VeteransAdministration

Journal of Rehabilitation Researchand Development Vol . 25 No. 3Pages 25—32

Rehabilitation of musicians with upper limb amputations

DEAN CHARLES, MSc, KELVIN B . JAMES, BSc, RICHARD B . STEIN, PhDDepartment of Physiology, University of Alberta, Edmonton, Alberta, Canada

Abstract—Three saxophone players with upper limbamputations have been successfully rehabilitated to playtheir musical instruments using skin-conductivity touchcontrol . Each attained a standard of musicianship suffi-cient to perform the standard repertoire of the instrumentin a concert setting . The mechanical and electricalmodifications to the saxophone are described, as well asthe principles of operation of the skin-conductivity touchcontrol module. The touch control module is commer-cially available for prosthetists who wish to fit musiciansor others with upper extremity amputations who requirerapid accurate control of a number of channels ofpowered prosthetic function.

Key words : Skin-conductivity touch control, upper limbamputation, powered prostheses, musical instruments,rehabilitation.

INTRODUCTION

If a person who has played a musical instrumentprofessionally loses a hand, the consequences to hislivelihood and his psychological outlook on life canbe severe . Non-musicians may not realize the extentto which the ability to play music. serves as anemotional balancing factor in the life of a profes-sional artist . When the limb is lost, the patient andhis physician may assume that musical rehabilitationis impossible . The powered electric hand, as applied

Address all correspondence to : Mr . Dean Charles, Department ofPhysiology, University of Alberta, Edmonton, Alberta T6G 2H7,Canada .

in clinical practice, only provides a grip functionand not the individual movements that a musicalinstrument requires . Thus, a patient may be coun-seled to change occupations and to forget hisprevious professional musical talents.

However, the technique of "skin-conductivitytouch control" offers the speed, dexterity, andaccuracy of control required for the sophisticatedtask of controlling a musical instrument . The suc-cessful rehabilitation of the three musicians (Figure1) may serve as an example for the more widespreadapplication of touch control to rehabilitate non-musicians with upper limb amputations . Touchcontrol also has been used to operate poweredhands, powered elbows, and powered wrist rotators,and is particularly applicable to high-level andbilateral amputees (2) . Any occupational task re-quiring rapid selective control of multiple channelsmay prove amenable to this technique.

Our objectives were to restore each individual'sability to earn a livelihood and to improve hismorale through the satisfaction of playing musicwell . Two conventional methods of controllingelectrically-powered prostheses are: 1) mechanicalswitches; and, 2) the surface electromyogram(EMG) . Although both have important applications,they are not without limitations . Switches can wearout, bind mechanically, abrade the skin, and bedifficult to adjust so that they do not require undueforce, and yet are not activated inadvertently.

The surface EMG avoids some of the mechanicalproblems, but introduces other difficulties . The

25

26

Journal of Rehabilitation Research and Development Vol . 25 No. 3 Summer 1988

Figure 1.Three musicians with upper limb amputations rehabilitated to play musical instruments . Left : H .D.M ., Center : R .V., Right : H .W.

EMG signal contains a substantial amount of lowfrequency noise (1) . Therefore, the signal is usuallyrectified and filtered with a circuit known as a leakyintegrator . This filtering introduces a delay, often ofthe order of 200 ms. Such a delay is acceptable forpowered electric hands, wrist rotators, and electricelbows, because the motors and gears of suchprosthetic devices have an inertia which introducescomparable delays.

However, a good musician may execute severalnotes of a rapid musical passage within the timerequired to integrate and process an EMG signalfrom biceps or triceps . Sixteenth notes at a tempo ofallegro, for example, may require execution of up to8 notes per second in a run . The EMG signal ascommonly obtained and processed does not provideenough high-speed channels for this application.

METHODS

Touch controlThe principle of operation for skin-conductivity

touch control is relatively simple (Figure 2) . Thesubject's skin contacts the reference (ground) of theelectronic circuit at more than one location to

increase the reliability of the connection . When hemoves his forearm to touch a chosen contact, avoltage divider circuit is formed between the 5 MS2resistor R1 and the skin resistance, R2 of his limb.Touch control can be used with skin resistances upto 20 MS2 for amputees with skin grafts or scars.

After contact, the input signal to the invertinginput of the operational amplifier falls from itsoriginal 12 V to a voltage lower than the referencevoltage applied to the noninverting input . Thechange in voltage is amplified and inverted by theoperational amplifier . The signal is conditioned toremove interference and to provide a clean 12 Vtransition corresponding to the playing of one note.

Control of a saxophoneThe next step is interpreting the control informa-

tion for the musical instrument and actuating thevalves of the saxophone in a smooth, reliable, andnatural manner . In the normal operation of asaxophone, the depression of a single key may closeone or more valves . The use of 5 keys by the righthand and 4 keys by the left hand are sufficient toplay the notes of a scale over 1 octave . Variation inlip tension on the reed, air pressure and otheraspects of the interface between the player's mouth

27

CHARLES et al . : Rehabilitation of Musicians with Upper Limb Loss

CLT POWER

R 1

Figure 2.Skin conductivity touch control : principle of operation .

5 MEGOHM RESISTORCONSTANT CURRENT SOURCE

2.4 MICROAMPERES PER CHANNEL

SIGNAL CONDITIONING

PATIENT'S LIMB SKIN RESISTANCE

R `

0OUTPUT TOSOLENOID

DRIVERS

and the instrument (referred to in general as theembouchure) allow switching between octaves . Avariable velocity of finger impact is important formusical expression on the piano and guitar, but thevalves of a saxophone are always closed quickly andcompletely . Musical expression is provided bychanges in the air pressure and embouchure . Thefact that proportional control of the valves was notrequired simplified the design of the prosthesis.

The combination of valves producing particularnotes can be stored in a permanent logic arraywithin the control circuitry and recalled instantlywhen the stump of the amputee touches a particularcontact associated with that note . Thus, the subjectneed not touch more than one contact simulta-neously to produce a single note . The diode matrixshown in the circuity of Figure 6 allows a fullmusical scale to be developed from contacts installedin a sequential order (see Subject-electronic interfacebelow).

Electro-mechanical designA solenoid matches the electro-mechanical re-

quirements well because of its speed, lightness, andhigh final closing power . A solenoid consists of ahollow cylindrical coil of insulated magnet wire withan iron core free to slide inside it . When electricalcurrent is applied, the core is pulled into the coil,

causing an extension of the core to protrude fromthe end of the coil . The force of this extended coredepresses the key of the saxophone, as illustrated inFigure 3 . When the current is turned off, the core isfree to move back to its original position . Therestoring force is provided by springs which arealready present for the keys of the saxophone.

The solenoids were matched to the stroke andforce required for the application . For the largetenor saxophones played by H .D .M . and H .W .,type TP12 x 13 solenoids (Guardian Electric Manu-facturing Co ., Chicago, IL) were used; while for thesmaller alto saxophone played by subject R .V .,Guardian type TP8 x 16 solenoids were used . Theforces generated ranged from 8 to 12 N with a traveldistance from 1 to 3 mm . The power drawn wasonly 4–7 watts per solenoid.

Both solenoids may be considered relatively long-throw solenoids because they still develop substan-tial force when the saxophone key is open . A shorterlength may be cosmetically more attractive on thesaxophone, but its shorter throw will result in asteeper force-stroke curve . More current will beneeded to overcome the initial friction of the keymechanism resulting in a much shorter battery life.The final closing force of a short-throw solenoidunder high current conditions may actually deformthe metal of the instrument .

28

Journal of Rehabilitation Research and Development Vol . 25 No . 3 Summer 1988

Figure 3.Three solenoids mounted

1

to activate saxophone keys.

i+/111111

uam

OUijf

,--"i RINGS

ORHOPIE L EY H

SHXOPHONE KEY MED 'i

MOUNTING POSTS SPHDED TO Si, XOPHONE

'U,

Several design constraints must be satisfied . 1)The final travel distance should be small to ensurefast closure of the valve . To do this, the restingposition of the plunger must be adjusted so that thevalve is partially closed . The adjustment should bemade with the assistance of an experienced saxo-phone player to check on the quality of the soundproduced . 2) The closing forces should be largeenough to create a positive air seal between the valveand the saxophone body, but the noise must becontrolled. To do this, the saxophone valve shouldclose just prior to the solenoid plunger coming to itsown internal end stop so that the pad on the valveseat acts as a noise damper . 3) Friction on the hingesof the valves must be minimized by careful perpen-dicular alignment of the plunger to the saxophonevalve seat . Four brass standoffs brazed onto theshell of the saxophone provide support and adjust-ments for aligning the mounting plate.

Subject-electronic interfaceA prosthetic shell was designed to hold the

contacts in an orderly array, to sense the notes thatthe subject wishes to play . The shell fits as a cylinderwhose diameter is slightly larger than the diameterof the stump. The difference in diameters creates asmall gap between the skin and the contacts, thusrequiring only small movements of the stump toinitiate different notes . This gap between the stumpand the touch contacts should be adjusted for eachseparate note to be played.

Large changes in clearance can be made byheating the plastic shell and deforming it under

pressure . Smaller changes can be made by placing orremoving washers underneath the contacts . In all 3subjects it proved necessary to start training withlarge clearances for ease of operation, reducing theclearances gradually as the subject progressed.Later, the smaller clearances enabled the subject toroll from one contact to an adjacent one withoutreleasing solenoids shared by both notes, whichresulted in a smoother playing technique. Thecontacts had to remain in the same position relativeto the body to prevent inconsistencies in the rhythmof the music . Three different methods of maintain-ing the contacts in the same relative position weredeveloped for the 3 saxophone players.

Our first subject (H .D .M .), who had an elbowdisarticulation, achieved good repeatability of noteselection with the prosthesis supported in positionmainly by a harness strap over his left shoulder . Thedistal end of the prosthetic shell was prevented fromexcessive movement by being held against his leg.He was the only subject with a single limb joint tocontrol (the shoulder), thus decreasing the require-ments of fixation points.

Subject R.V . was amputated at the midforearmlevel and achieved the most consistent results in asitting position with the prosthetic shell fixed to hisleg. By resting the elbow on the leg, the upper armwas supported, which allowed reproducible position-ing of the distal end of the stump in the shell.

The prosthetic shell was fixed to the armrest of achair for subject H .W . Having had a wristdisarticulation, his stump was the longest of the 3musicians. His elbow was supported by the arm-

29

CHARLES et al . : Rehabilitation of Musicians with Upper Limb Loss

Figure 4.

Arrangement of touch contacts inside plastic UVEXshell for tenor saxophone player : left-side amputation,H .D.M.

STAINLESS STEELTOUCH CONTACT POINTS

NSPARENTTIC SHELL WIRE TO TOUCH

CONTROL CIRCUITRY

chair, thereby limiting the total arm movement . Thiseliminated motion at the shoulder so that the stumpposition was mainly controlled by the elbow angle,and the repeatability of note selection was increased.

Power supplyBattery operation was mandatory for safety (the

touch control system requires low impedancegrounding to the skin) and the portability requiredfor use outdoors in a marching band . Practicalityrequired at least 2 hours of continuous playing andrechargeability . Batteries that met the requirementsof economy, weight, power, and rechargeabilitywere the 4 ampere-hour gel cells . Two 12 V gel cellswere incorporated into each portable case, providing24 V for the solenoids . A tap at 12 V operated theTC-2 touch control modules . For double insulationsafety protection, the charger switch was designed todisconnect the ground when the AC-powered batterycharger was in use.

Custom fitting of the modular componentsA modular approach is frequently efficient for

fitting subjects with diverse requirements . We there-fore used an extension of the same modularizedapproach that has proven successful in the morethan 50 powered prosthetic fittings with which wehave been involved (3) . The rehabilitation equip-ment differed in the number of solenoid channelsneeded to fit the alto horn (5 channels) as opposedto the tenor horn (4 channels) and in the shape andsupport system for the prosthesis which housed thetouch points . The same electronic control systemmodules (Type TC-2 touch control module, LeafElectronics Ltd ., 11583 80 Ave ., Edmonton, CanadaT6G OR7) were used for all channels of eachprosthesis . All 3 subjects were supplied with identi-

cal interchangeable portable control units havingpin-compatible plugs for connection to the saxo-phone and the skin contacts in the prosthetic shell.

Prosthetic shell for touch contactsFigure 4 and Figure 5 show the order of contacts

for left-arm and right-arm subjects respectively(Figure 4, H .D .M . ; Figure 5, R .V .) . These arrange-ments were based on the concept of mapping thelocation of the fingers of the missing hand to a circlearound the forearm . The prosthetic implementationof a musical instrument maps the scale in an orderlyprogression, the same as traditional instruments.The amputee musicians could then learn the controltechniques quickly.

Circuitry for operating electric actuatorsBipolar power transistors suffer from a voltage

drop of 0.6 V across each device . The powerMosfets used in this system for solenoid control

F q

EXTERNAL (OBSERVER) VIEW OF RIGHT STUMP

Figure 5.

Arrangement of touch contacts inside transparent solid plastictubing for alto saxophone player, R .V .

30

Journal of Rehabilitation Research and Development Vol . 25 No . 3 Summer 1988

Figure 6.Schematic diagram of diode logic arrayand V-Mosfet solenoid driver circuitryfor H.D.M.

+

HIGHESTSOLENOID

MIDDLESOLENOID

LOWESTSOLENOID

TC-2 TOUCH CONTROL

MODULES IOSFET SOLENOID DRIVERSV-

offer advantages of long playing time and portabil-ity . The V-Mosfet Power Transistors (TypeVN89AF, Intersil Inc ., Cupertino, CA) shown inFigure 6 were chosen as solenoid drivers for all 3subjects . The diodes across each V-Mosfet help toprevent damage due to high voltage inductivetransients from the solenoids when the drive signalturns off. The integrator formed by the 47 K12resistor and 0 .47 µF capacitor in the gate circuit ofeach V-Mosfet helps prevent transients and holdseach solenoid on long enough to permit the musi-cian to move his stump to the next touch pointbefore the saxophone valves reopen.

RESULTS

Subject 1 : H .D.M.The first saxophone player rehabilitated (H .D .M.)

had been amputated due to bone cancer . He had anormal range of motion above the elbow and couldposition the stump to contact any part of theinterior circumference of the prosthetic shell . Sev-eral different diameters of shells were tried, and thesize and shape was gradually modified using thetransparent plastic material "Uvex" with the goal ofmaking all 4 contact points equally easy to reachwith the distal portion of his stump (Figure 4).

Subject 2 : R .V.This subject was a music student at the University

of Western Ontario, London, Canada with a talent

for the alto saxophone at the time he lost his rightforearm in an industrial accident . The accidentappeared to end his hopes of playing the music hehad spent so much time and effort to learn.However, he learned to play the trumpet and wenton to become an accomplished secondary schoolmusic teacher.

The transparent prosthetic shell was positionedrelative to the subject's leg with a wide leather beltfor stability (see Figure 1) . This position places oneof the forearm bones (the radius) at the top of theprosthetic shell and the other (the ulna) at thebottom. Proprioceptive feedback from the end ofthe stump helps him to maintain the proper posi-tion . The auditory output of the horn also serves assensory feedback indicating proper arm positioning.His forearm has some rotational ability, whichallows the skin overlying the radius to contact "Eflat," "F natural," and "E natural" along the topof the prosthesis . The ulna can be moved quickly toreach the curved piece of metal which represents "Dnatural," independently of the other notes beingplayed at the time.

R .V. is a creative and imaginative person, andmade a number of improvements to the system afterreturning home. Certain portions of his stump wereless sensitive to touch than others, so he modifiedportions of the touch contacts to facilitate playingthe notes affected . He also removed the "F sharp"touch contact from the prosthetic shell, and placedit on the spatula of the saxophone itself, whichoperates the "G sharp" key of the saxophone . This

31

CHARLES et al . : Rehabilitation of Musicians with Upper Limb Loss

modification reduced the number of contacts beingoperated by the stump from 5 to 4, and moved oneof the contacts over to the sound hand . In this way,he obtained more speed and precision for playingserious (classical and orchestral) music.

R .V . always uses a small dab of Beckmanelectrode gel on the 2 bony protuberances, becausehis skin is not always moist enough to get a speedyreaction from the equipment . With these modifica-tions, he has given a number of public perfor-mances, playing university-level music, including asonata for saxophone and piano.

Subject 3: H .W.The third saxophone player (H .W .) had lost his

left hand (wrist disarticulation) in a paint mixingmachine in 1953 . He had a normal range of motionover all remaining joints . Thirty-two years hadpassed since he had played the saxophone with 2hands and he was 70 years old at the time of fitting.

The first attempts used a prosthetic shell held inplace with straps over the left shoulder, as was donesuccessfully with the first subject . Little progresswas made in 3 days with this arrangement becausethe subject could not find a stable reference point.An analogy can be made to a person first learning towrite with a pencil . If the elbow is not flat on a deskwhile manipulating the pencil with the wrist andfingers, there is no solid reference point to make themovements reproducible.

Several modifications were tried . 1) We made themovements more visible by installing the touchcontacts in the walls of short sections of transparentplastic tubing . The tubing was laid on a flat,easily-accessible table surface, with good visibility ofthe contacts . The learning process was graded bystarting out with tubing of a large diameter andworking down to smaller sizes.

2) This subject had a particularly hairy forearm,so a depilatory cream ("Neet") was applied toremove skin hair during the training period.Beckman electrode gel was applied to the skin toimprove the reliability in the timing of the skincontact.

3) A table-mounted prosthetic cup was made,rather than a shell covering the whole arm . Theimproved visibility afforded by the open cup allowed the subject and all members of the team to seeexactly where the arm was making contact.

4) The cup was mounted at the end of a support

board that was padded with foam rubber, andcovered with soft leatherette . A series of large-diameter, nickel-plated grounding contacts weredistributed along the board in 2 rows, spaced justfar enough so that the forearm would rest comfort-ably between and touch both rows . This eliminatedthe inconvenience of a separate ground wire con-nected to some other location on the body.

When a support for the contacts had beensatisfactorily shaped, the subject's performance be-gan to improve, but he had the most difficulty ofthe three in his attempts at relearning to play thesaxophone . Just as guitar players develop callouseson their fingertips, the horn player's lip must behardened somewhat against the pressure of the reed.The condition of this player's lip limited his practicetime and thus limited the initial learning of thecoordinated limb movements required . Conversely,the motivation for hardening the lip was not presentunless reasonable musical notes were being pro-duced.

Initially, he used gross movements and banged thestump against the side of the prosthetic shell toensure solid contact. Only after receiving a proper-sized prosthetic cup for the touch electrodes did hebegin to use finer movements, such as turning hisstump, utilizing its asymmetry within the cup in apartial rotation to improve the accuracy and speedof contact. Despite the problems, within 10 days hecould play many of the standard tunes he knewfrom playing in the big bands of the 1930's and1940's . After returning home he has joined withsome of his former colleagues to give informalconcerts.

DISCUSSION

With only 3 musicians, a statistical analysis is notmeaningful and we could not compare the resultswith the performance of each musician before helost his arm . Furthermore, the 3 played differentstyles of music and one's musical preferences willinfluence any assessment of the level attained . Someof the evaluation must be left to subjective impres-sions supported by published statements made byeach musician.

The first subject, H .D .M ., seemed to have thehighest motivation and attained a very high level ofmusicianship. The selections he mastered included,

32

Journal of Rehabilitation Research and Development Vol . 25 No. 3 Summer 1988

"Take the A Train" and Duke Ellington's "SatinDoll," which are generally considered in the upperechelon of jazz standards . He appeared on thetelevision production "That's Incredible" (firstbroadcast on Oct . 18, 1982) . The effects that themusical prosthesis had in boosting his morale areevident in statements he made when he was againfighting cancer.

"I couldn't care less if I had an arm or not," helaughed . "I don't worry any more about living ordying because all my life has a new meaning ; now Iknow where I'm going. You know, this isn't for myown self-glory . I'd like to use it in a way that can bea hopeful sign. I'll play any place . I'm just out tohelp every amputee who wants to be rehabilitated ."(Edmonton Journal, May 5, 1982)

"I never dreamt in a million years I would beplaying again," he said. "It's the greatest miracleGod ever put in my life . The greatest thing that everhappened to me ." (The News World, Nov. 16, 1982)

Although cancer claimed his life in June 1985, helived and played music, entertaining and inspiringothers, for several years after his fitting.

Subject R.V . returned to teaching music, includ-ing the saxophone, after his fitting . He commented:"I just can't tell what the limits of it are, because Ihaven't gotten anywhere near them yet . The systemis, for all intents and purposes, instantaneous . I'mgoing back and playing the pieces that I worked onat university but never performed . It's hard toimagine that the system is really as good as 10fingers . Right now I can see myself playing anythingbut the most difficult pieces ." (Haliburton CountyEcho, November, 1983)

Subject H .W . made the following comments whenasked what he would advise other amputee musi-cians in a videotaped interview on Sept . 17, 1985:"It is possible; I would most heartily recommendthat it is possible, and practical—beyond a doubt ."

Interested health care professionals may contactthe authors to arrange for receipt of a videotape ofall 3 musicians performing . The sound and picturetogether convey what is difficult to express on theprinted page.

In conclusion, 3 handicapped professional musi-cians have been successfully rehabilitated to play thesaxophone . The quality of rehabilitation achieved issufficient for professional musicianship in teaching

and performing . We have attempted to includeenough details here so that others will be able toduplicate our work and extend the benefits of touchcontrol to more people with upper limb amputa-tions . A control system capable of the level of speedand accuracy needed for rehabilitating a musicianshould provide excellent prospects for other occupa-tions that require specialized motor patterns . Futuredevelopments should make the possibilities evenmore dramatic and the applicability more wide-spread.

ACKNOWLEDGMENTS

The authors would like to acknowledge the contribu-tion of R. Taylor for assistance with the notation andmusical aspects of the saxophones . The EdmontonMusician's Association contributed funds toward modifi-cations of the first saxophone. Leaf Electronics Ltd .,Edmonton, Alberta, contributed control modules . A.G.Calder, C .P .(C), Edmonton Worker's CompensationBoard, and G . Locke, C .P.O.(C), Prosthetic-OrthoticDepartment of the Glenrose Hospital in Edmonton,Alberta, along with J . Isitt and D . Wong, Cross CancerInstitute, fabricated transparent "Uvex" prosthetic shellsfor the touch contacts . Components for the secondsaxophone, for R .V ., were funded by the OntarioWorker's Compensation Board . We thank the family ofthe late Hank DeMarco for the donation of the firstsaxophone, presently being used by Mr . H .W. Dr . R.Feldman, head of the Department of Physical Medicineand Rehabilitation in the University Hospital, providedvaluable encouragement and suggestions throughout thisproject . Part of the work was supported by grants fromthe Medical Research Council of Canada and the WarAmputations of Canada.

REFERENCES

Hogan N: A review of the methods of processing EMGfor use as a proportional control signal . Biotned Eng11(3) :81-86, 1976.Stein RB, Charles 1), Hoffer JA, Davis LA, Arsenault J,Moorman S, Moss B : New approaches for the control ofpowered prostheses : Particularly by high-level arm ampu-tees . Bull Prosthet Res 17(1) :51-62, 1980.Stein RB, Charles D, Walley M : Bioelectric control ofpowered limbs for amputees . In Motor Control Mecha-nisms in Health and Disease, JE Desmedt (Ed .), 39 :1093-1103, New York : Raven Press, 1983.

2.

3 .