Expandable Pedicle Screw Anchor for Pullout-Resistant Fixation
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Solution Overview
Problem
Existing pedicle screw fixation technologies face issues with screw loosening and pullout, particularly in patients with poor bone quality, such as osteoporotic bone, leading to instability and potential failure of spinal fusion constructs.
Innovation Solution
The use of expandable pedicle screw implants with expandable anchors and deployable teeth that create a strong press-fit in the bone, enhancing stability and osseointegration by filling unused pedicle space and engaging cortical bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pedicle screw fixation is used, then the procedure is simple and widely applicable, but screw loosening and pullout occur especially in poor bone quality
Solution Approach 1:
The pedicle screw incorporates an expandable proximal portion that can transition from a compressed insertion state to an expanded fixation state. The expandable anchor with expansion joints allows the screw to dynamically adapt its outer diameter to engage cortical bone more effectively, improving fixation stability without requiring a completely complex implant design
Solution Approach 2:
The pedicle screw is divided into distinct functional segments: a distal threaded portion for initial anchoring, an expandable proximal portion with expansion joints for enhanced cortical engagement, and a head portion for rod attachment. This segmentation allows each portion to perform its specific function optimally while maintaining overall structural integrity
2Strength
If expandable anchors with deployable teeth are used, then primary stability and osseointegration improve, but the device complexity increases
Solution Approach 1:
The expandable anchor features deployable teeth or anchors at its distal end that are specifically designed to engage cortical bone. These teeth are strategically positioned and shaped to provide localized mechanical interlocking and stress distribution, enhancing bone-implant interface strength without requiring complex mechanisms throughout the entire implant structure
Solution Approach 2:
The expandable anchor is designed to deploy its teeth or anchors after insertion but before final rod attachment. This preliminary action of deploying the teeth creates immediate mechanical interlocking with the cortical bone, establishing primary stability before the construct is fully loaded
3Force
If the expandable anchor is expanded to fill unused pedicle space, then screw pullout resistance improves, but the insertion process becomes more complex
Solution Approach 1:
The expandable anchor is designed in a nested configuration where the expansion joints and teeth are contained within the screw body during insertion. The anchor is inserted in a compressed state through the prepared pedicle tract, then expanded in situ to fill unused pedicle space and engage cortical bone, maximizing pullout resistance while maintaining insertion feasibility
Solution Approach 2:
An expansion tool or device is used as an intermediary to facilitate the expansion of the anchor after insertion. This intermediary tool engages with the expandable portions of the anchor and applies controlled force to expand the teeth or anchors into the cortical bone, simplifying the expansion process and reducing surgical complexity
Data Source
AI summary
Pedicle bone anchor implants, assemblies, and methods thereof. The implant may include an expandable anchor having a body with expandable sections separated by one or more expansion joints, a plurality of expandable teeth, or an expandable head. The expandable anchor has a collapsed configuration and an expanded configuration, thereby creating a press-fit in adjacent bone.