Study Design and Randomization
This was a prospective, randomized controlled clinical trial followed CONSORT guidelines and was approved by the Ethics Committee of Shin Kong Wu Ho-Su Memorial Hospital in Taiwan. The study was registered at ClinicalTrials.gov (NCT03198299). Written informed consent was obtained from the parents of participating children, who were subsequently randomly divided into 2 groups. Randomization was accomplished using computer-generated numbers with a block size of 4. When initially recruited, each participant received a sealed envelope revealing their group allocation. The participants were then randomly assigned to the treatment group (with customized medial arch-support insoles) and the control group (without customized medial arch-support insoles). The control group members were told they were on a 12-week waiting list to receive the customized insoles. All participants were blinded to their group allocation. An investigator blinded to group allocation evaluated the basic demographics, physical functional performance, physical function, and psychological well-being at the baseline and 12 weeks after the intervention (Figure 1).
Participants
From January 2016 to December 2016, a total of 45 children were recruited from the outpatient clinic at the Department of Physical Medicine and Rehabilitation, Shin Kong Wu Ho-Su Memorial Hospital in Taiwan. The children were brought by their parents for a regular physical check-up or for musculoskeletal counseling and had no complaints of any lower limb pain. The inclusion criteria of this study were healthy children from ages 3 to 10 who could walk independently for 15 meters. We excluded children with a confirmed diagnosis of developmental delay or pathological flat foot, previous foot surgeries or injuries, foot structural deformity, or neurological disorder.
Baseline Assessment
The investigator and the assessor were blinded to the group allocations. The participants of both groups and their parents were also blinded to their group allocations. Baseline characteristics including age and sex were collected, and body mass index was measured.
Clinical Measurements
We used the Foot Posture Index to determine the foot position. The child was instructed to stand with arms relaxed at their sides. The position of the joints and the deviation of the foot and ankle were observed. This test consisted of 6 items scored on a 5-point scale from −2 to +2. The final score was defined as highly pronated (+10 to +12), pronated (+6 to +9), normal (0 to +5), supinated (−1 to −4), and highly supinated (−5 to −12). Satisfactory interrater reliability has previously been reported [17].
Intervention
We provided information on the natural history of the pediatric flexible flat foot to the parents and children when they were initially recruited. Each participant in the treatment group was evaluated by a qualified physiatrist who used a heat gun to prepare customized foot insoles according to the children’s feet alignment. The subtalar joint was maintained in a neutral position, and the forefoot and hindfoot were not pronated or supinated during the process. The physiatrist first used a right thumb and index finger positioned at the talar head medially and laterally to maintain the subtalar joint in a neutral position [18]. Next, the physiatrist affixed the heated insole so that it adhered completely to the foot contour to enhance the MLA of the foot. During the process, the participant remained in a standing position to ensure the insole stayed in full contact with the sole of the foot. After molding, the physiatrist reexamined the situation with the participant standing on the insoles to ensure the neutral position of the subtalar joint. The insoles were remolded or modified as necessary. The details of this procedure were described in our previous studies [9,19,20]. The treatment group participants each received a pair of high-density ethyl vinyl acetate thermoplastic foot insoles with medial arch support. Participants were instructed to place the insoles inside comfortable shoes of their choosing. We suggested that shoes with a high, firm heel counter, wide toe box, and flat sole would be the most appropriate selection. The treatment group was instructed to wear the insoles for 1 hour on the first day and to increase the duration of wear by 1 hour per day to reach 5 to 10 hours within 1 week [21]. The control group participants, by contrast, were told they were on a waiting list to receive customized foot insoles after 12 weeks. All children were instructed to wear their shoes as usual at school and for outdoor activities for the duration of the intervention period.
Outcome Measures
Primary Outcome: Physical Functional Performance
Physical functional performance was evaluated by walking speed, stairs ascent and descent tests, the Five Times Sit-to-Stand test, and the Timed Up and Go test. Walking speed was calculated with the participant walking at a comfortable speed and at the fastest possible speed across a 10-meter long hard and flat surface. For the stairs ascent and descent tests, participants ascended or descended a flight of stairs (14 steps with a height of 18 cm each) as fast as possible. The Five Times Sit-to-Stand test evaluated lower limb strength and balance based on how long it took a participant to change from a seated to standing position 5 times. The Timed Up and Go test measured the time needed for a participant to rise from a sitting position, walk 3 meters, turn around, and promptly return to a sitting position. A longer time taken indicated a greater physical functional performance limitation.
Secondary Outcomes: Physical Functioning and Psychological Well-Being
The Pediatric Outcome Data Collection Instrument-Parent (PODCI) was used to evaluate physical functioning and psychological well-being. The PODCI consists of 6 domains: upper extremity and physical function, transfer and basic mobility, sports and physical function, pain and comfort, happiness, and global function. Each domain scales from 0 to 100, with 100 representing optimal functioning. The Chinese version of the PODCI has been found to have high reliability [22].
The Child Health Questionnaire-Parent Form (CHQ-PF28) is a parent-reported questionnaire used to assess the physical and psychosocial functioning of children. Our study appraised the participants’ well-being using 9 of the CHQ-PF28 scales: physical function; role/social functioning: emotional/behavior; role/social functioning: physical, bodily pain, behavior, mental health, self-esteem, general health perceptions, and changes in health [23]. Responses for each scale are summed and transformed into a score of 0 to 100. Higher scores indicate better functioning and quality of life [23].
Statistical Analysis
For an effect size of 0.86, an alpha level of 0.05, and a power of 75% for a randomized controlled trial with baseline and postintervention observations, at least 40 participants must be included (20 in each group) [24]. Given the probability of a 10% dropout rate, at least 44 participants (22 participants in each group) should be selected initially. The results are expressed as means and standard deviations. A chi-squared test and t-tests were used for baseline characteristics and outcomes comparisons. Paired t-tests were used to examine whether significant improvements occurred in the two groups after intervention, with T1 – T0 representing the difference between performance after the 12-week intervention (T1) and performance at baseline (T0). Student’s t-tests were used to compare the improvements between the two groups; 95% confidence intervals were used. The effect size was estimated, with effect size defined as no effect (0-0.19), small effect (0.20-0.49), intermediate effect (0.50-0.79), and large effect (0.80 or higher) [25]. Statistical significance was set at p < 0.05.