Polyaxial Surgical Screw Tulip Coupling Stability
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Solution Overview
Problem
Existing polyaxial surgical screw systems face instability during tilting and rotation, leading to accidental decoupling and potential injury, especially during minimally invasive surgeries where manual dexterity and precision are challenging.
Innovation Solution
A polyaxial surgical screw with a robust tulip design and a device for implantation that includes a shaped tip and a tubular body with a rotation component, allowing for stable coupling and decoupling under torsion, rotation, buckling, and tensile stress, while simplifying the coupling process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mechanical interlocking system with elastic portions is used to couple the tulip to the tubular body, then the coupling can be disengaged for extraction, but the coupling becomes unstable under rotational and shear stresses leading to accidental decoupling
Solution Approach 1:
The coupling system is divided into distinct functional segments: the tulip with spherical head for positioning, the tubular body for structural support, and the retention mechanism with arms and notches for secure locking. This segmentation allows each component to specialize in its function while maintaining overall stability.
Solution Approach 2:
The retention arms are pre-configured with notches that automatically engage with the spherical head of the tulip during the coupling process. This preliminary positioning ensures that the coupling is locked in place before any rotational or shear stresses are applied, preventing accidental decoupling.
2Manufacturing precision
If the tulip is tilted into the correct position during insertion, then the screw can be positioned correctly in the vertebra, but shear stress is generated that causes decoupling of the tulip from the threaded shank
Solution Approach 1:
The spherical head on the threaded shank allows the tulip to be tilted and rotated into the correct positioning angle without compromising the coupling. The spherical geometry accommodates multi-axis movement while maintaining continuous contact between the spherical head and the retention mechanism, distributing shear stresses evenly.
Solution Approach 2:
The retention arms act as intermediaries between the spherical head and the tubular body, absorbing and distributing the shear stresses generated during tilting and positioning. The arms with their notched configuration provide a mechanical interface that maintains coupling integrity while allowing the necessary angular adjustments.
3Object-affected harmful factors
If minimally invasive surgical techniques are used with small incisions, then surgical trauma is reduced and hospitalization time is shortened, but manual dexterity and precision during the procedure become more challenging
Solution Approach 1:
The tulip is nested within the tubular body during insertion through the small incision, allowing the entire assembly to pass through the minimally invasive access point. The nested configuration reduces the overall profile of the implant device while maintaining the functional integrity of all components.
Solution Approach 2:
The retention mechanism with its notched arms and spherical head configuration enables self-aligning and self-locking during insertion. The surgeon does not need to manually adjust or tighten additional fasteners; the coupling automatically secures itself as the components are inserted and positioned, reducing the complexity of manual operations.
Data Source
AI summary
Various implementations include a polyaxial surgical screw and a device for implanting the screw. The screw comprises: an internally hollow tulip displaying a first open end for accessing inside the tulip, a second end opposite to the first end, and a side wall extending between the first and the second end; and a threaded shank displaying a first end defining the tip of the screw and a second end opposite to the first one displaying a ball joint joined to the second end of the tulip to orient said shank with respect to the tulip itself. The tulip also comprises at least one elongated rod projecting from the side wall and extending from the first end in a direction opposite to the second end.