Static and dynamic pressure prediction for prosthetic socket fitting assessment utilising an inverse problem approach

The AERO prosthetic liner: socket pressure distribution, comfort and material composition

PURPOSE

This study aimed to evaluate the pressure distribution and comfort of transtibial prosthesis wearers using an affordable ethyl-vinyl acetate (EVA) roll-on (AERO) liner.

METHOD

Fifteen unilateral transtibial prosthesis users wore patella tendon bearing (PTB) sockets with a polyethylene foam (PE-lite) liner were enrolled this study. AERO liners were provided to all participants. Six force sensors were applied to the residual limb to evaluate pressure distribution during treadmill walking, and the socket comfort score (SCS) was used to evaluate comfortability. Fourier transform infrared (FT-IR) spectroscopy was performed on the EVA and PE-lite liners.

RESULTS

Eleven participants used prefabricated AERO liners and four participants used custom-made AERO liners. The pressure distribution was analysed by the coefficient of variation (CV): PE-lite was 75.7 ± 6.0 and AERO liner 83.3 ± 4.1. Residual limb pressure was significantly decreased when using the AERO liner (p = .0007), with a large effect size (r = 0.87). Mean SCS was 7.5 ± 1.3 and 8.9 ± 1.1 for PE-lite and AERO liner respectively.

CONCLUSION

Better pressure distribution and comfort were observed when the participants used the AERO liner. AERO had a greater proportion of calcium carbonate (CaCO3). These findings suggest that the AERO liner is a better off-the-shelf option for persons using traditional prosthetic sockets and liners.

Use of machine learning in the field of prosthetics and orthotics: A systematic narrative review

Although machine learning is not yet being used in clinical practice within the fields of prosthetics and orthotics, several studies on the use of prosthetics and orthotics have been conducted. We intend to provide relevant knowledge by conducting a systematic review of prior studies on using machine learning in the fields of prosthetics and orthotics. We searched the Medical Literature Analysis and Retrieval System Online (MEDLINE), Cochrane, Embase, and Scopus databases and retrieved studies published until July 18, 2021. The study included the application of machine learning algorithms to upper-limb and lower-limb prostheses and orthoses. The criteria of the Quality in Prognosis Studies tool were used to assess the methodological quality of the studies. A total of 13 studies were included in this systematic review. In the realm of prostheses, machine learning has been used to identify prosthesis, select an appropriate prosthesis, train after wearing the prosthesis, detect falls, and manage the temperature in the socket. In the field of orthotics, machine learning was used to control real-time movement while wearing an orthosis and predict the need for an orthosis. The studies included in this systematic review are limited to the algorithm development stage. However, if the developed algorithms are actually applied to clinical practice, it is expected that it will be useful for medical staff and users to handle prosthesis and orthosis.

A novel characterisation protocol of mechanical interactions between the ground and a tibial prosthesis for long jump

The mechanical study of Running Specific Prostheses (RSPs) is often limited to the blade. The setup developed and presented herein is a simple experiment, based on a mechanical testing machine and a camera, that assesses two indicators relevant to coaches and athletes in the field of athletics: secant stiffness and energy dissipation. The influence of four parameters on global prosthesis behaviour is evaluated: the load line offset, the prosthesis-ground angle, the sole type and the flooring type. The load line offset and the flooring type have little to no influence on their behaviour. The prosthesis-ground angle impacts the stiffness: an increase in the angle brings a significant decrease in stiffness, which strongly impacts the performance. The type of sole modifies the kinematics of the blade tip's interaction with the ground. However, this effect is less likely to enhance the sports practice since athletics imposes the use of spikes. The camera images allow assessing the local behaviour of the sole, thus enabling to follow its strain through the compression process.

The use of conformal lattice metamaterials for relieving stress in lower limb sockets: A numerical and exploratory study

Selecting the correct material for each application has always been important. Now, with lattice metamaterials engineers can take advantage of the properties of these metamaterials to best suit a specific application. This paper investigates transtibial lower limb socket stress reduction through the implementation of conformal lattice metamaterials. In this work, a model was obtained with a 3D scanner from a plaster cast taken from a participant with a trans-tibial amputation. Then a 3D socket model was created and two conformal patterns were added to the surface of the socket using nTopology®. Parametric studies to relate the lattice metamaterials constituent elements to their effective structural properties, when such are loaded in-plane and out-of-plane were also included. Pressure test simulations were performed to determine the stresses produced in the sockets. This study concludes with discussion of the results and provides information on how surface conformal patterns can improve socket performance, showing that surface-vertex-centroid patterns increase stiffness and relieve stresses.

Mapping Lower-Limb Prosthesis Load Distributions Using a Low-Cost Pressure Measurement System

Background

In the UK 55,000 people live with a major limb amputation. The prosthetic socket is problematic for users in relation to comfort and acceptance of the prosthesis; and is associated with the development of cysts and sores.

Objectives

We have developed a prototype low-cost system combining low-profile pressure sensitive sensors with an inertial measurement unit to assess loading distribution within prosthetic sockets. The objective of this study was to determine the ability of this prototype to assess in-socket loading profiles of a person with an amputation during walking, with a view to understanding socket design and fit.

Methods

The device was evaluated on four transtibial participants of various age and activity levels. The pressure sensors were embedded in the subject's sockets and an inertial measurement unit was attached to the posterior side of the socket. Measurements were taken during level walking in a gait lab.

Results

The sensors were able to dynamically collect data, informing loading profiles within the socket which were in line with expected distributions for patellar-tendon-bearing and total-surface-bearing sockets. The patellar tendon bearing subject displayed loading predominately at the patellar tendon, tibial and lateral gastrocnemius regions. The total-surface bearing subjects indicated even load distribution throughout the socket except in one participant who presented with a large socket-foot misalignment.

Conclusions

The sensors provided objective data showing the pressure distributions inside the prosthetic socket. The sensors were able to measure the pressure in the socket with sufficient accuracy to distinguish pressure regions that matched expected loading patterns. The information may be useful to aid fitting of complex residual limbs and for those with reduced sensation in their residual limb, alongside the subjective feedback from prosthesis users.

ARACAM: A RGB-D Multi-View Photogrammetry System for Lower Limb 3D Reconstruction Applications

In the world, there is a growing need for lower limb prostheses due to a rising number of amputations caused primarily, by diabetic foot. Researchers enable functional and comfortable prostheses through prosthetic design by integrating new technologies applied to the traditional handcrafted method for prosthesis fabrication that is still current. That is why computer vision shows to be a promising tool for the integration of 3D reconstruction that may be useful for prosthetic design. This work has the objective to design, prototype, and test a functional system to scan plaster cast molds, which may serve as a platform for future technologies for lower limb reconstruction applications. The image capture system comprises 5 stereoscopic color and depth cameras, each with 4 DOF mountings on an enveloping frame, as well as algorithms for calibration, segmentation, registration, and surface reconstruction. The segmentation metrics of dice coefficient and Hausdorff distance (HD) show strong visual similarity with an average similarity of 87% and average error of 6.40 mm, respectively. Moving forward, the system was tested on a known 3D printed model obtained from a computer tomography scan to which comparison results via HD show an average error of ≤1.93 mm thereby making the system competitive against the systems reviewed from the state-of-the-art.

Characterising Residual Limb Morphology and Prosthetic Socket Design Based on Expert Clinician Practice

Functional, comfortable prosthetic limbs depend on personalised sockets, currently designed using an iterative, expert-led process, which can be expensive and inconvenient. Computer-aided design and manufacturing (CAD/CAM) offers enhanced repeatability, but far more use could be made from clinicians’ extensive digital design records. Knowledge-based socket design using smart templates could collate successful design features and tailor them to a new patient. Based on 67 residual limb scans and corresponding sockets, this paper develops a method of objectively analysing personalised design approaches by expert prosthetists, using machine learning: principal component analysis (PCA) to extract key categories in anatomic and surgical variation, and k-means clustering to identify local ‘rectification’ design features. Rectification patterns representing Total Surface Bearing and Patella Tendon Bearing design philosophies are identified automatically by PCA, which reveals trends in socket design choice for different limb shapes that match clinical guidelines. Expert design practice is quantified by measuring the size of local rectifications identified by k-means clustering. Implementing smart templates based on these trends requires clinical assessment by prosthetists and does not substitute training. This study provides methods for population-based socket design analysis, and example data, which will support developments in CAD/CAM clinical practice and accuracy of biomechanics research.

Proof of Concept for the Detection of Local Pressure Marks in Prosthesis Sockets Using Structural Dynamics Measurement

The wear comfort of a prosthesis is of great importance for amputee patients. The wear comfort can be affected by changes in the interface between the residual limb and prosthesis socket, which can be caused by time-dependent volume fluctuations of the tissue, leading to unwanted local pressure marks. The basis to ensure time-independent wear comfort of a prosthesis is to identify these changes. Common techniques for identifying these variations have a negative impact on the sensitive interface between the residual limb and prosthesis. The following paper contains a proof of concept for the detection of local pressure marks without affecting the described interface using structural dynamics measurements, exemplarily shown at a prosthetic socket for transfemoral amputees in a test bench scenario. The dynamical behaviour of the investigated system is analysed in the form of frequency response functions acquired for different pressure locations and preloads using an impact hammer for excitation and a triaxial acceleration sensor. The frequency response functions show major changes for the various boundary conditions with respect to their frequency-dependent compositions. The results demonstrate how the utilised method enables the identification of changes in local pressure marks regarding the variation of position and magnitude.

Lower limb prosthetic interfaces: Clinical and technological advancement and potential future direction

The human-prosthesis interface is one of the most complicated challenges facing the field of prosthetics, despite substantive investments in research and development by researchers and clinicians around the world. The journal of the International Society for Prosthetics and Orthotics, Prosthetics and Orthotics International, has contributed substantively to the growing body of knowledge on this topic. In celebrating the 50th anniversary of the International Society for Prosthetics and Orthotics, this narrative review aims to explore how human-prosthesis interfaces have changed over the last five decades; how research has contributed to an understanding of interface mechanics; how clinical practice has been informed as a result; and what might be potential future directions. Studies reporting on comparison, design, manufacturing and evaluation of lower limb prosthetic sockets, and osseointegration were considered. This review demonstrates that, over the last 50 years, clinical research has improved our understanding of socket designs and their effects; however, high-quality research is still needed. In particular, there have been advances in the development of volume and thermal control mechanisms with a few designs having the potential for clinical application. Similarly, advances in sensing technology, soft tissue quantification techniques, computing technology, and additive manufacturing are moving towards enabling automated, data-driven manufacturing of sockets. In people who are unable to use a prosthetic socket, osseointegration provides a functional solution not available 50 years ago. Furthermore, osseointegration has the potential to facilitate neuromuscular integration. Despite these advances, further improvement in mechanical features of implants, and infection control and prevention are needed.

An investigation on effects of amputee's physiological parameters on maximum pressure developed at the prosthetic socket interface using artificial neural network

Technological advances in prosthetics have attracted the curiosity of researchers in monitoring design and developments of the sockets to sustain maximum pressure without any soft tissue damage, skin breakdown, and painful sores. Numerous studies have been reported in the area of pressure measurement at the limb/socket interface, though, the relation between amputee's physiological parameters and the pressure developed at the limb/socket interface is still not studied. Therefore, the purpose of this work is to investigate the effects of patient-specific physiological parameters viz. height, weight, and stump length on the pressure development at the transtibial prosthetic limb/socket interface. Initially, the pressure values at the limb/socket interface were clinically measured during stance and walking conditions for different patients using strain gauges placed at critical locations of the stump. The measured maximum pressure data related to patient's physiological parameters was used to develop an artificial neural network (ANN) model. The effects of physiological parameters on the pressure development at the limb/socket interface were examined using the ANN model. The analyzed results indicated that the weight and stump length significantly affects the maximum pressure values. The outcomes of this work could be an important platform for the design and development of patient-specific prosthetic socket which can endure the maximum pressure conditions at stance and ambulation conditions.

Sport-Specific Limb Prostheses in Para Sport

Prostheses form an essential part of participation in sport and physical activity for athletes with lower or upper limb amputation. These prostheses come in the form of everyday nonsport-specific prostheses, as well as sport-specific prostheses designed to enable participation in specific sports. Sport-specific prostheses are designed to the requirements of the sport to facilitate the achievement of peak performance without causing significant risk of injury. This article addresses the various factors associated with participation in sport and physical activity for individuals with amputation, including the various prostheses for upper and lower limbs and prostheses for different sports.

Sockets for Limb Prostheses: A Review of Existing Technologies and Open Challenges

In the prosthetics field, one of the most important bottlenecks is still the human-machine interface, namely the socket. Indeed, a large number of amputees still rejects prostheses or points out a low satisfaction level, due to a sub-optimal interaction between the socket and the residual limb tissues. The aim of this paper is to describe the main parameters (displacements, stress, volume fluctuations and temperature) affecting the stump-socket interface and reducing the comfort/stability of limb prostheses. In this review, a classification of the different socket types proposed in the literature is reported, together with an analysis of advantages and disadvantages of the different solutions, from multiple viewpoints. The paper then describes the technological solutions available to face an altered distribution of stresses on the residual limb tissues, volume fluctuations affecting the stump overtime and temperature variations affecting the residual tissues within the socket. The open challenges in this research field are highlighted and the possible future routes are discussed, towards the ambitious objective of achieving an advanced socket able to self-adapt in real-time to the complex interplay of factors affecting the stump, during both static and dynamic tasks.

Use of three-dimensional digital image correlation to evaluate mechanical response of prosthetic systems

BACKGROUND AND AIM

The need of comfortable and safe prosthetic systems is an important challenge for both prosthetists and engineers. The aim of this technical note is to demonstrate the use of three-dimensional digital image correlation to evaluate mechanical response of two prosthetic systems under real patient dynamic loads.

TECHNIQUE

This note describes the use of three-dimensional digital image correlation method to obtain full-field strain and displacement measurements on the surface of two lower limb prostheses for Chopart amputation. It outlines key points of the measurement protocol and illustrates the analysis of critical regions using data obtained on specific points of interest.

DISCUSSION

The results show that the use of three-dimensional digital image correlation can be a tool for the prosthetist to optimize the prosthesis considering features related to the material and design, in order to bear with real patient-specific load conditions. Clinical relevance Three-dimensional digital image correlation can support decision-making on new designs and materials for prosthetics based on quantitative data. Better understanding of mechanical response could also assist prescription for appropriate prosthetic systems.

Systematic Review of Studies Examining Transtibial Prosthetic Socket Pressures with Changes in Device Alignment

Suitable lower-limb prosthetic sockets must provide an adequate distribution of the pressures created from standing and ambulation. A systematic search for articles reporting socket pressure changes in response to device alignment perturbation was carried out, identifying 11 studies. These were then evaluated using the American Academy of Orthotists and Prosthetists guidelines for a state-of-the-science review. Each study used a design where participants acted as their own controls. Results were available for 52 individuals and five forms of alignment perturbation. Four studies were rated as having moderate internal and external validity, the remainder were considered to have low validity. Significant limitations in study design, reporting quality and in representation of results and the suitability of calculations of statistical significance were evident across articles. Despite the high inhomogeneity of study designs, moderate evidence supports repeatable changes in pressure distribution for specific induced changes in component alignment. However, there also appears to be a significant individual component to alignment responses. Future studies should aim to include greater detail in the presentation of results to better support later meta-analyses.

Techniques for Interface Stress Measurements within Prosthetic Sockets of Transtibial Amputees: A Review of the Past 50 Years of Research

The distribution of interface stresses between the residual limb and prosthetic socket of a transtibial amputee has been considered as a direct indicator of the socket quality fit and comfort. Therefore, researchers have been very interested in quantifying these interface stresses in order to evaluate the extent of any potential damage caused by the socket to the residual limb tissues. During the past 50 years a variety of measurement techniques have been employed in an effort to identify sites of excessive stresses which may lead to skin breakdown, compare stress distributions in various socket designs, and evaluate interface cushioning and suspension systems, among others. The outcomes of such measurement techniques have contributed to improving the design and fitting of transtibial sockets. This article aims to review the operating principles, advantages, and disadvantages of conventional and emerging techniques used for interface stress measurements inside transtibial sockets. It also reviews and discusses the evolution of different socket concepts and interface stress investigations conducted in the past five decades, providing valuable insights into the latest trends in socket designs and the crucial considerations for effective stress measurement tools that lead to a functional prosthetic socket.

Development of an air pneumatic suspension system for transtibial prostheses

The suspension system and socket fitting of artificial limbs have major roles and vital effects on the comfort, mobility, and satisfaction of amputees. This paper introduces a new pneumatic suspension system that overcomes the drawbacks of current suspension systems in donning and doffing, change in volume during daily activities, and pressure distribution in the socket-stump interface. An air pneumatic suspension system (APSS) for total-contact sockets was designed and developed. Pistoning and pressure distribution in the socket-stump interface were tested for the new APSS. More than 95% of the area between each prosthetic socket and liner was measured using a Tekscan F-Scan pressure measurement which has developed matrix-based pressure sensing systems. The variance in pressure around the stump was 8.76 kPa. APSS exhibits less pressure concentration around the stump, improved pressure distribution, easy donning and doffing, adjustability to remain fitted to the socket during daily activities, and more adaptability to the changes in stump volume. The volume changes were adjusted by utility of air pressure sensor. The vertical displacement point and reliability of suspension were assessed using a photographic method. The optimum pressure in every level of loading weight was 55 kPa, and the maximum displacement was 6 mm when 90 N of weight was loaded.

Review of the socket design and interface pressure measurement for transtibial prosthesis

Socket is an important part of every prosthetic limb as an interface between the residual limb and prosthetic components. Biomechanics of socket-residual limb interface, especially the pressure and force distribution, have effect on patient satisfaction and function. This paper aimed to review and evaluate studies conducted in the last decades on the design of socket, in-socket interface pressure measurement, and socket biomechanics. Literature was searched to find related keywords with transtibial amputation, socket-residual limb interface, socket measurement, socket design, modeling, computational modeling, and suspension system. In accordance with the selection criteria, 19 articles were selected for further analysis. It was revealed that pressure and stress have been studied in the last decaeds, but quantitative evaluations remain inapplicable in clinical settings. This study also illustrates prevailing systems, which may facilitate improvements in socket design for improved quality of life for individuals ambulating with transtibial prosthesis. It is hoped that the review will better facilitate the understanding and determine the clinical relevance of quantitative evaluations.