What triggers an episode of acute low back pain? A protocol of a replication case-crossover study

Objective To describe all the procedures of a study that will replicate a previous case-crossover study investigating physical and psychosocial transient exposure risk factors for triggering an episode of acute non-specific low back pain (LBP) at emergency departments in an emerging country. Methods This case-crossover study will recruit 350 patients, aged between 18 and 80 years, with a new episode of acute non-specific LBP seeking care at emergency departments from public hospitals in Brazil. We will collect information about exposure to a range of physical (eg, awkward postures, lifting children or animals, vigorous physical activity) and psychosocial triggers (eg, distraction, tiredness, alcohol consumption) that were examined in the previous study. The exposure to each trigger during the 2 hours preceding the onset of LBP (case window) will be compared with exposure in the 2-hour periods ending 24 (24-26 hours) and 48 (48-50 hours) hours before the onset of back pain (control window). Conditional logistic regression models will be built to estimate ORs expressing the magnitude of increased risk of developing LBP associated with each factor. Discussion This study will enable the confirmation of previous findings regarding transient exposure to factors that increase risk for an episode of acute LBP in a different setting (at emergency departments of an emerging country). To minimise the potential for recall bias, the maximum time between episode onset and interview will be 7 days; we will encourage participants to use their smartphones and diaries to remember the investigated period. Also, our interview script asked participants to nominate the key aspects of each day. Despite these efforts, the retrospective study design means it is not possible to completely exclude potential for recall bias. Furthermore, participants will be blinded to the case and control periods. Ethics and dissemination Ethics were granted by the Research Ethics Committee (\#20310219.8.0000.0064). Study findings will be disseminated through publications and conference presentations. (AU)