'You know you're going to get through this': Volunteers and long-term disaster recovery.

Back pain shows a strong relationship with disability, ranking sixth among the 10 leading causes of disability‐adjusted life years (DALYs) in the age group 50–74 years in 2019 (Diseases GBD and Injuries C ). In older adults, the mean back pain severity shows a remarkable reduction in the first 6 weeks after presentation in primary care; however, more than 60% of them still report non‐recovery after 3 months follow‐up (Scheele et al. ). More than two‐thirds of people present a recurrence within 12 months after recovery (da Silva et al. ), and some develop a persistent and disabling condition (Gomes et al. ). Thus, it is important to treat back pain as a lifelong symptom rather than to focus on single episodes, which means that it is important to focus on the clinical course of back pain (Axen and Leboeuf‐Yde ). Trajectory studies describing a course of repeated measures over time (Nagin ; Nguena Nguefack et al. ), explore subgroups of individuals based on their response patterns and can highlight heterogeneity in the clinical course (Nguena Nguefack et al. ). Previous studies have reported distinct trajectories of pain intensity and disability in patients with back pain. One Brazilian study in older patients with back pain reported three one‐year trajectories of pain intensity (‘pain recovery’, ‘incomplete pain recovery’ and ‘persistent severe pain’) and four one‐year trajectories for disability (‘disability recovery’, ‘incomplete disability recovery’, ‘persistent moderate‐severe disability’ and ‘persistent severe disability’) (Silva et al. ). An American study identified six one‐year pain intensity trajectories (‘moderate pain recovery’, ‘severe pain recovery’, ‘low, low moderate, moderate high and high pain’) and five one‐year disability trajectories (‘functional recovery’, ‘low, low moderate, moderate high and high disability’) in participants with low back pain (LBP) (Deyo et al. ). Both studies above showed the mean pain and disability scores decreased significantly in ‘recovery’ trajectories in the first 3 months while this dramatic decline was not found in other trajectories. And the prognosis was associated with biopsychosocial characteristics, like sex, BMI and comorbid conditions at baseline (Deyo et al. ; Silva et al. ). Trajectory studies are particularly relevant in older adults because this population remains under‐represented in low back pain clinical course research (Deyo et al. ; Paeck et al. ; Scheele et al. ; Wallwork et al. ) and may have distinct clinical and prognostic profiles compared with younger adults (Dionne et al. ; Fortin et al. ; Scheele et al. ). In the Netherlands, a previous study (Enthoven et al. ) focusing on older adults with back pain (BACE‐Dutch (BACE‐D) cohort study) identified three trajectories for pain intensity over a 3‐year follow‐up period: low pain trajectory, intermediate pain trajectory and high pain trajectory. Baseline characteristics (i.e., female, high body mass index, chronic back pain, more disability, lower physical summary score of the Short‐Form 36 questionnaire and negative expectation of recovery) were associated with the membership of intermediate and high pain groups (Enthoven et al. ). Yet, disability, as one of the three core outcome domains in LBP (Chiarotto et al. ), remains underexplored in this population (Wong et al. ). Moreover, existing trajectory research in older adults with back pain mainly focused on a relatively short period of time (1 or 3 years). Therefore, the aims of this study were: