Functional evaluation of bilateral subtalar arthroereisis for the correction of flexible flatfoot in children: 1-year follow-up

Highlights

The choice of optimal treatment for pediatric flexible flatfoot is controversial.

Arthroereisis of the subtalar joint is a viable and effective surgical option.

The kinematic effects of arthroereisis on foot joints posture are still unknown.

An expanding endorthotic-implant can restore frontal-plane mobility of foot joints.

Abstract

Background

Flexible flatfoot (FFF) is a common alteration of the foot diagnosed in the pediatric population causing pain and decreased quality of life. Surgical treatment via arthroereisis of the subtalar joint can be recommended when non-invasive options do not result in sufficient pain relief. While clinical outcome of subtalar joint arthroereisis is generally positive, no functional evaluation has thus far been reported following surgery.

Research question

The aim of this study was to assess the effects of two arthroereisis implants for the correction of bilateral FFF on foot and lower limb biomechanics during gait.

Methods

This is a prospective study following 13 children affected by bilateral symptomatic FFF. The patients underwent bilateral subtalar arthroereisis during the same surgery using two types of poly-L-lactide bioabsorbable implants: an expanding endo-orthotic implant, and a calcaneo-stop screw. Radiological parameters and gait analysis were performed preoperatively and at 1 year follow-up and compared to those from an age-matched normal-arched control population. Lower limb and multisegment foot kinematic analysis, along with EMG of the main ankle flexor/extensor muscles, were performed during level walking at comfortable speed. Paired non-parametric Wilcoxon signed-rank test was used to assess differences in radiological and kinematic parameters between pre-op and post-op assessments.

Results

All radiological parameters, and frontal-plane orientation of the rearfoot in double-leg standing were improved at 1-year follow-up in both implant groups (e.g calcaneo-stop: pre-op = 15 ± 7 deg; post-op = 6 ± 9 deg; p < 0.01). The endo-orthotic implant group showed significantly lower pronation/supination at the ankle and midtarsal joint. Activation of the tibialis anterior muscle was more physiological after surgery in both groups.

Significance

According to the present analysis, both implants appear effective in restoring physiological alignment of the rearfoot, however the endo-orthotic implant appeared more effective in restoring a more correct frontal-plane mobility of foot joints.

Introduction

Flexible flat foot (FFF) is a rather common pediatric foot deformity, usually asymptomatic, diagnosed in 10% of children [1]. The more evident morphological alterations characterizing FFF condition are the following: subtalar joint eversion; reduced medial longitudinal arch; calcaneus plantar flexion, and forefoot supination in weight bearing [2,3]. From a functional perspective, while normal feet pronate during the stance phase of gait and supinate during the propulsive phase [4], FFF is characterized by persistent foot pronation with inefficient propulsion during terminal stance, and thus abnormal function during loading response [5]. Altered foot pronation at foot contact also alters the biomechanics of lower limb joints, which may result in musculoskeletal injuries of the foot and leg [6,7].

Although the type of treatment for FFF is still a controversial issue in the orthopedic community [12], surgery can be recommended in case of symptomatic forms presenting pain along the medial side of the foot or in the leg and knee during gait, early muscle fatigue, gait alterations and Achilles tendon tightness [3,8,9]. According to the pathoanatomy of the FFF, surgical treatment can be performed via arthroereisis (Greek words for “joint raising”), arthrodesis or osteotomies. Arthroereisis of the subtalar joint is a widely used minimally-invasive procedure to restrict excessive subtalar pronation by inserting an implant in the sinus tarsi [10]. This surgical procedure can be performed with different implants: impact block devices, also known as calcaneo-stop, which prevent anterior translation of the talus through the application of a screw in the inferior part of the sinus tarsi; axing-altering devices, and self-locking wedges that reduce pronation by impeding the contact between lateral process of the talus and the inferior part of sinus tarsi [9].

Calcaneo-stop is a widespread, reliable and effective implant; a study including 398 patients showed good results in clinical aspects and X-ray measures, absence of complications and restoration of normal foot function [2]. Normalization of footprint in 80% of treated patients was also reported with this technique [10]. Further studies reported improvements in clinical outcome when compared to healthy population [3,11]. An expanding poly-L-lactide (PLLA) endo-orthotic implant has also been proposed for surgical treatment of FFF. This has been shown capable to restore the normal foot structure and results in good clinical and radiographic outcomes [12], enduring at 18 months [13] and at 4 years follow-up [4]. These implants are available in different shapes and materials, either medical-grade metals or bioabsorbable polymers. Bioabsorbable implants however have some advantage as they do not require a second surgery to remove the implant following restoration of the correct rearfoot alignment, once skeletal maturity is reached [14].

Despite the large available clinical evidence, the choice of the best arthroereisis implant for the correction of symptomatic FFF condition is still debated, also due to a lack of quantitative data on the effects of different surgical options on foot and lower limb function [15]. To the best of the authors knowledge, no functional evaluation via gait analysis of the outcome of surgical correction of FFF by means of subtalar arthroereisis has thus far been reported in the literature. The aim of this study was assessing the kinematic effects of two types of bioabsorbable implants – expanding endo-orthotic implant and calcaneo-stop - for the arthroereisis of the subtalar joint in FFF. In particular we wanted to test the hypothesis that these implants are effective in limiting excessive foot pronation in a cohort of children with FFF condition by means of multi-segmental foot kinematic analysis.