Poly-axial Spinal Fixation with Tactile Feedback Locking
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Solution Overview
Problem
In orthopaedic stabilization systems, particularly spinal fixation systems, there is a need to accommodate various angular orientations between elongated members and bone engaging components, which requires secure locking mechanisms that ensure proper component alignment during assembly, as limited visualization by the surgeon can lead to ineffective fixation.
Innovation Solution
A fixation system comprising a yoke with cross bores and resiliently deflectable fingers and tabs that provide tactile and audible feedback when properly seated, ensuring secure engagement of the spinal rod and bone screw, allowing for multi-axial angular orientations and stable fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bone screw with spherically-shaped head is used to accommodate multi-axial angular orientations, then adaptability is improved, but device complexity increases due to the need for additional locking mechanisms
Solution Approach 1:
The locking mechanism is divided into multiple independent components: a set screw for axial compression, resiliently deflectable fingers for radial engagement, and tabs with cross bores for positional verification. Each component performs a specific function, allowing the complex locking task to be broken down into manageable segments that can be assembled and verified independently.
Solution Approach 2:
The resiliently deflectable fingers act as intermediaries between the bone screw head and the yoke. These fingers deflect under load to engage the tabs in the cross bores, providing both locking force and tactile/audible feedback to the surgeon without requiring direct contact between the screw head and yoke, thus simplifying the overall assembly process.
2Ease of operation
If components are assembled in situ with limited visualization, then ease of operation is improved, but reliability decreases due to inability to verify proper component orientation
Solution Approach 1:
The resiliently deflectable fingers provide both tactile feedback (physical sensation of engagement) and audible feedback (clicking sound) to the surgeon during assembly. This dual feedback mechanism allows the surgeon to verify proper component orientation and locking engagement without requiring complex visualization systems or additional imaging equipment during the surgical procedure.
Solution Approach 2:
While not explicitly using color changes, the invention employs analogous sensory feedback mechanisms where the tactile and audible signals serve as indicators of proper assembly, similar to how color changes might indicate status in other systems. The deflection of fingers and engagement of tabs create detectable signals that confirm correct positioning.
3Strength
If a set screw is used to lock components together, then strength of fixation is improved, but ease of operation worsens due to difficulty in ensuring proper orientation before tightening
Solution Approach 1:
The resiliently deflectable fingers and tabs are designed to automatically engage and lock the bone screw head and yoke in the correct orientation before the set screw is tightened. This preliminary action ensures proper component alignment is achieved automatically during assembly, eliminating the need for the surgeon to manually adjust or verify orientation before applying the locking force of the set screw.
Solution Approach 2:
The locking mechanism is designed to be self-aligning and self-verifying. As the bone screw is inserted and the yoke is positioned, the resiliently deflectable fingers automatically deflect to engage the tabs in the cross bores, creating a self-locking arrangement that verifies proper orientation without requiring external adjustment or verification by the surgeon.
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
The system ensures proper alignment and secure locking of components, providing a stable fixation assembly with tactile and audible cues, enhancing the surgeon's confidence in assembly and maintaining the fixation even under tightening, thus addressing the challenge of variable angular orientations in spinal stabilization.
Implementation Method 1
resiliently deflectable fingers extending from the base to define a slot configured to receive the rod therebetween. Each of the resiliently deflectable fingers include a tab projecting outwardly therefrom and configured to be received within a cross bore in a corresponding one of the arms of the yoke. Each tab defines a beveled face configured to bear against the opposite arms of the yoke as the insert is advanced into the slot of the yoke to deflect the resiliently deflectable fingers toward each other until the insert is advanced far enough into the yoke for the tabs to align with the cross bores in the arms of the yoke. Once the tabs are aligned with the cross bores, the resiliently deflectable arms deflect outward to their natural configuration so that the tabs engage the cross bores.
Data Source
AI summary
A fixation system comprises a rod, a fastener including a head and an elongated shank, a yoke and an insert. The yoke includes opposite arms defining a slot to receive the rod, an opening to receive the shank, a surface for supporting the fastener head, and a cross bore through each of the arms. The insert has a base configured for slidable insertion between the yoke arms, and defining a rod supporting surface and an opening sized to receive the fastener shank. The insert further includes a pair of resiliently deflectable fingers extending from the base and including a tab projecting therefrom configured to be received within a cross bore. Each tab defines a beveled face configured to bear against the yoke as the insert is advanced into the yoke slot and to deflect the fingers inward until the tabs are aligned with the cross bores.