A Novel Instrumented Outsole for Real-Time Foot Kinematic Measurements: Validation Across Different Speeds and Simulated Foot Landing

Neuromuscular disorders, especially in patients with cerebral palsy (CP), lead to foot deformities and affect foot biomechanics leading to compromised gait. Thus, the foot kinematic measurement is of particular interest to understand and characterize the walking pattern. The present work aims to develop a wearable instrument to measure foot kinematics such as foot-to-ground angle (FGA) in 3-D planes and to measure the foot clearance, i.e., toe clearance (TC) and heel clearance (HC). A template-based outsole was developed that incorporated optical distance sensors located anatomically on the outsole and a magnetometer to measure the foot kinematics. The developed system was validated against the reference marker-based motion capture system from Noraxon, Scottsdale, Arizona, USA. The data from eight able-bodied participants were acquired simultaneously from both the systems (developed and the reference system) at three different walking speeds. A center of pressure (CoP)-based feedback was presented to the participants to shift the sagittal CoP anteriorly, posteriorly, and medially to simulate the walking pattern of patients with neuromuscular disorder at three different foot landing strategies. It was found that more than or equal to 96.48% values of the differences in both the systems is between the limit of agreement, values of Pearson’s correlation coefficient (PCC) were more than or equal to 0.76, and values of root mean square error (RMSE) were less than or equal to 3.45°. Furthermore, a wireless wristband was developed and validated for real-time vibrotactile feedback. Since instrumented outsole (IO) is wearable, low-cost, and easy to use and implement, it has a great potential in real-time foot kinematic measurements.