Polyaxial Bone Anchor Locking With a Superelastic Pressure Member
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Solution Overview
Problem
Existing polyaxial bone anchoring devices require high locking forces due to the deformation of a deformable portion during the clamping and locking of the rod, leading to inefficiencies in the locking process.
Innovation Solution
A polyaxial bone anchoring device with a pressure member featuring a deformable portion made of a highly elastic material, such as a nickel-titanium alloy, that functions as a toggle lever to reduce the force required for sequential locking of the head and rod, allowing for easier handling during surgery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a deformable portion is used in the pressure member to enable sequential locking, then the locking process can be performed with a single instrument, but the force required for locking increases significantly
Solution Approach 1:
The patent changes the material parameter of the deformable portion from conventional elastic materials to highly elastic materials (superelastic materials like Nitinol). This parameter change allows the material to undergo large deformations with lower applied forces, thereby reducing the locking force requirement while maintaining the sequential locking functionality with a single instrument
Solution Approach 2:
The patent employs composite material construction where the pressure member includes a deformable portion made of highly elastic material combined with other structural components. This composite approach allows the deformable portion to provide the necessary elasticity for sequential locking while the overall structure maintains sufficient strength to reduce the required locking force
2Reliability
If high locking forces are applied to secure the rod, then the locking reliability increases, but the ease of operation during surgery decreases
Solution Approach 1:
By changing the material parameter to highly elastic materials, the system achieves high locking reliability through the material's inherent superelastic properties rather than through high applied forces. This allows reliable locking while maintaining ease of operation during surgery
Solution Approach 2:
The highly elastic material provides self-service by automatically providing the necessary elastic recovery force to maintain reliable locking without requiring high external forces from the surgeon, thereby improving ease of operation while maintaining reliability
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 device enables secure locking of the head and rod with reduced force, maintaining the locked position of the head even when the locking member is loosened, facilitating adjustments and accommodating rods of different diameters.
Implementation Method 1
a deformable portion with a free end that is supported in the receiving part. A force is exerted onto the deformable portion of the pressure member that deforms the deformable portion from a first configuration to a second configuration
Implementation Method 2
The deformable portion is made of a highly elastic material, such as a nickel-titanium alloy
Implementation Method 3
maintaining the locked position of the head even when the locking member is loosened
Data Source
AI summary
A polyaxial bone anchoring device includes a receiving part having a longitudinal axis, a channel for receiving a rod, and an accommodation space for pivotably holding a head of a bone anchoring element, and a pressure member configured to be positioned in the receiving part and to exert pressure onto the head to lock the head in the receiving part. The pressure member includes a pressure exerting surface and a deformable portion having a free end, wherein the deformable portion is configured to assume at least a first configuration and a second configuration. The polyaxial bone anchoring device further includes a locking member configured to be inserted into the channel and to exert a force onto the deformable portion. When the head and the pressure member and the locking member are in the receiving part, the free end of the deformable portion is supported in the receiving part, and the locking member is movable in the channel along the longitudinal direction in such a manner that the locking member first contacts the deformable portion and exerts a force onto the deformable portion to bring the deformable portion from the first configuration into the second configuration thereby locking the head. Thereafter the locking member comes into contact with the rod and locks the rod.