Polyaxial Locking Mechanism for Bone Screw Stability
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Solution Overview
Problem
Screw-and-plate osteosynthesis systems have limited resistance to compression stresses parallel to the plane of the plate, and there is a need for improved bending strength between the threaded rod or screw and the plate.
Innovation Solution
A polyaxial locking mechanism featuring a circular ring-shaped body with a central opening, slot, circumferentially extending interior groove, and exterior grooves, allowing polyaxial movement before tightening, which enhances the fixation of bone screws and plates by creating a strong, form-fit contact upon rotation, utilizing materials like Ti6Al4V ELI and coatings for improved functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional screw-and-plate system is used, then the plate can be compressed over the bone to stabilize the assembly, but the resistance to compression stresses parallel to the plane of the plate is low
Solution Approach 1:
The aperture is divided into two functional parts: a cylindrical portion that receives the screw head and a conical portion that receives the locking mechanism. This segmentation allows each portion to perform its specific function optimally - the cylindrical part provides stable screw seating while the conical part enables the locking action to resist compression stresses.
Solution Approach 2:
The locking mechanism is nested within the conical portion of the aperture, and the screw head is nested within the cylindrical portion. This nested arrangement allows the locking mechanism to be housed within the plate structure itself, creating a compact assembly that resists compression stresses without adding external complexity.
2Adaptability or versatility
If a monoaxial-locking system is used, then the assembly strength is sufficient for postoperative stresses, but the ability to choose the angle of implantation of screws is limited
Solution Approach 1:
The locking mechanism incorporates a ball that can move within the conical portion, allowing the screw head to be positioned at various angles during insertion. Once locked, the ball settles into a fixed position that maintains the chosen angle while providing sufficient assembly strength. This dynamic capability enables angular adaptability without compromising postoperative strength.
3Strength
If the locking mechanism is tightened to fix the body, bone screw, and plate, then the bending strength increases, but the ability to reposition screws is lost
Solution Approach 1:
The locking mechanism is designed to be engaged in a preliminary loose state during surgery, allowing the surgeon to position the screw at the optimal angle. Once the desired position is achieved, the locking mechanism is tightened to fix the components. This preliminary action sequence enables both repositioning capability during surgery and high bending strength after fixation.
Data Source
AI summary
An improved polyaxial mechanism is disclosed. The mechanism preferably works in conjunction with a bone plate and fixation mechanism, such as a screw, rod, or the like. The improved polyaxial mechanism increases the strength of the locking among the locking mechanism, fixation mechanism, and bone plate. In addition, the improved polyaxial mechanism allows for easy locking among the elements, as well as more difficulty in unlocking the elements. A method for utilizing the improved polyaxial mechanism is also disclosed.