Modeling valuations for EuroQol health states

OBJECTIVES

It has become increasingly common for preference-based measures of health-related quality of life to be used in the evaluation of different health-care interventions. For one such measure, The EuroQol, designed to be used for these purposes, it was necessary to derive a single index value for each of the 243 health states it generates. The problem was that it was virtually impossible to generate direct valuations for all of these states, and thus it was necessary to find a procedure that allows the valuations of all EuroQol states to be interpolated from direct valuations on a subset of these.

METHODS

In a recent study, direct valuations were elicited for 42 EuroQol health states (using the time trade-off method) from a representative sample of the UK population. This article reports on the methodology that was adopted to build up a "tariff" of EuroQol values from this data.

RESULTS

A parsimonious model that fits the data well was defined as one in which valuations were explained in terms of the level of severity associated with each dimension, an intercept associated with any move away from full health, and a term that picked up whether any dimension in the state was at its most severe level.

CONCLUSIONS

The model presented in this article appears to predict the values of the states for which there are direct observations and, thus, can be used to interpolate values for the states for which no direct observations exist.

Variations in population health status: results from a United Kingdom national questionnaire survey

OBJECTIVE

To measure the health of a representative sample of the population of the United Kingdom by using the EuroQoL EQ-5D questionnaire.

DESIGN

Stratified random sample representative of the general population aged 18 and over and living in the community.

SETTING

United Kingdom.

SUBJECTS

3395 people resident in the United Kingdom.

MAIN OUTCOME MEASURES

Average values for mobility, self care, usual activities, pain or discomfort, and anxiety or depression.

RESULTS

One in three respondents reported problems with pain or discomfort. There were differences in the perception of health according to the respondent's age, social class, education, housing tenure, economic position, and smoking behaviour.

CONCLUSIONS

The EQ-5D questionnaire is a practical way of measuring the health of a population and of detecting differences in subgroups of the population.

Mechanical initiation of intervertebral disc degeneration

STUDY DESIGN

Mechanical testing of cadaveric lumbar motion segments.

OBJECTIVES

To test the hypothesis that minor damage to a vertebral body can lead to progressive disruption of the adjacent intervertebral disc.

SUMMARY OF BACKGROUND DATA

Disc degeneration involves gross structural disruption as well as cell-mediated changes in matrix composition, but there is little evidence concerning which comes first. Comparatively minor damage to a vertebral body is known to decompress the adjacent discs, and this may adversely affect both structure and cell function in the disc.

METHODS

In this study, 38 cadaveric lumbar motion segments (mean age, 51 years) were subjected to complex mechanical loading to simulate typical activities in vivo while the distribution of compressive stress in the disc matrix was measured using a pressure transducer mounted in a needle 1.3 mm in diameter. "Stress profiles" were repeated after a controlled compressive overload injury had reduced motion segment height by approximately 1%. Moderate repetitive loading, appropriate for the simulation of light manual labor, then was applied to the damaged specimens for approximately 4 hours, and stress profilometry was repeated a third time. Discs then were sectioned and photographed.

RESULTS

Endplate damage reduced pressure in the adjacent nucleus pulposus by 25% +/- 27% and generated peaks of compressive stress in the anulus, usually posteriorly to the nucleus. Discs 50 to 70 years of age were affected the most. Repetitive loading further decompressed the nucleus and intensified stress concentrations in the anulus, especially in simulated lordotic postures. Sagittal plane sections of 15 of the discs showed an inwardly collapsing anulus in 9 discs, extreme outward bulging of the anulus in 11 discs, and complete radial fissures in 2 discs, 1 of which allowed posterior migration of nucleus pulposus. Comparisons with the results from tissue culture experiments indicated that the observed changes in matrix compressive stress would inhibit disc cell metabolism throughout the disc, and could lead to progressive deterioration of the matrix.

CONCLUSIONS

Minor damage to a vertebral body endplate leads to progressive structural changes in the adjacent intervertebral discs.

The time trade-off method: results from a general population study

An important consideration when establishing priorities in health care is the likely effects that alternative allocations of resources will have on health-related quality-of-life (HRQoL). This paper reports on a large-scale national study that elicited the relative valuations attached by the general public to different states of health (defined in HRQoL terms). Health state valuations were derived using the time trade-off (TTO) method. The data from 3395 respondents were highly consistent, suggesting that it is feasible to use the TTO method to elicit valuations from the general public. The paper shows that valuations for severe health states appear to be affected by the age and the sex of the respondent; those aged 18-59 have higher valuations than those aged 60 or over and men have higher valuations than women. These results contradict those reported elsewhere and suggest that the small samples used in other studies may be concealing real differences that exist between population sub-groups. This has important implications for public policy decisions.

'Stress' distributions inside intervertebral discs. The effects of age and degeneration

We investigated the distribution of compressive 'stress' within cadaver intervertebral discs, using a pressure transducer mounted in a 1.3 mm diameter needle. The needle was pulled along the midsagittal diameter of a lumbar disc with the face of the transducer either vertical or horizontal while the disc was subjected to a constant compressive force. The resulting 'stress profiles' were analysed in order to characterise the distribution of vertical and horizontal compressive stress within each disc. A total of 87 discs from subjects aged between 16 and 87 years was examined. Our results showed that age-related degenerative changes reduced the diameter of the central hydrostatic region of each disc (the 'functional nucleus') by approximately 50%, and the pressure within this region fell by 30%. The width of the functional annulus increased by 80% and the height of compressive 'stress peaks' within it by 160%. The effects of age and degeneration were greater at L4/L5 than at L2/L3, and the posterior annulus was affected more than the anterior. Age and degeneration were themselves closely related, but the stage of degeneration had the greater effect on stress distributions. We suggest that structural changes within the annulus and endplate lead to a transfer of load from the nucleus to the posterior annulus. High 'stress' concentrations within the annulus may cause pain, and lead to further disruption.

Valuing health states: a comparison of methods

In eliciting health state valuations, two widely used methods are the standard gamble (SG) and the time trade off (TTO). Both methods make assumptions about individual preferences that are too restrictive to allow them to act as perfect proxies for utility. Therefore, a choice between them might instead be made on empirical grounds. This paper reports on a study which compared a "props" (using specifically-designed boards) and a "no props" (using self-completion booklets) variant of each method. The results suggested that both non props variants might be susceptable to framing effects and that TTP props outperformed SG props.

Intervertebral disc degeneration: evidence for two distinct phenotypes

We review the evidence that there are two types of disc degeneration. 'Endplate-driven' disc degeneration involves endplate defects and inwards collapse of the annulus, has a high heritability, mostly affects discs in the upper lumbar and thoracic spine, often starts to develop before age 30 years, usually leads to moderate back pain, and is associated with compressive injuries such as a fall on the buttocks. 'Annulus-driven' disc degeneration involves a radial fissure and/or a disc prolapse, has a low heritability, mostly affects discs in the lower lumbar spine, develops progressively after age 30 years, usually leads to severe back pain and sciatica, and is associated with repetitive bending and lifting. The structural defects which initiate the two processes both act to decompress the disc nucleus, making it less likely that the other defect could occur subsequently, and in this sense the two disc degeneration phenotypes can be viewed as distinct.

Personal risk factors for first-time low back pain

STUDY DESIGN

A prospective study of personal risk factors for first-time low back pain.

OBJECTIVES

To construct and validate a multivariate model to predict low back pain.

SUMMARY OF BACKGROUND DATA

Various physical and psychological factors have been reported to increase the risk of low back pain, but conflicting results may be attributable to inaccurate "clinical" measures and to poorly validated statistical models.

METHODS

A total of 403 health care workers aged 18-40 years volunteered for the study. None had any history of "serious" back pain requiring medical attention or time off work. The volunteers completed the following questionnaires: the modified somatic perception questionnaire, the Zung depression scale, and the Health Locus of Control. Anthropometric factors were quantified using standard techniques. The 3Space Isotrak device (Polhemus, VT) was used to measure lumbar curvature and hip and lumbar spine mobility. Leg and back strength and back muscle fatiguability were measured in functional postures. Postal follow-up questionnaires, sent after 6, 12, 18, 24, 30, and 36 months, inquired about back pain, and multivariate logistic regression was used to identify risk factors at each follow-up.

RESULTS

The response rate fell from 99% at 12 months to 90% at 36 months, at which time 90 volunteers reported "serious" back pain and 266 reported "any" back pain. The following were consistent predictors of serious back pain: reduced range of lumbar lateral bending, a long back, reduced lumbar lordosis, increased psychological distress, and previous nonserious low back pain. Only the latter three were consistent predictors of "any" back pain. Physical factors had the most influence in a sub-population of volunteers who were new to the job.

CONCLUSIONS

Personal risk factors explained up to 12% of first-time low back pain.

Health state valuations from the general public using the visual analogue scale

In the clinical and economic evaluation of health care, the value of benefit gained should be determined from a public perspective. The objective of this study was to establish relative valuations attached to different health states to form the basis for a 'social tariff' for use in quantifying patient benefit from health care. Three thousand three hundred and ninety-five interviews were conducted with a representative sample of the adult British population. Using the EuroQol health state classification and a visual analogue scale (VAS), each respondent valued 15 health states producing, in total, direct valuations for 45 states. Two hundred and twenty-one re-interviews were conducted approximately 10 weeks later. A near complete, and logically consistent, VAS data set was generated with good test-retest reliability (mean ICC = 0.78). Both social class and education had a significant effect, where higher median valuations were given by respondents in social classes III-V and by those with intermediate or no educational qualifications. These effects were particularly noticeable for more severe states. The use of such valuations in a social tariff raises important issues regarding the use of the VAS method itself to elicit valuations for hypothetical health states, the production of separate tariffs according to social class and/or education and the appropriate measure of central tendency.

The stages of disc degeneration as revealed by discograms

One hundred and thirty-nine discs from cadaveric lumbar spines were injected with a mixture of radio-opaque fluid and dye. Discograms were taken and the discs were then sectioned in the sagittal plane. Examination of the sections revealed that injected fluid did not at first mix with the disc matrix but pushed it aside to form pools of injected fluid. The location of these pools, and hence the appearance of a discogram, depended on the stage of degeneration of the disc. It is concluded that useful clinical information can be obtained from discograms.

Diurnal variations in the stresses on the lumbar spine

Two complementary experiments were performed, the first on living people and the second on cadaveric spines. In the first experiment, electronic inclinometers were used to measure the range of lumbar flexion of 21 volunteers in the early morning and in the afternoon. The results showed that the range of movement increased by 5 degrees during the day. In the second experiment, cadaveric lumbar motion segments were creep loaded to simulate a day's activity and their bending properties were measured before and after creep. The results showed that creep loading reduces the spine's resistance to bending (the effect being particularly marked in the disc) and increases the range of lumbar flexion by 12.5 degrees. The results of the two experiments were combined to show that in life, forward bending movements subject the lumbar spine to higher bending stresses in the early morning compared with later in the day. The increase is about 300% for the discs and 80% for the ligaments of the neural arch. It is concluded that lumbar discs and ligaments are at greater risk of injury in the early morning.

Sustained loading generates stress concentrations in lumbar intervertebral discs

STUDY DESIGN

Cadaveric motion segment experiment. Measurements on each specimen were compared before and after creep loading.

OBJECTIVES

To show how sustained "creep" loading affects stress distributions inside intervertebral discs.

SUMMARY OF BACKGROUND DATA

The central region of an intervertebral disc acts like a hydrostatic "cushion" between adjacent vertebrae. However, this property depends on the water content of the tissues and may be lost or diminished after creep.

METHODS

Twenty-seven lumbar motion segments consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate erect standing postures in life. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc in the midsagittal plane. Profiles of vertical and horizontal compressive stress were repeated after each specimen had been creep loaded in compression for 2-6 hours.

RESULTS

Creep reduced the hydrostatic pressure in the nucleus by 13-36%. Compressive stresses in the anulus were little affected when the profiles were measured at 1 kN, but at 2 kN, localized peaks of compressive stress appeared (or grew in size) in the posterior anulus after creep.

CONCLUSIONS

Increased loading of the apophysial joints causes an overall reduction in intradiscal stresses after creep. In addition, water loss from the nucleus causes a transfer of load from nucleus to anulus. Stress concentrations may lead to pain, structural disruption, and alterations in chondrocyte metabolism. Disc mechanics depend on loading history as well as applied load.

Electromyographic median frequency changes during isometric contraction of the back extensors to fatigue

STUDY DESIGN

This was a cross-sectional study involving 229 healthy, back pain-free individuals.

OBJECTIVES

To examine the relationship between electromyographic manifestations of fatigue and endurance time during isometric contraction of the back extensors to fatigue.

SUMMARY OF BACKGROUND DATA

Despite the wide-spread use of electromyography to monitor muscle fatigue, its relationship with endurance time has not been well investigated.

METHODS

Using skin-surface electrodes, electromyographic signals were recorded from thoracic (T10) and lumbar (L3) regions of erector spinae during an isometric endurance test, and the rate of change in median frequency of the electromyographic power spectrum (MFGRAD) was calculated.

RESULTS

MFGRAD was significantly higher at L3 than at T10. The best predictor of endurance time was given by the greater MFGRAD observed at either region. MFGRAD calculated over a submaximal time period (50% total time or 60 sec) also correlated significantly with endurance time. Women displayed a significantly longer endurance time and lower MFGRAD than men.

CONCLUSIONS

Endurance appears to be limited by the most fatigable region of the muscle group. MFGRAD is a suitable technique for monitoring back muscle fatigue, even when it is determined over a submaximal time period. The back extensors of women are less fatigable than those of men when the same task is performed.

The cost of treating osteoporotic fractures in the United Kingdom female population

Osteoporotic fractures represent a significant burden to society. The costs of osteoporotic fractures to the UK health care system have not previously been accurately described. In this paper, we quantify the health care and social care costs of fractures occurring in women aged 50 years and over in the UK. We used a variety of data sources. For acute hospital hip fracture costs existing published estimates were used whilst for social care costs a survey of resource use among fracture patients before and after hip fracture was utilized. We undertook a case-control study using the General Practice Research Database to estimate primary care costs. From these data we estimated that the cost of a hip fracture is about 12,000 Pounds, with non-acute hospital costs representing the larger proportion. The other fractures were less expensive, at 468 Pounds, 479 Pounds and 1338 Pounds for wrist, vertebral and other fractures, respectively. For all fractures the annual cost to the UK is 727 million Pounds. Assuming each male hip fracture costs the same as a female fracture, including these would increase the total costs to 942 million Pounds.

Bending and compressive stresses acting on the lumbar spine during lifting activities

Cadaveric studies have shown that intervertebral discs and ligaments are most vulnerable to injury when loaded simultaneously in bending and compression. The purpose of the present experiment was to measure bending and compressive stresses acting on the lumbar spine during forward bending and lifting activities, and to identify those aspects of lifting which increase the risk of injury. Twenty-one men and eighteen women lifted objects from the ground while the following parameters were varied: the angle of the knees ('squat' lift or 'stoop' lift), the mass of the object, its bulk, its distance in front of the feet, its distance away from the sagittal plane, and the speed of movement. Spinal compression was assessed by measuring the peak extensor moment generated by the back muscles and fascia during the lift. Extensor moment was calculated from the EMG activity of the erector spinae muscles, using corrections for muscle length, contraction velocity and electro-mechanical delay. The bending moment ('bending torque') acting on the intervertebral discs and ligaments was quantified by comparing dynamic measurements of lumbar flexion, obtained with the '3-Space Isotrak', with the normalised bending properties of cadaveric lumbar spines. Results showed that stoop lifting reduced the peak extensor moment by about 10% compared to squat lifting, but increased the bending torque by about 75%. Extensor moment and bending torque both increased substantially with increasing mass, bulk and distance from the feet. Non-sagittal plane lifts increased the bending torque by about 30%. The fastest lifts increased peak extensor moment by 60% but did not increase bending torque. We conclude that complex spinal loading during lifting tasks depends as much on the speed of movement, and the size and position of the object lifted, as on its mass. Analyses of spinal loading which consider only compressive forces do not give a full indication of the risk of injury to the intervertebral discs and ligaments.

Effect of discussion and deliberation on the public's views of priority setting in health care: focus group study

OBJECTIVE

To investigate the extent to which people change their views about priority setting in health care as a result of discussion and deliberation.

DESIGN

A random sample of patients from two urban general practices was invited to attend two focus group meetings, a fortnight apart.

SETTING

North Yorkshire Health Authority.

SUBJECTS

60 randomly chosen patients meeting in 10 groups of five to seven people.

MAIN OUTCOME MEASURES

Differences between people's views at the start of the first meeting and at the end of the second meeting, after they have had an opportunity for discussion and deliberation, measured by questionnaires at the start of the first meeting and the end of the second meeting.

RESULTS

Respondents became more reticent about the role that their views should play in determining priorities and more sympathetic to the role that healthcare managers play. About a half of respondents initially wanted to give lower priority to smokers, heavy drinkers, and illegal drug users, but after discussion many no longer wished to discriminate against these people.

CONCLUSION

The public's views about setting priorities in health care are systematically different when they have been given an opportunity to discuss the issues. If the considered opinions of the general public are required, surveys that do not allow respondents time or opportunity for reflection may be of doubtful value.

Spine biomechanics

Current trends in spine research are reviewed in order to suggest future opportunities for biomechanics. Recent studies show that psychosocial factors influence back pain behaviour but are not important causes of pain itself. Severe back pain most often arises from intervertebral discs, apophyseal joints and sacroiliac joints, and physical disruption of these structures is strongly but variably linked to pain. Typical forms of structural disruption can be reproduced by severe mechanical loading in-vitro, with genetic and age-related weakening sometimes leading to injury under moderate loading. Biomechanics can be used to quantify spinal loading and movements, to analyse load distributions and injury mechanisms, and to develop therapeutic interventions. The authors suggest that techniques for quantifying spinal loading should be capable of measurement "in the field" so that they can be used in epidemiological surveys and ergonomic interventions. Great accuracy is not required for this task, because injury risk depends on tissue weakness as much as peak loading. Biomechanical tissue testing and finite-element modelling should complement each other, with experiments establishing proof of concept, and models supplying detail and optimising designs. Suggested priority areas for future research include: understanding interactions between intervertebral discs and adjacent vertebrae; developing prosthetic and tissue-engineered discs; and quantifying spinal function during rehabilitation. "Mechanobiology" has perhaps the greatest future potential, because spinal degeneration and healing are both mediated by the activity of cells which are acutely sensitive to their local mechanical environment. Precise characterisation and manipulation of this environment will be a major challenge for spine biomechanics.

‘STRESS’ DISTRIBUTIONS INSIDE INTERVERTEBRAL DISCS

We investigated the distribution of compressive ‘stress’ within cadaver intervertebral discs, using a pressure transducer mounted in a 1.3 mm diameter needle. The needle was pulled along the midsagittal diameter of a lumbar disc with the face of the transducer either vertical or horizontal while the disc was subjected to a constant compressive force. The resulting ‘stress profiles’ were analysed in order to characterise the distribution of vertical and horizontal compressive stress within each disc. A total of 87 discs from subjects aged between 16 and 87 years was examined.

Our results showed that age-related degenerative changes reduced the diameter of the central hydrostatic region of each disc (the ‘functional nucleus’) by approximately 50%, and the pressure within this region fell by 30%. The width of the functional annulus increased by 80% and the height of compressive ‘stress peaks’ within it by 160%. The effects of age and degeneration were greater at L4/L5 than at L2/L3, and the posterior annulus was affected more than the anterior. Age and degeneration were themselves closely related, but the stage of degeneration had the greater effect on stress distributions.

We suggest that structural changes within the annulus and endplate lead to a transfer of load from the nucleus to the posterior annulus. High ‘stress’ concentrations within the annulus may cause pain, and lead to further disruption.

Lipoprotein-acid mucopolysaccharide complexes of human atherosclerotic lesions

Lipoprotein-acid mucopolysaccharide complexes occurring in different types of human atherosclerotic lesions were isolated and partially characterized. Complexes from fatty streaks and fibrous plaques were extracted from pooled tissues with 0.15 M NaCl, purified by gel filtration, and fractionated by ultracentrifugation. Both low and very low density lipoproteins were present; low density lipoprotein was predominant. The complexes were analyzed for uronic acid, cholesterol, phospholipid, and Ca-2+ contents; there was no significant difference in the relative molar ratios between complexes from fatty streaks and fibrous plaques. Acid mucopolysaccharides were isolated from the complexes and identified by electrophoresis and enzymatic studies. Chondroitin sulfate C and hyaluronic acid were found in complexes from fatty streaks and fibrous plaques. Heparin was detected only in fibrous plaques.

Discogenic origins of spinal instability

STUDY DESIGN

Cadaveric motion segment experiment.

OBJECTIVE

To show how two physical aspects of disc degeneration (dehydration and endplate disruption) contribute to spinal instability.

SUMMARY OF BACKGROUND DATA

The origins of spinal instability and its associations with back pain are uncertain. METHODS.: Twenty-one cadaveric thoracolumbar motion segments aged 48 to 90 years were secured in cups of dental plaster and loaded simultaneously in bending and compression to simulate full flexion, extension, and lateral bending movements. Vertebral movements, recorded using a two-dimensional "MacReflex" motion analysis system, were analyzed to calculate neutral zone (NZ), range of motion (ROM), bending stiffness (BS), horizontal translational movements, and the location of the center of rotation (COR). Intradiscal "stresses" were measured by pulling a miniature pressure transducer through the disc along its midsagittal diameter. All experiments were repeated after each of two treatments, which simulated physical aspects of disc degeneration: creep loading to dehydrate the disc and compressive overload to disrupt the endplate. Results were analyzed using ANOVA and linear regression.

RESULTS

Motion segment height was reduced by 1.0 (SD 0.3) mm during creep and by a further 1.7 (0.6) mm after endplate disruption. In flexion and lateral bending, the combined treatments increased NZ and ROM by 89% to 298%, and increased the "instability index" (NZ/ROM) by 43% to 61%. Translational movements increased by 58% to 86%, whereas BS decreased by 42% to 48%. In extension, ROM and NZ were little affected, although the COR moved closer to the apophyseal joints. Measures of instability increased most in lateral bending, and following endplate disruption. Stress concentrations in the posterior anulus fibrosus increased markedly after endplate disruption.

CONCLUSIONS

Two physical aspects of disc degeneration (dehydration and endplate disruption) cause marked segmental instability. Back pain associated with instability may be attributable to stress concentrations in degenerated discs.

Intervertebral disc degeneration can lead to "stress-shielding" of the anterior vertebral body: a cause of osteoporotic vertebral fracture?

STUDY DESIGN

Mechanical testing of cadaveric lumbar motion segments.

OBJECTIVES

To test the hypothesis that degenerative changes in the intervertebral discs can influence loading of the anterior vertebral body in a manner that makes it vulnerable to fracture.

SUMMARY OF BACKGROUND DATA

Measurements of systemic bone loss do not fully explain the patterns of osteoporotic vertebral fractures.

METHODS

Thirty-three cadaveric lumbar motion segments (aged 19-82 years) were subjected to 2 kN of compressive loading while positioned to simulate habitual erect standing postures and forwards bending. Intradiscal stresses were measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. "Stress profiles" were then integrated over area to calculate the force acting on the anterior and posterior halves of the vertebral body. These forces were subtracted from the applied 2 kN to determine the compressive force on the neural arch.

RESULTS

In motion segments with nondegenerated discs, <5% of the compressive force was resisted by the neural arch, and forces on the vertebral body were always distributed evenly, irrespective of posture. However, with severely degenerated discs, neural arch load-bearing increased to 40% in the erect posture, and the compressive force on the vertebral body was concentrated anteriorly in forwards bending, and posteriorly in erect posture.

CONCLUSIONS

Severe disc degeneration causes the anterior vertebral body to be stress-shielded during the usual erect posture, and yet severely loaded whenever the spine is flexed. This could help to explain why this region is frequently the site of osteoporotic fracture, and why forward bending movements often precipitate the injury.

Prescribing by general practitioners after an osteoporotic fracture

OBJECTIVES

Osteoporosis is a major cause of morbidity and cost. Patients sustaining one osteoporotic fracture are at increased risk of having another fracture. The objective of this study was to examine the use of "bone drugs" for the prevention of further osteoporotic fractures among patients who have had a "typical" osteoporotic fracture.

METHODS

This study took a random sample of 300 women aged 50 and over who had sustained either a vertebral, hip or Colles fracture in 1995 from the General Practice Research Database (GPRD) and compared their use of bone drugs with 300 age and practice matched controls.

RESULTS

Compared with age and practice matched control patients only vertebral fracture patients showed a statistically significant increase in the use of bone drugs in the year after fracture (39% and 2% for cases and controls respectively; 95% CI of difference 27% to 47%). Etidronate was the most commonly used compound.

CONCLUSION

The majority of patients sustaining an osteoporotic fracture are not prescribed any pharmaceutical agents for the secondary prevention of fracture one year after a primary fracture.

Time-dependent changes in the lumbar spine's resistance to bending

OBJECTIVE: To show how time-related factors might affect the risk of back injury. DESIGN: Mechanical testing of cadaveric lumbar motion segments. BACKGROUND: High bending stresses acting on the lumbar spine are associated with injuries to the intervertebral discs and ligaments. Since these soft tissues are viscoelastic, the bending stress ('bending moment') must depend on the speed of movement and the duration of loading, but this has not previously been quantified. METHODS: Forty-five cadaveric lumbar segments, consisting of two vertebrae and the intervening disc and ligaments, were loaded in combined bending and compression in order to simulate movements and postures in living people. The relationship between flexion angle and bending moment was determined at different loading rates, and after sustained loading in bending and in compression. RESULTS: Rapid flexion movements increased the peak bending moment by 10-15% compared to slow movements. On average, repeated flexion over a period of 5 min reduced the peak bending moment by 17%, and 5 min of sustained flexion reduced it by 42%. Two hours of compressive creep loading reduced the height of the intervertebral discs by 1.1 mm, increased the range of flexion by 12%, and reduced peak bending moment by 41%. CONCLUSIONS: The scale of these changes suggests that, in life, the risk of bending injury to the lumbar discs and ligaments will depend not only on the loads applied to the spine, but also on loading rate and loading history. RELEVANCE: The results show how time-dependent factors can increase the risk of bending injury to the osteoligamentous lumbar spine.

Biochemical effects of dithiolthiones

Administration of dithiolthiones to mice in single intragastric doses (2-4 mmol/kg body weight) or in the diet (0.5% for 14 days), and to rats in the diet (0.1% for 14 days) was found to increase glutathione levels and the activities of a number of enzymes in various tissues including the liver and lung. The enzymes affected were glutathione transferases (with chlorodinitrobenzene or dichloronitrobenzene), quinone and glutathione reductase, and glucose-6-phosphate and 6-phosphogluconate dehydrogenase, all of which are involved directly or indirectly in the detoxication of xenobiotics, including carcinogens. The dithiolthiones tested in mice were oltipraz, ADT, 116L and 129L, and in rats, oltipraz. Intragastric administration of dithiolthiones (oltipraz, ADT or 116L; two doses each of 1 g/kg body weight) did not increase glutathione levels or enzyme activities in murine mammary adenocarcinoma transplants. Increases in glutathione levels and enzyme activities similar to those found with dithiolthiones were observed when a semi-synthetic diet containing 10-40% lyophilized cabbage was fed to mice for 30 days. Dithiolthiones that are present in cabbage may play a role in the protective actions of diets high in vegetables against the toxic actions of xenobiotics. The biochemical effects of dithiolthiones reported here may account for the protective actions of these compounds.