Erich Hartwig

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.

Mechanically simulated muscle forces strongly stabilize intact and injured upper cervical spine specimens.

Although muscles are assumed to be capable of stabilizing the spinal column in vivo, they have only rarely been simulated in vitro. Their effect might be of particular importance in unstable segments. The present study therefore tests the hypothesis that mechanically simulated muscle forces stabilize intact and injured cervical spine specimens. In the first step, six human occipito-cervical spine specimens were loaded intact in a spine tester with pure moments in lateral bending (+/- 1.5 N m), flexion-extension (+/- 1.5 N m) and axial rotation (+/- 0.5 N m). In the second step, identical flexibility tests were carried out during constant traction of three mechanically simulated muscle pairs: splenius capitits (5 N), semispinalis capitis (5 N) and longus colli (15 N). Both steps were repeated after unilateral and bilateral transection of the alar ligaments. The muscle forces strongly stabilized C0-C2 in all loading and injury states. This was most obvious in axial rotation, where a reduction of range of motion (ROM) and neutral zone to <50% (without muscles=100%) was observed. With increasing injury the normalized ROM (intact condition=100%) increased with and without muscles approximately to the same extend. With bilateral injury this increase was 125-132% in lateral bending, 112%-119% in flexion-extension and 103-116% in axial rotation. Mechanically simulated cervical spine muscles strongly stabilized intact and injured cervical spine specimens. Nevertheless, it could be shown that in vitro flexibility tests without muscle force simulation do not necessarily lead to an overestimation of spinal instability if the results are normalized to the intact state.

Spinal navigation in tumor surgery of the thoracic spine: first clinical results.

In this clinical study, the accuracy of computed tomography-based and computer-guided decompression and insertion of pedicle screws in patients who have had tumor-related posterior surgery of the thoracic spine was evaluated. Eight patients with advanced metastatic disease were treated surgically using a posterior approach with the assistance of an optoelectronic navigation system. Postoperative computed tomography scans were obtained for all patients and provided information regarding decompression and transpedicle implant localization. In all eight patients accurate decompression of the spinal canal was seen. Using the navigation system, 22 of 26 scheduled transpedicle screws were inserted using computer guidance. Eighty-six percent (19 of 22) of the navigated pedicle screws were positioned centrally in the bone. Initial results indicate that computer-aided frameless navigation in tumor surgery of the thoracic spine is a safe system to improve surgical performance during posterior decompression and transpedicle stabilization. Although computed tomography-based computer-assisted spinal navigation is important, the system is not 100% accurate. Therefore, application of the navigation system should be restricted to experienced surgeons who can continue the operation using a conventional approach. Finally, detailed knowledge of the principles of the tracking systems is necessary to prevent possible misinterpretation of information provided by the computer.

Minimally invasive ventral spondylodesis for thoracolumbar fracture treatment: surgical technique and first clinical outcome

A new instrumentation system for ventral stabilization of the spine that can be used for an endoscopic and minimally invasive approach was developed. We describe the implantation technique and report on the first clinical results. This prospective study covers the first 45 patients to undergo this new technique since it was introduced in 1999. In all patients the operation was successfully performed in a completely minimally invasive procedure. Mono- and bisegmental stabilization was performed mainly at the thoracolumbar junction after initial posterior instrumentation in most cases. Lesions varied from fresh/old fractures to metastases (T5–L3). Pre- and postoperative follow-up included clinical examination and radiological visualization via X-ray and computed tomographic scan. Our experience with this minimally invasive procedure demonstrated the feasibility of the method.

Vertebral body replacement with a bioglass-polyurethane composite in spine metastases – clinical, radiological and biomechanical results

Abstract Metastatic spine lesions frequently require corpectomy in order to achieve decompression of the spinal cord and restoration of spinal stability. A variety of systems have been developed for vertebral body replacement. In patients with prolonged life expectancy due to an improvement of both systemic and local therapy, treatment results can be impaired by a loosening at the implant-bone interface or mechanical failure. Furthermore, early detection of a metastatic recurrence using sensitive imaging modalities like computed tomography (CT) and magnetic resonance imaging (MRI) is possible in these patients without artefact interference. The aim of our pilot study was to evaluate the clinical applicability and results of a new radiolucent system for vertebral body replacement in the lumbar spine. The system consists of bone-integrating biocompatible materials – a polyetherurethane/bioglass composite (PU-C) replacement body and an integrated plate of carbon-fibre reinforced polyetheretherketone (CF-PEEK) – and provides high primary stability with anterior instrumentation alone. In a current prospective study, five patients with metastatic lesions of the lumbar spine were treated by corpectomy and reconstruction using this new system. Good primary stability was achieved in all cases. Follow-up (median ¶15 months) using CT and MRI revealed progressive osseous integration of the PU-C spacer in four patients surviving more than 6 months. Results obtained from imaging methods were confirmed following autopsy by biomechanical investigation of an explanted device. From these data, it can be concluded that implantation of the new radiolucent system provides sufficient long-term stability for the requirements of selected tumour patients with improved prognosis.

Surface electromyography-verified muscular damage associated with the open dorsal approach to the lumbar spine

The dorsal approach is increasingly preferred in the surgical treatment of vertebral fractures. However, the access and the implants position cause muscle loss, which can lead to instability and a reduced capacity for rehabilitation. Morphological factors (bones, intervertebral discs) are typically blamed for chronic pain syndromes in the literature, while less importance is attached to functional factors (muscles). The objective of this study was therefore to investigate the isolated influence of dorsal spinal instrumentation on the back muscles by means of electromyography (EMG). A total of 32 patients with conditions after dorsal spondylodesis following the fracture of a vertebral body and 32 subjects with healthy backs were enrolled in this study. The EMG signal was recorded in three different muscle groups during isometric extension exercise. The evaluation was performed by comparing the mean rectified amplitudes of the three muscle groups in the patients and controls. The patients had significantly lower amplitudes in the multifidus muscle (MF) and significantly higher amplitudes in the iliocostal muscle (IL). Patients with severe pain were found to have lower electric muscle potentials in all investigated muscle groups than patients with mild pain. The muscle damage which was established in the multifidus muscle is compensated by increased activity in the iliocostal muscle. On the basis of anatomical considerations, the damage pattern can be identified as having been caused by surgery. It is extremely unlikely that trauma is the cause.

Molecular profiling of chordoma

The molecular basis of chordoma is still poorly understood, particularly with respect to differentially expressed genes involved in the primary origin of chordoma. In this study, therefore, we compared the transcriptional expression profile of one sacral chordoma recurrence, two chordoma cell lines (U-CH1 and U-CH2) and one chondrosarcoma cell line (U-CS2) with vertebral disc using a high-density oligonucleotide array. The expression of 65 genes whose mRNA levels differed significantly (p<0.001; ≥6-fold change) between chordoma and control (vertebral disc) was identified. Genes with increased expression in chordoma compared to control and chondrosarcoma were most frequently located on chromosomes 2 (11%), 5 (8%), 1 and 7 (each 6%), whereas interphase cytogenetics of 33 chordomas demonstrated gains of chromosomal material most prevalent on 7q (42%), 12q (21%), 17q (21%), 20q (27%) and 22q (21%). The microarray data were confirmed for selected genes by quantitative polymerase chain reaction analysis. As in other studies, we showed the expression of brachyury. We demonstrate the expression of new potential candidates for chordoma tumorigenesis, such as CD24, ECRG4, RARRES2, IGFBP2, RAP1, HAI2, RAB38, osteopontin, GalNAc-T3, VAMP8 and others. Thus, we identified and validated a set of interesting candidate genes whose differential expression likely plays a role in chordoma.

Thoracolumbar fracture stabilization: comparative biomechanical evaluation of a new video-assisted implantable system

Minimally invasive techniques for spinal surgery are becoming more widespread as improved technologies are developed. Stabilization plays an important role in fracture treatment, but appropriate instrumentation systems for endoscopic circumstances are lacking. Therefore a new thoracoscopically implantable stabilization system for thoracolumbar fracture treatment was developed and its biomechanical in vitro properties were compared. In a biomechanical in vitro study, burst fracture stabilization was simulated and anterior short fixation devices were tested under load with pure moments to evaluate the biomechanical stabilizing characteristics of the new system in comparison with a currently available system. With interbody graft and fixation the new system demonstrated higher stabilizing effects in flexion/extension and lateral bending and restored axial stability beyond the intact spine, as well as having comparable or improved effects compared with the current system. Because of this biomechanical characterization a clinical trial is warranted; the usefulness of the new system has already been demonstrated in 45 patients in our department and more than 300 cases in a multicenter study which is currently under way.

Die Therapie der aneurysmatischen Knochenzyste

ZusammenfassungDie aneurysmatische Knochenzyste ist eine seltene tumorähnliche Erkrankung, die jeden Skelettabschnitt involvieren kann und sich überwiegend im Kindes- oder Jugendlichenalter manifestiert. Differentialdiagnostische Schwierigkeiten bei der Abgrenzung gegenüber bestimmten benignen und malignen primären Knochentumoren erfordern neben dem Einsatz differenzierter bildgebender Verfahren häufig die histopathologische Beurteilung durch ein Knochentumorregister. Bedingt durch eine sehr heterogene biologische Aktivität und den Umstand, daß die Erkrankung überwiegend das wachsende Skelett betrifft, muß bei der chirurgischen Therapie sowohl hinsichtlich der Resektion als auch der Defektrekonstruktion auf ein breites Spektrum an Behandlungsmaßnahmen zurückgegriffen werden können. In einer retrospektiven Studie wurden die Behandlungsergebnisse bei 41 operierten Tumoren, davon 31 aktive und jeweils 5 latente bzw. aggressive Läsionen, untersucht. Während die therapieassoziierte Morbidität auch bei ausgedehnteren Destruktionen sowie aufwendigeren Rekonstruktionen vergleichsweise gering war, lag die Rezidivrate bei 19,5%. Die Analyse der Lokalrezidive zeigte, daß– unter Berücksichtigung der biologischen Aktivität des Primärtumors – jeweils ein inadäquates Resektionsverfahren zu Grunde lag. Der Umstand, daß das Lokalrezidivrisiko sowohl mit der Aggressivität der Primärläsion als auch mit der chirurgischen Radikalität korreliert, macht ein präoperatives Staging und eine stadiengerechte Therapie erforderlich.SummaryThe aneurysmal bone cyst represents a tumorlike lesion, which does not occur frequently. Every site of the skeleton may be involved. Although it can be observed at any age, it distinctly predominates from 10 to 20 years of age. Distinction of aneurysmatic bone cysts from certain benign or malignant bone tumours requires subtle imaging techniques and an experienced bone tumour pathologist. Since the lesion shows a heterogeneous biological behaviour and typically occurs in the growing skeleton, a wide range of surgical procedures must be provided concerning tumour resection and defect reconstruction. In the current retrospective study results of 41 surgically treated aneurysmal bone cysts, thereof 5 latent, 31 active, and 5 aggressive lesions, were investigated. While morbidity due to the therapeutic measures was comparatively low even in extended lesions and demanding reconstructions, a recurrence rate of 19.5% had to be observed in our series. Taking into consideration the biological activity of the lesion, analysis of the recurrences revealed inappropriate surgical margins had been chosen at the primary operation in all of these patients. Since the risk of a local relapse is linked both to aggressiveness of the primary lesion and to surgical radicality, therapy of aneurysmal bone cyst requires preoperative staging and stage-dependent surgical procedures.

Intramuscular pressure, tissue oxygenation and EMG fatigue measured during isometric fatigue-inducing contraction of the multifidus muscle

Simultaneous measurement of intramuscular pressure (IMP), tissue oxygen partial pressure (pO2) and EMG fatigue parameters in the multifidus muscle during a fatigue-inducing sustained muscular contraction. The study investigated the following hypotheses: (1) Increases in IMP result in tissue hypoxia; (2) Tissue hypoxia is responsible for loss of function in the musculature. The nutrient supply to muscle during muscle contraction is still not fully understood. It is assumed that muscle contraction causes increased tissue pressure resulting in compromised perfusion and tissue hypoxia. This tissue hypoxia, in turn, leads to muscle fatigue and therefore to loss of function. To the authors’ knowledge, no study has addressed IMP, pO2 and EMG fatigue parameters in the same muscle to gain a deeper sight into muscle perfusion during contraction. As back muscles need to have a constant muscular tension to maintain trunk stability during stance and locomotion, muscle fatigue due to prolonged contraction-induced hypoxia could be an explanation for low back pain. Sixteen healthy subjects performed an isometric muscular contraction exercise at 60% of maximum force until the point of localized muscular fatigue. During this exercise, the individual changes of IMP, pO2 and the median frequency (MF) of the surface EMG signal of the multifidus muscle were recorded simultaneously. In 12 subjects with a documented increase in intramuscular pressure, only five showed a decrease in tissue oxygen partial pressure, while this parameter remained unchanged in six other subjects and even increased in one. A fall in tissue pO2 was associated with a drop in MF in only five subjects, while there was no correlation between these parameters in the other 11 subjects. To summarize, an increase in IMP correlated with a decrease in pO2 and a drop in MF in only five out of 16 subjects. High intramuscular pressure values are not always associated with a hypoxia in muscle tissue. Tissue hypoxia is not automatically associated with a median frequency shift in the EMG signal’s power spectrum.