An experimental study of the interface pressure profile during level walking of a new suspension system for lower limb amputees

Testing protocols and measurement techniques when using pressure sensors for sport and health applications: A comparative review

Plantar pressure measurement systems are routinely used in sports and health applications to assess locomotion. The purpose of this review is to describe and critically discuss: (a) applications of the pressure measurement systems in sport and healthcare, (b) testing protocols and considerations for clinical gait analysis, (c) clinical recommendations for interpreting plantar pressure data, (d) calibration procedures and their accuracy, and (e) the future of pressure sensor data analysis. Rigid pressure platforms are typically used to measure plantar pressures for the assessment of foot function during standing and walking, particularly when barefoot, and are the most accurate for measuring plantar pressures. For reliable data, two step protocol prior to contacting the pressure plate is recommended. In-shoe systems are most suitable for measuring plantar pressures in the field during daily living or dynamic sporting movements as they are often wireless and can measure multiple steps. They are the most suitable equipment to assess the effects of footwear and orthotics on plantar pressures. However, they typically have lower spatial resolution and sampling frequency than platform systems. Users of pressure measurement systems need to consider the suitability of the calibration procedures for their chosen application when selecting and using a pressure measurement system. For some applications, a bespoke calibration procedure is required to improve validity and reliability of the pressure measurement system. The testing machines that are commonly used for dynamic calibration of pressure measurement systems frequently have loading rates of less than even those found in walking, so the development of testing protocols that truly measure the loading rates found in many sporting movements are required. There is clear potential for AI techniques to assist in the analysis and interpretation of plantar pressure data to enable the more complete use of pressure system data in clinical diagnoses and monitoring.

Commercially available pressure sensors for sport and health applications: A comparative review

Pressure measurement systems have numerous applications in healthcare and sport. The purpose of this review is to: (a) describe the brief history of the development of pressure sensors for clinical and sport applications, (b) discuss the design requirements for pressure measurement systems for different applications, (c) critique the suitability, reliability, and validity of commercial pressure measurement systems, and (d) suggest future directions for the development of pressure measurements systems in this area. Commercial pressure measurement systems generally use capacitive or resistive sensors, and typically capacitive sensors have been reported to be more valid and reliable than resistive sensors for prolonged use. It is important to acknowledge, however, that the selection of sensors is contingent upon the specific application requirements. Recent improvements in sensor and wireless technology and computational power have resulted in systems that have higher sensor density and sampling frequency with improved usability - thinner, lighter platforms, some of which are wireless, and reduced the obtrusiveness of in-shoe systems due to wireless data transmission and smaller data-logger and control units. Future developments of pressure sensors should focus on the design of systems that can measure or accurately predict shear stresses in conjunction with pressure, as it is thought the combination of both contributes to the development of pressure ulcers and diabetic plantar ulcers. The focus for the development of in-shoe pressure measurement systems is to minimise any potential interference to the patient or athlete, and to reduce power consumption of the wireless systems to improve the battery life, so these systems can be used to monitor daily activity. A potential solution to reduce the obtrusiveness of in-shoe systems include thin flexible pressure sensors which can be incorporated into socks. Although some experimental systems are available further work is needed to improve their validity and reliability.

Self-reported socket comfort, mobility, and balance-confidence of individuals with transtibial amputation using pinlock vs suction suspension

BACKGROUND

Improper suspension between the residual limb and prosthesis can result in pistoning, which may compromise skin integrity and reduce overall user comfort. In addition to objective measures of limb pistoning, user perspective may provide insight into suspension system effectiveness.

OBJECTIVES

The primary objective of this analysis was to explore differences in self-reported measures among adults with transtibial amputation (TTA) using pinlock vs suction suspension systems.

STUDY DESIGN

This is a secondary analysis of cross-sectional data.

METHODS

Participants (n = 48) were included if they (1) were ≥18 years of age, (2) were community-dwelling, (3) had a unilateral TTA of ≥6 months, and (4) were prescribed a prosthesis with either pinlock or suction suspension. Participants completed self-reported measures evaluating socket comfort (Socket Comfort Score [SCS]), prosthesis-enabled mobility (Prosthesis Evaluation Questionnaire-Mobility Section [PEQ-MS]; Locomotor Capabilities Index [LCI]), and balance-confidence (Activities-Specific Balance Confidence Scale [ABC]).

RESULTS

Participants using suction suspension reported significantly higher SCS as compared with participants using pinlock suspension (P ≤ .001). No differences were observed between groups for PEQ-MS, LCI, and/or ABC.

CONCLUSIONS

Individuals with TTA using suction suspension may report greater socket comfort than peers using pinlock suspension, but prosthesis-enabled mobility and balance-confidence may be similar. Future research is warranted to confirm these preliminary findings using a prospective, crossover study design that controls for all suspected factors that might influence socket comfort.

Textile-based Pressure Sensors for Monitoring Prosthetic-Socket Interfaces

Amputees are prone to experiencing discomfort when wearing their prosthetic devices. As the amputee population grows this becomes a more prevalent and pressing concern. There is a need for new prosthetic technologies to construct more comfortable and well-fitted liners and sockets. One of the well-recognized impediments to the development of new prosthetic technology is the lack of practical inner socket sensors to monitor the inner socket environment (ISE), or the region between the residual limb and the socket. Here we present a capacitive pressure sensor fabricated through a simple, and scalable sewing process using commercially available conductive yarns and textile materials. This fully-textile sensor provides a soft, flexible, and comfortable sensing system for monitoring the ISE. We provide details of our low-power sensor system capable of high-speed data collection from up to four sensor arrays. Additionally, we demonstrate two custom set-ups to test and validate the textile-based sensors in a simulated prosthetic environment. Finally, we utilize the textile-based sensors to study the ISE of a bilateral transtibial amputee. Results indicate that the textile-based sensors provide a promising potential for seamlessly monitoring the ISE.

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.

Design and Fabrication of a New Expandable Transtibial Liner with Manual Volume Control: A Prototype

Diurnal volume changes is one of the main factors influencing socket fit in transtibial prosthesis and causing pressure problem issues. Embedded bladder liners have been recently a potential approach to deal with this problem. The aim of this technical note was to introduce a new transtibial silicone liner designed based on hybrid socket theory.

To make expandability in the liner, an integrated wax structure was constructed over the selected areas of the positive model and then removed after lamination process. In addition, a mechanical system with manual control was designed to fit the liner with the residual limb volume by pumping the water in or out of the liner through connective tubes.

The results showed that this new design had high reliability in maintaining identical surface pressures after volume changes in laboratory trials. Therefore, it seems that selective expandability of this liner would accommodate residual limb volume fluctuations without disturbing effect on preliminary pressure pattern.

Clinical utility of pressure feedback to socket design and fabrication

BACKGROUND

The clinical utility of measuring pressure at the prosthetic socket-residual limb interface is currently unknown.

OBJECTIVES

This study aimed to identify whether measuring interface pressure during prosthetic design and fabrication results in closer agreement in pressure measurements between sockets made by different clinicians, and a reduction in pressure over areas of concern. It also investigated whether clinicians value knowing the interface pressure during the fabrication process.

STUDY DESIGN

Mixed methods.

METHODS

Three prosthetists designed a complete prosthetic system for a transtibial residual limb surrogate. Standardised mechanical testing was performed on each prosthetic system to gain pressure measurements at four key anatomical locations. These measurements were provided to the clinicians, who subsequently modified their sockets as each saw fit. The pressure at each location was re-measured. Each prosthetist completed a survey that evaluated the usefulness of knowing interface pressures during the fabrication process.

RESULTS

Feedback and subsequent socket modifications saw a reduction in the pressure measurements at three of the four anatomical locations. Furthermore, the pressure measurements between prosthetists converged. All three prosthetists found value in the pressure measurement system and felt they would use it clinically.

CONCLUSIONS

Results suggest that sensors measuring pressure at the socket-limb interface has clinical utility in the context of informing prosthetic socket design and fabrication. If the technology is used at the check socket stage, iterative designs with repeated measurements can result in increased consistency between clinicians for the same residual limb, and reductions in the magnitudes of pressures over specific anatomical landmarks.

CLINICAL RELEVANCE

This study provides new information on the value of pressure feedback to the prosthetic socket design process. It shows that with feedback, socket modifications can result in reduced limb pressures, and more consistent pressure distributions between prosthetists. It also justifies the use of pressure feedback in informing clinical decisions.

Evaluating shear and normal force with the use of an instrumented transtibial socket: A case study

Patients with transtibial amputation experience ulcers on their residual limb. The loading between the device and underlying material plays a role in loads transmitted to the skin. The objective was to evaluate normal and shear forces at the socket/liner interface during walking. A 53 year old male (85.45 kg and 177.8 cm) with a transtibial amputation participated in this case study. A transtibial prosthesis was instrumented with a load cell to measure normal and shear forces at the socket interface. Three conditions were evaluated during walking: gel liner, additional three ply sock and a hole in the gel liner. Shear and normal forces were highest with the addition of a three ply. Longitudinal shear stresses ranged from 0.4-7.66 kPa, transverse shear stresses ranged from 0.01-7.79 kPa and normal stresses ranged from 2.7-61.9 kPa. Increased shear and normal forces can cause a significant decrease in blood perfusion, linked to an increased risk of ulcer formation. Experimental force results are also important for future work involving finite element modeling of the skin/liner/device interface.

A physically-motivated model describing the dynamic interactions between residual limb and socket in lower limb prostheses

The amputee’s well-being and mobility are distinclty related to socket fit and resulting biomechanical interaction between residual limb and prosthetic socket. Understanding the dynamic interactions at the interface may lead to new socket standards. This paper introduces a physically-motivated reduced model of the interface, describing the dynamic interactions between residual limb and prosthetic socket. The model allows to investigate the sensitivity to changes of specific parameters in an isolated matter. A simulation study shows how stress distribution changes if friction coefficients are varied which might advance liner design.

Systematic review of effects of current transtibial prosthetic socket designs--Part 2: Quantitative outcomes

This review is an attempt to untangle the complexity of transtibial prosthetic socket fit and perhaps find some indication of whether a particular prosthetic socket type might be best for a given situation. In addition, we identified knowledge gaps, thus providing direction for possible future research. We followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, using medical subject headings and standard key words to search for articles in relevant databases. No restrictions were made on study design and type of outcome measure used. From the obtained search results (n = 1,863), 35 articles were included. The relevant data were entered into a predefined data form that included the Downs and Black risk of bias assessment checklist. This article presents the results from the systematic review of the quantitative outcomes (n = 27 articles). Trends indicate that vacuum-assisted suction sockets improve gait symmetry, volume control, and residual limb health more than other socket designs. Hydrostatic sockets seem to create less inconsistent socket fittings, reducing a problem that greatly influences outcome measures. Knowledge gaps exist in the understanding of clinically meaningful changes in socket fit and its effect on biomechanical outcomes. Further, safe and comfortable pressure thresholds under various conditions should be determined through a systematic approach.

A comparison of pressure distributions between two types of sockets in a bulbous stump

BACKGROUND

This article describes a total surface bearing prosthetic socket for a patient (25-year-old female) with a bulbous stump.

CASE DESCRIPTION AND METHODS

The subject had unstable excessive soft tissue at the distal end of the residuum. After 2 years of prosthetic use, she experienced several problems, including pain in the residual limb and knee joint. Pressure distribution was evaluated during ambulation. We also designed a total surface bearing socket with Velcro as suspension system to distribute the load evenly on the residual limb, and to facilitate donning procedure.

FINDINGS AND OUTCOMES

The main site of weight bearing in the old prosthesis (patellar tendon bearing) was anterior proximal region of the residual limb, especially the patellar tendon. The pressure was almost 10 times higher than the distal region during level walking. Pressures were distributed more evenly with the total surface bearing socket design, and the donning was much easier.

CONCLUSION

Pressure distribution within the socket could be affected by socket design and suspension system. Using the total surface bearing socket and Velcro as suspension system might facilitate donning of prosthesis and reduce traction at the end of residual limb during the swing phase of gait.

CLINICAL RELEVANCE

Proper socket design and suspension system based on the amputees' need can facilitate rehabilitation process and lead to the amputee's satisfaction. The pressure is distributed more uniformly over the residual limb by the total surface bearing socket compared to the patellar tendon bearing socket for lower limb amputees with unusual stump shape.

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

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

Clinical implication of interface pressure for a new prosthetic suspension system

BACKGROUND

Prosthesis suspension systems can alter the distribution of pressure within the prosthetic socket. This study evaluates a new suspension system for lower limb prostheses, and aims to compare the interface pressure and amputees' satisfaction with the new system compared with a common prosthetic suspension system (pin/lock).

METHODS

Ten transtibial amputees walked at a self-selected speed on a level ground with two different suspension systems, namely the pin/lock and HOLO system. The interface pressure was measured using the F-socket transducers at the proximal, middle and distal sites of residual limb. Furthermore, subjective feedback was logged to compare two systems.

RESULTS

The pressure was significantly higher at the proximal and distal areas with the pin/lock suspension system during the swing phase of gait (P<0.05). Subjective feedback also showed traction at the stump with the pin/lock system. There were no significant differences in the pressure applied to the mid-anterior and mid posterior stump for both suspension systems. However, the lateral and medial sides exhibited higher pressure with the new system during stance phase.

CONCLUSIONS

The intention of this study was to deepen understanding on the effect of suspension system on the load distribution over the residual limb. The new coupling system was proved compatible with the pin/lock system in terms of suspending the leg and amputee's satisfaction. On the other hand, the HOLO system could distribute the pressure more uniformly over the residual limb.

Gait biomechanics of individuals with transtibial amputation: effect of suspension system

Prosthetic suspension system is an important component of lower limb prostheses. Suspension efficiency can be best evaluated during one of the vital activities of daily living, i.e. walking. A new magnetic prosthetic suspension system has been developed, but its effects on gait biomechanics have not been studied. This study aimed to explore the effect of suspension type on kinetic and kinematic gait parameters during level walking with the new suspension system as well as two other commonly used systems (the Seal-In and pin/lock). Thirteen persons with transtibial amputation participated in this study. A Vicon motion system (six cameras, two force platforms) was utilized to obtain gait kinetic and kinematic variables, as well as pistoning within the prosthetic socket. The gait deviation index was also calculated based on the kinematic data. The findings indicated significant difference in the pistoning values among the three suspension systems. The Seal-In system resulted in the least pistoning compared with the other two systems. Several kinetic and kinematic variables were also affected by the suspension type. The ground reaction force data showed that lower load was applied to the limb joints with the magnetic suspension system compared with the pin/lock suspension. The gait deviation index showed significant deviation from the normal with all the systems, but the systems did not differ significantly. Main significant effects of the suspension type were seen in the GRF (vertical and fore-aft), knee and ankle angles. The new magnetic suspension system showed comparable effects in the remaining kinetic and kinematic gait parameters to the other studied systems. This study may have implications on the selection of suspension systems for transtibial prostheses.

Trial Registration

Iranian Registry of Clinical Trials IRCT2013061813706N1.

Interface pressure in transtibial socket during ascent and descent on stairs and its effect on patient satisfaction

BACKGROUND

Transtibial amputees encounter stairs and steps during their daily activities. The excessive pressure between residual limb/socket may reduce the walking capability of transtibial prosthetic users during ascent and descent on stairs. The purposes of the research were to evaluate the interface pressure between Dermo (shuttle lock) and Seal-In X5 (prosthetic valve) interface systems during stair ascent and descent, and to determine their satisfaction effects on users.

METHODS

Ten amputees with unilateral transtibial amputation participated in the study. Interface pressure was recorded with F-socket transducer (9811E) during stair ascent and descent at self-selected speed. Each participant filled in a questionnaire about satisfaction and problems encountered with the use of the two interface systems.

FINDINGS

The resultant mean peak pressure (kPa) was significantly lower for the Dermo interface system compared to that of the Seal-In X5 interface system at the anterior, posterior and medial regions during stair ascent (63.14 vs. 80.14, 63.14 vs. 90.44, 49.21 vs. 66.04, respectively) and descent (67.11 vs. 80.41, 64.12 vs. 88.24, 47.33 vs. 65.11, respectively). Significant statistical difference existed between the two interface systems in terms of satisfaction and problems encountered (P<0.05).

INTERPRETATION

The Dermo interface system caused less pressure within the prosthetic socket compared to the Seal-In X5 interface system during stair negotiation. The qualitative survey also showed that the prosthesis users experienced fewer problems and increased satisfaction with the Dermo interface system.

Evaluation of new suspension system for limb prosthetics

Background

Good prosthetic suspension system secures the residual limb inside the prosthetic socket and enables easy donning and doffing. This study aimed to introduce, evaluate and compare a newly designed prosthetic suspension system (HOLO) with the current suspension systems (suction, pin/lock and magnetic systems).

Methods

All the suspension systems were tested (tensile testing machine) in terms of the degree of the shear strength and the patient’s comfort. Nine transtibial amputees participated in this study. The patients were asked to use four different suspension systems. Afterwards, each participant completed a questionnaire for each system to evaluate their comfort. Furthermore, the systems were compared in terms of the cost.

Results

The maximum tensile load that the new system could bear was 490 N (SD, 5.5) before the system failed. Pin/lock, magnetic and suction suspension systems could tolerate loads of580 N (SD, 8.5), 350.9 (SD, 7) and 310 N (SD, 8.4), respectively. Our subjects were satisfied with the new hook and loop system, particularly in terms of easy donning and doffing. Furthermore, the new system is considerably cheaper (35 times) than the current locking systems in the market.

Conclusions

The new suspension system could successfully retain the prosthesis on the residual limb as a good alternative for lower limb amputees. In addition, the new system addresses some problems of the existing systems and is more cost effective than its counterparts.

Transtibial prosthesis suspension systems: systematic review of literature

BACKGROUND

Today a number of prosthetic suspension systems are available for transtibial amputees. Consideration of an appropriate suspension system can ensure that amputee's functional needs are satisfied. The higher the insight to suspension systems, the easier would be the selection for prosthetists. This review attempted to find scientific evidence pertaining to various transtibial suspension systems to provide selection criteria for clinicians.

METHODS

Databases of PubMed, Web of Science, and ScienceDirect were explored to find related articles. Search terms were as follows: "Transtibial prosthesis (32), prosthetic suspension (48), lower limb prosthesis (54), below-knee prosthesis (58), prosthetic liner (20), transtibial (193), and prosthetic socket (111)". Two reviewers separately examined the papers. Study design (case series of five or more subjects, retrospective or prospective), research instrument, sampling method, outcome measures and protocols were reviewed.

FINDINGS

Based on the selection criteria, 22 articles (15 prospective studies, and 7 surveys) remained. Sweat control was found to be a major concern with the available suspension liners. Donning and doffing procedures for soft liners are also problematic for some users, particularly those with upper limb weakness. Moreover, the total surface bearing (TSB) socket with pin/lock system is favored by the majority of amputees.

INTERPRETATION

In summary, no clinical evidence is available to suggest what kind of suspension system could have an influential effect as a "standard" system for all transtibial amputees. However, among various suspension systems for transtibial amputees, the Iceross system was favored by the majority of users in terms of function and comfort.

Finite element analysis of the contact interface between trans-femoral stump and prosthetic socket

Transfemoral amputees need prosthetic devices after amputation surgery, and the interface pressure between the residual limb and prosthetic socket has a significant effect on an amputee's satisfaction and comfort. The purpose of this study was to build a nonlinear finite element model to investigate the interface pressure between the above-knee residual limb and its prosthetic socket. The model was three-dimensional (3D) with consideration of nonlinear boundary conditions. Contact analysis was used to simulate the friction conditions between skin and the socket. The normal stresses up to 80.57 kPa at the distal end of the soft tissue. The longitudinal and circumferential shear stress distributions at the limb-socket interface were also simulated. This study explores the influences of load transfer between trans-femoral residual limb and its prosthetic socket.