Threaded Inner Chamber Bone Anchor for Spinal Fixation
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Solution Overview
Problem
Existing bone anchors used for spinal deformity correction often fail to achieve stable purchase in vertebral bodies, leading to undesirable movement and recurrence of spinal deformities due to inadequate screw purchase within the cancellous portion of the vertebra.
Innovation Solution
The development of bone anchors with an inner chamber that is threaded, providing a differential in force and surface tension between the inner and outer surfaces, which enhances stability, bone ingrowth, and healing by drawing additional bone into the chamber and placing it under compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If bone anchors are made shorter and wider to provide additional surface area for stable purchase in cancellous bone, then stability in cancellous bone is improved, but bicortical purchase is lost reducing overall fixation strength
Solution Approach 1:
The bone anchor is divided into distinct functional segments: a threaded outer surface for cancellous bone engagement and an inner chamber with its own threading for additional bone incorporation. This segmentation allows each portion to optimize for its specific function while working together to provide both stability and strength.
Solution Approach 2:
The inner chamber is nested within the body of the bone anchor, creating a concentric structure where the inner chamber threads engage bone material that is drawn into the chamber. This nested configuration allows the anchor to maintain a compact external profile while providing internal volume for enhanced bone engagement and compression.
2Strength
If bone anchors rely solely on cortical bone for purchase, then initial insertion strength is improved, but purchase is insufficient in vertebral bodies with thin cortex leading to movement and deformity recurrence
Solution Approach 1:
The bone anchor features different thread configurations at different locations: the outer surface has threads optimized for cancellous bone engagement, while the inner chamber has separate threading for drawing in and compressing bone material. This local differentiation of thread properties allows the anchor to reliably engage both cortical and cancellous bone components of the vertebral body.
Solution Approach 2:
The inner chamber is pre-configured with threading that actively draws bone material into the chamber during insertion and tightening. This preliminary action of drawing bone into the chamber occurs before final fixation, ensuring bone is incorporated and compressed into the anchor structure in advance, preventing subsequent movement.
3Device complexity
If traditional bone anchors are used without inner chamber threading, then device complexity is reduced, but bone ingrowth stimulation and healing acceleration are diminished
Solution Approach 1:
The inner chamber incorporates variable thread parameters including different pitch, depth, and direction compared to the outer threads. These parameter changes create differential force distributions that actively draw bone into the chamber and apply compression, stimulating bone ingrowth and accelerating healing without requiring complex external mechanisms.
Solution Approach 2:
The threaded inner chamber structure enables the bone anchor to self-compact and self-seal by drawing bone material into the chamber and compressing it during the natural tightening process. This self-service mechanism eliminates the need for additional active components or procedures to promote bone ingrowth, relying instead on the inherent mechanical properties of the threaded structure.
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
This design improves fixation and stimulates bone ingrowth, reducing the likelihood of spinal deformity recurrence by providing a more stable and effective anchor within the vertebral body.
Implementation Method 1
placing such bone under compression to accelerate healing and incorporation with the implant
Implementation Method 2
providing a differential in force and/or surface tension between various portions of the anchor
Data Source
AI summary
Bone anchors and related systems and methods for spinal deformity correction. In some implementations, two adjacent bone anchors may be advanced into respective, adjacent vertebral bodies of a spinal column. Cancellous bone may be compacted within respective inner chambers of the bone anchors. The inner chambers may comprise at least one of a plurality of bone engaging protrusions and a profile that increases in cross-sectional area, at least in part, from a proximal end of the inner chambers to a distal end of the inner chambers. A tether may then be coupled between the first and second bone anchors to apply a corrective force to at least a portion of the spinal column.