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PubMed · 7100940

The transitional lumbosacral osseous complex.

R E Wigh
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Abstract

The weight of the head and trunk is transferred to the lower extremities through that segment of the spine articulating either directly or indirectly with the ilii. When a lumbosacral transitional vertebra is present the position of the weight-bearing platform usually changes. A bony entity is formed delineated superiorly by the top of the transitional vertebra and inferiorly by the lower level of the sacroiliac joints. This segment is designated as the transitional lumbosacral osseous complex. Measurements of its length in the three phylogenetic categories in man, including measurements of the articulating portion of the sacrum in the human mode, showed a range of 68 mm to 157 mm and variations from 2.0 to 3.7 in vertebral lengths.

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Biomechanical PhenomenaHumansIliumLumbar VertebraeRadiographySacroiliac JointSacrumStress, MechanicalJournal Article

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BibTeXRIS

R E Wigh. 1982. The transitional lumbosacral osseous complex.. https://doi.org/10.1007/bf00349578

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PubMed1996

Is the nucleus pulposus a solid or a fluid? Mechanical behaviors of the nucleus pulposus of the human intervertebral disc.

STUDY DESIGN: A new technique to measure the viscoelastic behavior of the nucleus pulposus in shear was used to assess its solid and fluid characteristics. OBJECTIVES: To review existing knowledge on mechanical behaviors of the nucleus pulposus, and to develop a new technique to study the viscoelastic behaviors of isolated nucleus pulposus samples in torsional (pure) shear under transient and dynamic conditions. SUMMARY OF BACKGROUND DATA: Numerous studies have investigated the swelling behavior of the nucleus and found the swelling pressure to range approximately 0.05-3 MPa, depending on loading conditions. Very few studies, however, have investigated the load-deformational behaviors of the nucleus pulposus. METHODS: Thirteen nondegenerate samples of nucleus pulposus were harvested from lumbar discs and tested in torsional shear under transient and dynamic test conditions. A linear viscoelastic law with variable amplitude relaxation and dynamic frequency sweep experiments. The coefficients of the viscoelastic law were determined from the stress relaxation experiments, whereas the dynamic shear modulus and phase shift angle were determined from the frequency sweep. RESULTS: The nucleus exhibits significant viscoelastic effects in shear. Under transient conditions, the stress relaxed to values near zero, which is indicative of the "fluid-like" behaviors of the nucleus. Under dynamic conditions, however, the material parameters for the nucleus, magnitude of the complex modulus (7-21 kPa), and phase angle (23-31 degrees) were more characteristic of a viscoelastic solid. The authors' proposed stress-strain law exhibited excellent agreement with the viscoelastic data. CONCLUSIONS: In response to shear deformations, the nucleus pulposus exhibited significant viscoelastic effects, characteristic of a fluid and a solid. Whether the nucleus pulposus behaves more as a fluid or a solid in vivo depends on the rate of loading.

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PubMed1996

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