Weinstein Lovell and Winters Pediatric Orthopaedics 7e

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CHAPTER 30  |  The Child with a Limb Deficiency

FIGURE 30-41.  This young boy with a trans- verse transcarpal deficiency demonstrates the partial grasp at the flexor crease that, when combined with sensation, usually proves supe- rior in function to a prosthesis.

at higher levels. Some older children and adolescents will desire a cosmetic hand that would be used in certain circumstances or would provide a psychosocial benefit. Some cosmetic hands have a passive spring grasp to provide limited function. Prosthetic Management.  Generally, upper extremity prostheses and their control systems can be subdivided into three categories: passive, externally powered , or body-powered devices . The Ballif arm (circa 1400) was the first body-powered prosthesis to introduce the use of prosthetic hand operation by transferring shoulder movement to activate the terminal device (212). A har- ness over the contralateral shoulder is connected with a thin cable and housing to a terminal device. Through scapular abduction, the fixed cable is stretched over a greater distance and causes the prosthetic hook or hand to open or close, depending on the con- figuration of the terminal device. A good analogy is using a hand lever to activate the brakes on most bicycles. Most parents prefer a prosthetic hand over the cantered hook for cosmetic reasons. Unfortunately, the hook is far superior in function, but has fallen from favor because of the desire to have the prosthesis look as natural as possible, even at the sacrifice of function. Most hooks are canted in design, and this allows the child to see what is being grasped, as compared to the mechanical hand that obstructs the view and results in awkward arm positions to grasp objects. The externally powered prostheses are powered with motors and can be further subdivided into switch control or myoelectric control . In both systems, a battery, relay switch, electric hand, and electronic control system are present. It should be noted that the myoelectric hand is the only termi- nal device available for children using the externally powered prosthesis. In the myoelectric prosthesis (Fig. 30-42), the child contracts various muscles in the residual limb voluntarily, and an electrode placed on the surface of the skin acts to pick up the electromyographic signal. The signal is in turn amplified with the help of an electronic relay switch, and this, in turn, operates the electric hand (213). The entire system is generally

referred to as a one- or two-site system. This denotes the num- ber of electrodes that are used for signal recognition. The one-site system can be further categorized as voluntary opening–automatic closing, rate sensitive, and level sensitive. Myoelectric arms are generally fit before age 2 and utilize a volun- tary opening–automatic closing (cookie-cruncher) configuration. Muscle contraction opens the electric hand, and relaxation causes the hand to close automatically. After age 4 years, more advanced prostheses can be fit. These include rate-sensitive and level-sensi- tive control systems, which use one muscle to control two func- tions, and are generally fitted to children over 4 years of age, when two sites are not ­available. Because muscle contraction controls more than one joint in this case, the prosthesis is more difficult to learn to use. The choice of a system depends on the muscle signal strength, muscle control, and prosthetic design factors (31). In the two-site system, each electrode operates a specific task. Children can often operate this more complex system by 3 to 3 1/2 years of age. Contraction of wrist flexors closes the hand, whereas contraction of wrist extensors is used to open the hand. This system is used when children have demonstrated good control and use of their myoelectric prosthesis and can con- trol both the flexors and extensors independently of each other. Patients with a higher level of upper extremity amputation are generally good candidates for switch-controlled externally powered prostheses. The electrode is replaced with a miniature switch that can be of a push–pull configuration, a force-sensing resistor, or of a simple toggle design. The incorporation of these switches into the prosthesis depends primarily on the level of amputation and the design of the prosthetic socket or frame. Multiple Limb Deficiencies.  Management of the patient with multiple upper and lower limb deficiencies is a challenge that requires a team with experience to achieve the maximum function for the patient. The difficulties of bilat- eral upper extremity amputation have been covered earlier. Children with one upper and one lower extremity pose no