Fork-Coupled Prosthesis Sleeve for Torsional Strength
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Solution Overview
Problem
Existing reinforcing implants for anchoring shafts of prostheses on elongate bones, such as the femur or humerus, face challenges in achieving high force transmission and torsional strength while being complex to produce and difficult to manufacture with precise tolerances, especially when used on thin bones.
Innovation Solution
A reinforcing sleeve with fork-shaped receiving bushes and a separable coupling region using fastening screws, where the forks interact with fitting blocks to provide a clearance fit, allowing for easier production and tolerance compensation, enhancing force transmission and torsional strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wedge action connector with pocket-like recesses is used to achieve high force transmission and torsional strength, then the connection reliability is improved, but the manufacturing complexity and precision requirements increase significantly
Solution Approach 1:
The coupling region is divided into two separate receiving bushes that can be manufactured independently and then assembled together. Each receiving bush has a simplified internal structure without complex pocket-like recesses, reducing individual component manufacturing complexity while maintaining overall connection reliability through the assembled fork construction.
Solution Approach 2:
Instead of creating complex internal recesses within each receiving bush to achieve rotational securing, the invention inverts the approach by adding external fork structures to the receiving bushes. The forks extend outward and engage with corresponding features on the opposing bush, achieving rotational security through external geometry rather than internal complexity.
2Strength
If a wedge action connector with exact fit is used to ensure high torsional strength, then the rotational securing is improved, but the manufacturing precision requirements become extremely difficult to meet
Solution Approach 1:
The invention changes the geometric parameters of the coupling interface from exact-fit pocket-like recesses to clearance-fit fork structures. The forks have a defined width that corresponds to the inner width of the opposing fork, allowing for clearance fits rather than exact fits. This parameter change reduces manufacturing precision requirements while maintaining torsional strength through the planar bearing surfaces and fastening screws.
Solution Approach 2:
The fastening screws act as intermediaries that secure the fork structures together. Rather than relying on precise interlocking geometry, the screws provide the primary securing function, allowing the fork interfaces to use simpler clearance fits. This mediator approach decouples the torsional strength requirement from the fit precision requirement.
3Force
If the reinforcing implant is designed for high force transmission, then the operational reliability is improved, but the device size and complexity increase
Solution Approach 1:
The fork structures and receiving bushes are merged into integrated components. Each receiving bush has forks that are formed as integral parts of the bush structure, eliminating the need for separate fork components and reducing overall structural complexity. This merging maintains force transmission capability while simplifying the device architecture.
Data Source
AI summary
The invention relates to a connecting sleeve for anchoring shafts of two oppositely arranged prostheses, preferably on an elongate bone such as a femur or humerus. The reinforcing sleeve comprises two receiving bushes for one prosthesis shaft each and comprises a separable coupling region arranged therebetween for connection in such a manner as to resist shear forces and rotation. According to the invention, each receiving bush has, on the side thereof facing the coupling region, one fork of a pair of forks that interact with each other, and a fitting block is arranged on a base of the fork, the lateral surfaces of which fitting block have a distance that corresponds to an inner width of the fork, and the lateral surfaces are designed to contact flanks of the fork in a planar manner, at least one fastening screw being arranged transversely through the fork. The fork connection is simpler to produce than the known wedge connection and yet is sufficiently robust. Unlike in the case of the wedge connection, an exact fit is not required; a clearance fit between the fork and the fitting block is sufficient in principle, excessive play being eliminated by means of the fastening screw.