Side-Loading Implant Coupling With Cam Wedge Fixation
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Solution Overview
Problem
Existing implant systems face challenges in securely coupling components due to micromotion and stress concentration, particularly in anatomical regions with limited space, leading to potential fatigue failure and catastrophic failure.
Innovation Solution
A camming effect is created by a fixation bolt to distribute loads across substantial contact areas, generating a clamping action and frictional engagement over a substantial surface area, reducing stress concentration and risk of fatigue failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Morse taper coupling design is used to connect implant components, then the components can lock together securely, but the intramedullary part must be displaced away from adjacent osseous and soft tissues to provide sufficient room for assembly, which is not always possible and may cause soft tissue damage
Solution Approach 1:
The patent transitions from axial coupling (Morse taper requiring displacement away from tissues) to lateral coupling where the proximal end of the intramedullary part engages with the distal end of the stem component from the side. This dimensional change allows assembly without displacing the intramedullary part away from soft tissues, eliminating the harmful effect while maintaining secure coupling.
2Ease of operation
If a tongue-in-groove sliding connection is used for side loading, then one part can engage the other and slide along a predefined path, but micromotion between components occurs due to tolerance differences, resulting in stress concentration and potential fatigue failure
Solution Approach 1:
The fixation component is divided into distinct functional segments: a shaft portion that engages the intramedullary part, a cam portion that engages the stem component, and a nut portion that threads into the stem. This segmentation allows each portion to perform its specific function optimally while distributing loads across multiple engagement points, reducing stress concentration and micromotion.
Solution Approach 2:
The cam portion is designed with specific geometric parameters (cam angle, cam radius, cam profile) that transform the linear motion of the shaft into rotational motion of the cam, generating clamping force. By optimizing these parameters, the design achieves secure locking while distributing contact stresses over substantial surface areas, reducing fatigue failure risk.
3Stability of the object's composition
If a fixation bolt is advanced through a passage to secure components, then the components are fixed in position, but stress concentration occurs at the bolt-traversing junctions due to tolerance differences and micromovement
Solution Approach 1:
The cam portion acts as an intermediary element between the shaft and the stem component. Instead of directly bolting components together (which creates stress concentration at junctions), the cam mediates the connection by converting linear motion into rotational motion that generates distributed clamping force through friction and contact pressure over substantial surface areas.
Solution Approach 2:
The fixation component merges multiple functions into a single integrated structure: positioning (shaft), load distribution (cam), and securing (nut portion). This merging eliminates the need for separate bolts that would create stress concentration points, while maintaining stable component fixation through distributed contact forces.
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 design effectively reduces micromotion and stress concentration, enhancing the stability and longevity of the implant system by distributing loads and generating a frictional holding force.
Implementation Method 1
generate a frictional holding force between the at least one surface on the one of the terminal part and intramedullary part and the at least one surface on the other of the terminal part and intramedullary part that resists relative movement
Implementation Method 2
advancing the fixation component into an opening defined by at least one of the terminal part and intramedullary part and thereby producing a wedging action
Data Source
AI summary
An implant system and method of placing the implant system. The implant system has: an intramedullary part with a stem configured to be directed into a bone/bone part; and a terminal part which in turn cooperates with another mechanical or anatomical part. Connectors on the intramedullary part and terminal part cooperate so that the connectors thereon can be placed in a starting position and thereafter relatively moved within a first path to be engaged. A fixation component is advanced into an opening defined by the intramedullary part and/or terminal part to produce a wedging action that generates forces between cooperating surfaces/parts on the intramedullary part and terminal part applied in directions other than along the line of the first path of the terminal part and the intramedullary part.