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Biomedical subjects

J A Klein

Publications and source records attributed to J A Klein.

48 records · Page 3Linked to original sources
PubMed1983

Radial bulging of the annulus fibrosus during compression of the intervertebral disc.

An analysis of the bulging of the annulus fibrosus as a function of the height of the intervertebral disc during compression is presented. The theory was compared with the results of experimental tests on rabbit lumbar discs. When viewed in profile the ventral bulge closely resembled an arc of a circle; at each stage of compression it appeared to extend from the cranial to the caudal extremities of the annulus fibrosus. The radius of curvature of the arc was measured as a function of disc height and the results compared with theoretical predictions. Good agreement was obtained if it was assumed that about half the volume change swept out by the approach of the cranial and caudal end-plates was accommodated by the annular bulge. The lengths of the collagenous fibres reinforcing the outer lamella of the ventral annulus were estimated from the dimensions of the ventral bulge; no appreciable length increase appeared to accompany compression.

Animals↗
PubMed1983

Relocation of the bending axis during flexion-extension of lumbar intervertebral discs and its implications for prolapse.

All the lumbar discs were dissected from three freshly killed, adult rabbits. Ligaments and facet joints were removed but each disc remained attached to bone. The discs were securely mounted in specially constructed bending apparatus. Ventral disc height and bending angle were measured simultaneously allowing the bending axis position to be calculated. Except for lumbosacral discs, the axis shifted ventrally during the transition from flexion to extension. The existence of separate flexion and extension axes has been reported for human lumbar discs; it is argued that similarity of disc structure leads to similar mechanical behaviour in rabbit and human discs. The positions of the two bending axes are such that flexion, but not extension, could damage the annulus fibrosus of the intervertebral disc.

Animals↗
PubMed1982

Collagen fibre orientation in the annulus fibrosus of intervertebral disc during bending and torsion measured by x-ray diffraction.

X-ray diffraction has been used to measure the orientation of the collagen fibres in the ventral annulus fibrosus of intact L 1/2 rabbit intervertebral discs during in vitro bending and torsion. Fibres are tilted with respect to the axis of the spine. As predicted by theory, fibre tilt decreases in those regions of the annulus which are stretched by bending but increases in the slackened regions. Good agreements with the quantitative predictions of bending theory was obtained in three of the six series of experiments, the predicted trend being found in all six. Tilt direction alternates in successive lamellae of the annulus. When discs were subjected to both clockwise and counterclockwise torsion of 5 degrees, the two families of tilted fibres reoriented in the expected directions.

Animals↗
PubMed1982

X-ray diffraction demonstrates reorientation of collagen fibres in the annulus fibrosus during compression of the intervertebral disc.

The annulus fibrosus of the intervertebral disc is reinforced by tilted collagen fibres. It has been predicted that the tilt angle should increase as the disc was compressed. This prediction has now been confirmed using X-ray diffraction. Diffraction patterns were recorded from the ventral annulus of intact L1/2 rabbit discs during various stages of compression. At each stage the ventral height was measured. Fibre tilts were measured from the diffraction patterns and found to increase as the disc was compressed. For five out of six discs the quantitative dependence of tilt on compressed height was in good agreement with theoretical predictions; the sixth did not compress evenly but an increase in tilt was still observed.

Animals↗