Epidemiological differences between back pain of sudden and gradual onset.

Objective: To explore possible differences in risk factors for low back pain according to its speed of onset.
Methods: We analyzed longitudinal data from 1366 hospital nurses in England who initially had been free from low back pain for at least one month. Risk factors were ascertained from a self-administered baseline questionnaire, and outcomes from serial followup questionnaires. Hazard ratios (HR) for developing a first new episode of low back pain during followup were derived by Cox regression.
Results: Low back pain with gradual onset was significantly associated with psychological symptoms measured at baseline [HR 1.7 (95% CI 1.2, 2.4) and higher], but no such association was seen for sudden pain. Low back pain with sudden onset while at work was associated with exposure to specific patient-handling tasks [HR 1.8 (95% CI 1.1, 3.0) to 2.8 (95% CI 1.4, 5.5)]. However, symptoms that came on suddenly elsewhere were not related to occupational activity, and low back pain of gradual onset showed little relation to patient-handling.
Conclusion: These findings suggest that a useful distinction can be made according to the speed and circumstances of onset of low back pain. If confirmed, they have important implications for the evaluation of ergonomic interventions aimed at reducing back pain.