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  • 1
    ISSN: 1432-0932
    Keywords: Rachis cervical supérieur ; Ligament alaire ; Ligament transverse ; Anatomie ; Biomécanique ; Upper cervical spine ; Alar ligament ; Transverse ligament ; Anatomy ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The occipito-atlanto-axial joint is the most complex one of the human spine. Traumatic or inflammatory lesions in this region may lead to instability and neurological symptoms of clinical importance. This study reports the results of anatomical and biomechanical examination of 13 human upper cervical spine specimens and focuses on the viscoelastic behavior of the alar and transverse ligaments. Non-destructive tensile testing was performed on a uniaxial testing machine with 25 alar and 11 transverse ligaments at three different load rates of 0.1 mm/s, 1.0 mm/s, and 10.0 mm/s. The ligaments were further tested for relaxation over 300 s. Each ligament exhibited an initial neutral zone in which no tensile force could be measured during cyclic testing. This neutral zone was more significant in the alar ligaments than in the transverse ligaments with respect to the measured in situ length of the ligaments (11.2 vs 18.1 mm on average). Increasing axial deformation led to increased load in all ligaments. Hysteresis, i.e., the energy loss exhibited by viscoelastic material subjected to loading and unloading cycles, increased with higher displacement rates and higher tensile forces. In neutral position the alar ligaments were lax in all specimens. During axial rotation both alars tightened. Ligamentous resistance increased as the end of the range of motion (ROM) was approchaed during rotation. The neutral zone explains the laxity of the ligaments in midposition and allows mobility of the upper cervical spine with minimum expenditure of muscular energy. The ligaments become stiffer under higher loads and therefore contribute to a limitation of the ROM in the occipitio-atlanto-axial joint.
    Notes: Résumé L'articulation occipito-atlanto-axoïdienne est l'une des plus complexes du rachis humain. Les lésions traumatiques ou inflammatoires de cette région peuvent conduire à l'instabilité et à des troubles neurologiques importants. Cette étude rapporte les résultats d'une étude anatomique et biomécanique de 13 spécimens de rachis cervical supérieur et met l'accent sur le comportement visco-élastique des ligaments alaires et transverse. Des essais de mise en tension ont été réalisés sur 25 ligaments alaires et 11 ligaments transverses, en restant en deçà du point de rupture. Ils ont été effectués sur un appareil monoaxial, selon trois niveaux de charge différents: 0.1 mm/s, 1.0 mm/s et 10.0 mm/s. La détente ligamentaire a été en outre étudiée pendant 300s. Chaque ligament a montré une zone neutre initiale (NZ) dans laquelle aucune force de tension ne pouvait être mesurée au cours du cycle d'essai. Cette zone neutre était plus importante pour les ligaments alaires que pour les ligaments transverses, compte tenu de la longueur ligamentaire mesurée in situ (11.2 contre 18.1 mm en moyenne). L'augmentation de la déformation axiale a conduit à une augmentation des contraintes dans tous les ligaments. L'hystérésis, c'est à dire la perte d'énergie présentée par le matériel visco-élastique soumis à des cycles de mise en charge et décharge, augmentait avec l'amplitude du déplacement et l'intensité des forces de tension. En position neutre, les ligaments alaires étaient détendus sur tous les spécimens. Lors de la rotation axiale, les deux ligaments alaires se sont mis en tension. La résistance du ligament à la rotation s'est trouvée accrue en fin d'amplitude. La zone neutre explique la laxité des ligaments en position intermédiaire et permet la mobilité du rachis cervical supérieur avec un minimum de dépense d'énergie. Les ligaments se tendent sous des charges plus élevées et par conséquent contribuent à la limitation de ROM dans l'articulation occipito-atlanto-axoïdienne.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0932
    Keywords: Anatomy ; Pedicles ; Thoracic spine ; Pedicle instrumentation ; Biomechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Transpedicular screw fixation provides rigid stabilization of the thoracolumbar spine. For accurate insertion of screws into the pedicles and to avoid pedicle cortex perforations, more precise knowledge of the anatomy of the pedicles is necessary. This study was designed to visualize graphically the surface anatomy and internal architecture of the pedicles of the thoracic spine. Fifteen vertebrae distributed equally among the upper, middle, and lower thoracic regions were used. For the purpose of mapping surface anatomy, each pedicle was cleaned, spraypainted white, and marked with more than 100 fine points. Using an optoelectronic digitizer, three-dimensional coordinates of the marked points and three additonal points, representing a coordiate system, were digitized. A solid modeling computer program was used to create three-dimensional surface images of the pedicle. To obtain cross-sectional information, each pedicle was sectioned with a thin diamond-blade saw to obtain four slices, 1 mm in thcikness and 0.5 mm apart. The pedicle slices were X-rayed and projected onto a digitizer. The internal and external contours were digitized and converted into graphs by a computer. The pedicles exhibited significant variability in their shape and orientation, not only from region to region within the thoracic spine, but also within the same region and even within the same pedicle. These variations are extremely significant in light of current techniques utilized in transpedicular screw fixation in the thoracic spine. Information documenting the three-dimensional complexity of pedicle anatomy should be valuable for surgeons and investigators interested in spinal instrumentation.
    Type of Medium: Electronic Resource
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