Two-part Intramedullary Nail with Helical Spring Sheath
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Solution Overview
Problem
Existing intramedullary nails with solid or rigid nail cores face challenges in correct lateral insertion into the medullary canal, especially due to narrow kinks, and offer limited stability against bending and lateral/axial stress.
Innovation Solution
The intramedullary nail is designed with two separate parts: a sheath element with a helically wound spring element and a rod-shaped nail core that can be inserted into the sheath element after implantation, providing increased stability and flexibility during implantation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a solid or rigid nail core is used, then stability against bending and lateral/axial stress is improved, but ease of insertion through narrow kinks and bends deteriorates
Solution Approach 1:
The intramedullary nail is divided into two separate parts: a sheath element with a helical spring element and a rod-shaped nail core. The sheath element can be inserted first through the medullary canal, and the nail core is inserted subsequently into the sheath element. This segmentation allows the flexible sheath to navigate narrow kinks while the rigid nail core provides stability once inside.
Solution Approach 2:
The helical spring element in the sheath element provides dynamic flexibility during insertion, allowing the nail to adapt to the curvature of the medullary canal and narrow kinks. Once inserted, the spring element can be compressed to provide radial expansion and stability, transitioning from a flexible insertion state to a stable fixation state.
2Ease of operation
If a helical spring element is used in the sheath, then ease of insertion through bends and kinks is improved, but stability against bending stress after implantation deteriorates
Solution Approach 1:
By separating the nail into a sheath element with the helical spring and a rod-shaped nail core, the patent assigns different functions to each component. The spring element handles insertion flexibility, while the nail core provides the necessary stability and resistance to bending stress, resolving the contradiction between flexibility and strength.
Solution Approach 2:
The intramedullary nail combines two different material characteristics: the helical spring element (flexible, elastic) and the rod-shaped nail core (rigid, strong). This composite structure allows the nail to exhibit both flexibility during insertion and high stability against bending stress after implantation.
3Ease of operation
If the nail core is made elastically deformable, then ease of insertion is improved, but stability against lateral and axial stress after implantation deteriorates
Solution Approach 1:
The patent segments the nail into a flexible sheath element for easy insertion and a rigid nail core for providing stability. The nail core is specifically designed as a rod-shaped element that resists lateral and axial stress, while the sheath element with the helical spring handles the insertion process.
Solution Approach 2:
Different parts of the nail have different mechanical properties tailored to their specific functions. The sheath element with the helical spring is designed for flexibility and insertion, while the nail core is designed for rigidity and stress resistance. This local differentiation of material properties resolves the contradiction between ease of insertion and stability.
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
This design allows for easy implantation through bends or tight kinks and provides high stability against bending and lateral/axial stress after implantation, while maintaining flexibility during insertion.
Implementation Method 1
an external contour of the sheath element (10) comprises an elongate spring element (18), which is wound in a helical shape starting from the proximal end (12) and with respect to the longitudinal direction (L), wherein the extension of the external contour of the sheath element (10) can be reduced by tensioning the elongate spring element (18) in the winding direction and can be increased by detensioning the elongate spring element (18) counter to the winding direction
Data Source
AI summary
In an embodiment an intramedullary nail includes a sheath element extending in a longitudinal direction and having a proximal end, a distal end, and a substantially cylindrical interior, wherein an external contour of the sheath element, viewed perpendicularly to the longitudinal direction, includes an elongate spring element, which is wound in a helical shape starting from the proximal end and with respect to the longitudinal direction and wherein an extension of the external contour of the sheath element is reducible by tensioning the elongate spring element in a winding direction and is increasable by detensioning the elongate spring element counter to the winding direction, and a substantially rod-shaped nail core insertable into the interior through the proximal end of the sheath element, wherein the sheath element and the rod-shaped nail core are two separate parts.