Expandable Bone Screw Struts for Stable Anchoring in Osteoporotic Bone
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Solution Overview
Problem
Pedicle screws and other bone screws face significant issues with loosening, particularly in patients with compromised bone quality such as osteoporosis, leading to poor clinical outcomes and increased healthcare costs, due to the challenge of securely anchoring in vertebrae with varying bone densities and anatomical constraints.
Innovation Solution
A bone screw design featuring an expandable element with struts that applies radial and torsional forces through a compressible intermediate portion, allowing for bicortical or unicortical anchoring, enhancing stability and grip in bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pedicle screws are used with standard anchoring methods, then the surgical procedure is simple and quick, but the screw loosening rate is high especially in osteoporotic bone
Solution Approach 1:
The bone screw transitions from a static structure to a dynamic one through its expandable struts that can change configuration from linear to radial. This dynamic transformation allows the screw to adapt its anchoring mechanism to different bone densities, providing enhanced reliability in osteoporotic bone while maintaining a relatively simple initial insertion structure.
Solution Approach 2:
The screw body is segmented into multiple expandable struts that can independently engage with the bone. This segmentation allows each strut to provide individual anchoring points, increasing overall reliability without requiring a completely complex monolithic structure. The struts can be thought of as modular components that work together to solve the anchoring problem.
2Reliability
If bicortical anchoring approach is used to ensure secure screw anchoring, then screw stability is improved, but the surgical risk increases due to proximity to vital structures
Solution Approach 1:
The screw engages bone in multiple dimensions through its expandable struts that radiate outward in radial directions. This multi-dimensional engagement provides secure anchoring without requiring the strut to traverse the entire bone depth as in bicortical approaches. The struts engage cortical and cancellous bone at different depths and angles, distributing mechanical loads across multiple bone layers without penetrating through to the other side.
Solution Approach 2:
Each strut is designed with specific local properties including varying lengths, thicknesses, and engagement depths tailored to engage different bone types (cortical vs. cancellous). This local quality optimization allows each strut to provide targeted anchoring in the most suitable bone region, achieving high reliability without the need for deep bicortical penetration that would increase surgical risk.
3Reliability
If the bone screw struts are made longer to increase engagement with bone, then anchoring stability is improved, but the risk of cortical bone perforation and damage to vital structures increases
Solution Approach 1:
The struts are designed with asymmetric properties where each strut can have different lengths, thicknesses, and engagement characteristics. This asymmetry allows optimization of each strut's engagement depth to match the local bone quality and anatomy, providing sufficient anchoring stability while preventing any single strut from being excessively long and risking cortical perforation. The asymmetric design enables tailored engagement without uniform over-penetration.
Solution Approach 2:
The strut parameters (length, thickness, engagement depth) are optimized within specific ranges to achieve the desired balance between anchoring stability and safety. By carefully controlling these parameters, the design ensures sufficient bone engagement for reliability while maintaining safety margins that prevent cortical perforation and damage to vital structures.
4Object-affected harmful factors
If the bone screw struts are made thinner to reduce cortical bone damage, then the risk of bone perforation is reduced, but the screw's ability to engage and anchor in bone is compromised
Solution Approach 1:
The anchoring function is segmented across multiple struts rather than relying on a single thick strut. This segmentation allows each individual strut to be thinner and less aggressive, reducing the risk of cortical bone damage, while the collective action of multiple struts provides sufficient anchoring stability. The distributed engagement strategy compensates for the reduced individual strut strength.
Solution Approach 2:
The screw utilizes composite construction combining materials with different properties optimized for specific functions. The strut materials are selected to provide adequate strength and engagement capability while maintaining thinner dimensions that reduce cortical bone damage risk. The composite design allows optimization of both engagement effectiveness and safety margins.
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 expandable design improves screw anchoring, reducing loosening rates and enhancing stability in diverse bone qualities, including osteoporotic bone, by applying compressive and torsional forces that securely engage the screw within the bone.
Implementation Method 1
The expandable element of the bone screw may be shortened, which may exert a radial force (i.e., compression) and a twisting force (i.e., torsion) on the struts
Implementation Method 2
The expandable element of the bone screw may be shortened, which may exert a radial force (i.e., compression) and a twisting force (i.e., torsion) on the struts
Implementation Method 3
The struts may, in turn, exert compressive and torsional forces on bone into which the bone screw is inserted
Data Source
AI summary
A bone screw includes an expandable section with struts that expand and twist to engage bone and, thus, to secure the orthopedic screw within the bone. Expansion of the expandable section may occur as the expandable section is axially or longitudinally compressed. Such compression may be effected with an interior element of the bone screw and, optionally, with a tool. Methods for implanting bone screws are also disclosed.