Four-Year Treatment Effect of Custom-Made Foot Orthosis on Pediatric Symptomatic Accessory Navicular Bone Combined with Flexible Flatfoot

Abstract

Purpose

Congenital accessory navicular bone (ANB) is a common variant in the foot and is prone to cause several clinical symptoms. Wearing custom-made foot orthosis is considered a desirable option; however, there is limited evidence of its effectiveness. This study aims to report the mid-term effect of foot orthosis for symptomatic pediatric ANBs.

Methods

School-age children with symptomatic ANBs combined with flexible flatfoot in the authors' institute were recruited and got custom-made foot orthosis treatment. They were followed up over 4 years. The general characteristics of these children were collected before treatment, including age, gender, and body mass index (BMI). The indicators of foot symptoms, including frequency and location of pain, visual analogue scale (VAS), arch index (AI), and hind foot valgus angle (HVA), were measured during pretreatment and at the last follow-up.

Results

Twenty-seven children were recruited for this study. After 4 years of custom-made foot orthosis treatment, significant improvements showed in pain frequency, VAS, AI, and HVA (P < 0.001). Type II ANBs showed a higher pain index pretreatment (P < 0.001) and reduced after treatment (P < 0.001).

Conclusion

Mid-term effect of custom-made foot orthosis is inspiring in clinical symptoms of pediatric congenital ANBs combined with flexible flatfoot and may be an optional nonoperative treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43465-024-01210-7.

Introduction

Congenital accessory navicular bone (ANB) has been regarded as one of the most common accessory bones in the human foot [1, 2]. An ANB is a hindfoot bone that presents as a sesamoid in the tibialis posterior tendon [1]. In Geist classification, congenital ANBs could be divided into three classic categories [2]. In type I, there is no direct contact with the navicular, which remains embedded in the posterior tibial tendon. Type II usually fuses with the navicular through cartilage, and type III connects with the navicular to form a prominent cornuate navicular [1]. Type II and III ANBs are commonly symptomatic as painful bunions over the bony protrusion [1]. Flatfoot is a common deformity in children characterized by foot pain, fatigue and abnormal posture of feet when stepping [3–5]. Some studies have suggested that congenital ANBs are closely related to the occurrence of flatfoot in some children [3, 4, 6, 7]. ANBs may contribute to the development of flatfoot by disrupting the support of the foot arch [6, 7]. Symptoms in pediatric flatfoot are likely to improve with skeletal maturation as age grows [4, 8]. Congenital ANBs may be symptomatic due to the distortion of the normal anatomy of arch support [3, 9]. Children with mild symptomatic ANBs may be treated conservatively without surgery [1, 9].

An orthopaedic foot orthosis is an option for the nonoperative treatment of symptomatic ANBs [1, 3] and is also used for the pediatric symptomatic flatfoot. Several studies have been performed in the past 10 years [4, 10, 11]. Foot orthosis might improve the symptoms of flexible flatfoot by supporting the arch [12]. However, controversy regarding the benefit of such foot orthosis still exists. Only a few studies reported such foot orthosis’s therapeutic use for symptomatic flexible flatfoot [10, 13, 14]. Moreover, no survey on conservative management of pediatric symptomatic congenital ANB combined with flatfoot has been published. This study aims to present the clinical results of pediatric patients treated with custom-made foot orthosis in symptomatic ANBs combined with flexible flatfoots.

Patients and Methods

All consecutive patients with symptomatic ANB combined with flexible flatfoot were retrospectively reviewed at the corresponding authors’ institute between July 2016 and June 2017. The inclusion criteria were: (1) school-age children (aged 6 years or more), (2) with the complaint of foot pain over the bony protrusion (frequency > 15 times per month according the query to children and their guardian), (3) with radiograph indication of ANBs and flat feet, (4) treated with custom-made foot orthosis for more than 8 h a day, and (5) they were followed up over 4 years. The exclusion criteria were: (1) severe foot deformity or dysplasia, (2) had received operative treatment, (3) with spine or proximal lower extremity disease, (4) with foot trauma or neurological disease, and (5) with mental disorder under treatment. This study has been approved by the Ethics Committee of the authors’ institute. All methods were performed following the relevant guidelines and regulations. All the guardians of patients gave written informed consent for this study. They are fully informed about information or images of patients that might be published, the role of custom-made foot orthosis, and the way to use the foot orthosis. Data are collected by researchers not involved in the analysis and writing.

Diagnosis of ANB and flatfoot was made with the radiographic and physical examination. Saltzman et al. described the method for ANB radiographic examination [15]. ANBs are subsequently divided into three types by Geist classification [16]. Flexible flatfoot is when the foot looks normal during non-weight bearing, sitting, and flat foot on weight-bearing. Physical examinations such as the foot arch and hind foot valgus angle were performed in weight-bearing posture.

General characteristics of the patients, including age, gender, and body mass index (BMI), were collected before treatment. The evaluation indicators included frequency and location of pain, visual analogue scale (VAS), arch index (AI), and hindfoot valgus angle (HVA) were calculated before treatment and at the last follow-up. The 0 scale meant no pain, while the 10 scale meant maximum pain in VAS [17]. According to Cavanagh’s method, AI was calculated as the quotient of the midfoot area and the entire foot (except the toes) [18]. The types of feet can be divided into three categories by AI: high arch (AI < 0.21), normal arch (AI from 0.21 to 0.26), low arch (AI > 0.26), and low arch indicated the presence of flatfoot [18]. In physical examination, HVA is formed by the calcaneus’s vertical line and longitudinal axis [19]. It ranges from 0° to 5° normally and 5° to 10° for children with flatfoot [19]. The AI and HVA were measured by senior trained colleagues from department of physical therapy with 6 months intervals repeated during follow-up.

The custom-made foot orthosis was manufactured after a complete analysis of the symptomatic foot, including the range of motion, pain sites, and angles, which required detailed examination and foot scanners. The distribution of body weight on foot, foot position and movement during standing and walking were analyzed. After the design was completed, the foot orthosis could be produced using computer numerical control (CNC) or 3D printers with polyurethane components (Figs. 1, 2) and modified to suit the participants. The foot orthosis was advised to be used during daily walking and standing for 8 h at least per day and renewed according to the foot’s growth after 6 to 9 months.

Fig. 1.

Insoles (A) and the valgus angle change before (B) and after (C) wearing

Fig. 2.

Images of patient with (A) and without orthotics (B)

SPSS 25.0 was used to analyze the data. The paired t test and independent-sample t test were utilized. Statistical significance was considered when the P value was less than 0.05.

Results

Twenty-seven children were recruited for this study, including 13 boys and 14 girls. Family history of flatfoot and foot pain was not identified in this series. The average age was 8.0 ± 0.9 years (6.3 to 9.7 years). The average BMI was 16.4 ± 1.2, and there were no overweight children. The average follow-up period was 50.74 ± 1.46 months. All the children show good duration and compliance of brace wear.

The presence of ANBs was confirmed by X-ray radiography. According to Geist’s classification, 16 participants were categorized into type II, and the remaining 11 were classified into type III. No participants were found to have type I ANB. The locations of pain included arch (n = 15), plantar heel (n = 4), Achilles tendon (n = 6), and ankle joint (n = 2). No patient had multiple sites pain.

Frequency of pain, VAS, AI, and HVA significantly improved at the last follow-up (P < 0.001). The frequency of pain in the foot decreased from 20.56 ± 2.12 to 3.30 ± 1.44 (P < 0.001), and VAS reduced from 3.00 ± 0.83 to 1.15 ± 0.72 (P < 0.001). The AI showed significant reduction (L: 0.322 ± 0.024 to 0.252 ± 0.014, R: 0.321 ± 0.022 to 0.256 ± 0.014, P < 0.001), and mean HVA reduced significantly as well (L: 6.11° ± 0.97° to 4.44° ± 0.80°, R: 6.04° ± 1.02° to 4.48° ± 0.64°, P < 0.001) (Table 1) (Fig. 3). Independent-sample t test showed that participants with type II ANBs owned significantly higher VAS (3.56 ± 0.51) than type III (2.18 ± 0.41) before treatment with foot orthosis (P < 0.001) (Table 2). At the last follow-up, type II (1.94 ± 0.44) ANBs showed a better improvement than type III (1.00 ± 0.00; P < 0.001) (Table 3) HVA showed similar significance to VAS (P < 0.05; P < 0.05).

Table 1.

Comparison of foot symptom parameters after treatment

	Before treatment	Last follow-up	Paired t test
			Paired difference	t	Sig.(2-tailed)
Pain frequency	20.56 ± 2.12	3.30 ± 1.44	17.26 ± 2.55	35.157	< 0.001
VAS	3.00 ± 0.83	1.15 ± 0.72	1.85 ± 0.72	13.400	< 0.001
AI
Left	0.322 ± 0.024	0.252 ± 0.014	0.069 ± 0.021	17.198	< 0.001
Right	0.322 ± 0.022	0.256 ± 0.014	0.066 ± 0.017	20.512	< 0.001
HVA (°)
Left	6.11 ± 0.97	4.44 ± 0.80	1.667 ± 0.961	9.014	< 0.001
Right	6.04 ± 1.02	4.48 ± 0.64	1.556 ± 0.974	8.298	< 0.001

Fig. 3.

Hindfoot valgus and pressure distribution of feet before treatment and at last follow-up in hindfoot weight-bearing view. The hindfoot valgus angle is defined as the anatomical axis of the calcaneal line (red line) and vertical line (green vertical line) (a, c). Symptomatic ANBs with flatfoot in authors’ hospital appeared with hindfoot valgus (a) and collapse of arch (b); the HVA (c) and pressure distribution (d) got apparent relief after 4-year treatment

Table 2.

Comparison of foot symptom parameters before treatment according to ANB classification

		Type II	Type III	Independent-sample t test
				t	Sig.(2-tailed)
Pain		21.00 ± 2.00	19.91 ± 2.21	1.334	0.194
VAS		3.56 ± 0.51	2.18 ± 0.41	7.806a	< 0.001
AI	Left	0.32 ± 0.03	0.32 ± 0.02	0.423	0.676
	Right	0.32 ± 0.03	0.32 ± 0.02	0.455	0.653
HVA	Left	6.38 ± 1.03	5.73 ± 0.79	1.766	0.09
	Right	6.38 ± 1.09	5.55 ± 0.69	2.234	0.035

^aAdjusted t value (tʹ)

Table 3.

Comparison of difference in foot symptom parameters improvement after treatment according to ANB classification

		Type II	Type III	Independent-sample t test
				t	Sig.(2-tailed)
Pain		16.58 ± 3.05	16.18 ± 2.32	0.349	0.73
VAS		1.94 ± 0.44	1.00 ± 0.00	8.474a	< 0.001
AI	Left	0.06 ± 0.02	0.07 ± 0.02	−0.606	0.55
	Right	0.06 ± 0.02	0.06 ± 0.02	−0.379	0.708
HVA	Left	1.38 ± 0.81	1.09 ± 0.70	0.947	0.353
	Right	1.31 ± 0.79	0.64 ± 0.51	2.493	0.02

^aAdjusted t value (tʹ)

Discussion

ANB is a common anatomical variation in the foot [1, 2, 20]. Where the accessory ossification centre proximal to the navicular bone or talonavicular joint cannot fuse with the prominent navicular bone on time, a bony protrusion is formed [1, 20, 21]. It then appears as a congenital ANB. The incidence of congenital ANBs in the population is about 5% ~ 20% [2, 3, 7]. Most pediatric ANBs are asymptomatic, while some children complain of foot pain and difficulty walking [9, 20]. Symptomatic pediatric ANB is common in children with flatfoot [3, 4, 6, 7, 22]. It generally refers to foot deformity or defect of the medial longitudinal arch (MLA) [3–6, 13, 23]. Although congenital ANBs often produce symptoms in children, the relationship between ANB and flatfoot is unknown [22]. Symptomatic accessory naviculars are most commonly found in adolescents rather than young children. However, the youngest patient in this study was only 6 years old and confirmed with ANBs by X-ray. Although the spring ligament and the calcaneal cuboid ligament are the primary maintainers of the plantar arch, the tibialis posterior tendon could support MLA and the long lateral peroneal tendon. The tibialis posterior tendon inserts into the navicular bone, which acts as an inverter of the foot and provides necessary support to MLA [1, 24, 25]. The dysplasia of navicular bones affects the anatomy of muscles. It results in the inappropriate insertion of the tibialis posterior tendon into ANB, which leads to inadequate support to MLA and probably causes flatfoot [1, 20, 21]. Meanwhile, ANB frequently contacts and rubs against the medial malleolus in steps, causing symptoms including tenderness and achillobursitis [20, 26]. This study showed that more than half of the participants had pain in the foot arches. It might be because of the direct squeezing of ANB or the collapse of MLA. In this study, all participants diagnosed with symptomatic ANBs appeared with flatfoot. Nearly half of the patients had pain in the heel, Achilles tendon, or ankle joint, which might not only be due to the ANBs. This result may partly confirm the close association between ANB and flatfoot. Other factors, such as age, body mass, and wearing shoes, are associated with flatfoot [6, 27]. In this study, age and gender have no significant effect on the position of pain in the foot. All the children had normal BMI, and none were overweight.

Symptomatic pediatric congenital ANBs require treatment [1]. Patients with tolerable clinical symptoms are initially treated conservatively, such as reduced activity, plaster fixation, topical nonsteroidal anti-inflammatory drugs, and foot orthosis [1, 3, 20]. Surgery is necessary if conservative management fails [28, 29].

Wearing custom-made foot orthosis is a common strategy for symptomatic pediatric ANB because of its noninvasive nature [1, 30]. Foot orthosis is also considered in the treatment of flatfoot [23, 31, 32]. The hypothesis that external support can improve foot arch and hindfoot position development lacks evidence supporting implementation in paediatric orthopaedic routine practice [6, 32, 33]. The most accepted theory demonstrates that external devices cannot influence the natural course of the foot arch [13]. Whether symptomatic pediatric flatfoot benefits from custom-made foot orthosis is still controversial [34, 35]. The results of this study showed that wearing foot orthosis provides relief to symptomatic ANB with flexible flatfoot (Table 1). After 4 years of interventions, the HVA similarly goes down with the AI. The AI declines to about 0.26, almost in the normal range. The plantar mechanics and physiological structure of patients also showed a positive result (Table 1) (Fig. 3). The orthosis could restore and maintain the height of foot arches, contributing to the pressure distribution in the sole and symptom relief [36, 37]. Messer et al. demonstrated that about 28% of children (226 subjects with an average age of 11.8 years) with symptomatic ANB who had received conservative treatment experienced complete relief [30]. Smith and Mansoor et al. also held a positive opinion for nonoperative treatment for symptomatic ANB in their case reports [38, 39]. The positive effects on the psychological pressure of children and families by wearing foot orthosis have been discussed by Camurcu et al. and Aboutorabi et al., but the weight, appearance, and economic costs aroused a new burden [33, 37].

However, different types of ANBs may not lead to the same foot symptoms. The results showed that the degree of pain in children with type II ANBs is more severe before treatment. The difference in VAS between type II and III ANBs was statistically significant (P < 0.001) (Table 2) An unstable micromotion on the cartilaginous joint is formed between the type II ANB and navicular. Their movement may result in local pain being more pronounced [1, 40]. Type III ANBs are more stable and less pain-prone due to forming a stable bony connection [1, 2]. This founding partly proved that the clinical symptoms in participants were not all caused by flatfoot. The results showed that the pain index significantly improved in type II ANBs (P < 0.001). VAS in symptomatic type II ANBs decreased by 1.94 ± 0.44, while type III decreased by 1.00 ± 0.00 (Table 3) Custom-made foot orthosis may be more conducive to stabilizing symptomatic type II ANBs.

There are some limitations in this study. It is a retrospective study with limited cases and a relatively short follow-up period. The bias that flexible flatfoot in school-age children may regress spontaneously as age increases could not be avoided [3, 4, 6], because the foot arch of a child still has the potential to develop. Since foot orthoses do not alter foot anatomy, improving symptomatic pediatric ANB combined with flatfoot may be limited and impermanent. There is the possibility that improved arch and hindfoot indicators would worsen after removing the foot orthosis. The measurement method for hindfoot valgus angle is based on physical examination with limited reliability. Reliability of parameters such like VAS in children over the years also shows possible bias, and the effect on functional aspect could not be evaluated with an idea functional scale for this series without more bias. It would not be easy to conclude about the corrective effect of insoles on the foot arch without a control group. Further study, such as double-blind and randomized controlled trials with a comparable treatments and long-term follow-up, is necessary. Children with a high BMI should be included in further research, because obesity is a significant factor to consider when pain appears in children’s medial areas of the foot. The cost implications of customised bracing for ANB where its role is still debatable. Another limitation is that only children receiving custom orthotics as a treatment were included in this study, which brings selected bias to the results and conclusion that is not identified. Further analysis of all children with ANB over this period should be performed to avoid this selection bias of the results. Many confounding factors for pain/VAS in this series, such as depression, bullying, academic performance in school, parents behaviour/support, sports participation, associated Vitamin D deficiency, etc., should be take into consideration in further research with large number of participants. Some indicators, such as the change of participants’ body mass index and dynamic parameters of the foot, are desired for a more comprehensive evaluation of therapeutic effects in the future.

Conclusions

In conclusion, this study reported that a 4-year custom-made foot orthosis application would significantly relieve symptoms of pediatric symptomatic ANB with flatfoot. Foot orthosis has a good effect on type II and type III ANBs.

Supplementary Information

Below is the link to the electronic supplementary material.

Author Contributions

BY and XT contributed to the conception and supervision of this study; WS and GYJ performed the data analyses and visualization, and wrote the manuscript; ZMY, RZ, and XRL participated constructive discussions; XT and BY finalized the manuscript. All authors reviewed the manuscript.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article. No financial biases exist for any author.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The author(s) declared no potential conflict of interest with respect to the research, authorship, and/or publication of this article.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The Ethics Committee of Tongji Medical College, Huazhong University of Science and Technology (IORG No: IORG0003571) gave a final APPROVAL for this study. Although the data were collected anonymized and centrally, all guardians of patients signed written informed consent for participate.

Informed Consent

All guardians of patients signed written informed consent for participate.

Authorship Declaration

All authors listed meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors, and all authors are in agreement with the manuscript.