Precision of surface measurements for below-knee residua

Volume Fluctuations in Active and Nonactive Transtibial Prosthetics Users

This study aims to evaluate the validity and reliability of the Biosculptor’s Bioscanner system in capturing transtibial residual limb volume fluctuations in active and nonactive amputees during walking activity. Residual limb volume was obtained by measuring the limb circumference after amputees walked for 5 to 25 minutes for five consecutive days. The comparison of mean circumference between Bioscanner and manual measurements (i.e., tape measure) showed that the Bioscanner gave a higher estimation of circumference for the different amputees. Short-term changes in girth and volume due to an activity such as walking do not fluctuate uniformly. The results reflected as such as nonconsistence circumference change identified at different locations of the circumference profiles. Both amputees experienced a significant increase in circumference at the distal end of the limbs after 5 minutes of walking (7.35% change in nonactive and 8.83% in active amputees), and the measurement decreased as amputees walked longer. At 4-8 cm below the mid-patella tendon (pressure tolerant areas), both amputees experienced minor changes in the size of their circumference. The residual limb volume calculation resulted in the percentage difference between the two methods ranging from 2.4% to 9.3%. Pearson coefficient correlation obtained showed a high correlation between the two techniques, ranging from 0.97 to 1. The analysis of the limit of agreements showed that the majority of measurements were closed to the mean, suggesting that Bioscanner and manual techniques may be interchangeable and agree with one another. This study has implied that Bioscanner is comparable to the standard measurement method and may serve as an alternative tool in managing daily residual limb volume change.

Sensing and actuation technologies for smart socket prostheses

The socket is the most critical part of every lower-limb prosthetic system, since it serves as the interfacial component that connects the residual limb with the artificial system. However, many amputees abandon their socket prostheses due to the high-level of discomfort caused by the poor interaction between the socket and residual limb. In general, socket prosthesis performance is determined by three main factors, namely, residual limb-socket interfacial stress, volume fluctuation of the residual limb, and temperature. This review paper summarizes the various sensing and actuation solutions that have been proposed for improving socket performance and for realizing next-generation socket prostheses. The working principles of different sensors and how they have been tested or used for monitoring the socket interface are discussed. Furthermore, various actuation methods that have been proposed for actively modifying and improving the socket interface are also reviewed. Through the continued development and integration of these sensing and actuation technologies, the long-term vision is to realize smart socket prostheses. Such smart socket systems will not only function as a socket prosthesis but will also be able to sense parameters that cause amputee discomfort and self-adjust to optimize its fit, function, and performance.

Influences and trends of various shape-capture methods on outcomes in trans-tibial prosthetics: A systematic review

INTRODUCTION

In trans-tibial prosthetics, shape-capture methods are employed to create a representation of the residuum. Shape-capture methods can be grouped into the categories of 'hands-on', 'hands-off' and computer-aided design.

OBJECTIVE

This review examines the influences and trends of shape-capture methods on the outcomes of quality, comfort of user and clinical efficiency, in the population of trans-tibial prosthesis users.

STUDY DESIGN

Systematic Review.

METHOD

Databases and relevant journals were searched. Participants included trans-tibial prosthetics users/limb models. Interventions included shape-capture methods. Outcomes included quality, comfort of user and clinical efficiency.

RESULTS

Overall, 22 papers were evaluated; 8 papers evaluated hands-on and hands-off methods, 2 evaluated computer-aided design and 12 evaluated measurement systems used with shape capture. No papers relating to clinical efficiency were found.

CONCLUSION

Overall evidence was weak in suggesting that effects on outcomes were due to the sole influences of shape capture. However, studies suggest that hands-on methods are dependent on a prosthetist's skill. Hands-off methods, although repeatable, might still require experience to attain a good fit. Computer-aided design studies were mostly done on theoretical models. Shape-capture measurements require more consistent 'gold standards'. The relation between socket fit and comfort is still unclear. Overall, more research is required in each area.

CLINICAL RELEVANCE

A good fitting prosthetic socket is crucial for efficient and comfortable use of a prosthesis. To attain the best chances of a good fit, it is important that the characteristics of the residuum are captured as accurately as possible during the initial "shape capture" stage. This paper attempts to categorize and evaluate the existing shape capture methods on their influence and trends on various outcomes - Quality of shape capture, comfort of user and clinical efficiency.

Reliability and Validity of Measurement Tools for Residual Limb Volume in People With Limb Amputations: A Systematic Review

BACKGROUND

Measurements of residual limb volume often guide decisions on the type and timing of prosthetic prescription. To help inform these decisions, it is important that clinicians use measurement tools that are reliable and valid.

PURPOSE

The aim of this systematic review was to investigate the reliability and validity of measurement tools for residual limb volume in people with limb amputations.

DATA SOURCES

A comprehensive search on MEDLINE, EMBASE, CINAHL, Scopus, and Web of Science was performed on July 11, 2016.

STUDY SELECTION

Studies were included if they examined the reliability or validity of measurement tools for residual limb volume, were conducted on humans, and were published in English.

DATA EXTRACTION

Data were extracted from 11 reliability and 4 validity studies and included study characteristics, volumetric estimates, and reliability and validity estimates. The quality of the studies was also rated.

DATA SYNTHESIS

Data from 2 studies (38 participants) indicated good to excellent intrarater (intraclass correlation coefficient [ICC] ≥0.88) and interrater (ICC ≥0.88) reliability and high between-session reliability (coefficient of variation [CV] = 10%) for water displacement volumetry. One study (28 participants) reported excellent intrarater and interrater reliability (ICC ≥0.93) for the circumferential method, and data from 2 studies (19 participants) indicated high between-session reliability for the optical surface scanner (CV ≤9.8%). Three studies (26 participants) indicated good to excellent between-session reliability results for computed tomography (CV = 9.2%-10.9%). One study (7 participants) showed moderate within-session reliability (CV = 50%). Using water displacement volumetry as the gold standard, 2 studies (79 participants) indicated excellent validity for the circumferential method ( r ≥0.92; ICC ≥0.92). All studies reporting measures of reliability or validity were performed with people who had transtibial amputations.

LIMITATIONS

Only studies published in English and in which water displacement volumetry was used as the gold standard were included in this review. The reliability and validity of the quality rating scale used in this review have not been tested.

CONCLUSIONS

On the basis of a limited number of moderate- to high-quality studies with small sample sizes, circumferential and water displacement methods were found to be reliable, and the circumferential method was found to be valid in people with transtibial amputations. There are inadequate data for drawing conclusions about volume measurement methods in people with other types of limb amputations.

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.

A Framework for Measuring the Time-Varying Shape and Full-Field Deformation of Residual Limbs Using 3-D Digital Image Correlation

Effective prosthetic socket design following lower limb amputation depends upon the accurate characterization of the shape of the residual limb as well as its volume and shape fluctuations.

OBJECTIVE

This study proposes a novel framework for the measurement and analysis of residual limb shape and deformation, using a high-resolution and low-cost system.

METHODS

A multi-camera system was designed to capture sets of simultaneous images of the entire residuum surface. The images were analyzed using a specially developed open-source three-dimensional digital image correlation (3D-DIC) toolbox, to obtain the accurate time-varying shapes as well as the full-field deformation and strain maps on the residuum skin surface. Measurements on a transtibial amputee residuum were obtained during knee flexions, muscle contractions, and swelling upon socket removal.

RESULTS

It was demonstrated that 3D-DIC can be employed to quantify with high resolution time-varying residuum shapes, deformations, and strains. Additionally, the enclosed volumes and cross-sectional areas were computed and analyzed.

CONCLUSION

This novel low-cost framework provides a promising solution for the in vivo evaluation of residuum shapes and strains, as well as has the potential for characterizing the mechanical properties of the underlying soft tissues.

SIGNIFICANCE

These data may be used to inform data-driven computational algorithms for the design of prosthetic sockets, as well as of other wearable technologies mechanically interfacing with the skin.

Measurement properties and usability of non-contact scanners for measuring transtibial residual limb volume

BACKGROUND

Non-contact scanners may have potential for measurement of residual limb volume. Different non-contact scanners have been introduced during the last decades. Reliability and usability (practicality and user friendliness) should be assessed before introducing these systems in clinical practice.

OBJECTIVES

The aim of this study was to analyze the measurement properties and usability of four non-contact scanners (TT Design, Omega Scanner, BioSculptor Bioscanner, and Rodin4D Scanner).

STUDY DESIGN

Quasi experimental.

METHODS

Nine (geometric and residual limb) models were measured on two occasions, each consisting of two sessions, thus in total 4 sessions. In each session, four observers used the four systems for volume measurement. Mean for each model, repeatability coefficients for each system, variance components, and their two-way interactions of measurement conditions were calculated. User satisfaction was evaluated with the Post-Study System Usability Questionnaire.

RESULTS

Systematic differences between the systems were found in volume measurements. Most of the variances were explained by the model (97%), while error variance was 3%. Measurement system and the interaction between system and model explained 44% of the error variance. Repeatability coefficient of the systems ranged from 0.101 (Omega Scanner) to 0.131 L (Rodin4D). Differences in Post-Study System Usability Questionnaire scores between the systems were small and not significant.

CONCLUSION

The systems were reliable in determining residual limb volume. Measurement systems and the interaction between system and residual limb model explained most of the error variances. The differences in repeatability coefficient and usability between the four CAD/CAM systems were small. Clinical relevance If accurate measurements of residual limb volume are required (in case of research), modern non-contact scanners should be taken in consideration nowadays.

Validity and reliability of a novel 3D scanner for assessment of the shape and volume of amputees' residual limb models

Background

Objective assessment methods to monitor residual limb volume following lower-limb amputation are required to enhance practitioner-led prosthetic fitting. Computer aided systems, including 3D scanners, present numerous advantages and the recent Artec Eva scanner, based on laser free technology, could potentially be an effective solution for monitoring residual limb volumes.

Purpose

The aim of this study was to assess the validity and reliability of the Artec Eva scanner (practical measurement) against a high precision laser 3D scanner (criterion measurement) for the determination of residual limb model shape and volume.

Methods

Three observers completed three repeat assessments of ten residual limb models, using both the scanners. Validity of the Artec Eva scanner was assessed (mean percentage error <2%) and Bland-Altman statistics were adopted to assess the agreement between the two scanners. Intra and inter-rater reliability (repeatability coefficient <5%) of the Artec Eva scanner was calculated for measuring indices of residual limb model volume and shape (i.e. residual limb cross sectional areas and perimeters).

Results

Residual limb model volumes ranged from 885 to 4399 ml. Mean percentage error of the Artec Eva scanner (validity) was 1.4% of the criterion volumes. Correlation coefficients between the Artec Eva and the Romer determined variables were higher than 0.9. Volume intra-rater and inter-rater reliability coefficients were 0.5% and 0.7%, respectively. Shape percentage maximal error was 2% at the distal end of the residual limb, with intra-rater reliability coefficients presenting the lowest errors (0.2%), both for cross sectional areas and perimeters of the residual limb models.

Conclusion

The Artec Eva scanner is a valid and reliable method for assessing residual limb model shapes and volumes. While the method needs to be tested on human residual limbs and the results compared with the current system used in clinical practice, it has the potential to quantify shape and volume fluctuations with greater resolution.

Accuracy verification of magnetic resonance imaging (MRI) technology for lower-limb prosthetic research: utilising animal soft tissue specimen and common socket casting materials

Lower limb prosthetic socket shape and volume consistency can be quantified using MRI technology. Additionally, MRI images of the residual limb could be used as an input data for CAD-CAM technology and finite element studies. However, the accuracy of MRI when socket casting materials are used has to be defined. A number of six, 46 mm thick, cross-sections of an animal leg were used. Three specimens were wrapped with Plaster of Paris (POP) and the other three with commercially available silicone interface liner. Data was obtained by utilising MRI technology and then the segmented images compared to corresponding calliper measurement, photographic imaging, and water suspension techniques. The MRI measurement results were strongly correlated with actual diameter, surface area, and volume measurements. The results show that the selected scanning parameters and the semiautomatic segmentation method are adequate enough, considering the limit of clinical meaningful shape and volume fluctuation, for residual limb volume and the cross-sectional surface area measurements.

Residual limb volume change: systematic review of measurement and management

Management of residual limb volume affects decisions regarding timing of fit of the first prosthesis, when a new prosthetic socket is needed, design of a prosthetic socket, and prescription of accommodation strategies for daily volume fluctuations. This systematic review assesses what is known about measurement and management of residual limb volume change in persons with lower-limb amputation. Publications that met inclusion criteria were grouped into three categories: group I: descriptions of residual limb volume measurement techniques; group II: studies investigating the effect of residual limb volume change on clinical care in people with lower-limb amputation; and group III: studies of residual limb volume management techniques or descriptions of techniques for accommodating or controlling residual limb volume. We found that many techniques for the measurement of residual limb volume have been described but clinical use is limited largely because current techniques lack adequate resolution and in-socket measurement capability. Overall, limited evidence exists regarding the management of residual limb volume, and the evidence available focuses primarily on adults with transtibial amputation in the early postoperative phase. While we can draw some insights from the available research about residual limb volume measurement and management, further research is required.

Inter- and intra-observer reproducibility and validity of an indirect volume measurement in transtibial amputees

The objective of the study was to assess the measurement properties of an indirect volumetric measurement using segmental circumferential measurements fitted into a formula of a truncated cone (Sitzia's method) in long-term transtibial amputees. Twenty-eight participants with a transtibial amputation >1 year participated in the study. Two observers measured stump volume twice, two weeks apart, using both Sitzia's method and the water displacement volumetric method (criterion standard test). The mean differences and upper and lower limits of agreement between the water displacement volumetric method and Sitzia's method, between the first and second assessment, and between both assessors were calculated. Intra-class correlation coefficients (ICCs) were derived from random-effects two-way analysis of variance. Inter-observer agreements of both methods were high and ranged from 86-96%. Intra-observer agreement ranged between 57% and 71%. In both methods the inter- and intra-observer differences were not significant. ICCs ranged from 0.88-0.99 and were better for inter-observer compared to intra-observer reproducibility. Lower stump volumes were observed in Sitzia's method compared to water displacement volumetric method, with high ICC's (0.92-0.95) between both methods. Although Sitzia's method systematically underestimates stump volume, it is a reliable and feasible alternative to the criterion standard test. To determine its validity to detect (longitudinal) differences in stump volume, follow-up research is needed in participants with recent amputations.

A comparison of trans-tibial amputee suction and vacuum socket conditions

Daily volume loss of the stump leads to a poor fit of the prosthetic socket. A method of preventing this volume loss and maintaining a good fit was developed. A vacuum (-78 kPa) was drawn on the expulsion port of a total surface-bearing suction socket to hold the liner tightly against the socket. Stump volume of 10 trans-tibial amputees was measured prior to and immediately after a 30 minute walk with normal and vacuum socket conditions. Under the normal condition, the limb lost an average of 6.5% of its volume during the walk. In contrast, with the liner held tightly by vacuum, the limb gained an average of 3.7% in volume. It is believed that the difference observed between conditions resulted from a greater negative pressure developed during the swing phase of gait with the vacuum condition. X-rays revealed that the limb and tibia pistoned 4 mm and 7 mm less, respectively, under the vacuum condition. The combination of reduced pistoning and maintenance of volume is thought to account for the more symmetrical gait observed with the vacuum.

Precision and accuracy of computed tomography foot measurements

OBJECTIVE

To test the accuracy and precision of computed tomography (CT) imaging for describing the 3-dimensional structure of the foot in patients with diabetes mellitus and peripheral neuropathy.

DESIGN

Experimental, test-retest.

SETTING

Clinical CT scanner at a local hospital.

SPECIMENS

Two tissue-equivalent phantoms and 6 cadaver feet.

MAIN OUTCOME MEASURES

Measurements taken from CT data of phantoms and cadaver feet were compared with physical (caliper) measurements. The feasibility of creating a computer-aided design/rapid prototyping 3-dimensional model from CT data was assessed by using 1 cadaver foot.

RESULTS

No bias was found for phantom or cadaver CT measurements compared with caliper measurements. The mean difference between repeat scans of cadaver feet (1 observer) was 0.1 +/- 0.8 mm and between observers, 0.4 +/- 0.8 mm. Comparing caliper measurements of the rapid prototype model and actual foot measurements revealed an error of 0.3 +/- 0.4 mm.

CONCLUSION

CT-based 3-dimensional imaging produced accurate and precise foot measurements, enabling description of internal and external structures. This capability will be coupled with plantar pressure measurements to improve our understanding and treatment of foot ulcers in people with diabetes.

Below-knee residual limb shape change measurement and visualization

OBJECTIVE

The ability to measure and visualize shape change (deformation) of a residual limb within and between prostheses is an important step toward improved prosthetic fit assessment. The objective was to develop measurement and visualization methods for below-knee residual limb soft tissue shape change after donning and loading a prosthesis to detect small shape changes (30mm or less).

DESIGN

Spiral X-ray computed tomography imaging was utilized to acquire 3D volumetric data of the below-knee residual limb and prosthesis in situ from poor- and a good-fitting prostheses without and with a load. A new sum projection depth-shaded cylindrical mapping technique to measure and visualize small changes in shape was developed. From the volumetric data, the relative displacement of small lead markers placed on the residual limb's skin surface were measured using multiplanar reconstruction images and cylindrical maps. Displacement measurements averaging 15mm or less were obtained.

RESULTS

The precision and accuracy was 1mm and 2mm, respectively, when measuring the shape change or deformation of the skin surface from the sum projection cylindrical maps. The skin surface deformation was at least 7mm or greater when comparing marker locations between scans with the prostheses in situ.

CONCLUSION

These new image-based measurement and visualization methods provide a feasible means for measuring and displaying lower extremity residual limb shape change within and between different prostheses with and without loading.

Lower extremity residual limb slippage within the prosthesis

OBJECTIVE

The ability to measure skin surface slippage relative to the internal wall of a lower extremity prosthesis under various loading conditions is important for evaluation of socket fit and function, and creation of finite element models. Skin surface three-dimensional (3D) shape measurements with tracking of fiducial displacements in situ under axial loading of the prosthesis have not previously been reported. Analysis of slippage within the prosthesis has been performed using a new experimental measurement method based on spiral x-ray computed tomography (SXCT) imaging.

DESIGN

Small lead markers were placed on the residuum of an adult with a below-knee amputation, and SXCT scans were obtained with the prosthesis in situ under two static axial loading conditions (44.5N and 178N). The 3D scan data were used to assess slippage with three methods: gross displacement of the tibia and distal end of the residuum; relative displacement of markers; and distance measurements between markers.

RESULTS

The markers affixed to the below-knee skin surface within the prosthesis were measured. The skin slipped from 2 to 6 mm relative to the internal prosthesis wall when an additional load of 133.5N was applied in the axial direction to the distal end of the prosthesis. The tibial remnant moved 10.0 mm distally relative to the prosthesis internal wall.

CONCLUSION

This method provides a feasible means for measuring residuum skin slippage relative to the prosthesis and skin deformation relative to tibia within an in situ prosthesis under load.

Finite element modeling and experimental verification of lower extremity shape change under load

Prediction and measurement of residuum shape change inside the prosthesis under various loading conditions is important for prosthesis design and evaluation. Residual limb surface measurements with the prosthesis in situ were used for construction of a finite element model (FEM). These surface measurements were obtained from volumetric computed tomography. A new experimental method for modeling the shape of the in situ lower residual limb was developed based on spiral X-ray computed tomography (SXCT) imaging. The p-version of the finite element method was used for estimating the material properties from known load and displacement data. A homogeneous, isotropic, linear constitutive model with accommodation of the constitutive soft and hard tissues of the residuum was evaluated with static axial loading applied to the in situ prosthesis and compared with experimental results obtained in a human volunteer. Two FEMs were created for similar coronal cross sections of the below knee residuum under two loading conditions. Agreement between observed (from SXCT) and predicted (from FEA) residual limb shape changes inside the prosthesis were maximized with a single modulus of elasticity for the residuum soft tissue of 0.06 MPa, consistent with previously published results. This methodology provides a framework to predict and objectively evaluate FEMs and determine residuum material properties by inverse methods.