[Show abstract][Hide abstract] ABSTRACT: Lower limb prostheses that can generate net positive mechanical work may restore more ambulation modes to amputees. However, configuration of these devices imposes an additional burden on clinicians relative to conventional prostheses; devices for transfemoral amputees that require configuration of both a knee and an ankle joint are especially challenging. In this paper, we present an approach to configuring such powered devices. We developed modified intrinsic control strategies-which mimic the behavior of biological joints, depend on instantaneous loads within the prosthesis, or set impedance based on values from previous states, as well as a set of starting configuration parameters. We developed tables that include a list of desired clinical gait kinematics and the parameter modifications necessary to alter them. Our approach was implemented for a powered knee and ankle prosthesis in five ambulation modes (level-ground walking, ramp ascent/descent, and stair ascent/descent). The strategies and set of starting configuration parameters were developed using data from three individuals with unilateral transfemoral amputations who had previous experience using the device; this approach was then tested on three novice unilateral transfemoral amputees. Only 17% of the total number of parameters (i.e., 24 of the 140) had to be independently adjusted for each novice user to achieve all five ambulation modes and the initial accommodation period (i.e., time to configure the device for all modes) was reduced by 56%, to 5 hours or less. This approach and subsequent reduction in configuration time may help translate powered prostheses into a viable clinical option where amputees can more quickly appreciate the benefits such devices can provide.
PLoS ONE 06/2014; 9(6):e99387. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The clinical application of robotic technology to powered prosthetic knees and ankles is limited by the lack of a robust control strategy. We found that the use of electromyographic (EMG) signals from natively innervated and surgically reinnervated residual thigh muscles in a patient who had undergone knee amputation improved control of a robotic leg prosthesis. EMG signals were decoded with a pattern-recognition algorithm and combined with data from sensors on the prosthesis to interpret the patient's intended movements. This provided robust and intuitive control of ambulation--with seamless transitions between walking on level ground, stairs, and ramps--and of the ability to reposition the leg while the patient was seated.
New England Journal of Medicine 09/2013; 369(13):1237-42. · 54.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lower limb prostheses have traditionally been mechanically passive devices without electronic control systems. Microprocessor-controlled passive and powered devices have recently received much interest from the clinical and research communities. The control systems for these devices typically use finite-state-controllers to interpret data measured from mechanical sensors embedded within the prosthesis. In this paper we investigated a control system that relied on information extracted from myoelectric signals to control a lower limb prosthesis while amputee patients were seated. Sagittal plane motions of the knee and ankle can be accurately (>90%) recognized and controlled in both a virtual environment and on an actuated transfemoral prosthesis using only myoelectric signals measured from nine residual thigh muscles. Patients also demonstrated accurate (~90%) control of both the femoral and tibial rotation degrees of freedom within the virtual environment. A channel subset investigation was completed and the results showed that only five residual thigh muscles are required to achieve accurate control. This research is the first step in our long-term goal of implementing myoelectric control of lower limb prostheses during both weight-bearing and non-weight-bearing activities for individuals with transfemoral amputation.
Journal of NeuroEngineering and Rehabilitation 06/2013; 10(1):62. · 2.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recently developed powered lower limb prostheses allow users to more closely mimic the kinematics and kinetics of non-amputee gait. However, configuring such a device, in particular a combined powered knee and ankle, for individuals with a transfemoral amputation is challenging. Previous attempts have relied on empirical tuning of all control parameters. This paper describes modified stance phase control strategies - which mimic the behavior of biological joints or depend on the instantaneous loads within the prosthesis - developed to reduce the number of control parameters that require individual tuning. Three individuals with unilateral transfemoral amputations walked with a powered knee and ankle prosthesis across five ambulation modes (level ground walking, ramp ascent/descent, and stair ascent/descent). Starting with a nominal set of impedance parameters, the modified control strategies were applied and the devices were individually tuned such that all subjects achieved comfortable and safe ambulation. The control strategies drastically reduced the number of independent parameters that needed to be tuned for each subject (i.e., to 21 parameters instead of a possible 140 or approximately 4 parameters per mode) while relative amplitudes and timing of kinematic and kinetic data remained similar to those previously reported and to those of non-amputee subjects. Reducing the time necessary to configure a powered device across multiple ambulation modes may allow users to more quickly realize the benefits such powered devices can provide.
IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2013; 2013:1-6.
[Show abstract][Hide abstract] ABSTRACT: Technological advances have enabled clinical use of powered foot-ankle prostheses. Although the fundamental purposes of such devices are to restore natural gait and reduce energy expenditure by amputees during walking, these powered prostheses enable further restoration of ankle function through possible voluntary control of the powered joints. Such control would greatly assist amputees in daily tasks such as reaching, dressing, or simple limb repositioning for comfort. A myoelectric interface between an amputee and the powered foot-ankle prostheses may provide the required control signals for accurate control of multiple degrees of freedom of the ankle joint. Using a pattern recognition classifier we compared the error rates of predicting up to 7 different ankle-joint movements using electromyographic (EMG) signals collected from below-knee, as well as below-knee combined with above-knee muscles of 12 trans-tibial amputee and 5 control subjects. Our findings suggest very accurate (5.3±0.5%SE mean error) real-time control of a 1 degree of freedom (DOF) of ankle joint can be achieved by amputees using EMG from as few as 4 below-knee muscles. Reliable control (9.8±0.7%SE mean error) of 3 DOFs can be achieved using EMG from 8 below-knee and above-knee muscles.
IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2013; 2013:1-4.
[Show abstract][Hide abstract] ABSTRACT: We explored a new method for simple and accurate control of shoulder movement for externally powered shoulder disarticulation prostheses with a two-axis joystick. We tested 10 subjects with intact shoulders and arms to determine the average amount of shoulder motion and force available to control an electronic input device. We then applied this information to two different input strategies to examine their effectiveness: (1) a traditional rocker potentiometer and a pair of force-sensing resistors and (2) a two-axis joystick. Three nondisabled subjects and two subjects with shoulder disarticulation amputations attempted to control an experimental externally powered shoulder using both control strategies. Two powered arms were tested, one with powered flexion/extension and humeral rotation and one with powered flexion/extension and adduction/abduction. Overwhelmingly, the subjects preferred the joystick control, because it was more intuitively linked with their shoulder movement. Additionally, two motions (one in each axis) could be controlled simultaneously. This pilot study provides valuable insight into an effective means of controlling high-level, externally powered prostheses with a two-axis joystick.
The Journal of Rehabilitation Research and Development 01/2011; 48(6):661-7. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Some important walking functions are adversely affected or eliminated in prosthesis users because of reduced or absent ankle motion. This retrospective data analysis determined the effect of prosthetic ankle units on the characteristics of the ankle-foot roll-over shape in persons with bilateral transtibial amputations. Seventeen subjects were fitted with Endolite Multiflex Ankles to provide ankle plantar-/dorsiflexion during the stance phase of gait. Quantitative gait analyses were performed as subjects walked with (1) Seattle Lightfoot II feet (baseline condition) and (2) the prosthetic ankle units added. Roll-over shape radii and effective foot length ratio were calculated and compared for the two prosthetic configurations. When subjects walked with the ankle units, ankle motion increased (p < 0.001), peak ankle plantarflexion moment during stance decreased slightly, and ankle-foot roll-over shape radii were significantly decreased (p < 0.001) compared with the baseline condition. The effective foot length ratio of the roll-over shape was found to increase with walking speed (p < 0.001), but it was not significantly affected by the prosthetic ankle units (p = 0.07). Prosthetists and manufacturers are encouraged to consider the effect of combining prosthetic components on the overall characteristics of the prosthesis and the functions they impart to the user.
The Journal of Rehabilitation Research and Development 01/2011; 48(9):1037-48. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine whether the provision of prosthetic ankle motion improves walking performance in persons with bilateral transtibial amputations.
Crossover experimental design in which 19 persons with bilateral transtibial amputations were fitted with Endolite Multiflex Ankles (flexion unit) and Otto Bock Torsion Adapters (torsion unit) to increase relative motion between the prosthetic foot and socket in the sagittal and transverse planes, respectively. Quantitative gait analyses were performed on subjects as they walked with four prosthetic configurations: baseline without flexion or torsion units, with only the flexion unit, with only the torsion unit, and with both the flexion and torsion units. Data were compared with a control group of 14 able-bodied subjects.
The flexion unit increased ankle sagittal plane motion (6-7 degrees) and increased positive ankle power (about 0.17 W/kg). The torsion unit increased transverse plane ankle range of motion by 1-2 degrees. Responses from questionnaires indicated that 14 of the 19 subjects preferred the prosthetic configuration that included both the flexion and torsion units. Further, the subjects perceived that the increased prosthetic ankle motion was particularly beneficial for improving stability while they walked on uneven terrain.
Both the subjective and objective results suggest that prosthetic foot and ankle components that allow for greater sagittal and transverse plane rotations provide substantial benefit during walking and should be considered for persons with bilateral transtibial amputations. Nonetheless, clinicians should perform individual and appropriate assessments of patients to ensure that they are capable of using components that may improve mobility while possibly sacrificing some degree of stability.
American journal of physical medicine & rehabilitation / Association of Academic Physiatrists 01/2010; 89(1):34-47. · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Improving the function of prosthetic arms remains a challenge, because access to the neural-control information for the arm is lost during amputation. A surgical technique called targeted muscle reinnervation (TMR) transfers residual arm nerves to alternative muscle sites. After reinnervation, these target muscles produce electromyogram (EMG) signals on the surface of the skin that can be measured and used to control prosthetic arms.
To assess the performance of patients with upper-limb amputation who had undergone TMR surgery, using a pattern-recognition algorithm to decode EMG signals and control prosthetic-arm motions.
Study conducted between January 2007 and January 2008 at the Rehabilitation Institute of Chicago among 5 patients with shoulder-disarticulation or transhumeral amputations who underwent TMR surgery between February 2002 and October 2006 and 5 control participants without amputation. Surface EMG signals were recorded from all participants and decoded using a pattern-recognition algorithm. The decoding program controlled the movement of a virtual prosthetic arm. All participants were instructed to perform various arm movements, and their abilities to control the virtual prosthetic arm were measured. In addition, TMR patients used the same control system to operate advanced arm prosthesis prototypes.
Performance metrics measured during virtual arm movements included motion selection time, motion completion time, and motion completion ("success") rate.
The TMR patients were able to repeatedly perform 10 different elbow, wrist, and hand motions with the virtual prosthetic arm. For these patients, the mean motion selection and motion completion times for elbow and wrist movements were 0.22 seconds (SD, 0.06) and 1.29 seconds (SD, 0.15), respectively. These times were 0.06 seconds and 0.21 seconds longer than the mean times for control participants. For TMR patients, the mean motion selection and motion completion times for hand-grasp patterns were 0.38 seconds (SD, 0.12) and 1.54 seconds (SD, 0.27), respectively. These patients successfully completed a mean of 96.3% (SD, 3.8) of elbow and wrist movements and 86.9% (SD, 13.9) of hand movements within 5 seconds, compared with 100% (SD, 0) and 96.7% (SD, 4.7) completed by controls. Three of the patients were able to demonstrate the use of this control system in advanced prostheses, including motorized shoulders, elbows, wrists, and hands.
These results suggest that reinnervated muscles can produce sufficient EMG information for real-time control of advanced artificial arms.
JAMA The Journal of the American Medical Association 03/2009; 301(6):619-28. · 29.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study investigated the use of surface electromyography (EMG) combined with pattern recognition (PR) to identify user locomotion modes. Due to the nonstationary characteristics of leg EMG signals during locomotion, a new phase-dependent EMG PR strategy was proposed for classifying the user's locomotion modes. The variables of the system were studied for accurate classification and timely system response. The developed PR system was tested on EMG data collected from eight able-bodied subjects and two subjects with long transfemoral (TF) amputations while they were walking on different terrains or paths. The results showed reliable classification for the seven tested modes. For eight able-bodied subjects, the average classification errors in the four defined phases using ten electrodes located over the muscles above the knee (simulating EMG from the residual limb of a TF amputee) were 12.4% +/- 5.0%, 6.0% +/- 4.7%, 7.5% +/- 5.1%, and 5.2% +/- 3.7%, respectively. Comparable results were also observed in our pilot study on the subjects with TF amputations. The outcome of this investigation could promote the future design of neural-controlled artificial legs.
[Show abstract][Hide abstract] ABSTRACT: Targeted muscle reinnervation (TMR) is a surgical intervention to improve the control of myoelectric prostheses in high-level upper-limb amputation. This article briefly describes the procedure and presents the protocol for postoperative, preprosthetic care. We also recommend a guide to patient training using standard-of-care prosthetic devices controlled by up to four intuitive, independent, and isolated myoelectric signals. We discuss the advantages of this new control paradigm and methods for optimizing clinical outcomes for patients with high-level upper-limb amputations. This material is based on more than 6 years of experience treating patients with TMR in a research setting. Detailed results of this research are reported elsewhere.
The Journal of Rehabilitation Research and Development 01/2009; 46(4):481-8. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lower limb amputees form a large portion of the amputee population; however, current lower limb prostheses do not meet the needs of patients with high-level amputations who need to perform multi-joint coordinated movements. A critical missing element is an intuitive neural interface from which user intent can be determined. Surface EMG has been used as control source for upper limb prostheses for many years; for lower limb activities, however, the EMG is non-stationary and a new control strategy is required. This paper describes the work completed to date in developing a novel lower limb neural interface.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:2111-4.
[Show abstract][Hide abstract] ABSTRACT: To fit and evaluate the control of a complex prosthesis for a shoulder disarticulation-level amputee with targeted muscle reinnervation.
One participant who had targeted muscle reinnervation surgery was fitted with an advanced prosthesis and his use of this device was compared with the device that he used in the home setting.
The experiments were completed within a laboratory setting.
The first recipient of targeted muscle reinnervation: a bilateral shoulder disarticulation-level amputee.
Two years after surgery, the subject was fitted with a 6 degree of freedom (DOF) prosthesis (shoulder flexion, humeral rotation, elbow flexion, wrist rotation, wrist flexion, and hand control). Control of this device was compared with that of his commercially available 3-DOF system (elbow, wrist rotation, and powered hook terminal device).
In order to assess performance, movement analysis and timed movement tasks were executed.
The subject was able to independently operate all 6 arm functions with good control. He could simultaneously operate 2 DOF of several different joint combinations with relative ease. He operated up to 4 DOF simultaneously, but with poor control. Work space was markedly increased and some timed tasks were faster with the 6-DOF system.
This proof-of-concept study shows that advances in control of shoulder disarticulation-level prostheses can improve the quality of movement. Additional control sources may spur the development of more advanced and complex componentry for these amputees.
Archives of physical medicine and rehabilitation 12/2008; 89(11):2057-65. · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Prosthetists have been fitting externally-powered components to individuals with “shoulder disarticulation”, upper extremity amputations for decades. These components have ranged from momentary contact switches that permitted carbon-dioxide to pass through tubes in order to create an articulating motion, to force sensitive resistors (FSRs) that vary the amount of resistance between thin conductive plates in order to permit varied current to flow and provide input to an electrical motor. Activation of these types of inputs requires contact by the user with their remaining residual limb or, in the case of individuals with congenital deficiencies, phocomelic digits. A variety of pull switches have also been used to harness the body motions provided by the user, which activate an electro-mechanical switch used to drive a motor. With the use of coupled rotary potentiometers, the authors have chosen to investigate a unique approach to ipsilateral shoulder motion as a control source for two degrees of freedom.
[Show abstract][Hide abstract] ABSTRACT: To examine differences in gait characteristics between persons with bilateral transtibial amputations because of trauma and peripheral vascular disease (PVD); and to compare that with data from able-bodied controls that were previously collected and maintained in a laboratory database.
Observational study of persons with bilateral transtibial amputations.
A motion analysis laboratory.
Nineteen bilateral transtibial amputees.
No experimental intervention was performed. To standardize the effect of prosthetic foot type, subjects were fitted with Seattle Lightfoot II feet 2 weeks before quantitative gait analyses.
Temporospatial, kinematic, and kinetic gait data were recorded and analyzed.
Results showed that the freely selected walking speeds of subjects with PVD and trauma were 0.69 m/s and 1.11 m/s, respectively, while that of able-bodied control subjects was 1.20 m/s. When data were compared on the basis of freely selected walking speed, numerous differences were found in temporospatial, kinematic, and kinetic parameters between the PVD and trauma groups. However, when data from similar speeds were compared, the temporospatial, kinematic, and kinetic gait data demonstrated no statistically significant differences between the 2 amputee groups. Although not statistically significant, the PVD group displayed increased knee (P=.09) and hip (P=.06) flexion during the swing phase, whereas the trauma group displayed increased pelvic obliquity (P=.06). These actions were believed to represent different strategies to increase swing phase foot clearance. Also, the PVD group exhibited slightly greater hip power (P=.05) before toe-off.
Many of the differences observed in the quantitative gait data between the trauma and PVD groups appeared to be directly associated with their freely selected walking speed; the trauma group walked at significantly faster freely selected speeds than the PVD group. When their walking speeds were matched, both amputee groups displayed similar gait characteristics, with the exception that they might use slightly different strategies to increase foot clearance.
Archives of physical medicine and rehabilitation 08/2008; 89(7):1386-94. · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Targeted reinnervation is a surgical technique developed to increase the number of myoelectric input sites available to control an upper-limb prosthesis. Because signals from the nerves related to specific movements are used to control those missing degrees-of-freedom, the control of a prosthesis using this procedure is more physiologically appropriate compared to conventional control. This procedure has successfully been performed on three people with a shoulder disarticulation level amputation and three people with a transhumeral level amputation. Performance on timed tests, including the box-and-blocks test and clothespin test, has increased two to six times. Options for new control strategies are discussed.
IEEE Transactions on Neural Systems and Rehabilitation Engineering 03/2008; 16(1):46-50. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The function of current artificial arms is limited by inadequate control methods. We developed a technique that used nerve transfers to muscle to develop new electromyogram control signals and nerve transfers to skin, to provide a pathway for cutaneous sensory feedback to the missing hand.
We did targeted reinnervation surgery on a woman with a left arm amputation at the humeral neck. The ulnar, median, musculocutaneous, and distal radial nerves were transferred to separate segments of her pectoral and serratus muscles. Two sensory nerves were cut and the distal ends were anastomosed to the ulnar and median nerves. After full recovery the patient was fit with a new prosthesis using the additional targeted muscle reinnervation sites. Functional testing was done and sensation in the reinnervated skin was quantified.
The patient described the control as intuitive; she thought about using her hand or elbow and the prosthesis responded appropriately. Functional testing showed substantial improvement: mean scores in the blocks and box test increased from 4.0 (SD 1.0) with the conventional prosthesis to 15.6 (1.5) with the new prosthesis. Assessment of Motor and Process Skills test scores increased from 0.30 to 1.98 for motor skills and from 0.90 to 1.98 for process skills. The denervated anterior chest skin was reinnervated by both the ulnar and median nerves; the patient felt that her hand was being touched when this chest skin was touched, with near-normal thresholds in all sensory modalities.
Targeted reinnervation improved prosthetic function and ease of use in this patient. Targeted sensory reinnervation provides a potential pathway for meaningful sensory feedback.
The Lancet 03/2007; 369(9559):371-80. · 39.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The gait characteristics of persons with unilateral transtibial amputations are fairly well documented in the literature. However, much less is known about the gait of persons with bilateral transtibial amputations. This study used quantitative gait analysis to investigate the gait characteristics of 19 persons with bilateral transtibial amputations. To reduce variability between subjects, we fitted all subjects with Seattle Lightfoot II feet 2 weeks before their gait analyses. The data indicated that subjects walked with symmetrical temporospatial, kinematic, and kinetic parameters. Compared with nondisabled controls, the subjects with amputations walked with slower speeds and lower cadences, had shorter step lengths and wider step widths, and displayed hip hiking during swing phase. Additionally, compared with the nondisabled controls walking at comparable speeds, the subjects with amputations demonstrated reduced ankle dorsiflexion and knee flexion in stance phase, reduced peak ankle plantar flexor moment, reduced positive ankle power (i.e., energy return) in late stance, and increased positive and negative hip power. These results demonstrate the deficiencies in current prosthetic componentry and suggest that further research is needed to enhance prosthesis function and improve gait in persons with amputations.
The Journal of Rehabilitation Research and Development 02/2007; 44(4):491-501. · 1.69 Impact Factor