VeteransAdministration

al of Rehabilitation Researchevelopment Vol . 22 No . 3

10—42 Pages 99—102tee cal note*

A future prosthetic limb device

C. WILLIAM HALL, M.D.Southwest Research Institute, San Antonio, Texas 78284

INTRODUCTION

The first amputees were undoubtedly sur-vivors of accidental amputations . Similarly, thefirst adaptive device was probably a forked stickused as a crutch to substitute for the lost functionof an amputated leg . The eventual invention of apadded peg leg was a major technical break-through and became common practice for severalcenturies . There are historical accounts of armormanufacturers designing marvelously ingeniousartificial joints as early as the 15th and 16thcenturies (1) . It was not until the 20th century,however, that any significant technological gainswere made in prosthetic devices . Today, a widevariety of technically sophisticated prostheticappliances are available, many of which exhibitamazingly lifelike function and appearance.

As advanced as the new devices are, however,their use by amputees is still severely hamperedby problems at the interface between the ap-pliance and the residual limb, which is the sameproblem that faced the wearer of the peg legcenturies ago. Perhaps the most troublesomeproblem today is pain associated with the tissuesof the stump that must bear the weight of the

* Tear( i cat Notes are published in the Journal as a meansof exchanging information concerning an investigator's useof a particular scientific instrumentation or procedure, whichmight further the course of research. While

a 11

notes are subject to peer review and represent .contribution to the research literature, tcomparison studieR 'Ind are thus -'i ef'nrarticles ."

This work was supported bytract V101(134) P-341 .

body as it loads the prosthesis . Lower-limbamputees fitted with a good socket can oftenwalk great distances before experiencing pain.However, eventually the stump becomes painful,causing the wearer to limp, which puts unusualstresses on the rest of the musculoskeletal sys-tem and leads to general body fatigue . Soft tissuepressure pain could be eliminated if the body'sweight were to be transmitted directly from theskeletal system to the prosthesis, rather thanthrough intervening soft tissue.

PERCUTANEOUS LOAD-BEARINGSKELETAL EXTENSIONS

For some years, a small group of researchthe Unit ed States, Canada, and Germanybeen del _typing methods for pern-ing artificial limbs directly to tber of the amputated re& al 1clinical trials attempted wetGermany and MoonedMurphy (3) has publi2d,

the early develolpercutane(i i

(PLS .- :

100

JournE

tation

rch and development Vol . 22 No . 3 July 1985

The characteristic developmental problem fac-ing PLSE research is the identification of theappropriate biomaterial . This biomaterial mustbe suffic' strong to support all naturallyapplied is a, ,, must be mechanically stable andbiologically compatible with surrounding tissues,and must form a strong interfacial bond with theskin at the site of penetration. Most of theproblems have been solved, but the percutaneousexit site remains the focus of additional research.When the integument fails to remain intact,channels for microbial invasion are formed, re-sulting in a septic disaster . Except for this singleremaining research hurdle, the PLSE would nowbe an acceptable clinical reality.

Years of experimental frustration have ledinvestigators to accept the fact that penetrationof the skin at the end of an amputated stump willalways fail because prevalent biaxial stressestend to enlarge the exit site and tear the inter-facial bond . Early clinical trials of permanentlyattached devices undoubtedly failed for this rea-son. Recently, guarded claims of success havebeen offered as a result of using a device thatpenetrates the skin at right angles to the longaxis of the stump where the attendant stressesare more uniaxial and manageable (2). Thesepreliminary indications of success have helpedreduce the problem to that of optimum materialselection . An elusive solution in its own right, themost effective skin-interfacing material to datehas been velour fabrics of nylon or Dacron.

FIGURE 1Percutaneous load-bearing skeletal extension (1

ntly in this laboratory. Intramedulped

.ed

,intE(Ti,

r her

2 inan<

device 'menaces wegiiment .

hem).

FIGURE 2Morticed fit betw

end of tibia andpedestal . Skin elc ;

21aved exposureof lugs allow

) velourinterstices ti

toaffixing trifut

HALL : Futu.

Optimum Selection of Bone-InterfacingBiomaterial

A solution to the bone interfacing rrproblem appears more within our grasp.alumina, Bioglass®, porous polyethylene, andcertain porous metals have all been successfullyused. The most stable PLSE bone interface todate used porous sintered titanium mesh . Mate-rial choice and configuration are not the f ranswer, however, because r

r° al consmust also be considered. A

°interfacingmaterials will fail unless torq

intramed-ullary shaft is controlled. A ti

iethod fortorque control has been devil

nt tilizes themating of a step in the PLSE

lestal with amorticed step in the long bone end.

The design currently used in this laboratconsists of an intramedullary shaft endirstep-shaped pedestal with three radiating 1spaced at 120 degree intervals (Fig . 1) . The lugsare the skin-penetrating elements that provideanchorage to the external pylon . Portions of theshaft and pedestal are covered with poroustitanium for bone ing

,as the skin-

FIGURE 3Spanish goat with 'LSE cornered in an inspecnoninfected wound . Stance is that of nonamputated animal .

ting elements are 'ed with velourmplantation is accc ...r .red by amputat-lg bone (usually the tibia), enlarging e

Lary canal to accept the PLSE shying the distal end to fit the stepped

2) . T1 PLSE is installed wit'mallet

d l extensor and fle'oughtie wou

n dnef ' i and ,join,.rsso as to

pectesta'slight totendonsby sutu7complet _

sing a;appiic

niunediatelAfter 3 xx

removecdissecthbolted on t,

)apishe (Fig. o)leg fractn:flamingo frc

traumatic amputtment of a carbon fiber fishirbone and the skin sutured to

r sthesisd Thomas lc

allows the animal to walk)vering from anesthesia.

essin rr and splint arenosed by sharp

then

ight c

Lich

)portune horsesii used . One rare

Antonio Zoo had ang a seg-

aented to theadherent velour

early in the device'scollar. Canines were used

t hisT11~U -healed,

102

Journal of Rehabilitation Research and Development Vol . 22 No. 3 July 1985

development, but their incessant gnawing and

Because of the extreme forces applied to thelicking of the wound sites created continual

PLSE by these very active animals, a few of theproblems . Goats never disturb the wound, and

devices have had the intramedullary metal shafthealing is seldom a problem . After the external

break at a point near the pedestal attachment.pylon is bottled to the PLSE, goats usually walkimmediately with no apparent limp, pain, ordisturbance of gait . After application of an exter-nal pylon, the animals are turned out to pasturewith no medication or special dietary regimen;they have been allowed to breed and kid and havesurvived without difficulty for up to 14 months.Inevitably the percutaneous sites become infect-ed due to trauma or due to exposure to manure,mud, and the elements . Animals with infectionsare sacrificed and the PLSE is retrieved . Onegoat with a PLSE on a hindlimb jumped 6-foot-high corral fence and, although periodically seenat distances of several hundred yards, was neverrecaptured from the wilds of the brush country.

REFERENCES

CONCLUSION

Since there are many applications for genericpercutaneous devices, research efforts to solvethe skin-interfacing problem are being carriedout in several laboratories throughout the world.This final problem must be resolved before clini-cal use of the PLSE can be justified . However, itis predictable that implanting a PLSE will some-day become a standard orthopedic implant proce-dure, thereby alleviating some of the difficultiesencountered by today's amputees.

1. BIcK EM : Sourcebook of Orthopaedics . New York:Hafner, 1968.

2. DRUMMER G: Personal communication with E . F. Mur-phy, 1954.

3. HALL CW: Biocompatability of Orthopedic Implants,Vol . II, edited by D. F. Williams . Boca Raton, FL:Chemical Rubber Company Press, 1982, pp . 179-198.

4. MOONEY V, PREDECKI PK, RENNING J, GRAY J : J MaterRes Symp 2 (I) : 143-159, 1971.

5. MURPHY FE : History and philosophy of attachment ofprostheses to the musculo-skeletal system and of pas-sage through the skin with inert materials . J BiomedMatr Res Symp 4 : 275-295, 1973.