A Review of Prosthetic Interface Stress Investigations

Over the last decade, numerous experimental and numerical analyses have been conducted to investigate the stress distribution between the residual limb and prosthetic socket of persons with lower limb amputation. The objectives of these analyses have been to improve our understanding of the residual limb/prosthetic socket system, to evaluate the influence of prosthetic design parameters and alignment variations on the interface stress distribution, and to evaluate prosthetic fit. The purpose of this paper is to summarize these experimental investigations and identify associated limitations. In addition, this paper presents an overview of various computer models used to investigate the residual limb interface, and discusses the differences and potential ramifications of the various modeling formulations. Finally, the potential and future applications of these experimental and numerical analyses in prosthetic design are presented

The Design, Development, and Validation of a Residual Limb Evaluation System for the Real-Time Data Mapping of the Trans-Tibial Amputee Socket-Limb Interface for Prosthetic Fitment

Introduction: Skin problems are known to occur on the residual limb (RL) of trans-tibial amputees (TTAs). These are induced by an improper prosthetic socket fitment, alignment or component selection. It was identified that there is a lack of RL evaluation systems (RLESs) that are tailored for the prosthetic fitting procedure that analyse the pressures and temperatures on the RL, as well as the gait phases of stance. This observation established the hypothesis that a tactile RL evaluation device and recording software system can provide reliable socket-limb interface (SLI) information which can be used to identify vulnerable areas on the RL induced by the socket during the gait movements of TTAs. Methods: A prototype RLES was designed and developed. It was comprised of tactile pressure and temperature transducers, gait ground reaction force (GRF) transducers and device-specific software tailored for the evaluation of the RL within the SLI. A pilot study was designed to evaluate the capabilities of the RLES which entailed the evaluation of its skin temperature tracking ability, pressure measurement repeatability within the SLI, and ability to interpret the pressures during (natural) walking movements. Study participants were recruited through the private practice of prosthetist Eugene Russouw, as well as Vincent Palloti Hospital (South Africa, Cape Town) and consisted of two bilateral and three unilateral TTAs, who were enrolled in the pilot study. Each participant performed three experimental procedures: a static stand (SS); a straight-line walk (SLW); and a figure-of-8 walk (F8W). Skin temperature change due to loading and unloading was monitored during the SS procedure. Peak pressure results from the SLW and F8W procedures were gathered to evaluate the coefficient of variance (COV) between strides. This was used to evaluate the repeatability of the pressure measurements and allowed for a comparison between the SLW and F8W methods. GRF data collected from the SLW dataset was used to evaluate the RLES's ability to track gait phases. Results: The developed RLES software provided a tailored prosthetic fitting analysis platform (in the form of a graphical user interface) which allowed the user to perform a real-time, in-depth analysis of different RL areas, as well as provided an overview of all areas simultaneously. It provided functions for the recording, playback, and export of testing data which was used to evaluate the RLES capabilities. The RLES produced an average COV of 7.16%, which fell within the 6.94% ± 1.7% range in literature. The SS procedure produced an average temperature increase of 0.45 °C, found over all RL areas, which corresponds to similar studies in literature. This validated its ability to track RL skin temperature by producing the expected skin temperature change trend. Additionally, the RLES produced an expected TTA gait GRF curve (similar to literature) in which different gait phases could be identified. The comparison between the SLW and F8W methods found that pressure sore areas endured large pressures without relief from other movements (when compared to healthier areas), and suggests that the SLW and F8W comparison may be an important additional evaluation method during the prosthetic fitting procedure. The RLES identified all of the pressure sores presented within the 24 RL areas over all the TTA participants and suggested that a safe pressure threshold of 100 kPa is an appropriate guideline to be used during the prosthetic fitting procedure. Conclusions: The RLES proved to work efficiently and successfully within the study, and was capable of identifying vulnerable areas of pressure sores. With the high prevalence of skin problems on the RLs of TTAs, the implementation of a RLES during the fitting procedure, which can tailor the prosthesis design and fitment to the amputee, may potentially identify vulnerable areas of future skin problems and allow preventative actions to be performed

Clinical utility of pressure feedback to socket design and fabrication

Background: The clinical utility of measuring pressure at the prosthetic socket-residual limb interface is currently unknown. Objectives: This study aimed to identify whether measuring interface pressure during prosthetic design and fabrication results in closer agreement in pressure measurements between sockets made by different clinicians, and a reduction in pressure over areas of concern. It also investigated whether clinicians value knowing the interface pressure during the fabrication process. Study design: Mixed methods. Methods: Three prosthetists designed a complete prosthetic system for a transtibial residual limb surrogate. Standardised mechanical testing was performed on each prosthetic system to gain pressure measurements at four key anatomical locations. These measurements were provided to the clinicians, who subsequently modified their sockets as each saw fit. The pressure at each location was re-measured. Each prosthetist completed a survey that evaluated the usefulness of knowing interface pressures during the fabrication process. Results: Feedback and subsequent socket modifications saw a reduction in the pressure measurements at three of the four anatomical locations. Furthermore, the pressure measurements between prosthetists converged. All three prosthetists found value in the pressure measurement system and felt they would use it clinically. Conclusions: Results suggest that sensors measuring pressure at the socket-limb interface has clinical utility in the context of informing prosthetic socket design and fabrication. If the technology is used at the check socket stage, iterative designs with repeated measurements can result in increased consistency between clinicians for the same residual limb, and reductions in the magnitudes of pressures over specific anatomical landmarks. Clinical relevance This study provides new information on the value of pressure feedback to the prosthetic socket design process. It shows that with feedback, socket modifications can result in reduced limb pressures, and more consistent pressure distributions between prosthetists. It also justifies the use of pressure feedback in informing clinical decisions

A personalised prosthetic liner with embedded sensor technology:a case study

BACKGROUND: Numerous sensing techniques have been investigated in an effort to monitor the main parameters influencing the residual limb/prosthesis interface, fundamental to the optimum design of prosthetic socket solutions. Sensing integration within sockets is notoriously complex and can cause user discomfort. A personalised prosthetic liner with embedded sensors could offer a solution. However, to allow for a functional and comfortable instrumented liner, highly customised designs are needed. The aim of this paper is to presents a novel approach to manufacture fully personalised liners using scanned three-dimensional image data of the patient's residual limb, combined with designs that allow for sensor integration. To demonstrate the feasibility of the proposed approach, a personalised liner with embedded temperature and humidity sensors was realised and tested on a transtibial amputee, presented here as a case study. METHODS: The residual limb of a below knee amputee was first scanned and a three-dimensional digital image created. The output was used to produce a personalised prosthesis. The liner was manufactured using a cryogenic Computer Numeric Control (CNC) machining approach. This method enables fast, direct and precise manufacture of soft elastomer products. Twelve Hygrochron Data Loggers, able to measure both temperature and humidity, were embedded in specific liner locations, ensuring direct sensor-skin contact. The sensor locations were machined directly into the liner, during the manufacturing process. The sensors outputs were assessed on the below amputee who took part in the study, during resting (50 min) and walking activities (30 min). To better describe the relative thermal properties of new liner, the same tests were repeated with the amputee wearing his existing liner. Quantitative comparisons of the thermal properties of the new liner solution with that currently used in clinical practice are, therefore, reported. RESULTS: The liner machining process took approximately 4 h. Fifteen minutes after donning the prosthesis, the skin temperature reached a plateau. Physical activity rapidly increased residuum skin temperatures, while cessation of activity caused a moderate decrease. Humidity increased throughout the observation period. In addition, the new liner showed better thermal properties with respect to the current liner solution (4% reduction in skin temperature). CONCLUSIONS: This work describes a personalised liner solution, with embedded temperature and humidity sensors, developed through an innovative approach. This new method allows for a range of sensors to be smoothly embedded into a liner, which is capable of measuring changes in intra-socket microclimate conditions, resulting in the design of advanced socket solutions personalised specifically for individual requirements. In future, this method will not only provide a personalised liner but will also enable dynamic assessment of how a residual limb behaves within the socket during daily activities.</p

Examination of the performance characteristics of velostat as an in-socket pressure sensor

Velostat is a low-cost, low-profile electrical bagging material with piezoresistive properties, making it an attractive option for in-socket pressure sensing. The focus of this research was to explore the suitability of a Velostat-based system for providing real-time socket pressure profiles. The prototype system performance was explored through a series of bench tests to determine properties including accuracy, repeatability and hysteresis responses, and through participant testing with a single subject. The fabricated sensors demonstrated mean accuracy errors of 110 kPa and significant cyclical and thermal drift effects of up to 0.00715 V/cycle and leading to up to a 67% difference in voltage range respectively. Despite these errors the system was able to capture data within a prosthetic socket, aligning to expected contact and loading patterns for the socket and amputation type. Distinct pressure maps were obtained for standing and walking tasks displaying loading patterns indicative of posture and gait phase. The system demonstrated utility for assessing contact and movement patterns within a prosthetic socket, potentially useful for improvement of socket fit, in a low cost, low profile and adaptable format. However, Velostat requires significant improvement in its electrical properties before proving suitable for accurate pressure measurement tools in lower limb prosthetics

Quantitative analysis of interface pressures in transfemoral prosthetic sockets

Background: Among the different factors affecting socket comfort, the pressure applied on residual limb tissues is a crucial parameter for the success or failure of any prosthetic device. However, only a few incomplete data are available on people with transfemoral amputation, in this regard. This work aims at filling this gap in the literature. Methods: Ten people with transfemoral amputation wearing 3 different socket designs were recruited in this study: 2 ischial containment sockets featured by proximal trim lines that contain the ischial tuberosity and ramus and greater trochanter, 2 subischial sockets with proximal trim lines under the ischium level, and 6 quadrilateral sockets with proximal trim lines that contain the greater trochanter and create a horizontal seat for the ischial tuberosity. The pressure values at the anterior, lateral, posterior, and medial areas of the socket interface were recorded during 5 locomotion tasks (ie, horizontal, ascent, and descent walking, upstairs and downstairs) by using an F-Socket System (Tekscan Inc., Boston, MA). Gait segmentation was performed by exploiting plantar pressure, which was acquired by an additional sensor under the foot. Mean and standard deviation of minimum and maximum values were calculated for each interface area, locomotion task, and socket design. The mean pressure patterns during different locomotion tasks were reported, as well. Results: Considering all subjects irrespective of socket design, the mean pressure range resulted 45.3 (posterior)-106.7 (posterior) kPa in horizontal walking; 48.3 (posterior)-113.8 (posterior) kPa in ascent walking; 50.8 (posterior)-105.7 (posterior) kPa in descent walking; 47.9 (posterior)-102.9 (lateral) kPa during upstairs; and 41.8 (posterior)-84.5 (anterior) kPa during downstairs. Qualitative differences in socket designs have been found. Conclusions: These data allow for a comprehensive analysis of pressures acting at the tissue-socket interface in people with transfemoral amputation, thus offering essential information for the design of novel solutions or to improve existing ones, in this field

The development of an adaptive and reactive interface system for lower limb prosthetic application

Deep tissue injury (DTI) is a known problem correlating to the use of a prosthetic by a transtibial amputee (TTA), causing ulcer-like wounds on the residual limb caused by stress-induced cell necrosis. The magnitude of these stresses at the bone tissue interface has been identified computationally, far exceeding those measured at the skin's surface. Limited technology is available to directly target and reduce such cellular loading and actively reduce the risk of DTI from below-knee use. The primary aim of this project was to identify whether a bespoke prosthetic socket system could actively stiffen the tissues of the lower limb. Stabilising the residual tibia during ambulation and reducing stress concentrations on the cells. To achieve this, a proof-of-concept device was designed and manufactured, a system that allowed the change in displacement of a magnet to be responded to by counterbalancing load. The device was evaluated through experimentation on an able-bodied subject wearing an orthotic device designed to replicate the environment of a prosthetic socket. The chosen sensor effector system was validated against vector data generated by the Motek Medical Computer Assisted Rehabilitation Environment (CAREN.) The project explored a new concept of reactive loading of a below-knee prosthesis to reduce tibial/socket oscillation. The evaluation of the device indicated that external loading of the residual limb in such a manner could reduce the magnitude of rotation about the tibia and therefore minimise the conditions by which DTIs are known to occur. Efforts were made to move the design to the next iteration, focusing on implementing the target demographic.Deep tissue injury (DTI) is a known problem correlating to the use of a prosthetic by a transtibial amputee (TTA), causing ulcer-like wounds on the residual limb caused by stress-induced cell necrosis. The magnitude of these stresses at the bone tissue interface has been identified computationally, far exceeding those measured at the skin's surface. Limited technology is available to directly target and reduce such cellular loading and actively reduce the risk of DTI from below-knee use. The primary aim of this project was to identify whether a bespoke prosthetic socket system could actively stiffen the tissues of the lower limb. Stabilising the residual tibia during ambulation and reducing stress concentrations on the cells. To achieve this, a proof-of-concept device was designed and manufactured, a system that allowed the change in displacement of a magnet to be responded to by counterbalancing load. The device was evaluated through experimentation on an able-bodied subject wearing an orthotic device designed to replicate the environment of a prosthetic socket. The chosen sensor effector system was validated against vector data generated by the Motek Medical Computer Assisted Rehabilitation Environment (CAREN.) The project explored a new concept of reactive loading of a below-knee prosthesis to reduce tibial/socket oscillation. The evaluation of the device indicated that external loading of the residual limb in such a manner could reduce the magnitude of rotation about the tibia and therefore minimise the conditions by which DTIs are known to occur. Efforts were made to move the design to the next iteration, focusing on implementing the target demographic

A Scoping Review of Pressure Measurements in Prosthetic Sockets of Transfemoral Amputees during Ambulation:Key Considerations for Sensor Design

Sensor systems to measure pressure at the stump–socket interface of transfemoral amputees are receiving increasing attention as they allow monitoring to evaluate patient comfort and socket fit. However, transfemoral amputees have many unique characteristics, and it is unclear whether existing research on sensor systems take these sufficiently into account or if it is conducted in ways likely to lead to substantial breakthroughs. This investigation addresses these concerns through a scoping review to profile research regarding sensors in transfemoral sockets with the aim of advancing and improving prosthetic socket design, comfort and fit for transfemoral amputees. Publications found from searching four scientific databases were screened, and 17 papers were found relating to the aim of this review. After quality assessment, 12 articles were finally selected for analysis. Three main contributions are provided: a de facto methodology for experimental studies on the implications of intra-socket pressure sensor use for transfemoral amputees; the suggestion that associated sensor design breakthroughs would be more likely if pressure sensors were developed in close combination with other types of sensors and in closer cooperation with those in possession of an in-depth domain knowledge in prosthetics; and that this research would be facilitated by increased interdisciplinary cooperation and open research data generation.QC 20210810SocketSens

Fiber Bragg Gratings as e-Health Enablers: An Overview for Gait Analysis Applications

Nowadays, the fast advances in sensing technologies and ubiquitous wireless networking are reflected in medical practice. It provides new healthcare advantages under the scope of e-Health applications, enhancing life quality of citizens. The increase of life expectancy of current population comes with its challenges and growing health risks, which include locomotive problems. Such impairments and its rehabilitation require a close monitoring and continuous evaluation, which add financial burdens on an already overloaded healthcare system. Analysis of body movements and gait pattern can help in the rehabilitation of such problems. These monitoring systems should be noninvasive and comfortable, in order to not jeopardize the mobility and the day-to-day activities of citizens. The use of fiber Bragg gratings (FBGs) as e-Health enablers has presented itself as a new topic to be investigated, exploiting the FBGs’ advantages over its electronic counterparts. Although gait analysis has been widely assessed, the use of FBGs in biomechanics and rehabilitation is recent, with a wide field of applications. This chapter provides a review of the application of FBGs for gait analysis monitoring, namely its use in topics such as the monitoring of plantar pressure, angle, and torsion and its integration in rehabilitation exoskeletons and for prosthetic control

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.N/