Polyaxial Bone Anchoring Device With Axial Pressure-Member Locking
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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 adjustments without the instrument, and a design that permits temporary locking and unlocking of the head independently from the fixation of the rod, with extended tabs for minimally invasive surgery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyaxial bone anchoring device uses a pressure member that requires continuous instrument attachment to maintain locking position, 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 where it exerts pressure on the head to lock it in the receiving part, and a second position where it releases the head for adjustment. This dynamic positioning allows the device to transition between locked and unlocked states without requiring continuous instrument attachment, resolving the contradiction between locking stability and handling flexibility
Solution Approach 2:
The device incorporates a retention feature that automatically maintains the pressure member in the locking position after instrument removal. The pressure member and receiving part are designed with complementary geometries that self-lock when the pressure member is in the first position, eliminating the need for continuous external actuation and improving ease of operation while maintaining reliability
2Stability of the object's composition
If the head and rod are locked together as a single unit, then the structural stability is improved, but the adaptability deteriorates because adjustments to one component require unlocking the other
Solution Approach 1:
The locking mechanism is segmented into independent components: the pressure member controls the head locking independently from the rod fixation. This allows the head to be locked or unlocked separately from the rod, enabling flexible adjustments to either component without compromising the overall structural stability when both are locked
3Adaptability or versatility
If repeated adjustments of bone anchoring elements and rods are required during surgery, then the adaptability for correction is improved, but the loss of time increases due to multiple locking and unlocking cycles
Solution Approach 1:
The pressure member enables rapid transitions between locked and unlocked states through simple axial movement. During surgical correction, the pressure member can be quickly moved to the second position to unlock the head for adjustment, then returned to the first position to lock it again, minimizing the time required for repeated adjustments while maintaining full correction flexibility
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.