Effects of changes in cadence, prosthetic componentry, and time on interface pressures and shear stresses of three trans-tibial amputees

Optimal design and 3D printing of prosthetic socket based on the interface pressure between the socket and residual limb

BACKGROUND

At present, the quantifiable pressure distribution at the interface between the socket and stump is seldom applied in the design and fabrication of the socket.

OBJECTIVES

This study aimed to optimize the socket based on the interface pressure of residual limb-socket, thereby avoiding excessive local load on the residual limb, reducing the load on the pressure-sensitive (PS) regions and making the limb more evenly loaded.

METHODS

The residual limb was divided into the main load-bearing regions, the pressure-tolerant regions, and the PS regions according to the carrying capacity at its different regions. Based on these bearing regions, a mathematical function was developed, which applied modifications/adjustments to the socket design in a Computer Aided Design (CAD) environment by using the adjustment function. Besides, three adjusted sockets were produced by using selective laser sintering 3D printing technology.

RESULTS

The wearing of the 3D-adjusted printed sockets reduced the contact interface pressures in the distal tibial region and the fibular head region by 85.6% and 84.4%, respectively. In addition, the walking distance of the subject was increased by 18.34%, and the overall pressure distribution on the stump became more uniform.

CONCLUSIONS

The pressures in the original overpressure regions and the PS regions could reduce, whereas the pressure in the low-load regions of main load-bearing or pressure-tolerant regions could increase by modifying the socket with the pressure adjustment function. At the same time, the pressure among different regions was more uniform except for the sensitive regions.

Implantable biosensors for musculoskeletal health

PURPOSE

A healthy musculoskeletal system requires complex functional integration of bone, muscle, cartilage, and connective tissues responsible for bodily support, motion, and the protection of vital organs. Conditions or injuries to musculoskeeltal tissues can devastate an individual's quality of life. Some conditions that are particularly disabling include severe bone and muscle injuries to the extremities and amputations resulting from unmanageable musculoskeletal conditions or injuries. Monitoring and managing musculoskeletal health is intricate because of the complex mechanobiology of these interconnected tissues.

METHODS

For this article, we reviewed literature on implantable biosensors related to clinical data of the musculoskeletal system, therapeutics for complex bone injuries, and osseointegrated prosthetics as example applications.

RESULTS

As a result, a brief summary of biosensors technologies is provided along with review of noteworthy biosensors and future developments needed to fully realize the translational benefit of biosensors for musculoskeletal health.

CONCLUSIONS

Novel implantable biosensors capable of tracking biophysical parameters in vivo are highly relevant to musculoskeletal health because of their ability to collect clinical data relevant to medical decisions, complex trauma treatment, and the performance of osseointegrated prostheses.

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 simulations may be useful tools for estimating tissue loading within the socket, and thus provide insights into how prosthesis designs 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.

Results: Model-predicted values were similar to those reported previously in sensor-based experiments; increased stiffness resulted in greater average normal pressure and shear stress (p < 0.05).

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. The current results suggest that these effects may be subject-specific.

Compression and tension behavior of the prosthetic foam materials polyurethane, EVA, Pelite™ and a combination of polyurethane and EVA: a preliminary study

Materials with low-strength and low-impedance properties, such as elastomers and polymeric foams are major contributors to prosthetic liner design. Polyethylene-Light (Pelite™) is a foam liner that is the most frequently used in prosthetics but it does not cater to all amputees' limb and skin conditions. The study aims to investigate the newly modified Foam Liner, a combination of two different types of foams (EVA + PU + EVA) as the newly modified Foam Liner in terms of compressive and tensile properties in comparison to Pelite™, polyurethane (PU) foam, and ethylene-vinyl acetate (EVA) foam. Universal testing machine (AGS-X, Shimadzu, Kyoto, Japan) has been used to measure the tensile and compressive stress. Pelite™ had the highest compressive stress at 566.63 kPa and tensile stress at 1145 kPa. Foam Liner fell between EVA and Pelite™ with 551.83 kPa at compression and 715.40 kPa at tension. PU foam had the lowest compressive stress at 2.80 kPa and tensile stress at 33.93 kPa. Foam Liner has intermediate compressive elasticity but has high tensile elasticity compared to EVA and Pelite™. Pelite™ remains the highest in compressive and tensile stiffness. Although it is good for amputees with bony prominence, constant pressure might result in skin breakdown or ulcer. Foam Liner would be the best for amputees with soft tissues on the residual limbs to accommodate movement.

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.

How do transtibial residual limbs adjust to intermittent incremental socket volume changes?

BACKGROUND

Strategies to maintain prosthesis users' daily limb volume are needed.

OBJECTIVES

Test how intermittent incremental socket volume adjustments affect limb fluid volume and limb-socket distance.

STUDY DESIGN

Repeated measures.

METHODS

People with transtibial limb loss walked on an outdoor trail wearing a motor-driven adjustable socket that they adjusted a small amount, approximately 0.3% socket volume, every 2 min using a mobile phone app. Limb fluid volume and sensed distance between the socket and a target in their elastomeric liner were monitored. A gradual socket enlargement phase was followed by a gradual socket reduction phase.

RESULTS

An incremental socket enlargement significantly increased limb fluid volume (p < 0.001) but not sensed distance (p = 0.063). An incremental socket reduction significantly decreased both limb fluid volume (p < 0.001) and sensed distance (p < 0.001).

CONCLUSION

Participants' residual limb fluid volume increases during ambulation compensated for incremental socket volume increases. For incremental socket volume decreases, residual limb fluid volume decreases did not compensate and the socket fit became tighter.

CLINICAL RELEVANCE

Results support the hypothesis that for people without co-morbidities, intermittent incremental socket volume enlargements are an effective accommodation strategy to increase limb fluid volume while maintaining socket fit. Intermittent incremental socket volume reductions decreased limb fluid volume but also made the socket fit tighter.

Is skin pressure a relevant factor for socket assessment in patients with lower limb amputation?

BACKGROUND

Prosthetic rehabilitation improves the overall quality of life of patients, despite discomfort and medical complications. No quantitative assessment of prosthesis-patient interaction is used in routine protocols and prosthesis quality still results from the manufacturer's know-how.

OBJECTIVE

Our objective is to investigate whether pressure can be a relevant factor for assessing socket adequacy.

METHODS

A total of 8 transtibial amputee volunteers took part in this experimental study. The protocol included static standing and 2 minutes walking tests while the stump-to-socket interface pressures were measured. Questionnaires on comfort and pain were also conducted.

RESULTS

During static standing test, maximum pressures were recorded in the proximal region of the leg, with a peak value reaching 121.1 ± 31.6 kPa. During dynamic tests, maximum pressures of 254.1 ± 61.2 kPa were recorded during the loading phase of the step. A significant correlation was found between the pain score and static maximum recorded pressure (r= 0.81).

CONCLUSIONS

The protocol proposed and evaluated in this study is a repeatable, easy-to-set quantified analysis of the patient to socket interaction while standing and walking. This approach is likely to improve feedback for prosthesis manufacturers and consequently the overall design of prostheses.

An Inductive Sensing System to Measure In-Socket Residual Limb Displacements for People Using Lower-Limb Prostheses

The objective of this research was to assess the performance of an embedded sensing system designed to measure the distance between a prosthetic socket wall and residual limb. Low-profile inductive sensors were laminated into prosthetic sockets and flexible ferromagnetic targets were created from elastomeric liners with embedded iron particles for four participants with transtibial amputation. Using insights from sensor performance testing, a novel calibration procedure was developed to quickly and accurately calibrate the multiple embedded sensors. The sensing system was evaluated through laboratory tests in which participants wore sock combinations with three distinct thicknesses and conducted a series of activities including standing, walking, and sitting. When a thicker sock was worn, the limb typically moved further away from the socket and peak-to-peak displacements decreased. However, sensors did not measure equivalent distances or displacements for a given sock combination, which provided information regarding the fit of the socket and how a sock change intervention influenced socket fit. Monitoring of limb⁻socket displacements may serve as a valuable tool for researchers and clinicians to quantitatively assess socket fit.

A systematic review of shock-attenuating componentry for lower limb amputees

BACKGROUND

Shock-attenuating pylons are commonly fitted to prostheses in order to compensate for the anatomical and biomechanical shock-absorbing features of the lower limb removed upon amputation. However, studies concerning their shock-attenuating capacity are highly variable and, to date, have not yet been reviewed, making them difficult to interpret and apply in clinical practice.

OBJECTIVES

To synthesise and appraise the available literature examining the effectiveness of shock-attenuating pylons in attenuating shock upon limb loading compared to rigid pylons among lower limb amputees.

STUDY DESIGN

Systematic review.

METHODS

A comprehensive search of seven databases was conducted using search terms concerning amputation level, shock-attenuating and rigid pylons as well as measures of shock attenuation. All studies yielded were screened against established inclusion and exclusion criteria before eligible articles were appraised using the Quality Assessment Standard for Crossover Studies adapted from the Cochrane handbook.

RESULTS

Nine articles were eligible for inclusion. While there was a trend among studies to indicate only a limited positive effect of shock-attenuating pylons in attenuating transient impact forces, limitations to the study designs, namely, in sampling, poor reporting of methodological details and heterogeneity of outcomes made conclusive interpretation of results difficult.

CONCLUSION

While the current body of literature does not reconcile with claims made by manufacturers of shock-attenuating pylons, it is insufficient to conclusively determine how effective shock-attenuating pylons are, in comparison with conventional rigid pylons, in attenuating transient impact forces among lower limb amputees. Higher quality research is required to better guide decisions regarding prescription of shock-attenuating componentry in clinical practice. Clinical relevance When delivered well, research can provide clinicians with objective and reliable data that can be applied in their practice to guide prescription of componentry. However, methodological limitations to research may compromise the reliability of findings, thereby producing potentially misleading outcomes. These limitations must be recognised and appreciated such that findings may be interpreted accurately and applied appropriately.

A finite element model to assess transtibial prosthetic sockets with elastomeric liners

People with transtibial amputation often experience skin breakdown due to the pressures and shear stresses that occur at the limb-socket interface. The purpose of this research was to create a transtibial finite element model (FEM) of a contemporary prosthesis that included complete socket geometry, two frictional interactions (limb-liner and liner-socket), and an elastomeric liner. Magnetic resonance imaging scans from three people with characteristic transtibial limb shapes (i.e., short-conical, long-conical, and cylindrical) were acquired and used to develop the models. Each model was evaluated with two loading profiles to identify locations of focused stresses during stance phase. The models identified five locations on the participants' residual limbs where peak stresses matched locations of mechanically induced skin issues they experienced in the 9 months prior to being scanned. The peak contact pressure across all simulations was 98 kPa and the maximum resultant shear stress was 50 kPa, showing reasonable agreement with interface stress measurements reported in the literature. Future research could take advantage of the developed FEM to assess the influence of changes in limb volume or liner material properties on interface stress distributions. Graphical abstract Residual limb finite element model. Left: model components. Right: interface pressures during stance phase.

Development of Standardized Material Testing Protocols for Prosthetic Liners

A set of protocols was created to characterize prosthetic liners across six clinically relevant material properties. Properties included compressive elasticity, shear elasticity, tensile elasticity, volumetric elasticity, coefficient of friction (CoF), and thermal conductivity. Eighteen prosthetic liners representing the diverse range of commercial products were evaluated to create test procedures that maximized repeatability, minimized error, and provided clinically meaningful results. Shear and tensile elasticity test designs were augmented with finite element analysis (FEA) to optimize specimen geometries. Results showed that because of the wide range of available liner products, the compressive elasticity and tensile elasticity tests required two test maxima; samples were tested until they met either a strain-based or a stress-based maximum, whichever was reached first. The shear and tensile elasticity tests required that no cyclic conditioning be conducted because of limited endurance of the mounting adhesive with some liner materials. The coefficient of friction test was based on dynamic coefficient of friction, as it proved to be a more reliable measurement than static coefficient of friction. The volumetric elasticity test required that air be released beneath samples in the test chamber before testing. The thermal conductivity test best reflected the clinical environment when thermal grease was omitted and when liner samples were placed under pressure consistent with load bearing conditions. The developed procedures provide a standardized approach for evaluating liner products in the prosthetics industry. Test results can be used to improve clinical selection of liners for individual patients and guide development of new liner products.

When to biomechanically examine a lower-limb amputee: A systematic review of accommodation times

BACKGROUND

Hundreds of investigations examining biomechanical outcomes of various prostheses have been completed, but one question remains unanswered: how much time should an amputee be given to accommodate to a new prosthesis prior to biomechanical testing?

OBJECTIVE

To examine the literature for accommodation time given during biomechanical investigations to determine whether consensus exists.

STUDY DESIGN

Systematic review.

METHODS

A systematic search was completed on 7 January 2016 using PubMed and Scopus.

RESULTS

The search resulted in 156 investigations. Twenty-eight studies did not provide an accommodation or were unclear (e.g. provided a "break in period"), 5 studies tested their participants more than once, 25 tested only once and on the same day participants received a new prosthesis (median (range): above-knee: 60 (10-300) min; below-knee: 18 (5-300) min), and 98 tested once and gave a minimum of 1 day for accommodation (hip: 77 (60-180) days; above-knee: 42 (1-540) days; below-knee: 21 (1-475) days).

CONCLUSION

The lack of research specifically examining accommodation and the high variability in this review's results indicates that it remains undecided how much accommodation is necessary. There is a need for longitudinal biomechanical investigations to determine how outcomes change as amputees accommodate to a new prosthesis. Clinical relevance The results of this review indicate that little research has been done regarding lower-limb amputees accommodating to a new prosthesis. Improper accommodation could lead to increased variability in results, results that are not reflective of long-term use, and could cause clinicians to make inappropriate decisions regarding a prosthesis.

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.

Amputee socks: Sock thickness changes with normal use

BACKGROUND

Prosthetic socks are expected to decrease in thickness and have reduced volume accommodation with normal use. It is unknown, however, to what degree they reduce in thickness over time.

OBJECTIVE

The goal of this study was to determine a correlation between the age of a prosthetic sock (defined as the out-of-package time) and the resulting change in thickness under standardized weight-bearing and non-weight-bearing conditions.

STUDY DESIGN

Experimental, mechanical assessment.

METHODS

Used prosthetic socks were donated by donors with transtibial amputation. Sock thickness was measured on a custom instrument under conditions representative of normal use. Stress-thickness response was compared to that of equivalent new socks to quantify the effects of use on sock performance.

RESULTS

Sock thickness changed non-linearly over time. On average, socks were 75% ± 17% of their initial thickness after 1 month, while socks older than 1 month were 72% ± 18% of their initial thickness. The elasticity of socks did not change with age.

CONCLUSION

The volume accommodation provided by used socks cannot be reliably predicted by ply or age. Direct measurement of total sock thickness may provide meaningful insight to quantify prosthetic users' socket fit and guide volume accommodation recommendations.

CLINICAL RELEVANCE

The mean difference in thickness between 3-ply and 5-ply used socks was equal to the standard deviation of each ply group (0.3mm). Therefore, it is possible that a 3-ply sock worn for as a little as 1 month could have a greater thickness than a 5-ply sock worn for a month.

Socket Interface Pressure and Amputee Reported Outcomes for Comfortable and Uncomfortable Conditions of Patellar Tendon Bearing Socket: A Pilot Study

The objectives of the current study were to compare intra-socket pressure differences between comfortable and uncomfortable socket conditions, and the usefulness of subject perception of satisfaction, activity limitations, and socket comfort in distinguishing between these two socket conditions. Five unilateral trans-tibial amputees took part in the study. They answered the Socket Comfort Score (SCS) and Trinity Amputation and Prosthetic Experience Scale (TAPES) questionnaires before the interface pressure (in standing and walking) was measured for the uncomfortable socket condition at five regions of the residual limb. Participants were then provided with a comfortable socket and wore it for two weeks. Participants who were satisfied with the socket fit after two weeks repeated the SCS and TAPES questionnaires and interface pressure measurements. The differences between the test results of the two conditions were not statistically significant, except for the interface pressure at the popliteal region during the early stance phase, TAPES socket fit subscale, and the SCS. Due to large variability of the data and the lack of statistical significance, no firm conclusion can be made on the possible relationship between the interface pressure values and the patient-reported outcomes of the two socket conditions. A larger sample size and longer acclimation period are required to locate significant differences.

Adaptive sports technology and biomechanics: prosthetics

With the technologic advances in medicine and an emphasis on maintaining physical fitness, the population of athletes with impairments is growing. It is incumbent upon health care practitioners to make every effort to inform these individuals of growing and diverse opportunities and to encourage safe exercise and athletic participation through counseling and education. Given the opportunities for participation in sports for persons with a limb deficiency, the demand for new, innovative prosthetic designs is challenging the clinical and technical expertise of the physician and prosthetist. When generating a prosthetic prescription, physicians and prosthetists should consider the needs and preferences of the athlete with limb deficiency, as well as the functional demands of the chosen sporting activity. The intent of this article is to provide information regarding the current advancements in the adaptive sports technology and biomechanics in the field of prosthetics, and to assist clinicians and their patients in facilitating participation in sporting activities.

Mechanical and structural characterization of tibial prosthetic interfaces before and after aging under simulated service conditions

Prosthesis interface is one of the most important components to promote individual׳s health and comfort, as it establishes direct contact with the skin and transfers loads generated during gait. The aim of this study was to mechanically characterize, three commercial interfaces (block copolymer, silicone gel and silicone elestomer), under static and dynamic conditions, before and after undergoing a process of chemical aging in synthetic sweat for periods up to 90 days. Static mechanical compression tests were performed on the materials, as well as fatigue tests to assess their static and dynamic mechanical behaviors, respectively. For the second, a sinusoidal load was applied with an appropriate range of deformation for each material. Several analytical techniques were also used to characterize the materials, namely Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), and morphology characterization by Scanning Electron Microscopy (SEM). All the tested materials have strong viscoelastic behavior, showing a linear response for small deformations, followed by a nonlinear behavior for higher deformation. The block copolymer and the silicone gel are affected by aging in synthetic sweat in a similar way, with a significant increase of their rigidity after 30 days, followed by a progressive reduction. The silicone elastomer displays a continuous increase of rigidity along the 90 days of storage, being the most sensitive to aging affects. It also exhibits the lowest stiffness value, being suitable for uses that require maximum comfort. All materials demonstrate chemical and structural stability under service simulated conditions.

Postural control in response to altered sensory conditions in persons with dysvascular and traumatic transtibial amputation

OBJECTIVE

To compare the postural control of persons with a dysvascular transtibial amputation and traumatic transtibial amputation with able-bodied adults with and without a dysvascular condition in altered sensory testing conditions.

DESIGN

Cross-sectional study.

SETTING

University balance clinic.

PARTICIPANTS

The study participants (N=35) included: participants with a dysvascular transtibial amputation (n=9), participants with a traumatic transtibial amputation (n=9), age-matched able-bodied adults without a dysvascular condition (n=9), and able-bodied adults with a dysvascular condition (n=8).

INTERVENTIONS

Six Sensory Organization Test (SOT) conditions, which included standing with eyes open (condition 1) and closed (condition 2) on a static force platform with visual surround; standing with eyes open on a static force platform with movable visual surround (condition 3); standing with eyes open (condition 4) and closed (condition 5) on a movable force platform with static visual surround; and standing with eyes open on a movable force platform with movable visual surround (condition 6).

MAIN OUTCOME MEASURES

Bilateral anteroposterior (AP) and mediolateral (ML) center of pressure variables, namely root mean square distance (RMSD) and mean velocity (mVel), for each of the 6 SOT conditions.

RESULTS

The dysvascular transtibial amputation group demonstrated a higher AP RMSD (P≤.04) on the sound side than did the able-bodied adults without a dysvascular condition and the able-bodied adults with a dysvascular condition in SOT conditions 1 and 2, respectively. Both the dysvascular transtibial amputation group and the traumatic transtibial amputation group demonstrated a higher AP RMSD (P≤.002) than the able-bodied adults without a dysvascular condition in SOT conditions 3 and 4. The dysvascular transtibial amputation group showed higher AP mVel (P≤.002) on the sound side for SOT conditions 2 and 3, whereas both amputation groups showed higher AP mVel for SOT conditions 1 and 4 than the able-bodied adults with and without a dysvascular condition.

CONCLUSIONS

Postural control of the dysvascular transtibial amputation group was not different than the traumatic transtibial amputation group in challenging sensory conditions. However, when compared with the groups of able-bodied adults with and without a dysvascular condition, postural strategies distinct with amputation etiology were observed.

Amputee socks: thickness of multiple socks

BACKGROUND AND AIM

It is unclear how total sock ply and thickness are related when more than one sock is worn. The objectives were to determine whether the thickness of one multi-ply amputee sock of ply P was the same as the thickness of a stack of reduced-ply socks of total ply P, and whether the thickness of N single socks stacked one on top of the other was equal to the sum (1 to N) of the single sock thicknesses.

TECHNIQUE

Using a custom instrument, compressive stresses were applied while sock thickness was measured.

DISCUSSION

The thickness of one multi-ply sock of ply P was typically less than the thickness of a stack of reduced-ply socks of total ply P. The thickness of N single socks stacked one on top of the other was approximately equal to the sum (1 to N) of the single sock thicknesses.

CLINICAL RELEVANCE

Our findings suggest three 1-ply socks to be 20% greater in thickness than one 3-ply sock, and one 3-ply + two 1-ply socks to be 30% greater in thickness than one 5-ply sock.

Comparative study between Dermo, Pelite, and Seal-In X5 liners: effect on patient's satisfaction and perceived problems

Purpose. This study aimed to compare the effect of satisfaction and perceived problems between Pelite, Dermo with shuttle lock, and Seal-In X5 liners on the transtibial amputees. Material and Methods. A total of thirty transtibial amputees (17 male, 13 female) volunteered to take part in this research. Two prostheses were fabricated for each participant. Prosthetic Evaluation Questionnaire (PEQ) was filled in by the participants with the three liners. Results. The statistics highlight that Dermo liner showed significantly higher score (P = 0.05) in walking, walking on uneven surfaces, stairs walking, fitting, donning/doffing, sitting, suspension, and overall satisfaction with Dermo liner compared with Seal-In X5 and Pelite liners. Overall satisfaction was 34% higher with Dermo liner than Seal-In X5 liner and 28% higher than Pelite liner. Participants reported less problems with Dermo liner and significant differences (P < 0.05) were recorded between the three liners in sweating, skin irritation, frustration, and pain compared with Seal-In X5 and Pelite liners. Conclusion. Participants experienced high level of satisfaction and practiced fewer problems with Dermo liner. These results showed that there is good indication to believe that Dermo liner might be a good choice for transtibial users and might help the clinicians and prosthetic practitioners in selection criteria of prosthetic liners.

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.

Amputee socks: how does sock ply relate to sock thickness?

BACKGROUND

The term 'sock ply' may be a source of confusion in prosthetics practice because there may not be a consistent relationship between sock ply and sock thickness.

OBJECTIVES

The purpose of this study was to characterize how sock ply related to sock thickness for different sock materials commonly used in limb prosthetics. We also evaluated how sock thickness changed under loading conditions experienced while wearing a lower limb prosthesis compared with unstressed conditions.

STUDY DESIGN

Experimental. Mechanical assessment.

METHODS

Seven sock materials of varying ply and sheaths were tested using a custom instrument. Sock thickness under eight different compressive stress conditions and two different biaxial in-plane tensile strain conditions were measured.

RESULTS

For socks woven from a single material, thickness under walking stance phase conditions averaged 0.7, 1.2 and 1.5 mm for 1, 3 and 5-ply, respectively. For socks woven from several materials, the corresponding results were 0.4, 0.7 and 0.8 mm, respectively. Sock ply did not sum, e.g. a 3-ply sock was not three times the thickness of a 1-ply sock.

CONCLUSIONS

Sock thickness and compressive stiffness are strongly dependent upon sock material, interface pressure, and in-plane biaxial strain.

Remote monitoring of lower-limb prosthetic socket fit using wireless technologies

Accurate fitting of a lower-limb prosthetic socket is the most important factor affecting amputee satisfaction and rehabilitation. The technology is now available to allow real-time monitoring of in-service pressure distribution of prosthetic limbs. This paper proposes a remote interfacial pressure monitoring system necessary for the assessment of fit. The suitability of a wireless ZigBee network due to its relevant technical specification is investigated. The system enables remote monitoring of a prosthetic socket and its fit under different operating conditions thereby improving design, efficiency and effectiveness. The data can be used by prosthetists and may also be recorded for future training or for patient progress monitoring. This can minimize the number of iterations by getting it right first time, thereby minimizing the number of replacement prostheses.

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

OBJECTIVE

It has been recognised in a review of the developments of lower-limb prosthetic socket fitting processes that the future demands new tools to aid in socket fitting. This paper presents the results of research to design and clinically test an artificial intelligence approach, specifically inverse problem analysis, for the determination of the pressures at the limb/prosthetic socket interface during stance and ambulation.

METHODS

Inverse problem analysis is based on accurately calculating the external loads or boundary conditions that can generate a known amount of strain, stresses or displacements at pre-determined locations on a structure. In this study a backpropagation artificial neural network (ANN) is designed and validated to predict the interfacial pressures at the residual limb/socket interface from strain data collected from the socket surface. The subject of this investigation was a 45-year-old male unilateral trans-tibial (below-knee) traumatic amputee who had been using a prosthesis for 22 years.

RESULTS

When comparing the ANN predicted interfacial pressure on 16 patches within the socket with actual pressures applied to the socket there is shown to be 8.7% difference, validating the methodology. Investigation of varying axial load through the subject's prosthesis, alignment of the subject's prosthesis, and pressure at the limb/socket interface during walking demonstrates that the validated ANN is able to give an accurate full-field study of the static and dynamic interfacial pressure distribution.

CONCLUSIONS

To conclude, a methodology has been developed that enables a prosthetist to quantitatively analyse the distribution of pressures within the prosthetic socket in a clinical environment. This will aid in facilitating the "right first time" approach to socket fitting which will benefit both the patient in terms of comfort and the prosthetist, by reducing the time and associated costs of providing a high level of socket fit.

Biomechanics of Pressure Ulcer in Body Tissues Interacting with External Forces during Locomotion

Forces acting on the body via various external surfaces during locomotion are needed to support the body under gravity, control posture, and overcome inertia. Examples include the forces acting on the body via the seating surfaces during wheelchair propulsion, the forces acting on the plantar foot tissues via the insole during gait, and the forces acting on the residual-limb tissues via the prosthetic socket during various movement activities. Excessive exposure to unwarranted stresses at the body-support interfaces could lead to tissue breakdowns commonly known as pressure ulcers, often presented as deep-tissue injuries around bony prominences or as surface damage on the skin. In this article, we review the literature that describes how the involved tissues respond to epidermal loading, taking into account both experimental and computational findings from in vivo and in vitro studies. In particular, we discuss related literature about internal tissue deformation and stresses, microcirculatory responses, and histological, cellular, and molecular observations.

A mechanical model of the human ankle in the transverse plane during straight walking: implications for prosthetic design

In order to protect sensitive residual limb soft tissues, lower limb prostheses need to control torsional loads during gait. To assist with the design of a torsional prosthesis, this paper used simple mechanical elements to model the behavior of the human ankle in the transverse plane during straight walking. Motion capture data were collected from ten able-bodied subjects walking straight ahead at self-selected walking speeds. Gait cycle data were separated into four distinct states, and passive torsional springs and dampers were chosen to model the behavior in each state. Since prosthetic design is facilitated by simplicity, it was desirable to investigate if elastic behavior could account for the physiological ankle moment and include viscous behavior only if necessary to account for the inadequacies of the spring model. In all four states, a springlike behavior was able to account for most of the physiological ankle moments, rendering the use of a damper unnecessary. In State 1, a quadratic torsional spring was chosen to model the behavior, while linear torsional springs were chosen for States 2-4. A prosthetic system that actively changes stiffness could be able to replicate the physiological behavior of the human ankle in the transverse plane. The results of this study will contribute to the mechanical design and control of a biomimetic torsional prosthesis for lower limb amputees.

Development and analysis of modular uniaxial leg adapter

The adapters of modular prostheses are the structural components mostly likely to fail during the use of prostheses because of the high forces and moments occurring during the human gait. In this study, structural performance of a modular uniaxial leg adapter during gait is analysed utilizing computer software. By analysing the results, the relevant product was redesigned in order to prevent possible failures. Subsequently, the developed modular uniaxial leg adapter was tested in accordance with ISO 10328 in order to ensure the safety of the design. Further, the test results are compared with a finite element analysis to evaluate the performance of the numerical analysis.

Effects of fluid insert volume changes on socket pressures and shear stresses: case studies from two trans-tibial amputee subjects

Fluid inserts potentially help to overcome prosthetic fit problems resulting from stump volume change. The purpose of this investigation was to add fluid to fluid inserts positioned on the inner socket walls of trans-tibial prostheses and to assess their influence on socket stresses. Pressures and shear stresses were measured at 13 sites on the sockets of two trans-tibial amputee subjects while they ambulated at their self-selected walking speeds. Stresses at the transducer sites generally increased with greater fluid addition and, interestingly, both subjects found relatively high fluid insert volumes most comfortable. The magnitudes of stress change were larger than those resulting from alignment, cadence, and componentry changes as reported in the literature. Possible explanations for why subjects found settings that induced higher measured socket stresses more comfortable than those that induced lower measured stresses include: A reduced shear: pressure ratio; the short duration of the study; and reduced stresses at sites not monitored with transducers.

Real-time patient-specific finite element analysis of internal stresses in the soft tissues of a residual limb: a new tool for prosthetic fitting

Fitting of a prosthetic socket is a critical stage in the process of rehabilitation of a trans-tibial amputation (TTA) patient, since a misfit may cause pressure ulcers or a deep tissue injury (DTI: necrosis of the muscle flap under intact skin) in the residual limb. To date, prosthetic fitting typically depends on the subjective skills of the prosthetist, and is not supported by biomedical instrumentation that allows evaluation of the quality of fitting. Specifically, no technology is presently available to provide real-time continuous information on the internal distribution of mechanical stresses in the residual limb during fitting of the prosthesis, or while using it and this severely limits patient evaluations. In this study, a simplified yet clinically oriented patient-specific finite element (FE) model of the residual limb was developed for real-time stress analysis. For this purpose we employed a custom-made FE code that continuously calculates internal stresses in the residual limb, based on boundary conditions acquired in real-time from force sensors, located at the limb-prosthesis interface. Validation of the modeling system was accomplished by means of a synthetic phantom of the residual limb, which allowed simultaneous measurements of interface pressures and internal stresses. Human studies were conducted subsequently in five TTA patients. The dimensions of bones and soft tissues were obtained from X-rays of the residual limb of each patient. An indentation test was performed in order to obtain the effective elastic modulus of the soft tissues of the residual limb. Seven force sensors were placed between the residual limb and the prosthetic liner, and subjects walked on a treadmill during analysis. Generally, stresses under the shinbones were approximately threefold higher than stresses at the soft tissues behind the bones. Usage of a thigh corset decreased the stresses in the residual limb during gait by approximately 80%. Also, the stresses calculated during the trial of a subject who complained about pain and discomfort were the highest, confirming that his socket was not adequately fitted. We conclude that real-time patient-specific FE analysis of internal stresses in deep soft tissues of the residual limb in TTA patients is feasible. This method is promising for improving the fitting of prostheses in the clinical setting and for protecting the residual limb from pressure ulcers and DTI.

An Experimental and Theoretical Framework for Manufacturing Prosthetic Sockets for Transtibial Amputees

Selective laser sintering (SLS) is a powerful manufacturing technology that does not require part-specific tooling or significant human intervention and provides the ability to easily generate parts with complex geometric designs. The present work focuses on developing a manufacturing framework using this technology to produce subject-specific transtibial amputee prosthetic sockets made of Duraform PA, which is a nylon-based material. The framework includes establishing an overall socket design (using the patellar-tendon bearing approach), performing a structural analysis using the finite element method (FEM) to ensure structural reliability during patient use, and validating the results by comparing the model output with experimental data. The validation included quantifying the failure conditions for the socket through a series of bending moment and compression tests. In the case study performed, the FEM results were within 3% of the experimental failure loads for the socket and were considered satisfactory.

Changes in interface pressures and shear stresses over time on trans-tibial amputee subjects ambulating with prosthetic limbs: comparison of diurnal and six-month differences

For trans-tibial amputees maintenance over time of a quality fit of the prosthesis to the residual limb is an important clinical challenge. The purpose of this research was to compare diurnal and long-term (5 weeks to 6 months) interface stress changes as well as variance in the change in cross-sectional area down the length of the residual limb. If long-term changes were simply accentuated diurnal fluctuations then this result would suggest similar treatment methods should be used for both conditions. Interface pressures and shear stresses at 13 sites and residual limb shape were measured on eight trans-tibial amputee subjects using patellar-tendon-bearing prostheses. Data were collected at diurnal intervals (within the same day at least 5 h apart) as well as at long-term intervals (5, 10, 15, 20, and 25 weeks apart). Absolute diurnal interface stress changes were not significantly different from those at 5-weeks intervals but were significantly smaller than those at 15, 20, and 25-weeks intervals. Mean interface stress changes increased significantly (p<0.05) for increased session-to-session intervals. Variance of the change in cross-sectional area down the length of the residual limb was significantly smaller for diurnal intervals than for 6-months intervals, indicating that long-term changes were more localized than diurnal changes. These results indicate that long-term changes are not simply accentuated diurnal fluctuations, suggesting that different treatment methods should be used to treat each condition.

Static and dynamic pressure profiles of a patellar-tendon-bearing (PTB) socket

The purpose of this study was to evaluate the pressure distribution at the stump/socket interface in amputees wearing the patellar-tendon-bearing socket. A specially built strain gauged type pressure transducer was used for measuring this pressure distribution in four unilateral transtibial amputees. Pressure and gait parameters were measured simultaneously while they were standing and walking. Pressure profiles were compiled at 10, 25 and 50 per cent of gait cycle and compared with the pressure profiles predicted by Radcliffe in 1961. The subject's anterior-posterior pressure profiles were different from each other. However, at toe-off, each subject exhibited an increase in pressure at the patellar tendon. Their medial-lateral pressure profiles were similar: exhibiting high pressure at the medial proximal and lateral distal regions except for one subject who exhibited high pressure at the lateral proximal region instead. The subjects' pressure profiles did not resemble Radcliffe's anticipated pressure profiles. This was because ground reaction force was not the only factor affecting the resulting pressure profiles.

Interface pressure and shear stress changes with amputee weight loss: case studies from two trans-tibial amputee subjects

Interface pressures and shear stresses were measured at monthly intervals on two trans-tibial amputee subjects who lost more than 12% of their body weight over the course of the study. For one subject interface pressures and shear stresses during the weight-acceptance phase of gait decreased over the study interval at all 13 sites monitored, while the other subject experienced increased pressures distally but decreased pressures proximally. Subjects' stumps appeared to atrophy over the study interval, increasing distal end and patellar tendon loading, but not increasing interface shear stresses at other locations. Adding socks at the end of the study did not return interface pressures to first session values at all sites. It is expected that local stump shape changes occurred, causing a non-uniform change in interface stress patterns.

Gait analysis in prosthetics: opinions, ideas and conclusions

A review was performed of the literature of the last eleven years (1990-2000) with the topic: "clinical use of instrumented gait analysis in patients wearing a prosthesis of the lower limb". To this end a literature search was performed in Embase, Medline and Recal. Forty-five (45) articles were identified for study from which 34 were reviewed. The reviews were divided into five subtopics: 1) adaptive strategies in gait (12 studies); 2) the influence of different parts of the prosthesis on gait (12 studies); 3) pressure measurements in the socket in gait studies (4 studies); 4) the influence of the mass of the prostheses on gait (5 studies); 5) energy considerations in gait (2 studies). A considerable part of the studies concerned the adaptive strategies of the amputee in walking and running and the evaluation of different prosthetic feet. All aspects and outcomes were reviewed concerning the clinical relevance.