Effects of an auditory biofeedback device on plantar pressure in patients with chronic ankle instability

Highlights

• First study to assess effectiveness of auditory biofeedback on gait in CAI patients.

• Auditory biofeedback can reduce lateral plantar pressure in CAI patients.

• Auditory biofeedback can increase peroneus longus activity during walking.

• Auditory biofeedback may be a useful clinical tool to improve gait in CAI patients.

Abstract

Chronic ankle instability (CAI) patients have been shown to have increased lateral column plantar pressure throughout the stance phase of gait. To date, traditional CAI rehabilitation programs have been unable to alter gait. We developed an auditory biofeedback device that can be worn in shoes that elicits an audible cue when an excessive amount of pressure is applied to a sensor. This study determined whether using this device can decrease lateral plantar pressure in participants with CAI and alter surface electromyography (sEMG) amplitudes (anterior tibialis, peroneus longus, medial gastrocnemius, and gluteus medius). Ten CAI patients completed baseline treadmill walking while in-shoe plantar pressures and sEMG were measured (baseline condition). Next, the device was placed into the shoe and set to a threshold that would elicit an audible cue during each step of the participant's normal gait. Then, participants were instructed to walk in a manner that would not trigger the audible cue, while plantar pressure and sEMG measures were recorded (auditory feedback (AUD FB) condition). Compared to baseline, there was a statistically significant reduction in peak pressure in the lateral midfoot–forefoot and central forefoot during the AUD FB condition. In addition, there were increases in peroneus longus and medial gastrocnemius sEMG amplitudes 200 ms post-initial contact during the AUD FB condition. The use of this auditory biofeedback device resulted in decreased plantar pressure in the lateral column of the foot during treadmill walking in CAI patients and may have been caused by the increase in sEMG activation of the peroneus longus.

Introduction

Lateral ankle sprains are a common musculoskeletal injury during sports [1], [2] and recreational activities [3]. Approximately 30% of lateral ankle sprain patients will develop persistent instability and dysfunction for greater than 1 year [4]. Patients with residual symptoms of “giving way” and “feelings of instability” have been termed to have chronic ankle instability (CAI) [5]. CAI encompasses a wide variety of functional impairments, which can include altered gait kinetics and kinematics [6], [7], [8], [9], [10], [11], [12].

Pressure insoles and mats are commonly used to assess gait pathomechanics following injury. These tools can quantify the amount and timing of pressure application over various regions of the foot. CAI patients have demonstrated increased lateral loading and increased contact time of the lateral aspect of their foot when compared to healthy individuals [8], [11], [13]. This altered gait pattern is hypothesized to contribute to the high recurrence of sprain and residual instability.

In addition to altered gait mechanics, CAI patients demonstrate an increase in percent activation time for the peroneus longus across the gait cycle when compared to healthy controls [14]. Furthermore, the peroneus longus activates prior to initial contact in CAI patients, as opposed to mid-stance in healthy individuals [14]. Altered peroneus longus activation may be in response to the supinated foot to either pull the foot out of its current position or to provide more stability.

We believe incorporating gait training, in addition to traditional range of motion and sensorimotor training interventions, may cause a reduction in recurrent ankle sprains [15]. Gait training interventions for the knee and hip often utilize verbal or visual feedback (mirrors or cameras) to help patients correct abnormal motions [16], however, due to the complex motions that quickly occur at the ankle during walking as well as difficulties in visualizing the ankle with a mirror or anteriorly placed camera throughout the gait cycle, these techniques may be implausible to use to correct faulty ankle mechanics. Therefore, we developed a custom auditory biofeedback device that can be worn without altering shoewear.

The device has the capability to elicit a noise when pressure exceeds a set threshold of a sensor. We believe we can alter plantar pressure by placing the device's sensor beneath the head of the 5th metatarsal, which is a common place for CAI patients to have increased plantar pressure. If the device elicits a noise during walking, this will signify an increased lateral pressure and allow the individual to correct their next step by placing their foot in a more neutral or pronated position prior to heel contact and by shifting their center of pressure (COP) more medially after heel contact. The medial shift in COP can be completed by increased muscle activity of lateral ankle dynamic stabilizers, such as the peroneus longus. However, before incorporating this device into rehabilitation programs, its effectiveness of altering plantar pressure during walking must be evaluated. Therefore, our purpose was to determine if using an in shoe auditory biofeedback device can alter plantar pressure measures in CAI patients during a single intervention session and increase lower extremity muscle activity measured by sEMG. We hypothesize that CAI patients will be able to decrease their lateral foot pressure during walking in response to the auditory biofeedback and have an increase in peroneus longus and gluteus medius muscle activation prior to initial contact and throughout the stance phases of gait.