A parallel double-blinded randomized controlled study with a 6-month follow-up duration was carried out from February 2019 to April 2020. This study was approved by our institution. Prior to inclusion, all participants voluntarily participated in this study and gave written informed consent; and rights of participants were protected. Patients over 19-year-old with plantar fasciitis refractory to conservative treatment including stretching, resting, ice bag, and extracorporeal shock wave treatment (ESWT) etc. other than orthotics for more than 6 weeks were candidates for inclusion in this study. Furthermore, patients with visual analog scale (VAS) of 5 or higher pain when taking the first step were included. Exclusion criteria were previous insole use, injection around the foot and ankle within 3 months, pulselessness of dorsalis pedis and posterior tibial artery, other systemic inflammatory diseases, comorbidities that can mimic symptom such as Achilles tendinitis and subtalar arthritis, history of foot and ankle fracture, and hindfoot deformity. This study was registered on the clinical trials registry system and the manuscript was prepared according to the CONSORT statement.
Twenty-eight patients were enrolled from the outpatient clinic and informed consents were obtained. An excel-generated block randomization list, which was created by a clinician not involved in this trial for concealment, was used to randomly allocate patients to the newly designed three-spike insole (TSI) group or total contact insole (TCI) group. A blinded physician assessed the outcome data.
The sample size was calculated for a non-inferiority trial of 2 independent means between the groups using VAS as the main variable. For the determination of the minimal important difference (MID) of 2-cm on a 10-cm pain VAS, a 5% alpha set, 20% beta error, and standard deviation of 1.9 cm were established. [18,24] Twelve participants in each group were required for a minimal sample size; it was determined that each group consists of 14 patients, considering a possible loss of 10%.
We used a 3-dimensional (3D) printer (Mandme, ®PLABS) to produce an insole. Both feet of all patients were copied with Copyfoam and the copies were sent to a manufacturer. All insoles were manufactured from thermoplastic polyurethane (TPU, density 12 g/cm3) and had a 58 ± 5 Shore-A hardness filling up to 30% of the insole with TPU. Newly designed insole had three hemispheric spikes along the longitudinal medial arch starting from the center of plantar fascia. When a person’s foot is 28.5 cm long, the measured length of plantar fascia in Copyfoam was about 12 cm. Therefore, each spike was designed to have a 2 cm diameter to support approximately 50% of the medial longitudinal arch; height of the first and third spike was 0.8 cm and that of the middle one was 1.2 cm. The first and the third spikes were placed at the most distal and proximal points of the medial longitudinal arch that were thought to be appropriate for stimulating the fascia on the basis of foot posture on Copyfoam. The distance between the spikes differed among the patients depending on the length of the patient’s arch. Based on the initial copied foam, the total contact insole was manufactured to have structures supporting the arch on its medial border like the general customized total contact orthosis (Fig. 1).
At baseline, all participants were given either of the above-mentioned insoles according to the randomization for daily use for 6 months. They were instructed to wear it on shoes or slippers as much as they could in a day and were allowed to have no more intervention including stretching exercise during the research. All the participants were assessed by a blinded physician at baseline, 6 weeks, 3 months, and 6 months after wearing insole.
Symptoms, pedal function, and foot and ankle related quality of life were the target evaluation. Clinical outcomes were assessed using maximal pain VAS in a day, American Orthopaedic Foot and Ankle Society (AOFAS) score, Foot and Ankle Outcome Score (FAOS), Karlsson-Peterson (KP) score, Medical Outcomes Study Short Form-36 (SF-36) for quality of life, and Foot Function Index (FFI).
An intention to treat analysis was used — for the patients who were dropped out from further evaluations, the last data collected were used in the subsequent evaluations. Patient demographics and clinical outcomes are presented as mean ± SD or count (percentage). We used Mann-Whitney test for quantitative variables and Fisher’s exact test for categorical variables for comparison between the groups. Non-inferiority test was analyzed to assess the VAS between 2 groups. Friedman test was used to compare between two groups over time. Post hoc analysis with Mann-Whitney test was conducted with a Bonferroni’s correction, resulting in a significance level set at p < .0125. The level of statistical significance was set at p < .05. The Statistical Package for the Social Sciences (SPSS, version 21.0, IBM Corp., Armonk, NY, USA) was used for all statistical analyses.