Polyaxial Bone Screw Locking Bushing Mechanism
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Solution Overview
Problem
Current spinal immobilization systems require complex procedures to tighten spinal screw-assemblies at specific angles, involving the insertion and removal of rods and set screws, which complicates the surgical process.
Innovation Solution
A locking bushing mechanism that allows provisional locking of a polyaxial head on a fixed head of a bone screw, using an elongated housing with a sliding inner shaft and actuator to engage the bushing between the polyaxial head and the fixed head, enabling frictional locking without the need for initial rod or set screw insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rod and set screw are inserted to tighten the spinal screw-assembly at a specific angle, then the spinal screw-assembly can be securely locked, but the surgical procedure becomes more complex and time-consuming
Solution Approach 1:
The invention extracts the essential locking function from the complex rod-and-set-screw system and implements it through a simplified bushing mechanism. The bushing is inserted into the polyaxial head and secured with a set screw, separating the locking action from the rod insertion process and eliminating the need for complex sequential operations.
Solution Approach 2:
The bushing is pre-positioned within the polyaxial head before rod insertion, and the set screw is pre-installed to secure the bushing. This preliminary preparation allows the locking mechanism to be ready in advance, eliminating the need for complex post-insertion adjustments and reducing surgical steps.
2Strength
If a rod and set screw are inserted to tighten the spinal screw-assembly, then the components can be securely fastened, but the surgical time increases due to insertion and removal steps
Solution Approach 1:
The bushing and set screw are prepared and positioned in advance within the polyaxial head, creating a ready-to-lock mechanism before the rod is inserted. This eliminates the need for time-consuming insertion and removal of additional components during surgery, as the locking action is achieved through the pre-positioned set screw.
Solution Approach 2:
The time-consuming rod insertion and removal steps are eliminated by extracting the locking function to a separate bushing mechanism. The set screw directly secures the bushing against the polyaxial head, achieving fastening without requiring the rod to be inserted and removed for tightening purposes.
3Reliability
If the polyaxial head is locked with a distal end of couplers, then the head is securely fixed, but the locking mechanism becomes more complex
Solution Approach 1:
The invention extracts the locking function from the complex coupler system and implements it through a simple bushing secured by a set screw. The set screw engages the bushing, which is positioned against the polyaxial head, creating a straightforward locking mechanism that replaces the complex coupler-based approach.
Solution Approach 2:
The bushing serves as an intermediary element between the set screw and the polyaxial head. Instead of the set screw directly engaging the polyaxial head or complex couplers, the bushing mediates the connection, simplifying the overall mechanism while maintaining secure locking.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution simplifies the surgical process by allowing provisional tightening of spinal screw-assemblies at specific angles before rod or set screw placement, reducing procedural complexity and time.
Implementation Method 1
The distal portion forces the bushing into frictional engagement between the fixed head of the screw and the polyaxial head
Data Source
AI summary
An apparatus for provisionally locking a polyaxial head on a fixed head of a bone screw using a locking bushing includes an elongated housing with a proximal end and a distal end, the distal end having couplers for releasably coupling with the polyaxial head; an inner shaft slidably engaged within the housing and including a distal portion, a middle portion, and a proximal portion; and an actuator that selectively positions the inner shaft within the housing to engage at least one of the distal portion, the middle portion, and the proximal portion with at least one of the couplers and the bushing disposed between the distal portion and the fixed head of the bone screw.