Bone Anchor Drag Interface for Position Stability
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Solution Overview
Problem
Bone anchors with movable receiver members often experience unintended movement during provisional positioning in orthopedic or neurosurgical procedures, leading to alignment challenges and increased surgical complexity due to the lack of effective stabilization before locking.
Innovation Solution
Incorporation of drag interfaces, such as friction between a shank and a bushing, or between a bushing and a drag ring, along with over-rotation blocking features like grooves or lips, to maintain the relative position of the receiver member with respect to the shank before locking, preventing unintended movement while allowing intended free movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the receiver member is movably-coupled to the shank portion to allow freedom of movement during alignment, then the ease of operation is improved, but the stability of the object's composition deteriorates causing unintended movement and alignment challenges
Solution Approach 1:
A drag interface is introduced as an intermediary mechanism between the receiver member and shank portion. This drag interface provides controlled resistance to movement, allowing the receiver member to be repositioned when intentionally moved by the user while preventing unintended movement during provisional positioning. The drag interface thus mediates between the need for movability and the need for stability.
2Adaptability or versatility
If the receiver member is allowed to move freely during provisional positioning, then the adaptability is improved, but the loss of time increases due to repositioning and user fatigue
Solution Approach 1:
The drag interface acts as a mediator that reduces the need for frequent repositioning by maintaining the receiver member in the desired position once placed. This decreases surgical procedure time by eliminating the need for continuous adjustment or assistant support during rod introduction.
3Stability of the object's composition
If the receiver member is constrained to prevent movement, then the stability of the object's composition is improved, but the ease of operation deteriorates due to difficulty in alignment
Solution Approach 1:
The drag interface provides dynamic resistance to movement rather than fixed constraint. It allows the receiver member to move when intentionally repositioned by the user while preventing unintended movement during provisional positioning. This dynamic behavior enables both stability and ease of alignment.
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 drag interfaces and over-rotation blocking features ensure stable alignment and reduce surgical complexity by maintaining the desired position of the receiver member, thereby reducing user fatigue and procedural time.
Implementation Method 1
a drag ring that applies a frictional force to the bushing, the drag ring being disposed in a groove formed in the receiver member
Implementation Method 2
The bushing can exert a frictional force on the head of the shank
Implementation Method 3
friction generated by a biased saddle
Data Source
AI summary
Bone anchors and related methods are disclosed herein. In some embodiments, a bone anchor can include a drag interface. Exemplary drag interfaces include (i) friction between a shank and a bushing, (ii) friction between a bushing and a drag ring, (iii) friction generated by a biased saddle, and (iv) combinations of the above. The drag interface can help maintain the relative position between a receiver member and a shank of the bone anchor prior to locking the bone anchor, preventing unintended movement while still allowing free movement when intended by the user. In some embodiments, a bone anchor can include over-rotation blocking features, such as a groove, lip, or protrusion formed on a bushing of the bone anchor. Various other bone anchor features are also disclosed, including high aspect ratio drag rings and compressible drag posts.