MYOELECTRIC PROSTHESIS

-By Sreetama Das(Department of Biomedical Engineering,

4th year, JIS College of Engineering)

What is a prosthesis?

In medicine, a prosthesis (plural: prostheses; from Ancient Greek prósthesis, "addition, application, attachment") is an artificial device that replaces a missing body part, which may be lost through trauma, disease, or congenital conditions. Prosthetic amputee rehabilitation is primarily coordinated by a prosthetist.

Prosthesis formers:

METALS:

Metals are used for forming several of the rehab parts where support is the major concern.

Prosthesis formers(cont.)

COMPOSITES:

Used where strength is required

Prosthesis formers(cont.)

POLYMERS:

Used in most of the prosthesis to form the outer parts and the linings. Provides better comfort and bending.

What is a myoelectric prosthesis?

“Myoelectric” is the term for electric

properties of muscles. A myoelectric-

controlled prosthesis is an externally powered artificial limb that you

control with the electrical signals

generated naturally by your own muscles.

Basic diagram of a myoelectric limb

The working:A myoelectric prosthesis uses the existing muscles in your residual

limb to control its functions. One or more sensors fabricated into the

prosthetic socket receive electrical signals when you intentionally

engage specific muscles in your residual limb. Sensors relay

information to a controller, which translates the data into commands for the electric motors and moves

your joints. If muscle signals cannot be used to control the prosthesis, you may be able to use switches

with a rocker or pull-push or touch pad.

RELAYING OF INFORMATION FROM RESIDUAL LIMB TO ELECTRIC ARM VIA CIRCUITRY:

Components of a myoelectric prosthesis:

The limb consists ofa)A set of electrodesb) A circuitry that consists of operational

amplifiers, filters ,comparators, battery and feedback systems

c)A relay system between the circuitry and the robotic arm

The making:

The layout is made first and then the socket is made with silicone or other biocompatible polymers

The remaining empty socket after the stump is filled with the circuits, battery, telemetric operators etc. which are connected on both sides – the stump and the robotic arm.

The connections are done via electrodes or implant sensors.

Working principles of other types of myoelectric arms:

1)Implanted myoelectric sensors system:These work with implants instead of electrodes, that attach to the residual limb. The information regarding motor impulses are transferred via a transmitter and a telemetry controller.

Working principles of other types of myoelectric arms(cont..)

2)Real-time myoelectric control of a multi-fingered hand prosthesis using PCA:The controller here reverted the PCA algorithm and allowed to drive a multi-DoF hand by combining a two-differential channels EMG input with these two PCs. Hence, the novelty of this approach stood in the PCA application for solving the challenging problem of best mapping the EMG inputs into the degrees of freedom (DoFs) of the prosthesis.

Fig: Block diagram of a PCA controlled myoelectric arm

Working principles of other types of myoelectric arms(cont..)

3) RFID tag based myoelectric limbs: It refers to small electronic devices that consist of a small chip and an antenna. The chip typically is capable of carrying 2,000 bytes of data or less.

This typically works wirelessly, However, the limbs still remain battery powered.

Models of myoelectric prosthesis

•Deka Arm System (DEKA Integrated Solutions) • Dynamic Arm (Advanced Arm Dynamics) • Dynamic Mode Control hand Electrohand 2000 for children (Otto Bock) •ErgoArm hybrid system (Otto Bock) • i-LIMB™ (Touch Bionics) •LTI Boston Digital™ Arm Systems-various upper limb devices and components (Liberating Technologies Inc.) • Michelangelo® Hand (Otto Bock) •ProDigits™ (Touch Bionics) • SensorHand™(Advanced Arm Dynamics) •Utah Arm Systems (Motion Control)

Applications & Advantages:

Movements include: • Elbow flexion/extension• Wrist supination/pronation• Opening/closing of fingers

• Quick reflexes• Secure hold• Grasping objects• Comes in different sizes• Flexible in functioning• No need to learn functioning and handling of the arm

Other advantages:• Can be given to a child at the age of 18-24 months.• Comes with a one or two year guarantee.

Disadvantages:1) Motor and drive last about two to three years.2) With heavy use, the entire prosthesis may need to be replaced after only four or five years.3) When used on a child, the sockets need to be replaced every year due to growth.4) The material used in making it may result in skin irritations, inflammations, infections in the initial days.5) Relatively expensive.

Future of myoelectric prosthesis

Development of the “Intelligent arm”

Industrial robotic arm:

Waves of the brain while performing activities:

Integrating the prosthesis circuitry with a template matching program. Not all

templates are possible obviously, however, the daily basic brain activity signals can be

combined and incorporated into the ‘intelligent hand’. Thus, the mechanism

tries to match the wearer’s wave with the template and functions accordingly.

Bio-electronic feet to be developed in the near future:

References:

• http://www.ottobockus.com• http://openprosthetics.org• http://www.myoelectricprosthesis.com• Wikipedia• https://pdfs.semanticscholar.org• Journal of Neuro-engineering and Rehabilitation

by Biomed central

Thank youQuestions?