Spinal Receiver With Recessed Arms For Secure Instrument Engagement
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Solution Overview
Problem
Current bone screw and insertion instrument systems in spinal surgery face challenges with dislodgement due to torsional forces and size constraints, leading to inefficiencies in screw placement and increased procedural time.
Innovation Solution
A bone fixation system with a receiver having oppositely disposed arms and a longitudinally extending interlocking surface, combined with an insertion instrument featuring hooks that grasp the receiver's flat surfaces and outer recesses, providing a secure connection to prevent dislodgement during screw placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the head portion is designed to be as small as possible to avoid protruding from skin and impinging on adjacent anatomy, then the device size is reduced and ease of operation is improved, but the contact area of the insertion instrument with the receiver is reduced and the strength of the connection is weakened
Solution Approach 1:
The receiver is segmented into two oppositely disposed arms that define rod channels, creating multiple engagement surfaces. The insertion instrument has prongs that can engage with recesses on both arms simultaneously, distributing the connection strength across multiple contact points rather than relying on a single large contact area.
Solution Approach 2:
The connection interface is extended into the longitudinal dimension by creating recesses that extend inwardly from the outer surface of each arm. The prongs engage with these recesses at multiple depths and positions, effectively increasing the connection strength without increasing the lateral footprint of the head portion.
2Device complexity
If the contact area and depth of recesses are minimized due to size constraints, then the device compactness is improved, but the reliability of the connection between insertion instrument and screw is reduced
Solution Approach 1:
The recesses are strategically positioned and dimensioned to provide optimal engagement at specific locations on the receiver arms. The prongs are designed with specific geometries that match the recess shapes, creating localized high-strength engagement zones that maximize connection reliability within the compact overall structure.
Solution Approach 2:
The recesses are pre-formed in the receiver arms with precise geometries that guide the prongs into proper engagement positions. This preliminary structuring ensures that when the insertion instrument is applied, the connection is immediately established at the optimal locations without requiring adjustment or additional steps.
3Reliability
If the prongs are covered to close them onto the receiver, then the connection security is improved, but the ability to navigate between crowded anatomy is reduced
Solution Approach 1:
The prongs are designed to be dynamic rather than static - they can splay outwardly during navigation to pass through crowded anatomy, then close onto the receiver upon engagement. This dynamic behavior allows the prongs to adapt their configuration based on the operational phase, providing both navigation capability and connection security.
Solution Approach 2:
The insertion instrument employs a composite structure with flexible prong elements that can deform elastically. The prongs are made of material or designed with geometry that allows them to flex outward for navigation and then spring closed for secure engagement, combining the properties of flexibility and rigidity in a single component.
4Ease of manufacture
If torsional forces are applied during screw placement, then the screw insertion function is achieved, but the insertion instrument may dislodge from the screw
Solution Approach 1:
The insertion instrument combines multiple engagement features into a single integrated structure. The prongs simultaneously engage with recesses on both arms of the receiver, and the tower structure provides additional support and alignment. This merged structure distributes torsional forces across multiple engagement points, preventing dislodgement during screw insertion.
Solution Approach 2:
The recesses are designed with sufficient depth and appropriate geometries to accommodate the prongs with some compliance. This preliminary design feature acts as a cushion that absorbs the shock and lateral forces generated during torsional screw insertion, preventing the instrument from dislodging while still allowing effective force transmission for screw placement.
Data Source
AI summary
A bone fixation system is provided. The bone fixation system includes a receiver coupled to a bone fastener. The receiver includes an inner bore and channel that provides a seat for an elongate fixation rod. The inner surface of the receiver includes locations for an instrument to securely grasp the receiver from the inside of the receiver without obstructing the inner bore. The instrument is provided with hooks that uniquely grasp the receiver from the inside and outside of the receiver. The instrument also includes flexible prongs configured to engage recesses formed in the outer surface of the receiver. The prongs have prong extensions that conform in shape to the recesses. The prongs and recesses have three separated perimeter surfaces each having a component perpendicular to the longitudinal axis. The bone fixation system provides a strong connection between the screw and the instrument for the demands unique to spinal surgery.