Assessing Phase-Change Materials as Effective Long-Term Biosensors in Limb Prosthetics.

Monitoring and controlling the microclimate at the skin-socket interface of limb prostheses is an important, yet unresolved, clinical problem. Phase-change materials (PCMs) represent a promising biosensor technology that holds the potential to both detect and alter (i.e., stabilize) changes in the temperature of a hybrid biological/mechanical system, such as a prosthesis. The biologically inspired sensor capabilities of PCMs can enhance the internal socket conditions and offer improved comfort and suspension while minimizing skin injuries for prosthesis users. This study investigated how prosthetic liners equipped with PCM biosensors affected the long-term outcomes for prosthesis users. In this double-blinded longitudinal crossover study, a cohort of transtibial prosthesis users wore regular conventional liners for six months and PCM liners for another six months. Prosthesis utilization, physical performance, and gait symmetry were studied using Modus StepWatch, the 2-minute walk test, and the TekScan F-Scan gait test, respectively. Measured parameters from these various tests, acquired at multiple timepoints during the study, were compared pairwise between the two liners per individual. While the obtained quantitative data trends, such as the gait symmetry, favored the PCM liners, no statistically significant differences were found between the PCM and conventional gel liners in any of the study parameters.

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

BACKGROUND: Among the challenges of living with lower limb loss is the increased risk of long-term health problems that can be either attributed directly to the amputation surgery and/or prosthetic rehabilitation or indirectly to a disability-induced sedentary lifestyle. These problems are exacerbated by poorly fit prosthetic sockets. There is a knowledge gap regarding how the socket design affects in-socket mechanics and how in-socket mechanics affect patient-reported comfort and function. The objectives of this study are (1) to gain a better understanding of how in-socket mechanics of the residual limb in transfemoral amputees are related to patient-reported comfort and function, (2) to identify clinical tests that can streamline the socket design process, and (3) to evaluate the efficacy and cost of a novel, quantitatively informed socket optimization process. METHODS: Users of transfemoral prostheses will be asked to walk on a treadmill wearing their current socket plus 8 different check sockets with designed changes in different structural measurements that are likely to induce changes in residual limb motion, skin strain, and pressure distribution within the socket. Dynamic biplane radiography and pressure sensors will be used to measure in-socket residual limb mechanics. Patient-reported outcomes will also be collected after wearing each socket. The effects of in-socket mechanics on both physical function and patient-reported outcomes (aim 1) will be assessed using a generalized linear model. Partial correlation analysis will be used to examine the association between research-grade measurements and readily available clinical measurements (aim 2). In order to compare the new quantitative design method to the standard of care, patient-reported outcomes and cost will be compared between the two methods, utilizing the Wilcoxon-Mann-Whitney non-parametric test (aim 3). DISCUSSION: Knowledge on how prosthetic socket modifications affect residual bone and skin biomechanics itself can be applied to devise future socket designs, and the methodology can be used to investigate and improve such designs, past and present. Apart from saving time and costs, this may result in better prosthetic socket fit for a large patient population, thus increasing their mobility, participation, and overall health-related quality of life. TRIAL REGISTRATION: ClinicalTrials.gov NCT05041998 . Date of registration: Sept 13, 2021.

Does socket liner material affect clinical outcomes in lower limb prosthesis users? Insights from a randomized control trial.

Among the noted disadvantages of prosthesis suspension by flexible liner is the increased rate of perspiration within the socket, which has the potential to cause discomfort, suspension issues, and tissue damage. In recent years, phase change material technology has been adopted for the use in prosthesis liners. These promise to improve temperature control and, consequently, reduce sweating. Previous work has demonstrated that this approach is effective in slowing the temperature increase at the limb-socket interface, but it was not clear how this would translate to clinical outcomes. This study had the aim to compare conventional and phase change material liners regarding prosthesis utilization, physical performance, and patient-reported outcome measures. A randomized double-blind cross-over study design with 6-month intervention periods was used. Of the 42 enrolled participants, only 50% completed the protocol. The high attrition was in large part because of the COVID-19 pandemic that started disrupting daily life and thereby the data collection midway through the study period. The findings indicate that the temperature control liners were, by trend, associated with better prosthesis utilization. The found effects did not reach the level of statistical significance, which is likely a result of the unduly reduced sample size.

Residual limb shear strain during gait is correlated with patient reported outcomes for persons with transfemoral amputation.

The purpose of this study was to measure residual limb skin strain and strain rate within the socket during gait in individuals with a transfemoral amputation and to determine if skin strain during gait is related to patient-reported comfort and function. It was hypothesized that greater skin strain and skin strain rate would correlate to worse patient-reported outcomes. It was also hypothesized that skin strain would progressively increase from the distal to the proximal end of the residuum and maximum strain would occur shortly after heel strike. Dynamic biplane radiography (DBR), combined with conventional motion capture, was used to measure skin deformation within the socket during treadmill walking for 10 persons with unilateral transfemoral amputation. The questionnaire for persons with a transfemoral amputation (Q-TFA) was administered to assess prosthetic use, mobility, health problems, and global health. Q-TFA Prosthetic Use score and Problem score were negatively correlated with the peak shear strains in the proximal and distal regions of the residuum, respectively. Maximum shear strain increased progressively from proximal to distal regions of the residual limb. Within-subject variability in shear strain waveforms during gait was 0.7% or less, but between-subject variability was 3.3% to 5.0% shear. This study demonstrates that skin shear within the socket of persons with transfemoral amputation can be measured during gait using DBR and the results suggest that greater skin shear in the proximal region of the socket is related to decreased prosthetic use.

Motion of the residual femur within the socket during gait is associated with patient-reported problems in transfemoral amputees.

The purpose of this study was to provide a quantitative description of residual femur motion within the socket during gait and to explore the relationship between residual femur motion and patient-reported comfort and function. It was hypothesized that increased residual bone movement would correlate to worse patient-reported comfort and function. The secondary goals were to assess within-subject step-to-step variability and between-subject variability in residual femur motion within the socket during gait. Dynamic biplane radiography, combined with conventional motion capture, was used to measure residual femur motion within the socket during treadmill walking for 10 unilateral transfemoral amputees. The questionnaire for persons with a transfemoral amputation (Q-TFA) was administered to assess prosthetic use, mobility, health problems, and global health. Increased femur pistoning (proximal-distal translation relative to the socket) correlated with worsening Q-TFA problem and global scores (ρ = 0.741, p = 0.04 and ρ = -0.783, p = 0.02, respectively). Average residual femur rotation ROMs were 7.3°±3.7°, 10.8°±4.4°, and 7.7°±4.8° for anterior tilt, internal-external rotation, and varus-valgus, respectively. Average residual femur translation ROMs were 8.6 mm ± 3.0 mm, 28.4 mm ± 13.9 mm, and 20.4 mm ± 7.2 mm for medial-lateral, pistoning, and anterior-posterior directions, respectively. Within-subject rotational and translational variability during gait averaged 2.8° and 2.0 mm or less, whereas the between-subject variability was up to 9.4° and 18.6 mm, which demonstrates residual femur motion relative to the socket is repeatable within subjects, but inconsistent across subjects during gait. The results suggest residual bone motion within the socket is a potential mechanism behind patient-reported problems and suggests a target for intervention aimed at improving transfemoral amputee quality of life.

Effect of temperature-control liner materials on long-term outcomes of lower limb prosthesis use: a randomized controlled trial protocol.

BACKGROUND: In people living with limb loss, addressing the resulting functional deficit with prostheses increases the risk for secondary conditions such as pressure sores, impaired blood perfusion, and injuries from accidental falls. Any of those occurrences can render the prosthesis temporarily useless, making it challenging for users to engage in many activities of daily life, including work, exercise, and social participation. Many of the described issues originate at the interface between residual limb and prosthetic socket, where the objectives of sufficient weight distribution and suspension are conflicting with the necessity to facilitate heat exchange and limit contact pressure and friction. Recently, prosthesis liners that contain phase-change material have become commercially available, holding the promise that the micro climate at the interface between the residual limb skin and the prosthetic socket can be regulated to reduce the users' tendency to sweat. Preliminary studies on these liners indicate that the socket temperatures inside the socket stayed lower and rose slower than in conventional liners. However, the clinical relevance of those findings remains unclear. The purpose of this study is to investigate whether longer (6+ months) periods of use of phase-change material based temperature-control liners have clinically meaningful effects. METHODS: The protocol is a double-blind longitudinal cross-over research design. A sample of trans-tibial prosthesis users are wearing their regular gel or silicone liners for six months and phase-change material liners for another six months in a randomized sequence. Their prostheses is equipped with activity monitors to detect days when they could not wear their prosthesis. In six-week intervals, individuals' activity, physical performance, and overall prosthesis assessment is recorded using standardized methods. DISCUSSION: Expected results will inform prescription and reimbursement practice of phase-change material-based prosthesis liners and will help improve and economize prosthetic fitting for people with limb loss. The design and duration of the protocol, including randomization, blinding, and within-subject comparison, will generate scientific evidence of a comparably high level. Inclusion of a comparably large sample and different climates, e.g. across all four seasons, will make findings applicable to a large number of prosthesis users. TRIAL REGISTRATION: Clinicaltrials.gov, NCT03428815. Registered on 12 February 2018.

Evaluation of Gait Variable Change over Time as Transtibial Amputees Adapt to a New Prosthesis Foot.

A variety of prescribed accommodation periods have been used in published prosthesis intervention studies that have examined biomechanical outcomes. Few investigators included repeated measurements in their study design, leaving questions as to how measured outcomes change as amputees acclimate to a new prosthesis. This paper is the product of our investigation as to whether measured gait variables were affected by the duration of accommodation period, and to assess the relationship between measured outcomes and the subjective perception of the participants. A sample of transtibial amputees were recruited for this study. Gait data was collected by wearable sensor repeatedly, starting immediately after fitting the interventional foot and extending over a subsequent four days. Participants indicated their perceived accommodation quality on a visual analog scale (VAS). A total of twelve commonly used spatiotemporal gait parameters were analyzed. Friedman tests were used to determine overall differences across time points in both early (one hour) and late (day two through five) accommodation phases, for each gait variable. Statistically significant changes across the early phase were found for variables gait speed χ 2(2)=8.000, p=0.018, cadence χ 2(2)=7.185, p=0.028, and double support time on the sound side χ 2(2)=8.615, p=0.013. Across days two through five, no gait variable significantly changed. VAS scores correlated strongly with step count (r=1.000, p<0.001) and cadence (r=0.857, p=0.014). Longer accommodation periods resulted in less deviations of gait variables for the clinical assessment in the process of prosthetic rehabilitation. Trying out prosthetic interventions for less than one hour has yielded unreliable outcomes.

Feasibility of a mobile feedback system for gait retraining in people with lower limb loss-A technical note.

Gait retraining in people with musculoskeletal and/or neurological impairments requires sustained dedicated efforts by the patient and the rehabilitation therapist. Various technical approaches have been proposed and utilized to improve the effectiveness of training interventions. Among the most promising approaches is the provision of real-time feedback information to the patient, which has been used with success on treadmill-based interventions in the past. We are describing a mobile visual feedback system that is intended to work in the user's everyday-life environment. The data are captured by a small mobile load cell, processed in a wearable computer, and displayed to the user via smart-glasses. Preliminary testing of the initially selected feedback variable stance/step ratio (i.e., the duration of a step's stance phase in relation to the overall step's duration) confirmed that data quality is sufficient for purposes of generating feedback information and that the chosen variable is responsive to changes in gait symmetry. The presented work may inform future studies and developments on the topic of mobile visual feedback for gait rehabilitation.

Comparison of lower limb segment forces during running on artificial turf and natural grass.

INTRODUCTION: Artificial turf, soon after being introduced in the 1980s, became associated with an increased injury incidence in football players. While more recent generations of artificial turf have mitigated the problem, perception of the material is still widely negative. So, the decision to play the 2015 Fe'de'ration Internationale de Football Association Women s World Cup in Canada on artificial turf was met with vocal criticism by many players. One common approach is to assess injury incidence to quantify risk differences in playing surfaces. This, however, does not account for possible confounding variables or chronic injuries. Direct measurement of ground reaction forces is difficult because conventional multicamera-based motion capture and force plate equipment are limited in its use outside of dedicated laboratories. METHODS: We describe a method of generating realistic force data by using miniature load cells that are installed directly into the weight-bearing structure of the body. RESULTS: Pilot data show a significant (p<0.01) difference in peak forces on artificial turf (272% of body weight) and natural grass (229% of body weight). DISCUSSION: Invasive surgical procedures were avoided by installing the load cell into the prosthesis of an athlete with lower limb loss. As modern prosthetic devices allow a close approximation of able-bodied kinematics and kinetics, such prosthesis-based data are transferable to a general population.

A support vector machine approach to detect trans-tibial prosthetic misalignment using 3-Dimensional ground reaction force features: A proof of concept.

BACKGROUND: Prosthetists conventionally evaluate alignment based on visual interpretation of patients' gait, which is convenient, but largely subjective and depends on prosthetists' experience. OBJECTIVE: In this paper, we explore the feasibility of using a support vector machine (SVM) approach to automatically detect misalignment of trans-tibial prostheses through ground reaction force (GRF). METHODS: Alternate classification algorithms with varying kernels and feature sets were compared to assess the suitability for detection of a representative misalignment (six degrees of ankle plantar flexion) from normal alignment. A classical feature selection algorithm, Fisher Score, was further introduced to identify valuable features and reduce the dimension of feature sets. RESULTS: The SVMs achieved a detection accuracy of 96.67% at best within the same subject and 88.89%, respectively, for inter-subject. Combined horizontal and vertical components of GRF features provided the maximum detection accuracies. Propulsion peak force was identified as key variable of gait for misalignment prediction. CONCLUSIONS: As a proof of concept, the results demonstrate potential in applying this approach to detect prosthetic misalignment based on gait patterns, and is a step towards future developments of tools for early prevention of misalignment in clinical.

Self-efficacy in Prosthetics & Orthotics students who did and did not participate in short term study abroad programs - preliminary results.

It is conventional knowledge that travel is educational and that a study stay in a foreign country contributes to a student's personality formation and well-roundedness. The benefit of such experiences on attitudes that shape professional aptitude and career success may, however, be debated. It could be argued that exposure to experiences that are irrelevant to a student's chosen profession may have no sizeable impact - thus not justifying the invested time and money - or, in an extreme case, may even be detrimental to career success if the wrong conclusions are drawn. Examples for such occurrences may include the adoption of inappropriate belief systems, educational priorities, or work habits. In this study, it was investigated how a short-term study stay abroad was reflected in the self-efficacy of students and graduates of a professional Master of Science program. A cohort of U.S. American students of Prosthetics and Orthotics who had participated in non-compulsory study excursions to Germany and a comparable cohort of their peers who had not participated in such trips were asked to state their confidence in mastering specific hypothetical situations of daily work life. About one half of the subjects of each group had already graduated and were in residence at the time of the survey, whereas the remaining half was still in their first year of the study program. Answers were compared using descriptive statistics and qualitative analysis to investigate main and interaction effects of professional experience and short-term stay abroad. The results seem to support the hypothesis that the experience was beneficial, making the inclusion of respective course offerings recommendable.

Quantifying accommodation to prosthesis interventions in persons with lower limb loss.

Determining the appropriate amount of accommodation time is an important component of research protocol design in the field of limb prosthetics. Insufficiently short or excessively long accommodation periods may limit the external validity of findings and/or the economic efficiency and ethical innocuousness of a study. However, issuing general recommendations is difficult, as individual accommodation periods are affected by subject characteristics, the nature of the intervention, and possibly a number of environmental factors. We are discussing an approach to determine individual accommodation times based on the assumption that the process of becoming accustomed to a prosthetic intervention follows a similar exponential "learning curve" as many other learning processes that have been previously investigated. Initial data collected with a small subject sample gives some indication that gait cycle symmetry changes along the hypothesized curve trajectory. If those preliminary results can be confirmed it may be possible to extrapolate a subject's eventual level of accommodation based on a small data set that is easily collected during the first twenty minutes after introducing a prosthetic intervention.

Effect of observation on lower limb prosthesis gait biomechanics: Preliminary results.

BACKGROUND: The Hawthorne effect, a subcategory of reactivity, causes human behavior to change when under observation. Such an effect may apply to gait variation of persons with prosthetics or orthotics devices. OBJECTIVES: This study investigated whether the presence of observers directly affects the gait pattern of users of lower limb prostheses. STUDY DESIGN: Within-subject intervention study. METHODS: Primary outcome measures were gait parameters of initial double support time and upper body lateral tilt angle, which were collected with a mobile sensor attached to the subjects' back. To make subjects feel unwatched, a certain amount of deception was necessary, and two different conditions were created and statistically compared against each other: one in which the subjects were initially unaware of the attention of observers and another one in which the same subjects were aware of a group of observers. RESULTS: Data from two subjects using trans-femoral prosthesis are reported. Findings included a change in step initial double support percentage by up to 14.2% (p = 0.019). Considerable changes were also noted in secondary outcome measures including speed, stride length, and stride symmetry. CONCLUSIONS: A reactivity effect of observation exists in prosthetics gait analysis. More comprehensive studies may be motivated by these preliminary findings. CLINICAL RELEVANCE: Results of this study suggest that users of lower limb prostheses walk differently when their gait is being assessed (e.g. in the prosthetist's office) than in situations without observers. This may in part explain the clinical experience that modifications of prosthetic fit or alignment provide only short-term betterment.

Effects of physical exertion on trans-tibial prosthesis users' ability to accommodate alignment perturbations.

BACKGROUND: It has long been reported that a range of prosthesis alignments is acceptable in trans-tibial prosthetics. This range was shown to be smaller when walking on uneven surfaces. It has also been argued that findings on gait with prostheses that were obtained under laboratory conditions are limited in their applicability to real-life environments. OBJECTIVES: This study investigated the hypothesis that efforts to compensate for suboptimal alignments by active users of trans-tibial prostheses become less effective when levels of physical exertion increase. STUDY DESIGN: A 2 × 2 repeated-measures analysis of variance was conducted to compare the effects of physical exertion and subtle alignment perturbations on gait with trans-tibial prostheses. METHODS: The gait of eight subjects with trans-tibial amputation was analyzed when walking with two different prosthesis alignments and two different physical exertion levels. The main and interaction effects were statistically evaluated. RESULTS: Bilateral step length symmetry and measures of step variability within the same leg were found to be affected by the intervention. There was no significant effect on index variables that combined kinematic or kinetic measures. CONCLUSION: Findings showed that persons with trans-tibial prostheses responded heterogeneously to the interventions. For most variables, the research hypothesis could not be confirmed. CLINICAL RELEVANCE: Findings support the practice of allotting several sessions to the alignment of trans-tibial prostheses, as users' gait responds differently to perturbations when external factors (e.g. exertion) change. Furthermore, the found inhomogeneity in the population of persons with trans-tibial amputation supports the use of technical gait assessment methods in clinical practice.

Criterion and construct validity of prosthesis-integrated measurement of joint moment data in persons with transtibial amputation.

Prosthesis-integrated sensors are appealing for use in clinical settings where gait analysis equipment is unavailable, but accurate knowledge of patients' performance is desired. Data obtained from load cells (inferring joint moments) may aid clinicians in the prescription, alignment, and gait rehabilitation of persons with limb loss. The purpose of this study was to assess the accuracy of prosthesis-integrated load cells for routine use in clinical practice. Level ground walking of persons with transtibial amputation was concurrently measured with a commercially available prosthesis-integrated load cell, a 10-camera motion analysis system, and piezoelectric force plates. Ankle and knee flexion/extension moments were derived and measurement methods were compared via correlation analysis. Pearson correlation coefficients ranged from 0.661 for ankle pronation/supination moments to 0.915 for ankle flexion/extension moments (P < .001). Root mean squared errors between measurement methods were in the magnitude of 10% of the measured range and were explainable. Differences in results depicted differences between systems in definition and computation of measurement variables. They may not limit clinical use of the load cell, but should be considered when data are compared directly to conventional gait analysis data. Construct validity of the load cell (ie, ability to measure joint moments in-situ) is supported by the study results.