[Tissue changes in the intervertebral disk following hypokinesia in rats of different ages]

Effect of various duration of hypokinesia on structural-metabolic characteristics of the lumbar vertebral segment has been studied in Wistar rats. Hypokinesia results in certain morphological changes of the spongy bone and tissues of the intervertebral disk, demonstrating as delayed processes of ossification, disturbed course of organization into bundles of collagenous fibers of the fibrous ring, widening of the nucleus pulposus zone. Polarization-optical investigations reveal some disturbances in the macro-molecular organization of collagen, expressed as decreasing degree of its refraction and as redistribution of glycosaminoglycans towards increasing sulfated keratan sulfates.

Type VI collagen of the intervertebral disc. Biochemical and electron-microscopic characterization of the native protein

The collagen framework of the intervertebral disc contains two major fibril-forming collagens, types I and II. Smaller amounts of other types of collagen are also present. On examination of the nature and distribution of these minor collagens within bovine disc tissue, type VI collagen was found to be unusually abundant. It accounted for about 20% of the total collagen in calf nucleus pulposus, and about 5% in the annulus fibrosus. It was discovered by serially digesting disc tissue with chondroitin ABC lyase and Streptomyces hyaluronidase that native covalent polymers of type VI collagen could be extracted. Electron micrographs of this material prepared by rotary shadowing revealed the characteristic dimensions of tetramers and double tetramers of type VI molecules, with their central rods and terminal globular domains. Molecular-sieve column chromatography on agarose under non-reducing non-denaturing conditions gave a series of protein peaks with molecular sizes equivalent to the tetramer, double tetramer and higher multimers. On SDS/polyacrylamide-gel electrophoresis after disulphide cleavage, these fractions of type VI collagen all showed a main band at Mr 140,000 and four lesser bands between Mr 180,000 and 240,000. On electrophoresis without disulphide cleavage in agarose/2.4% polyacrylamide only dimeric (six chains) and tetrameric (12 chains) forms of type VI molecules were present. The ability to extract all the type VI collagen of the tissue in 4 M-guanidinium chloride, and absence of aldehyde-mediated cross-linking residues on direct analysis, showed that, in contrast with most matrix collagens, type VI collagen does not function as a covalently cross-linked structural polymer.

The penetration of antibiotics into the normal intervertebral disc

The role of antibiotics in the treatment of disc-space infection is controversial. This study assessed the tissue penetration of flucloxacillin and cephradine into the normal intervertebral disc after intravenous administration of a bolus dose of antibiotic. Twenty-five discs were removed from 12 adolescent patients having anterior spinal surgery to correct scoliosis; antibiotic had been administered between 30 minutes and four hours before operation. Despite high blood levels, no antibiotic could be detected by bioassay or by high-pressure liquid chromatography (h.p.l.c.) in any of the specimens from the nucleus pulposus or the annulus fibrosus.

The response of the canine intervertebral disc to immobilization produced by spinal arthrodesis is dependent on constitutional factors

Posterior lumbar spinal fusion was performed on five mature greyhounds. Two months prior to death, all of the surgical and five age-matched control greyhounds were given Na2(35)SO4 (1.0 mCi/kg) intravenously. All fusion animals were killed 6 months postoperation, and discs beneath the fusion mass as well as those adjacent to it (parafusion discs) were sampled separately and dissected into the nuclei pulposi and annuli fibrosi (AF). Proteoglycans (PGs) were extracted with 4.0 M GuHCl and then purified by CsCl density gradient ultracentrifugation. These PG monomers were subjected to Sepharose CL-2B chromatography, and their hydrodynamic size and ability to aggregate were determined. The level, extractability, and hydrodynamic size of PGs in the AF of fusion discs were found to be greater than those in control discs, as were the keratan sulfate core protein complexes prepared by chondroitin ABC lyase digestion. The ability of the 60-day-old PG subunit populations, isolated from fusion discs, to aggregate was also higher than controls. There was, however, no difference between the galactosamine/glucosamine, galactosamine/protein, glucosamine/protein, or hexuronate/protein ratios of PGs in fusion and control discs.

Postmortem changes in ultrastructures of the mouse intervertebral disc

To elucidate the effects of nutrition and oxygen deficiencies on the intervertebral disc, cell components of mouse intervertebral discs and their postmortem changes were observed by electron microscopy. The annulus fibrosus could be divided into an inner and outer region. The main cell components of the annulus fibrosus were fibroblast-like cells in the outer region and chondrocytes in the inner region. The nucleus pulposus consisted of massively packed notochordal cells. The cartilage plates could also be divided into two zones: articular cartilage and growth cartilage containing chondrocytes. Postmortem degenerative changes proceeded from the peripheral to the central parts of the intervertebral disc, ie, showing degeneration of first the fibroblast-like cells, next the chondrocytes, and finally, the notochordal cells. The findings suggest that cells situated at the periphery predominantly depend on aerobic metabolism, whereas the cells situated more centrally depend on anaerobic metabolism. Furthermore, postmortem changes of the nucleus pulposus were similar to age-related changes. The age-related changes or degeneration in the intervertebral disc appear to be related to deficiencies of nutrition or oxygen caused by changes in structures of the disc and the surrounding tissues.

Intervertebral disc nutrition. Diffusion versus convection

Nutrient diffusion across the vertebral endplate can occur by convection (bulk flow) or diffusion. Previous studies, using animal models, suggested diffusion as the primary mechanism of small-solute transport but did not adequately determine the contribution of bulk flow to total nutrient transport. This study was designed to reevaluate disc nutrition across the endplate. Ten microcuries of radioactive sulphate in aqueous solution were injected into L4 vertebral bodies of 13 rabbit spines following sacrifice. One hour of continuous passive flexion/extension in a physiologic range of motion was performed on five spines, while eight spines served as motionless controls. Autoradiographic techniques were used to analyze and compare the isotope uptake in the L4-L5 disc. There was no significant difference in disc uptake or the ratio of disc/bone uptake between the two groups. Motion does not significantly facilitate the transport of small solutes into the disc during short periods of time.

The relationship of actin to ligament contraction

A surgical model of a contracting ligament was established in a Z-lengthened, rat medial collateral ligament. These lengthened ligaments contracted back to a normal degree of tightness in a three-week period. Immunofluorescent actin staining of cryostat ligament sections was increased in these contracted ligaments, compared with sham-operated ligaments that had not contracted. In vitro culture of ligament fibroblasts confirmed that they (like fibroblasts from other systems) produce large, actin, stress fibers thought to be involved in cell contraction. Transmission electron-microscopic examination of normal ligament demonstrated the cytoplasm of fibroblast cell processes extending out to and surrounding collagen fibrils, indicating a closer involvement with established fibrils than was expected. On the basis of these observations, it is hypothesized that intracellular proteins, such as actin, allow the fibroblast to exert forces and actively contribute to the contraction of ligamentous tissues.

The effect of posture on diffusion into lumbar intervertebral discs

The diffusion of small solutes into the intervertebral discs of cadaveric lumbar motion segments was measured using a radioactive tracer technique. The motion segments were wedged and loaded to simulate erect posture and flexed sitting postures. The results show that erect posture favours diffusion into the anterior half of the disc compared to the posterior half. Flexed posture, by deforming the annulus fibrosus, reverses this imbalance.

Structural and metabolic changes characterizing the aging of various cartilages in mice

It is well documented that various organs and tissues in the body show a differential, non-homogeneous pattern of development and aging. The present study evaluates some of the morphological and metabolic changes characterizing the aging of different types of cartilages in normal male mice. Representatives of hyaline, fibrous, articular and elastic types of cartilage were obtained from animals ranging from 1 week to 1 year of age. Our determinations included the following: total body and organ weights, proteins and DNA concentrations, [3H]leucine and [35S]sulfate uptake. The biochemical assays were accompanied by morphological examinations of corresponding tissue specimens. This investigation clearly indicates that the growth and maturational activities of the various cartilages examined attained their completion at a very early stage of life (1-3 months postnatally). Thereafter, a phase of steady state prevails, followed by a gradual but continuous decline in the various metabolic activities. The morphological findings illustrate the nature of the age-related structural changes. The present findings indicate that a skeletal tissue such as cartilages of various types, tends to age early during the lifespan of the animal.

Gas in spinal articulations

The purpose of this review is to illustrate, some for the first time, a variety of gas collections in lumbar facet joints and intervertebral discs and in the sacroiliac joint.

Changes in mouse intervertebral-disc proteoglycan synthesis with age. Hereditary kyphoscoliosis is associated with elevated synthesis

Mice with hereditary kyphoscoliosis (ky/ky) develop intervertebral-disc degeneration at the cervico-thoracic junction. Disc proteoglycans were investigated to determine whether changes in synthesis or structure were associated with this. Elevated 35S-proteoglycan synthesis was found in one or more cervico-thoracic discs in 80-day-old ky/ky mice. The hydrodynamic size and aggregation properties of ky/ky-mouse disc 35S-proteoglycans extracted with 4 M-guanidinium chloride were normal. Increased proportions of small 35S-proteoglycans were extracted with 0.5 M-guanidinium chloride from discs of normal and ky/ky mice with increasing age.

Variations of the proteoglycans of the canine intervertebral disc with ageing

A group of young (2.0 +/- 0.6 years) (group 1) and old (9.7 +/- 1.5 years) (group 2) beagle dogs were given Na2 35SO4 (1.0 mCi/kg) intravenously 60 days prior to being killed to radiolabel their proteoglycans. Lumbar discs were removed and dissected into nucleus pulposus and annulus fibrosus. Proteoglycans were extracted at 4 degrees C from these tissues with buffered 4.0 M Gdn-HCl containing proteinase inhibitors, and purified by CsCl density gradient ultracentrifugation. The average hydrodynamic size and ability of the purified proteoglycans to aggregate in the presence of excess hyaluronic acid was determined by Sepharose CL-2B chromatography. The galactosamine/glucosamine ratios of these proteoglycans as well as their non-aggregating fractions were also ascertained. The proteoglycan content of discs of old animals was significantly less than in the young. The proportion of 35S-labelled, or non-labelled proteoglycans which could aggregate in the presence of hyaluronic acid was also much lower in the preparations isolated from the older discs. In contrast, the average hydrodynamic size of the non-aggregating proteoglycans isolated from the annuli fibrosi of group 2 animals were larger than the corresponding population of group 1 animals. Aminosugar analysis of these same proteoglycan fractions from older animals afforded galactosamine/glucosamine ratios (mean 1.81 +/- 0.14) which were less than the younger age group (mean 2.63 +/- 0.40). These data suggest that with ageing and degeneration the proteoglycans of the beagle disc undergo increased degradation with the accumulation in the annulus fibrosus of a population which is of larger average hydrodynamic size and richer in keratan sulphate than proteoglycans present in younger tissues.

Effects of hyperinsulinism and of diabetes on proteoglycans of the intervertebral disc in weanling sand rats

Weanling sand rats (Psammomys obesus) develop hyperinsulinemia or diabetes or both, if fed a standard laboratory diet without a supplement of fiber rich salt bush. The annuli fibrosi of hyperinsulinemic or diabetic animals, which are still hyperinsulinemic, show a slight but statistically significant increase in chondroitin sulfate and a lesser, statistically nonsignificant increase in keratan sulfate. Possible causes of these changes are discussed and the likelihood of a role of hyperinsulinism in their production is pointed out.

In situ calibration of an oxygen sensor in intervertebral discs

Intradiscal hypoxia has been suspected of playing a role in the pathogenesis of degenerative back diseases. Investigating this hypothesis requires quantitative methods for measuring PO2 in the intervertebral disc. Tissue oxygen tensions are usually measured with a membrane-covered oxygen-consuming sensor. Calibrating this sensor is complicated by the existence of an oxygen-diffusion gradient in front of the membrane. This article describes a method based on mass spectrometry to measure the oxygen tension in the intervertebral disc and an 'in situ' calibration technique, which is able to compensate for errors caused by the oxygen-diffusion gradient. The principle of the calibration technique is to measure the signal of an inert reference gas, whose partial pressure in the intervertebral disc is known, and to utilize the measured signal to estimate the magnitude of the oxygen-diffusion gradient.

Biomechanical properties of human intervertebral discs subjected to axial dynamic compression--influence of age and degeneration

This investigation was performed to study biomechanical properties of human intervertebral discs as a function of age. 178 specimens from 21 spinal sections (Th9-S1, 5-84 yr) were subjected to axial dynamic compression; the load being 950 +/- 540 N. The results revealed three distinct age ranges: From the first to the middle of the third decade: axial deformability decreases within the thoracic region, and remains almost constant within the lumbar spine; creep decreases in both parts. From the middle of the third to the beginning of the sixth decade: the biomechanical behavior scarcely alters. Afterwards: axial deformability remains unchanged; creep, however, again increases within the lumbar spine. The results reveal the discs behave most efficiently within the age range where the incidence of back pain is maximal.

In vitro method for measuring synthesis rates in the intervertebral disc

A method for culturing intervertebral disc tissue in vitro under conditions that control changes in hydration and minimize loss of proteoglycans has been developed. Disc slices were enclosed in small-pore dialysis tubing and incubated in medium containing polyethylene glycol (PEG). By varying the PEG concentration, different external swelling pressures could be applied to the tissue. The rate of glycosaminoglycan synthesis in rabbit and dog disc was then measured using [35S]sulphate as a precursor. Synthesis rates varied with final hydration of the tissue, and the highest rates were found at hydrations close to those found in vivo. Under conditions of controlled hydration, rabbit nucleus has a higher rate of glycosaminoglycan synthesis than annulus. However, the rates measured in sagittal slices of dog disc decreased from the outer to the inner regions of the anterior annulus, reaching a minimum value in the nucleus and then increasing again in the posterior part of the annulus. The results show that in the intervertebral disc, measured rates depend on culture conditions.

Secretory cells in the nucleus pulposus of the adult human intervertebral disc. A preliminary report

A light microscopical study was conducted to ascertain the type of cells in the nucleus pulposus of the adult human intervertrebral disc. Three lumbar intervertebral discs were removed from each of 15 male and female adults at autopsy (ages ranged from 19 to 62 years). The tissue was fixed in formalin, decalcified in formic acid, dehydrated in a graded series of ethanol, embedded in paraffin, and serially sectioned at 7-10 micron. Tissue sections were affixed to albuminized glass slides and stained either by hematoxylin and eosin or hematoxylin and Van Gieson's stain. The cells of the bulk of the nucleus pulposus consisted of chondrocytes and a few fibroblasts; however, the subchondral matrix of the nucleus pulposos contained numerous stellate cells with (from 1 to 8) unusually long (up to 80 micron) primary cytoplasmic processes that often branch into secondary processes. The cell processes contained cytoplasmic varicosities at various intervals along their lengths; and their endings often expanded into bulbous, vesicle-filled process terminals. The surrounding extracellular matrix usually contained numerous, vesicle-filled, eosinophil matrix bodies. Morphological similarities of cytoplasmic varicosities, process terminals, and matrix bodies, as well as the apparent budding of process terminals, suggest that these previously unidentified cells are secreting an unknown matrix component into the subchondral matrix of the nucleus pulposus of the adult human.

Advances in low-back pain

At the present time there is an epidemic of low-back pain in most industrialized countries. The exact origin of pain is unknown, and probably many structures can play a role. The natural history is extremely good. Only 10% suffer disabling back pain for more than six weeks; nearly 60% return to work within one week. The benefits of motion in the healing process of various connective tissues can be applied also for the back pain sufferer; in addition, the nutrition of the intervertebral disc is improved by moderate motion. Biomechanical factors with epidemiologically proven negative effects for the back pain sufferer have been measured and delineated. Thus, guided activation of large muscle groups is a benefit for the structures of the back as well as the body's own pain-reducing enkephalins. Present knowledge includes a detrimental effect of prolonged inactivation, including long-term bed rest and inactivity, which should be avoided. Better treatment methods, particularly in the surgical field, will evolve from technical advances in the diagnostic field. For the majority of the low-back pain patients who do not need surgical treatment, help will come in the next decade from a collaborative effort from politicians, industrial leaders and engineers, physicians, psychologists, and biomechanicians.

The effect of posture on the lumbar spine

A series of experiments showing how posture affects the lumbar spine is reviewed. Postures which flatten (that is, flex) the lumbar spine are compared with those that preserve the lumbar lordosis. Our review shows that flexed postures have several advantages: flexion improves the transport of metabolites in the intervertebral discs, reduces the stresses on the apophyseal joints and on the posterior half of the annulus fibrosus, and gives the spine a high compressive strength. Flexion also has disadvantages: it increases the stress on the anterior annulus and increases the hydrostatic pressure in the nucleus pulposus at low load levels. The disadvantages are not of much significance and we conclude that it is mechanically and nutritionally advantageous to flatten the lumbar spine when sitting and when lifting heavy weights.

The intrinsic vasculature of developing vertebral end plates and its nutritive significance to the intervertebral discs

The structure and anatomical relationships of cartilage canals in the developing vertebral endplates of rabbits and humans are described in this study. In newborn rabbits, we observed a similar morphology and topologic arrangement to that in human fetal spines. Each vascular organ consisted of an arteriole, a glomerular tuft of sinusoidal capillaries, recurrent venules, and supporting loose connective tissue. Because the canals terminate adjacent to the intervertebral discs, they may provide an important source of nutrition to the disc during development when it is sandwiched between two layers of thick hyaline cartilage and contains no intrinsic vascular supply.

Absence of keratan sulphate from skeletal tissues of mouse and rat

The absence of keratan sulphate synthesis from skeletal tissues of young and mature mice and rats has been confirmed by (1) analysis of specific enzyme degradation products of newly synthesized glycosaminoglycans, and (2) immunohistochemistry and radioimmunoassay using a monoclonal antibody directed against keratan sulphate. Approx. 98% of the [35S]glycosaminoglycans synthesized in vivo by mouse and rat costal cartilage, and all of those of lumbar disc, are chondroitin sulphate. The remainder in costal cartilage were identified as heparan sulphate in mature rats. In contrast, [35S]glycosaminoglycans synthesized by cornea of both species comprised both chondroitin sulphate and keratan sulphate. In mice keratan sulphate accounted for 12-25% and in rats 40-50% of the total [35S]glycosaminoglycans, depending on the age of the animal. Experiments in vitro with organ culture of cartilage and cornea confirm these results. Absence of keratan sulphate from mouse costal cartilage and lumbar disc D1-proteoglycans was corroborated by inhibition radioimmunoassay with the monoclonal antibody MZ15 and by lack of staining for keratan sulphate in indirect immunofluorescence studies using the same antibody.

[Water and electrolyte content of human intervertebral disks under varying load]

The human intervertebral disc acts as an osmotic system. Water, salt and other low-molecular substances penetrate the cartilage plates and anulus fibrosus. The content of water, sodium, potassium and ashes in different regions of 69 human lumbar intervertebral discs was examined before and after loading them with certain weights. Under load the disc looses water - anulus 11%, nucleus 8% - and gains sodium and potassium. The higher concentration of electrolytes in the disc after a long period of weight-bearing enlarge its osmotic absorptive forces and enable the disc to hold the rest-water also against a great amount of pressure. After reducing the pressure water is quickly reabsorbed and the disc gains height and volume. The pumping mechanism keeps up the nutrition and biomechanical function of the intervertebral disc.

Effects of spinal fusion on the proteoglycans of the canine intervertebral disc

Posterior lumbar two-level spinal fusion was undertaken in 10 mature beagles. The animals were sacrificed 6 and 12 months later. Two months before sacrifice control and experimental animals received intravenously Na2(35)SO4 (1 mCi/kg). Discs encompassed by the fusion and those adjacent to it were dissected into the nucleus pulposus and annulus fibrosus (AF), which were analysed separately. Proteoglycans (PGs) were extracted with 4.0 M guanidine HCl and purified by CsCl density gradient ultracentrifugation. The hydrodynamic size and ability of the PG subunits to aggregate in the presence of hyaluronic acid were investigated by Sepharose CL-2B chromatography. The PG subunits were analysed for their galactosamine (galN), glucosamine (glcN), hexuronic acid, and protein content or were subjected to digestion with papain or chondroitin-ABC-lyase to establish the size of the chondroitin (CS) and keratan (KS) sulphate chains and the KS-PG core protein complex. Decreased ability to aggregate of PGs isolated from discs 6 and 12 months after surgery was demonstrated. While their hydrodynamic size after 6 months was generally the same or smaller than those in control tissues, the PG population present after 12 months was larger, particularly in the AF. Analysis of PG subunits from fusion discs afforded galN/glcN, galN/protein, and hexuronic acid/protein ratios that were compatible with the presence in these tissues of PGs in which the proportion of CS attached to core protein was greater than in control tissues. These studies provide the first experimental evidence that a metabolic response of discs in a fused segment may be accompanied by the biosynthesis of a new PG population whose structure is similar to that present in immature tissues.