CLINICAL OUTCOME OF TRANSFEMORAL DIRECT SOCKET INTERFACE (PART 2)

BACKGROUND: Amputation at the transfemoral (TF) level reduces the rate of successful prosthetic fitting, functional outcome, and quality of life (QoL) compared with transtibial amputation. The TF socket interface is considered the most critical part of the prosthesis, but socket discomfort is still the most common user complaint. Direct Socket for transfemoral prosthesis users is a novel interface fabrication process where the socket is shaped and laminated directly on the residual limb and delivered in a single visit. OBJECTIVE(S): The aim of this study was to investigate if prosthetic users' quality of life (QoL), comfort, and mobility with a Direct Socket TF interface were comparable to their experience with their previous prostheses. METHODOLOGY: The pre/post design prospective cohort study included 47 subjects. From this cohort, 36 subjects completed the 6-months follow-up (mean age 58 years, 27 males). Outcomes at baseline included EQ-5D-5L®, PLUS-M™, CLASS, ABC, AMPPRO, and TUG. At 6-weeks and 6-months, subjects repeated all measures. Seven Certified Prosthetist (CP) investigators performed observations and data collection at six different sites (from July 2018 to April 2020). FINDINGS: Results showed significant improvement in all outcome measures for the 36 subjects that completed both 6-weeks and 6-months follow-ups. CLASS sub-scales showed significantly improved stability, suspension, comfort, and socket appearance. Improvement in K-Level and less use of assistive devices were observed with the AMPPRO instrument, indicating improved user mobility and performance. QoL was also increased, as measured in Quality-Adjusted-Life-Years (QALY) from the EQ-5D-5L. CONCLUSION: Evidence from the findings demonstrate that the Direct Socket TF system and procedure can be a good alternative to the traditional method of prosthetic interface delivery. Layman's Abstract After lower limb amputation, the goal for most people is to regain mobility and independence and return to normal daily activities. Typically, people with transfemoral amputation are less likely to receive a prosthesis or fully use a prosthesis as compared to people with transtibial amputation. Moreover, their quality of life is also lower. The Direct Socket TF method is a new way of fabricating a prosthetic socket for users with above-knee amputation, enabling fabrication directly onto the residual limb and delivery of the socket in a single visit. In this study, we wanted to understand how the effect of Direct Socket TF on prosthetic 'user's quality of life, health, mobility level, and balance would compare to their previous prosthesis. This new Direct Socket TF procedure was implemented in six different prosthetic clinics across the United States and used by 36 prosthetic users for six months. Our first article on this study describes increased user satisfaction with their new interface and the single visit service model. This second article on the same clinical investigation documents the significant improvement in outcomes compared to their original interface in terms of quality of life, confidence, mobility, comfort, stability, and activity level. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/36065/27923 Direct Socket TF – Summary (YouTube): https://www.youtube.com/watch?v=-fvVFqjgxjo How To Cite: Walker J, Marable W.R, Smith C, Sigurjónsson B.Þ, Atlason I.F, Johannesson G.A. Clinical outcome of transfemoral direct socket interface (part 2). Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.6. https://doi.org/10.33137/cpoj.v4i1.36065 Corresponding Author: Anton Johannesson, PhDTeamOlmed, Kistagången 12, 164 40 Kista, Stockholm, Sweden.E-mail: [email protected]: https://orcid.org/0000-0001-8729-458X

USING A SWEATING RESIDUUM/SOCKET INTERFACE SIMULATOR FOR THE EVALUATION OF SWEAT MANAGEMENT LINERS IN LOWER LIMB PROSTHETICS

BACKGROUND: Lab-based simulators can help to reduce variability in prosthetics research. However, they have not yet been used to investigate the effects of sweating at the residuum-liner interface. This work sought to create and validate a simulator to replicate the mechanics of residual limb perspiration. The developed apparatus was used to assess the effects of perspiration and different liner designs. METHODOLOGY: By scanning a cast, an artificial residuum was manufactured using a 3D-printed, transtibial bone model encased in silicone, moulded with pores. The pores allowed water to emit from the residuum surface, simulating sweating. Dry and sweating cyclic tests were performed by applying compressive and tensile loading, while measuring the displacement of the residuum relative to the socket. Tests were conducted using standard and perforated liners. FINDINGS: Although maximum displacement varied between test setups, its variance was low (coefficient of variation <1%) and consistent between dry tests. For unperforated liners, sweating increased the standard deviation of maximum displacement approximately threefold (0.04mm v 0.12mm, p<0.001). However, with the perforated liner, sweating had little effect on standard deviation compared to dry tests (0.04mm v 0.04mm, p=0.497). CONCLUSIONS: The test apparatus was effective at simulating the effect of perspiration at the residual limb. Moisture at the skin-liner interface can lead to inconsistent mechanics. Perforated liners help to remove sweat from the skin-liner interface, thereby mitigating these effects. Layman’s Abstract Simulators can be used in prosthetics research to make experiments more repeatable. In this study, a test apparatus was created to replicate the mechanical effects of residual limb sweating. An artificial residual limb was made from silicone and a 3D printed, transtibial bone model. Small holes were made throughout the silicone to act like pores, allowing water to travel to the outside surface, like sweat. The limb was loaded to mimic walking and its movement within the socket was measured. For some tests, water was added internally to see the effect of sweat. Two types of liner were used and compared; a standard one and one with perforations. In terms of movement, the results were generally consistent between each cycle for the dry tests. For standard liners, the addition of sweating increased the variability of movement approximately threefold (0.04mm v 0.12mm, p<0.001). However, with the perforated liner, sweating had little effect on movement (0.04mm v 0.04mm, p=0.497). The test apparatus simulated the effect of residual limb sweating. The findings indicate that moisture on the skin can lead to inconsistent movement, but perforated liners help to remove this moisture, which helps improve consistency of performance. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/35213/27472 How To Cite: McGrath M, Davies K.C, Gallego A, Laszczak P, Tang J, Zahedi S, Moser D. Using a sweating residuum/socket interface simulator for the evaluation of sweat management liners in lower limb prosthetics. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.3. https://doi.org/10.33137/cpoj.v4i1.35213 Corresponding Author: Dr. Michael McGrath, PhDResearch Scientist–Clinical Evidence,Blatchford Group, Unit D Antura, Bond Close, Basingstoke, RG24 8PZ, United Kingdom.Email: [email protected]: https://orcid.org/0000-0003-0195-970X

A Simulation-Based Analysis of The Effects of Variable Prosthesis Stiffness On Interface Dynamics Between The Prosthetic Socket and Residual Limb

Introduction: Loading of a residual limb within a prosthetic socket can cause tissue damage such as ulceration. Computational models and simulations may be useful tools for estimating tissue loading within the socket and thus provide insights into how interventions (e.g. prosthesis designs or rehabilitation techniques) affect residual limb-socket interface dynamics. The purpose of this study was to model and simulate residual limb-socket interface dynamics and evaluate the effects of varied prosthesis stiffness on interface dynamics during gait. Methods: A spatial contact model of a residual limb-socket interface was developed and integrated into a gait model with a below-knee amputation. Gait trials were simulated for four subjects walking with low, medium, and high prosthesis stiffness settings. The effects of prosthesis stiffness on interface kinematics, normal pressure, and shear stresses were evaluated. Mean group responses and a subject-specific case study were analyzed. Results: Model-predicted outcome values were similar to those reported previously in sensor-based experiments; however, there were no discernable effects of prosthesis stiffness on interface dynamics among the group data (p&gt;0.05). Subject-specific data showed decreased external rotation in the low stiffness trials, though high variability was present in the data. Conclusions: These methods may be useful to aid experimental studies by providing insights into the effects of varied prosthesis design parameters or gait conditions on residual limb-socket interface dynamics. Data suggest that these effects may be subject-specific.

Interface Pressure System to Compare the Functional Performance of Prosthetic Sockets during the Gait in People with Trans-Tibial Amputation

The interface pressure between the residual limb and prosthetic socket has a significant effect on the amputee’s mobility and level of comfort with their prosthesis. This paper presents a socket interface pressure (SIFP) system to compare the interface pressure differences during gait between two different types of prosthetic sockets for a transtibial amputee. The system evaluates the interface pressure in six critical regions of interest (CROI) of the lower limb amputee and identifies the peak pressures during certain moments of the gait cycle. The six sensors were attached to the residual limb in the CROIs before the participant with transtibial amputation donned a prosthetic socket. The interface pressure was monitored and recorded while the participant walked on a treadmill for 10 min at 1.4 m/s. The results show peak pressure differences of almost 0.22 kgf/cm2 between the sockets. It was observed that the peak pressure occurred at 50% of the stance phase of the gait cycle. This SIFP system may be used by prosthetists, physical therapists, amputation care centers, and researchers, as well as government and private regulators requiring comparison and evaluation of prosthetic components, components under development, and testing.

Key considerations for finite element modelling of the residuum–prosthetic socket interface

Background: Finite element modelling has long been proposed to support prosthetic socket design. However, there is minimal detail in the literature to inform practice in developing and interpreting these complex, highly nonlinear models. Objectives: To identify best practice recommendations for finite element modelling of lower limb prosthetics, considering key modelling approaches and inputs. Study design: Computational modelling. Methods: This study developed a parametric finite element model using magnetic resonance imaging data from a person with transtibial amputation. Comparative analyses were performed considering socket loading methods, socket–residuum interface parameters and soft tissue material models from the literature, to quantify their effect on the residuum’s biomechanical response to a range of parameterised socket designs. Results: These variables had a marked impact on the finite element model’s predictions for limb–socket interface pressure and soft tissue shear distribution. Conclusions: All modelling decisions should be justified biomechanically and clinically. In order to represent the prosthetic loading scenario in silico, researchers should (1) consider the effects of donning and interface friction to capture the generated soft tissue shear stresses, (2) use representative stiffness hyperelastic material models for soft tissues when using strain to predict injury and (3) interrogate models comparatively, against a clinically-used control.

Metamaterial Design for Targeted Limb-Socket Interface Pressure Offloading in Transtibial Amputees

While using a prosthesis, transtibial amputees can experience pain and discomfort brought on by large pressure gradients, at the interface between the residual limb and prosthetic socket. Current prosthetic interface solutions attempt to alleviate these pressure gradients by using soft homogenous liners to reduce and distribute pressures. This research investigates an additively manufactured metamaterial inlay with adjustable mechanical response in order to reduce peak pressure gradients around the limb. The inlay uses a hyperelastic behaving metamaterial (US10244818) comprised of triangular pattern unit cells which can be 3D printed with walls of various thicknesses controlled by draft angles. The hyperelastic material properties are modeled using a third order representation based on Yeoh 3rd order coefficients. The 3rd order coefficients can be adjusted and optimized to represent a change in the unit cell wall thickness to create an inlay that can meet the unique offloading needs of an amputee. Finite element analyses evaluated the pressure gradient reduction from: 1) A common homogenous silicone liner, 2) A prosthetist’s inlay prescription that utilizes three variations of the metamaterial, and 3) A metamaterial solution with optimized Yeoh 3rd order coefficients. When compared to a traditional homogenous silicone liner for two unique limb loading scenarios, the prosthetist prescribed inlay and optimized material inlay can achieve equal or greater pressure gradient reduction capabilities. These results show the potential feasibility of implementing this metamaterial as a method of personalized medicine for transtibial amputees by creating customizable interface solution to the meet unique performance needs of an individual patient.

Design, Characterization, and Evaluation of a Dynamic Soft Robotic Prosthetic Socket Interface

Prosthetic sockets are static interfaces for dynamic residual limbs. As the user’s activity level increases, the volume of the residual limb can decrease by up to 11% and increase by as much as 7% after activity. Currently, volume fluctuation is addressed by adding/removing prosthetic socks to change the profile of the residual limb. However, this is impractical and time consuming. These painful/functional issues demand a prosthetic socket with an adjustable interface that can adapt to the user’s needs. This paper presents a prototype design for a dynamic soft robotic interface which addresses this need. The actuators are adjustable depending on the user’s activity level, and their structure provides targeted compression to the soft tissue which helps to limit movement of the bone relative to the socket. Testing of the prototype demonstrated promising potential for the design with further refinement. Work on embedded sensing and intelligent feedback control should be continued in future research in order to create a viable consumer product which can improve a lower limb amputee’s quality of life.