A passive functional prosthesis offers very realistic cosmetics and can perform limited function. Examples of passive functional prostheses include:
· Custom silicone finger(s)
· Partial hand prosthesis
· A below elbow or above elbow prosthesis with little or no internal working parts, covered with a custom or non-custom cosmetic glove.
Advantages
· Cosmetic prostheses offer exceptional realism, especially when fabricated using silicone material.
· Passive prostheses do not include intricate, heavy mechanical components and, as a result, are lighter in weight.
· The design of these prostheses is usually simple
· Without delicate internal mechanisms, passive prostheses are usually easier to maintain.
· A passive prosthesis is best for a partial hand amputation because this amputation level cannot accommodate large working mechanical parts.
· Provide functions such as opposition, dexterity, and proprioception.
Specific advantages of finger(s) and partial hand passive prostheses:
Opposition & Dexterity
A passive prosthesis, such as a silicone thumb prosthesis, may not include any mechanical working parts, but the prosthesis itself allows the user to grasp objects. Additionally, if a person wearing a silicone thumb prosthesis taps the prosthesis on a table top, the vibrations travel from the table, through the prosthesis, and to the user’s remaining digit. This proprioception allows the user to have a better idea of where his or her thumb is in space. Finger prostheses can allow a user to hold objects, manipulate small objects, and to perform very complicated tasks, such as typing on a keyboard or playing piano.
Disadvantages
The disadvantages for passive functional prostheses for finger or partial hand amputation are:
· High cost for custom fabrication
· Limited availability of providers trained to fabricate silicone prostheses
· Possible insurance denial, unless medical necessity is justified
· Unreal expectations for cosmesis
· Decreased durability
The disadvantages for passive functional prostheses for higher level amputations, such as below elbow, are:
· Limited function
· Unable to perform bi-manual tasks
· Overuse Syndrome of the contralateral limb
It is evident that the emotional benefit of a cosmetically appealing prosthesis is highly underrated. For users deeply concerned by the appearance of a prosthesis, an unrealistic prosthesis can pose a significant obstacle in social interactions.
A body-powered conventional prosthesis is controlled by the amputee’s own body power and includes a system of cables, harness, and integrated mechanical parts.
Components on the prosthesis, such as the elbow and terminal device, are operated by harness system. The harness system is controlled by gross body movements, including:
· Scapular abduction or adduction
· Glen humeral flexion
· Shoulder depression & elevation
· Chest expansion
Advantages
· Durable construction
· Proprioception
· Less expensive than designs with external power source
· Lighter in weight than designs with external power source
· Reduced Maintenance
Disadvantages
· Grip force is limited by shoulder strength and rubber band tolerance
· Functional envelope, the area where the user can operate the prosthesis, is limited
· Harness can be uncomfortable and restrictive
· Poor cosmesis
· Possible overuse, nerve entrapment syndrome
A myoelectric prosthesis is a battery powered device operated by using miscle signals. These signals are amplified and are used as control impulses to operate the hand, wrist, or elbow.
Electrodes are placed inside the prosthetic socket and are positioned to be in contact with specific user muscles. The electrodes are controlled by EMG and are powered by a battery. The muscle action is picked up by the electrodes, amplified, and then sent into the control circuit in the elbow and/or hand. The circuit then interprets this information and runs the motor for either open/close, flex/extend, and grip force. This is a continuous process from thought all the way to function; a direct relationship that isn’t interrupted by some other body movement.
Advantages
· Wide functional envelope
· Typically more cosmetically appealing without cables, extensive harnesses, or hook terminal device
· With limited or no harnesses, increased comfort and increased range of motion
· Grip force is independent of the user’s strength or range of motion
· Control is patterned after natural body functions
· Less energy consuming than body-powered design
· More accurate control over the hand device
Disadvantages
· Battery maintenance
· Increases weight due to myoelectric components
· Increased overall maintenance and susceptibility to harmful elements, such as moisture
· Increased cost
· Elbow function requires nudge control by the user
A hybrid prosthesis includes both electric and body-powered components, usually a body-powered elbow and myoelectric hand.
Advantages
· Wide functional envelope
· Lighter weight than 100% myoelectric prosthesis with electric elbow
· Greater grip force than prosthesis with body-powered hand device
· Less harnessing than 100% body-powered prosthesis
· Feedback of forearm flexion velocity
· Reduced initial and maintenance costs
Disadvantages
· Control harness usually required
· Increased weight on harness
· Not suitable for high level amputations
A recreational prosthesis is designed for specific functions. The hand device can be used for recreational activities or for adaptive devices. Examples include:
· A standard socket attached to a terminal, hand, device designed to hold a billiard stick
· A standard socket attached to a fin for swimming
· A standard socket attached to a heavy-duty device designed for weight lifters
Advantages
· Increased user function and ability to resume previous hobbies/recreational activities
Disadvantages
· Insurance denial for coverage