The Instrumented Walker: Usage Patterns and Forces

Transcription

1 484 DEVCES The nstrumented Walker: Usage Patterns and Forces Avtal Fast, MD, Fkre S. Wang, ME, Ronald S. Adrezn, ME, Marc A. Cordaro, MS, Juan Rams, MD, Julan Sosner, MD ABSTRACT. Fast A, Wang FS, Adrezn RS, Cordaro MA, Rams J, Sosner J. The nstrumented walker: usage patterns and forces. Arch Phys Med Rehabl 1995;76: Studes documentng the forces that are transmtted through a walker's frame are stll scant. The purpose of ths study was to evaluate the pattern and magntude of forces that are transmtted through the frame of a walker durng ambulaton. A standard alumnum walker was nstrumented. Gauges, whch were mounted on all four legs, recorded axal, frontal, and sagttally orented forces. A custom made computerzed system regstered the forces durng 30 seconds of data acquston. Twelve patents wth ambulaton dysfuncton were tested wth ths system. Two dfferent usage patterns emerged from the study. One usage pattern was observed n patents who were usng the walker as a mean to reduce the amount of weght transmtted through the lower extremty. The second pattern was observed n patents wth severe balance problems. These patents used the walker to enhance ther balance and stablty. The system descrbed allows walker usage pattern analyss. Better understandng of force dstrbuton and usage patterns may lead to mproved or new walker desgn by the Amercan Congress of Rehabltaton Medcne and the Amercan Academy of Physcal Medcne and Rehabltaton Walkers are extensvely used by ndvduals wth dverse dsabltes. n spte of ther common usage and prolonged exstence, walkers have not changed n ther basc desgn. Clncans use the same walker for patents wth varous dseases wthout regard to the cause of the gat dysfuncton. Whereas the roles of canes and crutches as assstve devces have been explored, 1'2 only a few studes n the lterature have attempted to analyze the walker's usage pattern. 3,4 Before consderng desgn enhancement and modfcatons, a better understandng of the magntude and the drecton of forces that are transmtted through the frame of the walker as well as the usage patterns n a varety of gat dysfunctons s requred. The purpose of ths work was to develop an nstrumented walker, to evaluate the forces that are transferred through ts frame durng ambulaton, and to observe the walker's usage pattern by several patents wth gat problems. METHOD A standard, prevously used nonfoldng 4-1b alumnum tube frame walker wth adjustable leg length was nstrumented (fg 1). Stran gauges a were mounted on each leg at a heght of approxmately 15 nches from the ground. Two general purpose narrow wdth gauges b were mounted on each sde of the leg n the frontal (medolateral) plane, and the 45 stran rosette n the front and back of the leg was mounted n the sagttal (anteroposteror) plane. The arrangement of the gauges allowed measurement of both axal and bendng forces. The bendng forces were recorded n two axes: frontal and sagttal. From the Department of Physcal Medcne and Rehabltaton (Dr. Fast), Albert Ensten College of Medcne/Montefore Medcal Center; the Department of Physcal Medcne and Rehabltaton (Drs. Rams, Sosner), St. Vncent's Hosptal and Medcal Center; and ACW Research (Mr. Wang, Mr. Adrezn, Mr. Cordaro), New York, NY. No commercal party havng a drect fnancal nterest n the results of the research supportng ths artcle has or wll confer a beneft upon the authors or upon any organzaton wth whch the authors are assocated. Reprnt requests to Avtal Fast, MD, 150 East 210 Street, Bronx, New York by the Amercan Congress of Rehabltaton Medcne and the Amercan Academy of Physcal Medcne and Rehabltaton /95/ /0 Arch Phys Med Rehabl Vol 76, May 1995 Fg T h e nstrumented walker and nterface box as t was held durng testng.

2 !L.._f.! NSTRUMENTED WALKER, Fast 485 Characterstcs of Twelve Patents Patent's Age Gender Dagnoss 1 36 Male Rght Tb-Fb fracture, non-weght bearng 2 70 Female Cellults left leg 3 87 Female Left hemparess 4 85 Female S/P TA, left lower extremty weakness 5 58 Male Left Tb-Fb fracture 6 59 Male Rght below knee amputaton 7 32 Male Left below knee amputaton 8 65 Male Progressve supranuclear palsy 9 75 Female Gat dysfuncton, metastatc breast cancer Female COPD, CHF, gat dysfuncton Female Cerebral palsy-quadrparess Female Rght hemplega Abbrevatons: Tb-Fb, tbofbular; S/P, status post; TA, transent schemc attack; COPD, chronc obstructve pulmonary dsease; CHF, congestve heart falure. The stran gauges were connected by a shelded long cable to a custom nterface board. All the functons of the board were controlled by a personal computer through an analog and dgtal nput/output. The customzed system wth ts techncal specfcatons has been presented elsewhere. 5'6 A customzed calbraton apparatus was desgned to load the ndvdual legs wth a known axal and bendng loads. The output was lnearzed, and loadng and unloadng curves were obtaned for each leg n three planes. After the system was calbrated, the ndvdual walker legs were subjected to known statc and dynamc loads. The overall system error was found to be wthn plus or mnus 10%. Before clncal testng, the hardware was powered for 30 mnutes to allow temperature stablzaton of all the electronc components and the stran gauges. The software then "zeroed" each stran gauge whle the walker was unloaded. Whle tryng out the system before the actual clncal studes, the authors were able to demonstrate that the system was accurate enough to determne a subject's weght. f a subject bore weght on the upper extremtes, leanng on the walker, ell d lq2 lead k ull ld lql : te Jx). v!!, ulal ld 1'11, tll) v/ ' S tm (eec) L! f}... l 11 ml k A,q, 1, / ellt -t L l tm (leo),\! J ]'V [ ' ' ' 5 ll 15 Zl tm (me).~ 11 gl...! t Fg 2mAxal loadng pattern n a patent who s non-weght bearng on left lower extremty. The downward forces recorded n the axal loadng are represented by negatve values; anteror bendng forces are represented by negatve values; rght lateral bendng forces are represented by negatve values. The rear left dagram represents the rear left leg of the walker, the left front dagram the left front leg, and so on. A synchronous, regular loadng pattern n all four legs s apparent. Negatve numbers represent the load n pounds. Arch Phys Med Rehab! Vol 76, May 1995

3 486 NSTRJMENTED WALKER, Fast nmenl; l~ln bdl led Rll O,l , -, -1,1-1,l 5 11 ~dlq led ppl l, /~, 11 t/!tllv ll/lt/' jv V V tl~ hec) q ludlq lul Rlt13 "~! ~ L ~ 42.., /1ll.,., t/v 4, tll 7 lll/ 'v/j ~ t 11 V -1, ~ tm (ooc) kll lad qe7 ~ln l A LP fl l//j J /tllll Wll 1//! A lll/,vtl V 1 -~ " J! -5 + ~,. 4,! S ~ E 15 ~ " 1 ' S Zl ~ tlw (No) tm (mcl Fg 3--Same patent as n fgure 2. Anteroposteror bendng pattern. The downward forces recorded n the axal loadng are represented by negatve values; anteror bendng forces are represented by negatve values; rght lateral bendng forces are represented by negatve values. whle holdng the lower extremtes n mdar, the system accurately determned the subject's weght. The nstrumented walker weghed 4.751bs. Twelve patents wth varous dagnoses leadng to gat dysfuncton were tested. Seven of the patents were women and fve were men. Ther age ranged from 24 to 90 years (table). The purpose of ths research was explaned to each patent, and a verbal consent was obtaned. For each patent before testng, the heght of the walker was adjusted so that the patent's elbows were at 20 to 30 of flexon when the hands rested on the walker's handles. A physcal therapst or a physcan or both were standng next to the patent who was ambulatng. The patents ambulated at ther comfortable walkng speed. At the tme of ambulaton one of the examners was walkng alongsde the patent and carred an nterface box n hs hands. Ths enabled the examners to preserve the orgnal walker's weght (fg 1). All the patents that were tested had gat dysfuncton ether caused by neurologcal dsease, orthopaedc procedure, or general decondtonng and dffuse weakness (table). Each patent completed two trals of 30 seconds each. Data were acqured durng both trals. The frst run was consdered a practce run. Data from the second run are presented n ths artcle. The raw data was analyzed usng a 486/33 personal computer compatble. The electrc sgnals were converted from mllvolts to pounds usng the authors' custom-developed software and calbraton data. The results were then plotted wth axal and bendng loads n pounds versus tme n seconds for each leg. Three sets of prntouts were collected for each patent. Each set conssted of four dagrams representng the four legs of the walker. One set represented axal loadng; one represented anteror-posteror bendng; and the thrd represented medolateral bendng forces. The arrangement of graphc results represents the four legs of the walker: From the computer prntout, n whch 5-second ntervals were marked, an estmate of the walker's loadng pace could be made. RESULTS Data obtaned from two patents are presented here. These patents were chosen because they demonstrated two basc Arch Phys Med Rehabl Vol 76, May 1995

4 nmont b-ln nmnt b-ln ~llq 10ad pl~21. / 1.,[,, ~ 111 A.11~1,~ ~A1t-~ ~ ;~ ~ ~ ~ o', ll ll tl " of ' ',t.zl bendlq nd ~le3 [7 tm {~ ) NSTRUMENTED WALKER, Fast 487 t '! V / la...', 1'11!! "1' 1, j '.~ '!!,, /~(~.l la l/~.~ V e 35 / v -1.4~ l [ ~1 f n~llnll load p ,4 1,2[, 4,Z ~ ~.~ ~_ ~~ ~_... ~/~ L... Vlll Jl ~l f H [V 1 Vv~/% [t l/[... : ttt-tt... mdlq! "a Pd,,, V ' "! ~ ~ 3t 35 tm {No).8 ' L "' ~ ! tm (see) Fg 4--Same patent as n fgure 2. Medolateral bendng pattern. The downward forces recorded n the axal loadng are represented by negatve values; anteror bendng forces are represented by negatve values; rght lateral bendng forces are represented by negatve values. tm (=oc) \ Lr, tf 35 usage patterns that were representatve of the rest of the group. Patent 1 Ths patent (no. 5 n the table) sustaned a fracture of hs left tba and fbula. The patent was non-weght bearng on that extremty. At the end of 30 seconds of comfortable walkng, the patent covered about 20ft. Axal load (fg 2). Magntude of forces ranged from 20 to 491bs. The graphs representng the axal loadng demonstrated an mpressve synchronous regular loadng pattern n all four legs. As can be clearly observed, the patent loaded the walker n a regular rhythm--twce durng a 5-second perod. The patent tended to lean more heavly on the two front legs of the walker (35 to 501bs on the front legs vs 25 to 301bs on the hnd legs). The patent spent approxmately 2 seconds weght bearng on the walker as he or she swung to wth the weght-bearng leg. The amount of axal forces that were transmtted through the walker was changng from one cycle to the next by 2 to 71bs. By gross evaluaton, addng the "average" weght born by each leg, we estmated that 88% to 90% of the patent's weght went through the four legs of the walker whle the patent was swngng to the walker. Anteroposteror bendng (fg 3). The magntude of forces n ths plane was much lower compared wth the axal forces, typcally 2% to 3% of the axal forces for ths patent. The forces ranged from 0.5 to 41bs. Most of the anteror bendng forces were concentrated at the hnd legs: about 2 to 31bs. The front legs transmtted forces of lower magntude 0.8 to llbs. Smlar to the axal forces, the bendng forces were appled n a synchronzed and rhythmcal rate. n the fght front leg there was a greater varablty n the amount of bendng force from one gat cycle to the next. Medolateral bendng (fg 4). The forces ranged from 0.25 to 1.51bs. The sde-to-sde bendng forces were of low magntude smlar to those reflectng the anterorposteror data. Whereas the front legs tended to bend to the tght, the hnd legs tended to bend n an opposte drecton. n ths partcular patent, wth a left tbofbular fracture, these Arch Phys Med Rehabl Vol 76, May 1995

5 488 NSTRUMENTED WALKER, Fast ulal lull lq3! u lml lqz t ml ]1 ulal l!.!,v Zl ZS! l~l tm (u )...!f V Zl J,~al 10ad lql tn (K) - 1 vv [ zs ~l k 6 l... S Z5 :m!! 15 tm (No) tm (=eel Fg 5--Axal loadng pattern n a patent wth progressve supranuclear palsy. a forces may have resulted n a slght rotatonal moment. Ths pattern was qute ndvdual and was not observed wth any consstency n other patents. Patent 2 Ths patent (no. 8 n the table) had progressve supranuclear palsy. The patent was very ataxc and had a severe gat dysfuncton. Hs gat was slow, erratc, and unpredctable. Ths gat pattern resulted n recurrent falls. He ambulated best and felt more comfortable when he was holdng onto a wheelchar or a supermarket cart. These heavy objects provded hm wth stablty and enabled hm to be more secure. Whle walkng wth the walker, he appeared to be very unstable, occasonally veered to the sdes, and appeared n some dstress. At the concluson of 30 seconds of ambulaton, the patent progressed only 13ft. n another run (not presented here), the patent ambulated 9ft n the same perod of tme. The slow rate of ambulaton reflects hs severe ataxa and nablty to safely ambulate. Axal load (fg 5). Forces ranged from 2 to 28 pounds. An asymmetrcal rregular loadng pattern was apparent. The walker legs were loaded n an asynchronous fashon. Varyng, rregular forces were observed n each leg. Moreover, the loadng pattern of each leg was remarkably rregular and vared from one gat cycle to the next. The walker was loaded at a slower rate compared wth the frst patent, and the patent tended to lean on the walker for a relatvely prolonged tme perods. At tmes, the patent leaned on the walker for almost 3 to 4 seconds. Smlar to the prevous patent, the front legs of the walker bore more weght than the hnd legs. By gross estmate, only about 34% of the patent's weght was transmtted through the walker. Most of the load was borne by the two front legs and left hnd leg, whereas the rght hnd leg was bearng a small amount of weght only. Anteroposteror bendng (fg 6). The gauges dsclosed relatvely small bendng forces from 0.5 to 2.51bs. The greatest load was transferred through the front legs. The forces were appled n an asynchronous rate. At tmes, the forces were appled n opposte drectons smultaneously n dfferent legs. Whereas the rght front leg regsters dmnshng negatve force up to 0 (look at the 16 to 18-seconds tme frame), the hnd rght leg s loaded. The patent tends to load and unload the rght front leg for 2.5 to 3 seconds, whereas the rght hnd leg s loaded at a faster rate (look at tme perod 10 to 15 seconds). Arch Phys Med Rehabl Vol 76, May 1995

6 NSTRUMENTED WALKER, Fast 489 nmlq ld qd9 1 w kedq lad qo13,... t lead k ld b =, l 5 to S faallql ll 1,4 l.z Dqp1. '! l t tm (see) vv T Z, z.s[ -3.=! 5 ll 15 ZD ZS tm (aoc) tlno (80 ) Fg 6mSame patent as n fgure 5. Anteroposteror bendng pattern. l bndlnl Load q~7 tm (~)? S t =:.z [,6 - ~ -1,1-11,2 J 41,3 Medolateral bendng (fg 7). The magntude of forces ranged from 0.5 to 2.61bs. Only mnmal sde to sde bendng moments were observed. The bendng forces were hgher n the front legs and sgnfcantly lower n the hnd legs. The left hnd leg was loaded wth a very small amount of force most of the tme. Agan, durng most of the gat cycle, an asynchronous loadng pattern was noted. At 20 seconds, the left front and hnd legs regster forces n opposng drectons. DSCUSSON The authors have successfully nstrumented a walker and recorded the forces transmtted through ts frame durng 30 seconds of ambulaton. The system relably recorded the forces n dfferent planes as they were appled to the walker durng ambulaton. The data clearly depcted two dfferent walker usage patterns. One or the other of these patterns was observed n all the patents that were tested. The pattern descrbed n the frst patent was observed n those patents who used the walker n order to unload one of ther lower extremtes. These patents ambulated n a synchronous, rhythmc pattern and tended to transmt a sgnfcant porton of ther body weght (75% to 90% of body weght) through the walker's frame. Despte the fact that at a certan perod of tme, both of the patent' s lower extremtes were off the ground, less than full body weght was transmtted through the walker's frame n the axal drecton. t s beleved that ths resulted from the drecton n whch the forces were appled. As the patent hopped towards the walker, he was movng ntally upward and forward and then downward and forward. As a result, the axal vector regstered less than full body weght. The maxmal axal loadng n each of the walker's legs ranged from 20 to 501bs. These values were remarkably hgher than those observed n the second patent. The dfference between maxmal axal loadng n consecutve cycles was farly small and vared by not more than 25% (fg 2). The loadng forces that were obtaned n the anteroposteror and medolateral planes were sgnfcantly lower than the axal loadng forces (fgs 3 and 4). More weght was transmtted through the front legs and less through the hnd legs. The same regular rhythmc loadng, albet wth forces of lesser magntude, was observed n the stroke patents (Nos. 3 and 4) and n the decondtoned patents (Nos. 9 and 10). t should be stressed that both stroke patents had very mld strokes and were n the rehabltaton unt mostly for recondtonng rather than because of neurologcal defcts. Arch Phys Med Rehabl Vol 76, May 1995

7 NSTRUMENTED WALKER, Fast bonudnq lead ~pzl 1.0 ~d~ lml qel5 2,5 0.5,,,a k,j 4.5.L -1,5.Z. -2.5,3,6 ~dluu 8 ll 8mle t~ (Nc) V! ZO Z5 30 1,.=... A ~... [ t[,~.,, -L~ ~ Z tl~--(8oc) ~-,_~ '-',q.~ ,5 ll b , / ' [... ~... ~.!,.,.z ~...! O.t... ~... [ l--" J J ZlJ tlme (me) -v " Fg 7--Same patent as n fgure 5. Medolateral bendng pattern. tm (No) The data observed n the second patent were remarkably dfferent than those of the frst. Here, an asynchronous, less regular pattern was predomnant. The smultaneous, rhythmc loadng, as observed n the frst patent, was mssng n all four legs n the medolateral, anteroposteror, and axal plane as well. nstead, a random loadng pattern prevaled (fgs 5, 6, and 7). The magntude of axal forces gong through the frame of the walker was about 30% to 35% of the patent's body weght. The total loads n all four legs ranged from 1 to 301bs. The dfference between maxmal axal loadng n subsequent cycles was varable. (Changes by up to 60% to 90% were documented [fg 5].) The patent, who was full weght bearng on both lower extremtes, was usng the walker to enhance hs balance rather than to reduce the weght borne by hs lower extremtes. The amount of axal loadng was varable at dfferent phases of ambulaton and was determned by the severty of hs mbalance at that partcular moment. The second patent tended to bear weght through the walker for relatvely long perods of tme--up to approxmately 4 seconds at one tme. The rate of progresson was slow, and the patent covered short dstances. The frst patent, for comparson, leaned on the walker for shorter perods of tme averagng 2.5 seconds (fg 2). The second pattern s typcal for patents wth balance problems who ambulate slowly and use the walker n order to enhance ther stablty and balance. n the anteroposteror and the medal lateral planes, the magntude of forces was small and not very sgnfcant. n both planes the forces were appled rregularly and n an asynchronous fashon. As n the frst patent, these forces were much smaller than those that were regstered n the axal plane. Padro and colleagues have nstrumented a walker n a smlar fashon. They located the gauges at the lower tps of the walker's legs. 3'4 Ther results were somewhat smlar to the authors': The axal load n the walker peaked to 85% of body weght, whereas the medolateral and anteroposteror forces were of a much lower magntude. They presented data that were obtaned from one patent only, an amputee? Ther study, whch tred to develop a walker user rsk ndex, assumed that patents were usng the walker for full support. Ths study ncluded also ataxc patents and establshed ther walker usage pattern. t s beleved that n some stroke patents wth balance problems and hemparess, another usage pattern, a mxed one, may be observed. Despte the extensve use of walkers by many patents, the basc characterstcs of walkers have not changed. n the Arch Phys Med Rehabl Vol 76, May 1995

8 NSTRUMENTED WALKER, Fast 491 hosptal and clnc settng, the exact same walker s ntroduced to patents wth varous dsabltes (e, amputaton and cerebellar ataxa). As has been demonstrated, these patents have dfferent needs and use walkers dfferently. t s hoped that further research on ths subject wll lead to better understandng of walkers and to new walker desgns. Ths may enhance functonal ndependence n patents wth a wde range of dsabltes. References 1. Murray MP, Sereg AH, Scholtz RC: A survey of the tme magntude and orentaton of forces appled to walkng stcks by dsabled men. Am J Phys Med 1969;48: Shoup TE, Fletcher LS, Merrll BR: Bomechancs of crutch locomoton. J Bomech 1974;7: Padro RD, Deathe AB, Wnter DA: Walker user rsk ndex. A method for quantfyng stablty n walker users. Am J Phys Med Rehabl 1993; 72: Padro RD, Wnter DA, Deathe AB: A system for routne assessment of walker asssted gat. Cln Bomech 1993; 8: Adrezn R, Cordaro M, Wang F, Fast A: nstrumentaton and computer nterfacng of a standard walker to study user-walker nteracton dynamcs. Adv Boengneer Am Soc Mechanc Engneer 1992;22: Adrezn R, Cordaro M, Wang F, Fast A: A fnte element model of a walker and ts comparson to an nstrumented walker. Adv Boengneer Am Soc Mechanc Engneer 1993;26: Supplers a. Model CEA UR-350 general purpose 45 sngle plane rosette, 350 ohm gauge; The Measurements Group, PO Box 27777, Ralegh, NC b. Model CEA UN-350 general purpose narrow wdth 350 ohm gauge; The Measurements Group, PO Box 27777, Ralegh, NC Arch Phys Med Rehabl Vol 76, May 1995