Ellipsoidally-Shaped Humerus Head Prosthesis Anchoring
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Solution Overview
Problem
Existing shoulder joint prostheses, particularly humerus implants, suffer from high wear of the articular cartilage of the glenoid, leading to reduced mechanical stability and shorter lifespan, with prior designs either requiring an elongated shaft anchored in the humerus or resulting in excessive wear without adequate anchoring.
Innovation Solution
A humeral head prosthesis with a half-ellipsoidal articulating surface and a conical recess, anchored without a shank in the humerus shaft, featuring a bone screw component with offset center axis and a head adapter for improved anchoring and load distribution, reducing wear and enhancing mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a spherical cap prosthesis is used with simple cement-free anchoring, then the anchoring is simple and has excellent mechanical properties, but the wear of the articular cartilage of the glenoid increases significantly
Solution Approach 1:
The prosthesis head is designed with an ellipsoidal shape instead of a spherical cap, creating a more elongated articulating surface that increases the contact area with the glenoid. This geometric modification distributes the mechanical load over a larger surface area, thereby reducing the surface pressure and wear on the articular cartilage while maintaining the cement-free anchoring advantage
2Stability of the object's composition
If an elongated shaft is anchored in the humerus to provide stability, then mechanical stability is improved, but the device complexity and surgical difficulty increase
Solution Approach 1:
The prosthesis is divided into separate components: a head portion with the ellipsoidal articulating surface and an anchoring portion with conical recesses. The head is anchored directly into the humerus head without requiring an elongated shaft extending into the humerus shaft, simplifying the overall structure while maintaining mechanical stability through direct bone integration
Solution Approach 2:
The ellipsoidal shape of the prosthesis head provides inherent mechanical stability through its geometric form, which distributes loads more effectively than a spherical cap. This shape, combined with direct anchoring into the humerus head, achieves stability without the need for complex elongated shaft structures
3Ease of manufacture
If a spherical cap design is used, then the manufacturing is simple, but the contact area with the glenoid is small leading to high surface pressure
Solution Approach 1:
The ellipsoidal geometry of the prosthesis head creates an elongated articulating surface that naturally increases the contact area with the glenoid. This geometric modification, while slightly more complex than a spherical cap, remains manufacturable and provides significant benefits in load distribution and reduction of surface pressure on the articular cartilage
Data Source
AI summary
A humerus head implant includes a head cap, a fixing component, and a bone-screw component. The head cap has a shape of half-an-ellipsoid extending into a positive z-direction along the z-axis, in positive and negative x-directions, and in positive and negative y-directions. The extension along the x-direction is in a range of 0.8 to 0.95 of the extension in the y-direction. There is a conical recess having a center axis that is displaced in the negative y-direction with respect to the z-axis and configured to interface with a conical section of the fixing component. This allows for rotation of the head cap relative to the fixing component.