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Myoelectric prosthesis arm working | advantages, limitations

This page covers Myoelectric prosthesis arm or limb working principle. It mentions benefits or advantages of Myoelectric arm and drawbacks or disadvantages of Myoelectric arm.

Introduction: The word "Myoelectric" is made using two words viz. "Myo" meaning muscle and "electric" meaning electricity. Both combined refers to electric properties of muscles. Myoelectric arm is a prosthetic device which is electrically controlled. Like other prosthesis devices, Myoelectric limb provides user ability to control limb using impulse generated by his/her existing muscles. In medical domain, prosthesis means any artificial device which replaces missing body part e.g. arm, leg etc.

Myoelectric Prosthesis Arm Working principle

The artificial arm or limb are of two types viz. 1. passive and 2. functional. The passive arm does not have any grasping function. It has very good cosmetic apperance which provides real look.

The functional arm is either body powered or electric powered device. The cable operated hooks or hands are body powered prosthesis devices. They are operated by cable or harness system. The cable is pulled using back and shoulder muscles. This either opens or closes the hand.

Myoelectric Prosthesis Arm

The figure depicts components of a Myoelectric prosthesis arm. The battery is used to provide the power to the circuits on the prosthetic device. Let us understand working principle of this battery operated arm.
• Muscle impulses are generated due to muscle contraction of residual arm.
• Electrode sensors pick up these impulses from arm. These sensors are embedded on the surface between residual arm and prosthetic device.
• The impulses are converted into electric signals.
• The electric signals are given to electronic circuit which produces current.
• The current is amplified and filtered to strengthen input signals.
• The amplified current is used to drive the servo motor which actuates arm to either open or close as per user. Separate motors can also be used for wrist arm and all the fingers. One can program and use respective sensors and microcontroller logic to drive selective motors as per need. FSRs (Force Sensitive Resistors) based touch pads are used to activate the fingers.

Benefits or advantages of Myoelectric Prosthesis Arm or limb

Following are the benefits or advantages of Myoelectric Prosthesis device.
➨Myoelectric Prosthesis devices give immense happiness to the persons with various disabilities. They will get motivation to leave this life happily.
➨It provides movements of elbow, opening and closing of fingers, wrist supination/pronation.
➨It offers secure hold, quick reflexes and grasping of objects etc.
➨It is flexible in functioning and comes in various sizes.
➨It is very easy to learn and use.

Limitations or Drawbacks or disadvantages of Myoelectric Prosthesis Arm or limb

Following are the drawbacks or limitations or disadvantages of Myoelectric Prosthesis device.
➨Motor needs to be replaced at regular intervals as per its life.
➨It is relatively expensive and everyone can not afford it.
➨Materials used lead to skin irritations, inflammations, infections.
➨Frequent use of this prosthesis device require replacement of the entire arm in few years (about 3-5 years).
➨If used by children, sockets are required to be replaced as per growth in the child.

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