Bottom-Loading Bone Anchor Assembly for Spinal Fixation
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Solution Overview
Problem
Large diameter pedicle screws used in spinal connection systems face challenges due to increased size of the receiver head, which interferes with bony anatomy and limits polyaxial range of motion, and requires larger closure mechanisms, necessitating a non-top-loading polyaxial screw design.
Innovation Solution
A bottom-loading bone anchor assembly with a large diameter bone-engaging shank, featuring a receiver member with a bore larger than the opening, a bone-engaging shank with a head that fits through the bore, and an insert with a slot to retain the shank within the receiver member, allowing for a smaller closure mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a larger diameter pedicle screw is used to carry large loads or engage large pedicles, then the load-bearing capacity is improved, but the receiver head size increases which interferes with bony anatomy and limits polyaxial range of motion
Solution Approach 1:
The patent applies nesting by placing the shank inside the receiver member through a bore that is larger than the opening, allowing the shank to be positioned within the receiver without requiring the opening to be enlarged. This nested configuration enables the shank to pass through the bore and be retained by the closure mechanism while maintaining a compact receiver head profile that does not interfere with bony anatomy or limit polyaxial range of motion
Solution Approach 2:
The patent transitions from a top-loading approach to a bottom-loading approach, changing the dimensional path of shank insertion. Instead of inserting the shank through the opening at the top of the receiver head, the shank is inserted through a bore in the receiver member and retained at the bottom by a closure mechanism. This dimensional change allows the opening to remain small while still accommodating large diameter shanks
2Strength
If a larger diameter pedicle screw is used, then the load-bearing capacity is improved, but a larger closure mechanism is required which increases device complexity
Solution Approach 1:
The patent changes the insertion dimension from top-loading to bottom-loading, allowing the use of standard-sized closure mechanisms even with large diameter shanks. The closure mechanism engages the shank from the bottom through the bore, maintaining consistent closure mechanism dimensions regardless of shank diameter, thereby avoiding the need for progressively larger closure mechanisms
3Ease of operation
If the opening in the receiver head is enlarged to accommodate larger diameter screw shanks, then the assembly ease is improved, but the receiver head size increases which interferes with bony anatomy
Solution Approach 1:
The patent changes the insertion path from through the opening at the top to through a bore in the receiver member. This allows the opening to remain small for anatomical compatibility while the bore provides the necessary clearance for shank insertion and positioning
Solution Approach 2:
The insert is positioned within the receiver member before the shank is inserted through the bore. This preliminary positioning of the insert facilitates smooth shank insertion and positioning through the bore, ensuring proper alignment and retention without requiring a large opening
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
Enables secure engagement of large diameter screws without increasing the receiver head size, maintaining polyaxial range of motion and using consistent closure mechanisms, facilitating easier implantation and stability in spinal procedures.
Implementation Method 1
swaging a side of the receiver member inward to retain the insert and the head of the shank
Data Source
AI summary
A bone anchor assembly is described having a large diameter for fixing a spinal connection element to bone. The assembly includes a receiver member for receiving the spinal connection element, a bone-engaging shank for engaging bone and a first and second insert for retaining the head of the shank within the receiver member.