Pop-On Spinal Rod Cap Assembly for Splay Resistance and Revision
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Solution Overview
Problem
Existing spinal surgery implants face challenges with receiver-arm splay during locking and difficulty in revising previously implanted constructs due to the complexity of removing set-screws.
Innovation Solution
The system includes a cap with splay-resisting flanges and rotation-preventing/rotation-resisting wings that pop onto a receiver, preventing undesired splay and allowing easy removal through intentional splaying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If set-screws are used to lock the receiver to the rod, then securement is achieved, but removal and revision procedures become difficult
Solution Approach 1:
The locking mechanism is segmented into a cap component and a receiver component. The cap is popped onto the receiver and can be independently removed without affecting the bonescrew-vertebrae attachment, enabling easy revision procedures while maintaining securement during normal use
Solution Approach 2:
Instead of using a threaded set-screw that requires unscrewing for removal, the invention uses a pop-on cap that is pushed on for installation and can be pried off for removal. This inverted approach simplifies the removal process significantly, allowing quick access for revision procedures
2Ease of operation
If receiver arms are allowed to move during locking, then cap installation is facilitated, but unwanted splay occurs during normal use
Solution Approach 1:
The receiver arms are designed to be dynamically adjustable during installation, allowing them to splay outward to accommodate the pop-on cap. Once the cap is installed, the arms return to their stable, locked position, preventing unwanted splay during normal use
Solution Approach 2:
The cap installation process preliminarily splays the receiver arms outward to create clearance for the cap to be pushed onto the receiver. This preliminary action enables easy installation while the subsequent locked state prevents excessive splay during operation
3Reliability
If rotation prevention features are added to the cap, then cap rotation is prevented, but device complexity increases
Solution Approach 1:
The cap includes asymmetric rotation-preventing features such as wings or flanges that engage with corresponding asymmetric features on the receiver. This asymmetric design prevents cap rotation in both directions while maintaining a relatively simple overall cap structure
Solution Approach 2:
The rotation-preventing features are merged into the cap's wing structure. The same wings that provide leverage for popping the cap onto the receiver also serve as rotation-preventing elements by engaging with the receiver, thereby preventing cap rotation without adding separate complex mechanisms
Data Source
AI summary
A spinal-surgery system having a rod receiver and/or a cap having a generally cylindrical body, a set of opposing splay-resisting flanges, and a set of opposing rotation-preventing/rotation-resisting wings. Each wing has a lateral rotation-preventing portion and a lateral rotation-resisting portion. A receiver proximal end forms a wing-receiving cavity having a lateral rotation-preventing side and a lateral rotation-resisting side. Each flange has a proximal-facing splay-resist surface, and a distal-facing pop-on surface. Each receiver proximal protrusion has a proximal-facing sloped receiver pop-on surface, and a distal-facing sloped receiver splay-resist surface. Each rotation-preventing portion contacts a corresponding rotation-preventing side and each rotation-resisting portion contacts a corresponding rotation-resisting sides when the cap is popped on. The rotation-preventing portions contacting the rotation-preventing sides prevents cap rotation in a first direction. The rotation-resisting portion contacting the rotation-resisting side resists cap rotation in a second direction, but allows rotation in the second, forcing the arms to splay.