Upper Extremity Prosthesis

The prosthesis that Luke Skywalker got in Star Wars was a pretty smart arm. Technology is not quite there, but there is pretty amazing stuff available at present. (Picture: See Luke Sky Walker’s right prosthetic hand.)

Upper extremity prosthesis (arms) play by a totally different set of rules than lower extremity (limbs). For starters it is much easier to achieve socket comfort because the prosthesis doesn’t have to carry the whole body weight.The body (residual limb) has to carry the prosthesis, by this I mean that the prosthesis is suspended by an elbow, stump or shoulder and the only weight this body part has to carry is that of the artificial arm.

Cost, functionality and cosmetic appearance are important factors in deciding what prosthesis to manufacture. (Picture: Body Harness for conventional cable operated prosthesis.)

I must once again state that the most expensive is not always the best but if you want to drive the fastest and best looking car it would obviously cost more, and the same applies to prosthetic arms. Most people are satisfied with just a daily commuter and as for myself a GSXR 1000 does the job!

I do think that adjusting to an arm is more challenging than adjusting to a leg. The reason is that it has to do more functions than just walking; it has to touch (sensory), grip, turn, and release and psychologically patients become desponded. Furthermore it is not as easy to hide cosmetically as a prosthetic limb.

Upper limb prosthetics can be categorised as the following:


Body powered prosthesis


Conventional (body powered) prostheses require the upper extremity amputee to expend energy to manipulate the cable and harness which allow the elbow to extend or flex and the terminal device to open or close. For a below elbow amputee, one cable operates the hook or hand. For the above elbow amputee, more exertion and greater gross body motion are required to operate an elbow plus a terminal device. After training, many amputees find the required body motions become second nature. (Picture: Cosmetic hand, crutch rubber and functional hook attached to wrist insert.)

Patients usually choose to have a cosmetic or functional hand for socialising and light labour (office work), and a functional hook for precise gripping and heavy labour. The distal wrist insert can be attached to almost any device the patient would like to attach to the distal end of the wrist.

The cosmetic glove that covers the hand can be ordered in almost any form and colour to match the sound hand. However, body-powered prosthetics always require more effort and excessive body movements, whereas Servo and Myo Prosthetics can allow the patient to live a more natural life with fine movements that are easier to achieve. Further, where the amputee is concerned with his/her outward appearance and the image portrayed to others, the gross body movements required by a body powered prosthesis becomes a cosmetic factor. Where the physical limitations of the amputee are such that a conventional control system is less practical, the option to move to an externally powered device becomes an excellent alternative. Electric Prosthesis allows the amputee more function when the elbow is flexed as body powered prosthesis typically does not. This is more cosmetically acceptable and can attain a hard or light grip without significant effort. (Picture: Off the shelf cosmetic glove for prosthetic hand.)

Electronic prosthesis


When an electric or myo-electric (externally powered) prosthesis is indicated, control issues are simplified in some ways and become more involved in others. Three basic options are available to operate a powered prosthesis: switch control, myo-electric control, or a combination. Switches come in a variety of designs such as harness switches, push button switches which can be mounted inside or externally on the socket, and membrane push switches which are internally mounted. A switch requires some gross body motion to operate, for example, the push button is depressed by a chin, opposite limb, residual limb, or digit. A pull switch is cable operated and requires a few degrees of excursion, less than with a conventional prosthesis. Myo-electrics are the most comfortable and natural way to control artificial arms and hands. Small electrodes are placed on the skin where the electric activity of the muscle is (electro-myo-graphic – EMG – signal). The muscle signals are electronically amplified and used to move the components. The electrodes are installed in the socket when the arm is fitted and then connected to the myo-electric system. The patient is required to re-train muscles to build strength and control to use this system. The myo-electric system using Pro-Control allows the amputees to move the hand slowly or quickly instead of simply turning it on and off. (Picture: Myo-electric arm with electric hand and Greifer..)

As far as myo-electric prosthesis is concerned, a German Company Otto Bock is without the doubt the world leader. They have no competition in South-Africa and their products are tried and tested and user friendly to the prosthetics, offering them yearly courses, so there is no real point in comparing their products with any other manufacturer. Testing the patient's stump for muscle signals is a lot of fun. The sensors resting on the stump is attached to a PC and the patient can see their prosthetic hand opening, closing and rotating on the computer screen while they tense and relax their residual stump muscles. (Picture: Myo-electric testing apparatus.)


This is also a very good training method to see what the patient is capable of before deciding on the appropriate componentry. One of the latest and greatest products in Otto Bock’s line up of components is a Sensor hand. Sensors in the fingers keep constant watch over the object being held and before the object can slip the sensor hand readjust the grip automatically. This hand also regulates the force being applied on an object because the patient can not feel how tight the object is being gripped. All the electric hands are “I Robot” strong and can crush a wine glass with little effort.

(Picture: Life-like silicone left hand - Picture courtesy of Brian McKibbin Durban.)

Cosmetic prosthesis


Silicone hands and fingers can be manufactured to precisely match the amputated limb. Function and cosmetic appearance sometimes compete in this instance. In the case of fingers, technology has come to the point where a small metal insert can be anchored to the bone while still protruding through the soft tissue. The silicone finger can be attached to the metal insert thereby giving it some sensation, very good function and lifelike cosmetic appearance. A lot more can be said about bone anchoring and silicone techniques but it is in itself too big a field to cover in this article.

Rehabilitation


The most important factor when fitting upper limb prosthesis is the rehabilitation. Physiotherapy and especially Occupational therapy is vital. Upper limb prosthesis is the most discarded of all prosthetics; patients tend to give them half a go and thereafter put them away in the closet never to use it again. Many factors including functionality, cosmetic appearance and inadequate training contribute to this. So to all upper limb amputees, you really have to persevere and make the arm your own, otherwise you will discard it! May the force be with you! (Picture: One of my favourite patients. At this age Jaiden uses his left below knee prosthesis more than he would ever use his left upper limb.)

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