Objectives: To evaluate the proposed manual placebo in terms of success in blinding patients to treatment group assignment and outcomes between the treatment groups.
Design: Randomized controlled trial.
Setting: A chiropractic college research clinic in the midwestern United States.
Subjects: One hundred and eleven (111) individuals aged 18 years and over with subacute or chronic lowback pain.
Interventions: The active treatment consisted of flexion-distraction chiropractic manipulation and trigger point therapy and the control treatment of sham manipulation and effleurage; both groups received eight treatments over a 3-week period. The application of prescribed ranges of biomechanical forces for each treatment was standardized using specialized computerized equipment. "Nontreatment" aspects of the clinical encounter were to be standardized across groups. A primary clinician blinded to treatment assignment provided interpersonal interactions and treating clinicians delivered treatments with a minimum of interaction.
Outcome measures: The accuracy of the patient's perception of group assignment at visit 4 and the mean change in the Pain Disability Index (PDI) over the treatment period were the primary outcome variables.
Results: Patients in the control group were more likely to perceive their treatment assignment accurately than those in the active group (78% versus 54%, respectively). Patients in both treatment groups improved on the PDI and the Roland-Morris Questionnaire; there were no significant differences in improvement between the groups. Age, gender, prior chiropractic experience and expectation of treatment at baseline had no effect on outcomes.
Conclusions: Patients in the control group were not successfully blinded; however, patients' perceptions of treatment group assignment did not significantly affect outcomes. The clinically significant improvement in both groups, independent of patient or clinician expectations, suggests the presence of therapeutic factors common to both groups, other than biomechanical force. Further studies examining other aspects of the clinical encounter, considered separately from biomechanical force, are warranted before arbitrarily designating any intervention as a "placebo."