[1] AN ADDITIVE FABRICATION TECHNIQUE FOR THE CAM OF PROSTHETIC SOCKETS
Joshua S. (Rovick) Rolock, PhD; Dudley S. Childress,
PhD; Kerice Tucker
VA Lakeside Medical Center, Chicago, IL 60611;
Prosthetics Research Laboratory of Northwestern University
Medical School
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A711-2DA)
PURPOSE--This project was intended to develop a device and methodology for the automated production of sockets for artificial limbs. The device is to be used in conjunction with the computer-aided design (CAD) of sockets and represents a means for computer-aided manufacturing (CAM) of such sockets. The technology used in this application is inspired by recent advances in industrial prototyping in which additive fabrication principles are used to construct prototypes designed with CAD. Sockets for artificial limbs bear resemblance to prototypes in that they are one-of-a-kind geometric objects intended to be fabricated in single-unit quantities.
METHODOLOGY--The methodology is divided into three parts: 1) the method of operation of the socket fabricating device; 2) the method of preclinical evaluation of fabrication results; and 3) the method of clinical evaluation of fabricated sockets.
The device uses a technique of plastic deposition to fabricate sockets. Plastic material is melted and extruded through a shape-forming die to produce a a 5 mm wide ribbon of melted plastic 0.75 mm high. 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.
Tensile specimens are cut from pseudo-sockets fabricated using the device with regular, geometric shapes, which allow the specimens to conform to ASTM standards. These specimens are tested for ultimate tensile strength and fatigue life, and compared to similar values obtained from more traditional fabrication techniques and from factory-delivered extruded plate.
Clinical trials involve the fitting of sockets to persons with amputation and evaluating their mechanical performance over time. Participants in the study are provided with limbs incorporating sockets made using the device and are asked to use those limbs in unrestricted activity. Periodic follow-ups are made in which the sockets are evaluated for signs of mechanical degradation.
PROGRESS--The device is able to fabricate sockets during unattended operation. A 23-cm (9-in) long transtibial socket requires the deposition of 300 layers and takes between 50 and 60 min. Tensile and fatigue tests have been completed for two materials; polypropylene homopolymer and polypropylene copolymer. Clinical tests are underway and on-going. Methods of PE-LITE® liner production are being evaluated which utilize a technique for blow-molding. Additional materials are being investigated for future use.
RESULTS--Tensile and fatigue tests have indicated that polypropylene homopolymer is suitable for socket fabrication using the device and for unrestricted use of the fabricated sockets.
To date, a single subject has been using a transtibial socket made with the device for a period of 20 months, and two additional subjects have been using sockets for 3 months each. The first socket was recently evaluated and shows no visual signs of mechanical degradation. The active subject with transtibial amputation has used the socket exclusively for the entire time without restriction in activity.
Attempts have been made to produce PE-LITE liners for sockets fabricated using the device. A blow-molding technique shows promise for this application as well as for fabrication of replacement liners for any socket. A PE-LITE preform is heated in an oven, inserted into the socket, and pressure-formed to the shape of the socket by expansion of an internal bladder. Heat and pressure parameters are being determined for satisfactory results.
FUTURE PLANS--We plan to construct three prototype fabricating devices for placement and evaluation in a clinical setting. The evaluation phase will be used to recommend modifications and enhancements to the device prior to commercial development and marketing.
[2] DOD SOFTWARE AND EQUIPMENT DEVELOPMENT FOR IMPROVED COMPUTER-AIDED PROSTHETIC SOCKET DESIGN
Vern L. Houston, PhD, CPO; Jennifer J. Whitestone, BSBE;
Carl P. Mason, MSBE; Edward J. Lorenze, MD; Michael W.
Vannier, MD; Kenneth P. LaBlanc, BS, CPO; MaryAnne
Garbarini, MA, PT
VA Medical Center, New York, NY, 10010
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A795-DA)
PURPOSE--The objective of this project is to develop equipment and software, enabling effective and efficient computer-aided design and manufacture (CAD/CAM) of more intimately fitting, comfortable, and functional prosthetic sockets for US veterans with transtibial amputation.
METHODOLOGY--To achieve this objective, the following research protocol has been established:
PROGRESS--A "P-Scan" transducer with 1360 force-varying-resistive elements has been designed and fabricated for measurement of normal and gradient shear socket/residual limb interface stresses. A pneumatic, uniform force, servo-actuated test fixture has been designed and constructed, and associated software written, for testing, equilibration, and calibration of P-Scan transducers. A position controlled, stepper-motor-driven test fixture, with a linear servo-actuated, strain-gauge-instrumented force probe has also been designed and constructed, for precise measurement and testing of the output response of P-Scan transducer elements and element subarrays. Comprehensive laboratory testing of the P-Scan transducer measurement system is being conducted with these test fixtures. Software for analysis and visualization of P-Scan measurement data is also being developed. In addition, clinical testing of the P-Scan system with two subjects with transtibial amputation and a nonimpaired control subject has been performed.
A neural network algorithm and software for automated detection of preselected anatomical landmarks from optical digitizer camera output intensity measurements has been developed. The algorithm has been successfully tested with data from scans of 20 subjects. A database of the relative spatial locations of the 18 fiduciary landmarks most commonly utilized by prosthetists in PTB and PTS socket designs has been compiled from a sample of 57 persons with transtibial amputation. A maximum likelihood identification and registration algorithm and software have also been developed for identification and registration of the detected fiduciary landmarks in the optical digitizer measurements.
Laboratory tests have been conducted with the NY VA Medical Center Radiology and Cardiology Services' clinical diagnostic ultrasound systems. A prototype stepper-motor-driven scanning fixture has been fabricated, and numerous scans of the residual limbs of four subjects with transtibial amputation and the lower limb segments of five nonimpaired controls have been performed. From these tests, factors adversely affecting the signal-to-noise ratio, resolution, accuracy, and precision of the received interrogating acoustic signal have been identified. Potential remedies for these problems have been investigated. Unfortunately, many of the factors have been found to be conflicting, so only limited success has been achieved.
A prototype, servo-actuated, strain-gauge-instrumented, indentor has been designed and constructed for measurement of the mechanical properties of residual limb tissues. Tests measuring the uniaxial, compressive, mechanical creep response of residual limb/limb segment tissues of 15 subjects have been performed. In addition, multisite tests, mapping the mechanical response at nine locations over the residual limbs/limb segments of two subjects have been performed. A second order, nonlinear Odgen model has been fit to the steady state, elastic response measurement data, and a second order generalized nonlinear Kelvin model has been used to characterize the transient, viscoelastic component of the measurement data. The resulting "bulk soft tissue" models have been used in a nonlinear finite element analysis to predict residual limb tissue stress and strain distributions associated with various prosthetic socket modifications and design.
FUTURE PLANS--Refinement and enhancement of the project P-Scan transducer and stress measurement system shall continue. Development of new, improved, biomechanically based CAD socket modifications and designs is planned, utilizing the knowledge obtained in the tissue mechanical property measurement and modeling studies, and in the static and dynamic loading studies conducted in the project. Firmware for CAD system utilization of quantitative feedback of socket/residual limb interface stresses resulting from given socket design geometries and materials shall be developed.
[3] DIRECT MUSCLE ATTACHMENT: MULTIFUNCTIONAL CONTROL OF HANDS AND ARMS
Dudley S. Childress, PhD; Edward C. Grahn; Craig W.
Heckathorne, MS; Jack Uellendahl, CPO; Richard F.
ff. Weir, PhD; Yeongchi Wu, MD
Northwestern University, Prosthetics Research
Laboratory, Chicago, IL 60611;
email: d-childress@nwu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A306-4DA)
PURPOSE--To achieve significant improvement in the function of electric-powered upper-limb prostheses, we feel it is necessary to develop better control interfaces with inherent sensory feedback. Small tunnel cineplasties, or other surgical procedures which externalize the force and excursion of the muscle, could potentially provide this superior control. Connecting the muscle to a prosthetic component via a controller that embodies the concept of extended physiologic proprioception (epp) enables the physiological sensory feedback inherent in the skin, muscle, and other tissues of the cineplasty to inform the user of the state of the prosthesis. It is possible to envision multiple miniature tunnel cineplasties, each with an epp controller, providing independent multifinger control of hand prostheses. At higher levels small pectoral or deltoid tunnel cineplasties could augment existing control sources to improve control of multifunctional total arm prostheses. The goal of this research was to quantify the control capabilities of subjects with pre-existing tunnel cineplasties and to develop prostheses to test these ideas.
PROGRESS--All the control quantification experiments have been completed. Three subjects with biceps tunnel cineplasties and a single subject with two forearm tendon exteriorization cineplasties took part in these experiments. Subjects performed pursuit tracking experiments to quantify the dynamic control capabilities of the cineplasties, which capability was compared with other control methods: glenohumeral flexion with a conventional above elbow control harness; and again using the subject's contralateral elbow. Blind positioning experiments were performed to quantify static positioning capability in comparison to other control methods. Finally, the characteristics of the tunnel cineplasty of each subject were recorded for isometric and isotonic muscle contractions. We have also developed a prototype epp electric hand prosthesis for a subject with the exteriorized tendons. Control cables from the tendon tunnels are linked to the hand mechanism. Contraction of the flexor muscle closes the hand and contraction of the extensor muscle opens it.
RESULTS--Our results for the pursuit tracking experiments show that the dynamic performance of the muscle tunnel is statistically similar to that of the conventional control harness. Tracking performance with the intact contralateral elbow was superior to both. The blind positioning experiments showed similar results. The mechanical properties of the cineplastized muscle of each subject were obtained. The measurements included the isometric length-tension curve and the isotonic load-excursion and force-velocity relationships. These relationships are valuable for prosthesis design and give an indication of the condition of the cinplastized muscle.
IMPLICATIONS--Previous work done in our laboratory showed the superiority of position control over velocity control in pursuit tracking tasks. By inference this implies that control by tunnel cineplasty should be superior to velocity-control techniques. In addition, tunnel cineplasty offers a number of advantages over control conventional harness arrangements. Tunnel cineplasties in conjunction with electronic epp controllers may provide both force and excursion amplification while retaining a physiologically appropriate proprioceptive sense of position, velocity, and force; eliminate the need for proximal harnessing and consequent encumbrance of an otherwise intact physiological joint for certain prosthetic configurations; provide an additional control source to supplement other, more conventional control sources in the fitting of total arm prostheses; and make possible the direct control of individual fingers in prostheses for persons with wrist disarticulation or long transradial amputations
FUTURE PLANS--The next phase of this project involves the development of a new microprocessor-based epp controller that can be fine tuned to better match the characteristics of the controlling joint or muscle/tendon. These new controllers will then be used by a number of upper-limb amputees with pre-existing cineplasties to control test prostheses by way of direct muscle attachment.
[4] UPPER LIMB AMPUTEE SERVICES: THE VA APPROACH AS A MODEL SERVICE SYSTEM
Trilok N. Monga, MD; William H. Donovan, MD; Diane J.
Atkins, OTR; Mara D. Novy, BSE
Houston VA Medical Center, Houston, Texas 77030; Amputee
Program, The Institute for Rehabilitation and Research, 1333
Moursund, 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 standards have been developed to address the rehabilitative and ongoing support needs of persons with upper limb loss. The lack of such standards for them may be contributing to less than optimal outcomes for these 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 such persons, 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. At present, there is no objective, systematic approach to documenting the strengths and weaknesses of the VA's service program, nor for determining its appropriateness as a model that might be adopted in meeting the needs of other populations currently unserved by the VA.
METHODOLOGY--This project is designed to employ an expert approach, similar to the national consensus approach employed by the Center for Accreditation of Rehabilitation Facilities (CARF), to develop and test quality of care standards, which approach can then be used to assess the efficacy of replicating the VA's service approach in other settings. The Amputee Services Assessment Inventory (ASAI) will be developed and will include quality-of-care standards and indicators as well as a protocol for self-assessment. Also, this project is designed to increase the representation of VA-served patients in the National Upper Limb Amputee Database (NULAD) developed by The Institute for Rehabilitation and Research (TIRR).
PROGRESS--The six member ASAI Expert Advisory Board has met and developed a preliminary, 25-page questionaire to be used for pilot testing at the Houston VA Medical Center and at TIRR.
FUTURE PLANS--The preliminary ASAI will be modified as needed and tested at four additional VA, and four additional private, rehabilitation facilities. Site visits will be made at each of these facilities. The ASAI will ultimately be a tool for rehabilitation facilities to use in ongoing monitoring and improvement of services. An additional goal is to increase the representation in the NULAD of VA-served individuals, whose data will be compared to that of those served by other systems, to determine whether there are special needs or service issues in the VA population.
[5] 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, 2628 CD Delft, The
Netherlands; email: a.a.m.sol@wbmt.tudelft.nl
Sponsor: Delft University of Technology; the Phoenix Foundation; the State Department of Social Affairs
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 contour 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, can be placed out of sight in the interior of the prehensor. A rather simple mechanism was designed and constructed that converts the actions of the control cable into movements of the rotating finger of the prehensor. Due to the construction of the mechanism the pinching force is almost a constant throughout the opening width. All mechanical parts are placed into a frame. Integrated into the frame is a light weight friction wrist prosthesis. Also the frame is the pillar to the cosmetic cover made out of flexible polyurethane resin. This way several unique features were obtained:
RESULTS--In collaboration with our clinical partners of the rehabilitation centers De Hoogstraat en Sint Maartenskliniek, the new cosmetic prosthetic prehensor was clinically tested by 10 children. They all highly appreciate their new device. It has not caused any negative reactions or strange associations. The children are delighted by the bright colored appearance of the prehensor. Because of the smooth outline of the prehensor and the integration of the control cable, wear of clothing is reduced considerably. The mechanism of the prehensor proved to be reliable but is rather cumbersome to assemble.
FUTURE PLANS--In order to facilitate easy assembly of the prehensor, a new mechanism will be designed and constructed. Once this mechanism has proven to be reliable as well, the cosmetic prosthetic prehensor will be commercialized.
[6] LIGHTER WEIGHT ELECTRIC PREHENSOR
Dudley S. Childress, PhD; Edward C. Grahn; Craig W.
Heckathorne
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--One of the most effective configurations for a transhumeral prosthesis is the hybrid prosthesis, which combines a cable-actuated body-powered elbow and an electric-powered prehension device. The effectiveness of this configuration is attributed to two principal characteristics. First, the cable linking the elbow to the movement of the physiological shoulder provides control of the elbow's position, speed, and acceleration as well as perception of those quantities through the shoulder's proprioception. Second, the electric-powered prehension device produces grip forces three to four times greater than is possible with a cable-actuated split hook and allows maintenance of low forces for delicate handling without physiological effort to sustain the gripping force.
In spite of its advantages, the hybrid configuration is typically not appropriate for persons with short residual limbs, due to the weight of the electric prehension device. Flexing the mechanical elbow against the weight of the prehensor and forearm requires high operating forces generally not achievable by these persons. Furthermore, the prehensor's weight and its distal concentration of mass can significantly reduce the range of space in which the user can position the entire prosthesis using movement of the shoulder joint.
Although it is possible to utilize a mechanical elbow with a mechanism to counter-balance the weight of the electric prehensor and forearm or to use an electric elbow, and thus greatly reduce the operating forces associated with flexing the elbow, these configurations increase the overall weight of the prosthesis. Any increase in total prosthesis weight generally further compromises the range of space in which the user can position the prosthesis.
As an alternative, we have proposed to develop a lighter electric prehensor for use by adults. By reducing the weight of the prehensor, we believe it will be possible to fit the hybrid configuration to a broader range of persons with upper-limb amputations, especially persons with short transhumeral limbs, and without significantly compromising their ability to position the prosthesis in space.
METHODOLOGY--The Lighter-weight Electric Prehensor (LEP) is based on the design of our laboratory's Intermediate-size Electric Prehensor (ISEP), which, in turn, was derived from the design of our Synergetic Prehensor. The ISEP was intended for older children and adolescents. It had lower performance characteristics in comparison to the Synergetic Prehensor, so as to achieve a smaller package and simpler mechanical arrangement.
To develop the Lighter-weight Electric Prehensor for adults, the hook-like fingers of the ISEP will be converted from the #10 (child) to the #5 (adult) size. The gear drive will be modified to produce a maximum grip force of at least 44 N (10 lb-force) at the tips of the longer hook fingers. Speed of finger movement, which is approximately 40°/s with a 6-volt battery (65°/s with a 9.6-volt transistor type battery), may have to be reduced to achieve the specified grip force while maintaining low weight. Clinical observations suggest that slower finger closing speed may be an acceptable tradeoff for higher grip force.
With the #5-size hook fingers, we expect the LEP to weigh 230 gm (0.5 lb), two-thirds the weight of the Steeper Powered Gripper or Centri Ultralite Hand.
PROGRESS--Testing of our prototype units revealed that the commercial backlock mechanism, which prevents the fingers from being back-driven during gripping, was less efficient than had been estimated. As a consequence, the prototypes operated at considerably reduced performance from that predicted by our calculations. By changing the motor and gear ratio, we were able to partially compensate for the inefficiency of the backlock and achieve a maximum grip force of 32 N (7.2 lb-force) with a 6-volt battery or 46 N (10.4 lb-force) with a 9-volt battery. The speed of finger movement is 33.3°/s with a 6-volt battery (49.3°/s with a 9-volt battery).
Although these values are less than we had specified, further increase in force and speed would require significant weight-adding changes to the design. Given that the measured prehension force is still at least twice what can generally be achieved with a body-powered split hook at the transhumeral amputation level, we believe (pending user evaluation) that it is more important to keep the weight reduced rather than increase the performance through a new, heavier design.
FUTURE PLANS--We are preparing for a field evaluation of the current design. The evaluation period will be 3 months. The next phase of the project will depend on the outcome of this first evaluation.
[7] CLINICAL COLLABORATION TO IMPROVE HIGHER-LEVEL UPPER-LIMB PROSTHETIC FITTINGS
Dudley S. Childress, PhD; Craig W. Heckathorne; Jack E.
Uellendahl, CPO; Edward C. Grahn
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, 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 persons with amputations. 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 amputations. 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-powered and electric-powered components). In general, the dominant prosthesis of this bilateral pair is configured with all mechanical, cable-actuated components while the nondominant side incorporates either all electric or hybrid componentry.
PROGRESS--During the past year, we have been assessing the outcomes of these fittings and now have a high degree of confidence in this approach. We are especially convinced of the utility of the all mechanical, cable-actuated four-function control system used on the dominant side at the transhumeral and shoulder disarticulation levels. 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 single control cable and associated harness provide close coupling of the user and the prosthesis. Body movements and forces are transferred directly to the prosthetic components and the response of the components (their position, velocity, acceleration, and forces acting on them) are perceived through the intact proprioception of the user. We 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.
FUTURE PLANS--During the next year we will complete a manual for prosthetists describing the design and implementation of the four-function control system. In addition, we will continue our cooperative efforts to identify unresolved clinical problems.
[8] IMPROVING PROSTHETIC PREHENSION
Lawrence E. Carlson, DEng
Department of Mechanical Engineering, University of
Colorado, Boulder, CO 80309; e-mail:
lawrence.carlson@colorado.edu
Sponsor: National Institute on Disability and Rehabilitation Research, the National Institutes of Health
PURPOSE--The goal of this research is to improve both body-powered and externally powered prehensors. Projects include:
Vector Prehensor: a voluntary opening prehensor with grip force that can be easily adjusted to the demands of the task, improving efficiency of grasping and reducing mechanical energy demands.
Variable Mechanical Advantage Prehensor: a voluntary-closing device with enhanced gripping efficiency (i.e., rapid sizing with cable excursion coupled with large grip force generation).
General Prehension Research: improvements to prehension applicable to any type of prehensor, including anthropomorphic fingers with nonlinearly compliant structure and variable hardness finger materials.
Quantification of Prehensor Performance: methods to quantify grasping performance in the laboratory, including the degree of force and torque that can be effectively applied.
PROGRESS--A comprehensive laboratory testing program was undertaken to quantify the mechanical performance of typical prosthetic cable and housing systems. Four different cable materials and two different housing liners were tested over a range of bend angles and weights in order to deduce the determinants of prosthetic efficiency. It was found that prosthetic cable/housing systems follow the classical Coulomb friction model and the efficiency is therefore a function of only coefficient of friction and angle of bend. This allows practitioners in the field to estimate mechanical efficiency for any body-powered prosthetic system with a simple calculation.
The Vector Prehensors reported earlier are functional prototypes that have performed well in limited testing on persons with upper-limb amputation. However, we have not been able to produce the elastic power bands that provide the adjustable grip force with long enough fatigue lives to be practical for commercial use.
Finite-element modeling of the elastic bands, using ABAQUS and Patran3, is underway to analyze the bands that are failing and to design suitable bands. Preliminary results are encouraging. New band geometries have been modeled that have significantly lower stresses at comparable levels of load and deflection compared to the experimental bands that have inadequate fatigue performance. Presumably, lower stress will result in improved fatigue life.
FUTURE PLANS--We are currently completing the modeling of a variety of candidate bands. Fabrication of test power bands is underway. When we receive them, we will subject them to static and fatigue testing to determine if their actual performance matches that predicted by finite element modeling.
[9] 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 on Disability and Rehabilitation Research, U.S. Department of Education, Washington, DC 20202
PURPOSE--The goal of this research is to develop an improved body-powered hand for toddlers 1 to 4 years of age. Primary goals are for an affordable hand of acceptable cosmesis to provide useful grasp for children in their play activities, while requiring minimal harness force and excursion.
METHODOLOGY--We shall explore several hand design strategies and methods of harnessing the child's energies, addressing the needs of the toddlers and the desires of their parents. Prototypes will be field-tested and evaluated for mechanical performance, reliability, and cosmetic acceptability. Designs will evolve based on this feedback.
PROGRESS--Beginning November 1995, staff have met with
researchers and manufacturers having expertise in hand
design and use, and also reviewed studies on new materials
and children's prehensors.
Exploring Designs: Initially, a wide spectrum of
approaches is under investigation. Models, sometimes as
modifications of commercial units, have been built to embody
various principles and features, including:
PRELIMINARY RESULTS--Observation of toddlers suggests the need for focus on achieving stable spherical and cylindrical grasp patterns, with some fine-tip prehension. Grasping tests confirm the effectiveness of various combinations of grasp geometries, foams, and skins. Modifications of a CAPP II gripper for bidirectional control reduces input cable excursion requirement by 50 percent while doubling the force output. A cable-free device provides easy object insertion for grasp, while a hand equipped with nonbinding clutch mechanism provides secure capture.
FUTURE PLANS--Continued field testing and design iteration are needed to both refine and investigate new strategies. A test will be developed to evaluate the grasp characteristics of different combinations of foam and skin. Further collaboration with industrial partners will be sought.
[10] DEVELOPMENT OF A MULTIFUNCTION MYOELECTRIC CONTROL SYSTEM
B. Hudgins, PhD
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, New Brunswick, Canada E3B 5A3 email:
hudgins@unb.ca
Sponsor: Whitaker Foundation, Hugh Steeper Limited, and Natural Sciences and Engineering Research Council of Canada
PURPOSE--The purpose of this project is to develop a myoelectric control system that is easy to operate yet provides control of many independent prosthetic limb functions.
Myoelectric prostheses are well accepted by persons with transradial amputations but less accepted by those with higher level ones. The primary limitation at present lies in the control system. Although these systems have been successful for single device control (hand or elbow), the extension to the control of more than one device (either simultaneously or sequentially) has been difficult. It is the control systems that now limits the performance and, at times, the acceptance of the prosthetic fitting. For the person with transhumeral or higher amputation and especially for those with bilateral amputations, the need for improved control systems for multifunction prostheses is critical.
METHODOLOGY--The project was divided into two stages. The first, undertaken primarily during the initial 24 months of the project, 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.
PROGRESS--The control scheme developed during this phase of the project uses information collected from the patient to train a pattern classifier in the control system to recognize his or her specific contraction patterns. The classifier uses features extracted from the first 200 ms of myoelectric activity following the initiation of a contraction to determine intent, then matches this feature set with the features 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 feed forward 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 which 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 an approximate size of 1.5×2.5×0.5 in (3.80×6.35×1.27 cm) and can be built into the prosthetic arm. The device operates on standard 6 volt 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. This activity will be the focus for the remainder of the grant.
The results of this research will provide valuable guidance to designers of pattern-based myoelectric control systems and to the clinical staff who fit these systems. The new control system will yield a prosthetic limb that is more functional and easier to control.
[11] ELECTRIC HUMERAL ROTATOR
Dudley S. Childress, PhD; Edward C. Grahn; Craig W.
Heckathorne; Kenneth G. Kalan
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--It is recognized in prosthetics practice that humeral rotation (inward and outward rotation of the forearm along the axis of the humeral section) is generally helpful to the person with a unilateral transhumeral amputation and essential to the person with bilateral amputations. Currently, this motion is achieved using a rotating friction joint proximal to the elbow mechanism. Positioning of the joint is done manually if an intact limb is present, or by pushing the forearm of the prosthesis against objects in the environment. Our goal is to develop an electric-powered humeral rotator so that the forearm and prehensor of a transhumeral or shoulder disarticulation prosthesis can be positioned independently by the user. Positioning would be possible at any elbow angle, during dynamic activities, and without pushing or pulling the forearm against external objects. The rotator would also enable persons with high-level bilateral amputations to move their forearms inward or outward simultaneously to bring the prehensors together or to separate them. This facility would make bimanual manipulations more practical and easier to perform.
METHODOLOGY--The rotator design utilizes multiple miniature, permanent magnet, DC gearmotors to provide active powered rotation and powered locking. Two gearmotors driving (in parallel) an internal gear attached to the proximal plate of an elbow component provide torque for positioning the forearm. A third gearmotor drives a single-lead worm that mates with a worm gear attached to the shaft of one of the drive motors. When humeral rotation stops, this third motor and geartrain provide positive locking against further motion. The design parameters are a no-load output speed of 1.2 radian per second and a stall torque of 2.3 N-m (20 pound-inches). A high-friction coupling provides a safety "breakaway," allowing the forearm to rotate if external forces, such as from falling on the prosthesis, are greater than 8.1 N-m (72 pound-inches).
The rotator design is intended for use with either body-powered or electric-powered elbows. It can be accommodated in prostheses for short transhumeral or higher-level amputations and can be used unilaterally or bilaterally.
PROGRESS--Our tests of the first prototype have produced conflicting results related to the action of the locking motor when the drive motors are positioning the rotator. During positioning, the locking motor is powered so that the worm and worm gear are able to turn and free the drive mechanism. The voltage to the locking motor is adjusted so that it is neither turning too fast, leading the drive motors and pushing the rotator mechanism, nor turning too slowly, lagging the drive motors and retarding the rotation. The parameters for this adjustment have been different under different test conditions. We are re-examining our test procedures to determine the source of the difference. Possible causes include variance in motor parameters or mechanical inefficiencies that may have developed over the course of testing.
FUTURE PLANS--Once the conflict in the prototype's performance has been resolved, we will design and build a second, lighter prototype for field evaluation.
[12] MECHANICAL HUMERAL ROTATOR LOCKING MECHANISM
Dudley S. Childress, PhD; Robin W. McCall
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--The purpose of this project is to develop a mechanical humeral rotator locking mechanism for persons with transhumeral amputations. The device will allow the user to rotate the forearm section freely about the humeral axis when it is unlocked. This positioning is currently provided by a friction turntable that resists rotation with a preset constant friction. The unit can be locked in any position.
METHODOLOGY--The design goals for this project were determined by studying other types of humeral rotators and considering the needs and abilities of persons with bilateral transhumeral amputation. It was decided that the device should have an infinite number of locking positions and to hold against a minimum torque of 72 lbf-in, which is twice the recommended friction setting for a standard turntable. A two-position actuator was chosen over a momentary actuator because it would be easier for the user to operate. Cable travel of less than 0.5 inches with an actuating force of less than 7.2 lbf was a goal based on the capabilities of Northwestern University's Modular Electromechanical Lock Actuator. By meeting this goal, the device could be actuated by the electromechanical actuator or any manual method.
Various designs were evaluated with respect to these mechanical specifications and user needs. A multiple disk brake design was selected as the prototype locking mechanism. It was judged to resist the target torque with low actuating force, with a low height profile. This kind of design would be fairly easy to fabricate using standard machining methods. A ratcheted face cam was selected as the actuator. This design was easily fabricated and had a low profile.
PROGRESS--Several different disk materials have been tested. A prototype of the humeral rotator has been fabricated that meets the actuating force and cable excursion goals.
RESULTS--The prototype is capable of locking against a torque of approximately 78 lbf-in with an actuating force of 6.8 lbf at an excursion of 0.43 in.
FUTURE PLANS--An adapter plate will be made to allow this device to be mounted to the Hosmer E400 body-powered elbow. The device will be tested by an amputee user.
[13] VOLUNTARY CLOSING HAND PROSTHESIS
Just L. Herder, MSc; John P. Kuntz, PhD; Jan C Cool,
MSc; Dick H. Plettenburg, MSc.
WILMER group, Department of Mechanical Engineering,
Delft University of Technology, 2628 CD Delft, The
Netherlands; email: j.l.herder@wbmt.tudelft.nl
Sponsor: Delft University of Technology
PURPOSE--The objective of this project is the design of a useful body-powered hand prosthesis. This implies that not only motoric function will be regarded, but cosmesis, wearing comfort, and ease of operation as well. The project focuses on a device for persons with unilateral transradial amputation.
METHODOLOGY--In voluntary closing devices, operating force corresponds to pinching. To make full use of the feedback potential of this working principle, the operating mechanisms should transfer the actual pinching force to the operating member as purely as possible. Therefore, friction should be absent, and the counteraction by the cosmetic covering should be 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--The general rules of fist in glove characteristics prove to be of much practical value. Counteraction is considerably reduced, which facilitates the compensation of glove forces. A theory on the realization of exact solutions for simplified situations has been formulated and approximation methods for practical circumstances are under development. Several prototypes of prosthesis mechanisms incorporating RLMs with significantly improved efficiency have been made.
Normal operating forces seem to be in the range of high upper arm sensitivity. The mechanical advantage of the prosthesis operating mechanism is therefore chosen to be unity as a starting point.
FUTURE PLANS--The results of the projects are to be combined into a prototype of a voluntary closing hand prosthesis. With this prototype the principal hypothesis will be evaluated: are voluntary closing hand prostheses indeed better controllable than voluntary opening devices?
[14] DEVELOPMENT OF THE OMNI PASSIVE WRIST UNIT
Morris Milner, PhD, PEng, CCE; Stephen Naumann, PhD,
PEng; Ihsan Al-Temen, PEng; Zigmond Chong; Isaac Kurtz,
MHSc, PEng; George McMillan; Martin Mifsud, DipE, EngT; John
Bishop, EEngT; Sandra Ramdial, DipO&P, CP(C)
Bloorview MacMillan Centre, Toronto, ON, Canada M4G 1R8;
Variety Ability Systems Incorporated (VASI), Scarborough,
Ontario, Canada, M1N 2G2; email:
ortcmm@oise.utoronto.ca
Sponsor: Variety--The Children's Charity
PURPOSE--It is obvious that hand function would be improved markedly by the introduction of a wrist unit that could provide passive flexion and extension, in addition to its current feature of pronation and supination. It would also be desirable to have the resistance of the above movements readily adjustable to suit individual user needs.
PROGRESS--A compact design was completed to meet the above requirements. The new arrangement can provide flexion and extension totalling 60° in all directions. A preproduction unit was fitted to a client and assessed by the clinical service team. The feedback from the clinicians and user was positive. The product was released to VASI for production and is now available commercially. While the OMNI wrist prototype was shown at a conference in Europe, it was suggested that we integrate it with the current VASI powered wrist unit. This combination will offer more function, in particular to the person with high level amputation. In response to this, we designed and built three prototypes of this configuration to prove the arrangement. This spin-off product is now available from VASI.
[15] VASI 2-6 PROSTHETIC HAND ENHANCEMENTS: COSMETICS AND FUNCTION
Morris Milner, PhD, PEng, CCE; Stephen Naumann, PhD,
PEng; Ihsan Al-Temen, PEng; Zigmond Chong; Isaac Kurtz,
MHSc, PEng; George McMillan; Martin Mifsud, DipE, EngT; John
Bishop, EEngT; Sandra Ramdial, DipO&P, CP(C)
Bloorview MacMillan Centre, Toronto, Ontario, Canada M4G
1R8; Variety Ability Systems Incorporated (VASI),
Scarborough, Ontario, Canada, M1N 2G2; email:
ortcmm@oise.utoronto.ca
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) by acting on the following three recommendations: a) reduce the bulk in the palm area, b) make the ring finger and baby finger of the glove move with the other fingers when the hand closes, and c) incorporate pliable tips to the fingers and thumb.
PROGRESS--In response to these recommendations, we have made and are making the appropriate modifications. With the introduction of a smaller electronics package, we were able to redesign the hand cover and made it thinner in the palm area, hence more cosmetically appealing. The fingers and thumb were redesigned to improve the shape and orientation of the thumb. A wire type ring finger and baby finger were designed to couple to the middle finger. Movement of the smaller fingers are now driven by the middle finger. These changes were prototyped and evaluated by clinical team members. Concepts incorporating pliable material into the inferior surface of the fingers has begun.
FUTURE PLANS--It was decided that, prior to production, we fabricate four hand units with the above changes. This way we could have the new arrangement evaluated by VASI's representatives in North America and Europe prior to committing to production tooling. To help us in this effort, we contracted the Industrial Research and Development Institute (IRDI) to recommend more cost effective tooling technologies for the VASI 2-6 hand.
[16] CLINICAL AND LABORATORY STUDY OF AMPUTATION SURGERY AND REHABILITATION
David A. Boone, CP; Gayle E. Reiber, MPH, PhD; Douglas G
Smith, MD
Prosthetics Research Study, Seattle, WA 98122
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A092-7RA)
PURPOSE--Prosthetics Research Study (PRS) is completing an integrated program of eight research and development projects which address the continuum of care of the amputee from prevention of amputation to objective measurement of functional outcomes.
PROGRESS --The status of the eight programs is as
follows:
AFMA Technology Transfer Training Development
PRS developed the Automated Fabrication of Mobility Aids
(AFMA) training program to facilitate transfer of the AFMA
CAD/CAM technology to VA clinical service. In all, 46 VA
prosthetists from 36 sites have incorporated AFMA into
their routine patient care, resulting in significant annual
cost savings to the Prosthetic and Sensory Aids Service.
Over 1,847 AFMA prostheses have been made for Veterans by
the trainees of this program.
AFMA Lower Extremity Alignment
A method of computer-aided alignment of the lower extremity
prosthesis has been created. ANSI C software has been
completed that imports VA/Seattle ShapeMaker CAD/CAM socket
files for interactive graphical and numeric manipulation of
a simulated alignment fixture distal to the socket.
Alignment measurements are made relative to the surface
position of the two-point landmark of the long bone being
contained in the socket (femur or tibia). This alignment can
be modified in adduction or abduction angle,
flexion/extension angle as well as translation in the A-P or
M-L planes. The methods have been transferred to ShapeMaker
software version 4.0.
AFMA Lower Extremity Cosmesis
This project is ongoing and is expected to be completed by
October 1996. Software has been written to facilitate
carving of foam formed directly over the endoskeletal
components rather than the mandrel, in order to minimize
distortion of the contralateral shape. The AFMA cosmesis
process also lends itself to the central fabrication methods
used in the VA prosthetics clinics.
Prosthetic Alignment and Gait Evaluation Simulator
To improve the teaching and understanding of gait and
prosthetic alignment of persons with amputation, we have
completed the multimedia CD-ROM "Visual Interactive
Prosthetics" gait simulator. The user can adjust alignment
of a prosthesis on the computer screen and instantly see
pre-recorded video of the patient walking with the specified
alignment change. PRS has provided the CD-ROM to
approximately 30 universities and 30 medical clinics on six
continents. The American Board for Certification in
Prosthetics awards users of this program four continuing
education credits.
Custom Insoles For Diabetics
Veterans with diabetes mellitus with peripheral neuropathy
are at increased risk for foot ulcers and amputations.
Improper footwear precipitates many diabetic foot ulcers. A
6-month cross-over trial of 24 diabetic male veterans has
been completed. There were no breaks in the cutaneous
barrier of the foot with use of either computerized cork
insoles or a specially designed polyurethane insole combined
with the study shoe designed by PRS and NIKE. A proposed
3-year clinical trial has been approved by VA merit
review.
Amputee Management and Post-Amputation Protocols
We have completed a new edition of the PRS VA Amputee
Management Text which was last printed in 1969. A CD-ROM of the
PRS amputation and rehabilitation protocols is scheduled to
be completed in September 1996. In addition, during the past
year we have completed three book chapters on this topic.
Prosthetic Evaluation
The Prosthesis Force Transducer (PFT) has been developed at
PRS for the remote monitoring of the axial force and A/P and
M/L moments during the ambulation of persons with
amputation. In its current design, the transducer is 3.25 in
square by 0.78 in thick, weighs 13 ounces, and mounts to the
standard 2 in bolt circle used by most endoskeletal
prostheses. Electronics which fit into a small "fanny
pack" amplify the output from each load cell, convert it to
a digital signal, and transmit it to a remote computer via
wireless modem, allowing the subject to be untethered and to
perform any activity within transmission range
(
Measurement of Functional Outcomes
The goal of the Prosthetic Evaluation Questionnaire (PEQ) is
to complete the development of a validated, easy to
administer, questionnaire for comparing groups of prosthetic
patients. After two pilot surveys using the questionnaire,
we finalized the item pool and prototype questions, which
use a linear analog scale format. We then recruited 114
persons who use a lower limb prosthesis; 92 of these
subjects returned the baseline questionnaires, and all are
being used to test correlation of questions within scales.
Of the 92, 81 then completed a re-test between 2 and 6 weeks
following the baseline test. Twenty-one of these 81 subjects
had a major event that altered their prosthesis, residual
limb, or health between the two test dates. The remaining 60
subjects are being used to check the temporal stability of
the questions and scales. The analysis of correlation and
temporal reliability is currently being completed.
This year we used the PRS Gait Activity Monitor to investigate the levels and patterns of gait activity of 62 subjects with mobility impairment: 45 diabetics with peripheral neuropathy and 17 patients with dysvascular amputation. Each patient wore the monitor for 2 consecutive weeks, and kept an activity log for a portion of that time for the purposes of validation. Before and after each monitoring period, an accuracy trial involving indoor and outdoor walking as well as stair climbing and descent was performed to verify the performance of the monitor. In addition, the monitor itself was tested to verify the calibration. Data collection has been completed. Data analysis is in progress. The device has proven robust and highly accurate (99.69 percent), and patients reported no discomfort or difficulty with wearing the monitor.
[17] PROSTHETIC FITTING SYSTEMS RESEARCH PROJECT: PHASE 2
Michael W. Vannier, MD; Kirk E. Smith, AAS; Paul K.
Commean, BEE; Tom Pilgram, PhD; Barna Szabo, PhD; Ricardo
Actis, PhD; Robert H. Knapp, RT; Barry S. Brunsden; Kent
Meyers, PhD; Virginia Swanson, MD; Wayne Sprouse, CPO
Mallinckrodt Institute of Radiology, Washington
University Medical School, St. Louis, MO 63110; Department
of Mechanical Engineering, Washington University, St. Louis,
MO 63130-4899; Jefferson Barracks VA Medical Center, St.
Louis, MO 63125; Precision Prosthetics, St. Louis, MO 63123;
email:
Sponsor: National Institutes of Health/National Institute of Child Health and Human Development (NICHD), National Center for Medical Rehabilitation Research (NCMRR), Bethesda, MD 20892
PURPOSE--We seek to provide validated clinical instruments to the Orthotocs and Prosthetics profession and industry which provide quantifiable parameters for objective assessment of prosthesis fit, and capable of providing quantifiable measures necessary to achieve the "ideal" socket shape. There is a significant need, given a certain residual limb, for better means of predicting the quality of fit, specifying the optimal socket shape, and objectively evaluating the quality of fit in situ. An image-based method to evaluate in situ lower limb prostheses, focused on the socket/residuum interface and interrelationship to underlying supporting skeleton, can aid socket design, serve as a quality control method, and improve the assessment of residual limb function.
Geometric effects of poor fit and interface limitations are amenable to evaluation with spiral CT methods. This project employs nonlinear computational mechanics theory and p-version finite element analysis to conduct a thorough and systematic investigation of factors that govern the quality of fit. Experiments are performed to examine and predict the relationships among socket shape, static limb remnant geometry, and soft tissue envelope composition on responses to, as well as judgments of, lower limb prosthesis fit quality. Knowledge gained from these studies will contribute to understanding how the interaction of socket geometry and the residual limb influence the prosthesis function. The process by which prosthetists might improve results will be explained. The overall goal of our prosthetics research is to provide comprehensive 3-D static evaluation of lower limb prosthesis fit and residuum characteristics.
METHODOLOGY--An axial loading device was designed and built which allowed axial loading of the in situ prostheses during SXCT scanning to assess tissue shape change under static loading conditions.
For comparison of tissue deformation between a well- and poorly fitting prosthesis the two CT scans must be oriented within a common reference frame. Segmentation of the bony structure facilitates the registration process. The bone surface was extracted from both volumes and used to estimate the transformation matrix, which is used along with volumetric resampling to transform a target data set into the same coordinate space as the source data set (AnalyzeTM software).
Cylindrical maps are used to represent residuum trunk morphology, while the distal end is represented in polar coordinates. These maps display surface data, soft tissue thickness over bone, displacements between residuum scanned in air and with prosthesis in situ, and measurement of reference markers.
Boolean operations allow isolation and quantification of positive and negative change (local and global) in residuum morphology relative to a baseline scan. Errors due to registration and resampling have been shown to be small compared to volume shape differences.
Surface (optical) and volumetric (CT) data of transtibial (TT) residua were used to generate solid models and specify socket shape in SDRC I-DEASTM CAD software. Contour extraction methods were developed, rational and nonrational B-spline representations used for solid modeling.
We studied state-of-the-art imaging systems, solid modeling, and other software tools to determine the associated errors in mass property estimation by spiral CT, 3-D MR, and optical surface scanning using phantoms and cadaver parts.
PEGASYSTM p-version finite element analysis software was used to create 2-D finite element models of the TT residuum. Models were created of bone, skin and socket from contour information extracted from SXCT volumetric data using Analyze software. A 3-D model has recently been created. The 2-D model has been validated by comparison of FEA displacements to measured displacements from CT data obtained with the prosthesis in situ under known static load. The 3-D model is currently undergoing refinements and validation.
[18] 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
Bioengineering Unit, University of Strathclyde, Glasgow,
UK
Sponsor: Engineering Physics Science Research Council (EPSRC)
PURPOSE--This investigation is directed toward the generation of a Finite Element (FE) model of the residual limb of a person with transfemoral amputation (TFA). The model is capable of predicting the pressure distribution at the patient/prosthesis interface. This would lead to a better understanding of the biomechanics at the residual limb/socket interface.
METHODOLOGY--Prior to the creation of an accurate FE model, the mechanical properties of the tissues, geometrical details of the stump, and the loading and constraints the amputee undergoes during standing and during gait have to be determined. To validate the FE models created, stump/socket interface pressures were measured and compared with those predicted. In addition, the study also attempts to obtain a better understanding of the biomechanical characteristics at the stump/socket interface using interface pressure measurement and magnetic resonance imaging (MRI) techniques. The ongoing controversy regarding the quadrilateral (quad) and the ischial containment (IC) sockets also provided a suitable case study for the project.
PROGRESS--Two- and three-dimensional (2-D, 3-D) FE models of the TFA residual limb were attempted. Residual limb/socket interface pressure was measured for four TFA patients prescribed with both quad and IC sockets. Geometrical details of the lower limbs of five of five TFA patients were acquired using magnetic resonance imaging (MRI) techniques. Three sets of scans were taken for each subject in a supine position for the following situations : a) wearing a plaster cast which maintained the residual limb in a natural or undeformed state, b) wearing a quadrilateral socket, and c) wearing an ischial containment socket.
RESULTS--The 3-D FE models were able to predict interface pressures during various phases of the gait cycle and during standing. The predicted stress distribution pattern matches that of the measured pressure. The 2-D model, which included geometry of the musculature obtained from MRI, was able to show significant movement in the musculature due to prosthetic socket loading. High stresses were also predicted at regions where muscles are attached to bone.
[19] INVESTIGATION OF 4-BAR LINKAGE KNEES AS AN AID TO FLOOR CLEARANCE DURING PROSTHETIC SWING
Dudley S. Childress, PhD; Steven A. Gard, PhD; Jack E.
Uellendahl, CPO
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--The advantages of 4-bar linkage knees include stance-phase stability during gait and cosmesis for the person with a long transfemoral amputation. However, another distinct advantage is that the 4-bar knee is able to provide greater floor clearance during the swing phase of walking than a single axis knee. Four-bar knees may be especially beneficial for persons with transfemoral and hip-disarticulation amputations who have trouble with floor clearance during gait. We investigated the ability of commercially available 4-bar linkage knees to provide swing-phase foot clearance, and compared the results with a single-axis knee in order to demonstrate the distinct advantage these mechanisms provide.
METHODOLOGY--We investigated 4-bar linkage knees by simulating knee kinematics with a computer. Knees included in our study were subject to the following criteria: they had to have been adult endoskeletal units, commercially available during 1994-95, and to have rigid-linkages throughout knee flexion range.
The following knee units were evaluated in the course of our research: Hosmer VC4, Hosmer UltraRoeLite, Ohio Willow Wood Pendulum Senior, Otto Bock 3R23, 3R36, 3R60, and 3R70, and the USMC OHC.
We developed a computer model of a transtibial prosthesis into which the representation of a particular 4-bar knee could be inserted for evaluation. Leg parameters, such as the hip-toe distance and floor clearance, were calculated as the hip and knee joints were rotated systematically through their full ranges of motion. These results were compared with those obtained from a computer simulation of the prosthesis model incorporating a single-axis knee.
RESULTS--A plot of the simulated hip-toe distances versus the knee flexion angle for all of the knees clearly demonstrated the ability of the 4-bar linkage knees to shorten the prosthesis to a greater extent than the single-axis knee. We found that 4-bar knees have an apparent ankle dorsiflexion that allows them to effectively lift the toe of the prosthesis during swing to increase toe clearance. Contour plots were created to show the first 5 cm of toe clearance as a function of the hip and knee flexion angles for all of the knees analyzed. Some of the knees provided as much toe clearance at 30° as the single-axis knee had at 50°. The 4-bar knees increased floor clearance by 0.9-3.2 cm beyond that of the single-axis knee at a knee flexion angle of 49° and a hip flexion angle of 23°, which are the approximate swing leg joint angles at the time of minimum toe clearance.
FUTURE PLANS--We plan to measure the swing-phase hip and knee joint angles on the prosthetic side of above-knee amputees walking with different commercially available 4-bar knees. Curves of hip angle versus knee angle can be corrected for hip elevation, then overlaid onto the appropriate knee contour plot to show the amount of prosthetic toe clearance throughout swing. We may also use our computer model to determine what effect different prosthetic alignments have on the hip-toe distance and toe clearance for the 4-bar and single-axis knees.
[20] DEVELOPMENT OF A PAEDIATRIC ABOVE-KNEE ENDOSKELETAL RUNNING PROSTHESIS
Alan R. Morris, MASc; Stephen Naumann, PhD
Human Movement Research Programme, Bloorview MacMillan
Centre, Toronto, Ontario, M4G 1R8 Canada; email:
morrisa@ecf.utoronto.ca
Sponsor: Variety Ability Systems Inc.; The National Research Council; Ontario Rehabilitation Technology Consortium funded by the Ontario Ministry of Health
PURPOSE--The purpose of this research project is to develop a running prosthesis that will enable smooth and efficient gait for children between the ages of 5 and 12 with a transfemoral amputation.
PROGRESS--Since the inception of this project, progress has been made through: 1) development of a three-dimensional computer simulation of nondisabled and prosthetic gait; 2) design and manufacture of a prototype multicomponent above-knee prosthesis to be used in running and other intense physical activities, and 3) current field testing of the prototype prosthesis on clients of the Centre. Computerized simulation of walking and running gait was completed during an engineering master's thesis; the simulation was carried out on Dynamic Analysis and Design of Systems (DADS) mechanical engineering software using a 3-D forward dynamic method integrating acquired nondisabled gait data with a biomechanical model of the lower body. These results demonstrated sufficient promise to embark on development of a prototype. Following successful simulation of nondisabled movement, the biomechanical model was modified to approximate transfemoral prosthetic gait. Simulation of the prototype prosthetic gait demonstrated an improvement in the body's centre-of-mass trajectory and control of knee flexion during the swing and stance phases. As a result of this and other analytical work, various components were specified such as a polycentric knee linkage (stability), knee damping (stability/velocity control), and a shank-shock absorber (support control).
Thus far, development has been steady. Manufacture of prototype was completed in the Bloorview MacMillan Centre Machine Shop, resulting in a lightweight unit with a knee-to-foot length of approximately 13-14 inches, suitable for children of this age group. In order to ensure satisfactory strength of the components for testing on centre clients, cyclic testing of the device was carried out to meet International Standards Organisation test standards for lower-limb prosthetics. An electro-pneumatic testing device was developed to fatigue the knee unit over 6 million cycles to ensure design integrity. The knee was successful in exceeding these testing standards. Presently client testing of the device has been undertaken.
FUTURE PLANS--A suitable client of BMC's Prosthetics Department will test the knee unit for a 6-week period. The client will undergo quantitative gait analyses in BMC's Human Movement Laboratory, and metabolic (oxygen consumption) tests at Variety Village Recreation Centre to objectively determine whether his/her pattern of walking has changed and is more efficient from that with his/her conventional prosthesis. Following this preliminary evaluation, any identifiable design changes will be made, and a second round of testing will be carried out on a number of clients in centres across the province. The conclusion of the research and development phase of this project will be proceeded by commercial manufacture and distribution of the product.
[21] PROSTHETIC DESIGN FOR THE PATIENT WITH DYSVASCULAR BELOW-KNEE AMPUTATEE
Stanford Anzel, MD; Jacquelin Perry, MD; Edmund Ayyappa,
MS, CPO; Lara Boyd, MPT; JoAnne Gronley, DPT; Sreesha Rao,
MS; Ernie Bontrager, MS; Christopher Powers, PhD
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 #A735-RA)
PURPOSE--It has been assumed that with the advent of the dynamic elastic response feet to enhance push off, significant energy cost would be saved by those with transtibial amputations. However, this has not occurred. Major inefficiencies at both the hip and knee during the loading phase of walking continue to be found. The problem seems to be related to the mechanics of the prosthetic hind-foot. Current designs cause knee instability, requiring postural and muscular stabilization at the knee and hip, a demand that the already weak dysvascular patient has difficulty meeting. The purpose of this research was to quantitatively define by comprehensive gait analysis muscle activity and motion patterns of those wearing three prosthetic feet.
METHODOLOGY--Ten persons with dysvascular transtibial amputation were tested on separate occasions wearing three prosthetic feet: single-axis foot (SA), Seattle Litefoot (SL), and Flex Foot (FF). Comparisons were made with 10 nonimpaired controls. Dynamic electromyography (EMG) recorded the timing and intensity of the vastus lateralis, biceps femoris long head, semimembranosus, and lower gluteus maximus. To permit comparison of EMG intensity between subjects and muscles, all EMG data were normalized to a maximal isometric effort. Mean onset and cessation times were calculated and stretched or shrunk to 62 percent of the gait cycle (GC). All EMG onsets and cessations were reported as a percentage of the gait cycle. Dunnett's test was used to compare the control group with amputee performance. Repeated measures ANOVA determined the significant of differences between each foot type.
RESULTS--Although no significant difference in EMG intensity or onset timing was found between the three prosthetic feet or versus nonimpaired, a pattern of prolonged muscle activation was noted. Consistently, when wearing the SA foot, EMG cessation times were later than normal. This was most evident for the vastus lateralis, with those wearing the SA foot demonstrating quadriceps action until 40 percent GC (NC=21%GC, p<0.01). Similarly, the SL foot also had prolonged knee extensor action until 34 percent GC (p<0.05), while the FF was a more normal 26 percent GC. Quadriceps action when wearing the SA foot was significantly later in its cessation time from the other prosthetic foot designs (p<0.05).
Increased muscular activity also was evident in the hip extensors. Biceps femoris long head activity was prolonged for all three prosthetic foot designs when compared to normal (NC=13.6%GC, SA=42%GC, SL=41%GC, FF=41%GC, p<0.01). Similarly, the semimembranosus also was prolonged for both the SL and FF (SL=42%GC, FF=49%GC) when compared to nonimpaired (24%GC, p<0.05). Semimembranosus cessation for the SA occurred at 36 percent GC. Finally, lower gluteus maximus was significantly long in its action for the SA (33%GC, p<0.01) and FF (29%GC, p<0.05) when compared to nonimpaired (12%GC). The SL (26%GC) did not differ statistically from nonimpaired.
Two distinct patterns of motion were evident in the prosthetic ankle during loading response. The SA foot demonstrated the largest amount of plantar flexion, 8.9°, due to its mobile ankle design. Both the SL and FF, had much less plantar flexion ability during loading (SL=1.9° and FF=4.2°). This difference was not statistically significant. Peak plantar flexion occurred later than normal for the SL and FF.
Likewise, peak knee flexion during loading was diminished from normal for all prosthetic feet. Due to large amounts of variability, however, this was not significantly different. The timing of peak knee flexion was significantly later for the SA (23%GC, p<0.01) and SL (22%GC, p<0.01) from nonimpaired (13%GC). Loading response knee flexion normally results from the heel rocker. Disruption and prolongation of this shock absorbing mechanism is one likely contributor to prolonged vastii action. As heel rocker mechanics were inadequate, (occurring fast and uncontrolled for the SA foot, and late in both the SL and FF designs), the vastii must work harder despite the reduced knee flexion range to control tibial advancement.
While hip motion did not differ from normal there were marked amounts of anterior pelvic tilt throughout the gait cycle. In an effort to reduce the demands on the knee extensors and augment progression each amputee group demonstrated significantly greater forward trunk leans during loading (NC=0.91, SA=3.72, SL=3.75, FF=3.70°; p<0.01). By maintaining center of mass forward longer, (22%GC amputation, 10%CG nonimpaired; p<0.05), individuals with transtibial amputation decreased the demands on the quadriceps. This is a characteristic compromise used to protect weak quadriceps while maintaining advancement over the prosthetic foot.
FUTURE PLANS--Data analysis continues, focusing on integrating findings to improve prosthetic foot and ankle design criteria. Prosthetic foot designers will be encouraged to participate in the development of less demanding feet.
[22] PRACTICAL APPLICATIONS OF NEW CAD AND CAE TECHNIQUES TO SOCKET DESIGN
Dudley S. Childress, PhD; Keith E. Oslakovic, MS; John
W. Steege, MSME
Northwestern University, Prosthetics Research
Laboratory, Chicago, IL 60611;
email: d-childress@nwu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A521-3DA)
PURPOSE--This work intends to continue refinements in the application of the finite element analysis (FEA) technique to the design of transtibial prosthetic sockets based upon models of the prosthesis/residual limb. Additionally, we intend to develop computer design guidelines based upon the prosthesis/limb mechanics during gait as well as incorporate new techniques for determining complete below-the-knee limb geometry which do not rely on CT imaging.
METHODOLOGY--Our latest analyses of sockets has consisted of applying the contact algorithm to a physical model of the limb-socket system. A three-dimensional model of a generic, approximate residual limb was created and analyzed, using internal geometry generated from digitization of an anatomically accurate model of the joint capsule of a transtibial residual limb. These geometries were then mapped onto a pre-existing finite element mesh of a hollow capped end cylinder, resulting in a layer of elements whose outer surface is described by the tapered ellipse, and an inner surface described by the digitized model. The external surface data was then exported to a CAD/CAM socket program, ShapeMakerTM, and a standard PTB rectification template applied to the limb surface data. This geometry was then used to define a rigid nonuniform, rational, B-spline surface (NURBS) to be used in our model as an analytical description of the socket surface. This surface was then slowly moved onto the limb to simulate socket donning.
Using the same data as the FE model, we generated a physical model consisting of a polyester resin replication of the joint capsule geometry encased within silicone gel in the shape of a tapered ellipse, in order to simulate the soft tissues of the residual limb. The rectified socket geometry created in ShapeMaker was used to carve a positive mold for socket manufacture over which a polypropylene socket was vacuum-formed. Kulite pressure transducers were then mounted in the wall of the rectified socket at six locations for interface pressure measurement.
PROGRESS--An approximation made previously in our FE modeling was that the limb-socket interface was fixed, where no slippage or loss of contact may occur. We have begun work to more accurately model this interface using a contact analysis (CA) algorithm. We have completed an initial analysis of socket donning using CA and compared the results with both our previous method of modeling and measured data.
RESULTS--At all six transducer locations where stresses were measured on the physical model, CA results predicted slightly lower stresses than those measured, while the traditional FE models (applied radial displacements) predicted much higher stresses. Additionally, comparison of FEA generated plots of pressure versus time at each of the transducer locations are very similar to experimentally measured pressure/time plots, showing that contact analysis is capable of simulating the dynamic interface conditions arising during gait. A digital animation demonstrating this capability is displayed on our Web page (http://www.repoc.nwu.edu/).
FUTURE PLANS--The next step in our work is to integrate FE modeling with gait analysis techniques to create an improved methodology for socket design. We intend to use our contact methods to analyze the residual socket/limb system under simulated gait loads to investigate the effect of socket shape changes on overall socket fit. Our modeling procedure will enable us to quantify motions of the socket relative to the limb during gait, as a measure of socket stability, as well as quantifying tissue stresses as a measure of adequate support. Clinical assessment of sockets designed with varying quantitative parameter values will determine what are acceptable ranges for these parameter values. Finally, an optimization scheme will be developed to create socket shapes with optimal stability and support characteristics.
[23] SOFT TISSUE BEHAVIOR AND SENSATION OF LOWER EXTREMITY RESIDUAL LIMBS: A PILOT STUDY
M. Barbara Silver-Thorn, PhD; Arvind Pathak; Judith
Kosasih, MD
Marquette University, Milwaukee, WI 53233; Zablocki VA
Medical Center, Milwaukee, WI 53295; email:
barbara@silver.bien.mu.edu
Sponsor: Department of Veterans Affairs, VA Rehabilitation Research and Development Service, Washington, DC 20420 (Pilot Project #A93-673PA); National Science Foundation, Bioengineering and Aiding the Disabled Program, Arlington, VA 22230
PURPOSE--The goal of this study was to increase our understanding of the soft tissues of the residual limb in individuals with transtibial amputation. Such knowledge will augment prosthetic socket design and the evaluation of prosthetic fit. Two specific aims of the project were: to describe the sensory changes in the person with transtibial amputation because any loss of sensation may have significant impact in the successful use of a prosthesis, and to quantify the response of the residual limb bulk soft tissues to load.
METHODOLOGY--Sensory modalities of light touch, deep pressure, vibration, and superficial pain (pin prick) were examined on the residual and contralateral limbs of 16 veterans with transtibial amputation. In addition, in vivo rate-controlled (2, 5 and 8 mm/s) indentor tests were conducted on the residual limb tissues of 4 individuals who exhibited intact sensation of the residual and contralateral limbs using an indentor designed specifically for this project. Stress relaxation tests were also conducted. For these trials, indentation at 2 mm/s was applied until the desired displacement was achieved; the corresponding reaction force was monitored for 300 s.
PROGRESS--Six of the 16 subjects demonstrated normal sensation of the contralateral limb and impaired sensation of superficial pain, vibration, and/or light touch of the residual limb. Superficial pain was the most frequently impaired sensation, and vibration and superficial pain sensation appeared to be age dependent, with increased impairment observed in the elderly subjects. Deep pressure sensation was intact in all subjects. These preliminary data suggest that although neither the amputation nor the prosthetic rehabilitation resulted in impaired deep pressure sensation, these factors contributed to minimal impairment of light touch and vibration, and significant impairment of the superficial pain sensation.
RESULTS--The in vivo indentation tests indicated that the bulk soft tissue response to compressive load is nonlinear, and for the indentation rates tested, nearly independent of the loading rate. Significant inter- and intra-subject stiffness variations were observed. The stress relaxation studies indicated that approximately 80 percent relaxation may occur; the relaxation time constants generally ranged from 150 to 300 s.
FUTURE PLANS--Nonlinear numerical models (finite element analyses) simulating the tissue indentation trials are underway to develop constitutive equations for human bulk soft tissue. Additional subject trials are also being conducted.
[24] PROSTHETIC FITTING SYSTEMS RESEARCH PROJECT: PHASE 1
Michael W. Vannier, MD; Kirk E. Smith, AAS; Paul K.
Commean, BEE; James Cheverud, PhD; Tom Pilgram, PhD; Robert
H. Knapp, RT; Barry S. Brunsden
Mallinckrodt Institute of Radiology, Washington
University Medical School, St. Louis, MO 63110; email:
Sponsor: National Institutes of Health/National Institute of Child Health and Human Development (NICHD), National Center for Medical Rehabilitation Research (NCMRR), Bethesda, MD 20892
PURPOSE--Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) methods are increasingly used in the design and manufacture of prosthetic componentry including the socket itself. These methods offer potential for objective assessment of prosthesis fit quality. The measurements which drive the CAD/CAM process may come from a variety of sources. Before these measurements can be reliably used in the design/manufacturing process they must first be subject to scientific and statistical evaluation and compared to a previously accepted form of measurement or "gold standard." The overall goal of this research project was to establish the precision and repeatability of new 3-D imaging devices for accurate assessment of lower limb residua. We tested the ability of an optical surface scanner (OSS), a clinical spiral x-ray CT scanner (SXCT), and an electromagnetic point digitizer to repeatably and precisely measure residua in transtibial volunteers. Linear and volumetric measurements were obtained and compared to caliper and hydrostatic weighing methods respectively.
METHODOLOGY--An optical surface scanner was designed and built to facilitate lower limb residuum scanning. Four camera/projector sensors were configured to view the residual limb or plaster cast surface in overlapping segments. Utilization of multiple sensors allowed 360° coverage of residua including the distal end. A rigid mechanical structure was designed and built to which the sensors were mounted. The scanner design principle was based on triangulation between a projector and camera.
Spiral CT scanning was also evaluated for residua imaging. A spiral CT scanner (SOMATOM Plus S, Siemens Medical Systems, Inc., Iselin, NJ ) with slip-ring technology that allows continuous 1 s/revolution rotation of the X-ray source and detectors was used to obtain raw X-ray projection data. This scanner can acquire and store contiguous data sets obtained over a 32-s period with successive spiral turns of 1 mm with 1 mm collimation. Two advantages of spiral CT over conventional CT are a considerable reduction in radiation dosage and scan time, and improved definitive representation of soft tissue.
A 3SpaceTM electromagnetic point digitizer (Kaiser Aerospace and Electronics, Colchester, VT) consisting of a hand-held wand used to capture information with six degrees of freedom was also evaluated. The stylus of the wand is tracked in a calibrated feature space and the location digitized when a foot pedal is pressed.
RESULTS--Work on this project has demonstrated that measurements of surface geometry by manual, optical, and x-ray CT methods are accurate and reproducible and that volumetric images reconstructed from spiral x-ray CT provides accurate volumetric measurement of the limb remnant soft tissue envelope. Surface and volumetric residua data from the OSS and SXCT respectively were used to construct accurate 3-D solid models. The results demonstrate that the 3Space, OSS, and SXCT precision and repeatability are sufficient for quantitative studies and found substantial equivalence of these methods.
IMPLICATIONS--Any of these methods can be reliably used to acquire measurement data for input to a CAD/CAM package. For the more ardent task of prosthesis fit, evaluation spiral X-ray CT seems most appropriate. SXCT not only yields an accurate high resolution representation of surface morphology, but was also shown to yield high delineation of internal residuum morphology. This device was the only one of those examined capable of soft tissue morphology with a prosthesis in situ. Optical surface scanning would be well suited for diurnal evaluation (short-term) of residua when internal information is not required.
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Last revised Wed 05/26/1999
