Modular Screw Head Assemblies with Breakable Shear Clip
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Solution Overview
Problem
Current bone fastener devices for spinal fixation lack improved functionality, strength, and ease of manufacturing, particularly in securing spinal rods and bone fasteners effectively.
Innovation Solution
The design includes a tulip head with a breakable shear clip that expands radially to secure the bone fastener, a bearing washer for centering, and a support clip to retain the shear clip, allowing for secure attachment and angulation of spinal rods, along with a locking cap to compress the rod and restrict motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional bone fastener design is used, then the structure is simple, but the strength and functionality are insufficient
Solution Approach 1:
The bone fastener assembly is divided into multiple functional segments: a tulip head component, a breakable shear clip, a bearing washer, and a support clip. Each segment performs a specific function, allowing the system to achieve enhanced strength and functionality while maintaining manufacturability through modular design.
Solution Approach 2:
The bearing washer and support clip are positioned within the tulip head, and the shear clip is positioned within the bearing washer, creating a nested arrangement. This nesting allows multiple components to occupy the same spatial envelope, increasing functionality without proportionally increasing external dimensions or assembly complexity.
2Ease of operation
If a breakable shear clip mechanism is added, then the ease of assembly is improved, but the device complexity increases
Solution Approach 1:
The shear clip is pre-formed with a predetermined break point during manufacturing. During assembly, the screw head is inserted first, then the bearing washer and shear clip are positioned. The shear clip is designed to break at a specific location when compressed by the screw head, automatically expanding to secure the screw. This preliminary preparation of the break point eliminates the need for complex locking mechanisms while maintaining ease of assembly.
3Reliability
If multiple components are added for securement, then the reliability is improved, but the ease of manufacture decreases
Solution Approach 1:
The assembly is segmented into separately manufacturable components (tulip head, bearing washer, shear clip, support clip) that can be produced using standard manufacturing processes. This segmentation allows each component to be optimized for its specific function while maintaining compatibility with conventional manufacturing methods, thus achieving high reliability without sacrificing ease of manufacture.
Solution Approach 2:
The shear clip's material properties are specifically engineered to include a predetermined break point at a controlled location. This parameter change in the material structure allows the clip to transition from a solid form during assembly to a expanded form after breaking, providing reliable securing action while simplifying the manufacturing process compared to complex elastic or shape-memory alloy solutions.
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
This configuration enhances the securement and stability of spinal rods, providing improved strength and ease of assembly, while allowing for precise angulation and correction in spinal fixation procedures.
Implementation Method 1
The shear clip is breakable at a fracture site upon application of a force
Implementation Method 2
The bearing washer may be configured to center the shear clip within the tulip head to limit translation
Implementation Method 3
In the collapsed form, the split ring collapses and springs closed
Implementation Method 4
The locking cap may have an outer body defining a thread. The locking cap is threadable between the two arms of the tulip head to secure a rod therein
Data Source
AI summary
Orthopedic fixation devices, assemblies, and methods for securing a spinal rod. The orthopedic fixation device may include a tulip head with one or more internal components configured to secure a bone fastener. The tulip head may house a breakable shear clip that has an initial solid form. When the bone fastener is loaded into the tulip head, the shear clip breaks forming a split ring that expands radially outward to accept the screw head. Then, the shear clip collapses around the screw head, thereby securing the bone fastener to the tulip head. A spinal rod may be secured in the tulip head, for example, with a locking cap.