Polyaxial Pedicle Screw Retainer with Deflectable Tabs
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Solution Overview
Problem
Current spinal stabilization systems lack versatile and easily configurable vertebral anchors that can securely couple bone screws to a housing in a desired angular orientation, limiting their effectiveness in dynamic stabilization procedures.
Innovation Solution
The development of polyaxial bone anchors with a housing, retainer, and resilient spring mechanisms that allow for the secure positioning and retention of bone screws at various angular orientations, enabling flexible assembly and configuration to accommodate elongate stabilization members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional rigid fixation systems are used, then spinal alignment is restored, but the system lacks flexibility in angular orientation and configurability
Solution Approach 1:
The retainer is designed with resilient tabs that can deflect radially outward to allow insertion of the bone screw head at various angles, then return to a locked position to secure the screw. This dynamic mechanism enables polyaxial rotation while maintaining secure fixation, resolving the contradiction between angular flexibility and assembly simplicity
Solution Approach 2:
The vertebral anchor is divided into separate components: a housing, a retainer with deflectable tabs, and a bone screw with a head portion. This segmentation allows each component to be optimized independently - the retainer provides angular flexibility through its segmented tab structure, while the housing provides stable mounting, and the screw provides secure bone attachment
2Reliability
If the retainer outer diameter is larger than the housing bore diameter, then secure retention of the bone screw is achieved, but the retainer cannot be inserted into the housing
Solution Approach 1:
The retainer tabs are designed to change their radial dimension dynamically - they can be compressed radially inward during insertion to pass through the housing bore, then spring back to their original larger diameter to securely retain the bone screw head. This parameter change resolves the contradiction between retention security and assembly feasibility
Solution Approach 2:
The retainer is constructed with flexible, deflectable tabs that can temporarily deform to fit through the housing bore, then return to their rigid retained shape. This flexibility allows the retainer to transition between two states: insertable (compressed) and retainable (expanded), solving the apparent dimensional conflict
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
These anchors provide secure and adjustable fixation of elongate members, allowing for effective spinal stabilization while accommodating various spinal conditions, enhancing the flexibility and stability of spinal stabilization systems.
Implementation Method 1
a resilient spring means positioned in the bore of the housing and configured to urge the retainer toward the lower end of the housing
Data Source
AI summary
A polyaxial bone anchor including a housing, a bone screw, and a retainer for pivotably coupling the head of the bone screw to the housing. The retainer is positioned into the bore of the housing and includes a plurality of alternating tabs and slots circumferentially arranged to define a cavity for receiving the head portion of the bone screw therein. The retainer is axially moveable in the housing from a first position in which the head portion is not passable through the lower opening of the retainer to a second position in which the head position is passable through the lower opening of the retainer.