Work-related evaluation and rehabilitation of patients with non-acute nonspecific low back pain

Abstract

Low back pain (LBP) continues to be a major health problem causing personal suffering 4 and enormous socioeconomic costs 5-7. Most of the patients suffer from nonspecific LBP (NSLBP) 8-10, defined as not attributable to a recognisable known specific pathology 10. NSLBP is classified according to the duration and localisation of symptoms. Pain lasting longer than 4 weeks is non-acute 11.<br> Management of LBP should include a medical evaluation screening for specific pathology and for psychosocial 12 and work-related factors 9,12. Traditional impairment-based medical measures defining fitness for work are criticised for lacking predictive validity as only few objective physical or biomechanical measures are associated with return to work (RTW) 13-16. Currently, there are reforms in progress in many countries that move away from an ‘essentialist’ diagnostic approach 17 in disability determination towards an evaluation of functional capacity 7. Functional tests purporting to measure a patient’s physical capacity to perform work tasks are employed within Functional Capacity Evaluation (FCE). However, there is increasing evidence that not only physical but also psychosocial factors, such as perceived functional ability (PFA) or work tasks and ‘nonorganic-somatic-components’, influence FCE results and consequently decisions on work ability.<br> Modern treatment guidelines for non-acute NSLBP recommend multidisciplinary treatment, cognitive behavioural therapy, supervised exercises and early RTW. No evidence has been found that one form of exercise is superior to another 12. Although new studies have been published in the meantime, the effect of specific exercise characteristics on work disability is still unclear.<br><br>

Aims<br> 1) To test the validity of the Spinal Function Sort (SFS) assessing PFA for work-related activities by evaluating internal consistency, unidimensionality, concurrent and predictive validity, and responsiveness in a European rehabilitation setting for patients with non-acute NSLPB.<br> 2) To investigate the influences of ‘‘‘nonorganic-somatic-components’’, together with physical and other psychosocial factors, on the results of an FCE in patients with chronic NSLBP undergoing physical fitness for work evaluation.<br> 3) To assess the contribution of ‘nonorganic somatic components’ and ‘submaximal effort’ to lifting performance and to determine the concurrent validity of the ‘nonorganic somatic components with ‘submaximal effort’ during FCE in patients with chronic NSLBP.<br> 4) To determine whether exercise is more effective than usual care to reduce work disability in patients with non-acute NSLBP, and if so, to explore which type of exercise is most effective.<br><br>

Material and Methods<br> The different aims of the thesis required different research designs. Patients with non-acute NSLBP within working age, presenting with at least 6 weeks of sick leave, and with sufficient understanding of German, French or Italian were included in papers I, II, and III.<br> For paper I a prospective cohort study was used. This was embedded within a randomised controlled trial performed during inpatient rehabilitation investigating the effectiveness of a function-centred treatment compared with a pain-centred treatment with 3 and 12 month follow-up for working status 18,19. A total of 170 out of the 174 patients who participated in the randomised controlled trial were included in paper I. All measurements were taken by a blinded research assistant; work status was assessed with questionnaires sent to employers and the patients’ primary physicians, who were blinded to the patients’ group assignments. Internal consistency of the SFS was assessed with Cronbach’s alpha. A principal component analysis was performed to investigate unidimensionality.<br> SFS scores were correlated with fear avoidance beliefs (FABs), pain intensity, physical factors, and FCE. Predictive validity for work status at 3 and 12 month follow-up was investigated with Receiver Operating Characteristic (ROC) curve analysis and responsiveness by calculating Standardised Response Mean (SRM).<br> For papers II and III an analytical cross-sectional study was performed in three rehabilitation clinics in Switzerland. Included were 130 patients referred for physical fitness for work evaluation, with chronic NSLBP as their primary complaint. Evaluations were performed by two independent assessors. These were blinded to each other’s results. The first assessors assessed ‘grip strength’ and psychosocial factors including ‘nonorganic-somatic-components’. The second assessors undertook FCE tests and determined physical effort level during the lifting tests by applying observational criteria. Paper II analysed the influence of psychosocial and physical factors on FCE performance with robust regression analysis. Paper III investigated the contribution of ‘nonorganic-somatic-components’ and ‘submaximal effort’ to lifting performance with linear regression analysis and the concurrent validity of ‘nonorganic-somatic-components’ with ‘submaximal effort’ by calculating sensitivity and specificity.<br> Paper IV consists of a systematic review and meta-analysis. Studies were included if randomised controlled trials were performed, the primary diagnosis in all patients was non-acute NSLBP with a duration of at least four weeks, the experimental treatments used exercise alone or as part of a multidisciplinary treatment, work disability was the primary outcome, and if at least 90% of the patients under treatment were available for the job market in that they were either employed or unemployed but seeking work. Data sources were MEDLINE, EMBASE, PEDro, Cochrane Library databases, NIOSHTIC-2, and PsycINFO until August 2008. Work disability data were converted to odds ratios. Random effects meta-analyses were conducted.<br><br>

Results<br> Paper I revealed a high internal consistency of the SFS (Cronbach’s alpha = 0.98) and reasonable evidence for unidimensionality. Correlations of the SFS with work activities were high (Spearman’s rho> 0.6). ROC curve analysis revealed discriminating power for work status at 3 and 12 month by (area under curve =0.760, 95%CI: 0.689-0.822 resp. 0.787, 95%CI: 0.712-0.851). SRM within the two treatment groups was 0.18 and -0.31.<br> Paper II showed that between 42% and 58% of the variation in the FCE tests was explained in the final multivariate regression models. ‘Nonorganic-somatic-components’ were consistent independent predictors for all tests. Their influence was most important on forward bend standing and walking distance, and less on grip strength and lifting performance. PFA for work tasks was the most important predictor for lifting performance and also contributed significantly to grip strength and forward bend standing. In paper III ‘nonorganic-somatic-components’ and ‘submaximal effort’ were found to be independent contributors to lifting performance during FCE. The contribution of ‘submaximal effort’ was higher than that of ‘nonorganic-somatic-components’, shown by a higher change of coefficients ranging between 42–58% when ‘submaximal effort’ was added to the model compared to 14–17% when ‘nonorganic-somatic-components’ was added. Between 53%-63% of the patients with ‘nonorganic-somatic-components’ were classified as showing ‘submaximal effort’.<br> 23 trials met the inclusion criteria for paper IV. Three studies were excluded from meta-analysis as the presented data did not allow pooling. The remaining 20 studies allowed 17 comparisons of exercise interventions with usual care and 11 comparisons of two different exercise interventions. A statistically significant effect in favour of exercise on work disability was found in a long term follow-up (OR = 0.66, 95% CI 0.48 – 0.92) while this was not the case in the short term (OR = 0.80, 95% CI 0.51 – 1.25) and in the intermediate term (OR = 0.78, 95% CI 0.45 – 1.34). Meta-regression indicated no significant effect of specific exercise characteristics.<br><br>

Conclusions<br> PFA for work tasks can be validly assessed with the SFS in a European rehabilitation setting in patients with NSLBP and is predictive for future work status. PFA together with ‘nonorganic-somaticcomponents’ should be considered for interpretation of FCE. ‘Nonorganic-somatic-signs’ testing and determination of physical effort by observational criteria should not be interchangeably used for interpreting lifting performance during FCE. Exercise interventions have a significant effect on work disability in patients with non-acute NSLBP in the long term. No conclusions can be drawn regarding exercise types.