Uniplanar Spinal Screw Head for Controlled Pedicle Angulation
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Solution Overview
Problem
Existing spinal surgery techniques using polyaxial pedicle screws lack effective mechanisms to limit angulation in specific planes, leading to potential misalignment and instability during surgical procedures.
Innovation Solution
A spinal screw apparatus with a movable head that allows more angulation in one plane while restricting it in a perpendicular plane, featuring a proximal portion and distal portions with mechanical interlocks, and a collet mechanism to secure the screw head, limiting motion through sub-motion-limiters and a U-trough design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyaxial pedicle screws are used to allow angulation in various degrees of freedom, then the ease of operation is improved, but the stability of the object's composition deteriorates due to potential misalignment
Solution Approach 1:
The movable head is divided into multiple components: a proximal portion and at least one distal portion that are joinable together. This segmentation allows the head to provide both angulation freedom and alignment stability through the coordinated function of its parts, with the distal portion containing motion-limiting features that constrain screw movement after insertion.
Solution Approach 2:
The movable head is designed to be dynamically adjustable during insertion to allow angulation in various degrees of freedom, then becomes statically stable after assembly when the distal portion is attached. The transition from mobile to fixed configuration resolves the contradiction between ease of operation during insertion and stability during operation.
2Adaptability or versatility
If the movable head allows more angulation in one plane than in another plane, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The distal portion of the movable head features asymmetric geometry with different opening dimensions in perpendicular planes. The first opening allows greater angulation range than the second opening, creating uniplanar motion capability. This asymmetric design provides adaptability while maintaining relatively simple structural implementation through geometric constraints rather than complex mechanical mechanisms.
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.