Chapter 34C - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Upper-Limb Deficiencies: Externally Powered Prostheses
Francis J. Trost, M.D.
Dan Rowe, C.P.O.
Externally powered prostheses were first discussed by Reiter in a publication shortly after World War II. Further work in this field, however, was not actively pursued until the late 1950s and 1960s.
At that time, fueled by technological advances and the need created by the thalidomide disaster, attention was again focused on the possibility of producing externally powered prostheses. Efforts to accomplish this were undertaken in the Soviet Union, England, Canada, Italy, and Germany.
Efforts to improve and refine these devices have resulted in the development of a valuable adjunct used in the treatment of amputees. While much has been accomplished in this field, many problems remain to be solved, and at this time, external power is not the complete solution for all of the amputees' problems but, rather, is a valuable additional tool in the prosthetic armamentarium.
Because of the complexity of factors and components used in externally powered prostheses and because of the considerable cost involved, it is felt that most of these prostheses are best prescribed in specialty clinics composed of team members from the various disciplines concerned with the treatment of child ampu-tees.
Initially, externally powered prostheses were fabricated for the adult amputee, and the components were frequently too large for children. Because of the needs of the juvenile amputee and the influx of thalidomide babies, various modifications, including miniaturization of components, allowed children to be fitted with externally powered prostheses.
For unilateral amputees any prosthesis will always be an assistive device. Tasks requiring fine manipulation, unless bimanual, will always be accomplished by the normal or nonamputated limb. In the case of bilateral and high-level amputees (Fig 34C-1.), who have the greatest need for prosthetic assistance, externally powered prostheses still fall far short of meeting their needs in regard to spatial placement of the prosthesis and reliability. In view of this, it is not surprising that the most common externally powered prosthesis used clinically is the unilateral transradial prosthesis (Fig 34C-2.).
EXTERNAL POWER COMPONENTS
In discussing external power components, emphasis will be placed on the child amputee and the differences and special considerations that have to be given to them as children. Powered components for the adult are discussed in Chapter 6A. It should also be noted that teenagers who have reached adult size will have adult components available to them. Initially, components for small children were simply downsized adult components, but currently, in addition to downsizing, some components have been redesigned to meet the needs of the child amputee.
Basically, two external control systems are commercially available: myoelectric and electric switch. Other methods have been tried experimentally but have not yet appeared on the market. Pneumatic power was used initially, particularly in Europe, but despite some advantages, it has some major drawbacks and currently is seldom used as a power source.
The myoelectric system works by picking up the electrical activity generated by the muscles like an elec-tromyogram. This activity is picked up by an electrode, amplified, rectified and filtered, and sent to the motor. The electrode is placed over that portion of the muscle that gives an optimum response as determined by a myotester or, in the case of young children, small electric toys. The amplifier may be contained in the electrode or be separate. The signal may be processed in a digital or analog fashion. If the smooth filtered signal exceeds a certain basic threshold, the motor activates, and the component is engaged and continues its movement until its limits are reached or the signal is discontinued. The myoelectric signal therefore is simply a method of switching the component on and off
In a digital mode, regardless of the strength of the muscle contraction, the component is on or off. In the analog mode, response is graded depending on the force of the muscle contraction. Electrodes are usually one site, one function or one site, two functions.Attempts have been made to insert more functions in one site, but these are not yet widely available.
The other commonly used system is that of an electric switch that opens or closes a circuit and activates a component or turns it off. These are usually push or pull switches. The nudge control switch is a type of push switch. Rocker and toggle switches are also available. Another type of three-position pull switch can flex and extend an elbow and operate either a prehension activator or electric hook. Any of these switches can be controlled in a variety of ways. Many are fixed to the harness to allow pull by body movements, while some are pushed by use of the chin or other hand. In the high-level congenital amputee, functional limb residuals may be used to operate switches. Switch location must be individualized and can be very innovative (Fig 34C-3.).
Most of the powered terminal devices for children are hands. There is one powered split hook commercially available, but this is not often used. There are a number of hands available from different manufacturers. Some are very small so that the very young can be fitted with an appropriate size. They are built with a three-finger pinch, the active index and middle fingers opposing the fixed thumb and the remaining fingers being passive. Although the cosmetic gloves are usually made of polyvinylchloride (PVC), there are some made of silicone.
Characteristically, the fingers of the hand will open from 3.1 to 6.0 cm (1.34 to 2.36 in.) and will develop a closing force of 9.9 to 12.1 kg (4.5 to 5.5 lb). The time to cycle the fingers depends somewhat on the type of control system, temperature, moisture present in the socket, and other factors. The hand usually contains the motor and other mechanical parts.
Powered elbows for children are primarily switch controlled, although myoelectric elbows are also available. Elbows are added to a child's prosthesis some time after the terminal device is fitted just as with body-powered prostheses. Occasionally the elbow will be too fast for small children until they get used to it. Although cycling the elbow while holding something in the terminal device (live lift) is possible, the elbow is primarily a positioning device, as is the wrist (forearm) rotator. These components put the terminal device in a position where it can successfully accomplish a given task (Fig 34C-4.). Electric wrist (forearm) rotators are available for teenagers. They are also a positioning device, and their weight, along with all the other components, may make them burdensome for an amputee with a short residual limb. They are not used nearly as often as hands and elbows. Without them, rotational positioning of the hand is done passively. Humeral rotation and shoulder motion are done passively with friction joints.
Interesting combinations of external power as well as external power combined with body power can be used (Fig 34C-5.). A common combination is that of an externally powered elbow with a body-powered terminal device. Another possibility is a powered hand on one side and a cable-operated hook on the other. There are no large series addressing this issue of combinations of power, so fitting these various components still tends to be individualized and subjective.
The power source most commonly used for these prostheses is a 6-V nickel-cadmium rechargeable battery. Other voltages are occasionally used. Whenever possible, for cosmetic purposes it is fabricated into the prosthesis. Because of weight it should be kept as proximal as possible. In long transradial amputees it may have to be placed in a pod that protrudes somewhat from the prosthesis. In certain selected circumstances, the battery may have to be placed remotely on a belt or some type of harness. Resistance to wire breakage with remote units has improved with the advent of new materials (Fig 34C-6.). The number of cycles before recharging and the eventual life of the battery depends on the number of components it is powering and the care it is given. A battery should never be completely run down before it is recharged, and it should not be overcharged. To address this problem, many chargers now have an automatic shutoff when the battery is fully charged. Typically, it takes about 12 hours to recharge a battery with a 50-mA charger. To avoid the hysteresis effect a battery should be discharged sufficiently before it is recharged. With good care a battery will last about 2 years. Extra charged batteries should be available for uninterrupted use.
In fabricating externally powered prostheses it is important that the prosthetist be familiar with the prostheses and well trained in their fitting and repair. The placement of control sites, switches, and batteries, in particular, may be highly individualized. In general, weight, (especially that of the battery) should be as proximal as possible. The prosthetist should be skilled in the fabrication of self-suspending sockets allowing the amputee as much range of motion as possible while maintaining adequate suspension. Because of the weight of the components, suspension is especially important for powered prostheses. The flexible socket has been very helpful for the high-level amputee and seems to give superior suspension. Care must be taken to avoid "overgadgeting" amputees, especially children, to avoid frustration and prosthesis rejection.
ADVANTAGES OF EXTERNAL POWER
The major advantage of externally powered prostheses for below-elbow (transradial) amputees is the ability to combine cosmesis with function (Fig 34C-7.). This feature appears to be of major importance to the parents of young children where the child has little or no input into the selection of the prosthesis. Another major benefit in these prostheses is the lack of harnessing straps and control cables. Beside being uncomfortable at times, the straps and cables detract from the appearance of the prosthesis. Additional advantages claimed by amputees are ease of operation, comfort, the ability to operate the prosthesis in any position, and superior grip strength, especially when compared with voluntary-opening devices.
With above-elbow (transhumeral) prostheses using an externally powered elbow, "live lift" is possible. In children with limited shoulder or chest excursion, an externally powered elbow allows the available excursion to operate a body-powered terminal device.
Patients have shown a tendency to prefer the externally powered hand when grasping larger objects but to prefer the body-powered terminal device when handling small or flat things. This may be related to a number of factors including the larger grasping surface of the hand, the greater friction of the glove, the ability to use visual cues, and the bulk of the hand.
An uncommon but definite advantage of the powered prosthesis is found in the fitting of amputees whose residual limb is extensively scarred, particularly in areas where suspension straps or a control cable can exert excessive friction or pressure, as in the axilla. These can be eliminated if electrode placement can be successfully carried out. The same rationale applies to the amputee who lacks the body excursion or strength to operate and control a body-powered prosthesis but can activate a switch or electrode in an externally powered component. The externally powered prosthesis will provide a superior prehension force, which is particularly useful in high-level amputees who lack the power to operate a terminal device successfully (Fig 34C-8.). It should be noted that operation of externally powered components requires less energy expenditure than operation of body-powered components does, which is, again, especially important for the high-level amputee.
DISADVANTAGES OF EXTERNAL POWER
Many of the advantages of externally powered prostheses are subjective and dependent on amputee response. The disadvantages, on the other hand, are more objective and specific.
One of the biggest problems still to be solved in externally powered prostheses is that of durability of the various components. Through years of research and improvement, the transradial myoelectric system has achieved a high degree of reliability and durability. The electrical system rarely fails, although when it does, it is expensive to repair. However, the use of these prostheses demands certain restrictions of an amputee's activities, a feature that is particularly cogent when considering very young children. For example, myoelectric prostheses cannot be immersed in water. They cannot be used to hammer, to pry objects, or to play in water without some risk of damage to the device.
By far, the weakest link in this system is the cosmetic glove. Much work needs to be done to improve its durability. It tears quite easily and becomes soiled. Certain stains such as ball point pen ink and newsprint are virtually impossible to remove. The cost of replacing cosmetic gloves is significant (Fig 34C-9.).
Batteries need frequent recharging and periodic replacement. They are still quite heavy and, if they cannot be built into the prosthesis, must be located remotely. The thumb axis and hand frame commonly need repair and realignment in children.
One series of 47 children wearing myoelectric transradial prostheses required 1.9 repairs per year, and this group included only a few very young children. Very young children do not understand that they must make certain concessions to avoid damaging these devices.
The durability of externally powered elbows has been rather poor to date. Over a period of time, this has improved significantly, but the incidence of repair due to breakdown in children is still rather high and frequently means that the amputee will be without a prosthesis while the repairs are being made. Many of the powered elbows are not available in children's sizes and tend to be heavy.
The weight of externally powered prostheses is a frequent complaint of amputees using them, particularly those with short residual limbs. It does not appear to be a frequent cause for rejecting the prosthesis, but it is a common source of dissatisfaction. In addition, much of the weight is located distally in the limb, and thus an even greater force must be overcome when using the prosthesis. The greater the number of components used, the heavier the prosthesis becomes. This is particularly relevant for the higher-level amputee and for small children.
It has been stated by some that proprioception, which is limited with any prosthesis, is poorer with externally powered prostheses than with body-powered prostheses, although this is disputed by others.In tests done on measured tasks, externally powered prostheses have been shown to be twice as slow as body-powered prostheses and five times slower than the normal or nonamputated limb.
While large-grasp functions with the externally powered hand are equal or superior to split hook terminal devices, they appear to be inferior when used for fine motor activities or manipulating small objects. Powered hook-type terminal devices for children are rarely used, and only one model is commercially available.
Amputees at times will complain of inadvertent cycling of a powered component. Because of the bulk of the hands, it is sometimes difficult to get the prosthesis through the sleeves of garments.
A very important factor to consider in prescribing externally powered prostheses is the cost, both initially and for repairs. Although this varies in different parts of the country and is dependent on the type of prosthesis, the minimum cost for these devices is several thousand dollars. There has been reluctance on the part of many third-party payors to assume the cost of externally powered prostheses. An additional problem in children who are still growing is that this expense will have to be repeated as the child grows out of the prosthesis. This growth factor can be somewhat ameliorated by using socket liners. In clinics fitting a number of children, establishing a limb bank and recycling components can defray the cost somewhat.
At this time, the functions that can be fabricated into an externally powered prosthesis for small children include prehension and elbow motion. Not yet available commercially for small children are forearm (wrist) rotation, wrist flexion and extension, upper-arm rotation, or shoulder motion. These are passive only. This is not an indictment of powered limbs since these functions are not available in body-powered prostheses either, but one would anticipate that with further research these functions could be made available to child amputees using externally powered prostheses.
At what age should a child be provided with an externally powered prosthesis? Probably no question in the field of prosthetics in recent years has evoked so much controversy.
It has been shown that children benefit from early (under 1 year) fitting with a body-powered prosthesis in terms of prosthetic acceptance and use and in the development of bimanuality.
Based on the work of Sorbye and others, there are those who would recommend fitting children at a very young age with externally powered prostheses. Working in a fully funded program under ideal circumstances, they showed a high rate of compliance among their patients. Other investigators, however, have not been able to reproduce those results, and so the controversy continues.
All the evidence would suggest that very young children can learn to operate externally powered prostheses, so this is not the issue. Age alone should not be the criterion by which a certain prosthesis is selected.The main requirement to be addressed in selecting a specific type of prosthesis for any amputee is the patient's needs. These needs have to be met in the most appropriate manner possible. There is no one type of prosthesis that is optimal for every amputee. To make an intelligent choice and give valuable advice to the amputee one must be aware of and consider a myriad of factors. These include life-style and activities of the amputee, available components and their advantages and disadvantages, financial considerations, availability of knowledgeable prosthetists, distance from a prosthetic facility, availability of training, characteristics of the residual limb and supporting structures, as well as the motivation, expectations, and goals of the child and parents. Additionally, in young children, comprehension, strength, and attention span must be considered. Needs of the amputee change, and one must never be fixated on a certain type of prosthesis but be flexible and sensitive to the needs of the amputee at a given time in his life. The ability to evaluate all these factors is one of the advantages of the multidisciplinary amputee clinics.
It is a common occurrence for infants and very young children to wear and use a prosthesis for some time, even for several years, before they begin to use the prehensile capabilities of the prosthesis in a meaningful fashion. Fishman and Kruger in their survey of children with myoelectric and body-powered prostheses took special note of the children who simply wore their prostheses, those who used them functionally, and those who rejected them. Among the children under 6 years of age there was a much higher percentage of "passive" wearers, that is, children who wore the prosthesis but did not use it functionally.
In another series of children initially fit with body-powered prostheses there did not appear to be any difficulties encountered when they were switched from body power to external power at a later age, providing that the motivation to use external power was present.
In summary, when externally powered prostheses have been developed to the point that they are clearly superior in every facet of prosthetic care to any other type of prosthesis, widespread prescription will be warranted, but until then each amputee should be evaluated on an individual basis.
CONSIDERATION OF AMPUTATION LEVEL
The majority of externally powered prostheses have been fitted to transradial amputees. One reason for this is that there are many more child amputees in this category than there are at higher levels, whether acquired or congenital. Another reason is that the externally powered transradial prosthesis is functionally a better prosthetic device than the prosthesis for high-level amputees. The reasons for this relate to the available components and particularly to the residual-limb characteristics and the number of functions that need to be replaced. Unfortunately, the amputees with the greatest need (i.e., the higher-level amputees) are the least served by external power due to technological shortfalls. Because of this, the rejection rate and incidence of failure to use these prostheses are highest in this group. It is hoped that future research will solve these shortcomings and provide these amputees with a better, more useful assistive device. Initially, the following observation will be directed at unilateral amputees. Bilateral amputees will be specifically discussed later.
Historically, the transmetacarpal level of amputation has been a difficult level to fit with any type of prosthesis. The incidence of rejection is high. In amputees of this level, length usually is not a significant problem because the amputated limb is almost as long as the nonamputated limb. In addition, they retain that marvelous sense that any prosthetic device eliminates, namely, sensation. With retained carpal and metacarpal segments, they have some wrist and hand motion and lack only finger prehension. This function is usually accomplished with the opposite hand. Externally powered prostheses have practically no use at this level because, with the addition of the usual components, the forearm becomes disproportionately long and also because the function of the residual limb at this level, on balance, is equal or superior to that of a prosthetic device.
At the carpal level, an externally powered prosthesis, usually myoelectric, can be fabricated without creating an unsightly long arm. Some of the same prosthetic problems mentioned above are encountered, specifically in regard to length and sensation, especially if some of the carpal elements are retained. One advantage of this level is that suspension can be achieved with a modification of the expandable wall socket, thus eliminating the need for a Miinster-type socket and allowing the amputee to use whatever forearm rotation remains while retaining full elbow flexion and extension.
The transradial is by far the most common and most successful level of amputation that utilizes external power (Fig 34C-10.). Components for children are readily available. The powered hand with a three-finger pinch is the most common terminal device used. Only one powered hook-type terminal device is available for small children, and this is seldom utilized. Suspension is usually achieved by means of a modified Munster socket, although this socket configuration eliminates any residual forearm rotation. The prosthesis can be donned either by simply inserting the residual limb or with the use of a pull sock. The amount of elbow flexion varies with the height of the anterior trim line, which in turn, depends somewhat on the length of the residual limb and the purchase necessary to stabilize it.
Long transradial amputees may have problems in concealing the battery pack so that it will not protrude from the volar aspect of the socket. Conversely, amputees with very short residual limbs, such as in the short transverse deficiencies, may have problems with suspension and in supporting the weight of the prosthesis. Midforearm length is the ideal length for a myoelectric prosthesis. Forearm rotators are available for the larger child, but clinically they are not used a great deal since they add weight and battery drain.
Elbow disarticulation amputees again have problems with relative residual limb length in that the space required for an electric elbow will create an excessively long upper-arm segment and an asymmetrically short forearm segment. As children assume adult proportions in their adolescent years, they are able to use adult components, and this increases their options for external power.
The long to midshaft transhumeral amputation is ideal to accommodate an electric elbow. If the humeral segment is long enough, they will have functional shoulder motion and be able to support the weight of the prosthesis. With the longer residual limb, selection of control sites, especially for myoelectric use, is also easier (Fig 34C-11.).
High transhumeral, shoulder disarticulation, and forequarter amputation levels have numerous problems: the rejection rate is relatively high, and functional use is diminished. Weight is a problem, particularly in small children because the surface area available for body support of the socket is reduced (Fig 34C-12.). Location of adequate myocontrol sites may also be difficult. Training may be harder because these sites are situated on muscles that do not normally control the comparable prosthetic function. Sockets for these levels tend to get bulky and oppressive. They can become hot, although this can be alleviated somewhat by fenestration. The flexible socket and frame have also been helpful for these levels. It is felt by many amputees to be more comfortable, to give better suspension, and for some reason, to be cooler. Shoulder motion at these levels is only passive. A powered shoulder has yet to be made available.
Successful fitting of the bilateral amputee, at any level, with externally powered prostheses has been disappointing to date. There is an extremely high rejection of external power by these amputees who are so dependent on their prostheses. In addition, bilateral amputees usually reject prosthetic hands and prefer alternative terminal devices. This choice on their part probably relates to the comparative weight, durability, reliability, and ease of operation of bodyand externally-powered types of prostheses.
Congenital amputees often present the clinic team with unique characteristics that require imagination and ingenuity to fit prosthetically. Vestigial limbs, as in the case of high-level transverse deficiencies (phocome-lia), may be used to control microswitches or myoelectric controls (Fig 34C-13.). In some cases, socket and suspension fabrication may have to be very innovative. Although congenital amputees are classified prosthetically as to certain functional levels, the unusual features of their vestigial limbs frequently present opportunities to fabricate a unique prosthesis. It is always better to customize the prosthesis to meet the needs of the amputee than to modify the amputee to fit a preconceived prosthetic design.
Various authors recommend using a myoplastic closure in upper-limb amputations to facilitate externally powered control. This is easily accomplished in elective amputations, but in traumatic amputations this consideration may have to be sacrificed to the maintenance of length and skin coverage. There are other special considerations for amputations in children, but they are covered elsewhere in this text. However, it is worthwhile to mention again, in the context of externally powered limbs, the importance of retaining length and normal skin coverage, even if it means shifting skin flaps. This is done to cope with the weight and control site placement requirements of externally powered prostheses. Another surgical consideration is the decision about the fate of vestigial limbs or residual-limb anomalies. In general, they should not be ablated unless they have demonstrated themselves to be detrimental to the amputee's rehabilitation or prosthetic progress or unless they can be shown, after very careful consideration, to be of no value to the amputee (Fig 34C-14.).
TRAINING THE CHILD AMPUTEE WITH EXTERNALLY POWERED PROSTHESES
It has been well demonstrated that children of all ages, including toddlers, can be trained to operate externally powered prostheses.
The training method comprises several phases. These include testing for controllable myoelectric signal and training in the care, maintenance, control, and finally, the functional use of the powered prosthesis.
Although very young children can be taught to operate an externally powered prosthesis, much of the responsibility for care, maintenance, and actual training will fall to the parents, who have to be motivated to accept this role. In fact, it has been our experience that the motivation of a very young child with any prosthesis generally resides primarily in the parents, gradually giving way to the amputee as he incorporates the prosthesis into his normal living patterns. In addition to this, certain concessions have to be made to the very young child because of his age, attention span, and conceptual abilities. These will be referred to specifically as the process is described. The format followed is similar to that followed in the training of an amputee with any type of prosthesis, except that location and control of the switching device is unique to external power.
In fitting with a myoelectric prosthesis, location of control sites and muscle training is done by the pros-thetist, therapist, or both. A myotester is used to accurately locate the optimum control sites. The muscles to be used are palpated, and then the test electrode is moved until a maximum response is obtained on the myotester. In very young children, the use of toys that move when activated by the myoelectric activity of the child should be substituted for the myotester.
The amputee must learn independent contractions of muscle groups and, in the case of one site-two function controls, differential or graded muscle contraction. This can be facilitated by the use of movements of the phantom hand, although this is not available in very young or congenital amputees. One site should be taught at a time, and after they are all learned, combined function can be taught.
Training sessions should be kept to 30 minutes or less, depending on the attention span and endurance of the child. These sessions may have to be very short for the young child but can be supplemented later by watching the child play and encouraging him to use the prosthesis in his play activities. Short training sessions avoid muscle fatigue and soreness.
Other factors to consider are the developmental age of the patient, his ability to follow instructions, and the complexity and speed of the prosthetic components. While terminal devices can be fit at a very early age, elbow function, when needed, is usually added somewhat later.
Training time will vary, although most amputees can be taught to generate signals, and this does not seem to depend on the length of time since the amputation. In the young child the parents should be incorporated into the training program at the onset since their participation and cooperation is essential to a favorable outcome.
Once the prosthesis has been fabricated, its care and maintenance should be thoroughly discussed with the amputee and the parents. The location and function of each component of the prosthesis should be fully described. The amputee or parents are then instructed on how to don the prosthesis. This is done by inserting the residual limb, although sometimes a pull sock can be used to facilitate entry. If there is difficulty in inserting the residual limb, compounds such as talc or surgical lubricant can be used. The amount of time the prosthesis is worn each day should be gradually increased. The residual limb and socket should be cleaned each day to avoid irritation and odor. At the first sign of any significant irritation or breakdown, prosthetic wear should be discontinued until the problem is rectified. Various compounds are available to control odor or excessive sweating. Antiperspirant sprays are sometimes used successfully. Wearing a prosthesis in summer can be exceedingly hot, and it is not uncommon for the unilateral amputee to discontinue or reduce prosthetic wear during this season, especially if he is on vacation from school. This should not be a cause for undue alarm or fears of prosthetic rejection.
Cosmetic gloves are made of PVC. These gloves are quite easily stained or torn. Stains from ball point pens and newsprint are particularly hard to get out. Gentle soaps and hand lotions can be used to clean and keep the glove supple. The gloved terminal device can be immersed in water only if the glove is intact with no cuts or tears. If additional protection of the cosmetic glove from soiling or staining is needed, another ordinary glove should be worn over it. Rechargeable nickel-cadmium batteries are used to power the prostheses. The length of time they will keep a charge or their longevity is dependent on use, but in general a charge will last about a day, and the battery lasts about 2 years. Batteries occasionally can be totally discharged but should be recharged promptly. When the powered component slows down or operates erratically, the battery should be removed from the prosthesis and charged. Normal recharging time is about 12 hours. Activities that cause excessive jarring of the prosthesis should be avoided. Stress the fact that the prosthesis is a helping hand.
After the operation of the individual components of the prosthesis has been learned, the next step is to apply this to the control of the assembled prosthesis on the amputee. This phase of training focuses on accomplishing individual tasks with the prosthesis. Amputees learn to operate the components in various positions. They learn that the elbow and wrist (forearm) rotators are primarily positioning devices so that the terminal device can accomplish the task in the best possible position. Object training can then be started beginning with grasping objects of different shapes and sizes and moving them from place to place and then progressing to objects of varying densities and learning to moderate the force of grasp. Children over the age of 5 years can follow this pattern. Age-appropriate games and toys are useful in the very young child. Teenage boys frequently respond to challenges to accomplish various tasks. In multifunctional prostheses, each function should be learned individually and then combined or alternated. Basic control and function must be learned before proceeding to the functional use of the prosthesis. It is at this point that parents can be effectively used as an effective and cost-efficient extension of the training program since they spend much more time, especially with the young child, than the therapist can.
In the final phase of training, these learned functions are extended to include the more complex activities of daily living at whatever level is appropriate for the child's age. It is here that individuality should be stressed as well as the interaction of one limb with the other (e.g., stringing beads). Parents are invaluable in giving encouragement and suggestions to the amputee on how he might use his prosthesis in daily activities. Interaction and playing with siblings is helpful. Children 5 years and older can be taught to dress themselves, eat independently, and perform various other tasks. Older children can be instructed in the use of the internal hand switch, the method of "live lift" with a powered elbow, and how to "troubleshoot" simple malfunctions of the prosthesis.
RESULTS OF FITTING WITH EXTERNAL POWER
Fitting amputees with externally powered prostheses has previously been more prevalent in Europe and Canada than in the United States, although it has become much more common here in recent years.
In one study in a group of 40 children using transradial prostheses with external power, only 2 children rejected the powered prosthesis and preferred the split hook. It should be noted that all these children are unilateral amputees and that half of them have been monitored for 1 to 3 years. No one else has shown this high rate of success. More typically, acceptance rates for transradial powered prostheses is from 60% to 90%.Many of these studies are difficult to compare because of different variables in the study. In an interesting study done by Fishman and Kruger with a 3-year follow-up, of 120 children, 44% preferred the myoelectric prosthesis, 34% preferred the body-powered one, and 22% rejected all prostheses. They also noted that 68% were active users of their prostheses and 32% were passive wearers.H.J.B. Day found that in a study done on young children, only 25% actively used their prostheses and the rest wore the prostheses passively. Fishman and Kruger's study had 23 very young children, and the rejection rate among these children was higher than age average, which casts some doubt on the premise that the earlier the children are provided with external power, the less likely they are to reject it. The ability of the child to have the cost of his prosthesis underwritten probably also significantly affects whether or not external power is continued.
Bilateral amputees are obviously very dependent on their prostheses. The results of fitting them with external power, if they have a choice of body power, has been disappointing.
In higher-level amputees, that is, transhumeral and proximal, the rate of rejection also varies from series to series, although, if anything, it tends to be somewhat higher than in transradial amputees. The needs of the higher-level amputees are more complex and with current prostheses are not as well served as are the prosthetic needs of transradial amputees. Few studies of children with higher-level amputations have been done, but in one a 50% rejection rate was encountered. At the very high levels (very short transhumeral, shoulder disarticulation, or forequarter), rejection is high among unilateral amputees. Use of prostheses, whether body powered or externally powered, is poor in small children with very high-level limb loss, as for example, phocomelia or amelia, whether unilateral or bilateral. The prostheses are heavy, cumbersome, and hot for these little children with a small body mass, as well as awkward and imprecise for them to operate. In addition, their parents will frequently look after their bodily functions, or they become particularly adept with the use of their feet if they have usable lower limbs. Available funds would be better utilized, at least initially, for adaptive equipment for this group of small children rather than spending them for externally powered prostheses, except perhaps in research situations.
We would like to express our gratitude to Donabelle Hansen, R.P.T., for her help in preparing the training section of this text and to Eileen Hansen for her generous work in processing the manuscript an untold number of times.
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Chapter 34C - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles