During the last 20 years, flexible flatfoot (FF) has been increasingly treated by less-invasive surgery (LIS) in children and adolescents [1]. Currently, a similar trend has been observed in the second half of the past century where overtreatment was mainly conservative, consisting of insoles and orthopedic shoes [2], whereas today, flatfeet (FFT) appear to be overtreated by LIS [3]. The latter is based on exosinotarsal screws and endosinotarsal implants, which are an evolution of Grice subtalar arthroereisis (SA) [4]. These surgical techniques aim to rebuild the longitudinal arch of the foot by fixing both the medio-plantar shift of the talus and the calcaneal valgus, but, at the same time, limit the movement of the subtalar joint [4].

Both parents and physicians are concerned about FF, owing to the belief that it is a foot deformity that causes functional problems in children and adolescents [5,6], although that belief is not substantiated in the literature [7,8,9].

Another important cause for concern is that FF may worsen in adulthood, overburdening parents with the responsibility of preventing such an evolution by choosing appropriate treatment during childhood [10,11].

In this article, we attempt to provide proper context for FF, which, in our opinion and according to other reliable authors [12,13,14], should not be considered to be a true foot deformity, but rather a variation of the foot’s anatomy that sometimes becomes symptomatic, thus requiring treatment. To give the correct indication for the treatment of FF by LIS, owing to the increase in its frequency in recent years [1], we reviewed the literature on the epidemiology, etiopathogenesis, pathophysiology, clinical aspects, and treatment of this condition. The FF cases illustrated in this review are taken from the authors’ archives.

As this is a narrative review with a critical appraisal on less-invasive surgery, PRISMA methodology was not followed. Regarding the research method and sources of information, three authors of this review (F.D.M., E.M. and D.L.) searched the literature by consulting the Medline (PubMed), Cochrane Library and Google Scholar databases. Pertinent pamphlets retrieved from the websites of large hospitals and universities and foot and ankle textbooks were also considered and are quoted in the References section. This research was done independently by each of the three authors from 1 January 1952 to 1 November 2025.

To build an effective search string, the following keywords and phrases were used in various combinations to obtain the most pertinent articles: flexible flatfoot (FF), FF epidemiology, FF etiopathogenesis, FF pathophysiology, FF diagnosis, FF conservative treatment, FF less-invasive surgery, and subtalar arthroereisis. No language restrictions or filters were applied. The search included epidemiological studies carried out on large numbers of individuals and etiopathogenetic, pathophysiological, clinical and conservative treatment studies, systematic reviews, and meta-analyses, privileging those with a level of evidence of II–III and that attempted to minimize the risk of bias. Clinical studies treating syndromic FF and those with differential diagnosis from other pathologic and painful coexisting foot conditions mimicking symptomatic FF were also taken into consideration.

The search was particularly focused on less-invasive surgical treatment of FF by subtalar arthroereisis, mainly including studies published from 2006 to 2025, regardless of their level of evidence, which was most frequently level IV. A small number of articles on the surgical treatment of FF by the Evans-Mosca procedure and triple arthrodesis were also reviewed.

The three reviewers retrieved the data and independently analyzed each study selected; instances of disagreement were resolved by discussion among the four authors. When no data could be found on the peculiar aspects of the topic by the academic search engines, the authors’ opinion was called upon to fill the gap, but it was labeled as expert opinion (level of evidence V) and was not included in the evidence-based conclusions.

Response letters, comments, case reports and other articles dealing with surgical treatment of FF other than those previously mentioned, as well as articles dealing with the treatment of pathologic FF, were not considered. Institutional Review Board approval was obtained before starting this review, and written informed consent was obtained either from patients or their tutors for the publication of anonymized images.

Epidemiological studies, carried out all over the world, have highlighted three very important points: (1) In children, FF prevalence decreases spontaneously during the first decade of life because the longitudinal arch of the foot forms by itself with growth in that period [17,18,20] (Figure 3). (2) In adults, FF prevalence varies from about 12% to 15% of the general population [15,16,21]. (3) Most FFT are asymptomatic, with a low prevalence of symptomatic cases [15,16,17,18,19,21]. The studies by Harris and Beath and Lakstein et al. [15,16] have been disapproved by Giannini and Ceccarelli [92], who made the following remarks: “The assessments usually were based… on selected individuals such as soldiers, and therefore the assessments were about functionally good feet”. “In some cases patients become used to their relative disability and change their habits…”. “Feet with excessive pronation can be painful or, if not painful, may very likely lead to future problems, and thus should be treated” [92]. However, these remarks have limited evidence because both studies [15,16] were carried out on recruits before their enrollment as soldiers while, as far as we know, there is no evidence that children will systematically have problems in adulthood with FFT or with any other pathology of the locomotory apparatus caused by FF.

FF etiopathogenesis is still unknown. In fact, no histologic, histochemical, or biochemical study has been done so far to explain why, in FF, the fibrous structures supporting the longitudinal arch of the foot are lax. FF is often associated with the generalized joint laxity, which is a familial condition characterized by joint hypermobility, the pathogenesis of which is also unknown [27]. In cases of generalized joint laxity, the hyperextended thumb may touch the forearm. Both genu and cubitus recurvatum may also be present [27]. FF with generalized joints laxity is also associated with congenital benign hypotonia, a neurological disease whose pathogenesis of which is still unknown [29].

Furthermore, we still do not know why, in most FFT, the laxity of both capsules and ligaments of the longitudinal arch of the foot disappears and their normal strength is recovered during late childhood and adolescence. However, sex hormones might play a role in this structural change [93].

Severe FFT with diffuse ligamentous laxity is associated with diseases of the connective matrix such as Marfan disease, Ehlers–Danlos syndrome, and trisomy 21 or Down syndrome. The former is caused by the absence of fibrillin, a protein forming the outer layer of the elastic fibers; Ehlers–Danlos syndromes are caused by either a defect of the collagen structure or of its state of aggregation, while joint laxity in Down syndrome is caused by an increased synthesis of collagen type VI [30,31,32]. It may be assumed that the cause of the FF ligament’s laxity will eventually be discovered, as has occurred for the above-mentioned genetic diseases.

Both children and adolescents with high BMI are at risk of developing FF, genu valgum and lower limb joint pain [28]. They have less body control and functional ability and, quite often, poor coordination of movements. Obese children typically lead a sedentary lifestyle. They tend to refuse sports and any form of physical activity. The treatment of this condition is complex, involving mainly pediatricians and psychologists. It is evident that curing only FF plays a marginal role in this complex clinical condition [94].

The pathophysiology of FF is rather complex. Tarsal ROM is increased according to the Huson law [34], as is tibio-tarsal ROM, due to ligament laxity. Consequently, the talus shifts both medially and plantarly, and the malleolar mortise rotates internally to maintain the correct relationship of the tibio-tarsal joint, while the forefoot pronates to guarantee correct loading on the metatarsal heads. At the same time, the calcaneus shifts in valgus at the subtalar joint and, in long-standing cases, the consequent retraction of the triceps’ surae–tendo Achillis unit makes the Silfverskiöld sign positive [12,13,15]. Lower limb rotational deformities are also present in people with FF. In those cases, there is a significant decrease in the strength of hip external rotators, internal rotators, flexors, and extensors, which contributes to poor control of hip position [33].

Pain is the typical symptom of symptomatic FF. In some cases, excessive strain on some muscle-tendon units and capsules and ligaments on the medial side of the tibio-tarsal and tarsal joints, as well as overloading on the subtalar joint, can cause ankle and foot pain. High BMI, high levels of activity, improper footwear, and age-related loss of elasticity in tendons and ligaments may be determinant contributing factors for triggering pain in patients with FF.

Fatigue is the other symptom characterizing symptomatic FF. The current consensus is that the collapsed arch causes extra energy expenditure due to the lack of ground reaction force and consequent muscle imbalance, with some foot activators working more than others, which are inactive during gait [43].

Recent electromyographic and gait analysis studies have shown that foot muscle activity and foot ground contact in FFT are different from normal-arched feet [44,45]. However, different biomechanical behavior does not indicate pathological behavior producing either immediate or delayed symptoms like pain and fatigue, as shown by epidemiological studies [15,16,17,18,19,21]. However, in cases of easy fatiguability, all neuromuscular diseases must be ruled out [52], and the examining orthopedist should perform a careful diagnostic reassessment.

FF diagnosis is based first on a physical examination. In the standing position, the longitudinal arch of the foot is absent, but it reappears either after having elicited the Jack’s test or when the patient walks on tiptoes. In the lying position, with the patient prone and with foot manipulation bringing the hindfoot in supination and the forefoot in pronation, the longitudinal arch easily recovers because all of the foot joints are souple. Only in severe and long-standing FFT is may maneuver be unsuccessful because the alteration of the morphology of the tarsal joints hinders the re-establishment of the normal anatomic articular relationships. All of the other dynamic tests are negative in asymptomatic FF, including endurance tests, such as jumping on one foot at a time, that conversely may become positive in truly symptomatic FF patients.

Standing radiographs of the foot are useful to confirm diagnosis in doubtful cases [22], while dynamic radiographs and weight-bearing CT scans may be useful for both diagnosis and treatment [38,39]. On the contrary, footprints might provide false positivity in young children [12,13]. MRI is indicated either for differential diagnosis with pathologic FF or when abnormalities of the subtalar joint are suspected [40].

Differential diagnosis between FF and pathological flatfoot is easy because the latter is rigid and is not correctable by manipulation, as is FF. The only exception is peroneal spastic FF, which is stiff like pathological flatfoot. In that case, MRI is needed to evaluate the presence of tarsal coalitions that are pathognomonic of pathological flatfoot [12,46].

However, a crucial point is to make a correct differential diagnosis between a truly painful FF and other painful pathological conditions of the foot that may coexist with an asymptomatic FF, thus transforming it into a symptomatic FF. The most frequent pathological conditions needing differential diagnosis are Sever disease (Figure 1), Kohler I disease, accessory tarsal navicular, os trigonum syndrome, plantar fasciitis, growing pains, Freiberg disease, osteochondral lesions of the talus, osteoid osteoma of the foot bones and chronic ankle sprain (Figure 2). In overweight children and adolescents with FF leading a sedentary life, as well as in young people who seek surgery to improve their sport performance, when the referred symptoms do not correspond to the objective clinical signs, the physician should proceed with caution. In both cases, pain perception and treatment expectations may be influenced by psychosocial factors, body weight, family concerns, activity level, cosmetic concerns, and unrealistic expectations regarding surgery. As expert opinion, those clinical observations cannot be included in evidence-based conclusions.

Another important aspect is the esthetic appearance of FF, which mainly affects adolescent girls in whom FF may cause significant anxiety. Moreover, girls often have difficulty finding narrow shoes, and therefore they believe that surgery may solve this problem by modifying their FF into a thin-shaped foot. However, we have not been able to find, in the current literature, any reference for this clinical problem in relation to FF.

Indications for treatment should be carefully evaluated in a condition like FF that can be considered a variation of foot development; in fact, most FFT do not cause pain or functional limitations [12,13]. In symptomatic cases, conservative treatment should be first tried. According to recent systematic reviews and meta-analyses, customized insoles, particularly those made with the 3D-printed technology [55,57,58], either alone or associated with strengthening exercises of both leg and foot muscles [94], may be beneficial. However, a single universally recognized percentage of symptomatic FFT responding to insole treatment at various ages is not available, owing to the heterogeneity of research. In a randomized controlled trial of children with symptomatic FF, evaluated by PODCI and PedsQL questionnaires, Hsieh et al. [95] reported an improvement of both pain and function in 76.2% of cases with customized insoles worn for 12 weeks. On the other hand, Oerlemans et al. [56] carried out a systematic review and meta-analysis of both children and adults with FF treated by insoles, including only randomized controlled trials (RCTs) and prospective studies with a control group. Three out of four RCTs, including only children evaluated with validated scales, showed significant improvements of FF pain and function. However, owing to the heterogeneity of the outcome measures, the authors only considered, for their meta-analysis, three RCTs of adults with FF that used VAS as the outcome measure. The conclusion was that insoles provided a significant pain improvement only in adults.

It is even more difficult to give surgical indications for FF [14]. At first sight, this does not seem to be true, as shown by the numerous studies published in the last 20 years on LIS for the treatment of FF—most of them coming from Europe, North Africa, Asia, and South America (Table 1). The high number of symptomatic cases undergoing surgery every month, ranging from 2 to 13 cases with the risk of including misdiagnosed cases, seems to be in contrast with the low number of symptomatic cases reported by epidemiological studies [15,16,17,18,19,20,21]. However, we must consider that epidemiological studies reflect general populations, while surgical series represent selected surgical cohorts. Without considering this selection mechanism, the discrepancy between the data obtained from FF epidemiology and LIS can appear overstated. Another cause for concern is age at surgery: although the average age of the surgical cohorts ranges from 9.5 to 13.7 years, children ranging in age from 5 to 8 years are also included in almost all the surgical series (Table 1). However, the longitudinal arch of the foot is not completely formed before 9–10 years of age, which should also represent the minimum age for LIS. We are also concerned because, in some studies, surgery was not only indicated by symptomatic FF. Roth et al. (Table 1) reported on 94 FFT with and without pain evaluated by altered radiographic angles that normalized after SA in almost 97% of cases. De Pellegrin et al. (Table 1) reported on 732 FFT. Inclusion criteria for SA were not only pain and short Achilles tendon, but also Staheli arch index > 1 or from two to three altered radiographic angles. Franz et al. (Table 1) indicated surgery in 82 FFT by abnormal pedobarography that normalized following SA.

Most of the studies on LIS have a low level of evidence (IV–V). Furthermore, they vary by study design, length of follow-up, outcome measures, and complication rate, and no study reports the ratio between the operated FFT and the overall number of FFT observed in the clinic. In addition, screws used for exosinotarsal arthroereisis vary across the studies for both size and design (either cortical, or cancellous or cannulated), as well as for composition (stainless steel, titanium, bioabsorbable). The same is true for the implants used for endosinotarsal arthroereisis, which also vary in both design and composition (titanium, bioabsorbable polylactic acid, mixed titanium and polyethylene). The only factor that links all of these studies is the surgical outcome, which is either excellent or good in a very high percentage of cases, regardless of the results evaluation method (Table 1). For all of these reasons, we believe that no definite conclusion can be drawn from these studies.

Finally, LIS is not immune to complications, which may be either severe, requiring repeated surgery, or mild, requiring only conservative treatment. They vary according to the specific technique of SA—exosinotarsal or exosinotarsal—as well as to the material of the implant, either metallic or bioabsorbable. The percentage of the most frequent complications is reported in Table 1, although their direct comparison is limited by variability in definition, used implant and length of follow-up across studies. Higher quality studies are needed for a more precise definition of the risk of complication in FF LIS.

Comparative studies between exosinotarsal and endosinotarsal SA do not show significant differences in terms of outcomes, but rather in terms of complications that are different (Table 1). From an economic standpoint, exosinotarsal technique with a metallic screw has the lowest cost [81].

Our experience with FF surgery is in line with the North American pediatric orthopedic surgeons who only recently adopted LIS [89]. We gave indication for surgery to only 26 FFT during a 10-year period, and the age of the patients ranged from 11 to 14 years [90], while in North America, Sullivan at al. operated with exosinotarsal screw SA on only 37 FFT in 5 years and the age of their patients ranged from 9 to 13 years [89]. We also believe that LIS has no universal indication, and therefore severe FF long-standing cases in adolescents might need other reconstructive surgical techniques when both Jack’s test and tiptoe-walking, as well as dynamic diagnostic imaging, do not show restoration of the longitudinal arch of the foot [13,90]. Nonetheless, SA with the proper indication provides very good results by restoration of the medial longitudinal arch with the least surgical invasiveness, mainly in cases of marked ligament laxity [3,61] (Figure 4). In cases of tight Achilles tendon with prevalent calcaneus valgus deformity, Achilles tendon lengthening alone may be indicated if conservative treatment by stretching exercises fails [12].

The most important limitation of our narrative review is the low level of clinical relevance of many of the quoted articles dealing with LIS. In fact, most of them reach a level of evidence of IV–V, while most cross-sectional epidemiological studies, as well as many pathogenetic, pathological, electromyographic, clinical, and conservative treatment studies, often reach a higher level of evidence. Therefore, most of the studies on SA are mainly biased by different cohort sizes, different result evaluation methods, different lengths of follow-up, and lack of a control group to compare surgical outcomes. Readers are then advised to focus more on the clinical and radiographic outcomes rather than on statistical comparison and level of evidence of those studies. Future prospective randomized studies are needed to compare the advantages and disadvantages of FF surgical treatment with non-surgical approaches by long-term follow-up studies.

In summary, the definition of FF as a crippling deformity is supported by mixed evidence. Most FFT are asymptomatic during childhood, adolescence, and adulthood, and they do not need any treatment. In symptomatic cases, after careful diagnostic screening to avoid misdiagnosis with other coexisting diseases, conservative treatment is first indicated. In case of failure, surgery must be performed in residual cases by choosing the most appropriate technique according to the clinical-radiographic features of the individual FF case. SA may be considered in carefully selected children and adolescents because it is technically less demanding and has been associated with satisfactory outcomes in several series.

However, indication should be appropriately given to avoid overtreatment. In addition, parents must be reassured of the benignity of FF and not be burdened with the responsibility of preventing its unfavorable evolution into adulthood, firstly because such an evolution has so far only been supposed, and secondly because FFT that become symptomatic in adulthood may also be treated surgically with satisfactory results [91] (Figure 5). Based on the conclusions of this review, we report the indications for FF management in Figure 6.