Clinical Evaluation of the Modular Electromechanical Lock ... · prototype that underwent alpha testing with a bilateral high-level AE amputee . Results were en-couraging and demonstrated

Department ofVeterans Affairs

Journal of Rehabilitation Researchand Development Vol . 31 No. 2, 1994

Pages 148-152

CLINICAL REPORT

Clinical Evaluation of the Modular ElectromechanicalLock Actuator for Above-Elbow Prostheses:A Preliminary ReportPrepared by Mary E . Cupo, BS, KT, Health Science Specialist and Saleem J . Sheredos, BEE, MHCA,Rehabilitation Engineer, Program Manager, Technology Transfer Section, Rehabilitation Research andDevelopment Service, Department of Veterans Affairs, Baltimore, MD 21202-4051

Abstract—The Modular Electromechanical LockActuator (MELA) is the result of research and develop-ment (R&D) conducted under the direction of Dudley S.Childress, PhD, at the Northwestern University Prosthet-ics Research Laboratory (NUPRL), Chicago, Illinois.NUPRL, based upon their experience with prostheses forpersons with high-level, upper-limb amputations, devel-oped MELA to provide users with more efficient,versatile control and operation of their existing, cable-operated, positive-locking elbow and wrist components.The design of MELA has advanced to the point where ithas the potential to improve the functionality andeffectiveness of existing, body-powered or manuallypositioned above-elbow prostheses . This R&D effort hasresulted in a pre-market model that is now ready for thenational field evaluation part of the technology transferprocess coordinated through the VA Rehabilitation Re-search and Development Service, Technology TransferSection.

Key words : body powered above-elbow prostheses, high-level upper-extremity amputations, modular electrome-chanical lock actuator, technology transfer.

For further information, contact Mary E . Cupo, Health ScienceSpecialist, Department of Veterans Affairs, Rehabilitation Research andDevelopment Service, Technology Transfer Section, 103 South GayStreet, Baltimore, MD 21202-4051 . Phone: 410-962-2133.The research, development, and evaluation of MELA was sponsored bythe Department of Veterans Affairs, Rehabilitation Research andDevelopment Service, Washington, DC .

BACKGROUND

The mission of the Rehabilitation Research andDevelopment (Rehab R&D) Service is to support anintramural program for improving the quality of lifefor veterans with disabilities . The program is com-mitted to provide rapid transfer of rehabilitationresearch and development technology and dissemi-nation of information into the VA medical healthcare system . The outcome promotes greater func-tional independence in the activities of daily living(ADL) for veterans with disabilities and contributesto the nation's knowledge about disease, disability,and rehabilitation.

One of the highest priority areas of the RehabR&D Service involves prosthetics, amputations, andorthotics. The VA sponsors development in this areawhich results in artificial limbs that are lighter, fitbetter, are more comfortable, and permit the usermore natural movement for ADLs and rigorousactivities such as running, skiing, etc.

In keeping with the commitment to support theadvancement of technologies within priority areas,the VA Rehab R&D Service sponsored the develop-ment of a modular electromechanical lock actuator(MELA) for above-elbow (AE) prostheses (Figure

1) . This development effort was conducted underthe direction of Dudley S . Childress, PhD, at theNorthwestern University Prosthetics Research Labo-ratory (NUPRL), Chicago, Illinois.

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Figure 1.Modular Electromechanical Lock Actuator.

The developers at NUPRL believed that body-powered, positive-locking components, with theircomparative mechanical simplicity, general rugged-ness, and low cost had not been fully exploited.They felt that the mechanical AE prosthesis offereda significant advantage by providing a close cou-pling between the user and the prosthesis, since thecable control uses the person's otherwise intactmusculoskeletal and sensory systems for elbow/prehensor control and to position positive-lockingwrist components (for rotation and flexion) . It wasthe developer's belief that the dependency on me-chanical linkages to operate the locking mechanismsin these prostheses limited their effectiveness for theuser and complicated the prosthetic fitting . Thisconcept led to the design of a simple, modular,electromechanical lock actuator that can be used inconjunction with existing cable-operated elbows andpositive-locking wrist components .

PRODUCT DESCRIPTION

MELA is a simple, modular, electrically pow-ered lock actuator used in conjunction with existingcable-operated, positive-locking elbow and wristcomponents . The electromechanical lock actuatorand the electronic circuit are powered by a single9-volt rechargeable transistor battery . The deviceconsists of a 10-mm diameter gearmotor driving asteel screw into a brass nut (Figure 2) (1) . A steelcable is attached between the nut and the mechanicallocking mechanism . The weight of MELA is 0,92ounces (26 gm) and does not contribute significantlyto the total weight of the prosthesis . Its overalllength is 3 inches (76.2 mm). A momentary switchcontact is all that is necessary to operate the systemthrough the electronic circuit. When the motor isactivated the nut retracts, thereby pulling the cableand unlocking the mechanism. The next activationextends the nut, releasing tension in the cable whichallows the spring loaded mechanism to lock . Eachactivation alternates between locking and unlocking.

The drive components are encased in an anod-ized aluminum housing . The force produced by thedrive nut is 7 .2 lbf (32.0 N) minimum at stall with atotal travel of 0 .5 inches (12 .7 mm). No-load speedis 1 .0 inch/second (25 .4 mm/second) . The electricalcontrol circuit is the NU 118D v2 .3.

MELA's principal advantage is the loweredforce required to operate an electrical switch versusthe physical movements presently necessary formechanical elbow lock control of a body-powered

Figure 2.Typical mounting arrangements on Hosmer Dorrance E-400elbow with either outside or inside cable exit (2,3) .

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AE prosthesis . A second advantage is that greateroptions are available for placement and configura-tion of the switch control over that possible withexisting cable or lever controls (Figure 3).

SUBJECT CRITERIA

The two previously described advantages makeMELA particularly suited for persons with high-level AE amputations (unilateral and bilateral).These individuals, due to the shortness or absence ofa residual limb (or limbs), experience difficultyperforming the necessary shoulder movements re-quired to generate adequate cable excursion forcomplete prosthetic elbow and terminal device oper-ation. As a result, the prognosis in terms offunctional expectancy for these individuals is oftenpoor, especially in cases involving ascending ampu-tation of the arm(s) from approximately 30 percentof the humerus (humeral neck) through the shoulder

Figure 3.The type and location of the control switch can be fittedaccording to the particular user's ability .

joint (shoulder disarticulation) up to the mostproximal level (forequarter), usually involving theremoval of both the clavicle and scapula as shown inFigure 4 (4).

MELA can be used with any type of prostheticsocket . The developer has indicated the followingcriteria for screening appropriate subjects:

• Above-elbow, or higher, residual limb amputeeprosthetic users who use body power and havedifficulty operating their existing mechanical elbowlock—whether with a conventional harness, nudgecontrol, excursion amplifier, or other alternativearrangement to assist in elbow lock control• Prospective subjects may be either unilateral orbilateral amputees.

In addition, the developer states that there areno special prosthetic fitting methods required.MELA does not have to be modified to fit aparticular situation . The developer feels that practi-tioners will prescribe MELA because of its potentialto augment existing body-powered prostheses; thusproviding improved functional expectations andincreased independence for persons with high-levelAE amputations (Figure 5).

TECHNOLOGY TRANSFER PROCESS ANDRESULTS

Within the Rehab R&D Service, TTS provides asystematic progression of proven research findings

Figure 4.Above-Elbow Amputation Levels .

SHOULDER : FOREQUARTER

0% SHOULDER : DISARTICULATION

SHOULDER : HUMERAL NECK

30%

I SHORT ABOVE-ELBOW

50%

STANDARD ABOVE-ELBOW

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CLINICAL REPORT : Clinical Evaluation of MELA

—'Veterans/VA Clinics' ~~GG

Technology Transfer

Figure 6.The VA TTS gateway process .

Transition hamsOccurring At Anytimehr.Between Phases

Commercial Phase0Development Phaseft = Research PhaseT Technology Transfer Phase•= Dec. . Point - Go/Nh .o

Commercializationhaw hr.,. cnhmmoacee..mee

Figure 5.Bilateral, high-level AE amputee eating with the use of MELA.

into clinical use, product manufacture, and commer-cial availability (Figure 6) . This is accomplished,with collaboration from appropriate VA CentralOffice (VACO) Directors, by objective, multi-centerclinical research evaluation studies . These studiesvalidate the safety, reliability, effectiveness, andcommercial readiness of prototypic technologies andtechniques intended to optimize the independenceand quality of life of veterans and nonveterans withdisabilities . Successful results are transferred to theVA health care system and ultimately to the nationalhealth care system.

Research and development of the basic scien-tific concept for MELA resulted in a workingprototype that underwent alpha testing with abilateral high-level AE amputee . Results were en-couraging and demonstrated a need to continuedevelopment toward a commercial product . A re-quest for evaluation (RFE) was submitted to TTS to

bring MELA into the Rehabilitation R&D Service'stechnology transfer process.

The RFE is a screening process of research anddevelopment products and techniques to identifythose that have reached a stage of accomplishmentand are ready for consideration to enter the technol-ogy transfer program. Once the review process hasbeen completed, and results are positive, a recom-mendation to proceed with a national, multi-centerclinical study, with subsequent budget, is submittedto the Director, Rehab R&D Service . This approvalcommences the beta testing (evaluation phase) andmanufacture of the precommercial models for initi-ating the technology transfer process.

The MELA project received positive RFE re-view and approval from the Director, Rehab R&DService to proceed with the evaluation phase . Aprocurement contract for the manufacture of 12precommercial models was awarded to the HosmerDorrance Corp . (Campbell, CA), which is commit-ted to marketing MELA pending the outcome of theclinical trials . Throughout the evaluation phase, themanufacturer must demonstrate the ability to pro-vide the necessary technical support of the productand is the primary consultant . The developer be-comes a secondary consultant when and if the needfor design changes becomes apparent from subjectfeedback and product performance.

With collaboration of the Director, Prostheticand Sensory Aids Service (PSAS), VACO, TTS hascoordinated subject selection per criteria establishedin the evaluation protocol .

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DISCUSSION

This national, multi-center clinical evaluation isbeing conducted to determine the acceptance ofMELA by the target population and to identify anymodifications needed to improve optimal use of thedevice and to enhance its marketability. The follow-ing specific areas will be scrutinized in this evalua-tion:

• Prescription indications and contraindications• Fitting (i .e ., compatibility with existing body-powered AE componentry, use of existing versusspecial techniques, knowledge, tools, etc .)• Training requirements• Instructional materials (i .e., supplied manualsand/or tapes) will be evaluated for clarity, effective-ness, and completeness• Functional use and activities• Comparative acceptance to other alternative ar-rangements for existing, body-powered elbow lockcontrol• User acceptability in terms of ease of operation,cosmesis, and functional advantages• Reliability

• Durability• Maintenance and repair• Readiness for commercial availability.

During the course of the clinical trials, it maybe necessary to freeze the process in order to makenecessary design changes as a result of subjectfeedback . At this juncture, both the manufacturerand developer will collaborate to incorporate thechanges . Once completed, the evaluation will resumewith the revised models.

REFERENCES

1. Schurr DG, Cook TM. Upper extremity prosthetics.Prosthet Orthot 1990 :8 :151-71.

2. Childress DS . Instructional manual for manufacturer.Northwestern University Prosthetic Research Laboratory,Chicago, IL, Aug 1993.

3. Childress DS . Instructional manual for prosthetist . North-western University Prosthetic Research Laboratory, Chi-cago, IL, Aug 1993.

4. Kay HW, Newman JD . Relative incidences of newamputations Orthot Prosthet 1975 :29 :8 .