Semi-constrained Polyaxial Ankle Implant
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Solution Overview
Problem
Current ankle prosthetics face high failure rates due to inadequate design addressing the complex biomechanics of the ankle joint, limited access, and mismatched articular surfaces, leading to issues like loosening, wear, and stress concentration, particularly neglecting frontal plane motion influenced by the subtalar joint axis.
Innovation Solution
A semi-constrained polyaxial endoprosthetic ankle joint replacement with a dual bearing component and bone anchoring components allowing independent movement, incorporating a tibial and talar component with articulating surfaces that mimic natural ankle joint motion, including rotational and translational movements in the sagittal and frontal planes, while limiting transverse plane motion to reduce stress and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a semi-constrained ankle prosthesis with fixed bearing is used, then the implant provides stable attachment to bone, but the articular surfaces experience edge loading and high stress due to inability to accommodate natural joint motions
Solution Approach 1:
The bearing component is designed to move dynamically relative to both the tibial and talar components, allowing the implant to accommodate natural ankle joint motions including plantar/dorsiflexion, rotation, and translation. This dynamic capability distributes loads more evenly across the articular surfaces, reducing edge loading and stress concentration while maintaining stable bone attachment.
2Adaptability or versatility
If an unconstrained ankle prosthesis with mobile bearing is used, then the implant allows natural joint motion, but the interface between components lacks stability leading to increased loosening risk
Solution Approach 1:
The prosthesis employs different constraint levels at different interfaces: the bearing-tibial component interface and bearing-talar component interface have different geometric constraints and contact characteristics. This local differentiation allows natural motion at the articulating surfaces while maintaining stable attachment at the bone interfaces, resolving the contradiction between motion capability and component stability.
3Device complexity
If the bearing component is locked to the tibial component, then the implant structure is simplified, but the articular surfaces experience point loading and higher stress due to mismatched radii
Solution Approach 1:
The bearing component moves dynamically relative to both the tibial and talar components, allowing the implant to accommodate natural ankle joint motions including plantar/dorsiflexion, rotation, and translation. This dynamic capability distributes loads more evenly across the articular surfaces, reducing edge loading and stress concentration while maintaining stable bone attachment.
4Device complexity
If the prosthesis does not account for subtalar joint axis influence, then the implant design is simplified, but the talar component function and position are altered leading to abnormal wear
Solution Approach 1:
The prosthesis incorporates polyaxial movement capability that accounts for the influence of the subtalar joint axis on talar component position and function. By allowing motion in multiple axes rather than constraining movement to a single plane, the design accommodates the complex biomechanics of the ankle-hindfoot complex, distributing stresses more evenly and reducing abnormal wear.
Data Source
AI summary
A semi-constrained polyaxial ankle joint replacement implant has a dual bearing component, a tibial component or plate adapted for attachment to a tibia or fibula bone, and a talar component or plate adapted for attachment to a talus or calceneus bone of the foot. The dual bearing component includes a superior bearing providing gliding articulation/translation between it and the tibial component, and an inferior bearing providing gliding articulation/translation between it and the talar component. The tibial plate has peripheral transversely extending flanges that semi constrain or limit movement relative to the superior bearing and/or vice versa. The inferior bearing has a flange extending upwardly from the superior surface thereof that is received in an opening in the intermediate plate to semi constrain or limit movement relative between the two components.