Spinal Screw Movable Head Asymmetric Angulation Control
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Solution Overview
Problem
Current spinal surgery techniques using polyaxial pedicle screws lack effective mechanisms to restrict angulation in specific planes, leading to potential instability and limited control over screw movement relative to the movable head.
Innovation Solution
The design incorporates a spinal screw apparatus with a movable head that allows greater angulation in one plane than in a perpendicular plane, featuring a proximal portion and distal portions with mechanical interlocks, and a collet system to provide controlled motion limits, ensuring stability and precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If polyaxial pedicle screws are used to allow angulation in various degrees of freedom, then the ease of operation and adaptability are improved, but the stability and control over screw movement are worsened
Solution Approach 1:
The movable head is designed with non-uniform geometry, having different opening dimensions in different planes. The opening allows greater angulation in the first plane (e.g., 30 degrees) while restricting angulation in the second perpendicular plane (e.g., 5 degrees), creating directionally selective motion control that provides both adaptability and stability
Solution Approach 2:
The screw system transitions from a static fixed-head design to a dynamic movable head design that permits controlled motion. The movable head allows the screw to angulate during insertion to match anatomical curvature, then maintains stable positioning once inserted, providing dynamic adaptability during installation and static stability during operation
2Ease of operation
If polyaxial pedicle screws are used to allow multi-directional angulation, then the ease of operation is improved, but the control over screw movement is worsened
Solution Approach 1:
The movable head features an asymmetric opening geometry that is larger in one plane and smaller in the perpendicular plane. This local geometric variation provides intuitive visual and tactile guidance during insertion, making it easier for surgeons to achieve proper alignment while maintaining high positioning precision through the constrained motion path
3Adaptability or versatility
If the movable head allows substantial angulation in one plane, then the adaptability is improved, but the stability in perpendicular plane is worsened
Solution Approach 1:
The movable head opening has deliberately non-uniform dimensions, providing a larger aperture in the first plane to accommodate substantial angulation (e.g., 30 degrees) for adapting to spinal curvature, while maintaining a smaller aperture in the second perpendicular plane to restrict motion and provide stability (e.g., 5 degrees), thus simultaneously achieving both adaptability and stability in different directions
Data Source
AI summary
A spinal screw assembly is provided. The assembly may be provided with a screw and a movable head in which angulation of the screw relative to the movable head is constrained so that angulation within limits is allowed in one plane but lesser or no angulation is allowed in another plane. Methods to assemble the disclosed apparatus are also disclosed.