Expandable Tibial Stem With Retractable Anchoring for Implant Stability
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Solution Overview
Problem
Existing tibia stem components face issues with pistoning and loosening, and inadequate bone in-growth, leading to implant instability and migration, especially in cases of limited bone availability.
Innovation Solution
A retractable member in the tibial stem is controllably movable between retracted and deployed positions, engaging the intramedullary canal of the tibia to enhance anchoring, with a rotational actuator for controlled deployment and retraction, and a coating to promote bone in-growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tibial stem uses a fixed design without retractable members, then the device complexity is low, but the implant stability and anchoring strength are insufficient leading to loosening and migration
Solution Approach 1:
The patent applies the dynamics principle by incorporating retractable members that can transition between retracted and deployed positions. These members extend outward to engage the intramedullary canal bone surface, providing dynamic anchoring that adapts to the implant-bone interface. The rotational actuator enables controlled deployment of these members, transforming the static tibial stem into a dynamic system that can actively engage with bone tissue to prevent loosening and migration while maintaining manageable complexity through controlled actuation mechanisms.
2Reliability
If the tibial stem uses engaging features to anchor in bone, then the implant stability improves, but the ease of replacement deteriorates due to bone in-growth inhibition
Solution Approach 1:
The retractable members provide dynamic engagement that can be activated after initial implantation to enhance anchoring when needed, while their ability to be retracted allows for potential future removal or replacement. The rotational actuator system enables controlled deployment of these engagement features, providing strong anchoring through bone engagement while maintaining the capability to retract members if replacement becomes necessary, thus balancing stability with future retrievability.
Solution Approach 2:
The patent segments the anchoring function into separate retractable members that can be independently controlled. This segmentation allows the engagement features to be deployed only when needed for enhanced anchoring, rather than being permanently engaged. The modular nature of these retractable members, controlled by the rotational actuator, enables selective engagement and potential retraction, facilitating easier replacement compared to fully integrated engagement structures while still providing improved implant stability when the members are deployed.
3Strength
If retractable members are added to the tibial stem, then the anchoring strength improves, but the manufacturing complexity increases
Solution Approach 1:
The retractable members are nested within the tibial stem structure, housed in recesses or channels of the stem body. The rotational actuator is also nested within the stem, with its tool interface accessible through the tibial tray. This nesting arrangement allows the complex anchoring mechanism to be integrated into the existing stem geometry without requiring separate external components, thereby improving anchoring strength while minimizing the increase in manufacturing complexity through space-efficient integration.
Data Source
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AI summary
An ankle prosthesis is provided that includes a tibial stem (110) with a retractable member (130) configured to be controllably movable between a retracted position and an extended position so that in the extended position the retractable member engages the surface of the bone that defines an intramedullary canal so as to enhance anchoring of the tibial stem within the tibia.