Polyaxial Locking Interface With Corrugated Spherical Surfaces
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Solution Overview
Problem
Existing medical devices face challenges in preventing screws from migrating, unthreading, or backing out, particularly in retention interfaces and interlocking mechanisms between screw heads and sockets, which can lead to instability and failure in medical applications.
Innovation Solution
The development of a polyaxial locking interface featuring a head with external corrugations and a socket with internal corrugations, allowing for alignment or misalignment, providing alternating zones of contact and clearance to securely lock the head at various angles, thereby preventing migration and ensuring stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional screw-retention interface is used, then the structure is simple, but the screw may migrate, unthread, or back out leading to instability
Solution Approach 1:
The socket is formed with a spherical interior surface that receives and engages the spherical exterior surface of the head. This spherical geometry allows the head to be locked at various angular orientations while preventing migration and unthreading, resolving the contradiction between reliability and complexity by using curved surfaces to enable polyaxial locking.
Solution Approach 2:
The head is inserted into and nested within the socket, with the spherical exterior surface of the head fitting within the spherical interior surface of the socket. This nesting arrangement allows the smaller head component to be contained within the larger socket while maintaining engagement features that prevent backout and migration.
2Adaptability or versatility
If a fixed-angle locking interface is used, then the alignment is precise, but the adaptability to various angular orientations is limited
Solution Approach 1:
The locking interface transitions from a fixed-angle design to a dynamic polyaxial design where the head can be locked at various angular orientations. The spherical engagement surfaces allow the head to assume different angles relative to the socket while maintaining secure locking, providing adaptability to various angular orientations without compromising engagement precision.
Solution Approach 2:
The engagement interface is segmented into distinct zones: an upper engagement zone with alternating peaks and valleys for locking, a lower engagement zone for additional security, and a spherical interior surface for polyaxial movement. This segmentation allows the head to be secured at multiple angles while maintaining precise alignment through the distributed engagement features.
3Reliability
If a polyaxial locking interface with corrugations is used, then the screw is securely locked at various angles, but the manufacturing complexity increases
Solution Approach 1:
Both the head and socket are formed with spherical surfaces that can be manufactured using standard spherical machining or forming processes. The corrugations are created as alternating peaks and valleys on these spherical surfaces, which can be achieved through conventional manufacturing techniques, balancing locking security with ease of manufacture.
Solution Approach 2:
The corrugation features (peaks and valleys) are localized to specific zones on the spherical surfaces rather than covering the entire surface. The upper engagement zone contains alternating peaks and valleys for primary locking, while the lower engagement zone provides additional security features. This localized approach maintains manufacturing simplicity while achieving secure locking at various angles.
Data Source
AI summary
An interlocking interface retains a screw head in a socket to prevent migration of the screw head out of the socket, or to lock the screw head in the socket. The interlocking interface may retain or lock the screw at various polyaxial angles with respect to the socket. The screw head includes external corrugations. The socket includes an internal corrugated structure which interlocks with the external corrugations of the screw head when the screw is at various polyaxial angles with respect to the socket. A counterbore may be adjacent either or both ends of the socket.