Pes planus is a common condition in the young population and is frequently encountered in adults [
16]. From 2001 to 2016, the rate of hospital admissions in Italy for flatfoot patients under 15 years old increased from 28.97 in 2001 to 142.79 (× 100,000 inhabitants). The data harvested from the SDO reported that the most common treatment was the "Internal Fixation Of Bone Without Fracture Reduction, Tarsals And Metatarsals followed by Subtalar Fusion and Arthroereisis (Fig.
5). Pes planus could be divided clinically into flexible or rigid forms and etiologically in congenital or acquired forms [
17]. "Flexible flatfoot" does not have a proper code in ICD-9-CM. As other conditions of flatfoot involve a wide range of topics, the aim of this discussion is focused on the flexible form of flatfoot that constitutes the most common and benign condition [
18]. Most hospitalizations to treat flatfoot were performed in subjects from 10–14 years old. In this age class, young patients increase their sports activity, leading to an increment in symptomatic forms. Concerning the days of hospitalization, a progressive decrease during the years was found.
Most cases of flexible flatfoot do not need surgical intervention [
19‐
21]. The presence of symptoms is the essential consideration in determining whether to treat conservatively or surgically [
22‐
24]. Pain, fatigue of the foot muscles, quick and frequent shoe breakdown, ankle sprains, and calluses on the medial portion of the foot are some of the symptoms [
25]. Many instances are asymptomatic, and non-invasive treatments are frequently used (casting, orthoses and modified weight-bearing). Otherwise, there is no high-quality evidence that orthotics or surgery can reduce the odds of future problems. The use of orthotics in symptomatic form is contentious [
26,
27] and there is currently insufficient data to support this approach. Only a few non-comparative studies assessed the advantages of orthotics in patients with flexible flatfoot [
10,
28]. On the other hand, surgery may be useful in children who are in discomfort, with or without a short Achilles tendon [
29‐
31]. Soft tissue plications, osseous excisions, osteotomies (medial cuneiform osteotomy, medial slide calcaneal osteotomy, lateral column lengthening) [
32‐
34], tendon lengthening or transfers, arthroereisis, and combinations of these procedures could be used to treat flexible flatfoot caused by constitutional laxity or other acquired conditions (trauma, obesity, [
35‐
38] tumors, infections, neurological diseases). The most interesting finding of this study was related to the progressive rising trend in operative management for acquired flatfoot. The most frequent surgery performed is arthroereisis of the subtalar joint [
39,
40], which is minimally invasive and carries low surgical risks [
41,
42]. This data could probably constitute the most important outlier of the study. In fact, the recent increase in the trend of subtalar arthroereisis could have different reasons. The parents often perceive subtalar arthroereisis as “low risk” with a broader acceptance of surgery. However, no data regarding the reason for this increase could be obtained through the ICD-9-CM code; therefore, it is not possible to report a significant conclusion on this topic. Bernasconi et al. [
41] performed a systematic review on the use of arthroereisis to treat pediatric flatfoot. They reported a rate of complication that ranged from 0 to 11%. However, the American Orthopaedic Foot and Ankle Society reported 33% of complications (mainly implant mobilization) [
43]. Moreover, the review by Shah and colleagues [
43] reported the comparison between the trend to perform arthroereisis in non-United States- countries and the United States- countries. Authors sustained that the type of intervention could be influenced by the healthcare system payment [
43]. Further studies are required to assess the reasons for the progressive trend in pediatric flatfoot surgeries.
Our study has some limitations. The ICD-9-CM classification for all the procedures reported was used. However, various codes for the same surgical procedure might be used with the ICD-9-CM system. Indeed, different codes were used in SDO to record subtalar joint arthroereisis (i.e. subtalar joint arthroereisis, subtalar joint fusion and internal fixation of bone without fracture reduction, tarsals and metatarsals). The code "Subtalar fusion" was also used when absorbable screws were used for subtalar joint arthroereisis. A limitation of the ICD-9-CM code is that there is no specific ICD-9-CM code for the flexible flatfoot. Therefore, a flexible flatfoot is reported in the ICD-9-CM System either as “acquired” or “congenital forms”. This heterogeneity of codes may generate mistakes in data reporting and interpretation. Future endeavours should be focused on the differentiation between the two diagnoses.