U. Weber

Clinical Relevance of Accuracy of Pedicle Screw Placement: A Computed Tomographic-Supported Analysis

Study Design. The location of pedicle screws (n = 244) and the increase in the pedicle diameter were determined by computed tomography after screw removal in 50 patients with 360° lumbar fusions. The neurologic findings were examined before and after surgery. Objectives. To evaluate the correlation between the accuracy of pedicle screw placement and preoperative and postoperative neurologic findings. Summary of Background Data. Incorrect placement of pedicle screws that was detected by computed tomography has been published in several studies. Simultaneous pathologic neurologic deficits are thought to be created by an eccentric screw track. Methods. Two observers controlled the screw tracts and pedicle diameters. The results were compared with preoperative and postoperative neurologic findings. Results. Fifty‐nine percent (144 of 244) of screws were placed centrally in the pedicle. More than half of the eccentric screws (100, 41%; medial 79, 32.4%; lateral 21, 8.6%) penetrated the pedicle wall less than 2 mm (51; 20.9%). In only one patient (0.5%) a radicular irritation was found without objective electrophysiologic correlation when the screw was more than 6 mm medial to the pedicle wall. After screw removal, an insignificant increase in the size of the pedicle diameter in L1‐S1 was noted. Conclusions. Experienced surgeons implant pedicle screws with an accuracy of approximately 80%. The accuracy could be improved by using image‐guided insertion equipment. The neurologic symptoms are rarely influenced by an eccentric pedicle screw tract even if penetration of the pedicle wall is more than 6 mm. The results stress the importance of preoperative planning (pedicle diameter, pedicle angle, screw length) when implanting transpedicular fixators.

2000 Volvo Award winner in biomechanical studies: Monitoring in vivo implant loads with a telemeterized internal spinal fixation device.

Study Design. Implant loads were measured in 10 patients using telemeterized internal spinal fixation devices. Objective. To determine the postoperative temporal course of implant loads. Summary of Background Data. Little information exists regarding the temporal course of loads on internal spinal fixation devices. Methods. The telemeterized internal spinal fixator allows the measurement of three force components and three moments acting in the fixator. Implant loads were determined in up to 20 measuring sessions for different activities, including walking, standing, sitting, lying in the supine position, and lifting an extended leg while in the supine position. Results. Implant loads often increased shortly after anterior interbody fusion was performed. Several patients retained the same high level even after fusion had taken place. This explains the reason why screw breakage sometimes occurs more than half a year after implantation. The time of fusion could not be pinpointed from the loading curves. Conclusions. The results show that fixators may be highly loaded even after fusion has occurred. A flexion bending moment acts on the implant even with the body in a relaxed lying position. This means that already shortly after the anterior procedure, the shape of the spine is not neutral and unloaded, but slightly deformed, which loads the fixators. Pedicle screw breakage more than half a year after insertion does not prove that anterior interbody fusion has not occurred.

Infection of the Skin Caused by Corynebacterium ulcerans and Mimicking Classical Cutaneous Diphtheria

Extrapharyngeal infections caused by Corynebacterium ulcerans have rarely been reported previously, and diphtheria toxin production has usually not been addressed. This case demonstrates that strains of C. ulcerans that produce diphtheria toxin can cause infections of the skin that completely mimic typical cutaneous diphtheria, thereby potentially providing a source of bacteria capable of causing life-threatening diseases in the patients environment. Therefore, it is recommended to screen wound swabs for coryneform bacteria, identify all isolates, carefully assess possible toxin production, and send questionable strains to a specialist or a reference laboratory.

Comparison of loads on internal spinal fixation devices measured in vitro and in vivo

The loads on internal spinal fixation devices were measured using modified, telemeterized AO-Dick internal fixators. The implants allow measurement of the three force components and the three moments acting on the implant. The modified fixators were mounted on cadaver spines, and the implant loads were measured in the intact and postcorpectomy spines for different loading modes, including axial compression force, flexion, extension, lateral bending, and torsion. The in vitro experiment did not consider muscle forces. Modified fixators were also implanted in three patients, and the implant loads were determined before and after anterior interbody fusion with autologous iliac-crest bone grafts. The results for different in vitro loading modes were compared with those in vivo in order to demonstrate the extent to which the in vitro loads represent the real situation in patients. In several cases, the implant loads in the in vitro experiment differed strongly from those measured in patients. For flexion and lateral bending, a tensile axial force occasionally was measured in the in vitro experiment, while in the patients the axial force was always compressive. Extension was predominantly associated with extension bending moments in the in vitro study but with flexion bending moments in the patients. When muscle forces are not considered in the in vitro experiment, the loads on the fixators may differ significantly from the situation found in patients.

Internal spinal fixator stiffness has only a minor influence on stresses in the adjacent discs.

STUDY DESIGN Stresses in vertebral endplates and discs were calculated using the three-dimensional nonlinear finite-element model of a lumbar spine with an internal spinal fixation device. OBJECTIVE To determine the influence of fixator stiffness on stresses in the adjacent discs. SUMMARY OF BACKGROUND DATA There are few computer models of the lumbar spine with a fixator. Most of these models neglect the muscle forces. Fixator stiffness is assumed to influence greatly the stresses in the adjacent discs. METHODS Two three-dimensional nonlinear finite-element models were used to determine stresses in the lumbar spine for standing and 60 degrees flexion of the upper body. One model had an internal spinal fixator, the other did not. In a parameter study, the diameters of the longitudinal rod of the fixator were assumed to be 3, 5, 7, and 10 mm. In the computer model, the forces of the trunk muscles were simulated. RESULTS The diameter of the longitudinal rod strongly affected the fixator loads but hardly influenced the stresses in the vertebral endplates. The stresses in the bridged discs were strongly reduced. However, the internal fixator had only a minor influence on the stresses in the anulus fibrosus and the pressure in the nucleus pulposus of the adjacent discs. CONCLUSIONS The stiffness of an internal spinal fixation device has only a minor influence on stresses in the adjacent discs.

Operative Möglichkeiten zur Behandlung von Erkrankungen und Verletzungen der Wirbelsäule bei Patienten mit manifester Osteoporose

ZusammenfassungEine manifeste Osteoporose beeinflusst beim Vorliegen von Verletzungen oder Erkrankungen der Wirbelsäule die präoperative Planung. Deshalb sollte im Falle einer Operationsindikation sowohl beim Verdacht als auch beim Vorliegen einer Osteoporose die präoperative Bestimmung der Knochendichte erfolgen. Die Instrumentation der Wirbelsäule ist bei der operativen Versorgung oft nicht notwendig. Falls jedoch die Indikation dazu gestellt wird, sollte die Instrumentation multifokal fixiert werden und die vorliegende Deformität mit besonderer Vorsicht korrigiert oder auch nur teilkorrigiert werden. Beim Vorliegen einer Kyphose ist eine Beendigung der Instrumentation innerhalb der Kyphose unbedingt zu vermeiden.AbstractIn 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.

Changes in the loads on an internal spinal fixator after iliac-crest autograft

Spines are often stabilised posteriorly by internal fixation and anteriorly by a bone graft. The effect of an autologous bone graft from the iliac crest on implant loads is unknown. We used an internal spinal fixation device with telemetry to measure implant loads for several body positions and activities in nine patients before and after anterior interbody fusion. With the body upright, implant loads were often higher after than before fusion using a bone graft. Distraction of the bridged region led to high implant loads in patients with a fractured vertebra and to marked changes in load in those with degenerative instability. Leaving the lower of the bridged intervertebral discs intact led to only small changes in fixator load after anterior interbody fusion. A bone graft alone does not guarantee a reduction of implant loads.

In vivo measurement of implant loads in a patient with a fractured vertebral body

SummaryIt is not known what loads act on an internal spinal fixation device in patients with a fractured vertebral body. To measure the implant loads in vivo, telemeterized internal spinal fixators were implanted in a patient, and the implant loads measured for numerous body positions and activities before and after anterior fusion. The highest implant loads were found while the patient lifted both extended legs in a supine position. High implant loads were also measured for lateral bending during standing as well as for walking and carrying a load in one hand. The implant loads were small in recumbent positions. In contrast to findings in another patient, who was treated for degenerative instability, implant loads were smaller in the first months after anterior fusion than before. The indication for stabilization and surgical procedure strongly influence implant loads.

Loads on internal spinal fixation devices

SummaryThe loads acting on internal spinal fixation devices were measured for different activities in ten patients using telemeterized bisegmental implants. The highest loads were found for walking and lateral bending of the upper body while standing. When bending forwards the upper body, the fixator loads were only slightly altered. The forces and moments were not higher during sitting than during standing. Therefore, sitting should be allowed for patients with instrumented spines as soon as getting up is allowed. The forces and moments in the fixators were often altered due to anterior interbody fusion. Especially in patients with degenerative instability, the implant loads were higher after anterior interbody fusion than before. Braces were not able to markedly reduce the fixator loads. Therefore, it does not seem helpful to brace patients after mono- or bisegmental stabilization of the thoracic or lumbar spine.ZusammenfassungDie Belastung des Fixateur interne für die Wirbelsäule wurde mit instrumentierten Implantaten bei 10 Patienten für verschiedene Aktivitäten gemessen. Die höchsten Belastungen wurden beim Gehen und bei der Lateralflexion während des Stehens gefunden. Während der Ventralflexion des Oberkörpers änderte sich die Implantatbelastung nur geringfügig. Im Sitzen wurden keine höheren Fixateurbelastungen gemessen als im Stehen. Es spricht also wenig dagegen, Patienten, bei denen die Wirbelsäule mono- oder bisegmental stabilisiert worden ist, das Sitzen zu erlauben, sobald sie aufstehen dürfen. Durch die zusätzliche ventrale Stabilisierung mit Knochenspänen wurde die Belastung der bisegmentalen Implantate häufig deutlich geändert. Vor allem bei Patienten mit degenerativer Instabilität war sie nach der ventralen Stabilisierung oft wesentlich höher als vorher. Durch ein Korsett oder Mieder wurde die Implantatbelastung nicht reduziert. Es ist deshalb nicht notwendig, Patienten nach einer mono- oder bisegmentalen Stabilisierung der Brust- oder Lendenwirbelsäule mit einem Korsett zu versorgen.

Fractures of the distal radius. Changing therapeutic strategies

SummaryFractures of the distal radius represent one of the most common fractures and do have high social-economic relevance. For treatement they need practicable classification and therapeutic standards. The demand for stable osteosynthesis of A3-, B2-B3 and C1-C2-fractures is connected to dorsal or volar internal fixation with plate and practical autogenous cancellous bone grafting, even for the elder patient. The isolated external fixation with K-wires represent special situation. Supply of implants and biodegradable materials will support this development.ZusammenfassungDie Behandlung der Frakturen am distalen Radius erfordert aufgrund ihrer hohen Inzidenz und sozioökonomischen Relevanz eine einheitliche Klassifikation und Festlegung eindeutiger Therapiestrategien. Hierbei muß aus den Erfahrungen der konservativen und operativen Therapie der letzten Jahrzehnte gelernt werden und die Forderung nach einer stabilen osteosynthetischen Versorgung zur Vermeidung eines Korrekturverlusts in den Vordergrund treten. Die dorsale und palmare Plattenosteosynthese, ggf. in Verbindung mit einer Spongiosaplastik, muß heute als Standardverfahren zur adäquaten Therapie der nach AO definierten A3-, sowie B2-B3- und C1-C2-Frakturen, auch beim älteren Menschen, gelten. Die alleinige Kirschner-Draht-Osteosynthese dieser Frakturen sollte lediglich als Ausweichmöglichkeit gesehen werden. Das Angebot neuerer Implantate und Knochenersatzstoffe nimmt diese Entwicklung auf.Fractures of the distal radius represent one of the most common fractures and do have high social-economic relevance. For treatement they need practicable classification and therapeutic standards. The demand for stable osteosynthesis of A3-, B2-B3 and C1-C2-fractures is connected to dorsal or volar internal fixation with plate and practical autogenous cancellous bone grafting, even for the elder patient. The isolated external fixation with K-wires represent special situation. Supply of implants and biodegradable materials will support this development.