Pedicle Screw Thread Geometry for Load Dispersion
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Solution Overview
Problem
Conventional pedicle screws loosen under continuous load from patient movement, causing the spinal rod to separate from the clamp screw due to concentrated load distribution, leading to instability of the artificial spinal aid.
Innovation Solution
A pedicle screw design featuring a fixing screw thread with rectangular cross-section dents and protrusions and a clamp screw thread with right-angled trapezoid cross-section dents and protrusions, along with varying pitches, to create a predetermined gap and disperse external loads, ensuring a secure combination between the clamp screw and the fixing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the clamp screw thread is firmly tightened to the fixing screw thread, then the initial combination strength is improved, but the load becomes concentrated at specific positions causing the clamp screw thread to bend and push the fixing screw thread, leading to loosening under continuous load
Solution Approach 1:
The clamp screw thread is designed with dents and protrusions having right-angled trapezoid cross-sections that form a predetermined gap with the fixing screw thread's rectangular cross-section dents and protrusions. This local structural modification distributes the load across multiple contact points rather than concentrating it at single tight engagement points, preventing the clamp screw thread from bending and pushing the fixing screw thread under continuous load.
Solution Approach 2:
The screw threads are segmented into multiple dents and protrusions along their length, creating multiple load-bearing segments. This segmentation allows the load to be distributed across several discrete contact regions rather than being concentrated at a single point, enhancing the reliability of the combination under continuous loading conditions.
2Force
If the fixing screw thread and clamp screw thread receive load through their surfaces, then the threads are firmly engaged, but the load is not dispersed and the combination easily loosens
Solution Approach 1:
The predetermined gap formed between the right-angled trapezoid clamp screw thread and rectangular fixing screw thread creates localized load distribution zones. The load is received at specific dent and protrusion interfaces rather than being uniformly distributed, which prevents stress concentration and reduces the tendency for the threads to work loose under continuous loading.
Data Source
AI summary
A pedicle screw is provided to be inserted into and fixed to a pedicle of a spinal disease patient, and more particularly, a pedicle screw in which a screw thread of a clamp screw is formed to have dents and protrusions with trapezoid cross-sections so as to form a predetermined gap with a screw thread of a fixing unit having dents and protrusions with rectangular cross-sections when the clamp screw is combined with the fixing unit, and the screw thread of the clamp screw has different pitches to disperse an external impact so as to further firmly combine the clamp screw with the fixing unit.