The aim of this systematic review was to provide an overview of the effectiveness of orthoses for symptomatic flexible flatfeet in terms of patient-reported outcome measures compared to no orthoses or sham soles in children and adults.
Three of the four included RCTs in children with no orthoses as control group found that improvements in PROMs were significantly higher in the orthoses than in the control groups [19, 21, 22]. The only study not to specifically include symptomatic participants did not find any differences between the groups . Of the five included adult studies, two RCTs compared orthoses with sham soles and reported significantly higher PROM improvement in the orthoses group compared to the control group [21, 25]. The only prospective study, in which participants could choose between two different types of orthoses or an exercise program, noted improvement in all PROMs in all groups, with no significant differences observed between groups . The remaining two adult RCTs also reported no significant difference between the intervention and control groups [20, 23]. The difference in effectiveness of orthoses reported by the included studies could not be explained by differences in study design, population, follow-up, or any of the other parameters presented in the studies. It is therefore difficult to draw any firm conclusions. However, the meta-analysis showed that the overall decrease in VAS score at follow-up compared to baseline was significantly higher in the orthoses group than the no-orthoses or sham sole group in adults.
This systematic review evaluated differences in PROMs between orthoses and control groups to assess effectiveness of orthoses from a patient perspective. Besides the nine studies included in this review, six prospective studies in children [28–33], one RCT , nine prospective [35–43] studies, and one retrospective study  in adults were identified which also described effectiveness of orthoses in terms of PROMs. However, these studies did not meet several of our inclusion criteria, i.e. the presence of a control group with no orthoses or sham soles and follow-up measurements. When control groups were present, they consisted of patients without symptomatic flexible flatfeet, with other orthoses, or with tape. In the orthoses groups of these studies, improvements in PROMs over time were seen in five child studies and eight adult studies. These results should however be interpreted with caution, since three studies in our systematic review showed significant improvements in PROMs in control groups as well, without significant differences between the orthoses and control groups [20, 24, 26].
Although child and adult flatfeet differ in etiology, all ages are included in this review because of the wide overlap in diagnosing flatfeet, type of symptoms, method of measurement, and treatment (Table 1).
The main limitation of this review was the heterogeneity between included studies, which involved differences in patient characteristics, PROMs, conditions in which the PROM was measured, length of follow-up, and orthoses used, as well as the choice for sham sole or no soles as control group. The use of sham soles as a comparison group is questionable. The aim of using a sham sole in the control group is to decrease the psychological effect of the idea of being treated. However, it is important to be aware that a sham sole could have a positive influence on stability and thereby on PROMs.
There are 40 definitions of flexible flatfeet in children . As there is no universally accepted definition of flatfoot, studies investigating the effect of orthoses on flatfeet have conducted multiple diagnostic measurements based on physical examination and radiographs, which causes further heterogeneity [2, 9–11, 14, 46].
Only one RCT reported compliance and found that just half of the participants in the intervention group wore the orthoses most of the time or always, with lack of comfort as primary reason for not wearing them . Besides compliance, activity and/or supported physiotherapy are also known to affect the PROMS of orthoses usage. Only one study controlled for physiotherapy as confounder with two extra groups .
For future studies, it is recommended to give extra consideration to subject characteristics, the control group used, and whether there is physiotherapy involved. Randomized controlled trials on the effectiveness of orthoses for flatfeet could likewise benefit from the use of a universal PROM tool. A promising possibility may be the use of Patient Reported Outcomes Measurement Information System (PROMIS) to provide evidence-based medicine in orthopedic clinics . PROMIS offers a standardized tool to measure PROMs and allows for comparison of health outcomes across different disease states and populations regardless of age, culture, or disabilities.
Based on the results of this systematic review we cannot conclude that foot orthoses are useful for flexible flatfoot in children and adults. However, the meta-analysis showed a significant decrease in pain in the adult orthoses group after treatment compared to the no-orthoses and sham orthoses groups.