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Descript 371 p
Note Source: Dissertation Abstracts International, Volume: 46-12, Section: B, page: 4328
Thesis (Ph.D.)--The University of Vermont and State Agricultural College, 1985
A systematic study was conducted to assess the effects of the new parameters of loading rate and load exposure history upon the mechanical response of forty, unconstrained, lumbar motion segments. Changes in mechanical properties (main and coupled compliances and balance point locations) were assessed before and after cyclic or static load exposures. This study tried to establish the mechanical changes occurring in the intervertebral motion segment due to exposure to seated-posture loading environments with epidemiologic data showing an increased incidence of herniated lumbar nucleus pulposus in seated humans in static or vibration environments
The concept of determining the mechanical properties of the motion segments by axial compressive loads applied at the mechanical balance point was evaluated and proved. The balance point was that location where flexion-extension and lateral bend rotations were minimized in response to an axial compressive load. Motion segments demonstrated sensitivity to loads applied away from the balance point (a point generally located behind the geometric center of the disc and changed location with load exposure history). The balance point concept has implications in the way in which motion segments are tested and the way in which the musculature supports the lumbar spine
Load exposure history simulated sitting for one hour in either a static environment (office or factory seat) or a conservative vibration environment (car or truck driving). One hour load exposures produced significant changes in the mechanical characteristics of the segments. The segments were then subjected to a rapid, flexion-compression overload event to simulate a person catching a falling load. This caused further mechanical property changes
Motion segments also exhibited coupled viscoelastic mechanical responses
During testing, some segments exhibited a sudden large rotation in both flexion and lateral bend (suggestive of buckling) up to physiologic limits. This response occurred more often in the cyclically loaded L2-3 motion segments. The postero-lateral region of the disc may be at risk during such sudden combined rotations
Lumbar motion segments have shown sensitivity to load rate, load vector, load application point, and load history
This work was supported by PHS grant #1-RO3-OHO1758
School code: 0243
Host Item Dissertation Abstracts International 46-12B
Subject Engineering, Biomedical
Alt Author The University of Vermont and State Agricultural College
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