REVIEW ARTICLE |
https://doi.org/10.5005/jp-journals-10040-1292 |
Which Foot is at Risk? Understanding the Evolution of the Pediatric Flatfoot
1,2Department of Orthopedics, Childrens’ Orthopaedic Centre, Mumbai, Maharashtra, India
Corresponding Author: Ratna S Maheshwari, Department of Orthopedics, Childrens’ Orthopaedic Centre, Mumbai, Maharashtra, India, Phone: +022 24365050, e-mail: drratnajohari@gmail.com
Received on: 25 January 2023; Accepted on: 25 February 2023; Published on: 11 April 2023
ABSTRACT
Few subjects in orthopedics have had varied and diverse opinions expressed about every aspect of the condition, from etiology to treatment, as has the flexible flatfoot (FFF). FFF is common in infants and children, and the majority of them resolve by the 1st decade of life. Thus, FFF has been described as physiologic because it is usually flexible and painless and has been thought to be of no functional consequence. However, there is a mounting body of literature that persistent flat feet may not be as benign in terms of long-term function as was once thought to be. Despite being one of the most common concern scenarios encountered in the pediatric orthopedic outpatient department, there is an absence of a standard definition for pediatric flatfoot and a lack of clarity on the natural history of untreated persistent FFF. Looking at the precariousness surrounding flatfoot literature, we need to reevaluate if we can be confident of pain-free adulthood in untreated children with persistently severe flat feet. Excessive hindfoot motion in this entity can have far-reaching effects on the musculoskeletal chain distally and proximally. With this article, we will look deeper into the biomechanics of FFF, summarize our understanding of the literature on this entity with regard to evolution, and identify “red flag signs” in persistent FFF where intervention might be beneficial.
How to cite this article: Maheshwari RS, Johari AN. Which Foot is at Risk? Understanding the Evolution of the Pediatric Flatfoot. J Foot Ankle Surg (Asia-Pacific) 2023;10(2):48-55.
Source of support: Nil
Conflict of interest: None
Keywords: Achilles tendon, Flatfoot, Hindfoot, Pediatric flatfoot, Recurrent talotarsal joint dislocation.
INTRODUCTION
Flexible flatfoot (FFF) is a common concern area in children, often brought to the healthcare provider for an evaluation by worried parents. In spite of this, understanding of the issue and agreement regarding management is poor. The true prevalence is uncertain, as we do not have established clinical or radiographic criteria. The natural history of FFF is difficult to research and document, and there are other problems with the literature, including conflicting evidence, poor methodology, and lack of controlled studies.1-3
Our feet allow our entire body to be in an upright posture. Aligned and stable feet are of fundamental importance from the perspective of efficient bipedal human locomotion. Walking on misaligned, unstable, and persistent FFF could be compared to a car running on worn-out tires. Hindfoot instability and hypermobility can elicit a painful biomechanical chain proximally and distally.
Footprint-based measures cannot fully justify the three-dimensional, dynamic changes that occur in misaligned feet with every step. We need to look deeper at the dynamic biomechanics of hindfoot to better understand this entity. There is mounting evidence of hindfoot hyper pronation and instability4-36 affecting current and future functioning. However, due to a lack of natural history studies, it is difficult to understand what degree of “flatness” and/or associated factors in persistent FFF can negatively influence the quality of life.
Through this article, we aim to summarize the literature in terms of the epidemiology and evolution of pediatric flatfoot. In addition to further understanding hindfoot biomechanics in this entity, we will also summarize the literature in terms of long-term consequences associated with untreated persistent flatfeet. Ultimately, we attempt to highlight the “red-flag” signs to look for when evaluating persistent FFF.
EPIDEMIOLOGY, EVOLUTION AND PATHOPHYSIOLOGY OF FLEXIBLE FLATFOOT
The natural history of pediatric flatfoot is still not clearly elucidated. There is a lot of data, but it is debatable and of questionable standards of evidence. While it is expected that a child’s foot is going to be flat, there is no consensus on what is the normal range of “flatness.” It is also common knowledge that flatness decreases as age increases, but there is a lack of objective data with regard to this with each advancing year.37
In the first few years of life, flatfoot is the normal foot shape, as has been shown by epidemiologic studies. A child’s foot characteristically has a large fat pad on the inside arch. This fat pad slowly disappears as a child grows.38 As children begin to walk, the foot is entirely on the ground for balance. Progressively, the weight-bearing shifts to the first or second tarsometatarsal joint, which may induce a flatfoot posture. The arch slowly develops during childhood.39
Studies estimate that the flatfoot prevalence ranges from 0.6 to 77.9%.40 This broad prevalence range in FFF can be due to different age groups and different evaluation methods. More specifically, the prevalence of flatfoot in literature for the smaller age group of 2–6 years was summarized to be 37–59.7%, and for 8–13 years was noted as 4–19.1%, respectively.40 FFF has been noted to persist in only 3% of the adult population. So, we can conclude that FFF is a physiological phase in the majority of the pediatric population and that the prevalence decreases with increasing age.41-43
Statements in current literature regarding the timing of arch development vary widely. Some studies have concluded these changes to occur between the ages of 2–3 years, while others have suggested that the arch develops in preschool age or up to the age of 10 years.44-47 A study which examined different index measures for arch noted that arches developed very fast up to the ages of 5–6 years, following which the development reached a plateau but was still identified until the age of 12–13 years.48
Certain variables like age, body composition, sex, W-sitting, ligamentous laxity, genetics, age at which shoe wearing began, and types of footwear can all be considered as predisposing factors of flatfoot.49 Studies have summarized that boys are twice as likely as girls, and obese children are three times more likely than healthy weight control to have FFF.43 Apart from obesity as a risk factor, those with generalized joint hypermobility are also predisposed.40 Ethnicity has also been noted as a possible causative factor; a higher incidence of flatfoot deformity has been found in Blacks than in Caucasians50. Studies of specific populations (e.g., Chinese) have also suggested that early and consistent shoe-wearing is a factor that can hinder arch development.51 FFF can also be postulated to be genetic, as many parents/relatives tend to have fallen flat arches.
Flexible flatfoot (FFF) is often not an isolated occurrence, and in many of these feet, some combination of hypermobile subtalar complex, hyperflexible ankle joint, and contracture of the triceps surae muscle have been observed.52,53 These combined pathologies together are the likely cause of symptoms rather than just the collapsed arch.
HOW DOES THE ARCH DEVELOP?
Arch development is a multifactorial process. Muscles, ligaments, bones of the foot, leg alignment, and sometimes underlying predisposing medical issues all play a causative role. FFF can occur by itself or can be part of a larger clinical pathology.54
It is likely that the onset of bipedal gait causes the arch to develop.55,56 The biomechanical feedback of forces causes a change in the muscle and ligament strength, which likely affects arch development. Children are “flat-footed” initially due to innate ligamentous laxity and a lack of adequate neuromuscular control.57
Some authors believe that it is mainly muscle strength that is responsible for the maintenance of the longitudinal arch.58 A study investigated the activation of extensor muscle groups in those with flexible flatfeet.59 Arch flatness was found to be directly proportional to extensor muscle weakness. Some authors believe that the height of the arch and the shape of the foot is determined more by the bone ligament complex instead of the muscles.60 There have been observations correlating incompetence of spring ligament and flatness of the arch during weight-bearing.
Rotational bony alignment has also been analyzed with regard to FFF. Increased tibial torsion and increased hindfoot malalignment have been directly correlated with the severity of arch collapse.
A reduced incidence of flatfoot has been observed when studying barefoot populations. This seems to suggest that muscle strength and mobility may be important factors in early arch development. Evidence also seems to suggest that regular shoe wearing prior to age 6 or early use of arch supports may interfere with foot muscle and, therefore, arch development.61-63
HINDFOOT BIOMECHANICS
In FFF, during the stance phase of gait, the foot moves out from underneath the weight-bearing axis of the limb. The calcaneus, navicular, and cuboid bones move excessively from under the talus and eccentrically load the body weight on the sustentaculum tali. These bones stay “unlocked” longer than usual and hence are unable to provide adequate skeletal support for the body weight above.64
The hindfoot in the push-off phase of the gait cycle inverts and provides a rigid lever arm for propulsion. In FFF, especially associated with Achilles tendon tightness, the hindfoot is unable to invert appropriately as needed to create a rigid lever arm. This results in an inefficient push-off, which in turn leads to pain and muscle fatigue.
Balance of forces and alignment within the talotarsal joint (TTJ) is needed for a functional hindfoot, which converts the vertical force of the heel strike into a horizontal force. In the stance phase of the gait cycle, the TTJ is responsible for locking and unlocking the joints within the inner column of the foot. TTJ pronation unlocks the joints, which provides suppleness on an uneven weight-bearing surface at the beginning of the full, plantar foot contact portion of the gait cycle. At approximately one-fourth to one-third of the full-foot contact, the TTJ supinates to lock the bones.65 This locking of the bones provides the requisite strength for the foot as it prepares for heel lift and forward foot propulsion.
The primary component of a flexible “flatfoot” is the loss of stability and alignment of the TTJ65 (Figs 1 to 3). It stays unlocked longer than it should during stance, leading to excessive pronation. This causes abnormal transmission of the weight-bearing forces acting within the forefoot, mid, and hindfoot. The forces are higher than normal during the stance phase of the gait cycle and absent in the swing phase. TTJ displacement leads not only to bones being out of alignment but also overcompensation of ligaments and increase in the workload of muscles and tendons until the foot goes into the swing. This abnormal and excess loading of tissues occurs with every step taken.
Fig. 1: The talotarsal articulations
Fig. 2: The talocalcaneal articulation
Fig. 3: Recurrent and prolonged talotarsal unlocking and subluxation, the primary component of FFF
PROBLEMS WITH NO TREATMENT
The human musculoskeletal system can be described as interrelated body segments, with joints and muscles working together to perform movements. The flatness of the foot can affect compensatory changes, not affect and thus have an impact on the complete functional state of the locomotor system.
After the age of arch development is crossed, persistent hindfoot misalignment is not going to correct on its own. The joint above and below will start to compensate for handling the excessive forces. These abnormal forces elicit an inflammatory reaction, and if left unchecked, chronic inflammation can lead to joint damage as well. A study concluded that adolescents with moderate to severe flatfoot have nearly double the rate of anterior knee pain and intermittent low back pain.66 Another study highlighted that when the foot is placed in eversion, it causes subtalar pronation, and this results in increased internal knee and hip rotation.36 An increase in pelvic anteversion has also been noted as a result of hindfoot eversion, and additionally, a significantly higher hip external rotation was noted during the first half of the stance phase.67 When feet are misaligned and unable to lock in place during the toe-off phase, there is a 35% reduction in propulsive push-off muscle power.68
Hyperpronated hindfeet are the core causative factor for many chronic foot problems, such as plantar fasciopathy, posterior tibial tendon dysfunction, hallux valgus, hallux limitus, and tarsal tunnel syndrome. Other secondary problems that can be traced to hindfoot misalignment are growing pains, ankle joint problems, medial tibial stress syndrome, knee issues, hip problems, pelvic tilt, and even back vertebrae misalignment.4-36
The health-related quality of life is remarkably diminished in children with FFF.69 Children with FFF have an increased body mass index compared to children with normal feet.70 Walking on unstable and misaligned feet causes muscles to work harder in order to compensate. Due to this, pain ensues faster; thus, the activity needs to be stopped.71,73 The advice to lose weight through more physical activity in children with FFF is counterintuitive.
IDENTIFYING THE “FOOT AT RISK”
In the absence of enough literature support to create a guideline with regard to “foot at risk,” the senior author’s experience has been used for enlisting certain red flags with regard to FFF. Once the child is 10 years or older, the FFF can be considered to be permanent. When it comes to symptoms, one must inquire not just about the foot but also the knee, hip, and back problems. Also, ask for “functional” symptoms - activity-based increase in symptoms. Often these children may have a sedentary preference or postural fatigue. They may also have cramping sensations in the foot and arch. They may have developed proximal coronal and torsional issues as well as compensations.
The FFF group with equinus tends to be symptomatic and have severe misalignment early. Contracted and short Achilles tendon causes limitation in full ankle dorsiflexion. These forces get abnormally transferred to the midfoot. Over a period of time, this may result in the breakdown of tarsal joints. Radiographs show a decreased calcaneal pitch angle and a sag at the talonavicular joint. It can also often show talar spurring or osteophyte formation very early in life. Hence, vigilance in this group with regard to early regular follow-up, even prior to the first decade of life, is important. The FFF group with overall ligamentous laxity also worsens at a faster pace with regard to misalignment.
Significant misalignment of the feet can be quantified using weight-bearing radiographs. The weight-bearing radiographs must compare the neutral stance and relaxed stance in both the dorsoplantar (DP) and lateral views. Resting- or relaxed-stance position (where the talus slides off the calcaneus) weight-bearing radiographs are the most important in quantifying the degree of flatness. Certain validated radiographic measurements can show a normal or abnormal alignment of the feet.65 The DP view measurements include the talar second metatarsal angle along with the talar navicular head uncovering angle (Figs 4 and 5). On a lateral radiograph, look for opening/obliteration of the sinus tarsi, navicular position, and measurements which include talar declination angle, talar first metatarsal angle, calcaneal inclination, or pitch angle (Figs 6 to 10). The same has been summarized in Table 1.
| Radiographic angle | Normal range (degrees) | Abnormal range (degrees) |
|---|---|---|
| Talar second metarsal (DP) | <16 | >16 |
| Talar head uncovering (DP) | <7 | >7 |
| Calcaneal pitch/inclination (lateral) | 20–30 | <20 |
| Sinus tarsi (lateral) | Open | Partial/full obliteration |
| Talar declination | <21 | >21 |
| Talar first metarsal (Meary’s angle) lateral | 0 | >4 |
| Navicular position (lateral) | Plantar aspect is dorsal to the horizontal bisection of the cuboid | Plantar aspect of the navicular is plantar to the horizontal bisection of the cuboid |
| Calcaneal axial (posterior) | Rectus alignment | Valgus alignment |
Fig. 4: The talar second metatarsal angle. The normal values are <16°, more than that is abnormal
Fig. 5: The talar head uncoverage angle, normal is <7°
Fig. 6: The calcaneal pitch/inclination angle, <20° is abnormal; a value between 20°–30° is considered normal
Fig. 7: Obliterated sinus tarsi
Fig. 8: Talar first metatarsal angle, normal value is 0°, >4° is considered abnormal
Fig. 9: Talar declination angle, normal values are <21°; anything>21° is abnormal
Fig. 10: Navicular position; the plantar aspect of the navicular here is plantar to the horizontal bisection of cuboid
CONCLUSION
Many people suffer from the far-reaching effects of excessive hindfoot motion. This is due in part to a lack of awareness of the effects of this condition. The aim of this article was to provide an overview of areas of lacunae or areas that need deeper thinking. However, as with anything in medical practice, management is as much science as art. Clinical management will continue to evolve over the coming years as more long-term data becomes available. To facilitate this effectively, we need more well-designed prospective studies to address questions about the natural history of pediatric FFF, the effectiveness of interventions, and the evolution of persistent FFF into major adult pathologies.
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