurfte intraoperativ einen zusätzlichen Zeitaufwand von durchschnittlich 8,4 min für die Referenzierung je Wirbelkörper. Zur Beurteilung der Ergebnisse wurde eine korrekte Schraubenlage definiert als rein intraossäre Lage. Jede mediale oder laterale Perforation der pedikulären Kortikalis wurde als Fehllage gewertet.In der CT-Kontrolle zeigte sich eine vollständige intrapedikuläre Implantatlage bei 36 von 45 thorakalen (80%) und bei 22 von 27 navigationsgestützt eingebrachten lumbalen (81%) Pedikelschrauben. Die konventionelle Besetzung der Pedikel ergab im gleichen Zeitraum eine zentrale Platzierung thorakal bei 27 von 34 (79%) und lumbal bei 43 von 52 (83%) Schrauben. Eine radikuläre Begleitsymptomatik fand sich bei keinem der Patienten nach navigationsgestützter oder konventioneller Implantation. Die Analyse der beiden in der Studie verwendeten Implantatsysteme hinsichtlich der Präzision bei der Implantation zeigte im navigierten Kollektiv eine zentrale Lage der Schrauben des Druckplattenfixateur in 67% und des USS in 90% der Patienten, in der nicht navigierten Gruppe war die Verteilung ausgeglichen.Die anfängliche Benutzung des Navigationssystems führte, bevorzugt durch Fehler in der Referenzierung, zu einer erhöhten Inzidenz an Schraubenfehllagen. Im ersten 1/2 Jahr der klinischen Anwendung des Systems lagen 72% der Implantate korrekt im Pedikel, im zweiten 1/2 Jahr 80%.Durch die vorliegende Arbeit konnte gezeigt werden, dass die Anwendung der computergestützten Freihandnavigation in der Initialphase zur einer mit dem konventionellen Verfahren vergleichbaren Präzision von Implantatplatzierungen an der Wirbelsäule führt. Zu berücksichtigen ist allerdings eine Lernkurve für das Verfahren und eine Eignung des verwendeten Implantatsystems für die computerassistierte Anwendung, sodass mit zunehmender Erfahrung in dieser Technik von einer Reduktion der Fehlplatzierungen ausgegangen werden darf.AbstractA prospective clinical trial was performed to study the accuracy of pedicle screw placement of consecutive computer-aided and conventional techniques. Concerning the clinical performance of the navigation system, the average time of matching has been 8,4 minutes per vertebrae. For evaluation of the results, only complete intraosseous placement of the pedicle screw has been defined as correct position. Any medial or lateral perforation of the cortical structure of the pedicle was recorded as malplacement.In the CT-controlled patients complete intrapedicular placement of the screw was obtained in 36 of 45 thoracic (80%) and in 22 of 27 navigated lumbar (81%) pedicles. In the conventional cohort group 27 of 34 (79%) thoracal and 43 of 52 (83%) lumbar screws were completely in. No radicular neurologic damage, caused by a malplaced transpedicular screw has been observed in both groups.In the presented study is shown, that the application of the computer-assisted freehand navigation can improve results concerning the precision of spinal screw placement. Although, the spinal navigator has to consider a learning curve for the clinical inauguration of the system and the qualification of the implant system for computer-assisted application.

Computer-guidance in percutaneous screw stabilization of the iliosacral joint.

Nine patients with instability and one patient with degeneration of the iliosacral joint were treated surgically. The posterior pelvic ring was stabilized with the assistance of an optoelectronic navigation system. Registration was ensured by using fiducial screws in the iliac crest or by collecting landmarks on the external fixator. Computed tomography scans taken postoperatively provided additional information regarding implant localization in all patients. Accurate placement of 21 of 22 implanted iliosacral screws was observed. Two of the 21 screws touched the wall of the second sacral foramen without perforating the canal. One screw perforated the anterior wall of the sacrum because the navigated guide wire was bent during implantation. The initial results indicate that computer-aided frameless navigation in surgery of the iliosacral joint can facilitate surgical performance during screw stabilization in selected patients. Two important issues must be considered in the clinical application of this technique: first, any relative migration of the iliac and sacral bone structures between computed tomography scans taken preoperatively and intraoperative navigation may result in an intolerable inaccuracy of computer guidance. Second, bending of the guide wire of the tracked power drive, which cannot be accommodated by the navigation system, will lead to misguidance; therefore, only navigated drill sleeves should be used.

Strahlendosis im OP – ein Vergleich computerassistierter Verfahren

ZusammenfassungComputerassistierte Verfahren werden seit den 1990er Jahren in der Orthopädie und Traumatologie eingesetzt. Neben der seit dieser Zeit proklamierten erhöhten Genauigkeit im Vergleich zu konventionellen Operationsverfahren wurde als einer der Hauptvorteile der Computernavigation eine Verminderung ionisierender Strahlung im unfallchirurgischen OP angeführt. In vielen Studien konnte Ersteres belegt werden. Um Letzteres zu messen,wurde diese Studie durchgeführt. Ihr Ziel war es, Röntgendosen sowohl bei konventionellen als auch bei computerunterstützten Verfahren mit einem C-Bogen-Gerät des Typs SIREMOBIL Iso-C3D® (Fa. Siemens Medical Solutions) zu quantifizieren. Es sollte erstmals nachgewiesen werden, welche Verfahren in Hinsicht auf Minimierung der emittierten Röntgendosis überlegen sind. Die klinischen Messungen wurden ergänzt durch Labormessungen mit Hilfe einer Ionisationsmesskammer im Innern eines Standard-Plexiglasphantoms. Die Studie untersuchte in ihrem klinischen Teil an insgesamt 42 Patienten den Einsatz neuer, computerunterstützter Verfahren im Vergleich zu konventionellen Methoden anhand von Eingriffen an der unteren Extremität (n=14) und Wirbelsäulenoperationen (n=28). Als Verfahren wurden untersucht 1. die konventionelle Operationsmethode, 2. die CT-basierte Navigation, 3. die C-Arm-Navigation und 4. die Iso-C-3D-Navigation. Der Schwerpunkt der klinischen Untersuchungen lag dabei auf der Ermittlung von Strahlendosen mittels Thermolumineszenzdosimetrie sowie der Erfassung der Betriebszeiten des Röntgengeräts im Verlauf eines operativen Eingriffs. Die Erkenntnisse aus den klinischen Studien werden gestützt durch die Ergebnisse aus den Labormessungen. Es konnte gezeigt werden, dass die computerunterstützten Verfahren in allen untersuchten Bereichen eine deutliche Reduktion der Strahlenexposition bei verkürzten Durchleuchtungszeiten erreichen. Für die erst kürzlich,während der laufenden Studie, in den klinischen Betrieb eingeführte Iso-C-3D-Navigation wurde die größte Verminderung der Freisetzung von ionisierender Strahlung ermittelt.AbstractSince the 1990s, computer-assisted methods have been well-established in the field of orthopedics and traumatology. In addition to the proven improvement in the field of surgical precisioncompared with conventional techniques, the decrease in the amount of emitted ionizing radiation inside of the operating room was cited to constitute an additional major advantage of computer-based navigation. The goal of this study was to quantify X-ray dose values exposed during both conventional methods and computer-assisted procedures, the latter being performed using a C-arm device SIREMOBIL Iso-C3D (Siemens Medical Solutions). The clinical measurements were supplemented by laboratory experiments using a pinpoint ionization chamber placed inside a standard lucite phantom. The clinical part of the study investigated the application of new, i.e. computer assisted, techniques in comparison with conventional procedures on in total 42 patients experiencing surgery either on their lower extremities (n=14) or on the spine (n=28). The techniques applied were:(1) conventional surgical procedure, (2) CT-based navigation, (3) C-arm navigation, and (4) Iso-C3D-navigation. The main focus of the clinical evaluation was the determination of radiation dose values by means of thermoluminescence dose meters, accompanied by the registration of the operation times of the X-ray tube during a surgical intervention. The conclusions from the clinical studies are in agreement with the results from the laboratory measurements. Computer-assisted techniques led to a significant reduction in X-ray dose exposure and drastically shortened irradiation times. The most pronounced decrease in the emission of ionizing radiation was achieved in case of the Iso-C3D-navigation, which has only recently been introduced into clinical practice, i.e. during runtime of this study.

Influence of varying muscle forces on lumbar intradiscal pressure: An in vitro study

The purposes of this study were to determine the effect of including muscle forces in the experimental loading of the spine on the intradiscal pressure and to determine whether this effect correlates with previously established in vivo data. We modeled the spine muscles as of five distinct groups and isolated the effect of each group on the intradiscal pressure (L4-L5). Seven human lumbosacral spines were tested in pure flexion/extension, right/left lateral bending, and left/right axial rotation moments. Stimulated muscle activity strongly influenced load-pressure characteristics, especially for the multifidus. Without muscle forces active, pressure increased proportionately with increasing moment. With five pairs of symmetrical constant muscle forces active (80 N per pair) the pressure increased more than 200% in neutral position and did not increase with increasing moment. The pressure without muscle forces and without axial preload was 0.12 MPa, which is about the same found by earlier in vivo studies of anesthetized subjects in prone position. With simulated muscle forces, the pressure was 0.39 MPa and in the range found for non-anesthetized subjects. We conclude that simulating muscle forces substantially affects intradiscal pressure.

Internal fixation on the lower cervical spine – biomechanics and clinical practice of procedures and implants

The decision to opt for a particular internal fixation procedure of a traumatized unstable lower cervical spine should be based on analysis and implementation of scientific and clinical data on the biomechanics of the intact, the unstable and the implant-fixed spine. The following recommendations for surgical stabilization of the lower cervical spine seem, therefore, to be justified. Firstly, the surgical procedure should be to bring about decompression, realignment, and stability. Secondly, the anterior approach should be the primary and preferred one. With regard to surgical and positioning technique, this access clearly involves fewer problems than the posterior approach; if required, unrestricted additional cord decompression can take place; implant fixation is technically simple, and the fusion is under direct compression, thus allowing optimal fusion healing. The awareness of instability and type of implant permits functional therapy, above all for the paraplegic patient. Thirdly, for traumatic conditions, posterior methods should be reserved for exceptional indications. The restriction to this approach is that the anterior column must be intact and a multi-segmental fixation must be used. Posterior fixation seems, therefore, to be more appropriate for degenerative, rheumatoid or tumorous instabilities than for traumatic instabilities. The cerclage wire technique depends on intact osseous posterior elements, while after laminectomy only implants fixed with screws can create safe stability. The disadvantages of the posterior access for the proprioception of the cervical muscles and the subjective symptoms of the patient are known and must be taken into account. Fourthly, combined techniques are indicated for highly unstable or particularly complex injuries. On the cervicothoracic junction, or in cases of Bechterews disease, the decision is justifiably made in favor of this technique, which can be performed as a one-stage or two-stage operation. Finally, whenever possible, selection of the implant should take into account the foreseeable developments in diagnostic procedures, and therefore, in view of the modern imaging techniques likely to be used in any follow-up examinations required later, the implant chosen should be made of titanium.

Difference in metallic wear distribution released from commercially pure titanium compared with stainless steel plates

IntroductionStainless steel and commercially pure titanium are widely used materials in orthopedic implants. However, it is still being controversially discussed whether there are significant differences in tissue reaction and metallic release, which should result in a recommendation for preferred use in clinical practice.Materials and methodsA comparative study was performed using 14 stainless steel and 8 commercially pure titanium plates retrieved after a 12-month implantation period. To avoid contamination of the tissue with the elements under investigation, surgical instruments made of zirconium dioxide were used. The tissue samples were analyzed histologically and by inductively coupled plasma atomic emission spectrometry (ICP-AES) for accumulation of the metals Fe, Cr, Mo, Ni, and Ti in the local tissues. Implant corrosion was determined by the use of scanning electron microscopy (SEM).ResultsWith grades 2 or higher in 9 implants, steel plates revealed a higher extent of corrosion in the SEM compared with titanium, where only one implant showed corrosion grade 2. Metal uptake of all measured ions (Fe, Cr, Mo, Ni) was significantly increased after stainless steel implantation, whereas titanium revealed only high concentrations for Ti. For the two implant materials, a different distribution of the accumulated metals was found by histological examination. Whereas specimens after steel implantation revealed a diffuse siderosis of connective tissue cells, those after titanium exhibited occasionally a focal siderosis due to implantation-associated bleeding. Neither titanium- nor stainless steel-loaded tissues revealed any signs of foreign-body reaction.ConclusionWe conclude from the increased release of toxic, allergic, and potentially carcinogenic ions adjacent to stainless steel that commercially pure Ti should be treated as the preferred material for osteosyntheses if a removal of the implant is not intended. However, neither material provoked a foreign-body reaction in the local tissues, thus cpTi cannot be recommend as the ‘golden standard’ for osteosynthesis material in general.

Combined anteroposterior spinal fixation provides superior stabilisation to a single anterior or posterior procedure

Fusion is the main goal in the surgical management of the injured and unstable spine. A wide variety of implants is available to enhance this. Our study was performed to evaluate the stabilising characteristics of several anterior, posterior and combined systems of fixation. Six thoracolumbar (T11 to L2) spines from 13-week-old calves were first tested intact. Then the vertebral body of T13 was removed and the defect replaced and supported by a wooden block to simulate bone grafting. Dorsal implants consisting of a Universal Spine System (USS) fracture system and an AO Fixateur interne (AOFI), and ventral implants comprising of a Kaneda Classic, a Kaneda SR, a prototype of the VentroFix single clamp/single rod construct (SC/SR) and the VentroFix single clamp/double rod construct (SC/DR) were first implanted individually to stabilise the removal of the vertebral body. Simulating the combined anteroposterior stabilisations, all ventral implants were combined with the AOFI. The range of motion (ROM) was measured under loads of up to 7.5 Nm. The load was applied in a custom-made spine tester in the three primary directions while measuring the intervertebral movements using a goniometric linkage system. The dorsal systems limited ROM in flexion below 0.9 degrees and in extension between 3.3 degrees and 3.6 degrees (median values). The improved Kaneda System SR yielded a mean ROM of 1.8 degrees in flexion and in extension. The median rotation found with the VentroFix (SC/DR) was 3.2 degrees for flexion and 2.8 degrees for extension. Reinforcement of the ventral constructs with a dorsal system reduced the ROM in flexion and extension in all cases to 0.4 degrees and lower. In rotation, the median ROM of the anterior systems ranged from 2.7 degrees to 5.1 degrees and for the posterior systems from 3.9 degrees to 5.7 degrees, while the combinations provided a ROM of 1.2 degrees to 1.9 degrees. In lateral bending, the posterior implants restricted movement to 1.1 degrees, whereas the anterior implants allowed up to 5.2 degrees. The combined systems provided the highest stability at less than 0.6 degrees. Our study revealed distinct differences between posterior and anterior approaches in all primary directions. Also, different stabilisation characteristics were found within the anterior and posterior groups. Combinations of these two approaches provided the highest stability in all directions.