Polyaxial Pedicle Screw with Integrated Elastic Buffer
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Solution Overview
Problem
Existing dynamic stabilization devices for bones, particularly in the spinal column, face challenges in accommodating physiological movements due to the volume occupied by elastic elements between connectors, making it difficult to implant pedicle screws in closely spaced pedicles like L5/S1.
Innovation Solution
A polyaxial pedicle screw with a spherical segment-shaped head and threaded screw shank incorporates a hollow spherical segment with a recess for a rod-shaped connector, allowing swiveling and rotating movements, and an elastic plastic buffer body connected to a ram for damping properties, eliminating the need for external elastic means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If elastic elements are used between connectors for dynamic stabilization, then physiological movements are accommodated, but the volume occupied by these elements makes implantation difficult in closely spaced pedicles
Solution Approach 1:
The patent combines the elastic element and the connector into a single integrated component. The elastic element is formed as part of the connector structure itself, eliminating the need for separate elastic components and reducing the overall volume required for dynamic stabilization functionality.
Solution Approach 2:
The elastic element is nested within the connector structure, with the elastic portion contained within or integrated into the connector body. This nesting approach allows the elastic functionality to be housed within the existing connector volume, minimizing additional space requirements.
2Adaptability or versatility
If a movable ball element is used in the screw head for angular variability, then polyaxial movement is enabled, but the screw head requires a complex hollow structure with slot-shaped openings
Solution Approach 1:
The screw head is segmented into distinct functional components: a polyaxial mechanism for angular adjustment and a separate connector interface. This segmentation allows the complex hollow structure to be divided into manageable parts, simplifying manufacturing and assembly while maintaining polyaxial functionality.
Solution Approach 2:
Instead of creating a complex hollow structure to accommodate movement, the patent uses a solid or partially solid head design where the polyaxial mechanism is integrated through internal threading and geometric features that enable angular variability without requiring extensive hollow cavities or slot-shaped openings.
3Reliability
If the connector is firmly fixed after introduction for stability, then long-term stability is ensured, but physiological movements are restricted
Solution Approach 1:
The connector incorporates a dynamic elastic element that allows controlled movement within defined limits. The elastic portion can deflect and return, enabling physiological movements while maintaining connection stability. This dynamic design ensures long-term reliability by accommodating natural body movements rather than restricting them.
Solution Approach 2:
The connector design allows for parameter changes in terms of movement range and stiffness. By adjusting the geometry and material properties of the elastic element, the connector can be tailored to provide appropriate stability while maintaining the necessary degree of freedom for physiological movements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables physiological movements such as flexion, extension, lateral bending, and rotation by concentrating necessary functions within the screw head, reducing implantation challenges in closely spaced pedicles and ensuring long-term stability and reproducible behavior.
Implementation Method 1
In the hollow spherical segment there is a plastic buffer body (5), which is connected to a ram (6)... Due to the elastic properties of the plastic buffer body (5), the ram (6) and thus the connector (7) remain mobile
Implementation Method 2
an elastic plastic buffer body connected to a ram for damping properties
Data Source
Figure 1a~1b
Figure 2a~6
Figure 3a~3b
AI summary
Polyaxial pedicle screw with a head in the shape of a ball segment and with a threaded screw shank, wherein a hollow ball segment with a recess for receiving a rod-shaped connector is mounted in the head, in order to permit pivoting movements and rotation movements of the connector, wherein moreover, in the direction of the longitudinal axis of the threaded screw shank, the head in the shape of a ball segment has a cutout with an inner thread in which the rod-shaped connector can be moved in and out and, by means of the inner thread in the cutout, a grub screw can be introduced for blocking the hollow ball segment. According to the invention, a plastic buffer body is fitted in the hollow ball segment and is connected to a ram, wherein the ram has a head which engages in an associated annular groove in the plastic buffer body. Moreover, the plastic buffer body has a circumferential guide ring and a spherical guide stop at one end, wherein an opening for the ram is formed lying opposite the guide stop, and the edge of the opening bears on a shell, which in turn bears on the inner side of the hollow ball segment, in such a way that the plastic buffer body with its guide stop is fixed with pretensioning in the head shaped as a ball segment.