Spinal Set Screw Thread Geometry for Load Distribution
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Solution Overview
Problem
Current spinal implant systems face challenges in providing adequate stability and load distribution due to splaying of receiver arms under excessive loading, leading to decreased thread contact and increased risk of shear forces during engagement with set screws.
Innovation Solution
A spinal implant system featuring a set screw with a unique thread geometry, including a crest thickness of 45% of the thread pitch, and angled leading and trailing flanks, which resists splaying and shear forces by dispersing loads effectively, and a receiver with smooth rounded corners to prevent binding and cutting during engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thread geometry is used in the set screw, then the structure is simple and easy to manufacture, but the receiver arms experience splaying under excessive loading leading to decreased thread contact and reduced stability
Solution Approach 1:
The patent applies parameter changes by modifying the thread geometry with specific angular parameters (leading flank angle and trailing flank angle) and crest thickness (45% of pitch) to optimize load distribution and prevent receiver arm splaying, thereby improving reliability without excessive complexity
Solution Approach 2:
The patent employs asymmetry in the thread form by having different angles for the leading flank and trailing flank of the thread. This asymmetric geometry is specifically designed to distribute loads more effectively and resist splaying forces on the receiver arms, enhancing stability
2Strength
If the set screw engages the receiver with conventional thread design, then manufacturing is simple, but shear forces increase and thread contact decreases under excessive loading
Solution Approach 1:
The patent changes critical thread parameters including crest thickness (set at 45% of pitch) and flank angles to optimize the engagement between set screw and receiver. These parameter changes increase load capacity and reduce shear forces while remaining manufacturable using conventional machining processes
3Stability of the object's composition
If receiver arms are designed with standard geometry, then manufacturing is straightforward, but splaying occurs under excessive loading reducing overall system stability
Solution Approach 1:
The patent applies preliminary anti-action by designing the receiver arm geometry and thread engagement features that preemptively counteract splaying forces before they can cause failure. The rounded corners and specific geometric features are designed to prevent binding and cutting while maintaining structural integrity under load
Data Source
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AI summary
A surgical coupling member includes a shaft defining an axis and including at least one thread having an external thread form. The external thread form having a leading flank and a trailing flank. The external thread form defines a pitch and a crest, the crest having a width in a range of about 35% to about 50% of the pitch of the external thread form, wherein the leading flank and the trailing flank are angled in a proximal orientation relative to the thread axis, and wherein the external thread form is configured to interlock with an internal thread form of an implant receiver. Systems, spinal constructs, implants and methods of use are disclosed.