Unicortical Bone Anchor With Rotating Toggle Element
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Solution Overview
Problem
Current lateral mass screw fixation techniques for cervical spine stabilization pose risks to the vertebral artery and nerve root due to the small volume of bone involved and are suboptimal in osteopenic bone, leading to potential construct failure and the need for revision surgery.
Innovation Solution
A bone anchor system with a distal toggle element that rotates between stowed and deployed orientations, secured by a flange that abuts the cortical surface, providing enhanced fixation in unicortical bone, and a method for securing and disengaging the anchor using actuation mechanisms to minimize risk of injury and improve fixation strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If lateral mass screws are placed in as long a length of bone as possible to maximize fixation strength, then fixation strength is improved, but the risk of injury to the vertebral artery or nerve root increases
Solution Approach 1:
The bone anchor system divides the fixation function into two distinct components: a flange that engages the cortical bone surface and a toggle element that engages the cancellous bone interior. This segmentation allows each component to optimize its engagement depth independently, achieving strong fixation without excessive cortical penetration that could harm adjacent neural structures.
Solution Approach 2:
The invention transitions from traditional longitudinal screw engagement to a combination of surface abutment (flange against cortical exterior) and internal expansion (toggle element within cancellous bone). This dimensional shift enables fixation strength to be achieved through a different geometric approach that avoids deep cortical penetration.
2Device complexity
If lateral mass screws rely on a small area of cortical bone in combination with highly variable cancellous bone, then the device complexity is reduced, but the fixation reliability in osteopenic bone deteriorates
Solution Approach 1:
The bone anchor system divides the fixation function into two distinct components: a flange that engages the cortical bone surface and a toggle element that engages the cancellous bone interior. This segmentation allows each component to optimize its engagement depth independently, achieving strong fixation without excessive cortical penetration that could harm adjacent neural structures.
Solution Approach 2:
The toggle element is pre-configured in a compressed state during insertion, and upon deployment, it expands preliminarily to engage the cancellous bone before final tightening. This preliminary expansion ensures secure engagement in osteopenic bone where bone density is reduced, providing reliable fixation before the construct is fully loaded.
3Strength
If the distal toggle element is rotated from stowed to deployed orientation to abut the interior surface of the cortex, then fixation strength is improved, but the device complexity increases
Solution Approach 1:
The toggle element is designed to be dynamically deployable, transitioning from a compact stowed orientation during insertion to an expanded deployed orientation for fixation. This dynamic transformation allows the device to achieve strong fixation through mechanical expansion rather than requiring complex threading or expansion mechanisms, balancing strength enhancement with acceptable device complexity.
Data Source
AI summary
A bone anchor may include a shaft having a distal end and a distal toggle element rotatably coupled to the distal end such that the distal toggle element may be rotatable between: a stowed orientation in which the distal toggle element may be insertable into a bone through an aperture formed in a cortex of the bone; and a deployed orientation in which the distal toggle element may be positioned to abut an interior surface of the cortex around the aperture. The bone anchor may also include a flange having a shoulder that may be moveable distally toward the distal toggle element to abut an exterior surface of the cortex.