Do Children Outgrow Pes Planus?

I attempted to provide an answer to this question in a lecture I recently presented at the Western Foot and Ankle Conference. After exploring and studying the most recent published studies on the subject of pediatric flatfoot, I was astounded by some of the unsubstantiated conclusions made by the authors.

The condition known as pes planus has traditionally focused on a failure of development of the medial longitudinal arch of the human foot.¹ Early studies of maturation of the arch of the pediatric foot indirectly measured arch height with   footprint-based measures, utilizing ink blots or instrumented pedobarographs.   While most newborns have flat feet, footprint analysis studies show a rapid increase of arch height in the majority of children occurring between the ages of 2 and 9.²

However, an unanswered question is what percentage of children with significant flatfoot will fail to outgrow the deformity? A recent study of 1744 children ages 3–12 in China revealed a mean arch index of 0.27, which falls within the range of a “flat foot.”³ Furthermore, researchers have questioned the validity of footprint measures as they may reflect the contribution of “fat feet” to actual “flat feet.”⁴

The Foot Posture Index (FPI) has emerged as the gold standard to assess foot alignment in multiple planes.⁵ The FPI has also been validated as a reliable tool to assess posture of the pediatric foot.⁶ Besides evaluating the height of the medial longitudinal arch, the FPI assesses six parameters of alignment of the foot including frontal plane position of the calcaneus and transverse plane alignment of the forefoot to the rearfoot. Thus, the FPI moves beyond describing foot posture based upon arch height and instead quantifies the degree of rearfoot pronation or supination. A total FPI score classifies the foot beginning with “highly supinated” (score of -12) to “highly pronated (score of +12). A “normal” foot posture has a score ranging from 0 to +5.⁷

Using the Foot Posture Index, a group of researchers has made rather confusing conclusions about the “normalcy” of flat feet in children.^8,9 The first study, conducted by Gijon-Nogueron and coworkers, evaluated 3217 children with age range between 3–15 years.⁸ The mean FPI score of all the patients at initial evaluation was +4, which the researchers deemed “flat” despite the fact that the original descriptions of the FPI scoring system would place this score in the very mildly pronated or “normal” range.^5-7 Apparently, Gijon-Nogueron and colleagues equate a mildly pronated foot with a flat foot. In their conclusion, the researchers state “Importantly, the main finding is to denounce the paediatric flatfoot as deviant.”⁸

Running contrary to this conclusion is the fact that children with an FPI score of greater than +5 are considered pronated, and the data from the Gijon-Nogueron study showed that only 29% of children in the study population had pronated feet.⁸ Thus a pronated or flat foot in a child under age 12 could not be considered “normal” as the researchers propose.

A prospective study conducted by this same team used the FPI to determine the natural progression of foot posture in growing children.⁹ Martínez-Nova and coworkers used the Foot Posture Index to document maturation of the feet of 1032 children ages 5–11 years over a 3-year time period. Initially, only 20% of the children had FPI scores, which would classify them as “pronated” and 3 percent were highly pronated. This contradicts the conclusions of Gijon-Nogueron that flatfoot deformity in children is normal or “not deviant.”⁸   

The most important finding of the study from Martínez-Nova is that foot posture shows only mild clinical improvement over a 3-year period in growing children. In spite of this fact, the researchers report: “The FPI was significantly reduced after three years, from the initial mean FPI of 3.57 to a mean FPI of 3.33 after three years (P < .001).”⁹ Yes, a change in FFI score of 0.2 might be statistically significant, but could a clinician discern this minor difference?

Remarkably, Martinez-Nova and colleagues provide an answer to this same question, which casts doubt on their conclusion that foot posture significantly improves in growing children over a 3-year period. When evaluating the difference between boys and girls in the final FPI scores, the researchers concluded that the difference of 0.2 in FPI scores (boys 3.4 ± 2.6 vs girls 3.2 ± 2.7, P = .112) would be “clinically indistinguishable.”

Of most interest for clinicians is predicting rate of improvement of foot posture in growing children who are pronated (FPI score of 8–10) or highly pronated (FPI score of 11–12) before reaching the age of 11. Martinez-Nova and colleagues initially identified 218 children with pronated feet out of the total pool of 1032 patients.⁹ Of the 218 children who had pronated feet initially, 129 remained pronated after 3 years and 7 worsened to become highly pronated. Of the 36 children who were initially highly pronated, 26 improved over 3 years to become pronated while 7 remained highly pronated. Thus, the researchers appropriately concluded that a pronated foot posture can be expected to improve in “some but not all cases.”

The take-home message here is that clinicians should not tell anxious parents of a child who shows an obvious pronated and flatfoot posture that the deformity will improve with any certainty. Furthermore, there is a trend among certain researchers to downplay the appearance of flat feet in growing children. To state that pronated or flat feet are “normal” in growing children is simply not supported by recent research.

Dr. Richie is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is a Fellow and Past President of the American Academy of Podiatric Sports Medicine. Dr. Richie is a Fellow of the American College of Foot and Ankle Surgeons, and the American Academy of Podiatric Sports Medicine. Dr. Richie is the author of a new book titled "Pathomechanics of Common Foot Disorders," which is available from Springer at https://www.springer.com/us/book/9783030542009 . He discloses that he is Founder and President of Richie Technologies.

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References

1.    Labovitz JM. The algorithmic approach to pediatric flexible pes planovalgus. Clin Podiatr Med Surg. 2006;23(1):57–76.

2.    Onodera A, Sacco I, Morioka E, Souza P, De SM, Amadio A. What is the best method for child longitudinal plantar arch assessment and when does arch maturation occur? Foot. 2008;18(3):142–9.

3.    Wang J, Tang L, Tang J, et al. The typically developing pediatric foot - The data of the 1744 children in China. Foot Ankle Surg. 2022; 28(3):347–353.

4.    Mickle KJ, Steele JR, Munro BJ. The feet of overweight and obese young children: are they flat or fat? Obesity. 2006;14(11):1949–53.

5.    Redmond AC, Crane YZ, Menz HB. Normative values for the Foot Posture Index. J Foot Ankle Res. 2008;1(1):6.

6.    Morrison SC, Ferrari J. Inter-rater reliability of the Foot Posture Index (FPI-6) in the assessment of the paediatric foot. J Foot Ankle Res. 2009;2:26.

7.    Keenan AM, Redmond AC, Horton M, et al. The Foot Posture Index: Rasch analysis of a novel, foot-specific outcome measure. Arch Phys Med Rehabil. 2007;88(1):88–93.

8.    Gijon-Nogueron G, Martinez-Nova A, Alfageme-Garcia P, Montes-Alguacil J, Evans AM. International normative data for paediatric foot posture assessment: a cross-sectional investigation. BMJ Open. 2019;9(4):e023341.

9.    Martínez-Nova A, Gijón-Noguerón G, Alfageme-García P, Montes-Alguacil J, Evans AM. Foot posture development in children aged 5 to 11 years: a three-year prospective study. Gait Posture. 2018;62:280–284.