Development and preliminary evaluation of the VA Seattle foot

Vibration Suppression of a Composite Prosthetic Foot Using Piezoelectric Shunt Damping: Implications to Vibration-Induced Cumulative Trauma

OBJECTIVE

Energy-storage-and-return (ESAR) prosthetic feet have improved amputee mobility due to their efficient conversion of strain energy to mechanical work. However, this efficiency is typically achieved using light-weight, high-stiffness materials, which generate high-frequency vibrations that are potentially injurious if transmitted to biological tissues. To reduce the vibration which may cause cumulative tissue trauma, high-frequency vibration suppression by piezoelectric shunt damping patches on a commercial ESAR foot was evaluated.

METHODS

Two patches with either passive or active shunt circuits were placed on the foot to investigate vibration suppression during experimental tests where a plastic hammer was used to hit a clamped ESAR foot on the free end. Prosthesis bending moments at each modal frequency were obtained by finite element methods to identify piezoelectric patch placement.

RESULTS

Both shunt circuits decreased vibration amplitudes at specific modes better than the no shunt case, but also increased the amplitude at specific frequencies. The vibration suppression performance of the active shunt circuit deteriorated at the second mode, while the vibration suppression performance of the passive shunt circuit deteriorated at all frequencies above the third mode.

CONCLUSIONS

These results indicate piezoelectric shunt patches may be a viable strategy for decreasing vibrations of an ESAR foot, with active methods more efficient at suppressing high-frequency vibrations. Additional research is necessary to fine-tune the method for maximal vibration suppression.

SIGNIFICANCE

Overall, this study indicates that high-frequency vibration suppression is possible using piezoelectric patches, possibly decreasing the cumulative tissue damage that may occur with repetitive exposure to vibration.

ADVANCES REGARDING POWERED PROSTHESIS FOR TRANSTIBIAL AMPUTATION

The necessity for developing advanced prostheses are apparent in light of projections that the forecast for the number of people enduring amputation will double by the year 2050. The transtibial powered prosthesis that enables positive mechanical work about the ankle during the powered plantar flexion aspect of stance phase constitutes a paradigm shift in available transtibial prostheses. The objective of the review is to advocate the state of the art regarding the transtibial powered prosthesis. The historic origins of the prosthesis and motivations for amputation are clarified. The phases of gait and the compensatory mechanisms and asymmetries inherent with passive transtibial prostheses are described. The three general classes of transtibial prosthesis (passive, energy storage and return and powered prostheses) are defined. Subsystems that are integral to the powered prosthesis are explained, such as the series elastic actuator and control architecture. Gait analysis systems and their role for the test and evaluation of energy storage and return and powered prostheses are demonstrated. Future advanced concepts; such as the integration of titin into novel muscle models that account for force enhancement and force depression including their implications for cutting edge bio-inspired actuators are elucidated. The review accounts for the evolution of the prosthetic device with regards to the scope of transtibial amputation and assesses the current state-of-the-art.

Sport prostheses and prosthetic adaptations for the upper and lower limb amputees: an overview of peer reviewed literature

BACKGROUND

Sport prostheses are used by both upper- and lower-limb amputees while participating in sports and other physical activities. Although the number of these devices has increased over the past decade, no overview of the peer reviewed literature describing them has been published previously. Such an overview will allow specialists to choose appropriate prostheses based on available scientific evidence rather than on personal experience or preference.

OBJECTIVE

To provide an overview of the sport prostheses as they are described by the papers published in peer reviewed literature.

STUDY DESIGN

Literature review.

METHODS

Four electronic databases were searched using free text and Medical Subject Headings (MESH) terms. Papers were included if they concerned a prosthesis or a prosthetic adaptation used in sports. Papers were excluded if they did not originate from peer reviewed sources, if they concerned prostheses for body parts other than the upper or lower limbs, if they concerned amputations distal to the wrist or ankle, or if they were written in a language other than English.

RESULTS

Twenty-four papers were included in this study. The vast majority contained descriptive data and consisted of expert opinions and technical notes.

CONCLUSION

Data concerning the energy efficiency, technical characteristics and special mechanical properties of prostheses or prosthetic adaptations for sports, other than running, are scarce.

A methodology for studying the effects of various types of prosthetic feet on the biomechanics of trans-femoral amputee gait

This paper reports on a methodology developed for studying the effects of various types of prosthetic feet on the gait of trans-femoral amputees. It is shown that an analysis in three planes of motion of not only the prosthetic, but also the sound limb provides important information on the performance of prosthetic feet. Two male trans-femoral amputees were tested with four different prosthetic feet; the Springlite II, Carbon Copy III, Seattle LightFoot and the Multiflex foot. A detailed analysis of the results of one amputee and a summary of the most important results of a second subject is presented. The tests were carried out at normal (1.16 m s(-1)) and fast (1.56 m s(-1)) walking speeds. Three dimensional gait analysis was carried out to derive the time curves of the joint angles, intersegmental moments and power at the ankle, knee and hip joints at both the prosthetic and sound sides. A higher first peak of the ground reaction force at the sound side with the Seattle LightFoot compared to that with the Springlite II, may be the result of the lower late stance dorsiflexion angle with the former. Compared to the other two feet, the Carbon Copy III and the Springlite II showed higher prosthetic dorsiflexing moments and positive power at late stance, which could assist in the push-off. The 3D intersegmental loads at the ankle and knee can be used as a guide for design and for compilation of standards for testing of lower limb prostheses incorporating flexible feet.

Mass and mass distribution of below-knee prostheses: effect on gait efficacy and self-selected walking speed

OBJECTIVE

To study mass and mass distribution effect on function of below-knee prostheses.

DESIGN

Design modifications were done to produce proximal center of mass location versus distal center of mass location variations, and prosthesis weight was modified from 42% to 70% of normal limb weight. Work across joints of affected and unaffected extremities was compared to assess the ability of the prosthesis to substitute for function loss.

SETTING

University biomechanics laboratory.

PARTICIPANTS

Fifteen volunteers with below-knee amputations, residual limb length greater than 8.3 cm, but excluding Syme amputations.

INTERVENTIONS

Patients walked with all configurations at self-selected walking speeds and 120 m/min.

MAIN OUTCOME MEASURES

Self-selected walking speed and metabolic efficiency. Work across the joints of affected and unaffected sides was compared.

RESULTS

Proximal center of mass location produced a more efficient gait. Weight change from 42% to 70% of normal had no significant effect. Mechanical studies show that the prosthesis is a relatively poor substitute for the normal limb; most work is done by the nonamputated side. Particularly, the prosthesis failed to produce effective forward impulses on the body, resulting from push-off and deceleration of the swing leg.

CONCLUSIONS

For a proximal center of mass, lightweight distal components (e.g., feet) should be used; it is questionable whether further expenditure to develop ultralightweight prostheses would be cost effective for level walking.

Fatigue testing of energy storing prosthetic feet

This paper describes a simple approach to the fatigue testing of prosthetic feet. A fatigue testing machine for prosthetic feet was designed as part of the programme to develop an energy storing prosthetic foot (ESPF). The fatigue tester does not simulate the loading pattern on the foot during normal walking. However, cyclic vertical loads are applied to the heel and forefoot during heel-strike and toe-off respectively, for 500,000 cycles. The maximum load applied was chosen to be 1.5 times that applied by the bodyweight of the amputee and the test frequency was chosen to be 2 Hz to shorten the test duration. Four prosthetic feet were tested: two Lambda feet (a newly developed ESPF), a Kingsley SACH foot and a Proteor SACH foot. It was found that the Lambda feet have very good fatigue properties. The Kingsley SACH foot performed better than the Proteor model, with no signs of wear at the heel. The results obtained using the simple approach was found to be comparable to the results from more complex fatigue machines which simulate the load pattern during normal walking. This suggests that simple load simulating machines, which are less costly and require less maintenance, are useful substitutes in studying the fatigue properties of prosthetic feet.

Dynamics of below-knee child amputee gait: SACH foot versus Flex foot

Gait kinematics and dynamics during stance of unilateral, below-knee child amputees were analyzed for self-selected, comfortable (0.9 m s-1) and fast (1.3 m s-1) speeds with the SACH foot and the energy-storing Flex-foot prostheses. The three-dimensional movements of the lower limbs were recorded and synchronized with ground reaction forces for 12 subjects (7 girls and 5 boys, ages 6-16 yr). Each lower limb was modeled as a set of interconnected rigid links (thigh, leg, and foot) with frictionless joints (hip, knee, and ankle) to calculate moment and joint power profiles. Marked asymmetries were noted in ground reaction force, joint moment, and power profiles for the prosthetic versus the natural limb, but with the Flex foot the asymmetries were less pronounced than with the SACH foot. For the amputee wearing the Flex foot, greater moments and power were generated by the natural limb at the comfortable pace as compared to the SACH foot, but during fast walking, the SACH foot required greater output from the natural limb. With both prostheses, for the prosthetic limb the amputees used similar force, moment, and power patterns, but with significantly different amplitudes. At both speeds of walking, the Flex foot returned significantly more energy (66% at comfortable and 70% at fast walking) than the SACH foot (21% at comfortable and 19% at fast walking). Thus, the Flex foot had a greater potential for reducing the energy cost of walking at comfortable and fast speeds for the below-knee child amputee.

Comprehensive analysis of dynamic elastic response feet: Seattle Ankle/Lite Foot versus SACH foot

This study evaluated biomechanical and metabolic performance differences between two prosthetic foot designs in light of their mechanical properties. Ten unilateral below-knee amputee subjects, at least 1 year after amputation, capable of walking and running, were studied. Differences in heel and forefoot compliance explained differences in gait events and alignment. Increased efficiency of pushoff in the Seattle Ankle/Lite Foot exists as evidenced by the decrease loading on the opposite limb during double support and a less shortened step length on the sound side compared to the SACH foot. The natural frequency of oscillation for the prosthetic feet was determined to be too high to provide energy storage and release synchronized with kinematic requirements because neither metabolic cost savings nor differences in metabolic efficiency were found. Comfortable walking speed and the nadir of metabolic rate and efficiency are not different. Via accelerometer measurement, it was found that the more compliant and lossy SACH foot heel was less likely to transmit high frequency vibration.

The effect of footwear mass on the gait patterns of unilateral below-knee amputees

This study reports an investigation into the effect of shoe mass on the gait patterns of below-knee (BK) amputees. Ten established unilateral BK, patellar-tendon-bearing prosthesis wearers were assessed using a VICON system of gait analysis. Incremental masses of 50g (up to 200g) were added to the subjects' shoes and data captured as they walked along a 15m measurement field. Coefficients of symmetry of various parameters of the swing phase (knee frequency symmetry, swing time symmetry) were measured and their correlation was tested with the patient's preferred shoe mass and also their own shoe mass, all expressed as a proportion of body mass. The subjects' 'preferred' shoe mass (139-318g) showed the greatest symmetry in all the parameters examined (correlations 0.78-0.81 p less than 0.01 and less than 0.005), whereas there was no correlation between the subjects' own shoe mass (121-325g) and the symmetry coefficients measured.

Prosthetics, orthotics, and assistive devices. 1. General concepts

This self-directed learning module highlights the general concepts and new advances in the area of orthotics and prosthetics. This general overview is part of the chapter on prosthetics, orthotics, and assistive devices for the Self-Directed Medical Knowledge Program Study Guide for practitioners and trainees in physical medicine and rehabilitation. This section contains essential information on spinal, lower and upper limb orthotics, lower and upper limb prosthetics, juvenile prosthetics, kinesiology, motion analysis, and assistive devices such as canes and crutches. This article establishes a foundation on which the second, third, and fourth articles of this chapter will build. The three articles to follow review newer developments in specialized seating and assistive devices, prosthetics, and the orthotic management of selected disorders.