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

EMG-based prediction of step direction for a better control of lower limb wearable devices

BACKGROUND AND OBJECTIVES

Lower-limb wearable devices can significantly improve the quality of life of subjects suffering from debilitating conditions, such as amputations, neurodegenerative disorders, and stroke-related impairments. Current control approaches, limited to forward walking, fall short of replicating the complexity of human locomotion in complex environments, such as uneven terrains or crowded places. Here we propose a high-level controller based on two Support Vector Machines exploiting four surface electromyography (EMG) signals of the thigh muscles to detect the onset (Toe-off intention decoder) and the direction (Directional EMG decoder) of the upcoming step.

METHODS AND MATERIALS

We validated a preliminary version of the approach by acquiring EMG signals from ten healthy subjects, performing steps in four directions (forward, backward, right, and left), in three different settings (ground-level walking, stairs, and ramps), and in both steady-state and static conditions. Both the Toe-off intention and Directional EMG decoders have been tested with a 5-fold cross-validation repeated five times, using linear and radial-basis-function kernels, and by changing the classification output timing, from 200 ms before to 50 ms after the toe-off.

RESULTS

The Toe-off intention decoder reached a median accuracy of 83.34 % (interquartile range (IQR): 6.48) and specificity of 92.72 % (IQR: 3.62) in its radial-basis-function version, while the Directional EMG decoder's median accuracy ranged between 73.92 % (IQR: 5.8), 200 ms before the toe-off, to 92.91 % (IQR: 4.11), 50 ms after the toe-off, with the radial-basis-function kernel implementation. For both the Toe-off intention and Directional EMG decoders the radial-basis-function version achieved better performances than the linear one (Wilcoxon signed rank test, p < 0.05).

CONCLUSIONS AND SIGNIFICANCE

The combination of the two decoders proved to be a promising solution to detect the step initiation and classify its direction, paving the way for wearable devices with a broader range of movements and more degrees of freedom, ultimately promoting usability in uncontrolled settings and better reactions to external perturbations. Additionally, the encumbrance of the setup is limited to the thigh of the leg of interest, which simplifies the implementation in compact devices, concurrently limiting the sensors worn by the subject.

A qualitative study exploring healthcare professionals' perceptions of lower limb 3D printed sockets

PURPOSE

The purpose of this study was to explore healthcare professionals' (HCPs) perceptions and experiences related to 3D scanning and 3D printing for fabricating lower limb prosthetic sockets.

MATERIALS AND METHODS

This study used a qualitative descriptive approach. Participants were recruited through HCPs' professional associations, social media posts, and snowball sampling. Purposive sampling was used to attain variation in provider type. One-on-one telephone interviews were conducted using a semi-structured interview guide. Inductive thematic analysis was performed to identify the main themes.

RESULTS

Three themes were identified: (1) 3D scanning of the residual limb for designing prosthetic sockets is perceived as clean, quick, and convenient; (2) concerns about the strength and safety of 3D printed sockets for long-term use; (3) Adoption of 3D scanning and 3D printing technology for fabricating prosthetic sockets.

CONCLUSION

We identified perceived benefits and challenges with digital technologies for fabricating prosthetic sockets. To increase adoption, more research demonstrating its efficacy compared to conventional methods, increasing 3D printing material quality, and improving software training programs are needed.Implications for Rehabilitation3D printing and 3D scanning are emerging digital technologies that can be used as alternative methods for prosthetic socket manufacturing in the field of rehabilitation.Our research identified perceived benefits of using digital technologies for fabricating prosthetics sockets (3D scanning is perceived as clean, quick, and convenient) and perceived challenges (concerns about the strength and safety of 3D printed sockets for long-term use and a prolonged learning curve).To increase adoption of these digital technologies, more training should be provided to prosthetists and support provided to integrate new processes into staff workloads.

Biomechanical characteristics of transfemoral bone-anchored prostheses during gait: A review of literature

BACKGROUND

Osseointegration (OI) is an emerging technique that allows a direct connection between the bone and a titanium metal implant, allowing the direct attachment of bone-anchored prostheses (BAP) to address the problems associated with socket prostheses. This review article aims to compare the biomechanical features of gait when using a transfemoral BAP in comparison to healthy gait, and in comparison to the gait of traditional transfemoral socket prosthesis users.

METHODS

A computer-based literature search of electronic databases since inception (ranging from 1967 to 2004 depending on the database) to June 14, 2022, identified peer-reviewed articles focusing on the temporal-spatial, kinematic, kinetic, and electromyography data related to transfemoral BAP gait. Eight articles were included that focused on these biomechanical features of gait in adults with BAP and were compared with socket prosthesis users or healthy gait.

RESULTS

Compared with healthy participants, prosthesis users after OI surgery have slower speed and cadence, lower symmetry, longer duration of swing phase, increased pelvic and trunk motion, more hip extension, larger moments on the intact limb, and lower forces on the prosthetic side. Compared with transfemoral socket prosthesis gait, BAP gait shows faster cadence and longer duration of support phase. There are limited and inconsistent data on changes in trunk, pelvic, and hip motion with OI.

CONCLUSION

Based on this review, transfemoral BAP improve spatial-temporal parameters closer to normal gait when compared to socket gait, but there are persisting deficits compared with healthy gait. Additional studies are needed to confirm the changes in kinematics and kinetics when walking with a BAP.

Improvement in quality of life of transfemoral amputees: Comparison between 2 types of transfemoral sockets and their influence on functionality and user comfort - A case report

Among the components of lower limb prostheses, a perfectly adapted prosthetic socket is crucial to a successful rehabilitation process. Thus, developing a more comfortable socket could improve the quality of life for transfemoral (TF) amputees. The objective of this case report was to compare 2 TF sockets by evaluating the relationship between socket stiffness and user comfort and their influence on functionality to improve the quality of life of TF amputees. The participant received 2 different sockets: (A) flexible Flixt® socket; (B) conventional socket. He used each socket for 90 days, and after that was submitted to an evaluation at the Gait Laboratory (kinematic and dynamic analyses), completed the Prosthesis Evaluation Questionnaire, and performed Timed Up and Go test, 6-Minute March Test (6MWT), 10-Meter Walk Test, and Amputee Mobility Predictor test. After results were analyzed, the socket that obtained the best degree of satisfaction was assigned to the amputee participant. Combined measures showed that socket B does not considerably change the kinematic parameters neither dynamics parameters namely at stance phase. At Prosthesis Evaluation Questionnaire results, socket A had a better rating than socket B. The results of the Timed Up and Go test, 6MWT, 10-Meter Walk Test, and Amputee Mobility Predictor test obtained identical values, except for the 6MWT. This case report shows evidence of participant satisfaction improvement when using the flexible socket. The study also demonstrates that both sockets are quite effective.

An adaptive prosthetic socket for people with transtibial amputation

It is essential that people with limb amputation maintain proper prosthetic socket fit to prevent injury. Monitoring and adjusting socket fit, for example by removing the prosthesis to add prosthetic socks, is burdensome and can adversely affect users' function and quality-of-life. This study presents results from take-home testing of a motor-driven adaptive socket that automatically adjusted socket size during walking. A socket fit metric was calculated from inductive sensor measurements of the distance between the elastomeric liner surrounding the residual limb and the socket's inner surface. A proportional-integral controller was implemented to adjust socket size. When tested on 12 participants with transtibial amputation, the controller was active a mean of 68% of the walking time. In general, participants who walked more than 20 min/day demonstrated greater activity, less doff time, and fewer manual socket size adjustments for the adaptive socket compared with a locked non-adjustable socket and a motor-driven socket that participants adjusted with a smartphone application. Nine of 12 participants reported that they would use a motor-driven adjustable socket if it were available as it would limit their socket fit issues. The size and weight of the adaptive socket were considered the most important variables to improve.

Prosthetic Limb Attachment via Electromagnetic Attraction Through a Closed Skin Envelope

OBJECTIVE

Current socket-based methods of prosthetic limb attachment are responsible for many of the dominant problems reported by persons with amputation. In this work, we introduce a new paradigm for attachment via electromagnetic attraction between a bone-anchored ferromagnetic implant and an external electromagnet. Our objective was to develop a design framework for electromagnetic attachment, and to evaluate this framework in the context of transfemoral amputation.

METHODS

We first used inverse dynamics to calculate the forces required to suspend a knee-ankle-foot prosthesis during gait. We then conducted cadaveric dissections to inform implant geometry and design a surgical methodology for covering the implant. We also developed an in silico framework to investigate how electromagnet design affects system performance. Simulations were validated against benchtop testing of a custom-built electromagnet.

RESULTS

The physical electromagnet matched simulations, with a root-mean-square percentage error of 4.2% between measured and predicted forces. Using this electromagnet, we estimate that suspension of a prosthesis during gait would require 33 W of average power. After 200 and 1000 steps of simulated walking, the temperature at the skin would increase 2.3 °C and 15.4 °C relative to ambient, respectively.

CONCLUSION

Our design framework produced an implant and electromagnet that could feasibly suspend a knee-ankle-foot prosthesis during short walking bouts. Future work will focus on optimization of this system to reduce heating during longer bouts.

SIGNIFICANCE

This work demonstrates the initial feasibility of an electromagnetic prosthetic attachment paradigm that has the potential to increase comfort and improve residual limb health for persons with amputation.

Adverse effects of unilateral transfemoral amputation on para-alpine sit skiers and mitigation methods

OBJECTIVES

This study aimed to evaluate the adverse effects of unilateral transfemoral amputation on neuromuscular and kinematic parameters in alpine sit skiers, and to determine if additional restraints on the human-bucket interface could help mitigate the effects.

DESIGN

Cross-sectional, repeated measures study.

METHODS

Simulated skiing tests were conducted indoors involving 10 skiers with unilateral transfemoral amputation and 10 able-bodied participants. A Paralympic silver medalist performed slalom skiing tests on snow. These tests were conducted with and without additional strapping on the residual limb. Surface electromyography of trunk muscles and athletic performance was measured, and the asymmetry index was calculated.

RESULTS

Athletes were significantly dependent on muscle activation on the dominant side (asymmetry index = 7.8 %-28.3 %, p < 0.05). Worse athletic performance to the dominant side was found based on inclination angles of the indoor board (asymmetry index = -9.8 %, p = 0.014) and outdoor sit ski (-11.1 %, p = 0.006), and distance to the gate poles during skiing turns (18.6 %, p < 0.001). After using additional restraints, the above asymmetry index declined significantly (asymmetry index < 4.5 %, p < 0.05). Furthermore, athletic performance was significantly improved on both body sides by 11.1 %-30.7 % (p < 0.05).

CONCLUSIONS

Unilateral transfemoral amputation caused the dependence on the trunk muscles of the dominant side and the corresponding unilateral poor performance in athletes. Adjusting restraints in the human-equipment interface by additional strapping could mitigate the asymmetry issues and improve athletic performance.

Bone-anchored prostheses for transfemoral amputation: a systematic review of outcomes, complications, patient experiences, and cost-effectiveness

Introduction

Bone-anchored prostheses (BAP) are an advanced reconstructive surgical approach for individuals who had transfemoral amputation and are unable to use the conventional socket-suspension systems for their prostheses. Access to this technology has been limited in part due to the lag between the start of a new procedure and the availability of evidence that is required before making decisions about widespread provision. This systematic review presents as a single resource up-to-date information on aspects most relevant to decision makers, i.e., clinical efficacy, safety parameters, patient experiences, and health economic outcomes of this technology.

Methods

A systematic search of the literature was conducted by an information specialist in PubMed, MEDLINE, Embase, CINAHL, Cochrane Library, the Core Collection of Web of Science, CADTH's Grey Matters, and Google Scholar up until May 31, 2023. Peer-reviewed original research articles on the outcomes of clinical effectiveness (health-related quality of life, mobility, and prosthesis usage), complications and adverse events, patient experiences, and health economic outcomes were included. The quality of the studies was assessed using the Oxford Centre for Evidence-Based Medicine Levels of Evidence and ROBINS-I, as appropriate.

Results

Fifty studies met the inclusion criteria, of which 12 were excluded. Thirty-eight studies were finally included in this review, of which 21 reported on clinical outcomes and complications, 9 case series and 1 cohort study focused specifically on complications and adverse events, and 2 and 5 qualitative studies reported on patient experience and health economic assessments, respectively. The most common study design is a single-arm trial (pre-/post-intervention design) with varying lengths of follow-up.

Discussion

The clinical efficacy of this technology is evident in selected populations. Overall, patients reported increased health-related quality of life, mobility, and prosthesis usage post-intervention. The most common complication is a superficial or soft-tissue infection, and more serious complications are rare. Patient-reported experiences have generally been positive. Evidence indicates that bone-anchored implants for prosthesis fixation are cost-effective for those individuals who face significant challenges in using socket-suspension systems, although they may offer no additional advantage to those who are functioning well with their socket-suspended prostheses.

A scoring system to evaluate stability of percutaneous osseointegrated implants for transfemoral amputation with validation in the ITAP clinical trial

Percutaneous osseointegrated implants for individuals with lower limb amputation can increase mobility, reduce socket related pain, and improve quality of life. It would be useful to have an evaluation method to assess the interface between bone and implant. We assessed outpatient radiographs from the Intraosseous Transcutaneous Amputation Prosthesis clinical trial using an interface scoring system which summed and weighted equally measures of implant collar cortical ongrowth and radiolucency along the implant stem/bone interface. Radiographs from 12 participants with unilateral transfemoral amputations (10 males, 2 females, mean age = 43.2, SD = 7.4 years) in the clinical trial from cohort I (implanted in 2008/09) or cohort II (implanted in 2013/14) were collated (mean image span = 7.2, SD = 2.4 years), scale normalised, zoned, and measured in a repeatable way. Interface scores were calculated and then compared to clinical outcomes. Explanted participants received the lowest interface scores. A higher ratio of stem to residuum and shorter residuum's produced better interface scores and there was an association (weak correlation) between participants with thin cortices and the lowest interface scores. A tapered, cemented, non curved stem may provide advantageous fixation while stem alignment did not appear critical. In summary, the interface score successfully demonstrated a non-invasive evaluation of percutaneous osseointegrated implants interfaces when applied to the Intraosseous Transcutaneous Amputation Prosthesis clinical trial. The clinical significance of this work is to identify events leading to aseptic or septic implant removal and contribute to clinical guidelines for monitoring rehabilitation, design and surgical fixation choices.

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.

Hip and knee replacement in lower limb amputees: a scoping review

BACKGROUND

There are many consequences of lower limb amputation, including altered biomechanics of gait. It has previously been shown that these can lead to increased rates of osteoarthritis (OA). A common and successful treatment for severe OA is joint replacement. However, it is unclear whether amputees undergoing this surgery can expect the same outcomes or complication profile compared with non-amputees. Furthermore, there are key technical challenges associated with hip or knee replacement in lower limb amputees. This scoping review aimed to identify and summarise the existing evidence base.

METHODS

This was a systematic scoping review performed according to PRISMA guidelines. An electronic database search of MEDLINE (PubMed), Cochrane Library, EMBASE and CINAHL was completed from the date of inception to 1st April 2023. All peer reviewed literature related to hip or knee replacement among lower limb amputees was included.

RESULTS

Of the 931 records identified, 40 studies were included in this study. The available literature consisted primarily of case reports and case series, with generally low level of evidence. In total, there were 265 patients of which 195 received total hip replacement (THR), 51 received total knee replacement (TKR) and 21 received hip hemiarthroplasty. The most common reason for amputation was trauma (34.2%), and the main indication for joint replacement was OA (77.1%), occurring more frequently in the contralateral limb (66.7%). The outcomes reported varied widely between studies, with most suggesting good functional status post-operatively. A variety of technical tips were reported, primarily concerned with intra-operative control of the residual limb.

CONCLUSION

There is a need for more observational studies to clearly define the association between amputation and subsequent need for joint replacement. Furthermore, comparative studies are needed to identify whether amputees can be expected to achieve similar functional outcomes after surgery, and if they are at higher risk of certain complications.

Reliable in vitro method for the evaluation of the primary stability and load transfer of transfemoral prostheses for osseointegrated implantation

Osseointegrated transfemoral prostheses experience aseptic complications with an incidence between 3% and 30%. The main aseptic risks are implant loosening, adverse bone remodeling, and post-operative periprosthetic fractures. Implant loosening can either be due to a lack of initial (primary) stability of the implant, which hinders bone ingrowth and therefore prevents secondary stability, or, in the long-term, to the progressive resorption of the periprosthetic bone. Post-operative periprosthetic fractures are most often caused by stress concentrations. A method to simultaneously evaluate the primary stability and the load transfer is currently missing. Furthermore, the measurement errors are seldom reported in the literature. In this study a method to reliably quantify the bone implant interaction of osseointegrated transfemoral prostheses in terms of primary stability and load transfer was developed, and its precision was quantified. Micromotions between the prosthesis and the host bone and the strains on the cortical bone were measured on five human cadaveric femurs with a typical commercial osseointegrated implant. To detect the primary stability of the implant and the load transfer, cyclic loads were applied, simulating the peak load during gait. Digital Image Correlation was used to measure displacements and bone strains simultaneously throughout the test. Permanent migrations and inducible micromotions were measured (three translations and three rotations), while, on the same specimen, the full-field strain distribution on the bone surface was measured. The repeatability tests showed that the devised method had an intra-specimen variability smaller than 6 μm for the translation, 0.02 degrees for the rotations, and smaller than 60 microstrain for the strain distribution. The inter-specimen variability was larger than the intra-specimen variability due to the natural differences between femurs. Altogether, the measurement uncertainties (intrinsic measurement errors, intra-specimen repeatability and inter-specimen variability) were smaller than critical levels of biomarkers for adverse remodelling and aseptic loosening, thus allowing to discriminate between stable and unstable implants, and to detect critical strain magnitudes in the host bone. In conclusion, this work showed that it is possible to measure the primary stability and the load transfer of an osseointegrated transfemoral prosthesis in a reliable way using a combination of mechanical testing and DIC.

Preliminary characterization of rectification for transradial prosthetic sockets

Achieving proper socket fit is crucial for the effective use of a prosthesis. However, digital socket design lacks standardization and presents a steep learning curve for prosthetists. While research has focused on digital socket design for the lower-limb population, there is a research gap in upper-limb socket design. This study aimed to characterize the design (rectification) process for the transradial socket, specifically the three-quarter Northwestern-style design, towards the development of a more systematic, data-driven socket design approach. Fourteen (n = 14) pairs of unrectified and rectified plaster models were compared. Six common rectification zones were identified through shape analysis, with zones of plaster addition being the most prominent in terms of volume and surface area. A novel 3D vector mapping technique was employed, which revealed that most of the shape changes occurred in the anterior-posterior and proximal-distal directions. Overall, the interquartile range of each rectification zone demonstrated reasonable consistency in terms of volume, surface deviation, and 3D vector representation. The initial findings from this study support the potential for quantitively modelling the transradial socket design process. This opens the door for developing tools for categorizing and predicting socket designs across diverse populations through the application of techniques such as machine learning.

A pneumatic reconfigurable socket for transtibial amputees

Many transtibial amputees rate the fit between their residual limb and prosthetic socket as the most critical factor in satisfaction with using their prosthesis. This study aims to address the issue of prosthetic socket fit by reconfiguring the socket shape at the interface of the residual limb and socket. The proposed reconfigurable socket shifts pressure from sensitive areas and compensates for residual limb volume fluctuations, the most important factors in determining a good socket fit. Computed tomography scan images are employed to create the phantom limb of an amputee and to manufacture the reconfigurable socket. The performance of the reconfigurable socket was evaluated both experimentally and numerically using finite element modelling. The study showed that the reconfigurable socket can reduce interface pressure at targeted areas by up to 61%.

Methodology to Investigate Effect of Prosthetic Interface Design on Residual Limb Soft Tissue Deformation

BACKGROUND

Residual limb discomfort and injury is a common experience for people living with lower limb amputation. Frequently, inadequate load distribution between the prosthetic device and the residual limb is the root cause of this issue. To advance our understanding of prosthetic interface fit, tools are needed to evaluate the mechanical interaction at the prosthetic interface, allowing interface designs to be evaluated and optimised.

OBJECTIVE

Present a methodology report designed to facilitate comprehension of the mechanical interaction between the prosthetic interface and the residual limb. As a pilot study, this methodology is used to compare a hands-on and hands-off interface for a single transtibial prosthesis user using secondary Magnetic Resonance Imaging (MRI) data.

METHODOLOGY

MRI data of the residual limb while wearing a prosthetic interface is segmented into a hard tissue and a skin surface model. These models are exported as stereolithography (STL) files. Two methods are used to analyse the interface designs. Firstly, CloudCompare software is used to compute the nearest vertex on the skin surface for every vertex on the compiled internal bony surface for both interface types. Secondly, CloudCompare software is used to compare registered skin surfaces of the residual limb while wearing the hands-on and hands-off interfaces.

FINDINGS

The maximum and minimum nearest distances between the internal bony surface and skin surface were similar between interface types. However, the distribution of nearest distances was different. When comparing the skin surface while wearing both interfaces, where the fit is more compressive can be visualized. For the dataset used in this study, the classic features of a hands-on Patella Tendon Bearing interface and hands-off pressure cast interface could be identified.

CONCLUSION

The methodology presented in this report may give researchers a further tool to better understand how interface designs affect the soft tissues of the residual limb.

Toward the Development of User-Centered Neurointegrated Lower Limb Prostheses

The last few years witnessed radical improvements in lower-limb prostheses. Researchers have presented innovative solutions to overcome the limits of the first generation of prostheses, refining specific aspects which could be implemented in future prostheses designs. Each aspect of lower-limb prostheses has been upgraded, but despite these advances, a number of deficiencies remain and the most capable limb prostheses fall far short of the capabilities of the healthy limb. This article describes the current state of prosthesis technology; identifies a number of deficiencies across the spectrum of lower limb prosthetic components with respect to users' needs; and discusses research opportunities in design and control that would substantially improve functionality concerning each deficiency. In doing so, the authors present a roadmap of patients related issues that should be addressed in order to fulfill the vision of a next-generation, neurally-integrated, highly-functional lower limb prosthesis.

User perspectives of digital manufacturing for lower-limb prosthetic sockets

BACKGROUND

There is growing interest to use digital technology (DT) for manufacturing lower-limb prosthetic sockets to improve efficiency and clinical outcomes. However, little is known about how lower-limb prosthesis users perceive DTs, such as 3D scanning and 3D printing.

OBJECTIVES

This study aimed to provide an understanding of perceptions and experiences with DT for prosthetic socket manufacturing from the perspective of prosthesis users.

STUDY DESIGN

A qualitative descriptive research study.

METHODS

Nine lower-limb prosthesis users (mean age 56; 5 female; 4 male) participated in one-on-one semistructured telephone interviews. Inductive thematic analysis was performed to identify a codebook and emerging themes from the interview transcripts.

RESULTS

Two major themes were identified: (1) expectations and prioritization of 3D printed socket usability and (2) facilitators and barriers to uptake of DT among patients.

CONCLUSION

DT methods were found to be acceptable and feasible from a patient perspective, although technological advancements are still required, and real-time communication about the process may be vital for ensuring patient engagement. Consideration of these findings may improve patient satisfaction to emerging prosthesis treatment plans and ultimately support widespread adoption of DT as an additional tool for fabricating prosthetic sockets.

A Pneumatically Controlled Prosthetic Socket for Transfemoral Amputees

Amputees typically experience changes in residual limb volume in their daily lives. It causes an uncomfortable fit of the socket by applying high pressure on the sensitive area of the residual limb or by loosening the socket. In this study, we developed a transfemoral prosthetic socket for above-the-knee amputees that ensures a good socket fit by maintaining uniform and constant contact pressure despite volume changes in the residual limb. The socket has two air bladders in the posterior femoral region, and the pneumatic controller is located on the tibia of the prosthesis. The pneumatic system aims to minimize unstable fitting of the socket and improve walking performance by inflating or deflating the air bladder. The developed socket autonomously maintains the air pressure inside the prosthetic socket at a steady-state error of 3 mmHg or less by adjusting the amount of air in the air bladder via closed-loop control. In the clinical trial, amputee participants walked on flat and inclined surfaces. The displacement between the residual limb and socket during the gait cycle was reduced by up to 33.4% after air injection into the socket. The inflatable bladder increased the knee flexion angle on the affected side, resulting in increased stride length and gait velocity. The pneumatic socket provides a stable and comfortable walking experience not only when walking on flat ground but also on slopes.

Soft robotics-inspired sensing system for detecting downward movement and pistoning in prosthetic sockets: A proof-of-concept study

BACKGROUND

Vertical displacement of the residual limb within transtibial prosthetic socket, often known as "pistoning" or downward movement, may lead to skin breakdowns and ulcers. Downward movement is particularly difficult to self-manage for diabetic individuals living with amputation because of diminished sensation in the residual limb from peripheral neuropathy. Therefore, a customizable sensor at the distal end that can alert the users when high-risk downward movement and pistoning occurs is urgently needed.

OBJECTIVES

Presented herein for the first time is a lightweight, inexpensive sensing system inspired by soft robotics that can detect the occurrence and severity of downward movement at the distal end.

METHODS

The sensing system consists of a multilayered torus-shaped balloon, allowing easy integration with pin-lock socket systems. The design allows sensing of vertical displacement without imparting high reaction forces back onto the distal end. A benchtop compression tester was used to characterize system performance. Systematic and parametric benchtop tests were conducted to examine the sensor's physical characteristics. Long-term (24-h) stability of the sensor was also recorded.

RESULTS

Compared with water, air was determined to be a better medium with a higher linear full-scale span (FSS) because of its compressible nature. Repeatable 0.5-mm vertical displacements yielded a linear (>0.99 R2) FSS of 4.5 mm and a sensitivity of 0.8 kPa/mm. The sensing system is highly precise, with as low as 1% FSS total error band and average hysteresis of 2.84% of FSS. Over 24 h, a 4% FSS drift was observed.

CONCLUSION

Sensing system characteristics, coupled with low-cost, customizable fabrication, indicates promising performance for daily use to notify and alert transtibial prosthetic users of downward movement and/or pistoning.

Adjustable prosthetic sockets: a systematic review of industrial and research design characteristics and their justifications

BACKGROUND

The prosthetic socket is a key component that influences prosthesis satisfaction, with a poorly fitting prosthetic socket linked to prosthesis abandonment and reduced community participation. This paper reviews adjustable socket designs, as they have the potential to improve prosthetic fit and comfort through accommodating residual limb volume fluctuations and alleviating undue socket pressure.

METHODS

Systematic literature and patent searches were conducted across multiple databases to identify articles and patents that discussed adjustable prosthetic sockets. The patents were used to find companies, organisations, and institutions who currently sell adjustable sockets or who are developing devices.

RESULTS

50 literature articles and 63 patents were identified for inclusion, representing 35 different designs used in literature and 16 commercially available products. Adjustable sockets are becoming more prevalent with 73% of publications (literature, patents, and news) occurring within the last ten years. Two key design characteristics were identified: principle of adjustability (inflatable bladders, moveable panels, circumferential adjustment, variable length), and surface form (conformable, rigid multi-DOF, and rigid single DOF). Inflatable bladders contributed to 40% of literature used designs with only one identified commercially available design (n = 16) using this approach. Whereas circumferential adjustment designs covered 75% of identified industry designs compared to only 36% of literature devices. Clinical studies were generally small in size and only 17.6% of them assessed a commercially available socket.

DISCUSSION

There are clear differences in the design focus taken by industry and researchers, with justification for choice of design and range of adjustment often being unclear. Whilst comfort is often reported as improved with an adjustable socket, the rationale behind this is not often discussed, and small study sizes reduce the outcome viability. Many adjustable sockets lack appropriate safety features to limit over or under tightening, which may present a risk of tissue damage or provide inadequate coupling, affecting function and satisfaction. Furthermore, the relationship between design and comfort or function are rarely investigated and remain a significant gap in the literature. Finally, this review highlights the need for improved collaboration between academia and industry, with a strong disconnect observed between commercial devices and published research studies.

Moisture mitigation using a vented liner and a vented socket system for individuals with transfemoral amputation

Sweating and heat buildup at the skin-liner interface is a major challenge for persons with limb loss. Liners made of heat-non-conducting materials may cause sweating of the residual limb and may result in liners slipping off the skin surface especially on a warm day or during high activity, causing skin breakdown and affecting limb health. To address this, we evaluated the efficacy of the vented liner-socket system (VS, Össur) compared to Seal-In silicone liner and non-vented socket (nVS, Össur) in reducing relative humidity (RH) during increased sweat. Nine individuals with limb loss using nVS were randomized to VS or nVS and asked for activity in a 20-min treadmill walk. RH was significantly attenuated (p = 0.0002) and perceived sweating, as reported by prosthesis users, improved (p = 0.028) with VS, patient-reported comprehensive lower limb amputee socket survey (CLASS) outcomes to determine the suspension, stability, and comfort were not significantly different between VS and nVS. There are limited rigorous scientific studies that clearly provide evidence-based guidelines to the prosthetist in the selection of liners from numerous available options. The present study is innovative in clearly establishing objective measures for assessing humidity and temperatures at the skin-liner interface while performing activity. As shown by the measured data and perceived sweat scores provided by the subjects based on their daily experience, this study provided clear evidence establishing relative humidity at the skin-liner interface is reduced with the use of a vented liner-socket system when compared to a similar non-vented system.

In vitro and in silico methods for the biomechanical assessment of osseointegrated transfemoral prostheses: a systematic review

The amputee population according to the World-Health-Organization is about 40 million. However, there is a high abandon rate of socket prostheses for the lower limb (25%-57%). The direct connection between the external prosthesis and the patient's bone makes osseointegrated prostheses for transfemoral amputees advantageous (e.g., improvement of the motor control) compared to socket prostheses, which are currently the gold standard. However, similarly to other uncemented prostheses, the osseointegrated ones are at risk of aseptic loosening and adverse bone remodelling caused by stress-shielding. The preclinical assessment of these prostheses has already been evaluated using different methods which did not provide unanimous and comparable evidence. To compare data from different investigations, a clear and detailed overview of the methods used to assess the performance is necessary. In this review 17 studies investigating the primary stability, stress shielding and stress concentration of osseointegrated transfemoral prostheses are examined. Primary stability consists in the biomechanical stability upon implant insertion. Primary stability is assessed measuring extraction force (either with a pull-out or a push-out test) and micromotion at the interface between the implant and the host bone with LVDT (in vitro test) or numerical models. Stress-shielding causes adaptive changes in the bone density around metal implants, and thus in the bone strength and stiffness. Stress-shielding is assessed with strain gauges or numerical models measuring the load transfer and the strain distribution on the surface of the femur, and between the implant and the bone respectively. Stress concentration can lead to the formation of cracks inside the bone, resulting in fractures. The stress concentration is assessed measuring the load transfer and the strain energy density at the interface between the implant and the bone, using numerical models. As a result, a global view and consensus about the methods are missing from all these tests. Indeed, different setup and loading scenario were used in the in vitro test, while different model parameters (e.g., bone properties) were used in the numerical models. Once the preclinical assessment method is established, it would be important to define thresholds and acceptance criteria for each of the possible failure scenarios investigated.

Approach for Non-Intrusive Detection of the Fit of Orthopaedic Devices Based on Vibrational Data

The soft tissues of residual limb amputees are subject to large volume fluctuations over the course of a day. Volume fluctuations in residual limbs can lead to local pressure marks, causing discomfort, pain and rejection of prostheses. Existing methods for measuring interface stress encounter several limitations. A major problem is that the measurement instrumentation is applied in the sensitive interface between the prosthesis and residual limb. This paper presents the principle investigation of a non-intrusive technique to evaluate the fit of orthopaedic prosthesis sockets in transfemoral amputees based on experimentally obtained vibrational data. The proposed approach is based on changes in the dynamical behaviour detectable at the outer surface of prostheses; thus, the described interface is not affected. Based on the experimental investigations shown and the derived results, it can be concluded that structural dynamic measurements are a promising non-intrusive technique to evaluate the fit of orthopaedic prosthesis sockets in transfemoral amputee patients. The obtained resonance frequency changes of 2% are a good indicator of successful applicabilityas these changes can be detected without the need for complex measurement devices.

Design trends in actuated lower-limb prosthetic systems: a narrative review

INTRODUCTION

Actuated lower limb prostheses, including powered (active) and semi-active (quasi-passive) joints, are endowed with controllable power and/or impedance, which can be advantageous to limb impairment individuals by improving locomotion mechanics and reducing the overall metabolic cost of ambulation. However, an increasing number of commercial and research-focused options have made navigating this field a daunting task for users, researchers, clinicians, and professionals.

AREAS COVERED

The present paper provides an overview of the latest trends and developments in the field of actuated lower-limb prostheses and corresponding technologies. Following a gentle summary of essential gait features, we introduce and compare various actuated prosthetic solutions in academia and the market designed to provide assistance at different levels of impairments. Correspondingly, we offer insights into the latest developments of sockets and suspension systems, before finally discussing the established and emerging trends in surgical approaches aimed at improving prosthetic experience through enhanced physical and neural interfaces.

EXPERT OPINION

The ongoing challenges and future research opportunities in the field are summarized for exploring potential avenues for development of next generation of actuated lower limb prostheses. In our opinions, a closer multidisciplinary integration can be found in the field of actuated lower-limb prostheses in the future.

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 Workflow for Studying the Stump-Socket Interface in Persons with Transtibial Amputation through 3D Thermographic Mapping

The design and fitting of prosthetic sockets can significantly affect the acceptance of an artificial limb by persons with lower limb amputations. Clinical fitting is typically an iterative process, which requires patients' feedback and professional assessment. When feedback is unreliable due to the patient's physical or psychological conditions, quantitative measures can support decision-making. Specifically, monitoring the skin temperature of the residual limb can provide valuable information regarding unwanted mechanical stresses and reduced vascularization, which can lead to inflammation, skin sores and ulcerations. Multiple 2D images to examine a real-life 3D limb can be cumbersome and might only offer a partial assessment of critical areas. To overcome these issues, we developed a workflow for integrating thermographic information on the 3D scan of a residual limb, with intrinsic reconstruction quality measures. Specifically, workflow allows us to calculate a 3D thermal map of the skin of the stump at rest and after walking, and summarize this information with a single 3D differential map. The workflow was tested on a person with transtibial amputation, with a reconstruction accuracy lower than 3 mm, which is adequate for socket adaptation. We expect the workflow to improve socket acceptance and patients' quality of life.

Comparison of conventional socket attachment and bone-anchored prosthesis for persons living with transfemoral amputation - mobility and quality of life

BACKGROUND

For patients with transfemoral amputation experiencing issues with their sockets, bone-anchored prosthesis systems are an alternative and sometimes the only way to be mobile and independent. The present cross-sectional study aimed to investigate the gait performance and quality of life of a group of patients treated with bone-anchored systems compared to those of participants treated with a conventional socket-suspended prosthesis.

METHODS

A total of 17 participants with a socket-suspended and 20 with a bone-anchored prosthesis were included. Gait patterns were examined for symmetry, and performance was assessed using the six-minute walk test and the timed "Up & Go" test. Magnetic resonance imaging was performed to detect signs of osteoarthritis in both hips. Mobility in everyday life and quality of life were assessed using questionnaires.

FINDINGS

There were no differences between the groups regarding the quality of life, daily mobility, and gait performance. The step width was significantly higher for the patients using socket-suspended prosthesis. The socket-suspended group showed a significant asymmetry regarding the step length. In the socket-suspended group, the prosthetic leg showed significantly higher cartilage abrasion than the contralateral leg did.

INTERPRETATION

Large differences in the measured outcomes in both groups illustrate the very different capabilities of the individual participants, which is apparently not primarily determined by the type of treatment. For patients who are satisfied with the socket treatment and perform well, bone-anchored prosthesis systems may not necessarily improve their functional capabilities and perceived quality of life.

Validation of a Custom Interface Pressure Measurement System to Improve Fitting of Transtibial Prosthetic Check Sockets

Achievement of fit between the residual limb and prosthetic socket during socket manufacture is a priority for clinicians and is essential for safety. Clinicians have recognised the potential benefits of having a sensor system that can provide objective socket-limb interface pressure measurements during socket fitting, but the cost of existing systems makes current technology prohibitive. This study will report on the characterisation, validation and preliminary clinical implementation of a low cost, portable, wireless sensor system designed for use during socket manufacture. Characterisation and benchtop testing demonstrated acceptable accuracy, behaviour at variable temperature, and dynamic response for use in prosthetic socket applications. Our sensor system was validated with simultaneous measurement by a commercial sensor system in the sockets of three transtibial prosthesis users during a fitting session in the clinic. There were no statistically significant differences between the sensor system and the commercial sensor for a variety of functional activities. The sensor system was found to be valid in this clinical context. Future work should explore how pressure data relates to ratings of fit and comfort, and how objective pressure data might be used to assist in clinical decision making.

A finite element analysis of load distribution during donning and orthostatic posture in the ITOP hybrid subischial socket

INTRODUCTION

Pressure and shear stresses applied to the stump of a transfemoral amputee wearing a newly designed prosthetic socket have been analyzed by a finite element modeling approach.

METHODS

The new socket was developed by the Istituto Tecnico Ortopedico Preneste, and it was named the "hybrid subischial socket." This work aimed at understanding the loads' distribution on the stump surface in 2 operative conditions: at the end of the wearing phase and during the orthostatic posture. The model of the stump was composed of 4 different materials: the femoral bone, the muscle tissue, the fat, and the skin layers. Except for the bone (rigid), the biological tissues were modeled as Neo-Hookean, and their mechanical properties were taken from the literature. The socket was composed of a containment frame, made of carbon fiber composite material, a shell made of flexible silicone, and a liner made of hyperelastic silicone.

RESULTS

The results of our simulation show that the main support areas are located in a proper position, in agreement with the ideal principles of this prosthetic design, and the maximum pressures are well below the pain threshold reported in the literature for the same contact areas.

CONCLUSIONS

We can conclude that although the upper rim of the socket is well below the ischiatic area, the new socket design allows for a safe and comfortable support of the body weight. This is in agreement with the evidence of a good functionality and acceptance of this prosthetics gathered in the many real applications.

Temporal and spatial characteristics of bone conduction as non-invasive haptic sensory feedback for upper-limb prosthesis

Bone conduction is a promising haptic feedback modality for upper-limb prosthesis users, however, its potential and characteristics as a non-invasive feedback modality have not been thoroughly investigated. This study aimed to establish the temporal and spatial characteristics of non-invasive bone conduction as a sensory feedback interface for upper-limb prostheses. Psychometric human-subject experiments were conducted on three bony landmarks of the elbow, with a vibrotactile transducer affixed to each to provide the stimulus. The study characterized the temporal domain by testing perception threshold and resolution in amplitude and frequency. The spatial domain was evaluated by assessing the ability of subjects to detect the number of simultaneous active stimulation sites. The experiment was conducted with ten able-bodied subjects and compared to two subjects with trans-radial amputation. The psychometric evaluation of the proposed non-invasive bone conduction feedback showed results comparable to invasive methods. The experimental results demonstrated similar amplitude and frequency resolution of the interface for all three stimulation sites for both able-bodied subjects and subjects with trans-radial amputation, highlighting its potential as a non-invasive feedback modality for upper-limb prostheses.

Numerical Analysis of a Transtibial Prosthesis Socket Using 3D-Printed Bio-Based PLA

Lower-limb prosthesis design and manufacturing still rely mostly on the workshop process of trial-and-error using expensive unrecyclable composite materials, resulting in time-consuming, material-wasting, and, ultimately, expensive prostheses. Therefore, we investigated the possibility of utilizing Fused Deposition Modeling 3D-printing technology with inexpensive bio-based and bio-degradable Polylactic Acid (PLA) material for prosthesis socket development and manufacturing. The safety and stability of the proposed 3D-printed PLA socket were analyzed using a recently developed generic transtibial numeric model, with boundary conditions of donning and newly developed realistic gait cycle phases of a heel strike and forefoot loading according to ISO 10328. The material properties of the 3D-printed PLA were determined using uniaxial tensile and compression tests on transverse and longitudinal samples. Numerical simulations with all boundary conditions were performed for the 3D-printed PLA and traditional polystyrene check and definitive composite socket. The results showed that the 3D-printed PLA socket withstands the occurring von-Mises stresses of 5.4 MPa and 10.8 MPa under heel strike and push-off gait conditions, respectively. Furthermore, the maximum deformations observed in the 3D-printed PLA socket of 0.74 mm and 2.66 mm were similar to the check socket deformations of 0.67 mm and 2.52 mm during heel strike and push-off, respectively, hence providing the same stability for the amputees. We have shown that an inexpensive, bio-based, and bio-degradable PLA material can be considered for manufacturing the lower-limb prosthesis, resulting in an environmentally friendly and inexpensive solution.

Development of a Hip Joint Socket by Finite-Element-Based Analysis for Mechanical Assessment

This article evaluates a hip joint socket design by finite element method (FEM). The study was based on the needs and characteristics of a patient with an oncological amputation; however, the solution and the presented method may be generalized for patients with similar conditions. The research aimed to solve a generalized problem, taking a typical case from the study area as a reference. Data were collected on the use of the current improving prosthesis-specifically in interaction with its socket-to obtain information on the new approach design: this step constituted the work's starting point, where the problems to be solved in conventional designs were revealed. Currently, the development of this type of support does not consider the functionality and comfort of the patient. Research has reported that 58% of patients with sockets have rejected their use, because they do not fit comfortably and functionally; therefore, patients' low acceptance or rejection of the use of the prosthesis socket has been documented. In this study, different designs were evaluated, based on the FEM as scientific support for the results obtained, for the development of a new ergonomic fit with a 60% increase in patient compliance, that had correct gait performance when correcting postures, improved fit-user interaction, and that presented an esthetic fit that met the usability factor. The validation of the results was carried out through the physical construction of the prototype. The research showed how the finite element method improved the design, analyzing the structural behavioral, and that it could reduce cost and time instead of generating several prototypes.

Next-generation devices to diagnose residuum health of individuals suffering from limb loss: A narrative review of trends, opportunities, and challenges

OBJECTIVES

There is a need for diagnostic devices that can assist prosthetic care providers to better assess and maintain residuum health of individuals suffering from neuromusculoskeletal dysfunctions associated with limb loss. This paper outlines the trends, opportunities, and challenges that will facilitate the development of next-generation diagnostic devices.

DESIGN

Narrative literature review.

METHODS

Information about technologies suitable for integration into next-generation diagnostic devices was extracted from 41 references. We considered the invasiveness, comprehensiveness, and practicality of each technology subjectively.

RESULTS

This review highlighted a trend toward future diagnostic devices of neuromusculoskeletal dysfunctions of the residuum capable to support evidence-based patient-specific prosthetic care, patient empowerment, and the development of bionic solutions. This device should positively disrupt the organization healthcare by enabling cost-utility analyses (e.g., fee-for-device business models) and addressing healthcare gaps due to labor shortages. There are opportunities to develop wireless, wearable and noninvasive diagnostic devices integrating wireless biosensors to measure change in mechanical constraints and topography of residuum tissues during real-life conditions as well as computational modeling using medical imaging and finite element analysis (e.g., digital twin). Developing the next-generation diagnostic devices will require to overcome critical barriers associated with the design (e.g., gaps between technology readiness levels of essential parts), clinical roll-out (e.g., identification of primary users), and commercialization (e.g., limited interest from investors).

CONCLUSIONS

We anticipate that next-generation diagnostic devices will contribute to prosthetic care innovations that will safely increase mobility, thereby improving the quality of life of the growing global population of individuals suffering from limb loss.

Soft robotics in wearable and implantable medical applications: Translational challenges and future outlooks

This work explores the recent research conducted towards the development of novel classes of devices in wearable and implantable medical applications allowed by the introduction of the soft robotics approach. In the medical field, the need for materials with mechanical properties similar to biological tissues is one of the first considerations that arises to improve comfort and safety in the physical interaction with the human body. Thus, soft robotic devices are expected to be able of accomplishing tasks no traditional rigid systems can do. In this paper, we describe future perspectives and possible routes to address scientific and clinical issues still hampering the accomplishment of ideal solutions in clinical practice.

Osseointegration for Lower Limb Amputation: Understanding the Risk Factors and Time Courses of Soft Tissue Complications

PURPOSE

Lower-limb osseointegrated prostheses are a novel alternative to traditional socket-suspended prostheses, which are often associated with poor fit, soft tissue damage, and pain. Osseointegration eliminates the socket-skin interface and allows for weight-bearing directly on the skeletal system. However, these prostheses can also be complicated by postoperative issues that can negatively impact mobility and quality of life. Little is known about the incidence of or risk factors for these complications as few centers currently perform the procedure.

METHODS

A retrospective analysis was performed on all patients who underwent single-stage lower limb osseointegration at our institution between 2017 and 2021. Patient demographics, medical history, operative data, and outcomes were collected. Fisher exact test and unpaired t tests were performed to identify risk factors for each adverse outcome, and time-to-event survival curves were generated.

RESULTS

Sixty patients met our study criteria: 42 males and 18 females with 35 transfemoral and 25 transtibial amputations. The cohort had an average age of 48 years (range, 25-70 years) and follow-up period of 22 months (range, 6-47 months). Indications for amputation were trauma (50), prior surgical complication (5), cancer (4), and infection (1). Postoperatively, 25 patients developed soft tissue infections, 5 developed osteomyelitis, 6 had symptomatic neuromas, and 7 required soft tissue revisions. Soft tissue infections were positively correlated with obesity and female sex. Neuroma development was associated with increased age at osseointegration. Neuromas and osteomyelitis were both associated with decreased center experience. Subgroup analysis by amputation etiology and anatomic location did not show significant differences in outcomes. Notably, hypertension (15), tobacco use (27), and prior site infection (23) did not correlate with worse outcomes. Forty-seven percent of soft tissue infections occurred in the 1 month after implantation, and 76% occurred in the first 4 months.

CONCLUSIONS

These data provide preliminary insights into risk factors for postoperative complications arising from lower limb osseointegration. These factors are both modifiable (body mass index, center experience), and unmodifiable (sex, age). As this procedure continues to expand in popularity, such results are necessary to inform best practice guidelines and optimize outcomes. Further prospective studies are needed to confirm the above trends.

A review of user needs to drive the development of lower limb prostheses

Background

The development of bionic legs has seen substantial improvements in the past years but people with lower-limb amputation still suffer from impairments in mobility (e.g., altered balance and gait control) due to significant limitations of the contemporary prostheses. Approaching the problem from a human-centered perspective by focusing on user-specific needs can allow identifying critical improvements that can increase the quality of life. While there are several reviews of user needs regarding upper limb prostheses, a comprehensive summary of such needs for those affected by lower limb loss does not exist.

Methods

We have conducted a systematic review of the literature to extract important needs of the users of lower-limb prostheses. The review included 56 articles in which a need (desire, wish) was reported explicitly by the recruited people with lower limb amputation (N = 8149).

Results

An exhaustive list of user needs was collected and subdivided into functional, psychological, cognitive, ergonomics, and other domain. Where appropriate, we have also briefly discussed the developments in prosthetic devices that are related to or could have an impact on those needs. In summary, the users would like to lead an independent life and reintegrate into society by coming back to work and participating in social and leisure activities. Efficient, versatile, and stable gait, but also support to other activities (e.g., sit to stand), contribute to safety and confidence, while appearance and comfort are important for the body image. However, the relation between specific needs, objective measures of performance, and overall satisfaction and quality of life is still an open question.

Conclusions

Identifying user needs is a critical step for the development of new generation lower limb prostheses that aim to improve the quality of life of their users. However, this is not a simple task, as the needs interact with each other and depend on multiple factors (e.g., mobility level, age, gender), while evolving in time with the use of the device. Hence, novel assessment methods are required that can evaluate the impact of the system from a holistic perspective, capturing objective outcomes but also overall user experience and satisfaction in the relevant environment (daily life).

Osseointegration for Lower-Extremity Amputees: Operative Considerations from the Plastic Surgeon's Perspective

➢

Osseointegration for lower-extremity amputees, while increasing in frequency, remains in its relative infancy compared with traditional socket-based prostheses.

➢

Ideal candidates for osseointegration have documented failure of a traditional prosthesis and should be skeletally mature, have adequate bone stock, demonstrate an ability to adhere to a longitudinal rehabilitation protocol, and be in an otherwise good state of health.

➢

Lowering the reoperation rate for soft-tissue complications depends heavily on surgical technique and on the implant device itself; the current gold standard involves a smooth implant surface for dermal contact as well as maximal skin resection to prevent skin breakdown against the prosthesis. This may include the need for thighplasty to optimize skin reduction.

➢

Interdisciplinary peripheral nerve management, such as targeted muscle reinnervation, performed in tandem with a plastic surgery team can treat existing and prevent future symptomatic neuromas, ultimately improving pain outcomes.

Two case reports showing a rather striking abnormal finding of unknown origin localized to the cortex of an amputated femur

MRI scans of patients who have undergone leg amputation are rarely obtained; such scans may be performed when a mass is suspected to be related to the amputation or when inflammation (infection) is suspected, but the number of such cases is not large. In this study, however, we encountered 2 very striking cases in which short-tau inversion recovery coronal images taken for different purposes coincidentally showed a diffuse high signal intensity of the residual femoral cortex on the side wearing the artificial limb. Further examination of these images revealed that the superior margins of the artificial limb cup and the abnormal signal were almost identical and that the signal was only observed in the residual femur of the side using the artificial limb, suggesting that the change was caused by artificial limb usage. Despite the difficulty in imaging-pathologic correlation because the patients were still alive, we considered that the high signal was related to the characteristic microanatomy of the bone cortex and the mechanical changes caused by the effects of artificial limb usage on the residual femur. The 2 patients have not shown any specific events since then. Thus, while the residual femoral cortex may show findings of interest, these findings do not seem to require any specific treatment.

Design and evaluation of a prosthetic socket for a patient with diabetic‐related transtibial amputation: A case report

This is a report of a diabetic transtibial amputee with severe pain and ulcer in the antero‐distal of the tibia. A novel prosthetic socket with an antero‐distal silicone wall was designed. The result showed that the patient's satisfaction was increased and the average peak pressure was reduced by using the new socket design.

Reliability of three different methods for assessing amputee residuum shape and volume: 3D scanners vs. circumferential measurements

BACKGROUND

Objective and reliable methods are necessary to monitor and manage amputee residuum shape and volume and design prosthetic residuum-prosthesis interfaces. Portable 3D scanners are potential solutions for digitally recording the amputee residuum characteristics.

OBJECTIVE

To investigate test-operator reliability when measuring lower limb residuum shape and volume using two different types of 3D laser-free scanners compared with tape measurements generally adopted in clinic.

STUDY DESIGN

Ten lower limb amputees took part in this study. Residuum volume, cross sectional areas, and perimeter lengths were measured by three different operators on three different occasions using two types of 3D scanners (Artec Eva scanner and OMEGA Scanner 3D) and circumferential measurements.

METHODS

Variance components, intraclass correlation coefficients and intra-rater and inter-rater reliability coefficients were calculated for all measurement conditions.

RESULTS

Residuum volume outputs ranged from 569 to 3115 mL. The factor contributing mostly to the residuum volume error variance was the shape of the residuum (75.85%). Volume intraclass correlation coefficients for both intra-rater and inter-rater reliability exceeded 0.9 for all three conditions. Volume reliability coefficients ranged from 70.68 mL (Artec Eva intra-rater reliability) to 256.85 mL (circumferential measurements inter-rater reliability). Shape relative error reached the highest values for the circumferential measurements (>10% for the cross-sectional areas and >5% for the perimeters).

CONCLUSIONS

The Artec Eva scanner resulted in the lowest test-operator reliability coefficients. However, both investigated scanners are a potential alternative for measuring small and macroscopic changes in residuum characteristics.

Evaluation of the new, patient-adjustable socket system Varos in the early phase of prosthetic rehabilitation: a pilot study

BACKGROUND

Current prosthetic sockets often provide limited anatomical fit, especially in patients with residual limb volume changes and fluctuations.

AIM

To address these issues, Ottobock has developed the Varos Socket, a modular socket that can be adjusted by the user. The aim of this study was to evaluate the potential benefits and acceptance of a newly designed patient-adjustable socket in transfemoral amputees in early phase of prosthetic rehabilitation.

DESIGN

A prospective A-B-A pilot study was conducted.

SETTING

The setting of the study was an Orthopedic Rehabilitation Clinic.

POPULATION

Ten patients with unilateral transfemoral amputation and recent amputation.

METHODS

All patients underwent a standard rehabilitation program with physical therapy. The outcome measures included the Comprehensive Lower-limb Amputee Socket Survey (CLASS), Score Comfort Scale (SCS), a Socket Fit Scale, frequency of falls and stumbles, perceived pain, and satisfaction.

RESULTS

The total CLASS score and three sub-scores (i.e., stability, suspension, comfort) were significantly higher with Varos socket. Significantly improved comfort and quality of socket fit were observed as measured by the Socket-Comfort-Scale and Socket-Fit-Scale and a trend towards reduced residual limb pain. 87.5% of the patients reported higher satisfaction than with the standard socket.

CONCLUSIONS

The results suggest that the Varos socket improved comfort, stability, suspension, appearance, pain, and satisfaction in transfemoral amputees during the early rehabilitation program. A larger study and a longer observation period are warranted to confirm the results of this study.

CLINICAL REHABILITATION IMPACT

Quick and easy socket fitting as well as instant adjustability by the patient bear substantial potential to improve and accelerate the rehabilitation process in the early phase after amputation.

Understanding the adoption of digital workflows in orthotic & prosthetic practice from practitioner perspectives: a qualitative descriptive study

BACKGROUND

The implementation of digital technology (DT) in orthotics and prosthetics (O&P) has been slow despite recent research suggesting that the use of DT will continue to grow and become more prevalent within the industry. There is a need to further investigate DT in O&P practice and the current state of its use in the field.

OBJECTIVE

This study aimed to explore the views and experiences of practitioners using DT workflows in their O&P practice.

METHODS

In this qualitative descriptive study, 10 in-depth, semistructured interviews with O&P practitioners were conducted. A content analysis was performed to analyze the transcripts and identify key themes from the data.

RESULTS

The study examined the experiences of practitioners using or trying to use DT in their practices, and three key themes were identified on the implementation of digital practice: 1) technological advancement and scientific evidence; 2) marketplace, economic, and operational factors; and 3) industry mindset shift in embracing DT practice.

CONCLUSION

A collaborative effort involving academia, healthcare institutions, vendors, and individual practitioners will be required to facilitate the widespread adoption of DT in O&P. More work is required to overcome challenges from the technical, logistical, and cultural aspects.

The effect of prosthetic alignment on the stump temperature and ground reaction forces during gait in transfemoral amputees

BACKGROUND

Lower limb prosthetic alignment is a procedure mostly subjective. A prosthetic misaligned induces gait deviations and long-term joint diseases. The alignment effects for each lower limb and the stump stays uncertain.

RESEARCH OBJECTIVE

To identify the effect of the transfemoral alignment prosthesis on ground reaction forces and thermal images of the residual limb.

METHODS

The effect of misalignment and nominal alignment was evaluated in sixteen transfemoral amputees. The nominal alignment was considered as the optimal alignment for each subject. Misalignment included random variations in the anterior-posterior and medial-lateral translation of the prosthetic foot and the angle of flexion-extension, abduction-adduction, and internal-external rotation of the socket and prosthetic foot. The control group consisted of fifteen non-amputee individuals. The ground reaction force parameters and stump temperature were analyzed for each alignment condition. The statistical analysis included the one-way ANOVA, Kruskal-Wallis, and multiple comparison tests.

RESULTS

The prosthesis did not produce statistically significant changes in the average temperature of residual limbs. However, the temperature distribution on the stump skin was different (P < 0.05). The transfemoral prosthesis misalignment produced an irregular heat diffusion on the anterior, posterior, and lateral sides of the stump contour compared to the nominal alignment (P < 0.05). The sound limb did not show differences between nominal alignments and misalignments for most ground reaction force parameters. For almost all GRF parameters, significant differences were observed for the prosthetic limb between misalignment and nominal alignment (P < 0.001). The symmetry indices of ground reaction force parameters of transfemoral amputees did not show any kind of significant improvements after aligning the prosthesis nominally.

SIGNIFICANCE

The stump's temperature distribution and the ground reaction force findings for the prosthetic limb provide a better understanding of the alignment procedure of the transfemoral prosthesis and improve the amputees' compliance to the prosthesis.

Activity, socket fit, comfort and community participation in lower limb prosthesis users: a Cambodian cohort study

BACKGROUND

After amputation, many people become less active, feel lonely and lose independence. Understanding the factors associated with low physical activity levels and participation could contribute to defining key interventions which can support prosthesis users so they can live a more active and socially included lifestyle. This longitudinal observational study aims to assess relationships between physical activity, community participation, prosthetic fit, comfort and user satisfaction using actimetry, 3D scans and questionnaires in a Cambodian cohort of established lower limb prosthesis users.

METHODS

Twenty participants (5F:15M, nine transfemoral, eleven transtibial, 24-60 years old and 3-43 years since amputation) were recruited. They completed a questionnaire which included their demographics, community participation, prosthesis satisfaction and comfort at the start of the study, and between three and six months later. Their prosthetic sockets and residual limbs were 3D scanned at the start and end of the study. Accelerometers were embedded under the cosmesis on the shank of the prosthesis, to collect ten weeks of activity data.

RESULTS

Participants averaged 4470 steps/day (743-7315 steps/day), and wore their prosthesis for most waking hours, averaging 13.4 h/day (4.5-17.6 h/day). Self-reported measures of activity and hours of wear correlated with these accelerometer data (Spearman's rho rs = 0.59, and rs = 0.71, respectively). Participants who were more active wore their prosthesis for more hours/day (Pearson r = 0.73) and were more satisfied with socket fit (rs = 0.49). A longer residual limb correlated with better community participation (rs = 0.56) and comfort (rs = 0.56). Self-reported community participation did not correlate with a person's activity level (rs = 0.13), or their prosthesis comfort (rs = 0.19), and there was only weak correlation between how important the activity was to an individual, and how often they participated in it (rs = 0.37). A simple 0-10 scale of overall comfort did not provide enough detail to understand the types and severity of discomfort experienced.

CONCLUSION

Associations between perceived and measured activity levels correlated with socket satisfaction in this cohort of people with established lower limb amputations. The small sample size means these correlations should be interpreted with caution, but they indicate variables worthy of further study to understand barriers to community engagement and physical activity for prosthesis users in Cambodia, and potentially in other settings.

Air microfluidics-enabled soft robotic transtibial prosthesis socket liner toward dynamic management of residual limb contact pressure and volume fluctuation

Residual limb volume fluctuation and the resulting contact pressures are some of the key factors leading to skin ulcerations, suboptimal prosthetic functioning, pain, and diminishing quality of life of transtibial amputees. Self-management of socket fit is complicated by peripheral neuropathy, reducing the perception of pressure and pain in the residual limb. We introduce a novel proof-of-concept for a transtibial prosthetic socket liner with the potential to dynamically adjust the fit between the limb and socket. The core of the technology is a small air microfluidic chip (10 cm³ and 10 g) with 10 on-chip valves that enable sequential pressurizing of 10 actuators in custom sizes to match the pressures required by the residual limb's unique anatomy. The microfluidic chip largely reduced the number of electromechanical solenoid valves needed for sequential control of 10 actuators (2 instead of 10 valves), resulting in the reduction of the required power, size, mass, and cost of the control box toward an affordable and wearable prosthetic socket. Proof-of-concept testing demonstrated that the applied pressures can be varied in the desired sequence and to redistribute pressure. Future work will focus on integrating the system with biofidelic prosthetic sockets and residual limb models to investigate the ability to redistribute pressure away from pressure-sensitive regions (e.g., fibular head) to pressure tolerant areas. Overall, the dynamic prosthesis socket liner is very encouraging for creating a dynamic socket fit system that can be seamlessly integrated with existing socket fabrication methods for managing residual limb volume fluctuations and contact pressure.

Redundancy Reduction for Sensor Deployment in Prosthetic Socket: A Case Study

The irregular pressure exerted by a prosthetic socket over the residual limb is one of the major factors that cause the discomfort of amputees using artificial limbs. By deploying the wearable sensors inside the socket, the interfacial pressure distribution can be studied to find the active regions and rectify the socket design. In this case study, a clustering-based analysis method is presented to evaluate the density and layout of these sensors, which aims to reduce the local redundancy of the sensor deployment. In particular, a Self-Organizing Map (SOM) and K-means algorithm are employed to find the clustering results of the sensor data, taking the pressure measurement of a predefined sensor placement as the input. Then, one suitable clustering result is selected to detect the layout redundancy from the input area. After that, the Pearson correlation coefficient (PCC) is used as a similarity metric to guide the removal of redundant sensors and generate a new sparser layout. The Jenson-Shannon Divergence (JSD) and the mean pressure are applied as posterior validation metrics that compare the pressure features before and after sensor removal. A case study of a clinical trial with two sensor strips is used to prove the utility of the clustering-based analysis method. The sensors on the posterior and medial regions are suggested to be reduced, and the main pressure features are kept. The proposed method can help sensor designers optimize sensor configurations for intra-socket measurements and thus assist the prosthetists in improving the socket fitting.

Within-subject effects of standardized prosthetic socket modifications on physical function and patient-reported outcomes

Background

Among the challenges of living with lower limb loss is the increased risk of long-term health problems that can be either attributed directly to the amputation surgery and/or prosthetic rehabilitation or indirectly to a disability-induced sedentary lifestyle. These problems are exacerbated by poorly fit prosthetic sockets. There is a knowledge gap regarding how the socket design affects in-socket mechanics and how in-socket mechanics affect patient-reported comfort and function. The objectives of this study are (1) to gain a better understanding of how in-socket mechanics of the residual limb in transfemoral amputees are related to patient-reported comfort and function, (2) to identify clinical tests that can streamline the socket design process, and (3) to evaluate the efficacy and cost of a novel, quantitatively informed socket optimization process.

Methods

Users of transfemoral prostheses will be asked to walk on a treadmill wearing their current socket plus 8 different check sockets with designed changes in different structural measurements that are likely to induce changes in residual limb motion, skin strain, and pressure distribution within the socket. Dynamic biplane radiography and pressure sensors will be used to measure in-socket residual limb mechanics. Patient-reported outcomes will also be collected after wearing each socket. The effects of in-socket mechanics on both physical function and patient-reported outcomes (aim 1) will be assessed using a generalized linear model. Partial correlation analysis will be used to examine the association between research-grade measurements and readily available clinical measurements (aim 2). In order to compare the new quantitative design method to the standard of care, patient-reported outcomes and cost will be compared between the two methods, utilizing the Wilcoxon-Mann-Whitney non-parametric test (aim 3).

Discussion

Knowledge on how prosthetic socket modifications affect residual bone and skin biomechanics itself can be applied to devise future socket designs, and the methodology can be used to investigate and improve such designs, past and present. Apart from saving time and costs, this may result in better prosthetic socket fit for a large patient population, thus increasing their mobility, participation, and overall health-related quality of life.

Trial registration

ClinicalTrials.gov NCT05041998. Date of registration: Sept 13, 2021.

The Impact of Limited Prosthetic Socket Documentation: A Researcher Perspective

The majority of limb prostheses are socket mounted. For these devices, the socket is essential for adequate prosthetic suspension, comfort, and control. The socket is unique among prosthetic components as it is not usually mass-produced and must instead be custom-made for individual residual limbs by a prosthetist. The knowledge of what constitutes "good" socket fit is gained by expert prosthetists and technicians over years of experience, and rarely documented. The reliance on tacit knowledge makes it difficult to standardize the criteria for a well-fitting socket, leading to difficulties understanding the impact of socket fit. Despite its importance, the workflow for socket fitting is often overlooked in literature. Due to the customized nature of sockets, if information is provided in literature, generally only the type of socket and suspension mechanism is noted, with information regarding the fitting and manufacturing processes omitted. In this article, the concerns, issues and consequences arising from lack of upper and lower limb socket documentation are discussed from a researcher perspective, supported by healthcare professionals and socket fabrication specialists. Key changes are proposed to the way socket manufacturing and evaluation are documented to assist future research.