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  • 1
    Electronic Resource
    Electronic Resource
    Motion of threaded cages in posterior lumbar interbody fusion (2000)
    Springer
    European spine journal 9 (2000), S. 571-576 
    Details
    ISSN: 1432-0932
    Keywords: Key words Spinal fusion ; Implants ; Biomechanics ; Computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A high rate of pseudarthrosis and a high overall rate of implant migration requiring surgical revision has been reported following posterior lumbar interbody fusion using BAK threaded cages. The high rate of both pseudarthrosis and implant migration may be due to poor fixation of the implant. The purpose of this study was to analyse the motion of threaded cages in posterior lumbar interbody fusion. Six cadaveric human lumbar spine segments (three L2/3 and three L4/5 segments) were prepared for biomechanical testing. The segments were tested, without preload, under forces of axial compression (600 N), torsion (25 Nm) and shearing force (250 N). The tests were performed first with the segments in an intact state, and subsequently following instrumented stabilisation with two BAK cages via a posterior approach. These results were compared with those of a finite element model simulating the effects of identical forces on the segments with constructs. As the results were comparable, the finite element model was used for analysing the motion of BAK cages within the disc space. Motion of the implants was not seen in compression. In torsion, a rolling motion was noted, with a range of motion of 10.6° around the central axis of the implant when left/right torsion (25 Nm) was applied. The way the implants move within the segment may be due to their special shape: the thread of the implants can not prevent the BAK cages rolling within the disc space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005860000171
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  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of a new monocortical screw for anterior cervical fusion and plating by a combined biomechanical and clinical study (1999)
    Springer
    European spine journal 8 (1999), S. 382-387 
    Details
    ISSN: 1432-0932
    Keywords: Key words Spine ; Spine ; bone ; plates ; Spine ; screws ; Spine ; biomechanics ; Spine ; implant ; testing ; Spine ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this combined study was to evaluate the stability and safety of a new monocortical screw-plate system for anterior cervical fusion and plating (ACFP) according to Caspar in comparison with classical bicortical fixation. In the biomechanical part of the study two groups, each comprising six fresh human cadaveric spines (C4–C7), matched for bone mineral density, additionally resulting in almost the same mean age, were used. Range of motion and neutral zone were analyzed in flexion-extension, rotation (left, right) and lateral bending (left, right) using pure moments of ± 2.5 Nm for each specimen in the intact state, after discectomy at C5/6 and after discectomy at C 5/6 followed by bone grafting plus plating (Caspar plates), with either monocortical or bicortical screws. For all three motion planes, no significant difference could be found between the new monocortical and the bicortical fixation techniques. The clinical part of the study was performed as a prospective study on 30 patients suffering from symptomatic degenerative cervical disc disease in one segment. At the latest follow-up, no hardware- or graft-related complications were seen in any of the patients. Following these findings monocortical screw fixation can be recommended for the majority of anterior cervical fusion and plating procedures in degenerative disease, making the procedure quicker, easier, and safer. Bicortical screw fixation still has specific indications for multilevel stabilization, poor bone quality (osteoporosis, rheumatoid disease – as bicortical oversized rescue screw), unstable spines (trauma, tumour) and in particular for the realignment of kyphotic deformities (restoration of the normal lordotic curve). Due to the design of the study the results apply only to surgical treatment of monosegmental degenerative disc disease at the time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005860050191
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  • 3
    Electronic Resource
    Electronic Resource
    Die Primärstabilität von zwei Plif-Techniken (2000)
    Springer
    Der Orthopäde 29 (2000), S. 68-72 
    Details
    ISSN: 1433-0431
    Keywords: Schlüsselwörter Wirbelsäule • Lumbale Fusion • Biomechanik • Finite-Elemente-Studie ; Key words Spine • Posterior interbody fusion •¶Biomechanics • Finite-element-method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The purpose of this study was to compare the initial stiffness of two techniques for posterior interbody lumbar fusion (PLIF) by a finite element approach. Thus a finite element model of a human L3/4 spinal segment was generated. Stiffness of the intact model was tested under compression (600 N), torsion (25 Nm) and shearing forces (250 N) without preload. The results were compared to the stiffness following simulation of PLIF with two BAK-Cages and PLIF with two Harms-Cages and additional posterior screw-rod-osteosynthesis. PLIF with two BAK-Cages resulted in a loss of stiffness in compression, torsion and shearing. PLIF with two Harms-Cages and posterior osteosynthesis resulted in an increase of stiffness in compression, torsion and shearing.
    Notes: Zusammenfassung Ziel dieser Analyse ist der Vergleich der Primärstabilität nach PLIF mit 2 interkorporal implantierten „threaded cages“ mit der PLIF-Technik nach Harms (interkorporale Implantation von 2 Titankörben und hintere zuggurtende Osteosynthese, MOSS-MIAMI-System). Zum Vergleich der beiden Methoden wurde ein Finite-Elemente-Modell eines Segments L3/4 entwickelt. Die Initialsteifigkeit des intakten Modells wurde durch Computersimulation untersucht: axiale Kompression (600 N), Rotation (25 Nm) und Schub (250 N) wurden ohne Vorlast eingeleitet, der Bewegungsumfang und hieraus die Steifigkeit des intakten Präparats bestimmt. Danach wurden die Implantate über die Simulation eines dorsalen Zugangs in das Modell eingefügt, die Messungen mit den gleichen Kräften und Momenten wiederholt und die Steifigkeit des operierten Segments berechnet. Das MOSS-MIAMI-Modell wies sowohl unter Kompression, Rotation und Schubbelastung eine Zunahme der Initialsteifigkeit im Vergleich zu dem intakten Modell auf, während das „Threaded-cages-Modell“ eine deutliche Abnahme in Kompression, Rotation und Schub im Vergleich zum intakten Modell zeigte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00003698
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    Paper (German National Licenses)
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