Feasibility of blinding spinal manual therapy interventions among participants and outcome assessors: protocol for a blinding feasibility trial

Abstract

Introduction: Blinding is a methodologically important aspect in randomised controlled trials, yet frequently overlooked in trials of spinal manual therapy interventions for back pain. To help inform the blinding methods of a future, double-sham-controlled trial comparing spinal manual therapy and nerve root injection for sciatica, we set four objectives: (1) to assess the feasibility of blinding participants, randomly allocated to an active or sham-control spinal manual therapy intervention protocol, (2) to assess the feasibility of blinding outcome assessors within the trial, (3) to explore the influence of spinal manual therapy experience and low back pain on blinding, and (4) to explore factors contributing to perceptions about intervention assignment among participants and outcome assessors. Methods and analysis: Two-parallel-group, single-centre, sham-controlled, methodological blinding feasibility randomised trial. We will recruit between 60 and 100 adults with or without back pain and with or without experience of spinal manual therapy from Zurich, Switzerland. Participants will be randomised to either an active spinal manual therapy, or a sham-control spinal manual therapy protocol—both interventions delivered over two study visits, one to two weeks apart. The primary outcome is participant blinding using the Bang blinding index within each intervention arm immediately after each of the two study visits. Secondary outcomes are participant study-level blinding using the James blinding index, outcome assessor blinding (Bang and James blinding indices), self-reported factors influencing perceived intervention assignment among participants and outcome assessors, and participant-reported credibility and expectancy of study interventions. Other outcomes—included to mask the study objective from participants—include lumbar spine range of motion, self-rated general health, satisfaction with care, back flexibility, pain intensity and function. Treating clinician outcomes include intervention delivery fidelity and self-rated quality of intervention delivery. Ethics and dissemination: The independent ethics commission of Canton Zurich granted ethical approval for this study (KEK 2023 − 00381). Written informed consent will be obtained from all participants. Findings will be disseminated in scientific conferences and a peer-reviewed publication and inform the blinding component of a future randomised controlled trial comparing spinal manual therapy and nerve root injection for sciatica—the SALuBRITY trial. Trial registration number: NCT05778396

'Which treatment do you believe you received?' A randomised blinding feasibility trial of spinal manual therapy

“…A value of 1 is returned when all intervention beliefs correctly match actual intervention assigned. An arm-speci c BI between − 0.3 and 0.3 was prespeci ed as suggestive of 'adequate' blinding [10,20]. A sum BI was calculated measuring the between-arm difference in proportions of the same belief.…”

“…The trial protocol and statistical analysis plan are available [10]. This was an investigator-initiated, twoparallel-arm (allocation ratio 1:1), single-centre, placebo-controlled, blinding feasibility RCT.…”