Rotatable Crown Bone Fastener for Low-Force Spinal Rod Attachment
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Solution Overview
Problem
Current spinal implant systems for treating disorders such as scoliosis and degenerative disc disease often require complex assembly and high forces, which can put additional stress on vertebrae and complicate surgical procedures, while also lacking efficient mechanisms for secure attachment of spinal rods to vertebral members.
Innovation Solution
A modular bone fastener system featuring a receiver with a rotatable crown that translates a spacer to orient a band or ring for secure attachment of a spinal rod, allowing for manual assembly without instrumentation and minimizing pre-load on vertebrae, using a snap ring mechanism for secure fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex assembly mechanisms are used to secure spinal rods to vertebral members, then attachment reliability is improved, but device complexity and surgical procedure complexity increase
Solution Approach 1:
The bone fastener is divided into multiple components: a receiver that engages the spinal rod, a band that secures the rod to the vertebra, and a crown mechanism that controls assembly. This segmentation allows each component to perform its specific function simply, while collectively providing secure attachment without complex overall design
Solution Approach 2:
The crown mechanism enables the band to automatically orient itself into a capture orientation with the spinal rod through rotational movement. The system is self-assembling once the crown is rotated, eliminating the need for complex instrumentation or multi-step assembly procedures during surgery
2Strength
If high forces are applied during assembly to ensure secure fixation, then attachment strength is improved, but stress on vertebrae increases
Solution Approach 1:
The crown mechanism provides dynamic control over the assembly process, allowing gradual engagement of the band with the spinal rod through rotational movement. This dynamic approach distributes the assembly force over multiple small movements rather than requiring a single high-force application, reducing peak stress on the vertebrae
Solution Approach 2:
The crown acts as an intermediary mechanism between the surgeon's manual input and the band's engagement with the spinal rod. It translates simple rotational motion into the precise linear movement needed to orient the band, providing mechanical advantage and force distribution that protects the vertebrae from excessive stress
3Manufacturing precision
If specialized instrumentation is used for assembly, then manufacturing precision is improved, but ease of operation during surgery deteriorates
Solution Approach 1:
The bone fastener components are designed to self-align and self-assemble through simple manual manipulation. The crown's rotational movement automatically orients the band into the correct capture orientation with the spinal rod, eliminating the need for specialized alignment instruments or complex positioning procedures
Solution Approach 2:
The complex alignment and positioning functions that would normally require specialized instrumentation have been extracted from the assembly process and built into the inherent geometry of the bone fastener components. The receiver, band, and crown are shaped to guide themselves into proper alignment through simple manual manipulation
Data Source
AI summary
A bone fastener includes a receiver defining an implant cavity and having an inner surface defining a slot. A band is disposable within the slot. A spacer disposable within the slot. A crown is rotatable relative to the receiver to translate the spacer relative to the inner surface such that the spacer orients the band in a capture orientation with the shaft. A screw shaft connectable with the receiver by the band and configured to penetrate tissue. Implants, systems, instruments and methods are disclosed.