Polyaxial Bone Anchor Locking for Flexible Spinal Rod Adjustment
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Solution Overview
Problem
Existing polyaxial bone anchoring devices lack flexibility in handling during spinal surgery, requiring repeated adjustments of bone anchoring elements and rods, which complicates the correction and stabilization of multiple spinal segments.
Innovation Solution
A polyaxial bone anchoring device with a receiving part and a pressure member that allows for axial movement to lock and unlock the head relative to the receiving part, enabling independent adjustments of the head and rod positions, even without the instrument, and featuring a press-fit connection for temporary locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyaxial bone anchoring device uses a pressure member that requires constant instrument attachment for adjustments, then the device provides stable locking, but the ease of operation deteriorates due to repeated instrument attachment and removal
Solution Approach 1:
The pressure member is designed to be movable between a first position (non-locking) and a second position (locking), allowing the device to dynamically transition between locked and unlocked states. This dynamic mechanism enables the head to be adjusted relative to the receiving part when needed, while maintaining stable locking when the pressure member is in the second position, thus resolving the contradiction between locking stability and adjustment flexibility
Solution Approach 2:
The device incorporates a self-locking mechanism where the pressure member, when moved to the second position, automatically clamps the head of the bone anchoring element without requiring continuous instrument attachment. The receiving part and pressure member work together to maintain the locked state, allowing the system to serve itself in maintaining locking stability while enabling easy adjustment when the pressure member is repositioned
2Adaptability or versatility
If the device allows repeated adjustments of head and rod positions, then the adaptability improves for spinal correction, but the device complexity increases due to multiple components and mechanisms
Solution Approach 1:
The device is divided into distinct functional segments: a receiving part for holding the rod, a pressure member for locking the head, and a bone anchoring element with head. This segmentation allows each component to perform its specific function independently, enabling repeated adjustments of the head and rod positions through simple repositioning of the pressure member, thereby achieving high adaptability without excessive overall complexity
Solution Approach 2:
The pressure member serves multiple functions: it acts as a locking mechanism when in the second position, a positioning element when in the first position, and a structural component of the receiving assembly. This multi-functionality reduces the need for separate components for each function, maintaining device simplicity while enabling repeated adjustments for spinal correction
3Ease of operation
If the pressure member uses a press-fit connection for temporary locking, then the ease of operation improves, but the reliability may worsen due to potential slippage under load
Solution Approach 1:
The pressure member is designed to be movable between a first position (non-locking) and a second position (locking), allowing the device to dynamically transition between locked and unlocked states. This dynamic mechanism enables the head to be adjusted relative to the receiving part when needed, while maintaining stable locking when the pressure member is in the second position, thus resolving the contradiction between locking stability and adjustment flexibility
Solution Approach 2:
The device incorporates a self-locking mechanism where the pressure member, when moved to the second position, automatically clamps the head of the bone anchoring element without requiring continuous instrument attachment. The receiving part and pressure member work together to maintain the locked state, allowing the system to serve itself in maintaining locking stability while enabling easy adjustment when the pressure member is repositioned
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
Facilitates easier and more precise adjustments during spinal surgery by allowing temporary locking and unlocking of the head, simplifying the surgical procedure and enabling multiple correction steps without the need for constant instrument attachment.
Implementation Method 1
the pressure member is configured to remain in the locking position when the instrument is removed
Data Source
AI summary
A polyaxial bone anchoring device includes a receiving part with two legs defining a recess for receiving a rod and a pressure member for exerting pressure on a head of a bone anchoring element in the receiving part, the pressure member having an engagement portion. The engagement portion can extend at least partially into a leg and is directly engageable from outside the bone anchoring device to move the engagement portion axially for adjusting the pressure member from a non-locking position where the head is pivotable to a locking position where the head is clamped. When the pressure member is in the locking position and the engagement portion is free from any outside axial forces, a first contact surface of the receiving part cooperates with a second contact surface of the pressure member to hold the pressure member in the locking position.