Computer-socket manufacturing error: How much before it is clinically apparent?

Sanders, Joan E.; Severance, Michael R.; Allyn, Katheryn J.

doi:10.1682/jrrd.2011.05.0097

Cited by 26 publications

(35 citation statements)

References 11 publications

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“…However at present, these tools do not inform the design in a data-driven sense [28] since the actual design process remains a manual and experience based procedure. This may explain the reported preferential indifference among patients who used both a socket made using conventional and CAD/CAM techniques [29], and that design errors remain prevalent [30]. Further, non-invasive imaging has been used to study the geometry of the residual limb, e.g.…”

Section: Introductionmentioning

confidence: 99%

Automated and Data-driven Computational Design of Patient-Specific Biomechanical Interfaces

Moerman¹,

Sengeh²,

Herr³

2016

Preprint

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Abstract-Biomechanical interfaces are mechanical structures that form the connection between a device and a tissue region, and, through appropriate load transfer, aim to minimize tissue discomfort and injury. A patient-specific and data-driven computational framework for the automated design of biomechanical interfaces is presented here. Optimization of the design of biomechanical interfaces is complex since it is affected by the interplay of the geometry and mechanical properties of both the tissue and the interface. The proposed framework is presented for the application of transtibial amputee prostheses where the interface is formed by a prosthetic liner and socket. Conventional socket design and manufacturing is largely artisan, non-standard, and insufficiently data-driven, leading to discrepancies between the quality of sockets produced by different prosthetists. Furthermore, current prosthetic liners are often not patient-specific. The proposed framework involves: A) non-invasive imaging to record patient geometry, B) indentation to assess tissue mechanical properties, C) data-driven and automated creation of patientspecific designs, D) patient-specific finite element analysis (FEA) and design evaluation, and finally E) computer aided manufacturing. Uniquely, the FEA procedure controls both the design and mechanical properties of the devices, and simulates, not only the loading during use, but also the pre-load induced by the donning of both the liner and the socket independently. Through FEA evaluation, detailed information on internal and external tissue loading, which are directly responsible for discomfort and injury, are available. Further, these provide quantitative evidence on the implications of design choices, e.g. : 1) alterations in the design can be used to locally enhance or reduce tissue loading, 2) compliant features can aid in relieving local surface pressure. The proposed methods form a patient-specific, data-driven and repeatable design framework for biomechanical interfaces, and by enabling FEA-based optimization reduces the requirement for repeated patient involvement in the currently manual and iterative design process.

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Section: Introductionmentioning

confidence: 99%

Automated and Data-driven Computational Design of Patient-Specific Biomechanical Interfaces

Moerman¹,

Sengeh²,

Herr³

2016

Preprint

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show abstract

“…Measured socket shapes were aligned with the digital files from which they were created using custom software that was minimally sensitive to the distribution of shape erro [11] . A relative weight of 0.8 mean absolute distance and 0.2 shape similarity (mean negative hyperbolic arc tangent of the surface-normal dot product) was used [3] . We calculated the mean radial error and volume error for the fabricated socket vs. digital file to characterize the fabrication error.…”

Section: Methodsmentioning

confidence: 99%

“…Prosthesis users report socket fit is the single-most important issue related to use of a prosthesis [2] . Sockets oversized as little as 1.0% have been shown to be clinically distinguishable from properly-sized sockets [3] . While oversized sockets can be compensated with the addition of prosthetic socks [4,5] , socks create a soft layer that weakens the mechanical coupling between the limb and socket.…”

Section: Introductionmentioning

confidence: 99%

Effects of socket size on metrics of socket fit in trans-tibial prosthesis users

Sanders

Youngblood

Hafner

et al. 2017

Medical Engineering & Physics

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The purpose of this research was to conduct a preliminary effort to identify quantitative metrics to distinguish a good socket from an oversized socket in people with trans-tibial amputation. Results could be used to inform clinical practices related to socket replacement. A cross-over study was conducted on community ambulators (K-level 3 or 4) with good residual limb sensation. Participants were each provided with two sockets, a duplicate of their as-prescribed socket and a modified socket that was enlarged or reduced by 1.8 mm (~6% of the socket volume) based on the fit quality of the as-prescribed socket. The two sockets were termed a larger socket and a smaller socket. Activity was monitored while participants wore each socket for 4wk. Participants’ gait; self-reported satisfaction, quality of fit, and performance; socket comfort; and morning-to-afternoon limb fluid volume changes were assessed. Visual analysis of plots and estimated effect sizes (measure as mean difference divided by standard deviation) showed largest effects for step time asymmetry, step width asymmetry, anterior and anterior-distal morning-to-afternoon fluid volume change, socket comfort scores, and self-reported measures of utility, satisfaction, and residual limb health. These variables may be viable metrics for early detection of deterioration in socket fit, and should be tested in a larger clinical study.

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“…We aligned the insert and digital shapes for comparison using a technique we developed previously to compare shapes [8,9]. The technique used a combination of minimizing the volume difference and maximizing the shape similarity and was specifically formulated for use in prosthetics.…”

Section: Methodsmentioning

confidence: 99%

Technical note: Computer-manufactured inserts for prosthetic sockets

Sanders

McLean

Cagle

et al. 2016

Medical Engineering & Physics

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The objective of this research was to use computer-aided design software and a tabletop 3-D additive manufacturing system to design and fabricate custom plastic inserts for trans-tibial prosthesis users. Shape quality of inserts was tested right after they were inserted into participant’s test sockets and again after four weeks of wear. Inserts remained properly positioned and intact throughout testing. Right after insertion the inserts caused the socket to be slightly under-sized, by a mean of 0.11 mm, approximately 55% of the thickness of a nylon sheath. After four weeks of wear the under-sizing was less, averaging 0.03 mm, approximately 15% of the thickness of a nylon sheath. Thus the inserts settled into the sockets over time. If existing prosthetic design software packages were enhanced to conduct insert design and to automatically generate fabrication files for manufacturing, then computer manufactured inserts may offer advantages over traditional methods in terms of speed of fabrication, ease of design, modification, and record keeping.

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Computer-socket manufacturing error: How much before it is clinically apparent?

Cited by 26 publications

References 11 publications

Automated and Data-driven Computational Design of Patient-Specific Biomechanical Interfaces

Automated and Data-driven Computational Design of Patient-Specific Biomechanical Interfaces

Effects of socket size on metrics of socket fit in trans-tibial prosthesis users

Technical note: Computer-manufactured inserts for prosthetic sockets

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