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[001] TECHNOLOGY TRANSFER OF A COMPUTER-AIDED SOCKET FABRICATION TECHNIQUE
Joshua S. (Rovick) Rolock, PhD; Dudley S. Childress, PhD;
Kerice Tucker
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email: rolock@nwu.edu
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A0711-2DA)
PURPOSE--A device and methodology have been developed for the automated production of sockets for artificial limbs. The device is intended to be used in conjunction with the computer-aided design (CAD) of sockets as a means for computer-aided manufacturing (CAM) of such sockets. In this continuation work, further testing of the device will be carried out, including the manufacture of three prototype machines to be placed in clinical settings. With successful outcome of the testing phase, commercialization of the device will begin.
METHODOLOGY--The evaluation and final development of the device will take part in two phases. In the first, various enhancements to the device are being tried and evaluated while at the same time the laboratory prototype of the machine is being used for remote manufacture of sockets for clinical fittings. In the second, three beta prototype machines will be designed, manufactured, and placed in clinical settings for on-site production of sockets.
The device uses a technique of plastic deposition to fabricate sockets. Plastic material is melted and extruded through a shape-forming die as a ribbon of melted material. A computer-controlled manipulator directs the flow of the melted plastic so that multiple layers representative of cross-sectional contours through the socket are deposited successively, one upon another.
PROGRESS--The chief focus for device enhancements has been mechanisms for cooling of the melted plastic after deposition. Various means of air cooling have been investigated, including the use of refrigerated air and building the socket in a cabinet enclosure. As an alternative, liquid cooling has also been explored. Liquid cooling has necessitated a slight reconfiguration of the machine and a redesign of the extrusion die, but shows promise in reducing the time required for socket fabrication (20-30 min as opposed to 1-1.5 hrs for a typical transtibial socket). Before liquid cooling can be applied to the routine fabrication of sockets, the mechanical strength of fabricated components must first be established.
Clinical trial of sockets has been ongoing with two sockets still in use after 2 and 3 years, respectively. In preparation for more widespread clinical socket evaluation, a relationship has been established with a clinical group heavily involved in CAD/CAM. Socket data files are being sent to our laboratory via email. The sockets are fabricated using our laboratory prototype machine and shipped, overnight, to the clinical facility.
Planning meetings have taken place to discuss the design and construction of the three beta prototype machines. Work on them is expected to be complete by April 1998 and the machines placed in Seattle, Chicago, and New York for clinical evaluation.
FUTURE PLANS--Mechanical testing of water-cooled socket fabrications will commence soon.
The remote-site socket evaluation trials using the laboratory prototype machine will be ongoing throughout the term of the project.
The on-site socket evaluation trials will commence on completion and distribution of the three beta prototype machines. As important as the evaluation of the sockets, the beta prototypes will give feedback on the viability, reliability and ease of use of the prototype machines in a clinical environment and by clinical practitioners. This valuable information will be incorporated into final product design and ultimate commercialization.
[002] CLINICAL AND LABORATORY STUDY OF AMPUTATION SURGERY AND REHABILITATION
David A. Boone, CP; Douglas Smith, MD
Prosthetics Research Study, Seattle, WA 98122; email:
prs@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A92-7RA)
PURPOSE--The mission of the Prosthetics Research Study (PRS) is to advance the care for people having, or at risk of, limb loss. We address this broad mandate through fundamental prosthetics research, clinically implementing new technologies, and providing education in state-of-the-art techniques.
METHODOLOGY--In 1996-1997, PRS focused on three areas: the completion and validation of instruments for measuring outcomes of physical rehabilitation; the quantification of forces of lower limb prostheses in real-world settings using telemetered transducer instrumentation; and the electronic dissemination of research results and clinical practice guidelines.
PROGRESS--Validation of the Prosthesis Evaluation Questionnaire (PEQ), an easily administered questionnaire for comparing groups of prosthetic patients, was completed using data from 92 subjects, 60 of whom fulfilled all the requirements for the temporal stability measures. Ten scales were formed: 4 prosthesis scales, 2 mobility scales, 3 psychosocial scales, and 1 quality-of-life scale. Reliability tests showed that internal consistency was high as measured by Cronbach's alphas ranging from 0.73 to 0.89 (with one exception, 0.47); and test/retest was stable over 1 mo with intra-class coefficients ranging from 0.64 to 0.90.
The Gait Activity Monitor was used to measure the level of step activity of 62 subjects with diabetes and peripheral neuropathy, 17 of whom had lower limb amputation. Their average age was 67 years (range 41-85) years. Each subject was monitored for 2 consecutive weeks and completed the SF-36 questionnaire subsequent to monitoring. Self-selected walking velocity, fast walking velocity, and slow walking velocity were measured on each of three visits, during which subjects performed three trials at each walking speed in random order. The subjects averaged 3,288 steps per day (SD=2,064, maximum average=11,654, minimum=111). The average time with no step activity was 18.2 hours per day (SD=2.3, maximum=23.2, minimum=12.8). Average steps per day correlated significantly with three SF-36 scales: physical function (r= 0.419, p<0.01), vitality (r=0.3986, p<0.01), and bodily pain (r=0.2984, p<0.05). Self-selected walking velocity did not correlate significantly with average steps per day; however, the difference between the fastest walking velocity and self-selected walking velocity did correlate significantly with average steps per day (r=0.3011, p<0.05).
The Prosthesis Force Transducer (PFT) was developed at PRS as a new means of quantitatively examining gait and comparing prosthetic prescription and alignment in real world situations. Data can be collected ascending stairs or walking down a hill, for example. This device allows remote monitoring of the axial force and anteroposterior and mediolateral moments at the socket-pylon interface during ambulation of persons with amputation. Although not as accurate or comprehensive as a ground reaction force plate, the device has the advantage of portability, low cost, and the ability to collect data from multiple steps. Study of data collected with the device may enhance our understanding of the important parameters in prosthetic design and fitting. Because it provides real-time feedback, the device also has possible clinical uses in alignment and gait training. This device has been bench tested, and data were collected from three subjects during the last year. Design problems have been identified and a more robust and accurate device is currently being built for further study.
Post-operative prosthetic treatment protocols were published on the world wide web and CD-ROM. The web site contains over 1,000 cross-referenced pages and has received an award from the MedSite index as an outstanding information resource for amputation and prosthetics. Another CD-ROM resulting from this research demonstrates dynamic alignment of the transfemoral prosthesis. It is currently being used on 6 continents, in 17 countries, 29 universities, 25 private clinics, 13 rehabilitation centers, 4 US government agencies, and by the degree programs of the University of Washington and the University of Texas. Prosthetists in the U.S. earn 4 continuing education credits using the program.
[003] A SELF-ADAPTIVE DIGITAL PROCESSOR FOR PROSTHESIS CONTROL
Isaac Kurtz, MHSc; Stephen Farr, DIT, DCT; Gilbert Chau,
EEngT; Paul O'Brien, BEngT, BSc; Sandra Ramdial, DipO&P
(Clin/Tech), CP(C); Sheila Hubbard, P&OT; Stephen Naumann,
PhD
Bloorview MacMillan Centre, Toronto, ON Canada M4G
1R8
Sponsor: Ontario Rehabilitation Technology Consortium funded by the Ontario Ministry of Health; Variety--The Children's Charity
PURPOSE--The purpose of this project is to develop a microprocessor-based myoelectric controller for powered prosthetics. The digital controller calibrates itself automatically to the user's myoelectric signals and has the programmability to allow a broad range of control strategies. In addition to allowing persons with amputation to try out a variety of options without the need for calibration, the autocalibrating controller will accommodate changes in the inputs over the short and long term.
PROGRESS--A controller that can be used by users of transhumeral and transradial prostheses who wish to control two powered devices, such as an electric hand and an electric wrist rotator, has been developed. The original design, based on an industrial controller, has been replaced by a custom design based on the PIC16C84 microprocessor. The new controller is still small enough to fit inside VASI's VV5-9 electric hand and consumes very little power (approximately the same amount as the Otto Bock electrodes commonly used in prostheses) and has enough memory and speed to be able to implement virtually any commercially available control strategy. Production-grade prototypes of the controllers have been produced.
Graphical software for programming the microcontroller has been written for use with Windows 3.1. Data from this program are linked to the microcontroller through the computer's printer port, allowing a prosthetist and client to customize the controller. Seven of the microcontrollers have been dispensed to two children with bilateral transhumeral congenital limb deficiencies. Evaluation and clinical follow-up has shown that the controllers are reliable and flexible enough to meet a wide range of user needs.
FUTURE PLANS--In collaboration with the industrial partner for this project, VASI, a manual and a marketing and training plan for the microcontroller are being developed. Contractual arrangements with other prosthetic manufacturers for licensing the hardware and software used in this project are being pursued.
[004] GENERALIZED EPP POSITION CONTROLLER FOR ELECTRIC-POWERED UPPER-LIMB PROSTHESES
Dudley S. Childress, PhD; Richard F. ff. Weir, PhD;
Craig W. Heckathorne, MS; Edward C. Grahn; Jack Uellendahl,
CPO; Yiorgos Bertos
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email:
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2087-RA)
PURPOSE--Today's externally powered prostheses use switch or proportional controllers with open loop velocity control. It has been shown that position control is superior to velocity control in positioning tasks. Furthermore, prosthesis control schemes that employ the body's own actuating and sensing systems seem to be incorporated more readily by prosthesis users. Such schemes may result in more subconscious control than other control schemes. Open-loop, velocity control cannot provide this sensory feedback. We believe that extended physiological proprioception (EPP) and EPP controllers as applied to externally powered prostheses is a way of achieving good control. To explore these ideas we developed an analog EPP controller and have gained considerable experience in the fitting of EPP-controlled prostheses. Shortcomings of our analog controller and the availability of low-power, low-cost microcontrollers led us to develop a microprocessor-based EPP controller. The primary reason for going to a microprocessor-based design is one of flexibility:it allows us to linearize the nonlinear characteristic of the force sensitive resistors (FSR) we use to transduce force into voltage. The analog device could not operate well at the low forces and excursions that were present in several of the experimental fittings.
METHODOLOGY--The microprocessor-based EPP controller is designed around the PIC16C73 microcontroller produced by Microchip Technology Inc. This microcontroller has been specifically developed for embedded applications where small space, low power, and versatility are of paramount importance and consists of a central processor unit (CPU), 5 A/D input channels, 2 PWM output channels, EPROM and RAM and 15 general I/O channels integrated onto a single chip. It sells for around US$8. For a clock rate of 100kHz with a supply voltage of 5 VDC, a typical value of the supply current is 40 µA when active and less than 1 µA when in standby.
In the control of an externally powered prosthesis, the controller and FSR form part of a force-actuated position servo-mechanism. The FSR sensor, along with signal conditioning electronics, transduces an applied force to a DC voltage in a form that an A/D channel of the microcontroller can read. This value is then output by the microcontroller on one of its pulse width modulated (PWM) outputs to a H-bridge that drives the DC motor of the prostheses until the force at the FSR transducer goes to zero. User parameters can be changed, via rotary dip switches or the appropriate analog potentiometers, to tailor the controller to a particular client.
PROGRESS--A working prototype has been developed, and we are currently in the process of transferring this initial prototype to a surface mount circuit board for further evaluation. The current system draws less than 0.5 mA at a supply voltage of 5 V.
RESULTS--This microprocessor-based controller has a much more linear response than the analog one. In addition, the parameters of the controller can now be changed independently of each other. Much of the functionality of the controller is implemented in software, giving us flexibility in configuring different topologies (i.e., uni- or bi-directional). This controller can be used in situations where only low forces and excursions are available, such as in the case of miniature tendon/muscle cineplasties. It can also be tailored for the force variations of a particular person during the course of using the prosthesis.
FUTURE PLANS--We envision using this controller as a building block for a multiple degrees of freedom prostheses. The next step is to test the controller clinically.
[005] ESTABLISHING STANDARDS OF CARE: UPPER LIMB PROSTHETIC SERVICES
Trilok N. Monga, MD; William H. Donovan, MD; Diane J.
Atkins, OTR; Robert L. Abramczyk, ME
Houston VA Medical Center, Houston, Texas 77030; The
Institute for Rehabilitation and Research (TIRR), Amputee
Program, Houston, Texas 77030
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A855-RA)
PURPOSE--To date, no quality of care (QOC) standards have been developed to address the rehabilitative and ongoing support needs of persons with upper limb loss. This may be contributing to less-than-optimal outcomes for individuals who require diagnostic, therapeutic, and prosthetic services in order to function with maximal independence in the home, job, and other settings. The VA system, with its decades of service to persons with upper limb loss, may offer a model for quality of care that could be replicated in whole or in part by addressing the needs of people currently served through other systems, but there is presently no objective, systematic approach to documenting the strengths and weaknesses of its programs nor for determining their appropriateness for other populations.
METHODOLOGY--This project is designed to employ an expert approach, similar to the national consensus approach employed by CARF, to develop and test QOC standards for persons with upper limb loss. This can then be used to assess the efficacy of replicating the VA service approach in other settings. The Amputee Services Assessment Inventory (ASAI) has been developed and includes QOC standards and indicators as well as a protocol for self-assessment. A facility survey to be completed by program personnel evaluates the type and amount of treatment provided. A survey to be sent to persons with amputation from each participating facility also addresses the type and amount of services received, as well as outcomes measures and demographic information. This project will also increase the representation of VA-served persons with upper limb loss in the National Upper Limb Amputee Database developed by The Institute for Rehabilitation and Research (TIRR).
PROGRESS--The ASAI has been tested at three VA facilities (Houston, Palo Alto, and Seattle) and at five non-VA facilities (TIRR, Rehabilitation Institute of Chicago, University of Colorado, University of Michigan, and University of Virginia). Personnel at each facility completed a survey and coordinated a follow-up site visit by one of the investigators. Surveys will be now be sent to as many as 50 recent clients from each of participating locations.
FUTURE PLANS--The ASAI will ultimately be a tool for general use in ongoing monitoring and improvement of services for persons with upper limb loss. In the National Upper Limb Amputee Database, this data will be compared to that for individuals served by other systems to determine whether there are special needs or service issues in the VA population distinct from those identified for the general upper limb amputee population. Data analysis will examine upper limb amputee service delivery procedures, and recommendations for improvement will be made.
[006] THE WILMER COSMETIC PROSTHETIC PREHENSOR FOR CHILDREN
André A.M. Sol, BSc; Dick H. Plettenburg,
MSc
Wilmer Group, Department of Mechanical Engineering,
Delft University of Technology, Delft, The Netherlands;
email: a.a.m.sol@wbmt.tudelft.nl
Sponsor: Delft University of Technology, Delft, The Netherlands
PURPOSE--The standard split hook prosthesis is, despite its functionality, most often rejected by parents of a child with an upper limb defect because of the very poor and deterring outward appearance. The objective of this project is to develop a new prosthetic prehensor for these children that combines the functionality of the standard split hook prosthesis with an improved and appealing outward appearance.
METHODOLOGY--A shape study was performed to determine the outline of the new prehensor. The resulting outline is derived from the contor of a hand of a 4-6-year-old child. The length of the fingertips and the position of the rotating finger are approximately similar to a healthy hand. The connection to the forearm is harmonic and smooth. All mechanical parts, including the operating cable, are placed out of sight in the frame. Integrated within the frame is a lightweight friction wrist prosthesis. Also the frame is the pillar to the cosmetic cover made of flexible polyurethane resin. In this way, the outside of the prehensor is rugged and easy to maintain; the cover can be easily removed to access the mechanism; and the cover color can be chosen from a wide palette. Giving the cover a bright primary color emphasises the toy-like nature of the prehensor, thus advancing the acceptance and use of the prehensor by the child.
RESULTS--In collaboration with our clinical partners of the rehabilitation centres "De Hoogstraat en Sint Maartenskliniek," the Netherlands, the new cosmetic prosthetic prehensor was clinically tested by 10 children. They all appreciate their new device greatly. It has not caused any negative reactions or strange associations. The children are delighted by the bright-colored appearance of the prehensor. Because of its smooth outline and the integration of the control cable, wear on clothing is reduced considerably. The mechanism of the prehensor has proved to be reliable but is rather cumbersome to assemble. Therefore, a new mechanism has been designed.
FUTURE PLANS--Laboratory and clinical testing of the new prehensor mechanism is expected shortly. Successful completion of these tests will result in commercializing the cosmetic prosthetic prehensor.
[007] CLINICAL COLLABORATION TO IMPROVE HIGHER-LEVEL UPPER-LIMB PROSTHETIC FITTINGS
Dudley S. Childress, PhD; Craig W. Heckathorne; Jack E.
Uellendahl, CPO (RIC); Edward C. Grahn
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email:
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: National Institute on Disability and Rehabilitation Research, U.S. Department of Education, Washington, DC 22202
PURPOSE--Persons with higher level arm amputations (through or proximal to the elbow) and with bilateral arm amputations represent a relatively small proportion of prosthetic clients. Consequently, there is not the opportunity for developing a broad empirical foundation to guide clinical practice. Without guidelines, based on documented success in restoring function, it is difficult, at best, for clinicians to develop fittings with any degree of confidence in the outcome.
Our goal is to promote and develop principles and guidelines for improved higher-level and bilateral upper-limb prosthetic fittings. Toward that goal, we are using our research and development capabilities in direct collaboration with a clinical service program in prosthetics, the Prosthetic/Orthotic Clinical Services Department of the Rehabilitation Institute of Chicago (RIC). The RIC Amputee Program has a national and international reputation and, consequently, receives referrals of persons with high-level amputations from across the United States and abroad.
METHODOLOGY--Over the past 10 years, we have collaborated in the treatment of 36 persons with bilateral arm amputation. Of these, 23 had sustained high-level bilateral limb loss. To maximize manipulative capability and provide complementary function, we have developed prosthetic designs that incorporate multiple actively positioned components in a hybrid configuration (combining body- and electric-powered components). In general, the dominant prosthesis of this bilateral pair is configured with all mechanical, positive-locking, cable-actuated components while the nondominant side incorporates either all electric or hybrid componentry.
PROGRESS--We are continuing work on a manual for prosthetists describing the design and implementation of the four-function control system for body-powered transhumeral prostheses. In this configuration, a mechanical elbow, a wrist rotation unit, a wrist flexion unit, and a voluntary-opening split hook prehension device are arranged so that a single control cable can be used to position any one of the four components. The elbow and wrist components are held in place by mechanical locks. Whenever one of these components is unlocked, action on the control cable affects the position of that component. When all three components are locked, action on the control cable operates a voluntary-opening split hook prehension device. We have had considerable success with this configuration and believe, with the support of users' comments, that the extension of the user's physiological proprioception via the control cable reduces the mental effort required in positioning and using the prosthesis.
We are also continuing to work with Milo Collier and Associates (MICA) Corp. (Longview, WA) and Liberty Technology (Hopkinton, MA) on evaluation and refinement of the MICA locking shoulder joint, the only commercial locking shoulder joint available. We have been a proponent of locking prosthetic joints in preference to friction-type joints. A locking shoulder joint maintains the prosthesis as a rigid extension of the user's body when the user wants to exert forces on an object or support a heavy object. Additionally, this particular joint enables a person to handle and act upon objects above the level of the head, a significant functional advantage.
Since the introduction of the shoulder joint in the early 1990s we have assisted the RIC Prosthetic/Orthotic Clinical Services Department in fitting nine of the joints. We have made modifications to the joints, especially the locking actuator, to improve its operation. All modifications have been communicated to MICA and Liberty Technology. We also continue to monitor the users' experiences with the joints and relay that information as well. In addition to the MICA/Liberty Technology joint, we are evaluating a new locking shoulder under development by Cypromed (Ottestad, Norway).
FUTURE PLANS--We plan to complete the manual for prosthetists describing the design and implementation of the four-function control system and to disseminate our experiences with locking shoulder joints.
[008] LIFE INTERFACE FOR CLOSED LOOP CONTROL OF ARTIFICIAL LIMBS
Kenneth W. Horch PhD; Gurpreet S. Dhillon, MD (MbChb);
Douglas T. Hutchinson MD; Edward Diao MD; Steve M. Lawrence,
BS
Departments of Bioengineering and Orthopedic Surgery,
University of Utah, Salt Lake City, UT 84112; Department of
Orthopedic Surgery, University of California, San Francisco
CA, 94143-0728; email: k.horch@m.cc.utah.edu
Sponsor: National Institute of Neurological Disorders and Stroke of the National Institutes of Health, Bethesda, MD 20892
PURPOSE--Our long-term aim is to develop an interface to connect artificial limbs to the peripheral nerve stumps of persons with amputation. The purpose of this study was to investigate whether it is possible to selectively stimulate sensory neurons and record motor nerve activity, with the longitudinal intrafascicular electrodes (LIFEs) implanted in chronically transected nerves (>8 week duration).
METHODOLOGY--Subjects with chronic upper limb nerve injury and upper limb amputation undergoing elective surgery were invited to participate. LIFEs were constructed from a Teflon-insulated 25 µm Platinum-Iridium wire; 2.5 cm from its end is a 1 mm recording/stimulating zone. A 20 µm tungsten needle, attached to one end of the electrode, was used to thread this region through a 1 cm zone of a proximal nerve stump fascicle. A maximum of four LIFEs were implanted in four separate fascicles and exteriorized percutaneously. Nerve function was evaluated on 2 consecutive days postoperatively.
The subject was asked generate motor nerve activity by attempting to make movements of the missing limb (or dennervated muscles). These motor signals were channeled via a differential amplifier/filter to a loudspeaker, and via analog-to-digital converter to a DOS computer. The computer was programmed so that the position of a cursor was a direct function of the number of action potentials per unit time. By listening to audio sounds the subject selected the most appropriate movement that corresponded to a particular electrode. The subject was then asked to precisely control the selected movement and position a cursor in a randomly appearing target across the monitor.
The nature, intensity, and topographical location of referred sensations was assessed by having the subject report on the sensations elicited with different values of stimulating pulse width (50-500 ms), amplitude (1-100 µA) and frequency (50-500 Hz).
PROGRESS--Four subjects (two with amputation and two with chronic nerve transections) have been studied. Pt-Ir LIFEs are stiff wires in comparison to nerve tissue, and this has resulted in potential electrode drift within a fascicle. A new type of Kevlar fiber-based LIFE has been developed, with stimulation/recording properties similar to the Pt-Ir electrode but 50 times more flexible. Preliminary studies indicate it is biocompatible.
PRELIMINARY RESULTS--Subjects were able to generate and control motor nerve activity associated with missing/dennervated muscles after a short period of training. Localized referred sensations of touch and proprioception to the damaged nerve territories of the upper limb could be elicited by electrical stimulation of fibers in the proximal nerve stump. Subjects reported intensities of sensations that varied with logarithm of frequency of afferent nerve stimulation.
FUTURE PLANS--Once acute studies have been completed, we plan to study these subjects with 1- and 6-mo LIFE implants, respectively. Effects of chronic nerve stimulation, learning, CNS plasticity on the long-term efficacy of providing sensory feedback and motor control with the LIFE interface will be evaluated. These recording/stimulation data will be used by engineers at the Center for Engineering and Design, University of Utah, to design sensors and control systems for a neurally controlled artificial arm. Signals from the LIFE interface will then be channeled to the neuroprosthetic arm to evaluate how well subjects can execute closed-loop control.
[009] AN INVESTIGATION INTO THE EFFECTIVENESS OF FITTING POWERED UPPER LIMB PROSTHESES: THE UNB EXPERIENCE
Edmund Biden, DPhil, FCSME; R. Caldwell, CET; R.J.
Leckey, MD; D. Stocker, BScOT, MEd; D.F. Lovely, PhD
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, NB CANADA E3B 5A3; Stan Cassidy
Centre for Rehabilitation, Fredericton, NB, CANADA E3B 4R3;
email: biomed@unb.ca
Sponsor: None listed
PURPOSE--In the fall of 1981, the Institute of Biomedical Engineering (IBME) at the University of New Brunswick (UNB) opened a myoelectric fitting center, with the first client fitted January 1982. Since then, over 127 clients have passed through this center.
The overall goal of this retrospective study was to address two simple questions: What percentage of clients are still wearing and using a powered upper limb prosthesis? If a client is presently not wearing a powered prosthesis, then what are the reasons?
In addition, an attempt was made to gather information regarding basic wearing patterns for those clients who are still using a powered prosthesis.
METHODOLOGY--The study was conducted in three stages: Clients not seen as the center in the past 3 yrs were contacted by mail and asked to complete a written questionnaire. As clients return to the center for refitting, repair, or re-evaluation, the same questionnaire was completed. Clients missed by the first two steps were contacted by telephone and interviewed using the questions from the questionnaire. The questionnaire consists of only two pages: one for wearers and one for nonwearers.
RESULTS--Of the clients seen at UNB over the last 14 yrs, approximately two-thirds were below the age of 18 when first fitted. As our primary thrust is in powered upper limb prosthetics, most of these prostheses (;sl87 percent) have been myoelectrically controlled. From the active case load (i.e., those clients who have visited the center in the last 36 months) 90 percent are still using their prostheses. For the inactive group, only 35 percent reported that they continued to wear their prostheses.
In the wearers group, 48 percent used a powered prosthesis exclusively, and 14 percent used a nonpowered device exclusively, and 38 percent reported using more than one type of prosthesis. This tends to reflect the common usage of sports limbs designed for specific activities and cosmetic prostheses for social occasions.
The responses relating to patterns of prosthesis use were split into `where? ' and `how long?'. It was found that 83-87 percent of the wearers reported using their prostheses at work, school, or social events, with 69 percent responding that they used their prostheses only for recreation and play activities; 44 percent wore their prosthesis for all activities. About a third of wearers tend to use their prosthesis less on the weekends than through the week.
A substantial proportion, 17 percent, reported wearing their prosthesis all day (>12 hrs), and 66 percent indicated they use their prosthesis >4 hrs per day. Consequently, approximately 83 percent wear their prostheses >4 hours per day. The remaining 17 percent tend to use their prostheses only for specific tasks which they would not otherwise be able to complete.
In the nonwearer group, 88 percent reported that they got along well without it. Half of them also indicated that the prosthetic limb was uncomfortable, while the other half responded that the prosthesis did not compare to the function of their sound limb.
IMPLICATIONS--It is the view of the authors that the fitting of powered upper limb prostheses is effective. This is substantiated by the finding that overall, 76 percent of clients contacted are still wearing their prostheses and of those, 83 percent wear their prosthesis for more than 4 hours per day.
[010] DEVELOPMENT OF A MULTIFUNCTION MYOELECTRIC CONTROL SYSTEM
B. Hudgins, PhD
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, NB CANADA E3B 5A3; email:
biomed@unb.ca
Sponsor: None listed
PURPOSE--We seek to develop a myoelectric control system that is easy to operate, yet provides control of many independent prosthetic limb functions.
METHODOLOGY--During the initial 24 mo of the project, we determined the specifics of a new control strategy, based on the recognition of patterns in the myoelectric signal. This work involved computer simulations of control schemes using various waveform features to determine which provided the most information to the artificial neural network classifier. The results indicated that a control scheme that used information from two myoelectric channels provided a richer feature set and improved system performance at the expense of increased system complexity over the original single channel system. As well, the additional myoelectric channel gives the system the ability to operate as a degree-of-freedom (DOF) controller as opposed to the more restrictive state controller of the original design.
The resulting control scheme uses information collected from the person with amputation to train a pattern classifier to recognize his or her specific contraction patterns, using features extracted from the first 200 ms of myoelectric activity following the initiation of a contraction to determine the intent of the person. The classifier matches this feature set with the sets obtained during the initial system calibration. The closest match is used to select which device (hand/elbow/wrist) is to be controlled. Control of this device continues until the signal level returns to a predetermined low level.
Pattern classifiers based on alternate neural network structures were also investigated to determine the feasibility of implementing a classifier based on continuous data. In particular, a dynamic feedforward network which incorporates memory in the form of an FIR filter structure for each network weight has been shown to be appropriate for these transient myoelectric signals. Work is continuing with the goal of finding alternate feature representations and neural network structures that give continuous recognition of the raw myoelectric signal. The advantage of such a scheme is that system delay is reduced, compared to the present scheme that uses features from time-averaged data.
During the second or current stage of the project, a microprocessor-based multifunction control system has been designed that incorporates results from this project as well as the latest advances in electronic hardware. The current prototype is the result of several design iterations which have reduced the size and power consumption of the control system. The current device uses surface-mount technology on multilayer circuit boards to achieve a size of 3.8×6.35×1.27 cm and can be built into the prosthetic arm. The device operates on standard 6 V NiCad batteries drawing approximately 40 mA.
FUTURE PLANS--Clinical trials with this control system have begun at our fitting center in Fredericton. Arrangements have also been made with Hugh Steeper Ltd. (UK) to do test fittings on several of their current clients in their Roehampton and Birmingham clinics.
[011] THE INCORPORATION OF A SLIP-SENSING, CLOSED-LOOP CONTROL SYSTEM INTO A MYOELECTRIC PROSTHETIC HAND
Kathleen J.M. Surry, BESc; Stephen Naumann, PhD, PEng;
William Cleghorn, PhD, PEng
The Institute of Biomedical Engineering and the
Department of Mechanical and Industrial Engineering,
University of Toronto, Toronto, Ontario, Canada; Bloorview
MacMillan Centre, Toronto, ON Canada M4G 1R8
Sponsor: Variety Ability Systems, Inc.; Natural Sciences and Engineering Research Council of Canada, Ottawa, ON Canada K1A 1H5
PURPOSE--The current control scheme of the myoelectric prosthetic hand is of an open loop type. Myoelectric inputs (electromyographic, or EMG) from the user are translated to output by the motor, with no error feedback. This project proposes a method for integration of a supplemental, closed-loop controller to the prosthetic hand. Specifically, a slip control scheme will be incorporated into the hand so that the grip will tighten on an object as incipient slip is detected. In a conceptual sense, the supplementary controller will act as the hand's subconscious, much like the reactionary responses of an enervated hand.
METHODOLOGY--Piezoelectric ceramic sensors were built into two of the fingertips of a VASI (Variety Abilities Systems, Inc.) 5-9 child's prosthetic hand. Piezoelectric materials are defined by their unique ability to translate mechanical disturbances into electric signals without a directional bias. Such a robust sensor was deemed desirable for the rugged and unpredictable environment that a prosthetic hand is likely to experience. Electric signals from the sensors are filtered and brought into the digital domain for signal comparison and subsequent slip detection. Output from the digital algorithm controls the hand's motor when the myoelectric system is inactive.
PROGRESS--The initial slip controller design was updated to a more portable form, and testing of the slip sensing system is impending. The myoelectric hand, with the standard 1100:1 geared motor, is run off an external 6 V battery for convenience, while the slip control algorithm is executed in a desktop computer. This nonmobile version is sufficient for testing the feasibility and benefits of the system.
FUTURE PLANS--Control of a highly geared motor is imprecise and cumbersome, at best. Meaningful motor control from the digitally based slip detection algorithm can be designed in such a way, however, as to elicit the desirable response times with a practical level of accuracy. This system is currently being designed and will shortly be implemented and tested.
The future will see this project exploring other aspects such as material interfacings on the sensor surface, and the final miniaturisation of the controller for a compact fit into the prosthesis.
[012] VV 2-6 PROSTHETIC HAND ENHANCEMENTS: COSMETICS AND FUNCTION
Ihsan Al-Temen, PEng; Zigmond Chong; Isaac Kurtz, MHSc,
PEng; George McMillan; Martin Mifsud, DipE, EngT; Sandra
Ramdial, DipO&P (Clin/Tech), CP(C); Sheila Hubbard, P&OT;
Morris Milner, PhD, PEng, CCE; Stephen Naumann, PhD,
PEng
Bloorview MacMillan Centre, Toronto, ON Canada M4G
1R8
Sponsor: Variety--The Children's Charity
PURPOSE--The aim of this project is to improve the cosmetic appearance and function of the VASI 2-6 hand (for children 2 to 6 years of age).
PROGRESS--The bulk in the palm area has been reduced through redesign of the hand body and cover profiles. This significantly improves the hand's cosmesis. New tooling for production of the hand body and cover have been completed and were being tested in the first quarter of 1997; production parts should become available in the second quarter of 1997.
Another improvement, the coupling of the ring and baby fingers to move together with the other fingers when the hand closes has been prototyped. Tooling and final production details are pending.
A third improvement, the incorporation of pliable tips on the fingers and thumb, are in the design and prototyping stage. Evaluation of these finger tips is anticipated in the second half of 1997.
FUTURE PLANS--We plan to continually evolve the cosmesis and functionality of the VASI hands to meet the needs of our clients and to offer leading prosthetic technology in the marketplace.
[013] VOLUNTARY-CLOSING HAND PROSTHESIS
Just L. Herder, MSc; Jan C Cool, MSc; Dick H.
Plettenburg, MSc
Wilmer Group, Department of Mechanical Engineering,
Delft University of Technology, Delft, The Netherlands
email: j.l.herder@wbmt.tudelft.nl
Sponsor: Delft University of Technology, Delft, The Netherlands
PURPOSE--The objective of this project is the design of a voluntary-closing hand prosthesis for persons with unilateral transradial amputation. The prosthesis must have pleasant cosmetics, good wearing comfort, and easy operation.
METHODOLOGY--In voluntary-closing devices, operating force corresponds to pinching. To make full use of the feedback potential of this working principle, the prosthesis operating mechanism should transfer the actual pinching force to the operating member as purely as possible. Therefore, friction should be absent, and the counteraction of the cosmetic covering compensated for. Among the practical problems to overcome, the opened resting position, which is generally not acceptable for cosmetic as well as practical reasons, seems to be the most important one.
PROGRESS--This research is divided into several projects.
PRELIMINARY RESULTS--A prototype of a voluntary-closing hand prosthesis is under construction. It incorporates a low friction mechanism, while special attention is paid to the pivot of the elbow control lever. The thumb moves along its optimal trajectory, of which the elastic counteraction is reduced by a glove compensation mechanism.
FUTURE PLANS--We intend to extend the theory and design of statically balanced spring mechanisms to include nonlinear springs. The reliablity and durability of several low-friction mechanisms and compensation mechanisms will be tested. The prototype of the hand prosthesis is to be finished and evalulated in a laboratory setting.
[014] BODY-POWERED TODDLER HAND
Samuel Landsberger, ScD; Julie Shaperman, MSPH, OTR;
Vicente Vargas, BSME; Andrew Lin, BS; Richard Fite, CP;
Yoshio Setoguchi, MD; Donald McNeal, PhD
Rehabilitation Engineering Program, Rancho Los Amigos
Medical Center, Downey, CA 90242
Sponsor: National Institute of Disability and Rehabilitation Research, U.S. Department of Education, Washington, DC 22202
PURPOSE--We seek to develop an improved body-powered hand for toddlers one to four years of age. The primary design goals are for an affordable hand of acceptable cosmesis to provide useful grasp for children at play. Minimal energy input should be required to use the hand.
METHODOLOGY--Exploration of several hand design strategies and different methods of harnessing a child's energy has brought the project focus to center upon two designs. Neither requires a cable for activation but rather makes use of the energy of the opposing hand to insert objects. The two designs embody different balance points between form and function. One design aims for life-like appearance while the other departs from anatomical imitation to look "fun" and requires no cosmetic covering. Both designs are developing in close collaboration with the medical and technical staff at the Child Amputee Prosthetics Program at the Shriners Hospital of Los Angeles. A laboratory test of grasp performance helps with preliminary assessment of new designs. A parent preference study will focus on the decision-making process involved in selecting a prosthesis for the child. Prototypes are field-tested and evaluated for performance, reliability, and cosmetic acceptability once lab results are satisfactory. The design principle is to keep concepts and components as simple and rugged as possible, and small-lot manufacturing costs low.
PROGRESS--Research this year has been devoted to the following tasks:
New Hands
Prototypes of two of the most promising hand designs
from Year 1 are now built and field testing has begun. The
first design, dubbed the Easy-Feed hand, is a metal
endoskeleton structure fitted with compliant foam, silicone,
and a cosmetic glove covering. The shape approximates the
hand of a 2-year-old. Its purpose is to offer acceptable
cosmesis and grasp function to the youngest toddlers without
need of a cable harness. The primary design feature lies in
utilizing the power of the child's sound hand to insert and
remove objects. This accords with the natural usage pattern
of the prosthesis by a child with unilateral limb deficiency
as a nondominant limb serving the function of holding
objects for use rather than picking them up. As the toddler
develops more strength and cognitive skill, the hand
converts to cable-actuation and functions in either
voluntary opening or voluntary closing mode.
The second prehensor design, dubbed LN, is also cable-free and comprises a colorful exoskeleton structure requiring no covering. Instead of striving for precise human-like appearance, the design favors fun and function and includes two thumbs for a more versatile grip. A built-in clutch mechanism keeps the thumbs closed around objects until released via a spring-loaded wrist.
Clutch Module
This optional unit may be used with a cable-activated
hand to provide an automatic safety brake. When the child
relaxes the harness-input cable, the clutch engages
automatically to keep the hand closed around an object. When
the cable is again pulled, the hand opens to release the
object. For safety, an override spring permits object
removal.
Flexible Gloves
Up to half of the effort expended by a child to open a
prosthetic hand goes into the deformation of the stiff PVC
cosmetic glove. To minimize energy demands placed on the
toddler, some flexible glove designs are in development,
exploring both new materials and different shell
geometries.
Laboratory Testing and Prediction of Grasp
A lab test has been developed to help evaluate grip
performance of prosthetic hands. A variety of children's
toys are used to estimate the grasp capabilities of each new
design before testing on children. Strengths and weaknesses
are measured by applying forces to the objects corresponding
approximately to conditions of actual use.
Which Hand is Best for My Child?
A parent preference study protocol has been developed to
explore tradeoffs acceptable to parents weighing hand
appearance with function. Further, parents will use a
variety of prehensors to perform the same tasks as their
youngsters, for example playing with blocks, tricycles and
baseball bats. A hands-on test may influence a parent's
choice.
RESULTS--The first Easy-Feed hand has a large opening grasp of 3" span and provides a minimum pinch force of 1 lb. (adjustable). Objects may be inserted and removed by pushing and pulling. The LN hand has been produced in both colorful plastic and wood. Its unique geometry provides stable cylindrical grasp. Preliminary testing indicates openness of some parents and children to try this alternative design. Its operation requires cognitive skills beyond that of the youngest toddlers. Manufacturing costs and durability of both designs require further attention.
Gloves employing a compliant elastomer have been fabricated and field tested. While offering grip performance advantages over PVC and being easier to apply and remove, durability is a concern. Gloves of conventional vinyl material with altered geometries appear more promising in the short term, incorporating gussets, pleats and wrinkles to enable a large opening with reduced resistance. Cosmetic acceptability will be evaluated in clinic.
Lab testing of grip performance appears a helpful guide for efforts to enhance function. It enables some qualitative and quantitative comparison among different grasp geometries and compliant surfaces. Early evaluation should increase the value of each clinical trial.
FUTURE PLANS--Clinical testing and refinement of both hand designs will proceed. The clutch module will be made smaller and tested, and gloves of various configurations molded and evaluated for function and cosmesis. The grip test will be compared with clinical trials, and the parent study commenced. Collaborations with commercial manufacturers of prosthetic hands will be strengthened.
[015] A MULTI-DEGREE OF FREEDOM PROSTHETIC HAND FOR CHILD USER
Paul X.B. Hu, BASc; Stephen Naumann, PhD, PEng; William
L. Cleghorn, PhD, PEng; Denise Reid, PhD, OT; Sheila
Hubbard, Dip P&O, BSc (PT); Sandra Ramdial, CP(C)
The Institute of Biomedical Engineering and Mechanical
and Industrial Engineering Department, University of
Toronto, Toronto, Ontario, Canada; Bloorview MacMillan
Centre, Toronto, ON Canada M4G 1R8
Sponsor: Natural Sciences and Engineering Research Council of Canada, Ottawa, ON Canada K1A 1H5
PURPOSE--This project involved the development of a powered multifunctional hand prosthesis for children and young adults, focusing on modifying the current pincer type prosthesis. The new design should allow for better orientation of objects to be held, improve stability of the objects, and minimize compensatory motions during the prehension phase.
PROGRESS--The three most frequently used grasping patterns, tip grip (precision handling: writing and handling small objects), palmar grip (power grip: for larger or round objects like bike handles or balls), and lateral grip (used to hold flat objects such as keys) were defined, along with the motions of the fingers and the thumb related to these grips. Following verification of the design using computer simulation, a prototype hand was manufactured and tested by a 12-year-old subject, contrasting its performance with that of his currently worn hand. The subject performed all tasks equally well with both hands. However, with the new hand, compensatory body movements were minimized, and a larger variety of objects could be held with increased stability than with his current hand.
FUTURE PLANS--Concepts developed through this work will be incorporated into revised hand designs for VASI.
IMPLICATIONS--The hand appears to provide the user with significantly improved function when compared with currently available prostheses. A challenge beyond the scope of this project is the development of a flexible but durable glove.
[016] RECENT ADVANCES IN THE DEVELOPMENT OF PARTIAL HAND PROSTHESES
Edmund Biden, DPhil, FCSME; Greg Bush, BA, CP(c); Murray
Olive; Walter Young
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, NB CANADA E3B 5A3; email:
biomed@unb.ca
Sponsor: None listed
PURPOSE--Recently, two persons have presented with partial hand amputations in which the digits and distal ends of the metacarpals were missing, but the thumb was intact. One of these was a child with a congenital absence and the other an adult with loss of digits through a farming accident.
The child has been fitted with two different systems, the first based on the motor and finger group of an Otto Bock size 5 Electrohand 2000, and the second based on our own, in-house, design. The adult has been fitted with mechanical fingers having multiple locking positions. The prostheses have been used extensively.
METHODOLOGY--The original fitting of the child was accomplished by building up a powered finger unit from the motor and finger block of the Otto Bock hand. The hand's wrist attachment, thumb, and related linkages between the thumb and fingers were removed, leaving a unit approximately 1.2 mm in diameter and 45 mm long. This was then laminated to a socket that left the thumb exposed and free to move. Electrodes were placed over the thumb flexors/adductors and the extensors/abductors so that as the thumb was flexed or extended, the finger group mimicked the motion. The control method worked well, and the action of fingers and thumb together gave a natural grip that was easy to learn to control.
The child was an enthusiastic and active user, and eventually the modifications led to failure of the drive. This is in no way a criticism of the hand, which was being used in a way for which it had simply not been designed.
We have built a second unit around a MicroMo 1319 electric motor and a 246:1 gearbox. The unit is built so that a sleeve holding the fingers is attached to the output shaft of the gearbox, projects back over the gearbox housing, and rides on a pair of Teflon bushings. The fingers are brass rods inserted into a projecting mounting block on the sleeve. The casing, in which the motor and gearbox are mounted, is laminated into the prosthesis. The leads from the motor are brought out the end of the unit and two electrodes, a digital bridge, and a remote 6V battery pack complete the system. The range of finger motion of approximately 60°, and opening and closing for the unloaded unit is approximately 200 ms. The stall torque is 9 in-lbs. The unit was provided with a rubber bumper system to cushion the end points of the finger travel.
In both devices, the glove to cover the fingers has the thumb cut out and required a substantial amount of stretching to allow the fingers full range of motion.
The adult mechanical hand was built to provide a robust device for a farmer. It consists of a sleeve and core rather than the motor unit described above. All four fingers are attached to the core, which also has a three position lock activated by pressing on a button through the cosmetic cover. The fingers have a range of approximately 90° with the locked positions being with the fingers fully extended, partly flexed, and flexed to 90° so that the thumb can come into contact. The fingers were covered with an Otto Bock inner hand shell and then covered with an outer cosmetic glove with the thumb removed. The finished prosthesis ends just distal to the wrist, allowing relatively unrestricted wrist motion.
RESULTS--Both the powered and mechanical hands have had active use in the field. The original child-sized, powered prosthesis was used actively until it failed mechanically. The second model continues in the field.
FUTURE PLANS--Both fittings have been successful, and the mobile fingers have worked well and have been very functional for this particular form of partial hand amputation; both designs can be scaled up or down to accommodate different hand sizes.
[017] A MULTIFUNCTION CONTROL SYSTEM FOR POWERED UPPER EXTREMITY PROSTHESES
Thomas M. Kennedy, BEng; Stephen Naumann, PhD, PEng;
Isaac Kurtz, MHSc; William Cleghorn, PhD, PEng
The Institute of Biomedical Engineering and Mechanical
and Industrial Engineering Department, University of
Toronto, Toronto, ON, Canada; Bloorview MacMillan Centre,
Toronto, ON Canada M4G 1R8
Sponsor: None listed
PURPOSE--This research project is involved with the development of a multifunction control system for upper extremity prostheses for children and young adults. The focus of this work is to examine the input to the classifier, in order to qualitatively determine the choice most likely to yield a working system.
METHODOLOGY--There has been a great deal of investigation into classifiers/pattern recognition techniques for the purposes of discriminating prosthetic function. However, previous research has focused on development of better classification schemes, and the choice of input has not been considered in detail. Various parametric representations of the myoelectric (ME) signal have been chosen as input for these classifiers either for simplicity's sake, or because it was hypothesized that they would yield a better result. However, no comparison of their relative merits has been conducted. Furthermore, clinical implementation of the classifier was seldom considered, and investigations have almost always been conducted in controlled situations only, which does not allow for the large variations in the ME signal under normal conditions of use (i.e., loading, fatigue, residual limb movement). Therefore it is the purpose of this work to examine the ME signal produced under various conditions of use, and analyze it in order to determine the optimum parametric form for use as an input to a classifier. Furthermore, this choice of input will then be tested in order to determine if much improvement can be found using a conventional classifier (e.g., neural network) from previous works.
PROGRESS--Test subjects consisting of individuals with transradial amputation and congenital limb deficiencies, will be asked to perform six different types of contractions (the contractions will be different for each individual, depending on personal ability) under controlled conditions, loading, and during motion of the residual limb. The raw ME signals will be recorded from two electrode sites, corresponding to those used for each person's current prosthesis. The data will then be represented using as many spatial and spectral parameters as possible, and various sizes of time windows. Standard statistical packages will then be used to cluster the data. Since the intent of each contraction is known a priori, the success of each representation can be gauged, based upon the number of points incorrectly clustered, and a measure of how far away each misclassified point is from its correct cluster. In addition to the overall performance of each parametric representation, this test will yield information about which representations cluster the best for each particular contraction type. It may then be possible to use a combination of parameters in order to achieve the highest levels of discrimination. Data recording is tentatively scheduled for summer 1997, subsequent to ethical approval and equipment set-up. Analysis of the data will then be conducted.
IMPLICATIONS--The work is expected to yield the best parametric form of the ME signal for use in classification problems. Given this "best" input, any classifier can be tested in order to determine its optimum effectiveness.
[018] GAIT MECHANICS OF THE PARTIAL FOOT AMPUTEE
Mohammad Dorostkar, MD; Edmond Ayyappa, MS, CPO;
Jacquelin Perry, MD; Richard Chambers, MD; Judith Burnfield,
PT; Lara Boyd, MPT; Ernest Bontrager, MS; Sreesha Rao, MS;
Sara Mulroy, PhD, PT.
Pathokinesiology Laboratory, Rancho Los Amigos Medical
Center, Downey, CA 90242
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A861-RA)
PURPOSE--Diabetic pathology often requires an amputation; however, surgical advances are permitting preservation of more of the forefoot. This maintains the integrity of the leg, but changes the weight-bearing distribution of the foot and may lead to ulceration of the heel or residual foot segment. Clear understanding of the biomechanics of walking following partial foot amputation may identify criteria for surgical, orthotic, and prosthetic management that will enhance the durability of the residual foot. The purpose of this research is to: 1) compare the gait biomechanics of toe, metatarsal, ray, Lisfranc and Chopart level amputations with normal function; 2) analyze quantified pressure patterns of both residual and sound limbs; 3) determine the effects of amputation level on sound limb function; and 4) assess the efficacy of prosthetic/orthotic devices in altering gait characteristics of those with partial foot amputations.
METHODOLOGY--Comprehensive gait analyses are being conducted, including collection of kinematic and kinetic data, electromyographic activity in the main extensors in both the residual and sound limb, and foot pressure patterns. All of these data are being assessed with and without footwear. Additionally, the isometric strength of the major extensor muscle groups in each leg is being tested.
PROGRESS--To date, 36 individuals with partial foot amputations have participated in this study (15 toe, 10 metatarsal, 9 ray, 1 Lisfranc, and 1 Chopart level). Additionally, the reliability and validity of the Novel Pedar data collection system for foot pressure analyses has been established, using 10 individuals without foot pathology.
PRELIMINARY RESULTS--Comparisons were made of kinematic and strength patterns between six individuals with toe, and six with metatarsal, amputations during barefoot free walking conditions. Mean walking velocity was reduced for both toe and transmetatarsal amputation groups relative to normal (59.2 and 51.6 percent of normal, respectively) due primarily to decreased stride length (69.8 and 58.8 percent of normal, respectively). Cadence also was reduced (toe=83.6 percent; metatarsal=86.2 percent of normal). However, these between-group differences were not statistically significant.
Statistic analyses of ankle motion profiles revealed significantly less peak ankle dorsiflexion in terminal stance for those with metatarsal amputation than in those with toe amputation (metatarsal=6.8°; toe=10.9°; p<0.05). Additionally, peak dorsiflexion in terminal stance occurred significantly later for those with metatarsal amputation (metatarsal=53.2 percent of gait cycle, toe=49.0 percent of gait cycle, p<0.05).
Substantial decreases in muscle strength from normal were found in sound and residual limbs for both groups, although no statistically significant differences between groups were noted. Strength deficits were most pronounced in the residual limb ankle plantar flexors of both groups when compared to normal (metatarsal=30.1 percent of normal, toe=39.1 percent of normal).
The absence of a forefoot rocker in the metatarsal group compromised the ability of these individuals to progress forward, as evidenced by reduced peak ankle dorsiflexion in terminal stance. This, in combination with diminished calf strength, caused decreased velocity and stride length.
FUTURE PLANS--Data collection and analyses are ongoing with a target number of 70 participants. Specifically, the weight-bearing pressure patterns of both the residual and sound limb are being investigated to determine the efficacy of prosthetic inserts and footwear in preventing ulceration. The impact of partial foot amputation of the limb-loading patterns of the sound leg is also being analyzed.
[019] A STUDY TO DETERMINE THE BIOMECHANICAL EFFECTS OF SHOCK-ABSORBING PYLONS
Steven A. Gard, PhD; Dudley S. Childress, PhD
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email: sgard@nwu.edu;
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2133-RA)
PURPOSE--Vertical shock pylons are designed to function as shock absorbers for lower-limb prostheses by attenuating forces associated with walking and high-impact activities, such as running and descending curbs and stairs. Many persons with amputation seem to show a clear preference for walking with these devices, but the function of the devices during gait and the influence on the resulting pattern of walking is unclear. The purpose of this investigation is to perform mechanical analyses of commercially available vertical shock pylons to gain a better understanding of their function during walking.
METHODOLOGY--We are investigating three vertical shock pylons: the Flex Foot Re-Flex Vertical Shock Pylon (Flex), the Ohio Willow Wood Stratus Impact Reducing Pylon (Ohio), and the Seattle AirStance Pylon (Seattle). Static and dynamic testing of these devices, using a specially designed testing apparatus with attached mass, will permit calculation of the damped natural frequencies, spring constants, damping coefficients, and damping ratios, and indicate their abilities to store and return energy. Static testing allows the force versus deflection characteristic of each device to be determined. Creep rate is also measured. The dynamic testing involves step loading and unloading the vertical shock pylons while measuring the resulting axial displacement.
The Flex consists of graphite telescoping tubes in parallel with a carbon fiber compression spring for shock absorption and energy return. There are a total of nine spring stiffnesses available, accommodating subjects weighing anywhere from 45 to 147 kg. We are testing five of spring stiffnesses, evenly distributed across the range of stiffness values. Each stiffness is being tested with three weights that represent the high, low, and mean values of the manufacturer's recommended range of allowable body weights for that particular spring.
The Ohio consists of a viscoelastic compression ring seated within a telescoping housing. The ring is compressed with applied load, and returns to its original shape as load is removed. There are five stiffness rings available (very soft, soft, medium, firm, very firm), accommodating subjects' weights from 41 to 113 kg. We are testing all five, each at three weights representative of the maximum, minimum, and mean values for the manufacturer's recommended range of weight values for that particular ring.
The Seattle is a pressurized pneumatic cylinder that suspends weight on pressurized air; it is is designed to accommodate persons weighing up to 136 kg. Because pressure is controlled by an air pump and allows for a continuous range of values, we assumed three different body weights (BW) over the range of values recommended by the manufacturer and set the air pressure equal to 0.5 BW psi and 0.5 BW±25 percent BW psi.
PROGRESS--Laboratory testing of the three pylons has been completed; data are currently being reduced, and will be processed in order to calculate the desired parameters for characterizing the three shock-absorbing systems.
FUTURE PLANS--After the static and dynamic properties of the pylons have been fully characterized, we plan to perform clinical testing with the devices. Persons with unilateral transtibial amputation will be recruited for gait analyses, and we plan to have them walk both with and without the pylons, while kinematic measurements and ground reaction forces are acquired. By comparing measurements from two conditions, we can determine whether or not the devices significantly affect the pattern of walking. Gait parameters that we plan to investigate include speed, cadence, vertical displacement of the trunk, step length, stride length, and pelvic obliquity. The subjects' gait data will also be compared with that of controls to determine whether the mechanisms enable them to walk more normally.
[020] DEVELOPMENTAL ENHANCEMENT AND APPLICATION OF THE VA-CYBERWARE PROSTHETICS-ORTHOTICS OPTICAL LASER DIGITIZER
Vern L. Houston, PhD, CPO; Carl P. Mason, MSBE; Cathy M.
Cruise, MD; Kenneth P. LaBlanc, BS, CPO; MaryAnne Garbarini,
MA, PT; Project Consultant, Hans. R. Lehneis, PhD,
CPO
VA Medical Center, New York, NY 10010; email:
houston@is2.nyu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A514-4DA)
PURPOSE--The objectives of this project are to continue refinement and enhancement of the VA-Cyberware Prosthetics-Orthotics Optical Laser Digitizer and to conduct fundamental application studies with the optical digitizer to test and demonstrate its capabilities, effectiveness and efficiency in quantitatively characterizing the spatial geometry and surface topography of amputees' residual limbs and orthotics patients' limb segments.
METHODOLOGY--To achieve these objectives, the following research protocol was established:
PROGRESS--A new, second generation optical digitizer prototype, based on the design specifications developed in the project, correcting all the deficits identified in the original digitizer prototype, and further improving and enhancing its performance and capabilities, was constructed. Laboratory calibration and rigorous testing of the digitizer was begun. Work continued on porting and optimizing the software modules developed on an engineering workstation for digitizer control, measurement acquisition, processing, visualization, and analysis, to a PC platform for clinical prosthetics-orthotics deployment. Work on integrating and refining these modules into a single, composite, user-friendly, menu-driven program for use by prosthetics-orthotics clinicians was instituted. Automation and refinement of calibration and testing procedures to optimize the digitizer's spatial field of view, and correct acquired measurements for optical nonlinearities, thus increasing the digitizer's accuracy, continued. Enhancement and optimization of the control, tool path clearance, and the surface contour interpolation and smoothing software for the VA Prosthetics-Orthotics CAM milling machine was completed. Development and refinement of CAD system prosthesis and orthosis design templates based on optically digitized residual limb/limb segment measurements also continued.
FUTURE PLANS--Refinement and enhancement of the optical digitizer shall continue, based on feedback from advanced application studies. These studies shall include the compilation of a quantitative prosthetics and orthotics patient database of residual limb/limb segment geometries, measurements, and histories for use in developing improved prosthetic socket and orthosis designs; the compilation of a database of patient limb segment contours, areas, and volumes for correlation with, and quantitative assessment of, the efficacy of medical treatments and rehabilitation regimens; and the utilization of the digitizer as an educational tool for direct visualization of prosthetics-orthotics principles and analysis of clinical practices.
[021] TISSUE BIOMECHANICAL AND VASCULAR STUDIES FOR IMPROVED PROSTHETIC SOCKET DESIGN
Vern L. Houston, PhD, CPO; Carl P. Mason, MSBE; Luigi
Arena, MD, PhD; Gangming Luo, PhD; Kenneth P. LaBlanc, BS,
CPO; MaryAnne Garbarini, MA, PT; Cathy M. Cruise, MD
VA Medical Center, New York, NY 10010
Sponsor: G.T.H. LAMB Group, New York, NY
PURPOSE--The purpose of this project is to investigate residual limb tissue biomechanical and vascular characteristics and geometry, and quantify prosthetic loading so fundamental socket design principles and algorithms can be derived, that afford more intimately fitting, comfortable, and functional sockets for persons with lower limb amputation.
METHODOLOGY--To achieve this objective, the following research protocol has been delineated: for a "representative" sample of physiologically mature and prosthetically habituated persons with transtibial amputation:
PROGRESS--An electromechanical indentor with force/position feedback was constructed, and the biomechanical creep and stress relaxation responses of the residual limb tissues of 16 test subjects were measured, and subsequently mathematically modeled by viscoelastic exponential and steady state Ogden elastomeric material models. The residual limbs of three of these subjects one with "representative" soft durometer tissues, one with "representative" average durometer tissues, and one with "representative" firm durometer tissues were digitized optically and with a high resolution MR scanner. FE models of these residual limbs were created from the data compiled. The subjects' well-fitting, habituated sockets were also electromechanically digitized. Static and dynamic socket/limb interface stresses were then measured with VA-Tekscan P-Scan transducers for these subjects in their original, well-fitting sockets, and in two experimental sockets with popliteal depression and posterior brim design variations, but otherwise identical in design to the original sockets. MR high resolution morphological scans, angiograms, and flow velocity and volume scans of the popliteal arteries of the subjects in the respective sockets with 32 KG static, axial loads applied were acquired. Corresponding FE simulations of the socket application and loading tests were performed, and the resulting FEA predicted residual limb tissue displacements at five key locations were compared with actual MR measured displacements. Similarly, FEA predicted surface stresses were compared to actual P-Scan measured socket/limb interface stresses. The reasonably close approximation of the measured displacements and stresses by the FEA results, established the FE modeling techniques employed as useful and effective prosthetics design and analysis tools.
FUTURE PLANS--The project tissue biomechanical and vascular studies shall continue with a range of "representative" subjects. The biomechanical studies shall be expanded to include measurement and modeling of tissue anisotropic characteristics. Models of the principal vasculature shall be incorporated in the FE models developed to allow prediction of the effects of variations in socket design geometry and prosthetic loading upon residual limb circulation. With compilation of measurements for a statistically significant sample of subjects, the data acquired shall be analyzed to formulate quantitative socket design principles and development of CASD algorithms allowing determination of "how much" and "where" residual limb geometries need to be modified to achieve well-fitting, comfortable, and functional sockets.
[022] DEVELOPMENT OF A BIOMECHANICAL MODEL OF THE INTERFACE BETWEEN THE STUMP AND THE PROSTHESIS FOR TRANSFEMORAL AMPUTEES
Peter V.S. Lee, BEng, PhD; William D. Spence, MSc;
Stephan E. Solomonidis, BSc, ARCST, CEng, MIMechE; Tania S.
Douglas, BSc Eng, MS
Bioengineering Unit, University of Strathclyde, Glasgow,
UK; email: clfr67@strath.ac.uk;
peter@sharon.bioe.strath.ac.uk
Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
PURPOSE--A major limitation of present CAD/CAM systems, and indeed in clinical practice, is that no account is taken of the tissue properties of the residual limb or the actual loads and pressures transferred through it. The aim of this investigation is to generate a three dimensional (3-D) finite element (FE) model of the residual limb capable of predicting the load distribution at the patient/prosthesis interface. The introduction of FE analysis to CAD/CAM system can provide quantitative feedback to the prosthetist recommending rectification in the CAD software.
METHODOLOGY--The geometry of the residual limb FE model was obtained using magnetic resonance imaging (MRI) techniques. The subject was imaged wearing the quadrilateral and ischial containment type sockets. Images of the residual limb without socket were also captured. Prior to construction of the FE model, the transverse MRI images were processed digitally in order to extract tissue boundaries. The images were smoothed using a median filter, and boundaries were extracted using mathematical morphology based on shape analysis and description. The processed images were then reconstructed in 3-D by stacking the transverse images together.
The material properties of the soft tissue were estimated based on a mechanical indentation test. Load actions at the hip joint on the amputated side were introduced to the FE model. These kinetic data were collected suing a VICON motion analysis system and Kistler force platforms.
The FE model was validated by comparing the predicted interface pressure with measured pressures. A total of 36 sites on the socket walls were measured using a transducer incorporating a strain-gauged load cell.
PROGRESS--Other means of obtaining the geometry of the residual limb for FE modelling are being investigated. This includes the use of ultrasound imaging and anthropometric scaling techniques.
RESULTS--High pressures at the proximal brim of the quadrilateral socket and a more evenly distributed pressures in the ischial containment socket were predicted. Similarities were observed with the measured pressures. However, most predicted pressures were lower than measured pressures.
[023] HOW PROSTHETIC KNEE CENTER POSITION AFFECTS TOE CLEARANCE AND THE HIP-TOE DISTANCE
Dudley S. Childress, PhD; Steven A. Gard, PhD
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email:
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: National Institute on Disability and Rehabilitation Research, U.S. Department of Education, Washington, DC 22202
PURPOSE--We have previously shown that 4-bar linkage knees are able to provide more toe clearance than single-axis knees during the swing phase of prosthetic walking. These results led us to consider how the position of the knee's center of rotation (CoR) affects the amount of toe clearance, and the hip-toe distance, during prosthetic swing. Four-bar knees are polycentric mechanisms: the position of the knee's CoR varies with the knee flexion angle. In all of the 4-bar knees that we investigated, the instant CoR moves anteriorly during the first 10-20° of knee flexion, and with additional knee flexion it moves posteriorly. We believe that this movement of the instant CoR is how 4-bar knees are able to provide more swing-phase toe clearance than a single-axis knee. Therefore, we performed computer simulations to determine how changing the anterior-posterior position of a single-axis knee center would affect toe clearance. We also investigated how different bench-top alignments in a transfemoral prosthesis can affect the hip-toe distance and toe-clearance.
METHODOLOGY--The kinematics of a transfemoral prosthesis having a single-axis knee were simulated with a computer. The computer program was originally developed for evaluating the kinematics of 4-bar linkage knees, but it was modified to permit investigation of the changes in toe clearance and the hip-toe distance as the anterior-posterior position of a single-axis knee was varied. Simulations were performed using this computer model having its axis (CoR) aligned posteriorly, and then anteriorly, with respect to its typical position in the German alignment recommended by Otto Bock. The computer model also allowed us to compare differences between the toe clearances and hip-toe distances produced by two different methods of aligning transfemoral prostheses: the German and the TKA (trochanter-knee-ankle) alignments.
RESULTS--We found that the anterior positioning of the single-axis knee decreased the hip-toe distance to a greater extent than when the knee was in the German alignment position, whereas the posterior alignment increased the hip-toe distance. This resulted in a greater toe clearance for the anterior aligned knee center, and less toe clearance for the posterior positioning, when compared with the typical knee alignment.
These results help explain how 4-bar linkage knees are able to provide more toe clearance than a single-axis knee. Because 4-bar knees are polycentric joints, their knee centers move from a relatively posterior position at full extension, compared with the single-axis knee's CoR, to a relative anterior position during the first 10-20° of rotation. Doing so allows the 4-bar knees to increase the toe clearance by shortening the hip-toe distance more so than in the single-axis knee having a stationary CoR. This gives the 4-bar knees greater stance-phase stability through posterior positioning of the knee center, and greater swing-phase toe clearance because of the anterior movement of the CoR as the knee flexes.
We also used the computer model of the single-axis knee to compare the amount of toe clearance obtained with the German alignment and the TKA alignment, finding that the German places the single-axis knee slightly more anterior in the prosthesis than the TKA, which increases toe clearance.
[024] A KNEE JOINT FOR USE IN A PEDIATRIC SWIMMING PROSTHESIS FOR PERSONS WITH TRANSFEMORAL AMPUTATION
Gary M. Stefanov, BASc, PEng; Stephen Naumann, PhD,
PEng; Daniel Cribbs, CP(C)
Institute of Biomedical Engineering, University of
Toronto, Toronto, Ontario, Canada; Rehabilitation
Engineering Department, Bloorview MacMillan Centre, Toronto,
ON Canada M4G 1R8
Sponsor: Natural Sciences and Engineering Research Council of Canada, Ottawa, ON Canada K1A 1H5
PURPOSE--There are currently few alternatives for swimming prostheses for the person with transfemoral amputation, since most conventional prostheses will not stand up to repeated usage in water and related such elements as sand, chlorine, and salt that accompany participation in such activities. The majority of swimming prostheses are rigid units with no knee flexion capability. Those that do offer knee flexion require complex, expensive, and time-consuming methods of manufacture. The focus of this project is to design and develop a simple, easily manufactured knee joint for use in a pediatric swimming prosthesis. The device will have the capability to lock during gait but will also provide knee flexion capability to allow the child to sit or play at floor level.
PROGRESS--Initially, work has focused on outlining the design requirements for the knee joint. Design loads have been investigated based on anthropometric data for the heights and weights of the children in the target population, as well as their expected level of activity. Detailed investigations of the environments in which the knee joint will be required to operate have been undertaken to identify the conditions which the materials and construction must withstand without functional degradation. Concurrently, studies into appropriate chemically resistive polymer materials and low cost manufacturing processes have begun in anticipation of the detailed design phase.
FUTURE PLANS--Upon selection of the materials and manufacturing process, the detailed design phase will begin to develop the joint unit based on the identified criteria. Subsequently, a prototype knee joint will be manufactured for bench testing, as well as for functional testing with an appropriate subject. Outcomes of bench tests, functional tests, and user feedback will identify appropriate design modifications required to maximize the utility of the swimming knee.
[025] THREE-DIMENSIONAL MODELLING OF THE TRANS-FEMORAL RESIDUAL LIMB USING ULTRASOUND
Tania S. Douglas, BScEng, MS; Peter V.S. Lee, BEng, PhD;
Stephan E. Solomonidis, BSc, ARCST, CEng, MIMechE; William
D. Spence, MSc
Bioengineering Unit, University of Strathclyde, Glasgow
G4 0NW, Scotland, UK; email:
tania.douglas@strath.ac.uk
Sponsor: None listed
PURPOSE--Imaging methods that provide both the external and internal geometry of the residual limb would enhance CAD/CAM socket design and biomechanical modeling of the limb. Magnetic Resonance Imaging (MRI) and X-Ray Computed Tomography (CT) may be used for this purpose, but have several disadvantages. Other researchers have demonstrated the use of ultrasound for obtaining the geometry of the transtibial residual limb. The overall objective of this project is to construct a 3-D model of the residual limb of persons with transfemoral amputation using ultrasound B-scans. The initial aim is to define skin and bone in transverse images of the residual limb. The limb will be scanned while fitted with a prosthetic socket.
METHODOLOGY--Ultrasound B-scans of the residual limb are taken while the limb is immersed in a waterbath to which the ultrasound transducer is attached. The transducer is rotated in a horizontal plane around the residual limb and B-scans are taken at regular intervals. Image processing techniques are used to reconstruct transverse images of the limb and to extract the skin and bone boundaries from them. The transducer is translated vertically with respect to the limb in order to obtain sets of B-scans along its length, for 3-D reconstruction using standard software.
PROGRESS--Preliminary ultrasound scans of a leg of pork have been taken in the manner described above, and transverse images have been reconstructed. The transverse images show the boundaries of skin and bone, and work is in progress on optimizing the reconstruction process to reduce the blurring effects of subject movement during scanning. A scanning set-up has been designed and built for scanning the unloaded transfemoral residual limb.
FUTURE PLANS--The geometrical information obtained using ultrasound will be compared to that obtained using MRI. The effect of different socket types on the geometry of the residual limb will be studied. An investigation into the geometrical changes of the limb in response to loading is being considered.
[026] FINITE ELEMENT AND GAIT ANALYSIS: TOOLS FOR PROSTHESIS DESIGN
Dudley S. Childress, PhD; Keith E. Oslakovic,
MS
Northwestern University Rehabilitation Engineering
Research Program, Chicago, IL 60611; email:
d-childress@nwu.edu;
Web: http://www.repoc.nwu.edu/
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A521-4DA)
PURPOSE--The purpose of this project is the development of a new Computer Aided Design (CAD) tool based on finite element (FE) analysis of lower limb prosthetic sockets and clinical gait analysis data. The goal is to quantify aspects of socket fit such as load support, limb stability, and socket suspension, and subsequently generate a socket shape which optimizes each of these characteristics for a given limb shape.
METHODOLOGY--FE models of successfully fitted transtibial sockets and limb systems will be created in order to determine which quantitative parameters are representative of adequate load support, stability, and suspension. By analyzing a large database of socket shapes, we will determine acceptable ranges of values for each of these parameters. After determination of the parameter ranges, an experimental evaluation of sockets designed according to these principles will be used to determine the validity of the parameters identified in the previous phase. This will result in a set of target values for design parameters. Subsequent to experimental verification, the newly determined design guidelines will be used as a criteria for an automated optimized shape generation procedure.
Two hundred digitized residual limbs and sockets from successful CAD/CAM fittings will be made into FE models and analyzed under a typical gait loading pattern. Many different quantitative values from the results will be investigated in order to assess which are similar across all of these successful sockets, and which are representative of the characteristics of support, stability, and suspension. Some potential parameters include interface stress, magnitude of socket rotations relative to the limb, and axial translation distance. The results of these models will form a database from which acceptable ranges for each of these parameters will be determined. Subsequent to parameter identification, experimental evaluation of the effect of design parameter variation will be carried out. Three persons with transtibial amputation will be fit with sockets designed for varying levels of stability, support, and suspension, by adjusting the values of the design parameter representative of each characteristic. The quality of these sockets will be evaluated by the subjects themselves and by experienced prosthetists, to determine whether the parameter variation improved or worsened the socket with respect to support, stability, or suspension. This short-term evaluation will determine the validity of the parameters chosen. After appropriate ranges of values for each of the relevant parameters are established and verified, design optimization techniques will be applied to allow computer generation of shapes satisfying each design criterion. Various optimization methods will be evaluated. The method that provides the quickest convergence properties will be used for the final socket shape generation procedure.
PROGRESS--Currently we are collecting the limb shapes and socket files and converting these files to meshes for analysis. Software has been generated to completely automate this process. The model design algorithm appears capable of generating acceptable models across the database of limbs and sockets. The computer analysis of these models is currently under way. Concurrent with these analyses, software is being developed to facilitate the presentation and collection of the relevant data from the analysis results.
FUTURE PLANS--What comes next depends upon the outcome of the work. If the procedure makes good sockets, we will implement it in CAD/CAM trials.
[027] CLINICAL TESTING OF THE ENHANCED VA-CYBERWARE BK PROSTHETICS OPTICAL DIGITIZER
Vern L. Houston, PhD, CPO; Carl P. Mason, MSBE; Kenneth
P. LaBlanc, BS, CPO; Aaron C. Beattie, BS; MaryAnne
Garbarini, MA, PT; Gangming Luo, PhD
VA Medical Center, New York, NY 10010
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A2068-RA)
PURPOSE--The objectives of this project are to update the design of and the software for the VA-Cyberware BK Prosthetics Optical Laser Digitizer and to test the digitizer clinically to establish the level of temporal efficiency, repeatability, and consistency it affords in characterization and measurement of spatial geometry and surface topography of the residual limb of persons with transtibial amputation, in comparison to current CAD plaster wrap cast/electromechanical digitization techniques.
METHODOLOGY--To achieve these objectives, the following research protocol has been established:
PROGRESS--The design of the optical digitizer was upgraded to incorporate more advanced optoelectromechanical components, and to make it more robust, durable, and to require less maintenance in a clinical setting. An initial enhanced prototype was procured for development of testing and calibration devices and procedures, and five clinical prototype units ordered. Work was begun on porting digitizer control, data acquisition, processing, measurement, analysis, and automated landmark detection, identification, and registration software for use with the new, enhanced digitizer prototype. Development of installation, training, and user manuals for the digitizer was also begun in preparation for the clinical trials.
FUTURE PLANS--Clinical field testing of the digitizer shall commence following procurement and laboratory testing and calibration of the five prototype units. The test data compiled in the field trials of the digitizer shall be analyzed and recommendations made for incorporation of any enhancements and design refinements found to be appropriate. Further application studies with the digitizer shall include the compilation of a quantitative prosthetics and orthotics patient database of residual limb/limb segment geometries, measurements, and histories for use in developing improved prosthetic socket and orthosis designs; the compilation of a database of patient limb segment contours, areas, and volumes for correlation with, and quantitative assessment of, the efficacy of medical treatments and rehabilitation regimens; and the utilization of the digitizer as an educational tool for direct visualization of prosthetics-orthotics principles and analysis of clinical practices.
[028] INTERFACE MECHANICS IN LOWER-LIMB PROSTHETICS: EXPERIMENTAL MEASUREMENTS AND FINITE ELEMENT MODELING
Joan E. Sanders, PhD; Santosh G. Zachariah, PhD; Joan M.
Greve, BSBE; Aaron B Baker; Cindy Clinton, CP
Departments of Bioengineering, Rehabilitation Medicine,
and Mechanical Engineering, University of Washington,
Seattle, WA 98195; email:
sanders@limbs.bioeng.washington.edu
Sponsor: National Institute of Child and Human Development
PURPOSE--The purpose of this research is to use both experimental and analytical techniques to investigate residual limb characteristics and prosthesis design features that strongly influence the distribution of mechanical stress at the residual limb-prosthetic socket interface. A quantitative understanding of how different features influence interface pressures and shear stresses will provide useful tools for enhancing prosthetic design and fitting.
METHODOLOGY--Persons with unilateral transtibial amputations using total contact patellar-tendon-bearing prostheses are participating in this study. Using custom-designed instrumentation, pressures and shear stresses are measured at 13 socket sites simultaneously, and forces and moments in the shank are also monitored. Residual limb shape before and after the session is measured using a custom-designed silhouette scanner, a device that images the residual limb in less than 1 s and has a resolution of approximately 0.5 mm. To date, studies investigating effects of changes in alignment, changes in walking speed, changes in prosthetic componentry, and changes in time of day have been conducted. In addition to the experimental measurements, analytical finite element (FE) models are also being pursued so as to allow sensitivity analysis evaluation of features that cannot be well assessed experimentally (e.g., interface materials). Custom-written code is being used in combination with a commercial software package.
PROGRESS--To date, 29 data collection sessions have been completed and analysis of the experimental data is near completion. The FE model allows for nonlinear tissue properties and frictional contact at the residual limb-prosthetic socket interface.
RESULTS--Results from the experimental studies on the subjects have demonstrated some interesting trends: interface shear stresses in the proximal socket region tend to be directed proximally toward the brim rather than distally toward the foot; anterior-distal shear stresses tend to be of the highest magnitude of all measurement sites, and shear stresses tend to be directed towards the apex of the socket at that location if the subject does not distal end-bear; changes in alignment, componentry, and walking speed tend to have less of an effect changing interface stress magnitudes, than do session-to-session differences. In the FE modeling effort, an automated hexahedral mesh generator was developed, an important tool to allow effective modeling of nonlinear materials and contact surfaces that undergo large displacements.
FUTURE PLANS/IMPLICATIONS--A next step will be to evaluate the nonlinear analytical models to determine if the results match experimental findings. We are particularly interested in investigating effects of changes in residual limb shape on interface stress distributions, using the thermal expansion capabilities of the program to model residual limb shape changes.
[029] POSTURAL ADJUSTMENTS DURING STANDING IN BELOW-KNEE AMPUTEES
Alexander S. Aruin, PhD; John J. Nicholas, MD; Mark L.
Latash, PhD
Rehabilitation Foundation Inc. Wheaton, IL, 60189;
Department of Physical Medicine and Rehabilitation, Rush
University, Chicago, IL 60612; Pennsylvania State
University, PA 16802; email: aruin@rfi.org
Sponsor: The Rush University, Chicago, IL, 60612
PURPOSE--Postural control of persons with a limb amputation presents a very interesting model for the investigation of a central adaptation to the transformation of peripheral motor and sensory conditions. Both components of postural adjustments, compensatory and anticipatory are expected to be changed in such persons because of both mechanical and secondary, neurological reasons. We studied the role of adaptive changes within the central nervous system in anticipatory postural adjustments seen in persons with unilateral transtibial amputation.
METHODOLOGY--Six subjects with left transtibial amputation (TTA) and six age- and gender-matched controls participated in the study. The subjects stood on a biomechanical platform and performed fast bilateral shoulder flexions and extensions, load release (2 lb) from a rigid bar held in extended arms, or load catching (2 lb) on the bar described above. The EMG activity of 10 postural leg and trunk muscles from both the amputated and intact sides of the body and from anterior and posterior deltoid muscles; ground reaction forces and moments of forces; angles of the ankle, knee, and hip joints; and acceleration of the arms or bar were recorded. Integral EMG measures, horizontal displacements of the center of pressure (CP), and leg angle displacements were used to characterize the anticipatory adjustments.
RESULTS--Typically, changes in the activity of the postural muscles were observed from prior to the first visible changes in the activity of the prime mover to load release, or to load impact, in both groups of subjects. Generally, an increase in the activity was seen in muscles whose action opposed the expected postural perturbation. However, a clear asymmetry was seen in the patterns of EMG activity and mechanical variables recorded in TTA subjects from the intact and amputated sides of the body that was not seen in the control subjects. Anticipatory activity was seen in left and right erector spinae muscles. However, an anticipatory increase in the background activity of biceps femoris was seen only on the intact side, which stimulated an anticipatory extension of the right knee only. The subsequent changes in biomechanics of the body led to a rotation torque in the transverse plane at the level of the pelvis, exemplified by the anticipatory lateral displacement of CP and the horizontal component of ground reaction force. There are also compensatory reactions to balance perturbations induced by the movement 70-80 msec after movement initiation.
The results show that changes in postural adjustment of TTA exist not only in compensatory corrections, but also in anticipatory adjustments and may be considered adaptive in reacquiring balance skills after amputation. Rehabilitation approaches would benefit from understanding and taking advantage of the adaptive changes within the central nervous system.
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Last revised Fri 04/30/1999