Componentry - Upper Limb
When it comes to upper limb amputation and subsequent prosthetic fitting, little is understood about this very specialised procedure. The purpose of this article is to explain the types of prosthesis available, and to outline major advances in the last ten years.The arm is second only to the face in the amount of neural activity required to carry out activities associated with daily living. In the past, prosthetic replacement has only been able to slightly compensate for the loss of such a complex organ, but as the age of 'mechatronics' (combination of mechanics and electronics) advances, we are seeing prostheses with increased abilities become available to upper limb amputees.
· Trans-humeral amputation -between shoulder and elbow joints
· Elbow disarticulation -at elbow joint
· Trans-radial amputation -between elbow and wrist
· Wrist disarticulation - at wrist joint
· Trans-carpal amputation -between wrist and knuckles
· Partial hand - an incomplete loss of hand
· Finger amputations
CAUSES OF UPPER LIMB LOSS (thus not congenital upper limb difference) The two most common causes of upper limb loss are:
· Trauma - mostly secondary to road or work-related injuries. Trauma usually contriubtes to 75% of upper limb loss.
· Surgery- performed to remove a diseased or non functional part of the body.
These amputations occur at varying levels, including:
· Fore-quarter amputation -higher than shoulder
· Shoulder disarticulation - at shoulder joint
TYPES OF PROSTHESES
Experience has shown that upper limb amputees who do not wear a prosthesis have experienced:
· Bad first experience (poor comfort or poorly made)
· Unnatural look
· Adverse reactions from others
· Development of one- handedness
· Financial impracticalities
· Unawareness of options
· Limited functional ability
· Lack of sufficient prosthetic
Passive Functional or Cosmetic
A passive functional or cosmetic arm is a lightweight, low-function prosthesis.
Advantages of this type of system are:
Passive Functional / Cosmetic
The disadvantages are:
· Grip force of terminal device is limited to shoulder strength and rubber band/spring tolerance
· Range of motion is reduced due to harnessing
· Poor cosmesis due to harnessing and cable
· Possible Over-Use, Nerve Entrapment Syndrome due to harness
4. Myolectric/External Power
All muscles are powered by a very small electric charge that runs down the nervous system from the brain to the muscle
to be activated. A myoelectric prosthesis utilises this electric charge to control either a terminal device, a wrist or an elbow unit.
Small electrodes are placed over certain muscle bellies, and their job is to pick up these charges and translate them into movement of the specific prosthetic component.Advantages of this type of
· Cosmetic-only arm
· Inexpensive (NON-custom
· Provides opposition to sound arm
3. Body Powered/Conventional
A body powered or conventional prosthesis is an arm that utilises a harness and cabling to control a hand (also known as a terminal device) and an elbow unit. The harness system is controlled by gross body movements (scapular abduction, chest expansion, shoulder depression, extension, abduction, flexion, etc.).
Advantages of this type of system are:
· Heavy-duty construction
· Less expensive
· Lighter in weight
· Reduced cost and maintenance
· Greater range of movement as no external harnessing is required
· Increased cosmesis
· Greater grip force
Disadvantages of this system are:
· Increased cost and maintenance (initially)
· Increased weight (typically)
· Battery - charging and reduced water resistance
WHERE TO FROM HERE
In the last ten years we have seen two important factors play out when it comes to 'intelligent'
1. Reduced size with increased power in battery technology, and
2. Reduced size with increasedperformance of central processing units.
This means that prosthetic manufacturers are able to make smaller, lighter and quicker components available to upper limb amputees. In the last few
years we have seen devices like the I-LIMB™ from Touch Bionics and the Dynamic Arm from Otto Bock being released that are superior in function to older componentry. For more information regarding 'intelligent' prostheses, please visit the websites listed below.