PubMed · 4533913
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R Sangiuolo, J F Michel, P Pini. [Pain from a complete prosthesis].. https://pubmed.ncbi.nlm.nih.gov/4533913/
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STUDY DESIGN: An in vitro biomechanical cadaveric study. OBJECTIVES To elucidate the effect of flexion-extension cyclic loads on the motion behavior of lumbar spine after different discectomies. SUMMARY OF BACKGROUND DATA: Biomechanical cadaveric studies to evaluate the effect of discectomy have been performed and have indicated the relevance between the volume of removed disc materials and increase of motion in affected intervertebral disc. However, there are no biomechanical studies to investigate the motion behavior of injured intervertebral disc after cyclic loads. METHODS: Twenty-eight lumbar functional spinal units were randomized into fenestration, annulotomy, limited discectomy, and radical discectomy groups. Pure bending moments were applied to simulate various loading modes and determine the resulting displacements before and after surgery, and after cyclic loads of 1,000, 5,000, and 10,000 cycles at a frequency of 0.5 Hz and a force of +/-3.0 Nm. Change of range of motion (ROM) was compared among each group. RESULTS: Following surgery, in the radical discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. On the other hand, during cyclic loads up to 10,000 cycles, in the limited discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. CONCLUSIONS: These results demonstrate that the effect of cyclic loads after discectomy may increase ROM, leading to spinal instability even if the increase in ROM does not occur immediately after surgery for the minimum removal of nucleus pulposus case. Clinically, this may underscore the importance of postoperative lumbar support.
Despite the many studies on the visual control of grasping, little is known about how and when small variations in shape affect grasping kinematics. In the present study we asked subjects to grasp elliptical cylinders that were placed 30 and 60 cm in front of them. The cylinders' aspect ratio was varied systematically between 0.4 and 1.6, and their orientation was varied in steps of 30 degrees. Subjects picked up all noncircular cylinders with a hand orientation that approximately coincided with one of the principal axes. The probability of selecting a given principal axis was the highest when its orientation was equal to the preferred orientation for picking up a circular cylinder at the same location. The maximum grip aperture was scaled to the length of the selected principal axis, but the maximum grip aperture was also larger when the length of the axis orthogonal to the grip axis was longer than that of the grip axis. The correlation between the grip aperture--or the hand orientation--at a given instant, and its final value, increased monotonically with the traversed distance. The final hand orientation could already be inferred from its value after 30% of the movement distance with a reliability that explains 50% of the variance. For the final grip aperture, this was only so after 80% of the movement distance. The results indicate that the perceived shape of the cylinder is used for selecting appropriate grasping locations before or early in the movement and that the grip aperture and orientation are gradually attuned to these locations during the movement.
Diverse physical forces including deformation or strain, pressure, and shear stress affect the intestinal mucosa during normal function, and mucosal biology is altered in pathological states in which these forces alter. Taken together with evidence in other tissues and cell types that physical forces can affect cell biology, this has led to the hypothesis that repetitively applied physical forces can initiate intracellular signals that alter intestinal epithelial proliferation and phenotype. This review outlines the nature of such forces and summarizes in vivo and in vitro evidence in support of the paradigm that repetitive force is trophic for the intestinal mucosa via a complex cascade of intracellular signals.