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1.  The role of physical workload and pain related fear in the development of low back pain in young workers: evidence from the BelCoBack Study; results after one year of follow up 
Aims
To study the influence of work related physical and psychosocial factors and individual characteristics on the occurrence of low back pain among young and pain free workers.
Methods
The Belgian Cohort Back Study was designed as a prospective cohort study. The study population of this paper consisted of 716 young healthcare or distribution workers without low back pain lasting seven or more consecutive days during the year before inclusion. The median age was 26 years with an interquartile range between 24 and 29 years. At baseline, these workers filled in a questionnaire with physical exposures, work related psychosocial factors and individual characteristics. One year later, the occurrence of low back pain lasting seven or more consecutive days and some of its characteristics were registered by means of a questionnaire. To assess the respective role of predictors at baseline on the occurrence of low back pain in the following year, Cox regression with a constant risk period for all subjects was applied.
Results
After one year of follow up, 12.6% (95% CI 10.1 to 15.0) of the 716 workers had developed low back pain lasting seven or more consecutive days. An increased risk was observed for working with the trunk in a bent and twisted position for more than two hours a day (RR 2.2, 95% CI 1.2 to 4.1), inability to change posture regularly (RR 2.1, 95% CI 1.3 to 3.5), back complaints in the year before inclusion (RR 1.7, 95% CI 1.1 to 2.8), and high scores of pain related fear (RR 1.8, 95% CI 1.0 to 3.1). Work related psychosocial factors and physical factors during leisure time were not predictive.
Conclusion
This study highlighted the importance of physical work factors and revealed the importance of high scores of pain related fear in the development of low back pain among young workers.
doi:10.1136/oem.2004.015693
PMCID: PMC2078035  PMID: 16361405
low back pain; pain related fear; physical work factors; prospective; young workers
2.  Study protocol title: a prospective cohort study of low back pain 
Background
Few prospective cohort studies of workplace low back pain (LBP) with quantified job physical exposure have been performed. There are few prospective epidemiological studies for LBP occupational risk factors and reported data generally have few adjustments for many personal and psychosocial factors.
Methods/design
A multi-center prospective cohort study has been incepted to quantify risk factors for LBP and potentially develop improved methods for designing and analyzing jobs. Due to the subjectivity of LBP, six measures of LBP are captured: 1) any LBP, 2) LBP ≥ 5/10 pain rating, 3) LBP with medication use, 4) LBP with healthcare provider visits, 5) LBP necessitating modified work duties and 6) LBP with lost work time. Workers have thus far been enrolled from 30 different employment settings in 4 diverse US states and performed widely varying work. At baseline, workers undergo laptop-administered questionnaires, structured interviews, and two standardized physical examinations to ascertain demographics, medical history, psychosocial factors, hobbies and physical activities, and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of low back pain. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. The lifetime cumulative incidence of low back pain will also include those with a past history of low back pain. Incident cases will exclude prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.
Discussion
Data analysis of a prospective cohort study of low back pain is underway and has successfully enrolled over 800 workers to date.
doi:10.1186/1471-2474-14-84
PMCID: PMC3599364  PMID: 23497211
Epidemiology; Ergonomics; Cohort; Low back pain; NIOSH lifting equation
3.  Understanding and Prevention of Low Back Pain in Care Workers 
The aim of this study was to investigate the actual situation of low back pain (LBP) prevention in care workers with questionnaires, and this data were used to clarify and decrease LBP factors. Subjects were 52 care workers (30.7 ± 10.0 years old) in a nursing home who filled out two kinds of questionnaires about LBP, one about the prevalence of LBP (QN1) and the other about LBP control measures (QN2). They had either license of certified care worker, 1st or 2nd class care worker. The data were collected for the purpose of finding differences in age and career (QN1) and differences in LBP control measures (QN2) between subjects with and without LBP. The average career of the subjects was 19.1 ± 12.5 months, and the prevalence of LBP among them was 46.2% (24 care workers), of which 66.7% began having LBP after starting work as care workers. Moreover, 75.0% of these subjects began having LBP within a year after starting work. Further, of the 24 care workers with LBP, 66.7% reported constantly experiencing LBP. The major risk factors given for LBP in care work were transfer, the replacement of diapers, and movement in a half-sitting posture. Compared with LBP subjects, rates of taking preventative steps in the non-LBP group were low. More than 80% of the subjects with LBP engaged in prevention methods such as using body mechanics, learning the proper way to perform care activities, using LBP support belts, and increasing their skills and knowledge with regard to their job responsibilities. Most subjects began to engage in such prevention methods after the onset of LBP. The results of this investigation indicated that most subjects did not engage in measures to counter their LBP until after it had already started, and that they selected prevention methods which were easy to perform and effective. It is important for care workers to learn the best ways to inhibit pain and prevent the occurrence, or recurrence, of LBP. It is necessary for physical therapists to grasp the actual situation of LBP prevention as an occupational disease and to educate this.
doi:10.1298/jjpta.10.27
PMCID: PMC4316536  PMID: 25792882
low back pain; care workers; questionnaires
4.  Potential Risk Factors of Persistent Low Back Pain Developing from Mild Low Back Pain in Urban Japanese Workers 
PLoS ONE  2014;9(4):e93924.
Study Design
Two-year, prospective cohort data from the Japan epidemiological research of occupation-related back pain study in urban settings were used for this analysis.
Objective
To examine the association between aggravated low back pain and psychosocial factors among Japanese workers with mild low back pain.
Summary of Background Data
Although psychosocial factors are strongly indicated as yellow flags of low back pain (LBP) leading to disability, the association between aggravated LBP and psychosocial factors has not been well assessed in Japanese workers.
Methods
At baseline, 5,310 participants responded to a self-administered questionnaire including questions about individual characteristics, ergonomic work demands, and work-related psychosocial factors (response rate: 86.5%), with 3,811 respondents completing the 1-year follow-up questionnaire. The target outcome was aggravation of mild LBP into persistent LBP during the follow-up period. Incidence was calculated for the participants with mild LBP during the past year at baseline. Logistic regression was used to explore risk factors associated with persistent LBP.
Results
Of 1,675 participants who had mild LBP during the preceding year, 43 (2.6%) developed persistent LBP during the follow-up year. Multivariate analyses adjusted for individual factors and an ergonomic factor found statistically significant or almost significant associations of the following psychosocial factors with persistent LBP: interpersonal stress at work [adjusted odds ratio (OR): 1.96 and 95% confidence interval (95%CI): 1.00–3.82], job satisfaction (OR: 2.34, 95%CI: 1.21–4.54), depression (OR: 1.92, 95%CI: 1.00–3.69), somatic symptoms (OR: 2.78, 95%CI: 1.44–5.40), support from supervisors (OR: 2.01, 95%CI: 1.05–3.85), previous sick-leave due to LBP (OR: 1.94, 95%CI: 0.98–3.86) and family history of LBP with disability (OR: 1.98, 95%CI: 1.04–3.78).
Conclusions
Psychosocial factors are important risk factors for persistent LBP in urban Japanese workers. It may be necessary to take psychosocial factors into account, along with physical work demands, to reduce LBP related disability.
doi:10.1371/journal.pone.0093924
PMCID: PMC3979726  PMID: 24714616
5.  Cohort study of occupational risk factors of low back pain in construction workers 
OBJECTIVES—To identify work related risk factors of future low back pain (LBP) in a cohort of construction workers free of LBP at the start of follow up.
METHODS—The Hamburg construction worker study comprises 571 male construction workers who have undergone two comprehensive interview and physical examination surveys. A cohort of 285 subjects without LBP at baseline was identified. After a follow up of 3 years, the 1 year prevalence of self reported LBP was determined in the 230 men followed up (80.7%). Prevalence ratios (PRs) with 95% confidence intervals (95% CIs) of LBP at follow up according to self reported work tasks of construction workers measured at baseline were estimated from Cox's regression models which were adjusted for age, and anthropometric measures.
RESULTS—At follow up 71 out of 230 workers (30.9%) reported LBP during the preceding 12 months. Four work tasks (scaffolding, erecting roof structures, sawing wood, laying large sandstones) with an increased risk of 1 year prevalence of LBP at follow up were further evaluated. After further adjustment for occupation the relative risk was increased for workers who had reported ⩾2 hour/shifts laying large sandstones (PR=2.6; 95% CI 1.1 to 6.5). Work load of bricklayers was additionally estimated by an index on stone load (high exposure: PR=4.0; 95% CI 0.8 to 19.8), and an index for laying huge bricks/blocks (yes/no: PR=1.7; 95% CI 0.5 to 5.7).
CONCLUSIONS—The results suggest that self reported differences in brick characteristics (size and type of stone) and temporal aspects of the work of bricklayers (average hours per shift laying specified stones) can predict the future prevalence of LBP. The data have to be interpreted with caution because multiple risk factors were tested.


Keywords: construction industry; cohort studies; low back pain
doi:10.1136/oem.57.1.28
PMCID: PMC1739856  PMID: 10711266
6.  Development of a risk score for low back pain in office workers - a cross-sectional study 
Background
Low back pain (LBP) is common among office workers and is the most common cause of work-related disability in people under 45 years of age. The aetiology of LBP is widely accepted to be multi-factorial. Prognostic research into office workers at risk of developing LBP has received limited attention. The aims of this study were to develop a risk score to identify office workers likely to have LBP and to evaluate its predictive power.
Methods
397 office workers filled out a self-administered questionnaire and underwent physical examination. The questionnaire gathered data on individual, work-related physical and psychosocial data as well as the presence of low back pain in the previous 4 weeks. The physical examination included measurement of body weight, height, waist circumference, hamstrings length, spinal scoliosis, spinal curve, Backache Index and lumbar stability. Logistic regression was used to select significant factors associated with LBP to build a risk score. The coefficients from the logistic regression model were transformed into the components of a risk score.
Results
The model included six items: previous history of working as an office worker, years of work experience, continuous standing for >2 hrs/d, frequency of forward bending during work day, chair having lumbar support and Backache Index outcome. The risk score for LBP in office workers (The Back pain Risk score for Office Workers: The BROW) was built with a risk score ranging from 0 to 9. A cut-off score of ≥4 had a sensitivity of 80% and a specificity of 58%. The positive predictive value and negative predictive values were 70% each.
Conclusions
The BROW is easy and quick to administer. It appears to have reasonable sensitivity, specificity, positive predictive value and negative predictive values for the cut-off point of ≥4. The BROW is a promising tool for use to identify office workers in need of early interventions. Further prospective study is needed to validate the predictive performance of the BROW.
doi:10.1186/1471-2474-12-23
PMCID: PMC3036671  PMID: 21261997
7.  The predictive effect of fear-avoidance beliefs on low back pain among newly qualified health care workers with and without previous low back pain: a prospective cohort study 
Background
Health care workers have a high prevalence of low back pain (LBP). Although physical exposures in the working environment are linked to an increased risk of LBP, it has been suggested that individual coping strategies, for example fear-avoidance beliefs, could also be important in the development and maintenance of LBP. Accordingly, the main objective of this study was to examine (1) the association between physical work load and LBP, (2) the predictive effect of fear-avoidance beliefs on the development of LBP, and (3) the moderating effect of fear-avoidance beliefs on the association between physical work load and LBP among cases with and without previous LBP.
Methods
A questionnaire survey among 5696 newly qualified health care workers who completed a baseline questionnaire shortly before completing their education and a follow-up questionnaire 12 months later. Participants were selected on the following criteria: (a) being female, (b) working in the health care sector (n = 2677). Multinomial logistic regression analysis was used to evaluate the effect of physical work load and fear-avoidance beliefs on the severity of LBP.
Results
For those with previous LBP, physical work load has an importance, but not among those without previous LBP. In relation to fear-avoidance beliefs, there is a positive relation between it and LBP of than 30 days in both groups, i.e. those without and with previous LBP. No moderating effect of fear-avoidance beliefs on the association between physical work load and LBP was found among cases with and without LBP.
Conclusion
Both physical work load and fear-avoidance beliefs matters in those with previous LBP. Only fear-avoidance beliefs matters in those without previous LBP. The study did not find a moderating effect of fear-avoidance beliefs on the association between physical work load and LBP.
doi:10.1186/1471-2474-10-117
PMCID: PMC2759905  PMID: 19778413
8.  The role of physical and psychological factors in occupational low back pain: a prospective cohort study 
OBJECTIVE—To examine risk factors for onset of low back pain (LBP) in healthcare workers.
METHODS—Nursing students, during their 3 year training period, and 1 year after training were studied in a prospective cohort study, with repeated self reported measurements of determinants of LBP at 6 monthly intervals for 3 years during training, and after a 12 month interval there was an additional final follow up.
RESULTS—During training, increased risk of new episodes of LBP was associated with having had LBP at baseline, with part time work, and with a high score on the general health questionnaire (GHQ). A high GHQ score preceded the onset of LBP, in such a way that a high score at the immediately previous follow up increased risk of LBP at the next follow up. 12 Months after training, a history of recurring LBP during training increased the risk of a new episode as did having obtained work as a nurse. A high GHQ score at this follow up was also associated with a concurrently increased risk. Pre-existing GHQ score, either at the end of training or at baseline, had no effect on risk of LBP 12 months after training.
CONCLUSIONS—Other than a history of LBP, pre-existing psychological distress was the only factor found to have a pre-existing influence on new episodes of LBP. Increased levels of psychological distress (as measured by the GHQ) preceded the occurrence of new episodes of pain by only short intervening periods, implying a role for acute distress in the onset of the disorder. This finding suggests that management of the onset of occupational LBP may be improved by management of psychological distress.


Keywords: low back pain; nurses; psychological factors
doi:10.1136/oem.57.2.116
PMCID: PMC1739913  PMID: 10711279
9.  Low back pain predict sickness absence among power plant workers 
Background:
Low back pain (LBP) remains the predominant occupational health problem in most industrialized countries and low-income countries. Both work characteristics and individual factors have been identified as risk factors. More knowledge about the predictors of sickness absence from LBP in the industry will be valuable in determining strategies for prevention.
Objectives:
The aim of this longitudinal study was to investigate whether individual, work-related physical risk factors were involved in the occurrence of LBP sickness absence.
Methods:
A follow-up study was conducted among 489 workers, aged 18–65 years, at Kosovo Energetic Corporation in Kosovo. This cross-sectional study used a self-administered questionnaire to collect data on individual and work-related risk factors and the occurrence of LBP sickness absence. Logistic regression models were used to determine associations between risk factors and the occurrence of sickness absence due to LBP.
Results:
Individual factors did not influence sickness absence, whereas work-related physical factors showed strong associations with sickness absence. The main risk factors for sickness absence due to LBP among production workers were extreme trunk flexion (OR = 1.71, 95% CI = 1.05–2.78) as well as very extreme trunk flexion (OR = 6.04, 95% CI = 1.12–32.49) and exposure to whole-body vibration (OR = 1.75, 95% CI = 1.04–2.95).
Conclusion:
Reducing sickness absence from LBP among power plant workers requires focusing on the working conditions of blue-collar workers and risk factors for LBP. Increasing social support in the work environment may have effects in reducing sickness absence from LBP.
doi:10.4103/0019-5278.72241
PMCID: PMC2992865  PMID: 21120081
Low back pain; occupational; physical risk factors; sick leave
10.  A Novel Tool for the Assessment of Pain: Validation in Low Back Pain 
PLoS Medicine  2009;6(4):e1000047.
Joachim Scholz and colleagues develop and validate an assessment tool that distinguishes between radicular and axial low back pain.
Background
Adequate pain assessment is critical for evaluating the efficacy of analgesic treatment in clinical practice and during the development of new therapies. Yet the currently used scores of global pain intensity fail to reflect the diversity of pain manifestations and the complexity of underlying biological mechanisms. We have developed a tool for a standardized assessment of pain-related symptoms and signs that differentiates pain phenotypes independent of etiology.
Methods and Findings
Using a structured interview (16 questions) and a standardized bedside examination (23 tests), we prospectively assessed symptoms and signs in 130 patients with peripheral neuropathic pain caused by diabetic polyneuropathy, postherpetic neuralgia, or radicular low back pain (LBP), and in 57 patients with non-neuropathic (axial) LBP. A hierarchical cluster analysis revealed distinct association patterns of symptoms and signs (pain subtypes) that characterized six subgroups of patients with neuropathic pain and two subgroups of patients with non-neuropathic pain. Using a classification tree analysis, we identified the most discriminatory assessment items for the identification of pain subtypes. We combined these six interview questions and ten physical tests in a pain assessment tool that we named Standardized Evaluation of Pain (StEP). We validated StEP for the distinction between radicular and axial LBP in an independent group of 137 patients. StEP identified patients with radicular pain with high sensitivity (92%; 95% confidence interval [CI] 83%–97%) and specificity (97%; 95% CI 89%–100%). The diagnostic accuracy of StEP exceeded that of a dedicated screening tool for neuropathic pain and spinal magnetic resonance imaging. In addition, we were able to reproduce subtypes of radicular and axial LBP, underscoring the utility of StEP for discerning distinct constellations of symptoms and signs.
Conclusions
We present a novel method of identifying pain subtypes that we believe reflect underlying pain mechanisms. We demonstrate that this new approach to pain assessment helps separate radicular from axial back pain. Beyond diagnostic utility, a standardized differentiation of pain subtypes that is independent of disease etiology may offer a unique opportunity to improve targeted analgesic treatment.
Editors' Summary
Background
Pain, although unpleasant, is essential for survival. Whenever the body is damaged, nerve cells detecting the injury send an electrical message via the spinal cord to the brain and, as a result, action is taken to prevent further damage. Usually pain is short-lived, but sometimes it continues for weeks, months, or years. Long-lasting (chronic) pain can be caused by an ongoing, often inflammatory condition (for example, arthritis) or by damage to the nervous system itself—experts call this “neuropathic” pain. Damage to the brain or spinal cord causes central neuropathic pain; damage to the nerves that convey information from distant parts of the body to the spinal cord causes peripheral neuropathic pain. One example of peripheral neuropathic pain is “radicular” low back pain (also called sciatica). This is pain that radiates from the back into the legs. By contrast, axial back pain (the most common type of low back pain) is confined to the lower back and is non-neuropathic.
Why Was This Study Done?
Chronic pain is very common—nearly 10% of American adults have frequent back pain, for example—and there are many treatments for it, including rest, regulated exercise (physical therapy), pain-killing drugs (analgesics), and surgery. However, the best treatment for any individual depends on the exact nature of their pain, so it is important to assess their pain carefully before starting treatment. This is usually done by scoring overall pain intensity, but this assessment does not reflect the characteristics of the pain (for example, whether it occurs spontaneously or in response to external stimuli) or the complex biological processes involved in pain generation. An assessment designed to take such factors into account might improve treatment outcomes and could be useful in the development of new therapies. In this study, the researchers develop and test a new, standardized tool for the assessment of chronic pain that, by examining many symptoms and signs, aims to distinguish between pain subtypes.
What Did the Researchers Do and Find?
One hundred thirty patients with several types of peripheral neuropathic pain and 57 patients with non-neuropathic (axial) low back pain completed a structured interview of 16 questions and a standardized bedside examination of 23 tests. Patients were asked, for example, to choose words that described their pain from a list provided by the researchers and to grade the intensity of particular aspects of their pain from zero (no pain) to ten (the maximum imaginable pain). Bedside tests included measurements of responses to light touch, pinprick, and vibration—chronic pain often alters responses to harmless stimuli. Using “hierarchical cluster analysis,” the researchers identified six subgroups of patients with neuropathic pain and two subgroups of patients with non-neuropathic pain based on the patterns of symptoms and signs revealed by the interviews and physical tests. They then used “classification tree analysis” to identify the six questions and ten physical tests that discriminated best between pain subtypes and combined these items into a tool for a Standardized Evaluation of Pain (StEP). Finally, the researchers asked whether StEP, which took 10–15 minutes, could identify patients with radicular back pain and discriminate them from those with axial back pain in an independent group of 137 patients with chronic low back pain. StEP, they report, accurately diagnosed these two conditions and was well accepted by the patients.
What Do These Findings Mean?
These findings indicate that a standardized assessment of pain-related signs and symptoms can provide a simple, quick diagnostic procedure that distinguishes between radicular (neuropathic) and axial (non-neuropathic) low back pain. This distinction is crucial because these types of back pain are best treated in different ways. In addition, the findings suggest that it might be possible to identify additional pain subtypes using StEP. Because these subtypes may represent conditions in which different pain mechanisms are acting, classifying patients in this way might eventually enable physicians to tailor treatments for chronic pain to the specific needs of individual patients rather than, as at present, largely guessing which of the available treatments is likely to work best.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000047.
This study is further discussed in a PLoS Medicine Perspective by Giorgio Cruccu and and Andrea Truini
The US National Institute of Neurological Disorders and Stroke provides a primer on pain in English and Spanish
In its 2006 report on the health status of the US, the National Center for Health Statistics provides a special feature on the epidemiology of pain, including back pain
The Pain Treatment Topics Web site is a resource, sponsored partly by associations and manufacturers, that provides information on all aspects of pain and its treatment for health care professionals and their patients
Medline Plus provides a brief description of pain and of back pain and links to further information on both topics (in English and Spanish)
The MedlinePlus Medical Encyclopedia also has a page on low back pain (in English and Spanish)
doi:10.1371/journal.pmed.1000047
PMCID: PMC2661253  PMID: 19360087
11.  Cumulative Low Back Load at Work as a Risk Factor of Low Back Pain: A Prospective Cohort Study 
Purpose Much research has been performed on physical exposures during work (e.g. lifting, trunk flexion or body vibrations) as risk factors for low back pain (LBP), however results are inconsistent. Information on the effect of doses (e.g. spinal force or low back moments) on LBP may be more reliable but is lacking yet. The aim of the present study was to investigate the prospective relationship of cumulative low back loads (CLBL) with LBP and to compare the association of this mechanical load measure to exposure measures used previously. Methods The current study was part of the Study on Musculoskeletal disorders, Absenteeism and Health (SMASH) study in which 1,745 workers completed questionnaires. Physical load at the workplace was assessed by video-observations and force measurements. These measures were used to calculate CLBL. Furthermore, a 3-year follow-up was conducted to assess the occurrence of LBP. Logistic regressions were performed to assess associations of CLBL and physical risk factors established earlier (i.e. lifting and working in a flexed posture) with LBP. Furthermore, CLBL and the risk factors combined were assessed as predictors in logistic regression analyses to assess the association with LBP. Results Results showed that CLBL is a significant risk factor for LBP (OR: 2.06 (1.32–3.20)). Furthermore, CLBL had a more consistent association with LBP than two of the three risk factors reported earlier. Conclusions From these results it can be concluded that CLBL is a risk factor for the occurrence of LBP, having a more consistent association with LBP compared to most risk factors reported earlier.
doi:10.1007/s10926-012-9375-z
PMCID: PMC3563950  PMID: 22718286
Low back loading; Ergonomics; Workers; Longitudinal studies; Observational studies
12.  The greatest risk for low-back pain among newly educated female health care workers; body weight or physical work load? 
Background
Low back pain (LBP) represents a major socioeconomic burden for the Western societies. Both life-style and work-related factors may cause low back pain. Prospective cohort studies assessing risk factors among individuals without prior history of low back pain are lacking. This aim of this study was to determine risk factors for developing low back pain (LBP) among health care workers.
Methods
Prospective cohort study with 2,235 newly educated female health care workers without prior history of LBP. Risk factors and incidence of LBP were assessed at one and two years after graduation.
Results
Multinomial logistic regression analyses adjusted for age, smoking, and psychosocial factors showed that workers with high physical work load had higher risk for developing LBP than workers with low physical work load (OR 1.8; 95% CI 1.1–2.8). In contrast, workers with high BMI were not at a higher risk for developing LBP than workers with a normal BMI.
Conclusion
Preventive initiatives for LBP among health care workers ought to focus on reducing high physical work loads rather than lowering excessive body weight.
doi:10.1186/1471-2474-13-87
PMCID: PMC3404961  PMID: 22672781
Prospective cohort study; Low back pain; Physical work load; Health care work; Musculoskeletal disorders; Body mass index
13.  Risk factors for sickness absence due to low back pain and prognostic factors for return to work in a cohort of shipyard workers 
European Spine Journal  2008;17(9):1185-1192.
The purpose of this study was to determine risk factors for the occurrence of sickness absence due to low back pain (LBP) and to evaluate prognostic factors for return to work. A longitudinal study with 1-year follow-up was conducted among 853 shipyard workers. The cohort was drawn around January 2004 among employees in the shipyard industry. Baseline information was obtained by questionnaire on physical and psychosocial work load, need for recovery, perceived general health, musculoskeletal complaints, sickness absence, and health care use during the past year. During the 1-year follow-up for each subject medical certifications were retrieved for information on the frequency and duration of spells of sickness absence and associated diagnoses. Cox regression analyses were conducted on occurrence and on duration of sickness absence with hazard ratios (HR) with 95% confidence interval (95% CI) as measure of association. During the 1-year follow-up period, 14% of the population was on sick leave at least once with LBP while recurrence reached 41%. The main risk factors for sickness absence were previous absence due to a health problem other than LBP (HR 3.07; 95%CI 1.66–5.68) or previous sickness absence due to LBP (HR 6.52; 95%CI 3.16–13.46). Care seeking for LBP and lower educational level also hold significant influences (HR 2.41; 95%CI 1.45–4.01 and HR 2.46; 95%CI 1.19–5.07, respectively). Living with others, night shift and supervising duties were associated with less absenteeism due to LBP. Workers with a history of herniated disc had a significantly decreased rate of returning to work, whereas those who suffered from hand-wrist complaints and LBP returned to work faster. Prior sick leave due to LBP partly captured the effects of work-related physical and psychosocial factors on occurrence of sick leave. Our study showed that individual and job characteristics (living alone, night shift, lower education, sick leave, or care seeking during the last 12 months) influenced the decision to take sick leave due to LBP. An increased awareness of those frequently on sick leave and additional management after return to work may have a beneficial effect on the sickness absence pattern.
doi:10.1007/s00586-008-0711-0
PMCID: PMC2527417  PMID: 18649089
Low back pain; Sick leave; Prognosis; Recurrence; Return to work
14.  Validity of pressure pain thresholds in female workers with and without recurrent low back pain 
European Spine Journal  2006;16(2):267-275.
Recurrent low back pain (LBP) is a common pain condition in elderly workers in a variety of occupations, but little is known about its origin and the mechanisms leading to an often disabling sensation of pain that may be persistent or intermittent. In the present study we evaluated the pressure pain thresholds (PPTs) in subjects suffering from recurrent LBP, as well as in healthy controls, to investigate if recurrent LBP is associated with an increased sensitivity of the muscular and ligamentous structures located on the lower back. One hundred and six female workers, aged between 45 and 62 years and working either in administrative or nursing professions were examined. The subjects were classified into LBP cases and controls based on the Nordic questionnaire. Subjects indicating 8–30 or more days with LBP during the past 12 months were graded as cases. PPTs were measured on 12 points (six on each side of the body) expected to be relevant for LBP (paravertebral muscles, musculus quadratus lumborum, os ilium, iliolumbar ligament, musculus piriformis and greater trochanter), as well as on a reference point (middle of the forehead) using a digital dolorimeter. The PPTs on all points on the lower back highly correlated with each other and a high internal consistency was found with a Cronbach alpha coefficient > 0.95. There was a moderate and significant correlation of the PPT on the forehead with the PPT on the lower back with correlation coefficients ranging from 0.36 to 0.49. In LBP cases from administrative professions, the PPT on the forehead was significantly decreased (P < 0.05). The PPT on the lower back did not significantly differ between the four groups studied, namely nurses and administrative workers with and without recurrent LBP. These results give evidence that recurrent LBP is not associated with an altered sensitivity of the muscular and myofascial tissues in the lumbar region. Furthermore, they raise questions about the value of reference point measurements in recurrent LBP.
doi:10.1007/s00586-006-0124-x
PMCID: PMC2200678  PMID: 16680447
Pressure pain threshold; Low back pain; Reference point
15.  Prevalence and Pharmacologic Treatment of Patients with Low Back Pain Treated at Kosovo Energetic Corporation 
Medical Archives  2013;67(6):410-413.
ABSTRACT
Introduction:
Low back pain (LBP) is a common complaint among the general population with a subgroup developing chronic and disabling symptoms generating large societal costs. Recurrences and functional limitations can be minimized with appropriate conservative management, including medications, physical therapy modalities, exercise and patient education.
Objectives:
The purpose of this study was to determine the prevalence of low back complaints in industrial workers, to investigate whether individual risk factors involved in the occurrence of LBP, and to determine the most frequent used drug in LBP treatment.
Materials and Methods:
Data for this study were provided from Kosovo Energetic Corporation. A cross-sectional study design was utilized. Self-administered questionnaires were distributed among 228 industrial workers. Patient with LBP underwent a comprehensive clinical, radiological and biochemical evaluation.
Results:
showed that LBP occurred in 63.5% of workers. Individual factors did not show significant associations with LBP. Age (OR=0.99/95% Cl 0.95-1.03), weight (OR=1.13/95% Cl 0.99-1.06), height (OR=0.97/95% Cl 0.91-1.02), and work experience (OR=1.01/95% Cl 0.97-1.05) increase odds for LBP but not significantly. The most frequently used drugs in patients included in this study are NSAIDs. In 33 (55.0%) patients for the treatment of LBP two types of drugs are administered.
Conclusion:
Increased physical activity, health promotion and reduced body weight can prevent morbidity from LBP. A continuous consultation with the Clinical Pharmacist demonstrates effective way of dosage and drug re-evaluation for the patients with LBP.
doi:10.5455/medarh.2013.67.410-413
PMCID: PMC4272453  PMID: 25568510
LBP; prevalence; drug; treatment
16.  Association between sitting and occupational LBP 
European Spine Journal  2006;16(2):283-298.
Low back pain (LBP) has been identified as one of the most costly disorders among the worldwide working population. Sitting has been associated with risk of developing LBP. The purpose of this literature review is to assemble and describe evidence of research on the association between sitting and the presence of LBP. The systematic literature review was restricted to those occupations that require sitting for more than half of working time and where workers have physical co-exposure factors such as whole body vibration (WBV) and/or awkward postures. Twenty-five studies were carefully selected and critically reviewed, and a model was developed to describe the relationships between these factors. Sitting alone was not associated with the risk of developing LBP. However, when the co-exposure factors of WBV and awkward postures were added to the analysis, the risk of LBP increased fourfold. The occupational group that showed the strongest association with LBP was Helicopter Pilots (OR=9.0, 90% CI 4.9–16.4). For all studied occupations, the odds ratio (OR) increased when WBV and/or awkward postures were analyzed as co-exposure factors. WBV while sitting was also independently associated with non-specific LBP and sciatica. Vibration dose, as well as vibration magnitude and duration of exposure, were associated with LBP in all occupations. Exposure duration was associated with LBP to a greater extent than vibration magnitude. However, for the presence of sciatica, this difference was not found. Awkward posture was also independently associated with the presence of LBP and/or sciatica. The risk effect of prolonged sitting increased significantly when the factors of WBV and awkward postures were combined. Sitting by itself does not increase the risk of LBP. However, sitting for more than half a workday, in combination with WBV and/or awkward postures, does increase the likelihood of having LBP and/or sciatica, and it is the combination of those risk factors, which leads to the greatest increase in LBP.
doi:10.1007/s00586-006-0143-7
PMCID: PMC2200681  PMID: 16736200
Sitting; LBP; Sciatica; Epidemiology; Review
17.  Biopsychosocial Factors and Perceived Disability in Saleswomen with Concurrent Low Back Pain 
Safety and Health at Work  2010;1(2):149-157.
Objectives
To quantify disability level in salespeople with concurrent low back pain (LBP) and to determine the relative associations between demographic, occupational, psychosocial and clinical factors and back disability. LBP is the most common cause of work-related disability in people under 45 years of age and the most expensive cause of work-related disability, in terms of workers' compensation and medical expenses. Evidence suggests high prevalence of LBP in salespeople.
Methods
A cross-sectional survey was conducted in which 184 saleswomen with a current episode of self-reported LBP working in a large up-scale department store filled out a battery of 6 self-administered questionnaires and received a standardised physical examination.
Results
Saleswomen with concurrent LBP had low disability levels. Factors significantly associated with disability were pain intensity, measured by a visual analogue scale, in the past week (p < 0.001), physical and mental health status (p < 0.001, p = 0.003, respectively), fear avoidance scores for both work and physical activities (p = 0.031, p = 0.014, respectively), past history of LBP (p = 0.019), and self-reported frequency of pushing or pulling objects placed in high positions during work (p = 0.047). A significant level (45%) of the variance in disability status was explained by these variables.
Conclusion
In clinical management of LBP workers who required prolonged standing, such as salespeople, clinicians should look for modifiable risk factors associated with disability. Specific measures need to be taken to prevent disability due to LBP among salespeople.
doi:10.5491/SHAW.2010.1.2.149
PMCID: PMC3430890  PMID: 22953175
Occupational diseases; Risk factors; Functional status; Musculoskeletal disorders
18.  Stay@Work: Participatory Ergonomics to prevent low back and neck pain among workers: design of a randomised controlled trial to evaluate the (cost-)effectiveness 
Background
Low back pain (LBP) and neck pain (NP) are a major public health problem with considerable costs for individuals, companies and society. Therefore, prevention is imperative. The Stay@Work study investigates the (cost-)effectiveness of Participatory Ergonomics (PE) to prevent LBP and NP among workers.
Methods
In a randomised controlled trial (RCT), a total of 5,759 workers working at 36 departments of four companies is expected to participate in the study at baseline. The departments consisting of about 150 workers are pre-stratified and randomised. The control departments receive usual practice and the intervention departments receive PE. Within each intervention department a working group is formed including eight workers, a representative of the management, and an occupational health and safety coordinator. During a one day meeting, the working group follows the steps of PE in which the most important risk factors for LBP and NP, and the most adequate ergonomic measures are identified on the basis of group consensus. The implementation of ergonomic measures at the department is performed by the working group. To improve the implementation process, so-called 'ergocoaches' are trained.
The primary outcome measure is an episode of LBP and NP. Secondary outcome measures are actual use of ergonomic measures, physical workload, psychosocial workload, intensity of pain, general health status, sick leave, and work productivity. The cost-effectiveness analysis is performed from the societal and company perspective. Outcome measures are assessed using questionnaires at baseline and after 6 and 12 months. Data on the primary outcome as well as on intensity of pain, sick leave, work productivity, and health care costs are collected every 3 months.
Discussion
Prevention of LBP and NP is beneficial for workers, employers, and society. If the intervention is proven (cost-)effective, the intervention can have a major impact on LBP and NP prevention and, thereby, on work disability prevention. Results are expected in 2010.
Trial registration
ISRCTN27472278
doi:10.1186/1471-2474-9-145
PMCID: PMC2588446  PMID: 18959799
19.  Symptomatology of recurrent low back pain in nursing and administrative professions 
European Spine Journal  2007;16(11):1789-1798.
The aim of the present study was to explore if (a) recurrent low back pain (LBP) has different symptomatologies in cases from occupations with predominantly sitting postures compared to cases from occupations involving dynamic postures and frequent lifting and (b) if in the two occupational groups, different factors were associated with the presence of recurrent LBP. Hundred and eleven female subjects aged between 45 and 62 years with a long-standing occupation either in administrative or nursing professions, with and without recurrent LBP were examined. An extensive evaluation of six areas of interest (pain and disability, clinical examination, functional tests, MR examination, physical and psychosocial workplace factors) was performed. The variables from the six areas of interest were analyzed for their potential to discriminate between the four groups of subjects (administrative worker and nurses with and without recurrent LBP) by canonical discriminant analysis. As expected, the self-evaluation of physical and psychosocial workplace factors showed significant differences between the two occupational groups, which holds true for cases as well as for controls (P < 0.01). The functional tests revealed a tendency for rather good capacity in nurses with LBP and a decreased capacity in administrative personnel with LBP (P = 0.049). Neither self completed pain and disability questionnaires nor clinical examination or MR imaging revealed any significant difference between LBP cases from sedentary and non-sedentary occupations. When comparing LBP cases and controls within the two occupational groups, the functional tests revealed significant differences (P = 0.0001) yet only in administrative personnel. The clinical examination on the other hand only discriminated between LBP cases and controls in the nurses group (P < 0.0001). Neither MRI imaging nor self reported physical and psychosocial workplace factors discriminated between LBP cases and controls from both occupational groups. Although we used a battery of tests that have broad application in clinical and epidemiological studies of LBP, a clear difference in the pattern of symptoms between LBP cases from nursing and hospital administration personnel could not be ascertained. We conclude that there is no evidence for different mechanisms leading to non-specific, recurrent LBP in the two occupations, and thus no generalizable recommendations for the prevention and therapy of non-specific LBP in the two professions can be given.
doi:10.1007/s00586-007-0346-6
PMCID: PMC2223334  PMID: 17611784
Low back pain; Nurses; Sedentary work; Physical workplace factors
20.  The relationship between the magnetic resonance imaging appearance of the lumbar spine and low back pain, age and occupation in males 
European Spine Journal  1997;6(2):106-114.
The purpose of this study was to undertake a critical review of the potential role of magnetic resonance imaging (MRI) in the evaluation of low back pain (LBP) and to determine if there were differences in the MRI appearances between various occupational groups. The study group, 149 working men (78 aged 20-30 years and 71 aged 31–58 years) from five different occupations (car production workers, ambulance men, office staff, hospital porters and brewery draymen), underwent MRI of the lumbar spine. Thirty-four percent of the subjects had never experienced LBP Twelve months later, the examination was repeated on 89 men. Age-related differences were seen in the MRI appearances of the lumbar spine. Disc degeneration was most common at L5/S 1 and was significantly more prevalent (P < 0.01) in the older age group (52%) than in the younger age group (27%). Although LBP was more prevalent in the older subjects there was no relationship between LBP and disc degeneration. No differences in the MRI appearance of the lumbar spine were observed between the five occupational groups. Overall, 45% had ‘abnormal’ lumbar spines (evidence of disc degeneration, disc bulging or protrusion, facet hypertrophy, or nerve root compression). There was not a clear relationship between the MRI appearance of the lumbar spine and LBP. Thirty-two percent of asymptomatic subjects had ‘abnormal’ lumbar spines and 47% of all the subjects who had experienced LBP had ‘normal’ lumbar spines. During the 12-month follow-up period, 13 subjects experienced LBP for the first time. However, there was no change in the MRI appearances of their lumbar spines that could account for the onset of LBP. Although MRI is an excellent technique for evaluating the lumbar spine, this study shows that it does not provide a suitable pre-employment screening technique capable of identifying those at risk of LBP.
doi:10.1007/BF01358742
PMCID: PMC3454595  PMID: 9209878
Magnetic resonance imaging; Lumbar spine; Disc disease
21.  Non-specific low back pain in primary care in the Spanish National Health Service: a prospective study on clinical outcomes and determinants of management 
Background
The Spanish National Health Service is a universal and free health care system. Non-specific low back pain (LBP) is a prevalent disorder, generating large health and social costs. The objectives of this study were to describe its management in primary care, to assess patient characteristics that influence physicians' decisions, and to describe clinical outcome at 2 months.
Methods
A cross-sectional sample of 648 patients with non-specific low back pain was recruited by 75 physicians (out of 361 – 20.8%) working in 40 primary care centers in 10 of the 17 administrative regions in Spain, covering 693,026 out of the 40,499,792 inhabitants. Patients were assessed on the day they were recruited, and prospectively followed-up 14 and 60 days later. The principal patient characteristics that were analyzed were: sex, duration of the episode, history of LBP, working status, severity of LBP, leg pain and disability, and results of straight leg raising test. Descriptors of management were: performance of the straight leg raising test, ordering of diagnostic procedures, prescription of drug treatment, referral to physical therapy, rehabilitation or surgery, and granting of sick leave. Regression analysis was used to analyze the relationship between patients' baseline characteristics and physicians' management decisions. Only workers were included in the models on sick leave.
Results
Mean age (SD) of included patients was 46.5 (15.5) years, 367 (56.6%) were workers, and 338 (52.5%) were females. Median (25th–75th interquartile range) duration of pain when entering the study was 4 (2–10) days and only 28 patients (4.3%) had chronic low back pain. Diagnostic studies included plain radiographs in 43.1% of patients and CT or MRI scans in 18.8%. Drug medication was prescribed to 91.7% of patients, 19.1% were sent to physical therapy or rehabilitation, and 9.6% were referred to surgery. The main determinants of the clinical management were duration of the episode and, to a lesser extent, the intensity of the pain (especially leg pain), a positive straight leg raising test, and degree of disability. The main determinant of sick leave was the degree of disability, followed by the characteristics of the labor contract and the intensity of leg pain (but not low back pain). After at least 2 months of treatment, 37% of patients were still in pain and approximately 10% of patients had not improved or had worsened.
Conclusion
Although the use of X-Rays is high, determinants of physicians' management of LBP in primary care made clinical sense and were consistent with patterns suggested by evidence-based recommendations. However, after 2 months of treatment more than one third of patients continued to have back pain and about 10% had worsened.
doi:10.1186/1472-6963-6-57
PMCID: PMC1479820  PMID: 16707005
22.  Low back pain risk factors in a large rural Australian Aboriginal community. An opportunity for managing co-morbidities? 
Background
Low back pain (LBP) is the most prevalent musculo-skeletal condition in rural and remote Australian Aboriginal communities. Smoking, physical inactivity and obesity are also prevalent amongst Indigenous people contributing to lifestyle diseases and concurrently to the high burden of low back pain.
Objectives
This paper aims to examine the association between LBP and modifiable risk factors in a large rural Indigenous community as a basis for informing a musculo-skeletal and related health promotion program.
Methods
A community Advisory Group (CAG) comprising Elders, Aboriginal Health Workers, academics, nurses, a general practitioner and chiropractors assisted in the development of measures to assess self-reported musculo-skeletal conditions including LBP risk factors. The Kempsey survey included a community-based survey administered by Aboriginal Health Workers followed by a clinical assessment conducted by chiropractors.
Results
Age and gender characteristics of this Indigenous sample (n = 189) were comparable to those reported in previous Australian Bureau of Statistics (ABS) studies of the broader Indigenous population. A history of traumatic events was highly prevalent in the community, as were occupational risk factors. Thirty-four percent of participants reported a previous history of LBP. Sporting injuries were associated with multiple musculo-skeletal conditions, including LBP. Those reporting high levels of pain were often overweight or obese and obesity was associated with self-reported low back strain. Common barriers to medical management of LBP included an attitude of being able to cope with pain, poor health, and the lack of affordable and appropriate health care services.
Though many of the modifiable risk factors known to be associated with LBP were highly prevalent in this study, none of these were statistically associated with LBP.
Conclusion
Addressing particular modifiable risk factors associated with LBP such as smoking, physical inactivity and obesity may also present a wider opportunity to prevent and manage the high burden of illness imposed by co-morbidities such as heart disease and type-2 diabetes.
doi:10.1186/1746-1340-13-21
PMCID: PMC1277832  PMID: 16197555
Low back pain; risk factors; chiropractic; general health; Australian; Aboriginal; Indigenous
23.  Health care utilization and costs associated with adherence to clinical practice guidelines for early magnetic resonance imaging among workers with acute occupational low back pain 
Health services research  2013;49(2):645-665.
Objective
To estimate health care utilization and costs associated with adherence to clinical practice guidelines for the use of early MRI (within the first 6 weeks of injury) for acute occupational low back pain (LBP).
Data sources
Washington State Disability Risk Identification Study Cohort (D-RISC), consisting of administrative claims and patient interview data from workers’ compensation claimants (2002–2004).
Study design
In this prospective, population-based cohort study, we compared health care utilization and costs among workers whose imaging was adherent to guidelines (no early MRI) to workers whose imaging was not adherent to guidelines (early MRI in the absence of red flags).
Data collection/extraction methods
We identified workers (age>18) with work-related LBP using administrative claims. We obtained demographic, injury, health, and employment information through telephone interviews to adjust for baseline differences between groups. We ascertained health care utilization and costs from administrative claims for 1 year following injury.
Principal findings
Of 1,770 workers, 336 (19.0%) were classified as non-adherent to guidelines. Outpatient and physical/occupational therapy utilization was 52–54% higher for workers whose imaging was not adherent to guidelines compared to workers with guideline-adherent imaging; utilization of chiropractic care was significantly lower (18%).
Conclusions
Non-adherence to guidelines for early MRI was associated with increased likelihood of lumbosacral injections or surgery and higher costs for outpatient, inpatient, and non-medical services, and disability compensation.
doi:10.1111/1475-6773.12098
PMCID: PMC3864604  PMID: 23910019
24.  Health Care Utilization and Costs Associated with Adherence to Clinical Practice Guidelines for Early Magnetic Resonance Imaging among Workers with Acute Occupational Low Back Pain 
Health Services Research  2013;49(2):645-665.
Objective
To estimate health care utilization and costs associated with adherence to clinical practice guidelines for the use of early magnetic resonance imaging (MRI; within the first 6 weeks of injury) for acute occupational low back pain (LBP).
Data Sources
Washington State Disability Risk Identification Study Cohort (D-RISC), consisting of administrative claims and patient interview data from workers’ compensation claimants (2002–2004).
Study Design
In this prospective, population-based cohort study, we compared health care utilization and costs among workers whose imaging was adherent to guidelines (no early MRI) to workers whose imaging was not adherent to guidelines (early MRI in the absence of red flags).
Data Collection/Extraction Methods
We identified workers (age >18) with work-related LBP using administrative claims. We obtained demographic, injury, health, and employment information through telephone interviews to adjust for baseline differences between groups. We ascertained health care utilization and costs from administrative claims for 1 year following injury.
Principal Findings
Of 1,770 workers, 336 (19.0 percent) were classified as nonadherent to guidelines. Outpatient and physical/occupational therapy utilization was 52–54 percent higher for workers whose imaging was not adherent to guidelines compared to workers with guideline-adherent imaging; utilization of chiropractic care was significantly lower (18 percent).
Conclusions
Nonadherence to guidelines for early MRI was associated with increased likelihood of lumbosacral injections or surgery and higher costs for out-patient, inpatient, and nonmedical services, and disability compensation.
doi:10.1111/1475-6773.12098
PMCID: PMC3864604  PMID: 23910019
Low back pain; costs; utilization; diagnostic imaging; clinical practice guidelines; workers' compensation
25.  Before-after study to determine the effectiveness of an adjustable wood frame-foam and wool mattress bed-system (The Natura Mattress System) in reducing chronic back pain in adults 
Objective and Design:
The purpose of this 6-week Before-After trial was to investigate the effectiveness of the Natura Mattress System in reducing back pain by ≥ 1 unit on the 11-Point Pain Severity Scale (p ≤ 0.05), in chronic low back pain sufferers.
Subject Profile:
The subjects were adults recruited from within and outside the Canadian Memorial Chiropractic College (CMCC) Outpatient Clinic, with chronic low back pain (LBP) of ≥ 2 months duration at the time of entering the study.
Sample Size:
15 subjects were targeted to complete the study.
Outcome Measures:
The primary outcome measure consisted of: morning severity of pain as measured by an 11-point ordinal pain scale (Numeric Rating Scale or NRS). Secondary outcome measures consisted of: (1) daily quality of sleep as measured by a 4-point ordinal scale; (2) effect on daily activity as measured by a 4-point ordinal scale; and (3) daily quantity of analgesics. These outcomes were collected via a daily diary-type of questionnaire.
Statistical Analysis:
Baseline to 4-week post treatment-commencement differences were analyzed for statistical significance using Repeated Measures ANOVA, at the 0.05 level of significance. In addition, all outcome measures were graphed and examined descriptively for any clinically important changes across the 6 week time-frame of the study.
Methods Protocol:
Eligible subjects who read and signed the written informed consent form, were given a package containing a copy of the written informed consent form, and upon completing the 2 week baseline daily diary questionnaires, were contacted by the bed manufacturer, who arranged with the subject a date and time of mutual convenience to deliver the bed (twin or queen size). The subject was then required to complete 4 more weeks of diary questionnaires. Thank-you cards were sent to each subject who completed the study.
Results:
The sample consisted of 6 caucasian females and 7 caucasian males, between the ages of 22 and 75 years, with an average(sd) age of 37.0 (18.44) years. Five subjects were adult students, 5 had sedentary occupations, while 3 had relatively physical occupations. Baseline low back pain (LBP) severities of the sample ranged from 2 to 8 on the 11 point pain scale (NRS), with an average(sd) level of 3.0 (1.75). Average duration of the subjects’ chronic LBP state was 5.6 years, ranging from 3 months to 30 years. Only 2 subjects were taking LBP medications at the start of the study.
Conclusion:
For a generally well educated, young (20-40 years of age), caucasian population with mild-moderate chronic LBP, use of the Natura Bed can be expected to result in a clinically important reduction in pain severity upon both waking and at the end of the day, of at least 1 point (on the NRS) over a 4 week period (p ≤ 0.05).
Further research is recommended which utilizes the Randomized Clinical Trial (RCT) design to investigate the performance of the Natura Bed compared to other beds on the market, and assesses patient characteristics predicting suitability for the Natura Bed.
Images
PMCID: PMC2485300
sleep; bed; foam mattress; back pain; clinical trial

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