06-12-2012, 05:34 PM
Upper limb prosthetics
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Upper limb prosthetics are devices designed to replace, as much as possible, the function or appearance of a missing upper limb. Upper limb orthoses are devices designed to support, supplement, or augment the function of an existing upper limb. The image below illustrates various anatomic levels of upper limb amputations.
Design Features
General considerations
Characteristics of a successful prosthesis
Ideally, a prosthesis must be comfortable to wear, easy to put on and remove, light weight, durable, and cosmetically pleasing. Furthermore, a prosthesis must function well mechanically and require only reasonable maintenance. Finally, prosthetic use largely depends on the motivation of the individual, as none of the above characteristics matter if the patient will not wear the prosthesis.[1]
The following are considerations when choosing a prosthesis:
• Amputation level
• Contour of the residual limb
• Expected function of the prosthesis
• Cognitive function of the patient
• Vocation of the patient (eg, desk job vs manual labor)
• Avocational interests of the patient (ie, hobbies)
• Cosmetic importance of the prosthesis
• Financial resources of the patient
Most common reasons for an upper extremity amputation
Reasons for an upper extremity amputation vary, but they can be correlated by age range. Correction of a congenital deformity or tumor is commonly seen in individuals aged 0-15 years. Trauma is the most common reason for amputation in patients aged 15-45 years, with tumors being a distant second. Upper extremity amputations tend to be rare in patients who are older than 60 years, but they may be required secondary to tumor or medical disease.
Amputation levels
Anatomic levels of an upper extremity amputation are as follows (see the image below):
• Transphalangeal amputation: Resection of the thumb or fingers at distal interphalangeal (DIP), proximal interphalangeal (PIP), or metacarpophalangeal (MCP) levels, or at any level in between
• Transmetacarpal amputation: Resection through the metacarpals
• Transcarpal amputation: Resection through the carpal bones; transmetacarpal and transcarpal amputations are less advised because, except for select circumstances, they provide for decreased functional outcomes
• Wrist disarticulation: Transection between the carpals and radius/ulna
• Transradial amputation: Below-elbow amputation (may be classified as long, medium, or short)
• Elbow disarticulation: Transection through the elbow joint
• Transhumeral amputation - Above-elbow (Standard length is 50-90% of humeral length.)
• Shoulder disarticulation: Transection through the shoulder joint
• Interscapulothoracic disarticulation (forequarter): Amputation removing the entire shoulder girdle (scapula and all or part of the clavicle) (some surgeons choose to leave part of the medial clavicle)
Definitions of relevant terminology
• Residual limb: The preferred term for the remaining portion of the amputated limb
• Relief: A concavity within the socket that is designed for areas that are sensitive to high pressure (bony prominences)
• Buildup: A convexity that is designed for areas that are tolerant to high pressure (such as a bulge)
• Terminal device: The most distal part of a prosthesis that substitutes for the hand; it may be a prosthetic hand, a hook, or another device.
• Myodesis: Direct suturing of residual muscle or tendon to bone/periosteum
• Myoplasty: Suturing of agonist-antagonist muscles pairs to each other
• Prehensile: Grasp
Different types of prostheses
The continuum of prostheses ranges from mostly passive or cosmetic types on one end to primarily functional types on the other (see Table 1). The purpose of most prostheses falls somewhere in the middle. Cosmetic prostheses can look extremely natural, but they are often more difficult to keep clean, can be expensive, and usually sacrifice some function for increased cosmetic appearance.
Body-powered prostheses[3, 4]
Body-powered prostheses (cables) are usually of moderate cost and weight. They are the most durable prostheses and have higher sensory feedback. However, a body-powered prosthesis is more often less cosmetically pleasing than a myoelectrically controlled type is, and it requires more gross limb movement.
Externally powered prostheses[5, 6]
Prostheses powered by electric motors may provide more proximal function and greater grip strength, along with improved cosmesis, but they can be heavy and expensive. Patient-controlled batteries and motors are used to operate these prostheses. Currently available designs generally have less sensory feedback and require more maintenance than do body-powered prostheses. Externally powered prostheses require a control system. The 2 types of commonly available control systems are myoelectric and switch control.