Removable Head Facet Screw for Continuous Compression
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Solution Overview
Problem
Conventional lumbar fusion and facet screw systems lack the ability to provide continuous compression after screw insertion, limiting the effectiveness of facet joint immobilization and fusion in spinal surgeries.
Innovation Solution
A novel screw mechanism with a removable head, a locking nut, and a collet that allows for infinite compression and locking of the facet joint using an insertion tool, enabling sequential screw insertion, compression, and locking with a single implant/instrument engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional fixed-head screw is used, then the screw head abuts the cortical surface of the bone providing initial fixation, but compression is limited only by continued screw insertion after the screw head abuts the cortical surface
Solution Approach 1:
The screw is divided into two separable parts: a head portion that remains in the bone and a shaft portion that can be removed. This segmentation allows the shaft to be pulled out after insertion, enabling infinite compression capability while maintaining strong initial fixation through the head's abutation against the cortical surface.
Solution Approach 2:
The screw transitions from a static fixed-head design to a dynamic system where the shaft can be removed and repositioned. The collet and locking nut mechanism allows the shaft to be dynamically adjusted or removed, providing flexible compression control beyond the limitations of a fixed-head design.
2Ease of operation
If multiple separate instruments are used for screw insertion, compression, and locking, then each function can be performed independently, but the procedure becomes time-consuming and complex
Solution Approach 1:
The insertion tool integrates multiple functions into a single instrument: it provides a driver for screw insertion, a compression mechanism for applying force to the facet joint, and a locking mechanism with collet and locking nut. This merging eliminates the need for multiple separate instruments, reducing surgical time while maintaining functional independence.
Solution Approach 2:
The single insertion tool serves multiple purposes: inserting the screw shaft, compressing the facet joint, and locking the assembly. The universal design allows one instrument to perform what would traditionally require three separate tools, improving efficiency without sacrificing operational flexibility.
3Adaptability or versatility
If the screw shaft is made removable for infinite compression, then compression capability is improved, but the risk of screw head breakoff increases
Solution Approach 1:
By separating the screw into head and shaft portions, the design allows the shaft to be removed and repositioned for compression while the head remains anchored in the bone. This segmentation provides compression flexibility without compromising the integrity of the remaining head portion, as it is designed to stay in place providing stable fixation.
Solution Approach 2:
The head of the screw is designed with preliminary features including a breakoff section that is weaker than the shaft, ensuring that if breakoff occurs, it happens in a controlled manner at a predetermined location. This preliminary design of the breakoff section manages the risk by ensuring failure occurs at a safe, predictable location rather than randomly within the structure.
Data Source
AI summary
A facet screw system and method includes an implant assembly having a screw with a removable head, a locking nut, and a collet. An insertion instrument is used to insert the screw, compress the facet joint, locks the implant, and breaks off the head of the screw providing a lower profile implant.