Elsevier

Gait & Posture

Volume 47, June 2016, Pages 43-47
Gait & Posture

An optimized design of in-shoe heel lifts reduces plantar pressure of healthy males

https://doi.org/10.1016/j.gaitpost.2016.04.003Get rights and content

Highlights

  • An optimized heel lift design with an arch support was introduced.

  • The optimized heel lift reduced heel pressure without increasing forefoot pressure.

  • The arch support used in this study did not put additional load on the midfoot.

Abstract

Conventional heel lift with a flat surface increases the risk of foot problems related to higher plantar pressure and decreased stability. In this study, an optimized design of in-shoe heel lifts developed to maintain the midfoot function was tested to investigate if the plantar pressure distribution was improved. The design was based on three dimensional foot plantar contour which was captured by an Infoot 3D scanning system while the heel was elevated by a heel wedge. To facilitate midfoot function, an arch support was designed to support the lateral longitudinal arch, while allowing functional movement of the medial longitudinal arch. Twenty healthy male subjects were asked to walk along an 8 m walkway while wearing high-cut footwear with and without the optimized heel lift. Peak pressure, contact area and force–time integral were measured using the Pedar insole system. Range and velocity of medial-lateral center of pressure during forefoot contact phase and foot flat phase were collected using a Footscan pressure plate. Compared to the shoe only condition, peak pressure under the rearfoot decreased with the optimized heel lift, while no increase of peak pressure was observed under the forefoot and midfoot regions, indicating improved plantar pressure distribution. The findings of this study suggest that this optimized heel lift has better biomechanical performance than a conventional flat heel lift. Results from this study may have implications for insole and shoe last design, especially for people who need additional heel height without sacrificing midfoot function.

Introduction

In-shoe heel lift is adopted as a leg length adjustment device for leg length discrepancy [1], and is also recommended for the treatment of some lower extremity problems which are associated with overload in Achilles tendon and high peak pressure under the rearfoot [2], [3] (the terms “heel” and “rearfoot” are used interchangeably throughout the paper). However, it was suggested that heel lifts should be used with caution, because of an increase in peak pressure and pressure–time integral under the forefoot [4], [5]. High peak pressure is a risk factor for foot problems, as it may cause discomfort and is associated with some foot pathologies, e.g. diabetic foot ulcers [6]. Our previous study on flat heel lift also showed an increase in range and velocity of medial-lateral center of pressure (COP) during walking [5]. This increased movement of COP in medial-lateral direction indicates greater demand of stability control. Most of the tested heel lifts were heel wedges without contoured surface and arch support, which provide insufficient support to the elevated midfoot.

The foot rolls from heel to toe during walking. Each part of the foot is related to a different functional demand, with the heel mainly related to aspects such as absorbing impact, transferring load to the leg and the forefoot mainly related to propulsion. Numerous studies have focused on rearfoot motion control [7], [8] and forefoot load relief [6], while the midfoot as a linkage between the forefoot and rearfoot, has drawn far less attention.

The midfoot consists of a medial and a lateral longitudinal arch. The medial longitudinal arch of the human foot acts as a spring during locomotion which allows mechanical energy to be stored and recoiled to benefit gait efficiency [9]. Restraining arch movement would affect the windlass mechanism and lead to a possible decrease in the efficiency of sagittal plane motion. According to the sagittal plane facilitation theory, when there is a sagittal plane block or deficiency, the foot and ankle complex must compensate somewhere along the kinetic chain [10]. Moreover, the studies conducted by Wegener et al. showed that the midfoot joint plays an important role in energy production during the propulsion phase of both walking and running [11]. Interfering with the medial longitudinal arch function might have an impact on gait efficiency and increase risk for lower limb injuries. The lateral longitudinal arch is always in contact with the ground during locomotion in normal foot type, which is important to stabilize the heel-to-toe movement. With the heel elevated, however, both medial and lateral longitudinal arches are suspended, presenting a situation similar to a high arch foot. The midfoot has an important role in weight bearing and transferring load from the rearfoot to forefoot. Thus we assumed that the higher plantar pressure and decreased stability caused by flat heel lifts may be associated with the lack of support to the midfoot.

In order to improve the midfoot function when using heel lifts, a new design of arch support was developed and tested in this study. Arch support has been widely adopted as a type of insoles to enhance biomechanical performance, such as redistributing plantar pressure, relieving load on plantar fascia and decreasing knee adduction moment [12], [13], [14], [15], [16]. Arch support is also used in motion control shoes to improve foot balance by supporting the medial arch to control over-pronation [17]. Custom-made insoles with arch support and a contoured heel are used in foot care settings of diabetic patients [18]. As the contact area increases, load can be transferred from high load regions to adjacent areas [19]. Thus in order to distribute plantar pressure more evenly, the ‘total contact’ concept has been adopted to design insoles based on the plantar contour of the foot to provide full foot support. Total contact arch support has been shown to relieve load on plantar fascia effectively [12], however, these tests were conducted on cadavers, and thus its effects on foot dynamic function during locomotion is unknown. Previous studies suggested that the arch height varies between none weight bearing, standing and locomotion [20]. The “total contact” concept is valid to redistribute pressure over a rigid part, but if it is adopted for arch support design, it may induce a series of compensatory reactions by restraining the necessary motion of midfoot.

Therefore, we hypothesized that an optimized heel lift with a functional arch support that maintains the midfoot function may reduce the adverse effects of a flat heel lift, i.e. reducing peak pressure under forefoot and midfoot and reducing the range and velocity of the medial-lateral COP. Taking into account the characteristics of a heel lift and the shortcomings of the total contact insole, a new design of heel lift with a functional arch support is introduced. We hypothesized that the midfoot function would be preserved by fully supporting lateral longitudinal arch and allowing medial longitudinal arch the necessary range of motion, while also providing some support in case the foot over-pronated. This study is a sequel to our previous study on flat heel lift [5]. In order to make comparisons, the subject inclusion criteria, measurement protocol and the main researchers remained the same. Force–time integral, which is the integral of force with respect to the contact time, peak pressure and contact area were measured to study the plantar load distribution. The range and velocity of medial-lateral COP were recorded to assess stability. The purpose of this study was to determine the effect of the optimized heel lift on the plantar distribution and the stability control during walking. The results may provide implications for insole and shoe last design and could be beneficial for people needing leg length adjustment and heel pain relieve.

Section snippets

Subjects

Twenty healthy male adults gave informed consent and participated in this study. The average age of the subjects was 22.4 years (S.D. 0.9), average mass 57.5 kg (S.D. 9.5), average height 168.0 cm (S.D. 2.9). All participants had the same shoe size to avoid any effects of shoe size and for the convenience of center of pressure analyses. None of the subjects had a history of lower extremity injuries in the preceding year. All participants had normal arches, with the arch index (AI) was 0.21 < AI < 

Results

Comparison of contact area and peak pressure under forefoot, midfoot and rearfoot with and without the optimized heel lift are shown in Fig. 1, Fig. 2, respectively. Compared to the shoe only condition, the optimized heel lift increased the contact area under the midfoot (p < 0.001). The optimized heel lift did not increase peak pressure under forefoot and midfoot regions. There was a reduction on peak pressure under the rearfoot with the optimized heel lift compared to the shoe only condition (p <

Discussion

Compared to the shoe only condition, the increase of the midfoot contact area with the optimized heel lift indicates good support for midfoot. In the flat heel lift study, however, the midfoot contact area was considerably reduced by heel lifts [5]. This is partially because a heel lift rotates the foot onto metatarsophalangeal joints, lifting both the midfoot and rearfoot away from the ground. Moreover, the midfoot and rearfoot are not a rigid combination. The midfoot could be raised further

Conflict of interest statement

The authors declare that there are no known conflicts of interest related to this project that could have influenced this manuscript.

Acknowledgements

The authors would like to thank Richard Smith for his assistance in manuscript writing, Jin Zhou for his help on manufacturing the heel lifts and Yuhao Ding and Song Song for their assistance in data collection.

References (27)

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