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Difference between a prosthesis and an orthosis A prosthesis is a device designed to replace, as much as possible, the function or appearance of a missing limb or body part. An orthosis is a device designed to supplement or augment the function of an existing limb or body part. Characteristics of a successful prosthesis A prosthesis must be comfortable to wear, easy to don (put on) and doff (take off), light weight and durable, and cosmetically pleasing. Furthermore, a prosthesis must function well mechanically and have reasonable maintenance. Finally, compliance with a prosthesis largely depends on the motivation of the individual, as none of the above characteristics matter if the patient will not wear the prosthesis. Considerations when choosing a prosthesis
Most common reasons for an upper extremity amputation Reasons for amputation vary but can be correlated with 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 those aged 15-45 years, with tumors being a distant second. Upper extremity amputations tend to be rare in those older than 60 years, but they may be required secondary to tumor or medical disease. Most common amputation levels See Image 1 . Definitions of relevant terminology
The continuum of prostheses ranges from being mostly cosmetic on one end to being mostly functional on the other end. 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. Functional prostheses generally can be divided into 2 categories: body-powered protheses (cables) and myoelectric protheses. Body-powered prostheses Body-powered prostheses (cables) usually are of moderate cost and weight. They are the most durable prostheses and have higher sensory feedback. However, body-powered prostheses are less cosmetically pleasing than a myoelectric unit, and they require more gross limb movement. Myoelectric protheses Prostheses operated by myoelectricity may give more proximal function and increased cosmesis, but they can be heavy and expensive. They have less sensory feedback and require more maintenance. They function by transmitting electrical activity that the surface electrodes on the residual limb muscles detect to the electric motor. Two types of myoelectric units exist.
A typical below-elbow prosthesis includes a voluntary opening split hook, a friction wrist, a double-walled plastic laminate socket, a flexible elbow hinge, a single-control cable system, a biceps or triceps cuff, and a figure-of-8 harness. An above-elbow prosthesis is similar but substitutes an internal-locking elbow for the flexible elbow hinge, uses a dual control cable instead of a single control, and does not have a biceps or triceps cuff. |
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The major function of the hand that a prosthesis tries to replicate is grip. The 5 different types of grips are as follows:
Terminal devices generally are broken down into 2 categories: passive and active. Passive terminal devices The main advantage of a passive terminal device is its cosmetic appearance. With newer advances in materials and design, a device that is virtually indistinguishable from the native hand can be manufactured. However, passive terminal devices usually are less functional and more expensive than active terminal devices. Active terminal devices Active terminal devices usually are more functional than cosmetic; however, in the near future, active devices that are equally cosmetic and functional should be available. Active devices can be broken down into 2 main categories: hooks and prosthetic hands with cable or myoelectric-based devices. A prosthetic hand usually is bulkier and heavier than a hook, but it is more cosmetically pleasing. A prosthetic hand can be powered with a cable or myoelectricity. With the myoelectric device, the patient can initiate palmar tip grasp by contracting residual forearm flexors and can release by contracting residual extensors. The main mechanisms for opening or closing an active device are as follows:
Wrist unitsThe wrist unit functions as an attachment for the terminal device and can be positioned manually or myoelectrically. The wrist unit can be a quick disconnect unit, a locking unit, or a wrist flexion unit. Quick disconnect wrist unit This style is configured to allow easy swapping of terminal devices with specialized functions. Locking wrist unit Wrist units with a locking capacity prevent rotation during grasping and lifting. Wrist flexion unit In a patient with bilateral amputations, a wrist flexion unit can be placed on the longer residual limb (regardless of premorbid hand dominance) to allow midline activities such as shaving or manipulating buttons.
Elbow unitsElbow units are chosen based on the level of the amputation and the amount of residual function. Flexible elbow unit When the patient has sufficient voluntary pronation and supination as well as elbow flexion and extension, such as in a wrist disarticulation or a long transradial amputation, a flexible elbow hinge usually works well. Rigid elbow unit When a patient can achieve little or inadequate pronation and supination but does have adequate native elbow flexion, such as in a short transradial amputation, a rigid elbow hinge provides additional stability.
Shoulder and forequarter unitsWhen an amputation is required at the shoulder or forequarter level, function is very difficult to restore. This is due to a combination of the weight of the prosthetic components, as well as the increased energy expenditure necessary to operate the prosthesis. For this reason, some individuals with this level of amputation choose a purely cosmetic prosthesis to improve body image and the fit of their clothes.
Preamputation Ideally, a patient who needs an upper extremity prosthesis should be seen by the rehabilitation team prior to the surgery. This allows a chance to evaluate postoperative needs and desires and to begin range-of-motion exercises, strengthening, and training in activities of daily living. However, since most upper extremity amputations are traumatic in nature, this may not always be possible. Surgical procedure During the amputation surgery, several actions can be taken to maximize the function of the residual limb. These actions include the following:
Acute postsurgery The major issues in this phase are adequate wound healing, pain management, instruction in the performance of activities of daily living, mobility, range of motion, and strength. During this phase, a program to prepare the residual limb for the prosthesis should be initiated. A skin desensitization program consists of (1) gentle tapping on the distal portion of the residual limb to mature the site, (2) massage to prevent excessive scar formation, and (3) edema control with ace wraps, a rigid removable dressing, or a residual limb (stump) shrinker. Prosthesis fitting and testing A temporary prosthesis can be fit in surgery, so when the patient awakes he or she can visualize a limb in place. Temporary prostheses usually are fitted this early in healthy, young patients with traumatic amputations, in which case rehabilitation physicians work integrally with orthopedic specialists and prosthetists. Alternatively, in older patients or in those with vascular disease, a prosthesis is not fit until the suture line has completely healed. The prosthesis must be individually fitted to the patient. One size does not fit all. Prostheses are either preparatory or definitive. The advantage to using a preparatory prosthesis is that it is fitted while the residual limb is still maturing. A preparatory prosthesis allows the patient to train with the prothesis several months earlier in the process. A preparatory prosthesis often allows a better fit in the final prosthesis as the preparatory socket can be used to mold the residual limb into the desired shape. During this period, the patient “test drives” the prosthesis and learns what it can and cannot do. Sometimes a preparatory prosthesis is not feasible because of financial considerations. In this case, a patient can only be fitted for the definitive (final) prosthesis. If a patient is being fitted for a final prosthesis without ever having a preparatory prosthesis, delay fitting for the socket until the residual limb is fully mature (usually 3-4 mo).
Pain in the postoperative period must be distinguished between normal postoperative (ie, surgical) pain and phantom limb pain. Surgical pain usually responds well to opioids. Phantom limb pain usually is a burning, stinging, electric pain, and it can be increased with anxiety and stress. While phantom pain is quite common initially, if it is still present at 6 months postsurgery, the prognosis is unfavorable. Phantom pain may respond well to neuroleptics such as Elavil and Neurontin. Phantom limb sensation also must be differentiated from phantom limb pain. Phantom limb sensation is the sensation that the amputated limb is still present. Patients usually report that the absent hand/arm/limb is itching, tickling, or moving through space. Phantom sensation is perceived as a "funny" or "different" feeling but usually is not perceived as painful. Another common phenomenon is telescoping. Telescoping is the sensation that the distal part of the amputated extremity has moved proximally up the arm. A patient might report that it feels like the entire extremity has shrunk so that the hand is now up at the elbow. This is a normal part of the nerve healing process and usually fades with time. Three theories as to why patients experience phantom limb pain and sensation exist. One theory is that the remaining nerves continue to generate impulses. A second theory is that the spinal cord nerves begin excessive spontaneous firing in the absence of expected sensory input from the limb. The third theory is that there is altered signal transmission and modulation within the somatosensory cortex.
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