Flexible-Fin Intramedullary Stem for Canal-Conforming Fixation
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Solution Overview
Problem
Existing intramedullary stems face challenges in gaining adequate fixation within medullary canals due to shape incongruency and issues with longer or shorter stems, leading to unfavorable positioning and difficulty in achieving stable implantation.
Innovation Solution
An intramedullary stem with a hollow body and flexible fins that can flex and adjust to the medullary canal, providing better fixation and stress-shielding through a design with slits and living hinges, allowing the fins to bend inward for secure placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a longer intramedullary stem is used to achieve increased fixation within the medullary canal, then fixation stability is improved, but the stem may be pulled in an anterior direction to be tangent to the curvature of the canal, causing unfavorable positioning
Solution Approach 1:
The intramedullary stem incorporates flexible fins that allow the stem to dynamically adapt to the curvature of the medullary canal. The fins can bend and flex to conform to the canal's shape, preventing the stem from being pulled anteriorly while maintaining fixation stability throughout the length of the stem.
Solution Approach 2:
The stem includes thin flexible fin structures that act as compliant elements between the rigid stem body and the bone canal wall. These fins can deform elastically to accommodate canal curvature, allowing the long stem to maintain both fixation and proper positioning without rigid contact points that would cause anterior pull.
2Adaptability or versatility
If a shorter intramedullary stem is used to allow flexing along the curvature of the medullary canal, then adaptability to canal shape is improved, but adequate fixation within the medullary canal becomes difficult to achieve
Solution Approach 1:
The stem is segmented into a rigid central body portion and multiple flexible fin portions. The fin segments can independently bend and flex to adapt to local canal curvature variations, while the rigid body portion maintains structural integrity and provides stable fixation anchors at distributed locations along the stem length.
Solution Approach 2:
The flexible fins provide dynamic adaptability, allowing the stem to conform to the medullary canal's curvature while maintaining sufficient rigidity in the body portion to achieve adequate fixation. The fins act as compliant connectors that transmit loads while accommodating shape variations.
3Device complexity
If conventional straight cemented or press-fit stems are used, then simplicity of design is maintained, but the distal end of the stem drives the proximal end into an unfavorable position
Solution Approach 1:
The flexible fins act as compliant elements that prevent the distal end from rigidly driving the proximal end into unfavorable positions. The fins can deform to absorb positioning forces, allowing the stem to be inserted straightforwardly while automatically adjusting to achieve proper final positioning without complex alignment procedures.
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 flexible fin design enables improved fixation and stress-shielding, allowing the stem to dynamically adjust to the medullary canal, preventing pull-out and ensuring stable implantation without causing pain, while accommodating varying canal shapes and sizes.
Implementation Method 1
The fin is biased in a first position where the free end is external to an outer surface of the elongate body and is movable based on radially inward forces to push the free end toward the elongate body
Data Source
AI summary
An intramedullary stem includes an elongate body having a length extending from a first end to a second end and a lumen along at least a portion of the length. A first slit extends along the elongate body. The first slit is in between the first and second ends of the elongate body. A fin is attached to the elongate body at the first slit end and extends to a free end remote from the first slit end. The fin is biased in a first position where the free end is external to an outer surface of the elongate body and is movable based on radially inward forces to push the free end toward the elongate body. A second slit extends from the first end of the elongate body to an internal end along the elongate body. Also provided is a method of implanting an intramedullary stem into a bone.