Helical Anti-Splay Flanges for Spinal Rod Clamping
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Solution Overview
Problem
Conventional open-headed bone screws with threaded plugs face issues of radial splaying and loosening due to high torques required for secure rod locking, leading to potential failure and increased implant bulk when trying to minimize profile and intrusiveness.
Innovation Solution
The use of helical guide and advancement flanges with anti-splay contours on both inner and outer flanges, featuring radially interlocking lips and grooves, which resist splaying and allow for higher torque application without arm separation, enabling secure rod clamping and reduced profile implants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional threaded plugs are used to close open-headed bone screws, then the implant profile remains low, but radial splaying occurs under high torque leading to loosening and potential failure
Solution Approach 1:
The anti-splay lip and groove are pre-configured on the flanges to resist radial splaying forces before they occur. When torque is applied to tighten the rod, the anti-splay lip engages with the anti-splay groove to prevent the arms from splaying outward, thereby preventing loosening and failure while maintaining a low implant profile
Solution Approach 2:
The helical flanges incorporate curved, helical contours that wrap around the rod in a spiral pattern. This curved geometry provides mechanical interlocking that resists both axial displacement and radial splaying, allowing the closure to securely hold the rod while maintaining a compact, low-profile structure
2Force
If higher torque is applied to secure the rod in the open-headed bone screw, then clamping force increases, but radial outward forces cause splaying of the arms
Solution Approach 1:
The anti-splay lip and groove are pre-configured on the flanges to resist radial splaying forces before they occur. When torque is applied to tighten the rod, the anti-splay lip engages with the anti-splay groove to prevent the arms from splaying outward, thereby preventing loosening and failure while maintaining a low implant profile
Solution Approach 2:
The closure integrates multiple functions into a single component: the helical flanges provide both the clamping action on the rod and the anti-splay resistance. The anti-splay lip and groove are combined with the helical advancement mechanism, allowing one component to simultaneously secure the rod against axial movement and prevent radial splaying under torque
Data Source
AI summary
A spinal fixation device combines an open-headed anchor member, such as a bone screw or a hook with spaced apart arms forming a rod receiving channel. The arms have break-off arm extensions that are broken-off or separated after the rod is clamped. The closure and inner surfaces of the arms and tabs have mating helical anti-splay guide and advancement flanges formed thereon which radially interlock and mechanically cooperate to prevent splaying the arms and extensions as the closure is advanced into the rod receiving channel.