Bone Screw Head with Resilient Tabs for Aperture Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bone screws used in bone fixation often loosen or separate from the plate postoperatively due to insufficient purchase in the bone or forces from spinal movement, requiring invasive procedures for repair or replacement.
Innovation Solution
A fastener system with a head portion and anchor extension featuring resilient tabs that bend to fit through a narrowed aperture and then expand, secured by a threadable engagement and ramps to prevent backing out, ensuring a secure connection to the bone plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bone screw is designed with a standard head size, then it can be easily manufactured and installed, but it cannot be securely retained in a narrowed aperture of the implant
Solution Approach 1:
The bone screw head incorporates resilient tabs that can dynamically change their configuration between a compressed state during insertion and an expanded state for retention. The tabs resiliently deform to pass through the narrowed aperture and then expand to engage with the implant aperture, providing adaptive retention without permanent structural complexity.
Solution Approach 2:
The head portion utilizes changes in dimensional parameters through the resilient tabs. The tabs transition from a compressed configuration (allowing passage through the narrowed aperture) to an expanded configuration (providing secure retention in the implant aperture), thereby changing the effective size parameter of the head to match different operational requirements.
2Reliability
If the head portion is made larger than the narrowed aperture, then secure retention is achieved, but it cannot pass through the narrowed entry portion of the aperture
Solution Approach 1:
The resilient tabs provide a dynamic size adjustment mechanism that allows the head portion to transition from a larger retained configuration to a smaller insertable configuration. During installation, the tabs are compressed to reduce the head's effective size, enabling passage through the narrowed aperture, and then expand to provide secure retention afterward.
Solution Approach 2:
The head portion is pre-configured with resilient tabs that can be compressed in advance during the insertion process. This preliminary compression action allows the head to pass through the narrowed aperture, and upon insertion, the tabs naturally expand to provide retention, eliminating the need for separate expansion steps.
3Ease of operation
If resilient tabs are made bendable to reduce dimension, then the head can pass through the narrowed aperture, but the tabs may accidentally bend back and allow the screw to back out
Solution Approach 1:
The ramp feature is pre-positioned on the head portion to provide preliminary anti-action against tab bending. When the head is inserted into the implant, the ramp contacts the resilient tabs and prevents them from bending back to their original position, thereby preventing back-out while allowing controlled bending during insertion.
Solution Approach 2:
The ramp acts as an intermediary element between the resilient tabs and the insertion force. It mediates the interaction by providing a controlled surface that allows tabs to bend during insertion but prevents accidental bending back, thereby controlling the tab's dimensional changes to ensure reliable retention.
4Reliability
If a ramp is added to prevent tab bending, then back-out is prevented, but the device structure becomes more complex
Solution Approach 1:
The ramp is merged with the existing head portion structure rather than being a separate component. It is integrated into the head's geometry, combining the retention function with the existing tab structure. This merging approach provides the necessary back-out prevention while minimizing additional structural complexity.
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 effectively secures the bone screw to the implant, reducing the likelihood of loosening and the need for invasive procedures by providing a strong, stable connection that resists micromotion and other forces.
Implementation Method 1
a plurality of resilient tabs disposed on the anchor extension and/or the insert and forming a first dimension sized larger than a dimension of the narrowed entry portion, the plurality of resilient tabs bendable to form a second reduced dimension relative to the first dimension
Implementation Method 2
at least one ramp configured to contact the plurality of resilient tabs and to thereby prevent bending of the plurality of resilient tabs to form the second reduced dimension after the head portion has been passed past the narrowed entry portion into the aperture
Data Source
AI summary
A fastener, for example a bone screw, is sized to pass into an aperture of an implant, for example, a bone plate, the fastener having an anchor portion engageable with body tissue, and a head portion formed by an assembly of an insert and an anchor extension. The insert and anchor extension cooperate to form a reduced dimension passable into the aperture, and an expanded dimension not passable out of the aperture. The size of the assembly may be configurable, for example, by tabs, ramped surfaces, or an expanding diameter of a threadable insert.