In connection with patients with back pain, prognostic factors refer to all variables that are predictive of future events such as repeated/continued back pain, disability, return to work, costs, etc. Prognostic studies include both clinical studies of variables that are predictive of future events and epidemiological studies of aetiological risk factors. Ideally, in studies of prognostic factors, all patients should have received the same treatment or been in a randomised trial (Altman 2001).
The purpose of studies of prognostic factors is not just to predict disease more accurately or parsimoniously, but also to guide clinical decision-making, improve understanding of the disease process, improve design of clinical trials and to define risk groups.
Systematic reviews
Five SRs on risk factors were identified (Goldberg et al 2000, Hartvigsen et al 2000, Leboeuf-Yde 2000a,b, Lings and Leboeuf-Yde 2000). These studies were excluded because they evaluated risk factors for first-time back pain, which was evaluated in the prevention guidelines.
One SR was identified that included only patients with acute low back pain (Pengel et al 2003). However, this study was included because its purpose was to describe the course of acute low back pain and sciatica and to identify clinically important
prognostic factors for the subsequent resolution or persistence of pain. The study did not reveal any specific prognostic factors, reported that the methodology of most papers was poor, and concluded that prognostic factors should be assessed separately for patients in and out of work, respectively.
Six systematic reviews on prognostic factors for chronicity were identified (Borge et al 2001, Hoogendoorn et al 2000, Hunter 2001, Pincus et al 2002, Shaw et al 2001, Waddell and Burton 2001). Four papers included mixed populations of acute, subacute and chronic pain patients (Hoogendoorn et al 2000, Pincus et al 2002, Shaw et al 2001, Waddell and Burton 2001). Two papers included only patients with chronic low back pain (Borge et al 2001, Hunter 2001).
One of the systematic reviews covered back pain in the occupational setting
(Waddell and Burton 2001). Thirty-four systematic reviews, 28 narrative reviews, 22 additional relevant studies and 17 previous guidelines were included. Among the evidence statements given, the authors concluded that in the worker having difficulty returning to normal occupational duties at 4-12 weeks: there is strong
epidemiological evidence that the longer the length of absence from work due to CLBP, the lower the chances of ever returning to work, and that most clinical interventions are quite ineffective at returning people to work once they have been absent for a protracted period with CLBP; there is moderate evidence that changing the focus from purely symptomatic treatment to a “back school” (or multidisciplinary) type of rehabilitation, can produce faster return to work, less chronic disability and less sickness absence; and there is moderate evidence that temporary provision of lighter or modified duties facilitates return to work and reduces time off work (Waddell and Burton 2001). The authors also highlighted that individual and work-related psychosocial factors play an important role in persisting symptoms and disability, and influence response to treatment and rehabilitation. Workers' own beliefs that their low back pain was caused by their work and their own expectations about inability to return to work are particularly important.
One systematic review of 25 publications (18 cohorts) evaluated psychological predictors of chronicity/disability in prospective cohorts of low back pain
disability) as a result of psychological distress, depressive mood, and to a lesser extent somatisation, emerged as the main finding. The authors highlighted the need to clarify the role of other potentially important psychological factors, in particular fear avoidance and coping strategies, through rigorous prospective studies (Pincus et al 2002).
One systematic review of 13 studies evaluated psychosocial factors at work and in one’s private life as risk factors for chronic low back pain (Hoogendoorn et al 2000). Insufficient evidence was found for an effect of a high work pace, high qualitative demands, low job content, low job control, and psychosocial factors in private life. Strong evidence was found for low workplace social support and low job satisfaction as risk factors for back pain. However, the possibility that these risk factors may have been influenced by other confounding factors led the authors to conclude that there is evidence for an effect of work-related psychosocial factors on low back pain, but the evidence for the role of specific factors has not yet been established
(Hoogendoorn et al 2000).
Prognostic factors predicting extended disability following acute occupational LBP were evaluated in one systematic review of 22 studies (Shaw et al 2001). Significant prognostic factors included low workplace support, personal stress, shorter job tenure, prior episodes of LBP, heavier occupations with no modified duty, delayed reporting, severity of pain and functional impact, radicular findings and extreme symptom report.
No systematic reviews have been carried out on psychological predictors of prognosis (in relation to either natural history or treatment) in patients who already have chronic low back pain.
One systematic review that evaluated the prognostic value of physical examination findings in 10 studies reported that there is no satisfactory answer to the question of whether some physical examination tests have a prognostic value in the conservative treatment of low back pain (Borge et al 2001).
One systematic review of 6 studies evaluated medical history (Hunter 2001). It was concluded that there is moderate evidence that a history of similar pain and a longer duration of previous pain each predict the recurrence but not duration of subsequent pain episodes; limited evidence that a history of similar pain predicts poorer
outcomes after recurrent injury; and limited evidence that a longer time off work before treatment predicts poorer activity and poorer participation outcomes after recurrent injury.
Additional studies
A prospective population-based study investigated prognostic factors for return to work in a cohort of 328 employees sicklisted for 3-4 months because of low back pain (van der Giezen et al 2000). One year after the first day of sick leave, 198 employees had returned to work. The most important predictors of being at work in the final multivariate model were a positive subjective evaluation of the health status (OR 1.53) and a better job satisfaction (OR 1.26). These variables had a significantly larger impact on work status than more physical aspects of disability and physical requirements of the job.
One cohort longitudinal study involving 192 subacute and 61 chronic compensated workers with low back injuries tested a multivariate predictive model of occupational low back disability (Schultz et al 2002, 2004). The study found that positive
predictors of return-to-work 3 months after study's inception and of number of days lost due to low back disability within 18 months after the injury. However, only a small subsample (<30%) of the eligible chronic sample agreed to participate in the study, and the results thus raise questions concerning the generalisability of the results. A prospective cohort study investigating risk factors associated with the transition from acute to chronic occupational low back pain (Fransen et al 2002) included 854 new cases of work-related back injury; 3 months after the initial claim, 204 individuals were still receiving compensation payments. A combined multiple regression model of individual, psychosocial and workplace risk factors showed that poor perceived general health status (OR 1.9) was a significant predictor of chronicity while job dissatisfaction and poor workplace relationships did not identify workers at risk of developing chronic occupational disability.
The two aforementioned studies (Fransen et al. 2002, Schultz et al 2004) both involved a selected population (workers suffering a low back injury and receiving compensation payments) and the generalisability of the results to other populations needs further investigation.
A subanalysis of a randomised clinical trial compared patient expectations and treatment effect in 135 chronic low back pain patients receiving either massage or acupuncture (Kalauokalani et al 2001). Patient expectation regarding treatment benefit was found to be associated significantly with clinical outcome. As compared to patients with lower expectations, participants with higher expectation ratings for the treatment received had a fivefold greater likelihood of improved function after adjustment for sociodemographics, health status, and physical factors (95% CI 1.9- 15.4., p=0.002). The patients with high expectations for a specific treatment had significantly better functional outcomes if they actually received that treatment (p=0.03; R2=0.35).]
One additional prospective study (N=159) aimed to determine the prognostic value of a comprehensive medical assessment for the prediction of return-to-work status in subacute low back work-injured patients (Hunt et al 2002). A full medical assessment was carried out at baseline and a repeat examination was performed 3 months later, when return-to-work status was determined. The authors were unable to identify any medical variables (medical history subscales, physical examination subscales, and lumbar range-of-motion tests) that accounted for significant proportions of variance in return to work. They suggested that injured workers' subjective interpretations and appraisals may be more powerful predictors of the course of post-injury recovery than are exclusively medical assessments.
A randomized study compared manipulation, exercise and physician consultation to physician consultation alone in 204 patients with chronic low back pain. Severe affective stress predicted poor response to manipulation (OR 3.8 (95% CI 1.3 to 10.8)). Over 25 days sick leave during previous year (OR 19.6 (3.8 to 102.5)), poor life control 9.4 (1.9 to 47.0), and generalized somatic symptoms predicted outcome from physician consultation at 1 year (Niemisto et al 2004).
Summary of evidence
• There is strong evidence that low work place support is a predictor of chronicity in patients with acute back pain (level A).
• There is strong evidence that in the worker having difficulty returning to normal occupational duties at 4-12 weeks the longer a worker is off work with LBP, the lower the chances of ever returning to work; and that most clinical interventions are quite ineffective at returning people to work once they have been off work for a protracted period with LBP (level A).
• There is moderate evidence that psychosocial distress, depressive mood, severity of pain and functional impact and extreme symptom report, patient expectations, and prior episodes are predictors of chronicity (level B).
• There is moderate evidence that shorter job tenure, heavier occupations with no modified duty, radicular findings, are predictors of chronicity (level B).
• There is moderate evidence that no specific physical examination tests are of significant prognostic value in chronic non-specific LBP
Recommendations
Assess work related factors, psychosocial distress, patient expectations, and extreme symptom reporting in patients with chronic low back pain.
References
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