Background: Insoles are commonly prescribed to treat pathologies in a variety of patient groups; however, there is limited evidence to guide clinical decision-making. A well-validated sham insole is critical to conducting a double-blind placebo-controlled trial.
Objectives: The aims were to establish: (1) How are sham insoles constructed? (2) What measures are undertaken to ensure adequate blinding? (3) What methods are used to validate the biomechanical effects?
Study design: A systematic search of the methodology of level I-II therapeutic evidence.
Methods: Searches were conducted in MEDLINE, Embase, Cumulative Index of Nursing and Allied Health Literature, and Cochrane Central Register of Controlled Trials. Inclusion criteria were placebo-controlled clinical trials, sham insoles used, treatment insoles alter biomechanics, treatment insoles meet the ISO definition of foot orthotics, sham and treatment insoles tested in normal walking, and article available in English.
Results: The search generated 270 results. Twenty-four trials were included. 19% of sham insoles were described sufficiently to be replicated. The most common sham construction characteristics were full length, ethylene-vinyl acetate material, and flat insoles. 58% of studies were double-blinded; however, many did not describe any blinding methods. There is evidence that blinding the intervention details and a similar insole appearance is effective to blind participants. 13% of studies included a shoe-only condition to allow assessment of the biomechanical effects of sham insoles.
Conclusions: There is inconsistent construction, blinding, and biomechanical validation of sham insoles. This casts a substantial doubt on the quality and reliability of the evidence base to support the prescription of insoles.
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