Nutrition of the intervertebral disc: solute transport and metabolism

Oxygen and lactate concentrations measured in vivo in the intervertebral discs of patients with scoliosis and back pain

STUDY DESIGN

Oxygen concentrations in intervertebral discs were measured in 10 patients during discography and in 13 patients with scoliosis and 11 patients with back pain during spinal surgery. Lactate concentration profiles were measured in 12 of these discs. The discs were graded for degeneration by magnetic resonance imaging and histology where possible.

OBJECTIVES

To determine if oxygen and lactate levels in human discs vary with degree of degeneration. Failure of nutrient transport is thought to lead to disc degeneration.

SUMMARY OF BACKGROUND DATA

The disc is avascular. Oxygen is used by the disc cells, and lactate is produced. Low oxygen and high lactate concentrations have been measured in the center of healthy animal discs.

METHODS

Oxygen concentrations were measured amprometrically. The sterilized gold-needle electrode was introduced into the disc during discography or after the disc was exposed surgically via an anterior approach. Concentration profiles of each disc took approximately 5 minutes to measure. Lactate concentrations were measured biochemically on the excised disc segment.

RESULTS

Oxygen concentrations were highest at the disc surface and fell toward the center. Lactate concentrations showed the reverse profile. Oxygen levels were very variable, ranging from 5-150 mm Hg in the center of the nucleus. No correlation was seen with age, pathology, or degree of degeneration. Lactate concentrations ranged for the most part from 2 mmol/L to 6 mmol/L.

CONCLUSIONS

Concentrations of metabolites depend on cellular activity and on transport of the metabolite between the blood supply and the cell. The correlation between degeneration and nutrition cannot be determined only from metabolite concentrations; measurements of metabolic activity and nutrient transport rates also are required.

Evidence for a negative Pasteur effect in articular cartilage

Uptake of external glucose and production of lactate were measured in freshly-excised bovine articular cartilage under O2 concentrations ranging from 21% (air) to zero (N2-bubbled). Anoxia (O2 concentration < 1% in the gas phase) severely inhibited both glucose uptake and lactate production. The decrease in lactate formation correlated closely with the decrease in glucose uptake, in a mole ratio of 2:1. This reduction in the rate of glycolysis in anoxic conditions is seen as evidence of a negative Pasteur effect in bovine articular cartilage. Anoxia also suppressed glycolysis in articular cartilage from horse, pig and sheep. Inhibitors acting on the glycolytic pathway (2-deoxy-D-glucose, iodoacetamide or fluoride) strongly decreased aerobic lactate production and ATP concentration, consistent with the belief that articular cartilage obtains its principal supply of ATP from substrate-level phosphorylation in glycolysis. Azide or cyanide lowered the ATP concentration in aerobic cartilage to approximately the same extent as did anoxia but, because glycolysis (lactate production) was also inhibited by these treatments, the importance of any mitochondrial ATP production could not be assessed. A negative Pasteur effect would make chondrocytes particularly liable to suffer a shortage of energy under anoxic conditions. Incorporation of [35S]sulphate into proteoglycan was severely curtailed by treatments, such as anoxia, which decreased the intracellular concentration of ATP.

Effect of sustained loading on the water content of intervertebral discs: implications for disc metabolism

OBJECTIVE

To examine regional changes in the fluid content of human intervertebral discs by comparing sagittal plane "profiles" of hydration before and after mechanical loading.

METHODS

Cadaveric lumbar intervertebral discs were loaded to simulate a typical day's loading in vivo. Ten motion segments were subjected to a 1500 N compressive load for a period of 6 h with the superior vertebrae inclined by 4-8 degrees to simulate a slightly flexed posture. Immediately after loading the discs were frozen at -80 degrees C. Subsequently they were cut into slices perpendicular to the sagittal midline of the disc, and each slice was weighed before and after freeze drying. This enabled a profile of fluid content across the disc to be constructed. Fluid loss due to loading was estimated by comparing the water content of each loaded disc with that of an adjacent unloaded disc from the same spine.

RESULTS

After 6 h of creep loading, disc height approached, but did not quite reach, an equilibrium. The mean fluid loss from all discs was 18%. All regions except the outer 2 mm experienced a significant loss of fluid (P < 0.01). The posterior mid-annulus showed the greatest fluid loss (30%), while the nucleus lost 15%.

CONCLUSIONS

A comparison with previously published work suggests that fluid exchange of this magnitude will have a considerable effect on disc cell metabolism and on metabolite transport.

The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration

Very little is known about the turnover of extracellular matrix in the human intervertebral disc. We measured concentrations of specific molecules reflecting matrix synthesis and degradation in predetermined regions of 121 human lumbar intervertebral discs and correlated them with ageing and Thompson grade of degeneration. Synthesis in intervertebral discs, measured by immunoassay of the content of a putative aggrecan biosynthesis marker (846) and the content of types I and II procollagen markers, is highest in the neonatal and 2-5-yr age groups. The contents of these epitopes/molecules progressively diminished with increasing age. However, in the oldest age group (60-80 yr) and in highly degenerated discs, the type I procollagen epitope level increased significantly. The percentage of denatured type II collagen, assessed by the presence of an epitope that is exposed with cleavage of type II collagen, increased twofold from the neonatal discs to the young 2-5-yr age group. Thereafter, the percentage progressively decreased with increasing age; however, it increased significantly in the oldest group and in highly degenerate discs. We identified three matrix turnover phases. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of type II collagen. Phase II (maturation and ageing) is distinguished by a progressive drop in synthetic activity and a progressive reduction in denaturation of type 11 collagen. Phase III (degeneration and fibrotic) is illustrated by evidence for a lack of increased synthesis of aggrecan and type II procollagen, but also by an increase in collagen type II denaturation and type I procollagen synthesis, both dependent on age and grade of tissue degeneration.

Spinal compression at peak isometric and isokinetic exertions in simulated lifting in symmetric and asymmetric planes

OBJECTIVE: To determine if the spinal compression can be used as a criterion for the safety of the back. DESIGN: Various lifting strength activities were analysed using a 3-D biomechanical model to determine spinal compression forces. BACKGROUND: Despite many standards being set and the use of varied strategies, low-back injuries continue to be common in our society. Since the injuries occur to the tissues in the body, it may be more appropriate to investigate the effects of external loads on the tissues. Therefore it was decided to determine the spinal compression in standardized lifting tasks. METHODS: Twenty young adults (12 males and 8 females) performed maximal stoop and squat lifts in sagittal, 30 degrees lateral, and 60 degrees lateral planes at half, three-quarters, and full horizontal reach distances. The stoop lifts were performed in isokinetic and isometric modes; the isometric mode was performed with the hip at 60 degrees and 90 degrees. The squat lifts were also performed in isokinetic and isometric modes; the isometric mode consisted of postures with knee at 90 degrees and 135 degrees of flexion. In addition, the subjects also performed isometric lifts in stoop and squat postures at a self-selected optimum posture. During these activities the strength was measured using a static dynamic strength tester employing a load cell and force monitor. Three-dimensional postural recording was made using a 3-D Peak Performance Technologies imaging system. Using the postural and force data as input to a 3-D biomechanical model, the lumbosacral spinal compression was calculated. The values of strength and spinal compression were analysed and compared. RESULTS: The strength was significantly affected by the gender, the type of lift, plane of lift and reach of lift (P < 0.01); whereas the spinal compression was not affected by the reach at all. Two-way and three-way interactions were significant for strength (P < 0.02) but not for spinal compression. CONCLUSION: It was concluded that the spinal compression was the ultimate cost function in the safety of the back and as such preventative strategies should be based on this. RELEVANCE: The use of an appropriate cost function in a manner in which it can maximize the safety of the back will be of considerable value. Since injuries are biomechanical perturbation of the tissues, it is argued that the cost function be used in a manner where tissue load be considered as the primary factor.

The human lumbar endplate. Evidence of changes in biosynthesis and denaturation of the extracellular matrix with growth, maturation, aging, and degeneration

STUDY DESIGN

The authors measured concentrations of specific molecules reflecting matrix synthesis and degradation in 121 human endplates and correlated them with aging and grade of degeneration.

OBJECTIVES

Abnormal endplate development has been implicated in many spinal abnormalities, yet little is known about endplate matrix component turnover.

SUMMARY OF BACKGROUND DATA

Techniques are available to perform an in situ investigation of matrix component turnover with aging and degeneration.

METHODS

Newly synthesized aggrecan and Type I and Type II procollagens were measured with recently developed immunoassays. Percentage of denatured Type II collagen was assessed with a new enzyme-linked immunosorbent inhibition assay.

RESULTS

Synthesis in endplates, measured by content of an aggrecan marker (846) and content of Types I and II procollagen markers (CPI and CPII), is highest in the neonatal and 2- to 5-year age groups and steadily diminishes with increasing age. However, in the oldest age group and in highly degenerated discs, the CPI epitope level increased significantly. Percentage of denatured Type II collagen, assessed by the presence of an epitope exposed with the cleavage of Type II collagen, increased from the neonatal to the 2- to 5-year age groups. The percentage progressively decreased with increasing age. However, it significantly increased in endplates from highly degenerated discs.

CONCLUSIONS

The authors identified three matrix turnover phases, related to age and grade of degeneration. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of Type II collagen. Phase II (aging and maturation) is distinguished by a drop in synthetic activity and a reduction in denaturation of Type II collagen. Phase III (degenerative) is illustrated by an increase in Type II collagen denaturation and Type I procollagen synthesis, both related to grade of tissue degeneration.

Development and degeneration of the intervertebral discs

The intervertebral discs undergo profound changes in structure and composition during development and aging. They also degenerate much earlier than other cartilaginous tissues, and in severe cases may lose function completely. The reasons for this early degeneration are unknown, but external factors, such as mechanical overload on the spine, or smoking, may be involved. However, recent work has revived interest in the importance of genetic and developmental influences on the intervertebral discs.

Anatomy of intervertebral disc and pathophysiology of herniated disc disease

This discussion reviews developments in normal and abnormal disc biology over the past decade. The anatomic and biochemical structure of the disc is reviewed. Emphasis is placed on recent neurochemical changes identified in disc degeneration and disc herniation. Biomechanical considerations for the normal disc are presented. Influence of mechanical factors on disc nutrition, disc degeneration and disc herniation is reviewed. Biologic events underlying the diagnostic methods used in evaluating disorders of the intervertebral disc are presented. The biologic consequences of iatrogenic disc injury in discectomy are also discussed.

Ingrowth of blood vessels in disc degeneration. Angiographic and histological studies of cadaveric spines

Angiograms were made of twenty-two cadaveric lumbar spines to determine the presence of any new blood vessels between adjacent lumbar vertebrae and corresponding discs. The annulus and adjacent longitudinal ligaments were also analyzed histologically. A total of 105 intervertebral spaces were studied. It was found that the normal anastomosing arteries in the posterior longitudinal ligament were significantly obliterated with advancing degeneration of the disc (p < 0.001), whereas several tiny tortuous arteries--often running between the osteophytic spurs--were seen in the anterolateral aspects of the intervertebral spaces connecting the adjacent vertebrae. Histological examination of the anterolateral part of the annulus showed that the vascularity of the annulus increased significantly with degeneration of the disc (p < 0.001), and most of the arteries had a vertical orientation. Regression analysis showed that vascular changes occurred before degeneration of the disc at every lumbar level, suggesting that disturbances in the nutritional supply may precede degeneration. The correlation coefficient was 0.77 (95 per cent confidence limit, 0.52 to 0.90) for the increase in annular vascularity with an increase in the age of the individual at the time of death and 0.86 (95 per cent confidence limit, 0.69 to 0.94) for the increase in degeneration of the disc with an increase in age.

Effect of static load on matrix synthesis rates in the intervertebral disc measured in vitro by a new perfusion technique

The effect of static loading on matrix synthesis was measured in intact bovine coccygeal discs. The discs were maintained at 37 degrees C in a humid atmosphere and were perfused across their upper and lower surfaces for as long as 8 hours with media containing radioisotopes (3H-proline and 35S-sulphate) via porous filter disks embedded in Perspex (Plexiglas) holders. Static loads were applied to the disc with use of weights. The activity of free, nonincorporated isotope in the centre of the disc was monitored continuously with a microdialysis probe. Incorporated tracer in different regions of the disc was determined at the end of each experiment from the activity of the nondialysable tracer. Free tracer activity rose steeply over the first 3-4 hours of perfusion, as tracer diffused into the disc, and reached a steady value after 5-6 hours, as expected from diffusion theory. The rate of tracer incorporation estimated from the integrated value of free tracer concentration was constant for as long as 8 hours. Incorporation rates varied across the disc: the highest rates were in the inner layer of the annulus fibrosus, and the lowest rates were in the outer layer of the annulus. The rates for both 35S-sulphate and 3H-proline varied with load. The rates were lowest in the nucleus pulposus and the inner layer of the annulus fibrosus with a 0.5 kg load, and they almost doubled as the load was increased to 5-10 kg. Heavier loads (15 kg) led to a decrease in incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent advances in lumbar spinal mechanics and their clinical significance

Of the many problems associated with low back pain, those which are most amenable to biomechanical investigation are identified. Recent advances in lumbar spinal mechanics are then reviewed in five sections dealing with mechanical function, mechanisms of failure, movements in vivo, loading in vivo, and the biological consequences of mechanical loading. The discussion suggests that mechanical fatigue damage may frequently be the underlying cause of low back pain, even when degenerative changes are evident in the tissues, and the review ends by suggesting some priority areas for future research.

Responses of articular cartilage explant cultures to different oxygen tensions

Bovine articular cartilage explants were cultured under atmospheres of 6, 10, 24, 66 and 91% oxygen. [35S]Glycosaminoglycan, chondroitin sulphate and keratan sulphate synthesis were measured together with the pool size of UDP-N-acetylhexosamines, UDP-hexoses and UDP-glucuronate. UDP-xylose was not detected. [35S]Glycosaminoglycan synthesis was maintained at the same level as in fresh tissue when cultured over 7 days with 20% foetal calf serum present and under a 6% oxygen tension. Under normal atmosphere (24%) synthesis was stimulated and remained elevated throughout the incubation period. Under higher oxygen tensions, initial stimulation of glycosaminoglycan synthesis was followed by progressive inhibition. The [35S]chondroitin sulphate/keratan sulphate ratio was constant (approximately 16:1) between 6 and 24% oxygen tension, but increased to 50:1 at 91% oxygen. The UDP-N-acetylhexosamine pool was larger under anaerobic (6, 10%) and excessively aerobic (66, 91%) oxygen tensions than under a normal atmosphere (24%). The UDP-hexose pool was expanded under anaerobic conditions. The UDP-glucuronate pool showed little variation between 6 and 24% oxygen tensions, but contracted under very aerobic conditions. We found no evidence indicating that keratan sulphate synthesis was favoured under anaerobic conditions to compensate for decreasing chondroitin sulphate synthesis.

Proteoglycan synthesis in canine intervertebral discs after long-distance running training

The alterations and distribution of proteoglycan (PG) synthesis in the intervertebral discs of young dogs exercised with long-distance running (40 km/day) were studied with a method based on image analysis of tissue sections. Ten dogs were run on a treadmill daily for 55 weeks, and 10 dogs from the same litters served as controls. The daily running distance gradually was increased to 40 km and was maintained at that level for the final 15 weeks. Midsagittal disc segments C7-T1, T8-9, and L1-2 were labeled with 35SO4, and histological sections of the segments were apposed against autoradiographic film to determine the synthesis of PGs. Next, the same sections were stained with safranin O to estimate possible alterations in PG concentration. The radiographs and stained sections were digitized with a flatbed scanner and measured by image analysis. The lumbar discs of runners displayed a significantly lower rate of 35SO4 incorporation, while a tendency toward enhanced incorporation was seen in the cervical and thoracic discs. Safranin O staining showed a pattern just opposite to 35SO4 incorporation: decreased staining in the cervical and thoracic discs and increased staining in the lumbar discs of the runners. The results demonstrate qualitatively different influences of long-term running training on PG metabolism at the cervical, thoracic, and lumbar levels in young dogs.

Detection of lymph and blood vessels in the human intervertebral disc by histochemical and immunohistochemical methods

Twenty-four intervertebral discs from the lumbar region of postmortem human subjects were investigated by immunohistochemical and histochemical methods to evaluate the pattern of blood and lymph vessels of the discus intervertebralis and surrounding tissue at different ages. Antibodies against the basement membrane component laminin, and the lectin Ulex europaeus agglutinin as a marker for L-fucose in endothelial cells, were used to make the blood vessels visible. The 5'-nucleotidase activity in lymph endothelium served as a marker for lymphatic vessels. The dorsolateral parts of the connective tissue adjacent to the discus intervertebralis were well vascularized in all age groups examined. Vessels in the outer anulus fibrosus were detected in young individuals up to 20 years of age. Vascular canals, i.e. blood vessels in the cartilage end plate, were seen up to 7 years of age. Lymph capillaries are first described here penetrating the disc and peridiscal tissue and accompanying most of the small blood vessels into the areas specified.

Regulation of matrix synthesis rates by the ionic and osmotic environment of articular chondrocytes

Chondrocytes in cartilage are embedded in a matrix containing a high concentration of proteoglycans and hence of fixed negative charges. Their extracellular ionic environment is thus different from that of most cells, with extracellular Na+ being 250-350 mM and extracellular osmolality 350-450 mOsm. When chondrocytes are isolated from the matrix and incubated in standard culture medium (DMEM; osmolality 250-280 mOsm), their extracellular environment changes sharply. We incubated isolated bovine articular chondrocytes and cartilage slices in DMEM whose osmolality was altered over the range 250-450 mOsm by Na+ or sucrose addition. 35S-sulphate and 3H-proline incorporation rates were at a maximum when the extracellular osmolality was 350-400 mOsm for both freshly isolated chondrocytes and for chondrocytes in cartilage. The incorporation rate per cell of isolated chondrocytes was only 10% that of chondrocytes in situ both 4 and 24 hours after isolation. For freshly isolated chondrocytes, the rate increased 30-50% in DMEM to which NaCl or sucrose had been added to increase osmolality. In chondrocytes incubated overnight in DMEM, the rate was greatest in DMEM of normal osmolality and fell from the maximum in proportion to the change in osmolality. The effects of sucrose addition on incorporation rates were similar but not identical to those of Na+ addition. Changes in cell volume might be linked to changes in synthesis rates since the cell volume of chondrocytes (measured by Coulter-counter) increased 30-40% when the cells were removed from their in situ environment into DMEM. Synthesis rates can thus be partly regulated by changes in extracellular osmolality, which in cartilage is controlled by proteoglycan concentration. This provides a mechanism by which the chondrocytes can rapidly respond to changes in extracellular matrix composition.

Water content alters viscoelastic behaviour of the normal adolescent rabbit medial collateral ligament

Testing environment is an important factor in the outcome of mechanical tests on connective tissue. The purpose of this investigation was to determine the effect of ligament water content on ligament mechanical behaviour by altering the test environment. Water content of medial collateral ligament (MCLs) from 19 three-month-old New Zealand White rabbits was varied in subsets of ligaments pairs by means of immersion in 2, 10 or 25% sucrose or 0.9% phosphate-buffered saline (PBS) solutions for 1 h. One knee joint was cycled 50 times in the designated solution (experimental), while the contralateral knee (uncycled control) was simultaneously soaked in the same tank. Following cycling, the water contents of both test and control ligaments were determined. Water contents of 22 normal MCLs were determined immediately post-sacrifice and served as 'normal water content' controls. Normalized peak cyclic load changes were used as a measure of the viscoelastic behaviour of each MCL. Results demonstrated that only ligaments soaked (but not cycled) in a 10% sucrose solution had water contents (60.5 +/- 2.5%) which were statistically similar to the 22 fresh normal MCLs (63.9 +/- 6.0%). Ligaments soaked in PBS (74.0 +/- 1.3%) or 2% sucrose (69.2 +/- 2.3%) had significantly higher water contents compared to fresh normal MCLs. Ligaments with higher water contents (e.g. soaked in PBS or 2% sucrose) demonstrated greater cyclic load relaxation compared to ligaments with lower contents (e.g. soaked in 25 or 10% sucrose). Different fluid test environments can significantly alter ligament water content and, in turn, significantly affect ligament viscoelastic behaviour.

Electrochemical method for direct measurement of oxygen concentration and diffusivity in the intervertebral disc: electrochemical characterization and tissue-sensor interactions

A method was developed for the in vivo measurement of oxygen concentration and diffusivity in the intervertebral disc using a bare gold cathode. The effects of surface adsorption were quantified using electrochemical methods and it was demonstrated that valid data can be obtained despite interactions between the electrode and the macromolecules of the intervertebral disc. The technique is used to show the dependence of the oxygen transport properties on tissue water content.

Where is the lumbar pain coming from?

This presentation proposes that the majority of persistent lumbar pain comes from chemical abnormalities within the disc. On this basis, a review of clinical experience and basic studies suggests that active mechanical therapy is the most rational approach to treat the disc. Avoidance of the habituation to pain and inactivity is supported. Rest treatment becomes a societal question rather than a medical question. Ultimately assessment of disc chemistry with appropriate instrumentation will allow the instillation of therapeutic agents within the disc itself. Extended rest, and passive physical therapy no longer have a rational place in the treatment of persistent back pain.

Cysteine proteinase inhibitors of the canine intervertebral disc

Several species of cysteine proteinase inhibitors have been demonstrated in the greyhound intervertebral disc which were resolved into four species (Mr 15,800, 16,600, 17,200 and 17,800) by gelatin-SDS-polyacrylamide gel electrophoresis. Reductive alkylation did not affect their inhibitory capability nor their electrophoretic migration on gelatin-SDS-polyacrylamide gel electrophoresis. The cysteine proteinase inhibitors from the nucleus pulposus and annulus fibrosus were identical as assessed by the aforementioned criteria, although the level in the nucleus was found to be higher than that in the annulus. Ion-exchange chromatography demonstrated distinct acidic and basic forms of the disc cysteine proteinase inhibitor. The latter species was the most abundant and its Mr was determined to be 16,900 by gelatin-SDS-polyacrylamide gel electrophoresis. Both forms were shown to be strongly inhibitory against the cysteine proteinases, papain and ficin, but were less strongly inhibitory against cathepsin B (EC 3.4.22.1). Presumably these disc cysteine proteinase inhibitors play a regulatory role in the metabolism of proteoglycans and collagen by endogenous cysteine proteinases.

Nutrition of the intervertebral disc: acute effects of cigarette smoking. An experimental animal study

We have in the present experimental study investigated the influence of cigarette smoking on some nutritional parameters of the porcine intervertebral disc. The results from the acute smoking tests show a significant reduction in solute transport. Diffusion of sulphate, oxygen and methyl glucose was reduced by 30-40 per cent. This effect was obtained after exposure to smoke for 20-30 minutes. A smoking period of three hours reduced the transport efficiency to about 50 per cent. The effect of smoking decreased when the exposure ceased. The concentration gradients were close to normal after 2 hours "recovery". These findings suggest that cigarette smoking not only significantly affects the circulatory system outside the intervertebral disc, where the most pronounced effect is the reduction in solute exchange capacity, but also significantly deteriorates the cellular uptake rate and metabolite production within the disc.

Clinical consideration in referred muscle pain and tenderness. Connective tissue reactions

Muscle pain and tenderness is caused either by changes in the muscle itself or by disease promoting factors outside the muscle. This paper gives a review of referred causes of muscle pain and tenderness with special emphasis on pathology in the strong supportive types of connective tissue.

Respiratory gas pressures in the spine. Measurements in goats

Normal values of pO2, pCO2, pH, and intraosseous pressure were measured in situ in the lumbar spine of goats. In the lumbar bodies and discs no difference existed between values found cranially and caudally. pO2 was lower and pCO2 higher in the nucleus pulposus than in the adjacent lumbar bodies. This emphasizes the nutritional route to the disc via the vertebral end plate. Intraosseous pressures in the cranial and caudal levels of the lumbar spine did not differ, and the pressures were the same as otherwise found in cancellous bone. These are the first combined in situ measurements of several basic metabolic parameters in the normal spine using recordings with continuous mass spectrometry. They may constitute a basis for further investigation of metabolism in the structures of the spine.

Steindler award lecture. Cross the borders

The orthopaedic scientists of today, whether a clinician or a basic scientist, must cross both interdisciplinary and national borders to advance the field. Examples derived from the author's own experience of such border crossings are given, mainly as they relate to research in spinal disorders.

Metabolic and haemodynamic changes in the pathologic hypermobile spine

The purpose of the study was to evaluate whether pathologic hypermobility of the lumbar spine could produce haemodynamic, metabolic, and histologic changes similar to those found in osteoarthritis. Five adult goats were surgically made hypermobile in the lumbar spine by an extensive laminectomy involving exarticulation of the facet joints of the L4 and L5 levels. Seven months following the operation oxygen partial pressure (pO2), was measured in situ in the nucleus pulposus and in the adjacent lumbar body of the hypermobile segment. A segment three levels more cranially served for control. Mass spectrometry was used for continuous registration of pO2. Intraosseous pressure (IOP) was measured in the lumbar bodies of the same levels. Hypermobility averaged a 60 per cent increase at the operated segment as measured on flexion-extension radiograms preoperatively and 7 months postoperatively. The hypermobile discs had decreased in height as measured by CT scanning and this was confirmed by histologic sections. Significant hypoxia was found in the nucleus pulposus of the hypermobile segment, while increased pO2 and IOP existed in the adjacent lumbar body.

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.

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.

Studies of the lumbar vertebral end-plate region in the pig

The vertebral end-plates and the epiphyses from the lumbar region of the spine in juvenile pigs were studied. Cell density of the hyaline cartilage of the vertebral bodies was measured as well as cartilage thickness. The relative bone content in the region of the nucleus pulposus was calculated. A certain negative interrelationship between cartilage thickness and cell density of the hyaline cartilage of the vertebral bodies was found. The relative bone content of the cranial epiphysis was higher than that of the caudal epiphysis in the same motion segment at all levels of the lumbar spine. The difference was pronounced down to 2 mm from the cartilage/bone interface.

Carbohydrate metabolism and concentration profiles of solutes in the canine lumbar intervertebral disc

Utilization of glucose and oxygen by the cells as well as concentration profiles of solutes were studied in the canine intervertebral disc. Cell metabolism in this avascular tissue, being predominantly anaerobic, was found to be dependent on oxygen tension (this being especially pronounced in the region of 0.13-0.4 kPa (1-3 mmHg). A high production rate of lactic acid was found in the nucleus pulposus, whereas towards the periphery of the annulus fibrosus this rate gradually decreased. In the centrally located areas of the disc tissue, far away from the blood circulation, the highest concentrations of lactic acid were found. For the normal disc the energy demands seem to be met as even small amounts of oxygen account for a large energy source, whereas the cellular requirements are balanced up predominantly by glucose. In regions with extremely low oxygen tensions large amounts of glucose are consumed, but an additional potential energy pool of glycogen seems to be available.

Oxygen tension alterations in the intervertebral disc as a response to changes in the arterial blood

Measurements of oxygen tension in the canine lumbar intervertebral disc, by the use of a polarographic oxygen electrode, were performed. The oxygen tension in the arterial blood was changed by regulating the oxygen concentration in the inspired air. The alterations in oxygen tension in the nucleus pulposus, as a function of distance to the vertebral endplate were determined. The response times registered in the disc matrix were relatively short (within five min.), which implies an efficient solute transport from the vertebral blood pool underneath the hyaline cartilage into the avascular intervertebral disc.

Swelling of the intervertebral disc in vitro

Slices of the intervertebral disc swell rapidly in aqueous solutions. Following swelling, a large proportion of the proteoglycans leach out. These changes can introduce artifacts into in vitro experimental work. Swelling results from the large Gibbs-Donnan osmotic pressure of the proteoglycans which the collagen network of the disc is unable to oppose alone. Swelling can be prevented by applying pressure to disc slices either mechanically or with iso-osmotic solutions.