OPAL: a randomised, placebo-controlled trial of opioid analgesia for the reduction of pain severity in people with acute spinal pain—a statistical analysis plan

BACKGROUND: Low back and neck pain are a leading cause of disease burden globally. Opioids are recommended in guidelines for acute low back and neck pain; however, there is a lack of compelling efficacy data to support this. METHODS: The OPAL trial is a prospectively registered, triple-blinded, randomised, placebo-controlled trial. Patients with acute (≤12 weeks duration) back and/or neck pain receive guideline care plus either an opioid (oxycodone + naloxone, up to 20 mg per day) or a placebo for up to 6 weeks or earlier, if pain is resolved. The primary outcome is pain measured using the Pain Severity Score of the Brief Pain Inventory with the primary time point being 6 weeks. Secondary outcomes include physical function, time to recovery, quality of life, adverse events and risk of opioid misuse. Outcomes are collected at weeks 2, 4, 6, 12, 26 and 52. Analysis will be done on an intention-to-treat principle. p values of < 0.05 will be considered significant and 95% confidence intervals will be reported. Repeated-measures linear mixed models will be used to assess the effect of the treatment group on the primary outcome and continuous secondary outcomes. Adverse events will be compared between groups using Fisher’s exact test. Cost-effectiveness analyses will be conducted if a treatment effect on pain is seen at week 6. Subgroup analyses will be performed to assess whether pain duration and pain location are treatment effect modifiers. DISCUSSION: The OPAL trial will provide important evidence about whether a short course of opioids is effective in the treatment of acute non-specific low back and/or neck pain. This pre-specified statistical analysis plan details the methodology for the analysis of the OPAL trial results. TRIAL REGISTRATION: ACTRN12615000775516. The trial has completed recruitment. Follow-up on the last patient will be completed in March 2022.