Background: Flexible flat foot is a normal observation in typically developing children, however, some children with flat feet present with pain and impaired lower limb function. The challenge for health professionals is to identify when foot posture is outside of expected findings and may warrant intervention. Diagnoses of flexible flat foot is often based on radiographic or clinical measures, yet the validity and reliability of these measures for a paediatric population is not clearly understood. The aim of this systematic review was to investigate how paediatric foot posture is defined and measured within the literature, and if the psychometric properties of these measures support any given diagnoses. Methods: Electronic databases (MEDLINE, CINAHL, EMBASE, Cochrane, AMED, SportDiscus, PsycINFO, and Web of Science) were systematically searched in January 2017 for empirical studies where participants had diagnosed flexible flat foot and were aged 18 years or younger. Outcomes of interest were the foot posture measures and definitions used. Further articles were sought where cited in relation to the psychometric properties of the measures used. Results: Of the 1101 unique records identified by the searches, 27 studies met the inclusion criteria involving 20 foot posture measures and 40 definitions of paediatric flexible flat foot. A further 18 citations were sought in relation to the psychometric properties of these measures. Three measures were deemed valid and reliable, the FPI- 6 > + 6 for children aged three to 15 years, a Staheli arch index of > 1.07 for children aged three to six and ≥ 1.28 for children six to nine, and a Chippaux-Smirak index of > 62.7% in three to seven year olds, > 59% in six to nine year olds and ≥ 40% for children aged nine to 16 years. No further measures were found to be valid for the paediatric population. Conclusion: No universally accepted criteria for diagnosing paediatric flat foot was found within existing literature, and psychometric data for foot posture measures and definitions used was limited. The outcomes of this review indicate that the FPI – 6, Staheli arch index or Chippaux-Smirak index should be the preferred method of paediatric foot posture measurement in future research. Keywords: Foot posture, Pes planus, Pes planovalgus, Flat feet, Child, Paediatric, Validity, Reliability, Foot posture index – Six item version (FPI-6), Staheli arch index, Chippaux-Smirak index * Correspondence: firstname.lastname@example.org International Centre for Allied Health Evidence, University of South Australia, Adelaide, South Australia 5001, Australia School of Health Sciences, University of South Australia, Adelaide, South Australia 5001, Australia Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 2 of 13 Background measures what it is intended to measure . Validity of Flexible flat foot (also known as pes planus or planovalgus) a foot posture measure can be expressed in several ways. in children, when there is the appearance of a lowered For example, criterion-related validity would be the abil- medial longitudinal arch, with or without rearfoot eversion ity of one measure of flat foot to predict results of an-  is one of the most frequently reported reasons to seek other measure of flat foot that is assumed to be valid, orthopaedic opinion . Yet, in typically developing chil- such as comparing a foot print indices to a plain film dren, normative data indicates ‘flat’ is normal for children radiograph as the reference standard . Or construct up to eight years of age , due to age appropriate osseous validity, which in broad terms determines if the measure and ligamentous laxity, increased adipose tissue and imma- has enough ‘sensitivity’ to detect when the condition exists ture neuromuscular control [4, 5]. Although variable, the (e.g. a measure with high sensitivity has a low level of ‘flatness’ of this foot posture reduces over the first decade false-positive diagnoses), and ‘specificity’ to detect when of life [3, 6–9]. However, some children with a flexible flat the condition does not exist (e.g. a measure with high spe- foot posture report lower limb pain  and have demon- cificity has a low level of false-negative diagnoses) . To strated reduced lower limb function . Furthermore, be confident that a diagnosis of flat foot is correct, the adults with flexible flat feet report significantly increased measure used needs to be both valid and reliable for the levels of back and lower limb pain  and reduced quality population to which it’sapplied. of life . The challenge for health professionals is in iden- The primary aim of this systematic review was to in- tifying when a child’s foot is, or isn’t, in keeping with devel- vestigate how paediatric foot posture is measured and opmental expectations, particularly in relation to foot how paediatric flat foot posture is defined. The second- posture and/or function; in order to reassure, monitor or ary aim is to identify the psychometric properties of the intervene accordingly [14, 15]. Therefore, the measure used foot posture measures used to determine if these mea- to indicate where a foot posture is outside of the expected sures are valid and reliable for this population. flatness in children (i.e. the diagnoses of flat foot) needs to be valid, reliable and appropriate for developing foot pos- Methodology ture typically observed. Protocol and registration Flat foot is diagnosed through a variety of measures, The systematic review was guided by the PRISMA including plain film radiographs (e.g. x-ray), static foot protocol . The registered protocol is listed on PROS- posture measures and footprint analysis . Plain film PERO, registration number: CRD42016033237. radiographs are considered the reference standard to de- termine flat foot magnitude; however, this method is Information sources and search strategy costly, involves radiation risk, and is not routinely used The following databases were searched from inception in clinical practice . Plain film radiographs, static to Jan 2017: MEDLINE [Ovid], CINAHL, EMBASE, The postures or footprint methods allow flat foot description Cochrane Library, AMED, SportDiscus, PsycINFO, and by analysing different angles or measures and, in many Web of Science. The search terms are outlined within cases, comparing these to known population norms. The Table 1. prevalence of paediatric flat foot has been reported as Medical subject headings (MeSH) were exploded, com- low as 0.6% and as high as 77.9% (age range 5 to 14 years bined with relevant keywords and truncated as necessary. and 11 months to 5 years respectively), [18, 19]. Whilst Searches were limited to English language studies. Further an explanation of this broad variation may be due to the studies were sought from a review of reference lists, changing foot posture as the child develops, there is concern that the measures of flat foot may not differen- Table 1 Search terms for systematic review of the literature on tiate between what is an expected level of ‘flatness’ in flexible flat foot in paediatrics children and abnormal presentations . To the best of Search Terms the authors knowledge, there is no comprehensive re- Foot/ OR Feet view of the psychometric properties of flat foot measures AND as they apply to the paediatric population . Child/ OR Infant/ OR asolescen*/ OR “preschool”/ The two core elements of psychometric properties are AND reliability and validity . Reliability relates to the in- herent variability of a foot posture measure and the posture*/ OR “biomech*”/OR “footprint*”/OR “morphology*”/OR “navicular height”/OR “foot posture ind*”/OR “p?ediatric flat foot error that is attributable to the rater and the tool used, proforma”/OR “arch ind*”/OR “arch height ind*”/OR “foot mobility expressed as the stability of the data when measured by: magnitude”/OR “hindfoot posture”/OR “arch insert”/OR “medial arch”/ one observer over two or more occasions (i.e. intra-rater OR “foot posture measure*”/OR “foot function ind*”/OR “p-ffp” [paediatric flat foot proforma]/ OR “pffp” [paediatric flat foot proforma]/ reliability); or two or more observers (inter-rater reliabil- OR “fpi”/OR “fmm”/ ity), . Validity relates to the extent to which a tool Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 3 of 13 conference proceedings and personal communications Data extraction was in keeping with the aims of the with content experts (Fig. 1). In addition, studies refer- study and included; study design, participant age range, enced within the final included articles that cited psycho- sample size, ethnicity/country of study, foot posture metric properties of the measures and criteria used to measure(s), flat foot definition and relevant psychomet- define flat foot were sourced (Fig. 1). ric data related to QAREL and a purpose-built criterion described below. Eligibility criteria The outcomes of interest in validity studies were sensi- Studies were included if published in peer-reviewed jour- tivity, specificity and correlation with a reference standard nals, participants were aged ≤18 years and the outcomes (e.g. plain film radiographs). Validity was assessed with a included a definition and measure of flat foot. Table 2 purpose-built criterion (Additional file 1), covering: re- displays the full inclusion and exclusion criteria. ported validity of the flat foot measure and definition; age Title, abstract and full-text screening was independently (in years) of the test population; differences in the cited conducted by two investigators (MP, HB/SM) with a third protocol reported and included study protocol; and, a reviewer (CW) consulted in the event of non-agreement pragmatic determination of whether validity was demon- (Fig. 1). strated for a paediatric population (yes/no/with caution). For example, a yes was assigned if a paediatric sample was Critical appraisal of bias and data extraction used for validity testing, the study protocol matched the A priori decision was set to include all studies meeting cited protocol and sensitivity / specificity or correlations the criteria regardless of potential risk of bias and in- with reference standard were moderate or above; a no clude all measures of flat foot where validity and reliabil- would be assigned if the study population was adult or ity measures reached a moderate or above rating (see sensitivity/specificity or correlations with reference stand- data management for rating parametres), [22, 24, 25]. ard were below moderate. With caution was assigned if Fig. 1 Flow chart of search strategy Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 4 of 13 Table 2 Inclusion and exclusion criteria Inclusion Exclusion Sample included individuals with pes planus Participants with a history of rigid pes planus Definition of pes planus, with criteria described > 18 years of age Conducted/described measures, which were Participants who had acutely painful or aimed at diagnosing pes planus inflammatory conditions (e.g. juvenile arthritis) (e.g. rearfoot posture, arch height and footprint measures) Children (≤18 years of age) Empirical studies English language the study population had been paediatric but aspects of Data management sensitivity/specificity or correlation with a reference stand- Data were synthesized in table form. Correlations with ard had mixed results (Additional file 1). reference standards and inter-rater reliability outcomes The reliability outcome of interest was inter-rater were presented as Intraclass Correlation Coefficients agreement. Inter-rater reliability studies were appraised (ICCs) , kappa coefficients  or sensitivity and using the QAREL checklist [26, 27] and a purpose-built specificity data . For consistency, outcomes were assessment (Additional file 1). The 11 item QAREL tool rated according to Fig. 2. All other responses displayed assesses: if the test evaluated a sample of representative as descriptive only or awarded a yes/no/with caution re- subjects; was it performed by raters representative of sponse. Outcomes were required to be deemed valid and those standardly using the measure; were raters blinded reliable to be accepted as appropriate. to i) the findings of other raters, ii) their own prior find- Due to the heterogeneity of the included studies, a ings iii) the reference standard outcomes, iv) other clin- meta-analysis was not conducted. Instead, a descriptive ical information, and v) cues that were not part of the synthesis of the results was undertaken. procedure; was the order of examination randomised; was the time interval between measures suitable; did Results they apply the protocol appropriately; and, was the stat- Study selection istical analysis correctly conducted. Each item was The search strategy identified 1101 unique titles (Fig. 1). scored as yes, no, unclear or not applicable rating. The Following screening, a total of 27 articles were included QAREL score is the number of items that received a in the review. ‘yes’ rating (Additional file 1). The purpose-built criteria covered five criteria; definition of flat foot used, age (in years) of the test population; differences in protocol re- ported between the cited and included article; inter-rater Participants reliability measure and outcome; and, a pragmatic deter- A total of 15,301 child participants were included minant of whether reliability was demonstrated for a within the 27 studies (Table 3). Participants ranged paediatric population (yes/no/with caution). The assign- between 3 and 18 years of age. Sample sizes ranged ment of yes/no/with caution were based on similar out- from 22 to 5866 (Table 3). In one study, all partici- comes as for validity ratings (Additional file 1). pants were male . Four studies separated partici- Two investigators independently extracted data and pants into overweight and normal weight groups for assessed articles against the QAREL criteria and analysis [29–32]. Ethnicity or country of study was re- purpose-built criteria (HB, MP/CW) with any discrepan- ported in 26 studies, representing 15 different ethnici- cies resolved by a fourth reviewer (SM). ties or countries (Table 3). Fig. 2 Rating parametres applied Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 5 of 13 Table 3 Summary of included studies Author (date) Study N Study Study aim Participants Mean age (SD), Ethnicity Foot posture code design range in years* or measure used Country of study Abolarin  560 Cross- To determine the role of age School children 6–12 Nigerian Instep et al. (2011) sectional and type of foot wear as predictors of flatfoot Aharonson,  82 Case- To establish foot-ground Children with 4–6 Caucasian Rearfoot Arcan & series pressure patterns flexible flat foot eversion Steinback (1992) Foot ground pressure Plantarflexion of talus angle Calcaneal pitch angle AP talocalcaneal angle Bok et al. (2016)  21 Cohort To evaluate the effects of Children with 9.9 (1.6), 8–13 South Rearfoot different foot orthoses flexible flat foot Korean eversion (plus inversion angles on plantar one of the pressure during gait following) AP talocalcaneal angle Lateral talocalcaneal angle Talus-first metatarsal angle Calcaneal pitch angle Chang et al.  1228 Cohort To establish a new classification School children 7.3 (1.1), 6–10 Taiwanese Staheli arch (2014) of flatfoot by characteristics of index frequency distribution in Chippaux- footprint indices Smirak index Chen et al.  1319 Cohort To analyse and compare Children with 5.2, 3–6 Taiwan Clarke’s angle (2011) footprint measures of flexible flat foot Chippaux- preschool aged children Smirak Index Staheli arch index Chen et al.  605 Cohort To determine the prevalence Children with & 4.4, 3–7 Taiwanese Chippaux- (2014) of flatfoot in children with without Smirak index delayed motor development developmental coordination disorder Chen et al.  21 Cohort To investigate the effects of Children with & 6.3, 5–11 Taiwanese Arch index (2015) foot wear on joint range of without flat motion, ground reaction foot forces and muscle activity Drefus et al.  30 Cross- To determine the intra and Children 9.6 (2.0), 6–12 United Rearfoot (2017) sectional inter-rater reliability of the States eversion Arch height index Arch height index (sitting/ standing) Evans and  728 Cross- 9.1 (2.4), 3–15 Australia FPI-6 Karimi (2015) sectional and Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 6 of 13 Table 3 Summary of included studies (Continued) Author (date) Study N Study Study aim Participants Mean age (SD), Ethnicity Foot posture code design range in years* or measure used Country of study To explore the relationship Over and United between foot posture and normal weight Kingdom body mass children Ezema et al.  474 Cross- To determine associated Children 6–10 Nigerian Staheli arch (2014) sectional personal characteristics index of flatfooted school children Galli et al. (2014)  70 Cohort To determine if children Children with & 9.6 (1.7), 4–14 Italy Arch index with Down syndrome were without Down characterised by an syndrome accentuated external foot rotation in gait Galli et al. (2015)  64 Cohort To characterise quantitatively Children with & 8.6 (2.4), 5–13 Italy Arch index the foot-ground contact without parameters during static cerebral palsy upright standing García-Rodríguez  1181 Cross- To estimate prevalence and School children 4–13 Spanish Plantar et al. (1999) sectional number of unnecessary footprint treatments of flatfooted children Kothari et al.  95 Cross- To investigate the relationship Children with & 11 (2.9), 8–15 United Arch height (2016) sectional between foot posture and the without flat Kingdom index proximal joints foot Morrison, Ferrari  22 Quasi- To report clinical findings of Male children Median age 7.5, 6–11 United FPI-6 & Smillie (2013) RCT foot posture and lower limb with Kingdom hypermobility and evaluate developmental the impact of foot orthoses coordination on spatio-temporal gait disorder parameters. Nikolaidou &  132 Cohort To develop a footprint-based School children 10.4 (0.9), 9–11 Greek Arch index Boudolos (2006) classification technique for the Chippaux- rational classification of foot types Smirak index Martirosov’sK index Clarke’s angle Pau et al. (2016)  130 Cohort To screen plantar pressures Overweight, 9.3 (2.0), 6–13 Italian Arch index during level walking with a obese and backpack among normal, normal weight overweight and obese school children children Pauk, Ihnatouski  93 Cohort To assess differences in plantar Children with & 12.6 (1.9), 9–16 Poland Clarke’s angle & Najafi (2014) pressure distributions and without flat Calcaneal reliability of the Clarke’s angle foot pitch Calcaneal first metatarsal angle Pauk & Szymul  73 Case- Comparing vertical ground Children with & 10.8 (3.6), 4–18 Poland Clarke’s angle (2014) control reaction force data between without flat Rearfoot flat and neutrally aligned feet foot eversion Pfeiffer et al.  835 Cohort To establish prevalence and Children 3–6 Austrian Rearfoot (2006) cofactors of flatfoot, and eversion estimate number of unnecessary interventions received Reimers,  759 Cohort To establish foot deformity Children and 3–17 Denmark Chippaux- Pedersen & and triceps surae length in adolescents Smirak index Brodersen (1995) Danish children Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 7 of 13 Table 3 Summary of included studies (Continued) Author (date) Study N Study Study aim Participants Mean age (SD), Ethnicity Foot posture code design range in years* or measure used Country of study Selby-Silverstein,  26 Cohort To determine if foot orthoses Children with 3–6 North Rearfoot Hillstrom & immediately affected gait of flat foot, with & American eversion Palisano (2001) children with Down syndrome without Down or excessively pronated feet syndrome Stavlas et al.  5866 Cross- To determine foot morphology Children 6–17 Greek Footprint (2005) sectional evolution in children between evaluation 6 and 17 years of age Tashiro et al.  619 Cross- To investigate the relationship Children 11.2 (0.7), 10–12 Japan Staheli arch (2015) sectional between toe grip strength index and foot posture Twomey et al.  52 Cohort To investigate differences in Children with & 11.2 (1.2), 9–12 Not Clarke’s angle (2010) kinematics during walking gait without flat reported Arch index foot Navicular height Villarroya  116 Case- To evaluate the measures of, Obese & non- Boys 12.4 (1.6), Girls 11.9 Spanish Clarke’s angle et al. (2009) control and foot arch types, in different obese children (1.5), 9–16.5 Chippaux- weight children using Smirak index radiographic and footprint indices Calcaneal pitch Talus-first metatarsal angle Yan et al. (2013)  100 Case- To examine changes in dynamic Obese & non- 10.3 (0.7), 7–12 China Arch index control plantar pressure distribution in obese children children of different weight *where available AP – anteroposterior, FPI-6 – foot posture index – 6 item, LAC - longitudinal axis of calcaneus, LAF - longitudinal axis of foot, MLA – medial longitudinal arch, NR – not reported, mm – millimetres Additional information regarding foot posture parametres can be found in Additional file 2 Study design Of the 20 foot posture measures used, six were plain The majority of included studies were cohort [30, 33–44] film radiographs of angles including calcaneal pitch (or and cross-sectional [29, 45–52], with a respective 13 and 9 calcaneal inclination), anterior-posterior talocalcaneal of each study design. Of the other five included articles, (AP talocalcaneal), plantarflexion of talus, lateral talocal- three were case control [31, 32, 38], one was a case series caneal, calcaneal-first metatarsal and talus-first metatar- , and one was a quasi-randomised controlled trial . sal angles (Table 4). Nine were footprint indices (Chippaux-Smirak index, Arch index, Clarke’s angle [or Footprint angle, Alpha angle], Staheli Arch index, Foot- Primary findings print index, Martirosov’s K index, Footprint evaluation, Foot posture measures and definitions Instep and Plantar footprint), (Table 4). There were four Across the 27 included studies, 20 foot posture measures static foot measures (rearfoot eversion, Arch height were used, involving 40 definitions of flat foot (Table 4). index, Foot Posture Index–6 item version [FPI-6] and Ten of the 27 studies used multiple measures of flat foot. navicular height) and one plantar pressure study [Foot One study featured a novel method of footprint evalu- Ground Pressure], (Table 4). ation . Methodological variations existed across stud- The Arch index was the most frequently used ies, with different parameters and angles assessed measure (n = 7), with the Chippaux-Smirak index and following measurement, and different methods for rearfoot eversion also frequently employed (n =6 re- obtaining the footprint/angle and determining flat foot spectively), (Table 4). A further seven measures were (Table 4, Additional file 2). used in more than one study (Clarke’sangle (n =5), Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 8 of 13 Table 4 Rating of reported validity and reliability for foot posture measures and definition of flexible flat foot in paediatric populations Foot posture measure Study Flat foot Age range of Validity as reported in Reliability as reported in Rating of code definition participants in paediatric population paediatric population validity/ used years reliability (Yes/No/With caution) Plain film Calcaneal pitch [33, < 20° 4–6&8–13 Nil Nil No/No radiograph 53] angles  < 23° 4–18 Nil Nil No/No  ≤ 15.4° 7–12 NR  Nil No/No AP talocalcaneal  > 25° 4–6 Nil Nil No/No  > 30° 8–13 Nil Nil No/No Plantarflexion of  > 23° 4–6 Nil Nil No/No talus Lateral  > 45° 8–13 Nil Nil No/No talocalcaneal Calcaneal first  145°-170° 4–18 Nil Nil No/No metatarsal Talus-first  >4° 7–13 Nil NR , NA  No/No metatarsal  Foot print Arch index [35, ≥ 0.26 3–6, 5–13, 4–14 Nil Nil No/No indices 54],   ≥ 0.26 10 NR  Substantial , NR  No/Yes [30, > 0.26 6–13 Nil Nil No/No 32, 42] Chippaux-Smirak  ≥ 59% 6–9 Nil Excellent  No/Yes  > 62.7% 3–7 Moderate NR With caution/ No  > 62.7% 3–7 Moderate  Nil With caution/ No , ≥ 45% 10 NR NR No/No  ≥ 45% 3–17 Nil Nil No/No  ≥ 40% 9–16 Moderate  Nil With caution/ NR  No Clarke’s angle  ≤ 14.04 3–6 Moderate  Nil With caution/ No  ≤ 20° 10 Nil NR [37, 59] No/No  < 42° 9–16 Excellent  Nil With caution/ No  < 42° 4–18 Nil Nil No/No  < 29.9° 9–16 Moderate ,NR  Nil With caution/ No Staheli arch  ≥ 1.28 6–9 Nil Excellent  No/Yes index  > 1.07 3–6 Moderate NR With caution/ No  > 1.15 6–10 NR [59, 61] Nil No/No  > 0.89 10–12 Nil Nil No/No Footprint index  < 0.25 9–12 Nil Nil No/No Martirosov’sK  ≥ 1.25 10 Nil NR  No/No index Footprint X>Y 6–17 Nil NR  No/No evaluation Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 9 of 13 Table 4 Rating of reported validity and reliability for foot posture measures and definition of flexible flat foot in paediatric populations (Continued) Foot posture measure Study Flat foot Age range of Validity as reported in Reliability as reported in Rating of code definition participants in paediatric population paediatric population validity/ used years reliability (Yes/No/With caution) Instep  100 mm 6–12 Nil Nil No/No Plantar footprint  ≥ 50% 4–13 Nil Nil No/No Static foot Rearfoot  > 10° 4–6 Nil Nil No/No measures eversion  ≥ 4° 8–13 Nil Nil No/No  ≥ 4° 6–13 Nil NA  No/No  > 5° 4–18 Nil Nil No/No  > 5° 3–6 Nil NR  No/No  > (7° - age) 3–6 Nil Substantial  No/Yes Arch Height  ≤ 0.37 6–13 NR  Substantial NR [82, No/Yes Index 83]  < 0.31 8–15 Nil Nil No/No FPI-6  ≥ +6 3–15 Not rated^  Substantial  With caution/ Yes  ≥ +4 6–11 Nil Excellent  No/Yes Navicular height  < 20 mm 9–12 Nil Nil No/No Other Plantar pressure  54% 4–6 Nil Nil No/No measures analysis (FGP) AP – anterioposterior, FPI-6 – foot posture index – 6 item version, NR – not reported in cited text, NA – not available, FGP – foot ground pressure Notes: See data management for ratings of reliability and validity. *See Additional file 1 for rating parametres. ^RASCH analysis Calcaneal pitch and Staheli arch Index (n = 4), and, AP Quality and appropriateness of reported psychometric talocalcaneal, Talus-first metatarsal angle, Arch height properties for a paediatric population index and FPI-6 (n = 2 respectively)), (Table 4). Nine alter- Two studies investigated the validity of the foot posture nate assessment measures were used once across the in- measures used with their studies [34, 38], five studies cluded studies: plantarflexion of talus, lateral talocalcaneal [29, 37, 47, 48, 56] justified their choice by citing seven angle, calcaneal-first metatarsal angle, and; Footprint existing studies [57–63] and one study did both . No index; Martirosov’s K Index; instep; Plantar Footprint; na- foot posture measures were assessed with a ‘yes’ ranking vicular height; and, Foot Ground Pressure (Table 4). in relation to their validity for a paediatric population The most commonly used flat foot definition was the (Table 4, Additional file 1). The Chippaux-Smirak index, Arch Index ≥0.26, used four times across the 27 included Clarke’s angle, Staheli arch index and the FPI-6 respect- studies. An Arch index of >0.26 was used twice, and ≥0.28 ively were ranked as relevant to a paediatric population used once in three further studies. A Chippaux-Smirak ‘with caution’ (Table 4, Additional file 1). Index of ≥45 and >62.70% were used twice (n = 2 respect- The quality of the reliability testing, in relation to a ively). Other definitions used twice across the included paediatric population, was also limited. Four studies inves- studies were talus-first metatarsal angle, rearfoot eversion tigated the reliability of the measure used to determine flat 5° and 4°, and a Clarke’s Angle of <42° (Table 4). foot within their studies [37, 41, 46, 47], five studies [28, Thirteen of the included 27 studies did not investigate 29, 34, 39, 51] justified their choice by citing seven existing or report the psychometric properties of the measures studies [64–70] and three studies did both [31, 37, 47]. used to determine paediatric flat foot [30, 32, 33, 35, 36, Two cited articles were not available to assess [64, 67]. 40, 45, 49, 50, 52–55], (Table 4), leaving 8 of the 20 foot The Arch index, Chippaux-Smirak index, Staheli arch posture measures used within this systematic review index, rearfoot eversion, Arch height index and the FPI-6 without reported validity or reliability outcomes to jus- received a ‘yes’ ranking as relevant to their reliability for a tify their use. Specifically; plain film radiograph measures paediatric population (Table 4, Additional file 1), with only of AP talocalcaneal angle, plantarflexion of talus, lateral the Chippaux-Smirak index, the Staheli arch index and talocalcaneal angle, calcaneal first metatarsal angle; the rearfoot eversion reported as having almost perfect repeat- Instep; Plantar footprint; navicular height; and, Foot ability within this population (Table 4). However, alterna- Ground Pressure, (Table 4, Additional file 1). tive studies investigating the Chippaux-Smirak index, Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 10 of 13 Staheli arch index and the FPI-6, as well as the Clarke’s olds and ≥1.28 in 6 to 9 year olds, Table 3). This finding is angle were assessed as relevant to a paediatric population not consistent with existing normative data and suggests ‘with caution’ (Table 4,Additional file 1). these definitions should be used with caution. Further- more, concerns exist that two-dimensional indices are limited in their ability to assess a three-dimensional con- Summary of results struct . It is suggested that categorising the foot pos- From the 27 studies included, data were extracted for ture based on footprint data disregards the complexity 20 foot posture measures involving 40 definitions of flat and multi-planar motion of the foot . This greatly chal- foot within a paediatric population (Table 3). Eight of lenges the validity of the measures using this construct. At the included 27 articles investigated the reliability or val- a minimum, these measures are reportedly influenced by idity of the flat foot measures used, six further articles the weight of the participants . justified their choice of measure by citing existing psy- The FPI-6 is a composite tool that assesses multiple com- chometric data and 13 articles neither justified nor re- ponents of foot posture, relative to the age of the partici- ported psychometric properties for their measures of pant, and presents as an overall score between − 12 to + 12 choice (Table 4). Seven measures, involving 11 defini- , (Additional file 2). The ‘with caution’ rating assigned tions of flat foot, were determined to have reported val- to the validity of the FPI-6 was due to the results including idity or reliability specific for a paediatric population an adult population . A flat foot definition ≥ +6 for (Table 4). Of these measures, no measure had strong data a paediatric population is well supported in the litera- to support validity and reliability of the measure in paedi- ture in terms of normative data [3, 69, 74, 75]and it is atric samples, and only three were reported to have mod- considered as the only flat foot scale that accommodates erate or with caution validity data and moderate or above differences between normal and overweight/obese chil- reliability data for a paediatric population. Specifically, dren . Furthermore, only the FPI-6 was tested with a these three measures were the Chippaux-Smirak index of broad age range (i.e. children aged 5 to 16 years old [69, >63%, ≥59% and ≥40% (for children aged six to nine, three 70]). Interestingly, the FPI-6 was only used in two of the to seven and nine to 16 years respectively), the Staheli include studies [28, 29], despite being the recommended arch index of >1.07 and ≥1.28 (for children aged three to foot posture measure associated with the GALLOP pro- six and six to nine respectively) and the FPI-6 of ≥ + 6 (for forma  (an opinion and evidence based proforma for children aged three to 15 years), (Table 4). assessment of gait and lower limbs in paediatrics). The topic of paediatric foot posture remains contro- Discussion versial [39, 77] with little consensus on how this fre- There was a modest body of evidence reporting paediat- quently observed foot type should be measured, defined ric specific measures of foot posture. There was no con- or assessed. Importantly, it is acknowledged that a flat sistently used measure to determine paediatric flexible foot posture outside of expected norms may not require flat foot in the literature and the choice of foot posture management. Clinician’s evaluation of the child, directed measure, in relation to the validity and reliability, was by a validated tool such as the paediatric flat foot pro- rarely justified. Within the scope of this review, only forma (p-FFP)  assist the clinician in determining three measures of flexible flat foot had any published when intervention may be required. What this review data to support validity and reliability of the measure has highlighted, however, is an issue central to the dis- within a paediatric population; the Chippaux-Smirak course surrounding this topic. That is, much of the evi- index, Staheli arch index and the FPI-6. However, each dence that guides clinician assessment and intervention of these measures were deemed to have limitations. into paediatric flexible flat foot are potentially based on The Staheli arch and Chippaux-Smirak, used four and unsubstantiated measures. It is essential this is addressed six times respectively across this review, are foot print in- in future research. Valid and reliable diagnoses of flat dices, based on the width of the midfoot compared to the foot appropriate to the paediatric population is required width of the rearfoot (Staheli arch) or metatarsals (Chip- to i) inform the clinician when the foot posture is not in paux-Smirak), when the foot is in bipedal weight-bearing keeping with expected development, and ii) allow re- relaxed stance, expressed as a ratio (Additional file 2). As search to be appropriate and clinically applicable. the child’s arch develops with age, the ratio should de- Considering the difficulties associated with static foot crease accordingly. This is supported by normative data print analysis, researchers and clinicians may need to . The definition of flat foot for the Chippaux-Smirak consider the FPI-6 or alternative composite tools (such index within this review did decreased linear to age: 62.7% as the foot mobility magnitude model ) or dynamic in 3 to 6 year olds, to ≥40% in 9 to 16 year olds (Table 3). measurement to better understand paediatric foot struc- However, the definitions of flat foot for the Staheli arch ture. Indeed, paediatric based studies have shown a sig- index did not decrease as expected (e.g. >1.07 in 3 to 6 year nificant difference between static structure and dynamic Banwell et al. Journal of Foot and Ankle Research (2018) 11:21 Page 11 of 13 foot function  which may be of clinical relevance. As Additional files there was a paucity of dynamic measures in the included Additional file 1: Table A1. Reported validity data and population studies, further investigation may be beneficial. This observed from included studies. Table A2. Reported validity data, extends also to a lack of understanding on the ability of population and protocol observed from cited studies. Table A3. these measures to detect change over time. For Reported inter-rater reliability, population observed and QAREL score for included data. Table A4. Reported inter-rater reliability, population ob- researchers to adequately assess development of, and served, protocol observed and QAREL score for cited data. Table A5. intervention effects in, paediatric flexible flat foot, mea- QAREL checklist outcomes for inter-rater reliability data of included and sures need to be robust and applicable. cited articles. (DOCX 35 kb) Thereareanumberofkey limitationsinthisstudy.Only Additional file 2: Table A4. Summary of foot posture tools. (DOCX 4276 kb) English language studies were included in the search strat- egy and the risk of bias of the included studies was not Abbreviations assessed with a specific critical appraisal tool. Many of the AP : anteroposterior; FGP : foot ground pressure; FPI-6 : foot posture index – included studies did not cite support for their choice of 6 item; GALLOP: Gait and Lower Limb observations of Paediatrics proforma; measure or did not cite appropriately. Indeed, many of the ICCs: Intraclass Correlation Coefficient; LAC : longitudinal axis of calcaneus; LAF : longitudinal axis of foot; MLA : medial longitudinal arch; NA : not studies reporting existing data assumed it was obtained ap- available; NR : not reported propriately and transferrable to their study. For example, Villarroya et al. (2009) quoted psychometric data for the Funding CMW is funded by a National Health and Medical Research Council Early Chippaux-Smirak index from the Kanatli, Yetkin and Cila Career Research Health Professional Fellowship. (2001) article, which relates to the validity of the Staheli arch index; and Mathieson et al. (1999) was quoted in Availability of data and materials Nikolaidou et al. (2006) even though it obtained data from Data sharing not applicable to this article as no datasets were generated or analysed during the current study. an adult population. Many studies did not describe their methods or population clearly (Table 2), and two texts were Authors’ contributions unavailable to the authors [64, 67]. Therefore, these results The protocol for the systematic review was written by MP/HB. Quality of studies, data extraction and analysis was undertaken by MP, HB, CW and SM. should be interpreted accordingly. This systematic review All authors contributed to the manuscript draft and approved of the final was also limited by a paucity of literature in relation to foot manuscript. posture assessment in the paediatric population. Within the Ethics approval and consent to participate limits of this study, even the reference standard measures Not applicable. (e.g. plain film radiographs) had little psychometric data. Although this review had a broad scope, it did not account Competing interests The authors declare that they have no competing interests.\ for studies which looked solely at the psychometric proper- ties of a measure without a definition of pes planus. There- Publisher’sNote fore, future studies may search for these measures Springer Nature remains neutral with regard to jurisdictional claims in individually. Furthermore, this systematic review process published maps and institutional affiliations. was underpinned by best practice in the conduct of system- Author details atic reviews (PRISMA), however, potential publication and International Centre for Allied Health Evidence, University of South Australia, language bias should be acknowledged. Adelaide, South Australia 5001, Australia. School of Health Sciences, University of South Australia, Adelaide, South Australia 5001, Australia. Allied Health, Peninsula Health, Frankston, VIC 3199, Australia. School of Primary Conclusion and Allied Health, Monash University, Frankston, VIC 3199, Australia. A synthesis of available literature reveals that there is not a universally accepted criterion for diagnosing ab- Received: 15 January 2018 Accepted: 11 May 2018 normal paediatric flat foot within existing literature, and psychometric data for the measures and definitions used References was limited. Within the limits of this review, only three 1. 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Published: May 30, 2018