Bone Fastener With Breakable Head Tabs For Spinal Fixation
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Solution Overview
Problem
Existing spine fixation assemblies face issues with screws disengaging from rods or plates due to stresses from vertebral element motion, leading to a need for a locking mechanism to prevent accidental disengagement.
Innovation Solution
A bone fastener with a self-contained locking mechanism, featuring a threaded main body and a head with breakable structures that flex and capture within a groove, preventing disengagement by forming a secure lock with the spinal vertebrae.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional screw is used to secure the spinal plate to vertebral elements, then the installation is simple, but the screw may disengage from the rod or plate due to stresses from vertebral motion
Solution Approach 1:
The screw head is segmented into a body and separate breakable structures (lips or tabs) that can flex independently. These breakable structures are initially in a first configuration that allows insertion through the plate, then break to a second configuration that locks against the plate surface, preventing disengagement while maintaining structural integrity of the main screw body.
Solution Approach 2:
The breakable structures transition from a flexible, movable state during insertion to a fixed, locked state after breaking. This dynamic transformation allows the fastener to adapt its configuration based on the insertion process, providing ease of installation followed by secure retention under stress.
2Reliability
If a locking mechanism is added to prevent screw disengagement, then the reliability improves, but the ease of operation decreases
Solution Approach 1:
The breakable structures automatically perform the locking function through their own structural design. When the screw is inserted and subjected to insertion forces, the breakable structures naturally break from their first configuration to their second locked configuration without requiring additional tools, manual intervention, or complex locking steps. The structure serves its own locking purpose.
3Reliability
If the screw head is enlarged to prevent disengagement, then the retention improves, but the ease of manufacture decreases
Solution Approach 1:
Rather than enlarging the entire screw head, the retention function is achieved through segmented breakable structures attached to or integrated with the screw head body. These structures are smaller, thinner elements that can be manufactured separately or as lightweight integrations, reducing material usage and manufacturing complexity compared to a fully enlarged head design.
Solution Approach 2:
The breakable structures are designed as thin, flexible lips or tabs that provide the necessary locking function without adding significant bulk or material. These thin-film-like structures are easier to manufacture and integrate than solid, enlarged head components, while still providing effective retention when they break into the locked configuration.
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 bone fastener effectively secures the spinal plate assembly to vertebral elements, preventing accidental disengagement due to stresses, ensuring stable fixation and minimizing the risk of screw backout during spinal motion.
Implementation Method 1
the head comprises a cylindrical main body and one or more breakable structures configured to be flexed and inserted into the groove and then break and unflex upward and remain captured within the groove
Data Source
AI summary
An implantable cervical plate assembly includes a cervical plate, one or more bone fasteners. The cervical plate comprises an elongated asymmetric body having one or more through-openings extending from the front surface to the back surface of the elongated asymmetric body. The one or more bone fasteners are configured to be inserted through the one or more through-openings, respectively. The bone fasteners comprise a threaded main body and a head that includes one or more breakable structures configured to be broken when inserted into a groove and then unflex and remain captured within the groove.