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  • 1
    ISSN: 1433-0431
    Keywords: Key words Orthopaedic surgery • Computer assistance • Image-interactice navigation • Transpedicular screw fixation ; Schlüsselwörter Orthopädische Chirurgie ; Computerassistenz ; Bildinteraktive Navigation ; Transpedikuläre Verschraubung
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Computerassistenz ist für den Bereich der Orthopädischen Chirurgie ein relativ neues und dennoch sich rasch entwickelndes Feld. Durch Modifizierung teilweise bereits aus der Neurochirurgie bekannter stereotaktischer Systeme haben mehrere Arbeitsgruppen diese Techniken zunächst für die bildinteraktive Insertion von Pedikelschrauben nutzbar gemacht. Der vorliegende Artikel faßt bisher geleistete Arbeiten insbesondere in der In-vivo-Applikation zusammen, beschreibt den aktuellen Stand der Forschung und gibt einen Ausblick auf zukünftige Entwicklungen.
    Notes: Summary Computer assisted orthopaedic surgery is a new but rapidly evolving field. Based on previous research and development in the area of stereotactic neuronavigation a few groups have adapted these technologies for the image interactive insertion of pedicle screws. The present paper summarizes past and current work in the field of computer assisted orthopaedic surgery and describes the state of the art of research and future innovations, particularly in in vivo applications.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0932
    Keywords: Key words Spine ; Interbody ; Fusion ; Compression ; Biomechanics ; Implant ; Posterior ; lumbar intervertebral fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    European spine journal 4 (1995), S. 114-122 
    ISSN: 1432-0932
    Keywords: Thoracic spine ; Biomechanics ; Pedicle screw ; Pedicle hook ; Pull-out test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pedicle hooks which are used as an anchorage for posterior spinal instrumentation may be subjected to considerable three-dimensional forces. In order to achieve stronger attachment to the implantation site, hooks using screws for additional fixation have been developed. The failure loads and mechanisms of three such devices have been experimentally determined on human thoracic vertebrae: the Universal Spine System (USS) pedicle hook with one screw, a prototype pedicle hook with two screws and the Cotrel-Dubousset (CD) pedicle hook with screw. The USS hooks use 3.2-mm self-tapping fixation screws which pass into the pedicle, whereas the CD hook is stabilised with a 3-mm set screw pressing against the superior part of the facet joint. A clinically established 5-mm pedicle screw was tested for comparison. A matched pair experimental design was implemented to evauluate these implants in constrained (series I) and rotationally unconstrained (series II) posterior pull-out tests. In the constrained tests the pedicle screw was the strongest implant, with an average pull-out force of 1650 N (SD 623 N). The prototype hook was comparable, with an average failure load of 1530 N (SD 414 N). The average pull-out force of the USS hook with one screw was 910 N (SD 243 N), not significantly different to the CD hook's average failure load of 740 N (SD 189 N). The result of the unconstrained tests were similar, with the prototype hook being the strongest device (average 1617 N, SD 652 N). However, in this series the difference in failure load between the USS hook with one screw and the CD hook was significant. Average failure loads of 792 N (SD 184 N) for the USS hook and 464 N (SD 279 N) for the CD hook were measured. A pedicular fracture in the plane of the fixation screw was the most common failure mode for USS hooks. The hooks usually did not move from their site of implantation, suggesting that they may be well-suited for the socalled segmental spinal correction technique as used in scoliosis surgery. In contrast, the CD hook disengaged by translating caudally from its site of implantation in all cases, suggesting a mechanical instability. The differences in observed hook failure modes may be a function of the type and number of additional fixation screws used. These results suggest that additional screw fixation allows stable attachment of pedicle hooks to their implantation site. Hooks using additional fixation screws passing obliquely into the pedicle apparently provide the most rigid attachment. The second fixation screw of the prototype hook almost doubles the fixation strength. Thus, the prototype hook might be considered as an alternative to the pepdicle screw, especially in the upper thoracic region.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0932
    Keywords: Thoracic spine ; Pedicle hook ; Fixation screw ; Biomechanics ; Pull-out test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The pull-out force of thoracic spinal pedicle hooks secured by long fixation screws engaging the posterior portion of the vertebral endplate was measured. The perfomance of these hooks was compared with that of hooks using a shorter screw and different screw orientation such that the vertebral endplates were not perforated. The longer and differently angulated screws, engaging the endplate, significantly enhanced the fixation potential of the hooks.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0932
    Keywords: Key words Biomechanics ; Stability ; Implant ; Interbody ; fusion ; Translaminar screws
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The immediate stabilization provided by anterior interbody cage fixation is often questioned. Therefore, the role of supplementary posterior fixation, particularly minimally invasive techniques such as translaminar screws, is relevant. The purpose of this biomechanical study was to determine the immediate three-dimensional flexibility of the lumbar spine, using six human cadaveric functional spinal units, in four different conditions: (1) intact, (2) fixed with translaminar screws (TLS), (3) instrumented with anterior interbody cage insertion with the BAK system and (4) instrumented with BAK cage with additional TLS fixation. Flexibility was determined in each testing condition by measuring the vertebral motions under applied pure moments (i.e. flexion-extension, bilateral axial rotation, bilateral lateral bending) in an unconstrained manner. Anterior fixation with the BAK alone provided significant stability in flexion and lateral bending. Additional posterior TLS significantly reduced the motion in extension and axial rotation. TLS fixation alone resulted in smaller rotations than BAK fixation in all loading directions. Based on these results, it seems that interbody cage fixation with the BAK system stabilizes the spine in some, but not all, loading directions. The problematic loading directions of extension and axial rotation can be substantially stabilized by using translaminar screw fixation. However, one should emphasize that the degree of stability needed to achieve solid fusion is not known.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Knee surgery, sports traumatology, arthroscopy 4 (1996), S. 100-110 
    ISSN: 1433-7347
    Keywords: Biomechanics ; Cryosectional anatomy ; Quadriceps tendon ; Fatellar tendon ; Patellar ligament ; Knee joint ; Cruciate ligament reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Sports Science
    Notes: Abstract Structural tensile properties analyses of 10-mm-wide central sections of quadriceps tendon-bone (QT-B) and bone-patellar ligament (B-PL) complexes from young male donors (mean age 24.9 years, range 19–32 years) were complemented by a cryosectional analysis: each QT-B complex was composed of the segment of the quadriceps tendon with the proximal half of the patella attached, each B-PL complex was composed of the distal half of the patella with the patellar ligament attached. A servohydraulic materials testing machine was used to assess ultimate failure load of 16 unconditioned and 16 preconditioned QT-B and B-PL complexes at an extension rate of 1 mm/s. Ligaments/tendons were preconditioned during 200 cycles from 50 to 800 N at 0.5 Hz. On cryosections the quadriceps tendons were significantly longer and thicker and exhibited a significantly larger bony attachment area than the patellar ligaments. Cross-sectional areas of 10-mm-wide, full-thickness, central parts of unconditioned quadriceps tendons were significantly greater and measured 64.6±8.4 mm2 with respect to the cross-sectional area of patellar ligament, measuring 36.8±5.7 mm2 (P〈0.0025). Ultimate failure loads for unconditioned complexes resulted at 2173±618 N for QT-B complexes and at 1953±325 N for B-PL complexes (P=0.43). Ultimate failure load values measured 2353±495 N for preconditioned QT-B complexes and 2376±152 N for preconditioned B-PL complexes, respectively (P=0.77). Despite the fact that initial testing length, area of unconditioned QT-B and B-PL complexes were significantly different, displacement at ultimate load, energy to failure and total energy were not. In terms of ultimate tensile strength, the 10-mm-wide central part of the QT-B complex compared favourably to the tensile properties of the human femur-anterior cruciate ligament-tibia complex from a comparable young age group. The evidence from anatomic, cryosectional and structural properties analyses suggests that the QT-B complex may be a valuable and versatile adjunct to the surgeon's armamentarium in reconstructive cruciate ligament surgery.
    Type of Medium: Electronic Resource
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