Evaluation of the effect of shape on a contemporary CAD system

Reliability and validity of 3D limb scanning for ankle-foot orthosis fitting

BACKGROUND

Recent decreases in the cost of 3D scanners and improved functionality have resulted in increased adoption for ankle-foot orthosis (AFO) fittings, despite limited supporting data. For 3D limb scanning to be a feasible alternative to traditional casting methods, a consistent and accurate representation of limb geometry must be produced at a reasonable cost.

OBJECTIVES

To evaluate the repeatability and validity of multiple lower limb measurements obtained using low-cost 3D limb scanning technology.

STUDY DESIGN

Prospective, randomized, crossover-controlled, cross-sectional, reliability, and validity study.

METHODS

Physical measurements and 3D limb scans were completed for 30 participants. 11 measurements were selected for comparison based on their relevance to AFO fittings. Validity was assessed by comparison of physical and scan-based measures using Pearson's correlation coefficients and root mean square differences. Reliability was assessed using intraclass correlation coefficients and minimal detectable change (MDC) values. Bland-Altman plots were generated for data visualization.

RESULTS

All correlation values were above or equal to 0.80. Most intraclass correlation coefficient values were above 0.95. MDC values for physical and scan-based measurements differed by less than 2.0 mm. Scan MDC values were around or below 4 mm for foot and ankle measures and under 6 mm for circumference and length measures.

CONCLUSIONS

The results of this study demonstrate that low-cost 3D limb scanning can be used to obtain valid and reliable measurements of 3D limb geometry for the purpose of AFO fitting, when collected using the clinically relevant standardized conditions presented here.

A review of history of CAD/CAM system application in the productionof transtibial prosthetic socket in developing countries (from 1980to 2019)

The development of the CAD/CAM (Computer-aided design and computer-aided manufacturing) system has globally changed the fabrication and delivery of prosthetics and orthotics. Furthermore, since the introduction of CAD/CAM in the 1980s, many successful CAD/CAM system are available in the market today. However, less than 20% of amputees have access to digital fabrication technology and large portion of the amputees are from the developing countries. This review designed to examine selected studies from 1980 to 2019 on CAD/CAM systems in the production of transtibial prosthetic sockets. A review was conducted based on articles gathered from Web of Science, Pubmed and Science Direct. From the findings, 92 articles found related to CAD/CAM-derived transtibial prosthetic socket (TPS). After a further screening of the articles, 20 studies were chosen and only one study was done in a developing country. The results showed an increase interest in CAD/CAM application in Transtibial prosthetic socket (TPS) production for both developed and developing countries, yet the technology has not fully utilised in the developing countries. Factors such as resources, accessibility, knowledge-gap and lack of experienced prosthetists remain the major causes of the lack of CAD/CAM system studies. Large-scale trials are required to employ digital fabrication in the developing regions, consequently advancing the production of high-quality CAD-CAM-derived TPS where most prosthetic and orthotics are needed.

Residual limb volume fluctuations in transfemoral amputees

This study constitutes the first attempt to systematically quantify residual limb volume fluctuations in transfemoral amputees. The study was carried out on 24 amputees to investigate variations due to prosthesis doffing, physical activity, and testing time. A proper experimental set-up was designed, including a 3D optical scanner to improve precision and acceptability by amputees. The first test session aimed at measuring residual limb volume at 7 time-points, with 10 min intervals, after prosthesis doffing. This allowed for evaluating the time required for volume stabilization after prosthesis removal, for each amputee. In subsequent sessions, 16 residual limb scans in a day for each amputee were captured to evaluate volume fluctuations due to prosthesis removal and physical activity, in two times per day (morning and afternoon). These measurements were repeated in three different days, a week apart from each other, for a total of 48 scans for each amputee. Volume fluctuations over time after prosthesis doffing showed a two-term decay exponential trend (R2 = 0.97), with the highest variation in the initial 10 min and an average stabilization time of 30 min. A statistically significant increase in residual limb volume following both prosthesis removal and physical activity was verified. No differences were observed between measures collected in the morning and in the afternoon.Clinical Trials.gov ID: NCT04709367.

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 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.

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.

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.

Central fabrication: carved positive assessment

BACKGROUND

It is estimated that only 24% of practitioners use CAD/CAM regularly. Socket manufacturing error may be a source of the limited use of central fabrication.

OBJECTIVES

The purpose of this study was to investigate the differences in shape between computer-manufactured, centrally fabricated carved models and electronic file shapes, to determine if carving was a major source of socket manufacturing error in central fabrication.

STUDY DESIGN

Experimental, mechanical assessment.

METHODS

Three different trans-tibial model shapes were sent electronically to each of 10 central fabrication facilities for the fabrication of positive foam models. A custom mechanical digitizer and alignment algorithm were used to measure the model shapes and then compare them with the electronic file shapes.

RESULTS

Volume differences between the models and the electronic file shapes ranged from -4.2% to 1.0%, and averaged -0.9 (SD = 1.1)%. Mean radial error ranged from -1.2 mm to 0.3 mm and averaged -0.3 (SD = 0.3) mm. Inter-quartile range was between 0.3 mm and 2.7 mm and averaged 0.6 (SD = 0.5) mm. The models were significantly smaller than sockets made from the same electronic file shapes (p < 0.01), but the range of mean radial error and the interquartile range were not significantly different between the models and sockets.

CONCLUSIONS

The results demonstrated that there was considerable variability in model quality among central fabricators in the industry, and that carving was not the sole source of socket fabrication error.

CLINICAL RELEVANCE

The results provide insight into the severity and nature of carving error by central fabrication facilities. Because we found a wide range of model quality, there is not a consistent fabrication problem across the industry, but instead some central fabrication facilities practice the art of model fabrication better than others.