Prosthetic Liner with Differentiated Knit Fabric to Prevent Pistoning
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Solution Overview
Problem
Prosthetic liners with uniform extensibility fail to address pistoning and skin breakdown issues, as they either constrain knee flexion or require expensive constructions with reinforcing matrices, and existing solutions for localized extensibility are limited to specific locations.
Innovation Solution
A prosthetic liner with differentiated knitting that reduces longitudinal stretch at the distal end while maintaining transverse stretch, using low extensibility strips that can be applied anywhere on the liner to control distal distraction and pistoning, and customizable to accommodate various anatomical needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If uniform extensibility is used throughout the liner, then the liner is simple to manufacture, but it fails to address pistoning and skin breakdown issues
Solution Approach 1:
The liner incorporates regions of differentiated knit fabric with varying extensibility characteristics. Specifically, the distal end features lower longitudinal extensibility (0-30% stretch) compared to the proximal end (55-125% stretch), allowing localized control over pistoning while maintaining overall liner functionality.
2Reliability
If the distal end has lower longitudinal elongation to prevent pistoning, then pistoning is reduced, but knee flexion is constrained
Solution Approach 1:
The differentiated knit fabric creates distinct zones: the distal end (4-12 inches from closed end) has reduced longitudinal stretch (0-30%) to prevent pistoning, while the proximal end maintains high longitudinal stretch (55-125%) to accommodate knee flexion during ambulation.
Solution Approach 2:
The liner is segmented into functional regions with different knit structures. The distal region uses tighter knit patterns for pistoning control, while the proximal region uses looser knit patterns for flexibility, allowing each zone to perform its specific function independently.
3Reliability
If a reinforcing matrix is added to reduce longitudinal stretch at the distal end, then pistoning is prevented, but the construction becomes expensive
Solution Approach 1:
Instead of adding a separate reinforcing matrix layer, the patent modifies the knit fabric parameters directly. By adjusting yarn composition, stitch type, and knit density in the distal region, the desired low extensibility (0-30% longitudinal stretch) is achieved through the base fabric structure itself, eliminating the need for additional reinforcing layers and associated manufacturing steps.
4Ease of operation
If high longitudinal elongation is used throughout the liner, then knee flexion is facilitated, but the prosthesis moves up and down during ambulation
Solution Approach 1:
The liner implements spatially varying extensibility: the proximal end maintains high longitudinal elongation (55-125%) to facilitate knee flexion, while the distal end incorporates reduced longitudinal elongation (0-30%) to anchor the prosthesis and prevent vertical movement during ambulation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces pistoning and skin breakdown by allowing for variable stretch characteristics, preventing distal distraction, and providing a cost-effective, customizable solution for improved patient comfort and prosthetic functionality.
Implementation Method 1
The distal region has a vertical stretch of 0-30% from a resting position and a horizontal stretch of 10-200% from a resting position as compared to the proximal region, which preferably has a vertical stretch of 55-125% from a resting position and a horizontal stretch of 100-175% from a resting position
Implementation Method 2
The low extensibility material limits the longitudinal stretch of the liner while maintaining transversal stretch
Data Source
AI summary
A prosthetic liner having a lower longitudinal stretch in the distal region than in either the proximal or optional intermediate region. The distal region may stretch anywhere from 0-30% vertically and 10-200% horizontally as compared to the proximal region's vertical stretch of 55-125% and 100-175% horizontally. A variety of stitches may be used at the distal end to implement this lowered longitudinal stretch. The liner also has an interior layer of elastomer gel. The design of this prosthetic liner is primarily to prevent the “pistoning” of the amputee's residual limb within the liner and for comfort over pressure-sensitive areas of the residual limb. The liner also includes the use of a low extensibility material which is adhered to the fabric portion of a prosthetic liner or orthotic liner either internally or externally and limits the longitudinal movement while allowing for transversal movement.