Double-Helix Bone Screw for Flexural Fixation and Bone Ingrowth
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Solution Overview
Problem
Current bone fixation implants are stiff under compression, limiting bone growth and graft volume, and lack sufficient flexural capacity, leading to weak pullout strength and restricted bone integration.
Innovation Solution
A double helix bone screw design with opposing inner and outer helices, allowing for flexible compression and tension, increased bone graft volume, and enhanced bone integration through additive manufacturing for customized properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid body implant design is used, then implant strength is improved, but flexural capacity and bone growth promotion deteriorate
Solution Approach 1:
The solid body implant is segmented into a lattice structure with interconnected struts and nodes, creating internal voids while maintaining external integrity. This segmentation allows the implant to flex under load while preserving overall strength, and provides internal space for bone graft material.
Solution Approach 2:
The implant utilizes a porous lattice structure with controlled porosity throughout the body. This porous construction enables bone ingrowth through the implant while maintaining mechanical strength through the geometry of the lattice. The porosity also allows for flexural deformation under compressive loads.
2Adaptability or versatility
If slot style cavities are used in solid body, then bone growth through implant is improved, but bone graft volume is limited
Solution Approach 1:
The design transitions from two-dimensional slot cavities to a three-dimensional lattice structure with interconnected channels in multiple directions. This dimensional expansion allows bone growth to occur through the implant from multiple pathways simultaneously, while the internal void spaces throughout the lattice provide extensive volume for bone graft packing.
3Strength
If threaded screw design is used, then pullout strength is improved, but surface bone on-growth is limited
Solution Approach 1:
The implant surface is constructed with a porous lattice pattern rather than smooth machined surfaces. This porous surface architecture dramatically increases the surface area available for bone on-growth and osseointegration, while the threaded geometry maintains pullout strength through mechanical engagement with the bone.
4Adaptability or versatility
If metal 3D printed triangular body is used, then surface roughness for bone growth is improved, but pullout strength deteriorates
Solution Approach 1:
The design combines the benefits of 3D printed porous titanium for bone growth surfaces with traditional threaded geometry for mechanical anchorage. The composite structure integrates the roughened porous surface architecture with load-bearing threaded elements, achieving both enhanced bone on-growth and maintained pullout strength.
5Manufacturing precision
If conventional machined screw is used, then manufacturing precision is improved, but bone graft volume and surface area are limited
Solution Approach 1:
The design changes the manufacturing approach from conventional machining to metal 3D printing, which enables the creation of complex lattice structures with controlled porosity parameters. This parameter change allows for optimized bone graft volume and surface area while maintaining the precision needed for surgical implantation through digital modeling and additive manufacturing control.
Data Source
AI summary
A surgical screw is provided for use in fixing or fusing bone. The screw may include each of an inner and an outer helical thread that extends along its length. The geometries of the helices and the relationship between the inner thread and the outer thread may improve the performance of the screw. For example, the two helices may operate to improve the manner in which the screw can be strained.