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Objectives: Long-duration activity-limiting neck/back pain is common, but the knowledge of what work and lifestyle factors that influence the prognosis is sparse. The objective was therefore to evaluate if two factors, good self-perceived work ability and no daily smoking, are associated with a favourable prognosis of long-duration activity-limiting neck/back pain in a working population, and if these exposures have a synergistic prognostic effect.

Design: A prospective cohort study based on three subsamples from the Stockholm Public Health Cohort.

Settings: A working population in Stockholm County, Sweden.

Participants: Individuals, 18-61 years old, reporting long-duration activity-limiting neck/back pain the previous 6 months at baseline in 2010 (n=5177).

Measures: The exposures were: self-perceived work ability (categorised into good, moderate and poor) and daily smoking (no/yes). The outcome in 2014 was 'absence of long-duration activity-limiting neck/back pain' the previous 6 months representing a favourable prognosis of reported problems at baseline in 2010. Risk ratios (RRs) and risk differences (RDs) with 95% CI was estimated by general linear regressions, and the synergistic effect was estimated by the synergy index (SI) with 95% CI.

Results: Participants with moderate or good work ability, respectively, had an adjusted RR for a favourable prognosis of 1.37 (95% CI 1.11 to 1.69), and 1.80 (1.49 to 2.17) in comparison with participants with poor work ability. The corresponding adjusted RD were 0.07 (0.02 to 0.11) and 0.17 (0.12 to 0.22). Participants not smoking on daily basis had an adjusted RR of 1.21 (1.02 to 1.42), and an adjusted RD of 0.05 (0.01 to 0.10) for a favourable outcome compared with daily smokers. The adjusted SI was 0.92 (0.60 to 1.43).

Conclusion: For participants with long-duration activity-limiting neck/back pain, moderate or good self-perceived work ability and not being a daily smoker were associated with a favourable prognosis but having both exposures seemed to have no synergistic prognostic effect.