Cartilaginous endplate avulsion is associated with modic changes and endplate defects, and residual back and leg pain following lumbar discectomy.

OBJECTIVE: While cartilaginous endplate (CEP) avulsion is a common finding in discectomy due to lumbar disc herniation, its roles in residual back and leg pain, associations with Modic changes (MCs) and endplate defects (EPD) remain unknown. DESIGN: Patients with a single-level lumbar disc herniation who underwent endoscopic discectomy were studied. On MR images, the adjacent endplates of the herniated disc were assessed for MCs and EPD. The presence of CEP avulsion was examined under endoscopic and visualized inspection. Back and leg pain were evaluated by a numeric rating scale (NRS) and the Oswestry Disability Index. Associations of CEP avulsion with adjacent MCs, EPD, and residual back and leg pain were examined. In addition, histological features of avulsed CEP were determined using gross staining and immunohistochemical methods. RESULTS: A total of 386 patients were included. CEP avulsion was found in 166 (43%) patients, and adjacent MCs and EPD were observed in 117 (30.3%) and 139 (36%) patients. The presence of CEP avulsion was associated with greater age, adjacent MCs (OR = 2.60, 95%CI [1.61-4.19]) and EPD (OR = 1.63, 95%CI [1.03-2.57]). Among the 187 patients with ≥2 years follow-up, CEP avulsion was associated with residual back pain (OR = 2.49, 95%CI [1.29-4.82]) and leg pain (OR = 2.25, 95%CI [1.04-4.84]). Histologically, the avulsed CEP was characterized by multiple defects, apparent inflammation, and nucleus invasion, as well as the upregulation of IL-1ß, caspase-1, and NLRP3 inflammasome. CONCLUSION: CEP avulsion was associated with MCs, EPD, and residual back and leg pain after discectomy, which may be attributed to NLRP3 inflammasome related inflammations.

Do variations in paraspinal muscle morphology and composition predict low back pain in men?

This longitudinal study aimed to clarify the longstanding controversy over whether variations in paraspinal muscle morphology (e.g., size, composition and asymmetry) are predictors of low back pain (LBP). A sample of 99 Finnish men were included in this population-based longitudinal study. Data were collected through a structured interview, physical examination and magnetic resonance imaging (MRI). Baseline measurements of the lumbar multifidus and erector spinae muscles were obtained from T2-weighted axial images at L3-L4 and L5-S1, and interview data were obtained at baseline, 1- and 15-year follow-ups. Few of the paraspinal muscle parameters investigated were predictors of change in LBP frequency, intensity or sciatica at 1- and 15-year follow-ups in the population-based sample, and findings were not consistent across muscles and spinal levels. However, greater multifidus and erector spinae fatty infiltration at L5-S1 was associated with a higher risk of having continued, frequent, persistent LBP at 1-year follow-up. None of the relationships observed was confounded by body mass index or the amount of physical activity at work or leisure. This longitudinal study provided evidence that variations in paraspinal muscle morphology on MRI have a limited, if not uncertain, role in the short- and long-term predictions of LBP in men.

Ageing workers with work-related musculoskeletal injuries.

BACKGROUND: Older workers often take longer to recover and experience more missed workdays after work-related injuries, but it is unclear why or how best to intervene. Knowing the characteristics of older injured workers may help in developing interventions to reduce the likelihood of work disability. AIMS: To describe and compare several characteristics between younger and middle-aged working adults (25-54 years), adults nearing retirement (55-64 years) and adults past typical retirement (≥65 years), who sustained work-related musculoskeletal injuries. METHODS: In this cross-sectional study, Alberta workers' compensation claimants with subacute and chronic work-related musculoskeletal injuries were studied. A wide range of demographic, employment, injury and clinical characteristics were investigated. Descriptive statistics were computed and compared between the age groups. RESULTS: Among 8003 claimants, adults 65 years or older, compared to those 25-54 and 55-64 years, had lower education (16 versus 10 and 12%, P < 0.001) and were more likely to work in trades, transport and related occupations (50 versus 46 and 44%, P < 0.001), to have less offers of modified work (57 versus 39 and 42%, P < 0.001), more fractures (18 versus 14 and 11%, P < 0.001) and no further rehabilitation recommended after assessment (28 versus 18 and 20%, P < 0.01). CONCLUSIONS: Injured workers past typical retirement age appeared to be a disadvantaged group with significant challenges from a vocational rehabilitation perspective. They were less likely to have modified work options available or be offered rehabilitation, despite having more severe injuries.

Does functional capacity evaluation predict recovery in workers' compensation claimants with upper extremity disorders?

OBJECTIVES: Functional capacity evaluations (FCEs) are commonly used to determine return-to-work readiness and guide decision making following work related injury, yet little is known of their validity. The authors examined performance on the Isernhagen Work Systems' FCE as a predictor of timely and sustained recovery in workers' compensation claimants with upper extremity disorders. A secondary objective was to determine whether FCE is more predictive in claimants with specific injuries (that is, fracture) as compared to less specific, pain mediated disorders (that is, myofascial pain). METHODS: The authors performed a longitudinal study of 336 claimants with upper extremity disorders undergoing FCE. FCE indicators were maximum performance during handgrip and lift testing, and the number of tasks where performance was rated below required job demands. Outcomes investigated were days receiving time-loss benefits (a surrogate of return to work or work readiness) in the year following FCE, days until claim closure, and future recurrence defined as whether benefits restarted, the claim reopened, or a new upper extremity claim was filed. Cox and logistic regression were used to determine the prognostic effect of FCE crudely and after controlling for potential confounders. Analysis was performed separately on claimants with specific and pain mediated disorders. RESULTS: Most subjects (95%) experienced time-loss benefit suspension within one year following FCE. The one year recurrence rate was 39%. Higher lifting performance was associated with faster benefit suspension and claim closure, but explained little variation in these outcomes (r2 = 1.2-11%). No FCE indicators were associated with future recurrence after controlling for confounders. Results were similar between specific injury and less specific groups. CONCLUSIONS: Better FCE performance was a weak predictor of faster benefit suspension, and was unrelated to sustained recovery. FCE was no more predictive in claimants with specific pathology and injury than in those with more ambiguous, pain mediated conditions.

Material handling performance of patients with chronic low back pain during functional capacity evaluation: a comparison between three countries.

PURPOSE: Functional Capacity Evaluations (FCEs) are batteries of tests designed to measure patients' ability to perform work-related activities. Although FCEs are used worldwide, it is unknown how patients' performances compare between countries or settings. This study was performed to explore similarities and differences in FCE performance of patients with chronic low back pain (CLBP) between three international settings that utilize the same FCE protocol. METHODS: Standardized FCEs were performed on three cohorts of patients with CLBP: A sample from an outpatient rehabilitation context in The Netherlands (n = 121), a Canadian sample in a Worker's Compensation context (n = 273), and a Swiss sample in an inpatient rehabilitation context (n = 170). Patients were undergoing FCE as part of their usual clinical care. Means and standard deviations of maximum performance on the FCE material handling items were calculated and differences compared using ANOVA. Multivariable linear regression was used to determine the relationship between country of origin and FCE performance while controlling for potential confounders including, age, sex, duration of back pain problems, and self-reported pain and disability ratings. RESULTS: Compared to the Dutch sample, the mean performance of patients in the Canadian and Swiss samples was consistently lower on all FCE items. This association remained statistically significant after controlling for potential confounders. CONCLUSIONS: Considerable differences were observed between settings in maximum weight handled on the various FCE items. Future FCE research should examine the effects of a number of potentially influential factors, including variability in evaluator judgements across settings, the evaluator-patient interaction and patients' expectations of the influence of FCE results on disability compensation.

Determinants of psychomotor speed among 61 pairs of adult male monozygotic twins.

BACKGROUND: Declining psychomotor speed is an indicator of the aging process, and it is influenced by genetics and environmental factors. The present study examined the relative effects of familial aggregation (reflecting a combination of genetics and early environmental influences), and occupational, lifestyle, and health factors on psychomotor speed. METHODS: Hand and foot psychomotor speed was studied with 61 pairs of monozygotic male twins aged 35-67 years from the population-based Finnish Twin Cohort. The determinants of visual simple and choice reaction times were analyzed with multiple regression analysis. RESULTS: Familial aggregation, reflecting genetic influences and shared environmental effects, explained in mean 47% of decision times, 31% of movement times, and 37% of response times (decision time and movement time combined). Age, cardiovascular morbidity, lifetime vigorous and frequent exercise participation, and mean lifetime daily hours sitting at work explained 0-19% of hand psychomotor speed and 0-10% of foot speed, depending on the outcome. The predicted increase in decision times due to the presence of cardiovascular morbidity was 11-35 ms. The predicted increase for hand and contralateral foot response times between ages 45 and 55 was 18-41 ms. Smaller effects were noted for each year of strenuous exercise and each hour/day of average lifetime sitting at work. CONCLUSIONS: Results indicate that cardiovascular status, age, strenuous exercise, and work play a role in psychomotor speed, but a rather minor one. In contrast, genetic and shared early environmental influences as revealed from familial aggregation were relatively strong, yet a major proportion of the variability in psychomotor speed remained unexplained.

Disc degeneration and bone density in monozygotic twins discordant for insulin-dependent diabetes mellitus.

The effects of insulin-dependent diabetes mellitus on bone density and connective tissue degeneration have theoretical interest and practical relevance. Several experimental studies in animals have demonstrated the harmful effects of insulin deficiency on connective tissues. However, clinical studies in humans have produced somewhat contradictory results, most likely due to difficulties controlling for general degeneration and factors associated with diabetes. In nine pairs of monozygotic twins discordant for insulin-dependent diabetes mellitus, we compared femoral and lumbar bone mineral density (assessed by dual-energy x-ray absorptiometry) and spinal degeneration (assessed by magnetic resonance imaging). The bone densities were, on average, 0.1-0.3% lower (p = 0.87-0.96) in diabetic patients. However, after controlling for smoking, we found that the bone density in the femoral neck was 2.5% (0.025 g/cm2) lower in diabetic individuals than in their twins (p = 0.09). The five magnetic resonance imaging parameters used to evaluate disc degeneration did not differ between diabetic patients and their twins. In conclusion, our results provide no evidence that insulin-dependent diabetes mellitus has any major effect on bone density or disc degeneration.

The effect of lifelong exercise on psychomotor reaction time: a study of 38 pairs of male monozygotic twins.

PURPOSE: The aim was to study the effect of lifetime physical activity on psychomotor speed. METHODS: Foot and dominant hand visual simple and choice psychomotor reaction times were studied among monozygotic twins (38 pairs) aged 35-69, discordant for lifetime exercise histories. RESULTS: There was a trend that some components of psychomotor reaction time were faster for frequent than for occasional exercisers, but the findings were not consistent for the hand and feet. After controlling for occupational physical activity, only choice decision time for the hand (26 ms, P < 0.01) and choice reaction time for the contralateral foot (51 ms, P < 0.05) both remained 7% faster. There was no trend for systematic differences in reaction times between twins engaged in regular exercise versus their siblings exercising infrequently. CONCLUSIONS: Results suggest a somewhat smaller effect of exercise than reported in previous studies. Reaction time may be significantly affected only by vigorous, frequent exercise. Thus, health promotion through exercise may be unlikely to have notable effects on reaction time.

Lifetime exercise and disk degeneration: an MRI study of monozygotic twins.

Participation in some competitive sports has been shown to increase disk degeneration; however, the long-term effects of recreational physical activities are unclear. We investigated the effects of endurance exercise and power sports on disk degeneration in monozygotic male twins with contrasting lifetime exercise histories. The effects of endurance exercise were studied in 22 discordant twin pairs (mean lifetime frequencies of 3.9 vs 1.1 times/wk), and the effects of power sports were investigated in 12 discordant pairs (2,300 vs 200 h of weightlifting). The age range of the twins was from 35 to 69 yr. No differences in MRI findings between co-twins discordant for endurance exercise were found at any of the spinal regions. Subjects with more power sport involvement had greater disk degeneration in the T6-T12 region (P < 0.03), but similar findings were not present in the lumbar spine. Controlling for recalled back injuries, occupational loading, smoking, and driving did not significantly affect the results. No signs of beneficial or harmful effects of lifetime endurance exercise on disk degeneration were seen. Increased power sport participation was associated with slightly greater disk degeneration in the lower thoracic spine, but not in the lumbar spine.

Similarities in degenerative findings on magnetic resonance images of the lumbar spines of identical twins.

Although the etiology of most degenerative changes in the lumbar spine is unclear, genetic factors may play an important role. To investigate this link, we reviewed magnetic resonance images of the lumbar spines of identical twins to assess the degree of similarities in degenerative findings in the discs. Observers who were blinded to twinship evaluated sagittal T1-weighted and T2-weighted magnetic resonance images of the lumbar spines of forty male identical twins (twenty pairs) with respect to changes in the end plates, desiccation of the discs, bulging or herniated discs, and decrease in the height of the disc space. Similarities between co-twins were significantly greater than would be expected by chance. Whereas smoking status and age explained 0 to 15 per cent of the variability in the various degenerative findings in the discs, 26 to 72 per cent of the variability was explained with the addition of a variable representing co-twin status. These findings are compatible with a marked genetic influence and warrant further investigation.

The influence of occupation on lumbar degeneration.

In many countries, back problems have been defined as occupational injuries. The belief underlying this injury model is that back symptoms are caused primarily by work-related mechanical factors that damage the structures of the spine, either through a single incident or repeated loading. Although the etiopathogenesis of degenerative findings in the disc and their relation to pain are poorly understood, changes in the disc are suspected of underlying many back symptoms. The focus of this article is on examining the relation between occupational factors and disc degeneration. Occupational factors suspected of accelerating spinal degeneration include accident-related trauma; heavy physical loading and materials handling, including lifting, bending, and twisting; prolonged sitting; and sustained nonneutral work postures and vehicular driving. There is evidence to suggest that occupational exposures have an effect on disc degeneration. However, these factors explain little of the variability in degeneration found in the adult population. Furthermore, the lack of a clear dose-response relation between time spent in various occupational loading conditions and degenerative findings adds to doubts about a strong causal link. The contribution of suspected occupational risk factors appears to be particularly modest when compared with familial influences, which reflect the combined effects of genes and early childhood environment. These findings challenge the dominant role assumed for occupational loading in disc degeneration and associated back problems, and suggest a more complex etiology.

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins.

STUDY DESIGN: Retrospective cohort. OBJECTIVES: To determine the relative contributions of anthropometric factors, physical activity, back and neck pain, overall health, and familial aggregation (the combined effects of genetics and childhood environment) to different measurements of adult back muscle function. SUMMARY OF BACKGROUND DATA: Many methods of muscle testing are employed in the attempt to predict, prevent, treat, and rehabilitate low back pain. Poor correlations between the test results suggest that they are measuring different attributes and have different determinants. METHODS: Muscle function tests, magnetic resonance images, and a detailed interview were obtained in 65 pairs of monozygotic male twins. RESULTS: Familial aggregation was the strongest determinant of isokinetic and psychophysical lifting and static back endurance, explaining 56%, 32%, and 15% of the variances, respectively, beyond that which age alone predicted. Back pain and physical loading in work and leisure explained 2%, 0%, and 23% of the variances. CONCLUSIONS: The combined effects of genetics and childhood environment play a dominant role in determining adult back muscle function. Physical loading at work and leisure, back and neck pain history, overall health, and anthropometric factors had a comparatively minor role, suggesting that the potential of interventions to increase and sustain back muscle function in healthy adults, measured through these tests, may be limited. The relative contributions of constitutional, behavioral, and environmental factors differ substantially in the three tests, and provide insights into what these commonly used tests actually reflect or measure. This knowledge can be used to guide more appropriate selection and interpretation of results of back muscle function tests.

Digital assessment of MRI for lumbar disc desiccation. A comparison of digital versus subjective assessments and digital intensity profiles versus discogram and macroanatomic findings.

During magnetic resonance imaging, a vast amount of digital data on anatomic structures is translated into images, which are then assessed subjectively. The development of an objective, sensitive method to directly assess the digital data would have clear benefits, particularly for clinical research on disc degeneration. The study goals were to develop a method of digital assessment of disc desiccation and to compare digital signal intensity profiles with discographic patterns and macroanatomic findings. Proton density-weighted MRIs were obtained from 45 males (9-77 years) and digital analysis was done with a freely selectable region of interest facility. The adjacent cerebrospinal fluid (CSF) was used as a reference for disc signal-intensity scores, and the disc to CSF-intensity ratio provided "adjusted digital scores." The CSF-adjusted digital method yielded reproducible scores that correlated with the subjective assessments. However, the CSF-adjusted digital scores were more sensitive than the subjective assessments, identifying findings that otherwise were undetected in younger subjects. Additionally, 10 cadaveric spines were evaluated using MRI with T2 and proton density-weighted sequences, discography, and macroanatomic dissection. MRI disc-intensity profiles were determined along a midsagittal line drawn through the disc. The profile of the digital scores along this line was then compared with discograms and macroanatomic sections. In all cases of disc degeneration on discograms, changes were present in the intensity profile. Based on both the living subjects and the cadaveric specimens, the digital assessments and disc intensity profiles appear to demonstrate disc degeneration, particularly in early stages.

1995 Volvo Award in clinical sciences. Determinants of lumbar disc degeneration. A study relating lifetime exposures and magnetic resonance imaging findings in identical twins.

STUDY DESIGN: Retrospective cohort. OBJECTIVES: To investigate the effects of lifetime exposure to commonly suspected risk factors on disc degeneration using magnetic resonance imaging, and to estimate the effects of these suspected risk factors relative to age and familial aggregation, reflecting genetic and shared environmental influences. SUMMARY OF BACKGROUND DATA: Structural and biochemical changes associated with disc degeneration are suspected as the underlying conditions of many back-related symptoms. Little is known about the determinants of disc degeneration. METHODS: Based on lifetime discordance in suspected environmental risk factors for disc degeneration, 115 male identical twin pairs were selected. An in-depth interview was conducted of occupational and leisure time physical loading, driving, and smoking. Disc degeneration was evaluated using observational and digital magnetic resonance imaging assessment methods. RESULTS: Heavier lifetime occupational and leisure physical loading was associated with greater disc degeneration in the upper lumbar levels (P = 0.055 - 0.001), whereas sedentary work was associated with lesser degeneration (P = 0.006). These univariate associations did not reach statistical significance in the lower lumbar region. In multivariate analyses of the upper lumbar levels, the mean job code explained 7% of the variability in observational disc degeneration scores; the addition of age explained 16%, and familial aggregation improved the model such that 77% of the variability was explained. In the lower lumbar levels, leisure time physical loading entered the multivariate model, explaining 2% of the variability. Adding age explained 9%, and familial aggregation raised the variability in disc degeneration scores explained to 43%. CONCLUSIONS: The present study findings suggest that disc degeneration may be explained primarily by genetic influences and by unidentified factors, which may include complex, unpredictable interactions. The particular environmental factors studied, which have been among those most widely suspected of accelerating disc degeneration, had very modest effects.

1991 Volvo Award in clinical sciences. Smoking and lumbar intervertebral disc degeneration: an MRI study of identical twins.

The primary objective of this study was to determine whether disc degeneration, as assessed through magnetic resonance imaging, is greater in smokers than in nonsmokers. To control for the maximum number of potentially confounding variables, pairs of identical twins highly discordant for cigarette smoking were selected as study subjects. Data analyses revealed 18% greater mean disc degeneration scores in the lumbar spines of smokers as compared with nonsmokers. The effect was present across the entire lumbar spine, implicating a mechanism acting systemically. This investigation demonstrates the efficiency of using carefully selected controls in studying conditions of multifactorial etiology, such as disc degeneration.

The long-term effects of physical loading and exercise lifestyles on back-related symptoms, disability, and spinal pathology among men.

STUDY DESIGN: Historical cohort, including selected subgroups. OBJECTIVES: To understand the long-term effects of exercise on back-related outcomes, back pain, sciatica, back-related hospitalizations, pensions, and magnetic resonance imaging findings were studied among former elite athletes. SUMMARY OF BACKGROUND DATA: Exercise and sports participation have become increasingly popular, as have recommendations of exercises for back problems, but little is known about their long-term effects. METHODS: Questionnaires were returned by 937 former elite athletes and 620 control subjects (83% response rate). Identification codes allowed record linkage to hospital discharge and pension registers. Magnetic resonance images were obtained of selected subgroups with contrasting physical loading patterns. RESULTS: Odds ratios for back pain were lower among athletes than among control subjects, with significant differences in endurance, sprinting and game sports, and wrestling and boxing. No differences in the occurrence of sciatica or in back-related pensions and hospitalizations were seen. When comparing lumbar magnetic resonance images of 24 runners, 26 soccer players, 19 weight lifters, and 25 shooters, disc degeneration and bulging were most common among weight lifters; soccer players had similar changes in the L4-S1 discs. No significant differences were seen in the magnetic resonance images of runners and shooters. CONCLUSIONS: Maximal weight lifting was associated with greater degeneration throughout the entire lumbar spine, and soccer with degeneration in the lower lumbar region. No signs of accelerated disc degeneration were found in competitive runners. However, back pain was less common among athletes than control subjects and there were no significant differences in hospitalizations or pensions. No benefits were shown for vigorous exercise compared with lighter exercise with respect to back findings.

Magnetic resonance imaging findings and their relationships in the thoracic and lumbar spine. Insights into the etiopathogenesis of spinal degeneration.

STUDY DESIGN: Descriptive epidemiologic study about magnetic resonance imaging findings in the spine. OBJECTIVES: To describe the prevalence of magnetic resonance imaging findings in a general population at spinal levels T6-S1, and to examine the relationships of these findings within each spinal level and between levels. SUMMARY OF BACKGROUND DATA: The prevalence of specific findings and the associations between findings and spinal levels can provide general insights into the etiopathogenesis of spinal degeneration. METHODS: Subjects consisted of 232 men from a population sample (mean age 49.3 years). Signal intensity, disc bulging, disc herniation, and endplate irregularities were among 11 findings assessed from magnetic resonance images. RESULTS: The disc signal intensities were assessed to be lowest in the lumbar and middle thoracic regions. Disc bulging and disc height narrowing were most common in the lower levels of both the thoracic and lumbar regions. All magnetic resonance imaging findings except herniations and endplate irregularities were clearly associated with age. Osteophytes were most highly associated with disc bulging in levels T6-L3, and with endplate irregularities in the lower lumbar levels. Disc herniations were not consistently associated with any other findings. The disc levels that most highly correlated are grouped as follows: T6-T10, T10-L4, and L4-S1. CONCLUSIONS: With the exception of endplate irregularities and herniations, the magnetic resonance imaging findings appeared to be associated with the same pathogenic process. The interaction of mechanical factors and spinal structures varies between spinal levels, and the degeneration common in the lower parts of the thoracic and lumbar spine could be an outcome of vulnerability for torsional forces. Some gross guidelines for grouping findings can be drawn from disc level correlations.

Observer variability in the assessment of disc degeneration on magnetic resonance images of the lumbar and thoracic spine.

STUDY DESIGN: Intraobserver and interobserver reproducibility study. OBJECTIVE: This study investigates the variability in the interpretation of degenerative disc findings using magnetic resonance imaging. SUMMARY OF BACKGROUND DATA: Magnetic resonance imaging has been used for years in clinical diagnostics, primarily to investigate disc herniation and spinal stenosis. Less attention has been paid to other disc findings and their assessment reliability. METHODS: Three independent readers evaluated magnetic resonance images of the lumbar and the lower and middle thoracic spines of 122 subjects by grading 12 aspects of the intervertebral discs and adjacent endplates using written definitions and example images. Images of 20 subjects were reevaluated for the assessment of intraobserver agreement. RESULTS: Agreement was highest in the lower lumbar and poorest in the middle thoracic spine. Intraobserver agreement was generally fair to excellent for almost all variables in the lumbar and lower thoracic spine (most intraclass correlation and kappa coefficients for these regions were above 0.70). Interobserver agreement was notably lower than intraobserver agreement, except for osteophytes and endplate defects in some regions. CONCLUSIONS: Intraobserver agreement in the evaluation of disc degeneration was at an acceptable level, in general, in the lumbar and lower thoracic spine. However, assessments were substantially more variable between readers, which limits comparisons of evaluations between different readers.

Intragenic polymorphisms of the vitamin D receptor gene associated with intervertebral disc degeneration.

STUDY DESIGN: A study in genetic epidemiology of disc degeneration, based on lifetime exposure data, findings on magnetic resonance imaging, and genotyping of intragenic markers. OBJECTIVES: To pursue the potential correlation between common allelic variations in the vitamin D receptor locus and degeneration of the intervertebral disc. SUMMARY OF BACKGROUND DATA: Familial aggregation has been observed in intervertebral disc degeneration, but the relative significance of the genetic component and shared environmental influences is unknown. The identification of relevant candidate genes associated with disc degeneration would specify a genetic component and increase our understanding of the etiopathogenesis of disc degeneration. METHODS: From the population-based Finnish Twin cohort, 85 pairs of male monozygotic twins were selected based on exposure to suspected risk factors for disc degeneration. Interview data were gathered on relevant lifetime exposures, and thoracic and lumbar disc degeneration was determined through quantitative and qualitative assessments of signal intensity on magnetic resonance imaging, and qualitative assessments of disc bulging and disc height narrowing. Possible associations were examined between disc degeneration measures and two polymorphisms of the coding region of the vitamin D receptor locus. RESULTS: Two intragenic polymorphisms of the vitamin D receptor gene revealed an association with disc degeneration. Quantitatively assessed signal intensities of thoracic and lumbar (T6-S1) discs were 12.9% worse in men with the Taql tt genotype and 4.5% worse in men with the Tt genotype, compared with signal intensity in men with the TT genotype (age adjusted P = 0.003). A similar pattern was found between disc signal intensity and Fokl genotypes; men with the ff and Ff genotypes had mean signal intensities that were 9.3% and 4.3% lower, respectively, than those in men with FF genotypes (age-adjusted P = 0.006). The summary scores of qualitatively assessed signal intensity, bulging, and disc height were 4.0% and 6.9% worse in men with Ff and ff genotypes, respectively, when compared with those in men with the FF genotype (age-adjusted P = 0.029). CONCLUSION: Specific vitamin D receptor alleles were associated with intervertebral disc degeneration as measured by T2-weighted signal intensity, demonstrating for the first time, the existence of genetic susceptibility to this progressive, age-related degenerative process.

A prospective study of work perceptions and psychosocial factors affecting the report of back injury.

A longitudinal, prospective study was conducted on 3,020 aircraft employees to identify risk factors for reporting acute back pain at work. The premorbid data included individual physical, psychosocial, and workplace factors. During slightly more than 4 years of follow-up, 279 subjects reported back problems. Other than a history of current or recent back problems, the factors found to be most predictive of subsequent reports in a multivariate model were work perceptions and certain psychosocial responses identified on the Minnesota Multiphasic Personality Inventory (MMPI). Subjects who stated that they "hardly ever" enjoyed their job tasks were 2.5 times more likely to report a back injury (P = 0.0001) than subjects who "almost always" enjoyed their job tasks. The quintile of subjects scoring highest on Scale-3 (Hy) of the MMPI were 2.0 times more likely to report a back injury (P = 0.0001) than subjects with the lowest scores. The multivariate model, including job task enjoyment, MMPI Scale-3, and history of back treatment, revealed that subjects in the highest risk group had 3.3 times the number of reports in the lowest risk group. These findings emphasize the importance of adopting a broader approach to the multifaceted problem of back complaints in industry and help explain why past prevention efforts focusing on purely physical factors have been unsuccessful.