Spinal Rod Segmentation for Low-Profile Rigidity
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Solution Overview
Problem
Current spinal stabilization systems face challenges in providing a cost-effective, rigid screw and rod construct that maintains a low profile while ensuring sufficient strength, especially for large deformity corrections, and often require material incompatibility to prevent complications.
Innovation Solution
A spinal stabilization system featuring a pair of connecting rods with an elongate round and elongate head portion, secured by a cross connector assembly with recessed portions and flexible fingers, allowing for adjustable length and snap-fit engagement, which provides greater rigidity and strength without increasing the profile or requiring material incompatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If larger diameter rods are used to improve strength for large deformity corrections, then the strength and rigidity of the screw and rod construct is improved, but the profile of the construct increases and material costs increase
Solution Approach 1:
The connecting rod is segmented into three distinct portions: a round portion for receiving in the bone screw, a neck portion connecting the round portion with the head portion, and an elongate head portion for receiving in the cross connector. This segmentation allows each portion to be optimized for its specific function, achieving high strength at connection points while maintaining a slender overall profile.
Solution Approach 2:
The connecting rod exhibits local quality variations through its different portions. The round portion has a circular cross-section optimized for rotational engagement with the bone screw, while the head portion has a non-circular cross-section (rectangular, oval, or triangular) optimized for secure engagement with the cross connector. This localized optimization provides maximum strength where needed without increasing the overall profile.
2Strength
If larger diameter rods are used to improve strength for large deformity corrections, then the strength and rigidity of the screw and rod construct is improved, but the material costs increase
Solution Approach 1:
By segmenting the rod into functionally optimized portions, the design achieves maximum structural efficiency with minimum material. The neck portion acts as a stress-transfer bridge between the round and head portions, allowing the use of smaller overall dimensions while maintaining strength through strategic material placement rather than uniform thickening.
3Strength
If the cross connector assembly is designed to secure the connecting rod with recessed portions and fingers, then the rigidity and strength of the construct is enhanced, but the device complexity increases
Solution Approach 1:
The cross connector assembly utilizes asymmetric recessed portions with fingers that match the asymmetric geometry of the connecting rod's head portion. This asymmetric design provides inherent mechanical interlocking and rigidity through geometric complementarity rather than through complex fastening mechanisms, thereby enhancing strength while limiting complexity.
4Adaptability or versatility
If the connecting rod has different cross-sectional shapes along its length, then the engagement with bone screws and cross connectors is optimized, but the manufacturing precision requirements increase
Solution Approach 1:
The connecting rod features locally optimized cross-sectional geometries: a circular cross-section at the round portion for optimal engagement with the bone screw, and a non-circular cross-section (rectangular, oval, or triangular) at the head portion for optimal engagement with the cross connector. These localized geometric variations are designed to be manufacturable with standard precision capabilities while providing superior adaptability to different spinal conditions and implant configurations.
Data Source
Figure 1~2
Figure 3~5
Figure 5A
AI summary
A spinal stabilization system includes a connecting rod, a rod bending device, and a plurality of bone screws. The connecting rod includes an elongate round portion, an elongate head portion and a neck portion connecting the elongate round portion with the elongate head portion. The rod bending device includes an elongate body defining an aperture configured and dimensioned to receive the connecting rod therethrough in a single orientation. The bone screws include a housing portion and a screw shaft distally extending from the housing portion. The housing portion includes an inner housing and an outer housing slidably surrounding at least a portion of the inner housing. The inner housing defines a slot configured and dimensioned to releasably secure the elongate round portion of the connecting rod therein. The outer housing is movable relative to the inner housing between an unlocked state and a locked state.