The load on lumbar disks in different positions of the body.
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Humans↗
Biomedical subjects
A Nachemson
Publications and source records attributed to A Nachemson.
Nutrition of the intervertebral disk. An in vivo study of solute transport.
The main mechanism for solute transport within the intervertebral disk is passive diffusion. The 2 routes for the exchange of solutes with the blood vessels outside the disk are via the periphery of the annulus, and through the end-plates. While the periphery of the annulus is completely permeable, the bone--disk interface is only partially so. In the region of the nucleus the effective area through which solute transport is taking place constitutes some 85% of the actual bone/disk interface; in the region of the inner annulus it is reduced to only 35% while the bone--disk interface at the outer annulus is almost completely impermeable. These figures, calculated from tracer diffusion experiments correlate very well with the qualitative observations of blood vessel contact. Apart from its dependence on the permeability of the endplate, solute diffusion is also determined by the nature of the solute. For example, a negatively charged solute such as the sulphate ion is considerably excluded from the nucleus, which limits its rate of penetration via the endplates. The sulphate uptake by the disk cells to produce glycosaminoglycans is low and comparable to that in articular cartilage.
Animals↗
Reduction, stability, and strength provided by internal fixation systems for thoracolumbar spinal injuries.
Anterior, posterior, and combined thoracolumbar spinal injuries were simulated in human cadaver specimens and then stressed in flexion, before and after stabilization, with Weiss Springs, Roy-Camille plates, vertebral body plates, and Harrington compression and distraction rods. The reduction, stability, and strength were determined for each implant-injury combination. For posterior ligamentous injuries, the Harrington compression system on the laminae gave reduction in extension, stability to that of the intact spine, and failure at 87.6 Nm bending load with 14.1 J energy absorption. For anterior vertebral body fracture, Harrington distraction rods from three vertebrae above to three below the injury gave a reduction in extension with stability similar to that of the intact spine. Failure occurred at 81.6 Nm load, one-third greater than with rods two levels above to two below, and 14.0 J energy absorption, twice that for the short rod. The more unstable combined anterior and posterior injury was satisfactorily reduced only by the long distraction system, which failed at 44.1 Nm load, twice that for the short rod, and 5.7 J energy absorption. By accurately determining what structures have been injured, and appropriate fixation device can be selected and the strength of the stabilized spine estimated. A thorough understanding of the biomechanics of the spine is essential for successful clinical utilization of these experimental data.
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