Prosthetic Arm

Prosthetic arm

1. Introduction

Prosthetic arm is an artificial component designed specially to replace a real arm. Usually, it is used to replace arm lost by injury or congenital abnormality. In medical field, the doctors use prosthetic arm on the patient that had undergone arm amputation operation. Amputation refers to the removal of body extremity by surgery.

The prosthetic arm is usually designed according to the customer demand. As the result, various types of prosthetic arms can be found in the market nowadays. Different type of prosthetic arm can perform different type of task. Ever since the history of prosthetic arm started, a lot of changes have been made to its design. The study of the history of prosthetic arm will be conducted to trace these changes.

This research paper will focus mainly on the typical prosthetic arm as there are too many types of prosthetic arm exist in the world. However, an analysis of certain prosthetic arm designs will also be included in the research paper to have a clear idea on this device.

A typical prosthetic arm is controlled by transforming residual shoulder movements or muscle signals into the simplest movement commands. So, this device typically can only perform one task at a time.

2. History

The first recorded user of prosthetic arm in the history is Marcus Sergius; a Roman general who lost his right arm in the second Punic War (218-201 BC). His hand was then replaced by a special iron that allowed him to hold his shield. It was recorded by Pliny the Elder, a Roman scholar. During these times, most of the prosthetics were made by wood or steel.

Next in 1508, an infamous German knight Gotz von Berlichingen had two prosthetic iron hands to replace his right arm. Like Marcus, he also lost his arm in a battle. His prosthetic arm was different than the previous designs and was considered to be very revolutionary; it is capable of holding objects from a sword to a feather pen.

An artist drew this picture to reflect his idea of how Gotz arms may have looked like:

In 1529, Ambroise Pare introduced amputation into the medical field. He also was the person responsible for the design of artificial limb shortly after that. Later in 1898, Dr. Vanghetti invented an artificial limb that could move via muscle contraction.

3. Uses

As discussed earlier, early prosthetic arm came in different types and each of them can perform a different kind of tasks. There are prosthetics arm designed to hold a certain objects and there are also prosthetic arms that was designed to looks like a real arm but does not have any capabilities. Once again, this diversity makes the research on each type of prosthetic arm becomes almost impossible. That is why the main focus will be given to the typical prosthetic arm.

Back to the topic of discussion, the first recorded prosthetic arm user had his arm replaced by a specially designed iron to hold his shield. Early designs have a poor quality as most of them were made of wooden or steel pegs. However, the quality of the design has improved since then and the ability to move has also been added to it. In 1536, Ambroise Pare had expanded the use of prosthetic arm in the medical field.

In the early times, more focus is given to the replacement of the missing arms than its own capabilities. This is one reason for the poor quality of prosthetic arms. Moreover, most of the prosthetic arm users at that time had their prosthetic arm designed only for one or two goals. For example, in Marcus Sergius case, he had his prosthetic arm designed specifically just to hold his shield.

4. Technical aspects

4.1. Types and dynamics

There are two common types of prosthetic arms nowadays; the first type is controlled by transforming residual shoulder or arm movements into a few simplest movement commands. A cable attached to the residual shoulder or arm will act as a controller extension between the prosthetic arm and the real body. Basically, the movement of the prosthetic arm is the alternate movement of the attached body part. This type of prosthetic arm can be called cable-operated prosthetic arm.

The second type of prosthetic arm comes from a more advanced technology; it will picks up nerve signals produced by the slightest muscle tension and translates the signals into movement (Boykin, 2008). This type of prosthetic arm is called myoelectric prosthetic arm. In comparison, the second type has more functions than the first type. It also resembles the real arm in many aspects.

The most basic task every typical prosthetic arm must be able to do is gripping or holding something. Even the first recorded prosthetic arm was made for the sole purpose of holding a shield. Nowadays, it is very hard to determine the gripping strength of every single prosthetic arm as there are too many types of prosthetic arm exist in the market. The variation of its strength could depend on the type of material, user skills and the uniqueness of the design itself.

In Kate Baggott's article titled 'Upgrading the Prosthetic Hand', she talked about a lightweight prosthetic hand that uses hydraulics. This prosthetic hand is claimed to be better than artificial hands that use motorized finger in term of its behaviour, weight and flexibility. The most interesting part is it can give five different gripping strengths. The prosthetic hand uses lightweight miniature hydraulics. This hydraulics is connected to elastic chambers that can flex the joints of the fingers. When the sensors on the palm and fingers