Deformable Toggle Lever in Bone Anchor Coupling Device
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Solution Overview
Problem
Existing polyaxial bone anchoring devices require high locking forces to secure the rod, which can lead to force loss due to deformation of the pressure member, making the locking process inefficient and potentially unsafe.
Innovation Solution
A coupling device with a pressure member that includes a deformable portion acting as a toggle lever, transforming from an angled to a straight configuration, allowing increased pressure on the head without further deformation during rod locking, and a locking member that advances without deforming the pressure member, reducing force loss and enhancing clamping force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the locking member deforms the deformable portion of the pressure member to lock the rod, then the rod can be secured, but high locking forces are required and force is lost during deformation
Solution Approach 1:
The head is locked in the receiving part before the rod is locked. The deformable portion is first used to lock the head by deforming under the locking member, then the locking member is advanced further to lock the rod without additional deformation of the deformable portion. This preliminary action sequence ensures that the force generated during deformation is not wasted on subsequent locking operations.
Solution Approach 2:
The locking process is divided into two distinct phases: first locking the head using the deformable portion, then locking the rod using the already-deformed state of the pressure member. This segmentation allows the locking forces to be applied sequentially rather than simultaneously, reducing the total force requirement and preventing force loss.
2Reliability
If high locking forces are applied to secure the rod, then the locking is more secure, but the deformable portion may be damaged or the bone anchor may be compromised
Solution Approach 1:
The head locking is performed as a preliminary action before rod locking. The deformable portion absorbs the deformation force during head locking, then the locking member is advanced further to lock the rod without causing additional deformation. This prevents excessive force from being applied to the deformable portion and bone anchor, maintaining component strength while ensuring reliable locking.
3Ease of operation
If a single instrument with a single drive portion is used for sequential locking, then ease of operation is improved, but the device complexity increases
Solution Approach 1:
The locking member is designed with a single drive portion that can perform multiple functions: first deforming the deformable portion to lock the head, then advancing further to lock the rod. This multi-functionality allows a single instrument to complete the entire sequential locking process, improving ease of operation during surgery while the internal complexity is contained within the coupling device design.
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 solution enables higher clamping forces on the rod, increasing the safety and efficiency of the locking process while allowing for sequential locking of the head and rod with a single instrument, improving handling during surgery and accommodating various bone anchors and rod diameters.
Implementation Method 1
the deformable portion functions similar to a toggle lever that transforms from an angled configuration into a less angled or substantially straight configuration
Implementation Method 2
a force is exerted onto the deformable portion and deforms the deformable portion from a first configuration to a second configuration, wherein the pressure exerted by the pressure member onto the head increases
Data Source
AI summary
A coupling device for coupling a bone anchor to a rod includes a receiving part having a longitudinal axis, a channel for receiving a rod, and an accommodation space for holding a head of a bone anchor, a pressure member having a first portion for holding and clamping the head and a deformable portion with a free end, and a locking member. The pressure member is expandable for inserting the head and adjustable to lock the head. When the deformable portion is at a first configuration, the free end of the deformable portion is supported by the receiving part, and at least part of the locking member is movable to exert a force on the deformable portion for adjusting the deformable portion to a second configuration where at least part of the deformable portion is farther away from the longitudinal axis compared to the first configuration.