Tech Briefs

Force Feedback Modulated Joint Control for Prosthetic Ankle

Prosthesis automatically adjusts gait, incline, and heel height.

Human gait is an infinitely variable and complex feedback system to maximize efficiency and stability in movement. Typical prosthetic technology utilizes fixed springs to maximize energy return but do nothing to adapt to the variable environment experienced by users. The Magellan microprocessor foot/ankle (MFA) system, developed by Orthocare Innovations, utilizes sophisticated, patented control schemes based on real-time force feedback loops to increase efficiency and optimize a real world gait.

altA prosthesis for a lower limb amputee typically consists of a custom socket fit to the residual limb of the patient, a connector of some length (usually an aluminum or carbon fiber tube), and a foot. The foot is most often a carbon fiber laminate spring assembly designed for optimal energy return during gait. A patient is fit in a prosthetist’s office by either purely subjective means, through a prosthetist’s observation of the patient’s gait, or subjective/ objective, his/her judgment supported by a gait analysis tool. Although this can produce excellent results for that specific environment (flat, level walking at a self-selected speed in a single, patient-selected pair of shoes) the normal activities of daily living for a patient are such that long bouts of walking like this is the aberration rather than the norm.

Typical patients vary their gait speed, encounter hills and stairs, and change footwear (with varying heel heights). Any of these day-to-day changes dramatically reduces the efficiency of the carefully designed and set prosthesis made by the prosthetist.

The Magellan MFA is unique by analyzing patient gait and optimizing ankle angle within the first step. As a result, people with amputations can experience improved gait efficiency, reduced pain, increased comfort, and higher activity by simply walking in their preferred manner.

Prior implementations of microprocessor prostheses have struggled with cognitive burden, forcing users to behave in unnatural ways or learn non-intuitive techniques to induce changes. The Magellan MFA uses a two-tiered approach to integrate the prosthesis seamlessly into the lives of users, and make a significant impact in prosthetic technology.

First, real time perturbations in terrain or environment that a user experiences are all dealt with automatically, naturally, and virtually instantaneously. The device utilizes a microprocessor control in communication with patented prosthesis forcesensing technology, to analyze the forces generated with every movement the wearer makes. Utilizing compact and fast proprietary micro-hydraulic control technology, the ankle is repositioned in real-time for optimized gait efficiency and balance. Advanced artificial intelligence algorithms automatically learn the unique gait characteristics of the individual user and then optimize the ankle control just for them. (See Figure 1)

Another unique innovation is that the device is fully integrated into smartphone applications, which can enable users to connect and interact with their prosthesis via a Bluetoothlinked app on a smartphone or tablet.

Beyond patient interface, however, is the integration of the device in end-to-end care for the patient. The Magellan MFA also utilizes the mobile device platform to allow users to interface with their prosthetists, provide status reports for their device, and communicate and describe discomfort and pain that may be indicative of problems that, if addressed early, can prevent significant future injury.

This article was written by David Boone, CP, MPH, PhD, Chief Technology Officer and Co-Founder at Orthocare Innovations LLC, Oklahoma City, OK. For more information, visit http://info.hotims.com/45602-166.