Modular Lower Extremity Prosthetics

A new term is entering prosthetics. The term is "M odular”. A modular prosthesis is one which can be assembled to a high degree from prefabricated parts and can be adjusted on the amputee very rapidly to bring it to optimum function.

A new term is entering prosthetics. T he term is "M o d u la r" . A m odular prosthesis is one which can be assem bled to a high degree from prefabricated parts and can be adjusted on the am putee very rapidly to bring it to optim um function. Clinical services at the M anitoba R ehabilitation H ospital in W innipeg, C anada, were the first to em ploy m odular pros thetics on a routine basis and this has been going on since 1965. D evelopm ent o f the m od u lar system for lower ex trem ity am putees w as carried out on an evolutionary basis using w hat engineers had learned in the design and clinical testing o f devices o f this sort prior to 1965. T he W innipeg system used not only currently available hardw are, however, but hardw are designed in W innipeg to fill in the gaps which blocked use o f m odular prosthetics up until then.
T he aim was to bring into being a com prehensive system for lower extrem ity am putees which would utilize existing com ponents and introduce w hat new designs were necessary to m ake the m odular system w ork clinically. Design objec tives were to develop needed com ponents so th at a bare m inim um would be required. T he evolutionary process used to develop the system was based on m eeting any o f the needs in the rehabilitation system which w ould reduce delays and interruptions to reh abilitation program m es even if usefulness were limited to only parts o f the program m es. Thus, in the beginning, prefabricated sockets were used with conventional tem porary prostheses so that both conditioning of the stum p and training on a prosthesis could be carried out sim ultaneously ra th e r th an sequentially as was pre viously the case. A t first, sockets for above the knee am p u tees were put into service. F o u r sockets left and right were used, these being adjustable in girth and varying in size so that as stum p m aturation proceeded, the sockets could be adjusted tighter and, when the full range o f a particular socket had been used up, the am putee could be transferred to a sm aller size to carry on with conditioning and training. Over the past seven years alm ost 200 cases with am putation through the thigh have received their early training and conditioning with these tem porary adjustable plastic lam in ate sockets. Since then com parable tem porary sockets have been designed and used extensively on B /K am putees five I socket sizes, left and right, satisfying the needs o f the bulk of new B /K am putees being rehabilitated in W innipeg.
Lim itations o f these devices led us quickly into the design of alternative com ponents. A single axis knee-shank unit, which incorporated the Berkeley Pneum atic Swing Phase C ontrol Cylinder and a wedge-disc alignm ent coupling, were designed and were soon sufficiently useful to serve as tem porary devices for B /K and A /K am putees. A lthough they were initially restricted for use to in-patients, designs soon became dependable enough to use on out-patients. Finally, the devices were sufficiently reliable for use in the final or definitive limb. T hen it was possible to initiate am putees into their rehabilitation program m es early with devices which would serve them through all phases o f rehabilitation, including the post-rehabilitation phase. A hip fork was designed to perm it construction o f a m odular prosthesis for nip disarticulation am putees also. T he three types o f prosthese are now available for all stages for B/K , A /K and H /D amputees. T he alignm ent coupling, called the W edge-Disc-Alignment U nit, could be used at different levels in any o f ^ three categories o f prostheses. SA CH feet were used in all because they are well standardized and provide adequate junction. The H ip D isarticu latio n am putees use the same Knee-shank unit as the A /K am putees, and the N o rth -Western University H ip Jo in t is used, a device which is single axis and has alignm ent adjustability built into it.
T hus it can be seen th at only three elem ents had to be designed to m ake the system w orkable for these three levels o f a m p u ta tio n ; the W innipeg Single Axis K nee-Shank Unit, the W edge-Disc A lignm ent U nit and the W innipeg Hip F ork.
Recently, a knee disarticulation unit has been designed which is now being introduced for clinical testing. F urther, redesign o f the Berkeley Pneum atic Swing Phase C ontrol U nit has been com pleted to im prove reliability, simplify m anufacturing, and to reduce weight. Im proved SA C H feet have also been designed. It is cosm etic restoration, along with non-adjustability of alignm ent th at has been the stum bling block to the in tro duction o f m odularized prostheses into clinical services. F o r the W innipeg system fo u r cosm etic cover m oulds were m ade w hich could be m atched to six right a n d six left feet, giving the system one sta n d ard calf shape for cosm etic restoration o f prostheses for the B /K am putees. T his single shape has adequately m et the needs o f approxim ately 30 per cent o f the 300 am putees provided with m odular B /K prostheses. Program m es to develop a greater range of shapes are currently underw ay for both the W innipeg m odular system a n d o th er m odular system s such as the B O C K a n d B L A C H F O R D system s being introduced in G erm any a n d England. A m erican developers a re also m aking good headw ay in the developm ent o f cosm etic covers w hich can be a d ap ted to the C anadian a n d British systems as well as the A m erican system o f m od u lar pros theses now in design. As an alternative, prostheses which do not fall w ithin the cosm etic restoration system s currently available, covers are m ade o f polyester plastic lam inates fabricated over sculptured rigid polyurethane foam cast a ro u n d the pylon structures, or over prefabricated blanks o f rigid polyurethane which are sculptured. T he plastic shells obtained are separated from the foam after fabrication for installation on the m odular limbs. In W innipeg the thigh sections o f hip disarticulation prostheses are covered with a truncated cone o f sponge rubber covered with leather. A lthough soft covers have been designed for the knee-shank unit, the bulk o f the A /K am putees receive thin plastic lam inate shells for dressing up their prostheses.
A crucial factor in m odular prostheses is the capacity to quickly exchange sockets. D eterioration o f socket fit due to stum p shrinkage has long been a source o f trouble for am putees o f all levels. T he new am putees w ho pass through the typical rehabilitation services a re especially prone to stum p shrinkage, often requiring two o r three sockets within the first year a n d a fu rth er change a fter that. In W innipeg a receptacle system is used to connect the socket to the rest o f the prosthesis. T he receptacles currently being used are m ade on a custom basis. Before the socket is com pleted a plaster extension is cast on to the end o f it a n d a plastic shell fabricated w hich intim ately fits the m ore proxim al p arts o f the socket a n d fills o u t thigh shape fo r the A /K am putees, o r is tailored dow n for easy containm ent within the cosm etic cover for the B /K am putees. T he base o f a receptacle is m ade flat a n d at the correct alignm ent angle for attach m en t o f the rest o f the com ponents. T he system w ould be im proved if prefabricated attachm ent brackets were designed to link the socket on to the rest o f the pros thesis. F o r H ip D isarticulation a n d Hem i Pelvectomy am putees no receptacle is required. F o r the knee disarticu lation am putee the receptacle is being designed to form an integral p art o f the knee so th at the socket can be plugged into one w hich is o f the correct size.
T he B /K prosthesis consists o f a SA C H foot w ith a W edgedisc A lignm ent U n it bolted o n to it, a piece o f tubing to m ake u p shank length, a second W edge-disc Alignm ent U nit bolted on to the socket receptacle and the socket plugged in (Fig. 1). T he A /K prosthesis consists o f a SA CH fo o t a n d W edge-disc A lignm ent U nit, the W innipeg Kneeshank U nit, a second W edge-disc A lignm ent U nit between the knee a n d the receptacle, a n d the receptacle with the socket plugged in (Fig. 2). T he A /K prosthesis also has a clam p-on valve housing for use with a H o sm a r suction socket valve. W hen belts are used for suspension, a tta ch m ents are m ade to the receptacle leaving the socket free. Sockets are bonded to receptacles in the final process of com pleting the limb. T he H ip D isarticulation Prosthesis consists o f a SA C H foot, W edge-disc A lignm ent U nit on the foot, tubing to m ake up shank length plugged into the W innipeg Single Axis K nee-shank U nit, a W edge-disc A lignm ent U nit w ith tubing a d ap ter, tubing to m ake up thigh length, the W innipeg H ip F o rk with a third Wedgedisc A lignm ent U nit bolted on, the N orthw estern U niversity H ip Jo in t, a n d the socket bolted on to the hip joint. Fig. 1(b) The same type o f prosthesis on a B/K amputee, with supracondylar suspension.
T he K nee D isarticulation prosthesis consists o f a SA C H foot, with a W edge-disc A lignm ent U nit attached, shank tubing plugged o n to a second W edge-disc A lignm ent U nit which bolts to the cast alum inium upper sh an k section, the upper shank section w ith side arm s dovetailed a n d setscrewed. These fit into clevises lam inated into the kneereceptacle section. T he socket plugs into the knee-receptacle unit. T he knees are pneum atically controlled for the K nee D isarticulation, A /K , a n d H ip D isarticulation level p ro s thesis. C onventional suspension system s are used. T o date, over 300 B /K am putees have been provided with m od u lar prostheses in W innipeg. A pproxim ately 150 A /K am putees have received them . A bout tw o dozen H /D am putees use them . N o knee disarticulation am putees have yet been fitted with the entire system w orked o u t fo r them , although h a lf a dozen are wearing a prelim inary design which includes B O C K side joints, plastic lam inate housings fo r the attachm ent o f the low er side arm s, a n d the pneu m atic swing phase co n tro l unit. W hen upper shank sections are available these will be phased into clinical services.
T he future o f m odular system s is assured for low er ex trem ity am putees a n d there is no reason to d o u b t that such system s will be developed for arm a n d orth o tic patients. U se o f m od u lar prosthesis will expand as the cosm etic restoration problem s are better solved. M ean while, those systems w hich have been proven o u t clinically should be used for cases a n d rehabilitation processes w hich can gain from them . People interested in bringing m o d u la r ization into clinical services w here they have not been used before should introduce them for handling their new am putees within the rehabilitation setting. As confidence a n d com petence develop, they can, as we did, extend the range o f application until all clinical cases can be adequately dealt with using m odular co m ponents for every phase o f care. L ooking ahead to w hat can be expected o f well-developed m odular com ponents, these predictions can be m ade on the basis o f W innipeg experience. R ehabilitation tim e will be reduced by approxim ately 50 per cent. N ot all o f this is due to m odularization however. O th er factors include early initiation o f rehabilitation, greater fam iliarization with m odern am putee handling procedures a n d closer control over m anagem ent o f the am putee d uring the early phases o f care. But, no d o u b t, based on experience gained at W innipeg, it can be safely said th at at least a 30 per cent reduction in service tim e can be a ttrib u te d to the speed and facility w ith w hich adjustm ents in alignm ent, adjustm ents in length a n d socket replacem ents can be carried out. The system reported here m akes it easy for the prosthetist to provide prostheses quickly as patients enter the rehabilita tion stream . (M odifications in alignm ent and length can be carried o u t right in clinic if necessary.) M odularization will perm it the developm ent o f highly centralized m anufacturing a n d assem bly o f prostheses by technicians fam iliar w ith the system for delivery to the rehabilitation scene w ithin a couple o f days. Cosm etic restoration, currently less th an adequate, m ust be brought to a better state if furth er tim e gains are to be m ade in p reparating prosthesis. Also a linking system better th an the receptacles currently used would speed up fabrication. C urrently, fabrication tim e w ith the W innipeg system is approxim ately half th a t required for conventional prostheses.
If a m ethod were developed by which socket and leg shape could be defined num erically, the tim e-consum ing processes currently used for these tw o aspects could be reduced, but, m ore im p o rtan t, greater system atization and statistical m aterial accum ulation w ould lead to stan d ard iza tion o f m any shapes now m ade by laborious hand craft m ethods. Such a system involves three dim ensional shape sensing and reproduction. A n exam ple m ethod o f sensing is photogram m etry. A n object is p h otographed steriographically, distances betw een surface points a n d a reference system are defined in num erical term s. T he d ata can then be used to program m e num erically controlled carvers which can produce the shape directly, in m irror image, sm aller or larger, on com m and.
Such m echanization, centralization, m odularization and the developm ent o f m ore m odern tools for the prosthetist to use a t the clinical scene (such as an electrical alignm ent unit, designed in W innipeg, which can be used by either prosthetist o r am putee to align a foot while the am putee walks) should lead to the prospect o f having the prescription for a prosthesis filled w ithin a day or tw o of prescription, a prosthesis sufficiently adjustable in all im p o rta n t features to perm it the prosthetist to bring it into optim um function, and m aintain it so, very quickly and easily.