Effects of insoles adapted in flip-flop sandals for persistent heel pain: a protocol for a sham-controlled randomised trial

INTRODUCTION: Persistent heel pain is a prevalent complaint affecting up to 10% of the population. Insoles adapted in flip-flop sandals are an alternative treatment for pain and function of individuals with persistent heel pain, showing improvement within 12 weeks of treatment. Most studies considered foot posture and biomechanics to prescribe insoles for persistent heel pain, but few verified the effects of a 12-week treatment on pain catastrophising. This study will investigate the effects of insoles adapted in flip-flop sandals on pain intensity, function, functional walking capacity and pain catastrophising of individuals with persistent heel pain. METHODS AND ANALYSIS: This is a protocol for a sham-controlled randomised trial. Eighty individuals with persistent heel pain will be assessed and randomised into two intervention groups: insoles adapted in flip-flop sandals and flip-flop sandals with sham (ie, flat) insoles. Assessments will be conducted at baseline (T0), after 6 weeks (T6), 12 weeks postintervention (T12) and after a 4-week follow-up (T16). The primary outcome will be the pain intensity, and secondary outcomes will be foot function, functional walking capacity and pain catastrophising. Analysis of variance with mixed design (if normal distribution) or Friedman’s test (if not normal distribution) will verify intergroup and intragroup differences. Bonferroni post hoc tests will be performed in case of significant group or time interaction. Intent-to-treat analysis will be used, and a significance level of 5% and 95% CIs will be considered. ETHICS AND DISSEMINATION: This study was approved by the research ethics committee of the Federal University of Rio Grande do Norte (registry no. 4,018,821). Results will be disseminated to individuals, submitted to a peer-reviewed journal and disclosed in scientific meetings. TRIAL REGISTRATION NUMBER: NCT04784598.