Spline Drive Bone Anchor Torque Transmission
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Solution Overview
Problem
Existing bone anchors compromise on bending/shear strength when exposed to high torque/force during insertion or removal, particularly in dense bone applications.
Innovation Solution
A bone anchor with an externally threaded shaft and a head featuring a spline drive mechanism, including equidistantly spaced longitudinally elongate recesses, which enhances torque reception and transmission without compromising structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small bone screws are used, then the implant size is reduced, but the bending/shear strength is compromised when exposed to high torque/force
Solution Approach 1:
The head is segmented into multiple recesses (at least three) that are equidistantly spaced around the longitudinal axis. Each recess can independently receive and transmit torque, distributing the mechanical load across multiple segments rather than concentrating it in a single location, thereby maintaining strength in smaller implants
Solution Approach 2:
The torque transmission is extended from a single-point or single-plane engagement to a three-dimensional arrangement with recesses distributed circumferentially around the longitudinal axis. This multi-dimensional torque distribution increases the moment of inertia and resistance to bending and shear forces
2Force
If high torque/force is applied during drilling, tapping, or inserting the anchor, then the insertion capability is improved, but the anchor's bending/shear strength is compromised
Solution Approach 1:
The torque transmission path is segmented into multiple recesses that distribute the applied force across different locations in the head, preventing stress concentration at any single point and maintaining structural integrity under high load
Solution Approach 2:
Each recess is specifically configured with side walls and opposing ends to optimize local torque reception, while the overall head structure maintains uniform strength distribution through the equidistant spacing of recesses around the longitudinal axis
Data Source
AI summary
A threaded bone anchor includes a plurality of recesses formed lengthwise along an exterior cylindrical surface for engagement with a driver instrument through which a user applies clockwise or counterclockwise torque for the insertion or removal of the bone anchor into and from bone. The bone anchor includes a cross-sectional geometry that minimizes the anchor's outer diameter, survives high insertion/removal torque without compromising the anchor's bending/shear strength, and allows a mating clamp to be attached to the entire non-threaded surface, including the recessed portion.