My­o­elec­tric Pros­thet­ics

BioSpectrum (Asia) - - Technologies -

A my­o­elec­tric pros­the­sis is one which is con­trolled by the elec­tri­cal ac­tiv­ity of a mus­cle, i e. by a my­o­elec­tric sig­nal. They are pow­ered by elec­tric­ity from a bat­tery, in which case the My­o­elec­tric sig­nal con­trols the flow of en­ergy from the bat­tery to an elec­tric mo­tor. My­o­elec­tric con­trol of pros­the­sis or other sys­tem uti­lizes the elec­tri­cal action po­ten­tial of the resid­ual limb’s mus­cles that are emit­ted dur­ing mus­cu­lar con­trac­tions. These emis­sions are mea­sur­able on the skin sur­face at a mi­cro­volt level. The emis­sions are picked up by elec­trodes and are am­pli­fied for use as con­trol sig­nals to the func­tional el­e­ments of the pros­the­sis. The my­o­elec­tric emis­sions are used only for con­trol. Be­cause the elec­tri­cal sig­nals are not pow­er­ful enough to op­er­ate the elec­tric mo­tors in the pros­the­sis, a recharge­able 6-volt bat­tery, which is ac­com­mo­dated in a socket in the pros­the­sis, is used to op­er­ate the mo­tors which, in turn, pro­duce the move­ments of the pros­the­sis. De­spite the ef­forts of the me­dia and oth­ers to con­vince us that a MY­O­ELEC­TRIC pros­the­sis is some­thing new from the space age, it is worth men­tion­ing that the first PROS­THE­SIS, my­oeIec­tric pros­the­sis was cre­ated in the pe­riod 1944-1948 by Rein­hold Reiter, then a physics stu­dent at Mu­nich Univer­sity and so on.

Three Cat­e­gories of Up­per-limb Pros­thet­ics used in my­o­elec­tric pros­the­ses are three ma­jor cat­e­gories

of up­per-limb pros­thet­ics: (1) cos­metic, (2) body pow­ered and (3) my­o­elec­tri­cally con­trolled self-pow­ered pros­the­ses. The pri­mary pur­pose of an arm pros­thetic is to mimic the ap­pear­ance and re­place the func­tion of a miss­ing limb. While a sin­gle pros­thetic that achieves both a nat­u­ral ap­pear­ance and ex­treme func­tion­al­ity would be ideal, most artificial limbs that ex­ist to­day sac­ri­fice some de­gree of one for the other. As such, there is a wide spec­trum of spe­cial­ized pros­thet­ics that range from the purely cos­metic (which are in­ert) to the pri­mar­ily func­tional (whose ap­pear­ance is ob­vi­ously me­chan­i­cal). My­o­elec­tric pros­thet­ics are an at­tempt to serve both pur­poses of an artificial limb equally, with­out sac­ri­fic­ing ap­pear­ance for func­tion­al­ity.

My­o­elec­tric pros­thet­ics have a num­ber of ad­van­tages over body-pow­ered pros­thet­ics. Since it uses a bat­tery and elec­tronic mo­tors to func­tion, the my­o­elec­tric artificial limb does not re­quire any un­wieldy straps or har­nesses to func­tion. In­stead, it is cus­tom made to fit and at­tach to the re­main­ing limb (whether above the el­bow or be­low) with max­i­mum sus­pen­sion us­ing suc­tion tech­nol­ogy. Once it is at­tached, the pros­thetic uses elec­tronic sen­sors to de­tect minute mus­cle, nerve, and EMG ac­tiv­ity. It then trans­lates this mus­cle ac­tiv­ity (as trig­gered by the user) into in­for­ma­tion that its elec­tric mo­tors use to con­trol the artificial limbs move­ments. The end re­sult is that the artificial limb moves much like a nat­u­ral limb, ac­cord­ing the men­tal stim­u­lus of the user. The user can even con­trol the strength and speed of the limb’s move­ments and grip by vary­ing his or her mus­cle in­ten­sity. As well, the acute sen­sors and mo­tor­ized con­trols en­able greater dex­ter­ity, even al­low­ing the ma­nip­u­la­tion and use of small items like keys or credit cards through func­tion­ing fin­gers. In ad­di­tion to this ex­treme func­tion­al­ity, the myo-elec­tric artificial limb needs not sac­ri­fice any of its cos­metic ap­pear­ance. The most ad­vanced ver­sions of these pros­thet­ics are in­cred­i­bly nat­u­ral and on par with purely cos­metic limbs.

The weight and the cost are cur­rently the pri­mary dis­ad­van­tages of these. Their heavy weight is due to the fact that the my­o­elec­tric artificial limb con­tains a bat­tery and mo­tor in­side, and un­like the body­pow­ered pros­thetic, it does not use any har­nesses to counter-bal­ance the weight across the body. This is an ad­mit­ted trade-off for a more nat­u­ral ap­pear­ance. As well, as the tech­nol­ogy de­vel­ops, the weight of each com­po­nent will even­tu­ally be­come lighter and less of a prob­lem. The other dis­ad­van­tage of my­o­electrics is the cost. While it is cur­rently more ex­pen­sive than other kinds of pros­thet­ics, it also of­fers the best qual­ity in re­gard to both cos­met­ics and func­tion­al­ity. Like the prob­lem of weight, it is es­ti­mated that the cost will even­tu­ally di­min­ish as the tech­nol­ogy be­comes cheaper to re­pro­duce.

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