Polyaxial Fastener Retaining Ring Expansion Mechanism
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Solution Overview
Problem
Existing bone fixation systems in the cervical spine face complications such as screw loosening and failure due to insufficient purchase in bone, leading to undesirable invasive procedures for repair or replacement, and pose risks due to proximity to the spinal cord during installation.
Innovation Solution
A fastener system with a polyaxial head and resilient retaining ring that expands to secure within an implant aperture, preventing backing out by maintaining a larger diameter when expanded, allowing for secure fixation without the need for screws to pass through vertebrae and reducing the risk of hardware failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a screw passes completely through the vertebrae to achieve secure fixation, then the fixation strength is improved, but the risk of damaging the spinal cord and the complexity of the surgical procedure increases
Solution Approach 1:
The invention extracts the fastening function from the screw shaft and relocates it to the head of the screw. The expanding mechanism in the head provides secure anchoring without requiring the screw to pass through the entire vertebrae, thereby eliminating the need for deep drilling near the spinal cord while maintaining fixation strength.
Solution Approach 2:
Instead of securing the screw by passing it through the bone, the invention inverts the approach by securing the screw head from the entry side through expansion within the aperture. This reverses the traditional direction of force application and anchoring, allowing fixation without penetrating through the vertebrae.
2Device complexity
If traditional screws are used to secure implants, then the device complexity is reduced, but the reliability of fixation decreases due to screw loosening and backing out
Solution Approach 1:
The screw head incorporates an expanding mechanism that transitions from a compressed state during insertion to an expanded state after positioning. This dynamic transformation allows the screw to adapt to the aperture dimensions and create a secure, reliable fixation that prevents loosening and backing out, while the expansion mechanism remains relatively simple in structure.
3Reliability
If the fastener head is made large to prevent backing out, then the fixation reliability is improved, but the ease of insertion through the aperture decreases
Solution Approach 1:
The fastener head utilizes a dynamic expanding mechanism that allows it to be inserted in a compressed, space-efficient state and then expand to a larger configuration once positioned. This dynamic size change enables both easy insertion through the aperture and reliable fixation after expansion, resolving the contradiction between size and insertability.
Solution Approach 2:
The expanding mechanism is nested within the fastener head structure, allowing the head to maintain a compact form during insertion and then deploy outward to engage the aperture walls. This nesting approach enables the head to effectively transition from a small insertable form to a large securing form without requiring two separate components.
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
The fastener system provides reliable and secure fixation of implants, reducing the risk of hardware failure and invasive procedures, while allowing for polyaxial movement and accommodating bone graft compression without excessive bulk or tissue irritation.
Implementation Method 1
the ring formed with a resilient material, the ring resiliently expandable from a first compressed configuration having a first dimension to a second relaxed configuration having a second dimension, the second dimension larger than the first dimension
Data Source
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AI summary
A polyaxial fastener is secured within an implant with a retaining ring. The ring is assembled onto a circumferential groove formed in the fastener head. The groove and ring are positionable, when the fastener is installed into an implant, at a wide portion of the mating polyaxial aperture in the implant. The ring is compressible into the groove to form a narrowed diameter, which is passable into a narrow diameter of the aperture, near an entrance to the aperture. The ring is released to expand and increase an overall diameter of the head and ring assembly, thereby rending the assembly too wide to pass by the narrow entrance to the aperture, thereby securing the assembly within the implant.