Abstract
1. Eighteen normal discs from cadavers and seventy-five specimens of abnormal disc material obtained at laminectomy have been compared.
2. Imbibition pressure, and not osmotic pressure, is the important factor in maintaining hydration of the nucleus, and the comparison has been based on this finding. The terms "free imbibition index" and "effective imbibition index" are suggested as being readily determinable means of expressing the functional efficiency of a nucleus.
3. A reduction in imbibition pressure was a constant feature of the specimens obtained at operation. No evidence was found to support the theory that hyper-hydration or engorgement of the nucleus plays a part in disc protrusion. A reduction in imbibition pressure can, however, be expected in itself, by a combination of mechanical and hydrostatic effects, to cause disc derangements.
4. The reduced imbibition pressure of abnormal discs is related to abnormal loss of, or deterioration in, the protein/polysaccharide of the nucleus. The premature onset of, or some disturbance in, the normal ageing process is a prime cause of mechanical derangement of the disc.
