Occupational stressors, perceived injustice, and pathways to pain interference and insomnia among workers with headache or low back pain

Objective: Perceived injustice is a psychosocial risk factor associated with delayed recovery and poor occupational outcomes among workers with pain conditions. We examined a theory-informed pathway linking occupational stressors, perceived injustice, pain interference, depressive symptoms, and insomnia, while evaluating selected measurement properties of the Japanese Injustice Experience Questionnaire-Short Form (IEQ-SF-J). Methods: This cross-sectional online survey included 600 Japanese workers (300 with headache and 300 with low back pain). Structural validity of the IEQ-SF-J was evaluated using exploratory and confirmatory factor analyses (CFA) and item response theory. Construct validity was examined using Spearman correlations. Structural equation modelling (SEM) estimated indirect associations between job demands or low job control and pain interference, depressive symptoms, and insomnia, with perceived injustice specified as a latent intervening construct. Results: CFA supported a unidimensional structure (comparative fit index = 0.993; root mean square error of approximation = 0.080). Internal consistency was acceptable (Cronbach's ; = 0.82; McDonald's {omega}; = 0.90), and test-retest reliability was moderate (intraclass correlation coefficient = 0.60). IEQ-SF-J scores correlated significantly with pain interference, insomnia, and depressive symptoms. Job demands and low job control showed significant indirect associations with all three outcomes involving perceived injustice. Conclusions: The IEQ-SF-J showed supportive evidence for several measurement properties and occupied a theoretically coherent position in associations linking occupational stressors with pain interference, depressive symptoms, and insomnia among workers with headache or low back pain.