Shape Memory Femoral Stem Radial Expansion Locking
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Solution Overview
Problem
Conventional femoral implants face issues such as loosening due to stress shielding, bone resorption, and periprosthetic infection, with cemented implants degrading over time and cementless implants requiring bone ingrowth and longer recovery periods, while also risking bone fracture during insertion.
Innovation Solution
A femoral stem hip implant made of shape memory material, such as Nitinol, that expands radially upon temperature increase to provide a locking force against the bone, stabilizing the implant and reducing stress shielding, and potentially incorporating a drug or porous coating to prevent infection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If cemented femoral implant is used, then initial stability is improved, but long-term reliability deteriorates due to cement degradation and loosening
Solution Approach 1:
The implant utilizes shape memory material that changes its physical state from martensitic (soft, insertable) to austenitic (rigid, stable) in response to temperature change from surgical room temperature to body temperature, providing both initial stability during insertion and long-term reliability through automatic rigidification
Solution Approach 2:
The implant exploits the phase transition of shape memory material between martensitic and austenitic phases, where the material is soft and formable at low temperature for easy insertion, then automatically transforms to a rigid phase at body temperature to provide long-term structural stability and reliability
2Reliability
If cementless femoral implant is used, then long-term reliability is improved through bone ingrowth, but initial stability deteriorates requiring extended recovery period
Solution Approach 1:
The implant changes its mechanical properties through temperature-induced phase transition, being soft at insertion temperature for easy bone engagement, then automatically becoming rigid at body temperature to provide immediate initial stability without requiring extended bone ingrowth period
Solution Approach 2:
The implant performs the stabilization action automatically upon insertion through its shape memory effect, eliminating the need for preliminary bone preparation or extended recovery periods required by conventional cementless implants
3Strength
If conventional rigid prosthesis is used, then strength is improved, but stress shielding occurs causing bone resorption
Solution Approach 1:
The implant's elastic modulus dynamically changes with temperature and phase state, being more compliant during insertion to minimize stress shielding, then achieving optimal strength at body temperature while maintaining better stress distribution compared to conventional rigid implants
4Adaptability or versatility
If shape memory material is used, then adaptability is improved through temperature-induced expansion, but device complexity increases
Solution Approach 1:
The implant performs self-adjustment of its mechanical properties through automatic phase transition in response to body temperature, eliminating the need for external control mechanisms or complex actuation systems while providing temperature-responsive adaptability
Solution Approach 2:
The implant replaces complex mechanical actuation systems with a passive thermal-responsive phase transition mechanism, where body temperature automatically triggers the martensitic-to-austenitic transformation to achieve the desired expansion and locking
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 shape memory implant achieves increased primary stability, reduces recovery time, and minimizes stress shielding, while also preventing wear particle-induced inflammation and bone loss, thus enhancing long-term stability and reducing the risk of bone fracture during insertion.
Implementation Method 1
the shape memory material within the proximal portion is in a compressed state by application of a plurality of compressive forces at a temperature below an austenitic finish temperature of the shape memory material so that the cross-section of the shape memory material expands through shape memory effect via the formation of austenite in response to a temperature increase after insertion into the aperture thereby causing a locking-force to be exerted against an inner surface of the aperture
Data Source
AI summary
A femoral stem hip implant for insertion into a surgically created aperture in a femur includes a monolithic femoral stem made of shape memory material. The stem is configured to be inserted into the aperture, has a proximal portion and a longitudinal axis. The shape memory material within the proximal portion has a cross-section perpendicular to the longitudinal axis. At least a portion of the shape memory material within the proximal portion is in a compressed state by application of a plurality of compressive forces at a temperature below an austenitic finish temperature of the shape memory material so that the cross-section expands through shape memory effect via the formation of austenite in response to a temperature increase after insertion into the aperture thereby causing a locking-force to be exerted against an inner surface of the aperture, the locking force being sufficient to stabilize the implant in the aperture.