Bull . Prosth . Res ., BPR 10-32, 208-223, Fall 1979

TECHNICAL NOTES

Harnessing Techniquefor Myoelectric Arm Prosthesis

(A Technical Note)

Moshe Solomonow, Ph. D., Charlotte Adair, and John H. Lyman,Ph. D ., University of California, Los Angeles, School of Engineeringand Applied Science, Biotechnology Laboratory, 3116 Engineering I,Los Angeles, California 90024.

One of the most serious obstacles in the clinical implementation ofmyoelectric control arm prostheses is the interface with the amputee,particularly the high level or the bilateral amputee . The need withmany systems to monitor reliably up to nine myoelectric signals frommuscles as remote as the upper trapezius, pectoralis and latissmus-dorsi requires complex harnessing techniques which to now have notbeen clinically practical . For laboratory testing, investigators haveused tapes and cement to secure myoelectric signal (VIES) recordingelectrodes to the patient's skin . Difficulties in reaching areas on theback, in applying the electrodes at the exact same location with anysystem, and in donning the electrodes, makes this approach unac-ceptable to the patient, necessitating the development of a new typeof harness.

The design priorities guiding development of the new harness wereas follows : (i) reliability of electrode contact with the skin, (ii) comfortin wearing the device for a prolonged period of time, (iii) cleanliness,and (iv) economy.

A T-shirt was designed and fabricated to fit an above-elbow am-putee subject . The material of choice was a two-way-stretchable Mil-liskina, a fabric similar to those used in leotards worn by athletes anddancers.

The material (when the garment is properly designed and fitted tothe subject) . tightly conforms to body contours as a "second skin"under all movement conditions . The fabric chosen does not demon-

a

is the registered trade mark of a fabric manufactured by Milliken & Com-pany.

208

Technical dotes

strate "creep" when stretched for prolonged periods of time, and itmaintains its original elastic properties after laundering.

The sleeve on the amputation side was sewn together to create abuilt-in stockinette ("stump sock") . The amputee was then tested foroptimal MES sites from nine muscles, which were marked on his skinwith a pen. The T-shirt was then worn, and the nine MES sites, whichwere visible through the fabric, were marked on it for electrodeplacement.

The electrodes used were domes, plated with silver or gold bycommercial procedures . The domes were permanently attached totheir appropriate locations on the T-shirt, with the "male" snap fas-tener on the garment's exterior . The basic domes were readily obtain-able in fabric and sewing stores, and were plated especially for thisapplication. The T-shirt fabric was reinforced by small circular piecesof stronger cotton fabric at the electrode sites, to prevent runs of theelastic material and for added strength.

A shielded wire was attached to the "female" snap fastener, andthen snapped onto the electrode assembly . Wires from all electrodeswere attached to a connector which was plugged to the prosthesiscontrol system . Figure 1 shows a schematic of the electrode assembly.

This arrangement allowed easy, two-step donning and doffing forthe amputee . First, the T-shirt is worn, then the prosthesis, using aconventional figure-eight or saddle-type harness, is donned . Theconnector is then plugged into the prosthesis . Removal of the devicefollowed the reverse procedure . To date, a unilateral high above-

FEMALE SNAPFASTENER

SHIELDED WIRE

I

FASTENER

TO AMPLIFIERS

FIGURE -- Schematic of the electrode assembly.

7 MALE SNAP

Bulletin of Prosthetics Research—Fall 1979

elbow amputee has been able to follow the above procedures withouttraining. It is anticipated that training will be required for bilateralpatients.

210

Technical Notes

Since all electrodes, snaps, and the fabric were laundry-proof, andthe electrode wires could be disconnected easily, the garment could belaundered as often as necessary . The wires, however, should bemarked with numbers to guide correct reconnection to the appropri-ate electrode assemblies.

Figure 2 shows an illustration of the harness.Preliminary testing and evaluation of the harness and prosthesis

de, ?•onstrate the following:

FIGUiit 2 . ni), above, shows amputee with myoelectric arm pros'Liesis in place overthe T-shirt T erns . Illustrations (a), (b), and (c) opposite show distribution of theelectrodes located at nine MES sites, and the electrode wires leading to connectorwhich plugs into prosthesis control system . Wires are easily disconnected to allowT-shirt, with electrodes attached, to be laundered .

Bulletin of Prosthetics Research - Fall 1979

1. Continuous and reliable electrode/skin contact during move-ment ;

2. Accurate placement of electrodes over muscle sites during useand from day to (lay;

3. Si tplicity of unaided donning and doffing;4. C~ cifort during prolonged wearing periods;

of maintaining cleanliness;6. 1 lability (so far, 3 mo of use) ; and7. Inexpensiveness (cost is less than $20 for T-shirt and electrode

assemblies).In summary, it was shown that by using a certain readily available

material, a simple T-shirt could be made and configured with appro-priate electrodes to provide a satisfactory amputee/prosthesis inter-face for myoelectric arm prostheses . The new harness also showspotential for use in other rehabilitative applications, such as elec-trotactile displays for amputees, and sensory augmentation devicesfor the blind and deaf, surface electrical stimulation of muscles forscoliotic and paralyzed patients, electrotactile lumbosacral braces, andso forth . Further experiments on additional applications aresuggested .

Low Cost Assistive Device Systemsfor A High Spinal-Cord-Injured Person

in the Home Environment --- A Technical Note°

Gerhard Schmeisser, Ma ®, Professor of Orthopedic Surgery, Thejohns Hopkins University, Baltimore, Maryland, and Woodrow Seamatone, B.A>E,, Principal Engineer, Applied Physics Laboratory, Thejohns Hopkins University, Laurel, Maryland.

Introduction

Two important needs for the high spinal-cord-injured person areindependent mobility and manipulative capability . Advancement inpowered wheelchairs over the past several years is now enabling bet-ter mobility . Mouthsticks enable an extensive variety of low-forcemanipulative functions within a limited distance of the operator ' shead . Robotic arms are being developed to increase the ability ofquadriplegics to perform manipulative functions.

---a This report was prepared as part of NAVSEA Contract N) 24-78-53€34, this portionsponsored by the Veterans Administration Rehabilitative Engineering Research andDevelopment Service.

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Harnessing Techniquefor Myoelectric Arm Prosthesis(A Technical Note)Moshe Solomonow, PhD, Charlotte Adair, and John H. Lyman, PhD