Bone Anchor Extension Device with Nested Sleeve Coupling
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Solution Overview
Problem
Existing extension devices for bone anchors in minimally invasive surgery lack robustness and safety in preventing translational and rotational movements, which complicates surgical steps like compression and distraction.
Innovation Solution
A system comprising a first sleeve and a second sleeve with a coupling structure, including an interlocking bushing, that inhibits translational and rotational movements relative to the receiving part of the bone anchor, ensuring a secure connection for rod placement and subsequent surgical adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing extension devices are used for bone anchors, then the device can be inserted through small skin incisions, but the connection lacks robustness and allows unwanted translational and rotational movements
Solution Approach 1:
The extension device is divided into two separate sleeves (first sleeve and second sleeve) that can be independently positioned and secured. The first sleeve engages with the receiving part while the second sleeve engages with the rod, allowing each component to be optimized for its specific function and secured independently to eliminate unwanted movements
Solution Approach 2:
The second sleeve is positioned within the first sleeve, creating a nested configuration. This allows the extension device to maintain a compact profile while providing multiple engagement points. The nested structure enables both sleeves to be secured to their respective components (receiving part and rod) simultaneously, enhancing overall connection stability
2Adaptability or versatility
If the extension device allows controlled movement for surgical adjustments, then surgical flexibility is improved, but connection stability deteriorates
Solution Approach 1:
The extension device provides dynamic adjustability during surgery by allowing the second sleeve to be positioned at different locations along the first sleeve. Once the desired position is achieved, the connection is secured to maintain stability. This enables surgical adjustments (compression and distraction) to be performed by repositioning the rod relative to the bone anchor while maintaining a stable locked connection during each adjustment phase
3Reliability
If a robust coupling structure is implemented to prevent movement, then connection stability is improved, but device complexity increases
Solution Approach 1:
The coupling function is segmented between two separate sleeves rather than using a single complex coupling mechanism. Each sleeve has a relatively simple structure optimized for its specific engagement (first sleeve with receiving part, second sleeve with rod), reducing overall structural complexity while achieving robust connection stability through the combined action of both sleeves
Solution Approach 2:
The nested configuration of the second sleeve within the first sleeve allows the device to maintain a compact profile without requiring additional external coupling components. This integrated nested structure achieves robust connection stability while minimizing device complexity by eliminating the need for separate coupling mechanisms
Data Source
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AI summary
An extension device for a bone anchor is provided, wherein the bone anchor comprises an anchoring section (100) for anchoring in a bone and a receiving part (200, 200') connected to the anchoring section, the receiving part comprising a central axis (C) and a channel (204) for receiving a rod, wherein sidewalls of the channel form two free legs (205a, 205b). The extension device further comprises a first sleeve (1, 1', 1") with a first sleeve axis (c) that is coaxial with the central axis (C), wherein the first sleeve (1, 1', 1") is configured to be detachably coupled to the receiving part (200, 200'), and a second sleeve (2, 2', 2", 2"') with a second sleeve axis, wherein the second sleeve is positioned within the first sleeve (1, 1', 1"). The first sleeve (1, 1', 1") is configured to contact to the receiving part (200, 200') and the second sleeve (2, 2', 2", 2"') is configured to be coupled to the receiving part so as to hinder or inhibit a rotational movement of the second sleeve (2, 2', 2", 2"') relative to the receiving part (200, 200'). The second sleeve (2, 2', 2", 2"') is connected to the first sleeve (1, 1') through a coupling member (3) that is configured to advance in the first sleeve (1, 1', 1") together with the second sleeve (2, 2', 2", 2"') in an axial direction. The first sleeve (1, 1', 1") comprises a protrusion (120a, 120b) and/or a recess at an inner surface thereof that is configured to engage a complementary structure (206a, 206b) at an outer surface of the receiving element (200, 200') to provide a form-fit connection between the first sleeve (1, 1', 1") and the receiving part (200, 200') such as to inhibit a translational movement of the first sleeve relative to the receiving part along the central axis.