Helical Splined Orthopedic Anchor for Cancellous Bone Fixation
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Solution Overview
Problem
Conventional orthopedic surgery anchoring methods face challenges in securely attaching bone structures, particularly in cancellous bone, where screws tend to shear out due to the porous nature, and there is a need for improved anchoring solutions that promote bone regrowth and secure joinder between bones.
Innovation Solution
The development of anchors with a central aperture or channel along a curved center line, featuring splines that extend radially and progress helically with a long pitch, allowing for malleted insertion into cortical and cancellous bone, providing a larger surface area for resistance and promoting bone growth through porosity and texturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional screws are used for anchoring in cancellous bone, then the anchoring method is simple and familiar, but the pull-out strength is severely compromised due to the porous nature of cancellous bone causing thread shearing
Solution Approach 1:
The anchor is divided into multiple helical splines that wrap around a central core, creating multiple independent engagement points with the bone. This segmentation allows the load to be distributed across multiple splines rather than a single threaded structure, preventing catastrophic failure from thread shearing in cancellous bone while maintaining overall structural integrity
Solution Approach 2:
The splines are nested around a central core, with each spline wrapping helically around the core structure. This nested configuration allows the anchor to maintain a compact form factor while providing extensive surface area for bone engagement, solving the contradiction between structural complexity and anchoring strength
2Strength
If screws with conventional thread pitch are used, then the screw structure is compact, but the actual purchase (physical engagement) with cancellous bone is much less compared to cortical bone
Solution Approach 1:
Instead of relying solely on axial thread engagement, the splines extend radially outward from the central core, creating engagement in the radial dimension. This multi-dimensional engagement approach increases the effective purchase area with cancellous bone without requiring a proportional increase in anchor length, as the splines capture bone material in both axial and radial directions
3Strength
If anchors are designed to secure bone structures firmly, then anchoring strength is improved, but bone regrowth or through growth around the anchor is restricted
Solution Approach 1:
The anchor features localized apertures and porous regions at specific positions along its length, particularly in zones where bone regrowth is desired. These localized openings allow bone ingrowth and remodeling in specific areas while maintaining continuous spline structures in other regions to provide firm anchoring, thus achieving both strong fixation and biological integration
4Ease of operation
If conventional threaded anchors are used, then the insertion method is straightforward, but the risk of coring out (shearing) the bone material is high
Solution Approach 1:
A pilot hole is created in the bone before inserting the anchor, pre-clearing the path and reducing the mechanical resistance during insertion. This preliminary action allows the splined anchor to be driven into place with controlled force, preventing the sudden stress concentrations that cause coring out, while still maintaining straightforward insertion procedures
Data Source
AI summary
A long-pitch, helical anchor (where long pitch is greater than length, itself greater than twice maximum diameter; and very long, extra-long, or hyper pitch exceeding several lengths of such anchor, typically at least 2 and usually 5 or 6) includes splines radially extending and helically progressing circumferentially around and axially along an elongate core. The center line or axis may be solid, all splines meeting near the center line. In other embodiments, the center line passes along the center of a lumen or channel of a hollow core, while the splines extend radially outward from, and axially along a length of the core. Installation may be from a posterior access or a lateral-posterior access, fixing two bones in two degrees of freedom, three degrees of freedom, or multiple anchors fixing the bones firmly in three degrees of freedom.