Saeed Zahedi

Development and validation of a 3D-printed interfacial stress sensor for prosthetic applications.

A novel capacitance-based sensor designed for monitoring mechanical stresses at the stump-socket interface of lower-limb amputees is described. It provides practical means of measuring pressure and shear stresses simultaneously. In particular, it comprises of a flexible frame (20 mm × 20 mm), with thickness of 4mm. By employing rapid prototyping technology in its fabrication, it offers a low-cost and versatile solution, with capability of adopting bespoke shapes of lower-limb residua. The sensor was first analysed using finite element analysis (FEA) and then evaluated using lab-based electromechanical tests. The results validate that the sensor is capable of monitoring both pressure and shear at stresses up to 350 kPa and 80 kPa, respectively. A post-signal processing model is developed to induce pressure and shear stresses, respectively. The effective separation of pressure and shear signals can be potentially advantageous for sensor calibration in clinical applications. The sensor also demonstrates high linearity (approx. 5-8%) and high pressure (approx. 1.3 kPa) and shear (approx. 0.6 kPa) stress resolution performance. Accordingly, the sensor offers the potential for exploitation as an assistive tool to both evaluate prosthetic socket fitting in clinical settings and alert amputees in home settings of excessive loading at the stump-socket interface, effectively preventing stump tissue breakdown at an early stage.

Design of an efficient back-drivable semi-active above knee prosthesis

This paper presents the design and development of an electrical above knee prosthesis, which works as a passive knee prosthesis in part of gait cycle phases and as an active knee prosthesis during other portions. During the passive mode, the system works as a non-holonomic system, and the dynamic coupling between the thigh segment and the knee prosthesis is used to control the prosthesis. Therefore, this knee prosthesis is designed to be back-drivable in passlve mode. In order to present a proper design for the knee prosthesis, the mechanism synthesis and analysis for the proposed back-drivable semi-active knee prosthesis are covered in this paper.

Motor electrical damping for back-drivable prosthetic knee

The paper presents a model and analysis of a back-drivable knee prosthesis. In this context, the investigation into the design, modelling and analysis of a back-drivable semi-active prosthetic knee is presented. A mathematical model has been developed for evaluating the electrical damping characteristics of the DC motor in passive mode. The analysis shows that a single actuator could be suitable to work in active mode to provide mechanical power and in passive mode as a damper dissipating energy.

Comparison of passive and active prosthetic knee joint kinematics during swing phase of gait

The goal of this paper was to assess this hypothesis that a powered prosthetic knee, to which net power is delivered, is capable of emulating the swing phase of the biological knee better than an energetically passive knee. Lower extremity was modeled as a two-degree of freedom linkage, for which hip and knee were joints. Based on an inverse dynamics approach, computer simulations were carried out to calculate both active and passive prosthetic knee angles during swing phase of gait. Results showed that since an active prosthetic knee can deliver power, it can mimic the normal knee flexion angle better than a passive one. Consequently, it can lead to a more symmetric, and therefore, more efficient gait.

Inertia Properties of a Prosthetic Knee Mechanism

The prosthetic knee mechanism should be able to assist amputees during activities of daily living and improve their quality of life. The inertia asymmetry between intact and the prosthetic sides is one of the reasons for amputee gait asymmetry. This paper shows how to calculate the overall inertia properties during the design process.

A COMPUTER SIMULATION OF THE EFFECT OF MUSCLE LOSS ON HIP JOINT EFFORT DURING THE STANCE PHASE OF TRANSFEMORAL AMPUTEE GAIT

The effect of muscle loss on the energy expenditure of hip joint, and its individual muscles, during stance phase of gait, was studied using a computer simulation. With each muscle as an ideal force generator, the lower extremity was simulated as a two-degree of freedom linkage with the hip and knee as its joints. Kinematic data and ground reaction forces were recorded by a gait analysis system. The forces exerted by muscles were determined to produce recorded hip and knee joint angles. Simulation results showed that, due to muscle loss, the work done by hip joint of the transected limb is more than that of the intact limb. Also, as more muscles are removed from the transected limb, residual muscles should do more work to flex or extend the hip. This finding is in line with the common practice in transfemoral amputation, according to which, it is important to maintain the length of residual limb as much as possible.

Simulation of the Effect of Amputation Level on Individual Muscle Forces of Transfemoal Amputees

The purpose of this study was to quantify individual muscle forces for different levels of amputation, during swing phase of the above the knee amputees. The lower extremity was modeled as a two-degree of freedom linkage that its joints were located at hip and knee. Only the movement in the sagittal plane was considered to be important, and each muscle was modeled as an ideal force generator. The kinematic data were collected using a motion analysis system. Calculated muscle forces correspond to the electromyography activity of muscles. Results show that the forces of residual hip extensor forces become higher when other extensors are removed, and residual hip flexor forces become higher when other hip flexors are removed. This result is in line with common practice in amputation surgery according to which the surgeon should maintain the length of residual limb as much as possible.

Rethinking the foam cosmesis for people with lower limb absence

Background and aim: A recent survey of people with lower limb absence revealed that patients’ satisfaction with their foam cosmesis is lower than desired. The aim of this project was to improve the lifelike appearance, functionality and durability of the cosmesis through a user-centred design methodology. Technique: Concept development and prototyping led to a new cosmesis design which features a cut-out located at the knee, inserted with an artificial patella made of a more rigid foam. It also features a full-length zip which provides easy access for maintenance. The new cosmesis was then mechanically tested for over 1 million cycles and clinically tested by six transfemoral prosthesis users over 18 patient months. Discussion: The new design is significantly more durable than the current standard model and has an enhanced lifelike appearance. It has potential to improve users’ body image and reduce costs for healthcare providers. Clinical relevance This study contributes to practice by offering a new cosmesis design with enhanced appearance and durability, with the potential to improve patients’ body image and reduce costs associated with cosmesis fitting and maintenance.

Microprocessor knees with ‘standing support’ and articulating, hydraulic ankles improve balance control and inter-limb loading during quiet standing

Introduction Trans-femoral amputees are at risk of musculoskeletal problems that are in part caused by loading asymmetry during activities, such as prolonged standing, particularly on uneven or sloped ground. Methods Four prosthetic conditions were tested; microprocessor knee ‘standing support’ mode activated (ON) and deactivated (OFF), combined with a rigidly attached foot (RA) and with an articulating, hydraulic ankle-foot (HA). Five trans-femoral amputees and five able-bodied controls were measured using a motion capture system and a force plate while standing, facing down a 5° slope. Ground reaction force distributions and centre-of-pressure root-mean-square (COP RMS) were calculated as outcome measures. Results Compensatory kinematic adjustments were observed for RA conditions but not for HA conditions. HA-OFF reduced ground reaction force degree-of-asymmetry for all five amputees, compared to RA-OFF. RA-ON reduced ground reaction force degree-of-asymmetry for four amputees, compared to RA-OFF. In terms of balance, the HA conditions reduced the mean inter-limb COP RMS by 24–25% compared to equivalent RA conditions, while ON conditions reduced it by 9–11%, compared to equivalent OFF conditions. Conclusions It is important to consider both prosthetic knee and ankle technologies when prescribing devices to trans-femoral amputees. The combination of hydraulic ankle and knee standing support technologies produced outcomes closest to normal biomechanics.

The influence of a microprocessor-controlled hydraulic ankle on the kinetic symmetry of trans-tibial amputees during ramp walking: A case series

Introduction Asymmetrical limb loading is believed to cause health problems for lower limb amputees and is exacerbated when walking on slopes. Hydraulically damped ankle-feet improve ground compliance on slopes compared to conventional prosthetic feet. Microprocessor-controlled hydraulic ankle-feet provide further adaptation by dynamically adjusting viscoelastic damping properties. Method Using a case series design, gait analysis was performed with four trans-tibial amputees. There were two walking conditions (ramp ascent and descent) and two prosthetic foot conditions (microprocessor-control on and off – MPF-on and MPF-off). Total support moment integral ( M I sup ) and degree-of-asymmetry were compared across foot conditions. Results During ramp descent, the transition of prosthetic ankle moment from dorsiflexion to plantarflexion occurred earlier in stance phase with MPF-on, slowing the angular velocity of the shank. During ramp ascent, the MPF-on dorsiflexion/plantarflexion moment transition occurred later, meaning less resistance to shank rotation in early stance and increasing walking speed by up to 6%. For both slope conditions, sound limb M I sup was universally decreased with MPF-on (4–13% descent, 3–11% ascent). Discussion Microprocessor-control of hydraulic ankle-feet reduced the total loading of the sound limb joints, for both walking conditions, for all participants. This may have beneficial consequences for long-term joint health and walking efficiency.