Lauren Kark

Use of gait summary measures with lower limb amputees

Gait summary measures have been developed as a convenient method to communicate overall gait pathology. These measures are primarily used in the context of paediatric cerebral palsy and their use remains largely untested in other disability groups. This study assessed the suitability of gait summary measures for use with lower limb amputees. Modified (m) versions of three published gait summary measures were investigated - the Gillette Gait Index (mGGI), the Gait Deviation Index (mGDI) and the Gait Profile Score (mGPS) in conjunction with the Movement Analysis Profile (MAP). Twenty unilateral lower limb amputees underwent three-dimensional gait analysis. All measures reported significant differences between levels of amputation on the prosthetic limb. The mGGI and mGPS detected significant differences between the levels of amputation on the intact side, but the mGDI did not. All gait summary measures were moderately to strongly correlated with leg-length normalised self-selected walking speed and strong correlations were reported between all measures. The MAP exposed common strategies in amputee gait and showed that sagittal hip and knee kinematics contributed predominantly to overall gait deviation in this population group. The mGGI, mGDI and mGPS identified, quantified and stratified gait pathology, indicating that any of the gait measures investigated in this study can be applied as outcome measures in research and case management in lower limb amputees.

Patient satisfaction following lower-limb amputation: the role of gait deviation

Background: Patient satisfaction is an important measurement in healthcare for administrators, clinicians and patients. Objectives: This study investigated the role of gait deviation in patient satisfaction following lower-limb amputation and prosthesis prescription. Study design: A cross-sectional study was done. Methods: Twenty community-based unilateral lower-limb amputees, 12 transtibial and 8 transfemoral, were recruited from support groups. Participants completed the prosthesis evaluation questionnaire (PEQ) with embedded satisfaction-related questions, the timed-up-and-go test and the six-minute walk test, and also underwent quantitative three-dimensional analysis. Kinematic deviation was summarized using the gait profile score (GPS). Results: Satisfaction levels were generally high (median 80 + /100). Sociodemographic variables did not correlate significantly with any of the satisfaction measures (−0.35 ≤ r ≤ 0.54). Satisfaction correlated strongly with the PEQ scales, particularly ambulation, prosthetic utility, frustration, perceived response and social burden (r ≥ 0.70). By contrast, the relationships between satisfaction and performance-based outcome measures were not significant (−0.45 ≤ r ≤ 0.43), and the GPS did not correlate with any satisfaction measures (−0.23 ≤ r ≤ 0.15). Conclusions: In this study of high functioning amputees, gait deviation was unimportant to the amputee, while self-reported functional ability and attitudes toward the prosthesis were the strongest correlates of satisfaction following lower-limb amputation. Clinical relevance For the high functioning individuals with lower-limb amputation in this study, gait deviation was not a significant correlate of patient satisfaction. Results suggest that improving self-perceived functional ability and attitudes toward the prosthesis, rather than minimizing gait deviation, will improve patient satisfaction.

Determining possible thrombus sites in an extracorporeal device, using computational fluid dynamics-derived relative residence time

The prediction of conditions that may result in thrombus formation is a useful application of computational fluid dynamics. A number of techniques exist, based on the consideration of wall shear stress and regions of low blood flow; however, no clear guideline exists for the best practice of their use. In this paper, the sensitivity of each parameter and the specific mechanical forces are explained, before the optimal indicator of thrombosis risk is outlined. An extracorporeal access device cavity provides a suitable geometry to test the methodology. The recommended method for thrombus prediction considers areas with a calculated residence time (RT) and shear strain rate (SSR) thresholds, here set to RT>1 and SSR < 10 s− 1. Evidence of thrombosis was found for physiological waveforms with an absence of reverse flow, which is expected to ‘wash out’ the cavity. The predicted thrombosis sites compare well with evidence collected from explanted devices.

The Hemodynamic Effects of Hemodialysis Needle Rotation and Orientation in an Idealized Computational Model

Maintaining the patency of vascular access is essential for performing efficient hemodialysis. Appropriate cannulation technique is critical in maintaining the integrity of vascular access. This study focused on analyzing the hemodynamic effect of needle rotation, which is performed to alleviate the pressure if the needle becomes attached to the blood vessel wall. The hemodynamic benefits (normal wall shear stress [WSS] and smooth flow with no oscillatory motion) of this technique are investigated in an idealized model of the cephalic vein in order to determine a needle position that will reduce conditions known to contribute to vascular access failure. A computational fluid dynamics study was conducted, with antegrade and retrograde orientations simulated on the arterial needle, whereas the venous needle is placed in the antegrade orientation. In every case, needle rotation offered no hemodynamic benefit in minimizing the conditions known to cause endothelial damage, a precursor to vascular access failure. Venous needle rotation reduced the maximum WSS by 30%. However, the WSS was above the range, which may damage the endothelial layer. The arterial needle in the antegrade orientation produced a large region of oscillatory shear, whereas a retrograde orientation produced a region of smooth flow in the vicinity of the needle with only a small region of oscillatory shear. The flow through the venous needle back eye was negligible, whereas the arterial needle back eye was more efficient in the retrograde orientation. Therefore, the venous needle should not be rotated, whereas the arterial needle may be rotated to alleviate pressure with consideration given to the orientation of the needle.

In Vitro Mechanical Testing of Braided Polyurethane Elastic Fiber and Braided Polyester for Equine Laryngoplasty

OBJECTIVES In vitro comparison of the mechanical properties of braided polyurethane elastomer (Lycra®) and braided polyester (Ethibond™) (1) when inserted into the muscular process of the arytenoid cartilage and (2) as suture loops. STUDY DESIGN Experimental. ANIMALS Equine cadaver larynges (n = 15). METHODS The muscular processes (n = 30) of the arytenoid cartilages were dissected from each larynx and embedded in a resin base. Lycra® and Ethibond™ prostheses were randomly allocated to the left or right muscular process and each underwent cyclic fatigue (25-50 N) followed by load-to-failure testing. Isolated suture loops of Lycra® (n = 25) and Ethibond™ (n = 25) also underwent the same cyclic fatigue followed by load-to-failure testing (n = 20) or a creep testing protocol (25 N for 10 min; n = 5). RESULTS Lycra® prostheses pulled through the cartilage in a significantly greater proportion of cyclic tests (P = .015) and at lower mean (±SD) loads, (95.9 ± 23.4 N) during load-to-failure testing than Ethibond™ prostheses (155.2 ± 24.4 N; P = .0041). Lycra® had a significantly greater displacement with and without a cartilage interface when compared to Ethibond™ (P < .001, P < .002). The Lycra® isolated suture loops failed at significantly greater loads (233.0 ± 38.7 N) during load-to-failure testing than Ethibond™ loops (201.6 ± 47.4 N; P = .042). CONCLUSIONS Lycra® prostheses embedded in laryngeal cartilage pulled through the cartilage at lower loads than Ethibond™ prostheses. Lycra® suture loops were stronger than Ethibond™ suture loops. Lycra® had greater displacement than Ethibond™ in all tests as suture loops or when embedded in cartilage.

A prosthesis-specific multi-link segment model of lower-limb amputee sprinting

Lower-limb amputees commonly utilize non-articulating energy storage and return (ESAR) prostheses for high impact activities such as sprinting. Despite these prostheses lacking an articulating ankle joint, amputee gait analysis conventionally features a two-link segment model of the prosthetic foot. This paper investigated the effects of the selected link segment model׳s marker-set and geometry on a unilateral amputee sprinter׳s calculated lower-limb kinematics, kinetics and energetics. A total of five lower-limb models of the Ottobock® 1E90 Sprinter were developed, including two conventional shank-foot models that each used a different version of the Plug-in-Gait (PiG) marker-set to test the effect of prosthesis ankle marker location. Two Hybrid prosthesis-specific models were then developed, also using the PiG marker-sets, with the anatomical shank and foot replaced by prosthesis-specific geometry separated into two segments. Finally, a Multi-link segment (MLS) model was developed, consisting of six segments for the prosthesis as defined by a custom marker-set. All full-body musculoskeletal models were tested using four trials of experimental marker trajectories within OpenSim 3.2 (Stanford, California, USA) to find the affected and unaffected hip, knee and ankle kinematics, kinetics and energetics. The geometry of the selected lower-limb prosthesis model was found to significantly affect all variables on the affected leg (p < 0.05), and the marker-set also significantly affected all variables on the affected leg, and none of the unaffected leg variables. The results indicate that the omission of prosthesis-specific spatial, inertial and elastic properties from full-body models significantly affects the calculated amputee gait characteristics, and we therefore recommend the implementation of a MLS model.

Concurrent multibody and Finite Element analysis of the lower-limb during amputee running

Lower-limb amputee athletes use Carbon fiber Energy Storage and Return (ESAR) prostheses during high impact activities such as running. The advantage provided to amputee athletes due to the energy-storing properties of ESAR prostheses is as yet uncertain. Conventional energy analysis methods for prostheses rely upon multibody models with articulating joints. Alternatively, Finite Element (FE) analysis treats bodies as a deforming continuum and can therefore calculate the energy stored without using these rigid-body mechanics assumptions. This paper presents a concurrent multibody and FE model of the femur, tibia, socket and ESAR prosthesis of a transtibial amputee athlete during sprinting. Gait analysis spatial data was used to conduct an offline simulation of the affected legs stance phase in COMSOL Multiphysics. The calculated peak elastic strain energy of the prosthesis was 80J, with an overall RMSE of simulated marker displacement of 4.19mm. This concurrent model presents a novel method for analyzing in vivo ESAR prosthesis behavior.

Quantifying prosthetic gait deviation using simple outcome measures

AIM To develop a subset of simple outcome measures to quantify prosthetic gait deviation without needing three-dimensional gait analysis (3DGA). METHODS Eight unilateral, transfemoral amputees and 12 unilateral, transtibial amputees were recruited. Twenty-eight able-bodied controls were recruited. All participants underwent 3DGA, the timed-up-and-go test and the six-minute walk test (6MWT). The lower-limb amputees also completed the Prosthesis Evaluation Questionnaire. Results from 3DGA were summarised using the gait deviation index (GDI), which was subsequently regressed, using stepwise regression, against the other measures. RESULTS Step-length (SL), self-selected walking speed (SSWS) and the distance walked during the 6MWT (6MWD) were significantly correlated with GDI. The 6MWD was the strongest, single predictor of the GDI, followed by SL and SSWS. The predictive ability of the regression equations were improved following inclusion of self-report data related to mobility and prosthetic utility. CONCLUSION This study offers a practicable alternative to quantifying kinematic deviation without the need to conduct complete 3DGA.

An eight-legged tactile sensor to estimate coefficient of static friction

It is well known that a tangential force larger than the maximum static friction force is required to initiate the sliding motion between two objects, which is governed by a material constant called the coefficient of static friction. Therefore, knowing the coefficient of static friction is of great importance for robot grippers which wish to maintain a stable and precise grip on an object during various manipulation tasks. Importantly, it is most useful if grippers can estimate the coefficient of static friction without having to explicitly explore the object first, such as lifting the object and reducing the grip force until it slips. A novel eight-legged sensor, based on simplified theoretical principles of friction is presented here to estimate the coefficient of static friction between a planar surface and the prototype sensor. Each of the sensors eight legs are straight and rigid, and oriented at a specified angle with respect to the vertical, allowing it to estimate one of five ranges (5 = 8/2 + 1) that the coefficient of static friction can occupy. The coefficient of friction can be estimated by determining whether the legs have slipped or not when pressed against a surface. The coefficients of static friction between the sensor and five different materials were estimated and compared to a measurement from traditional methods. A least-squares linear fit of the sensor estimated coefficient showed good correlation with the reference coefficient with a gradient close to one and an r2 value greater than 0.9.

Reliability and validity of the iSense optical scanner for measuring volume of transtibial residual limb models

Background: Residual limb volume is often measured as part of routine care for people with amputations. These measurements assist in the timing of prosthetic fitting or replacement. In order to make well informed decisions, clinicians need access to measurement tools that are valid and reliable. Objectives: To assess the reliability and criterion validity of the iSense optical scanner in measuring volume of transtibial residual limb models. Study Design: Three assessors performed two measurements each on 13 residual limb models with an iSense optical scanner (3D systems, USA). Intra-rater and inter-rater reliability were calculated using intraclass correlation coefficients. Bland Altman plots were inspected for agreement. Criterion validity was assessed using a steel rod of known dimensions. Ten repeated measurements were performed by one assessor. A t-test was used to determine differences between measured and true rod volume. Results: Intra-rater reliability was excellent (range of intraclass correlation coefficients: 0.991–0.997, all with narrow 95% confidence intervals). While the intraclass correlation coefficients suggest excellent inter-rater reliability between all three assessors (range of intraclass correlation coefficients: 0.952–0.986), the 95% confidence intervals were wide between assessor 3 and the other two assessors. Poor agreement with assessor 3 was also seen in the Bland-Altman plots. Criterion validity was very poor with a significant difference between the mean iSense measurement and the true rod volume (difference: 221.18 mL; p < 0.001). Conclusions: Although intra-rater reliability was excellent for the iSense scanner, we did not find similar results for inter-rater reliability and validity. These results suggest that further testing of the iSense scanner is required prior to use in clinical practice. Clinical relevance The iSense offers a low cost scanning option for residual limb volume measurement. Intra-rater reliability was excellent, but inter-rater reliability and validity were such that clinical adoption is not indicated at present.