Spinal Rod Reducer Instrument with Force Limiting Mechanism
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Solution Overview
Problem
Existing rocker reducer instruments for spinal surgery lack secure engagement with implanted receivers, often causing slippage and potential damage to adjacent tissue or bone, and apply excessive compressive force during rod reduction.
Innovation Solution
The development of rocker reducer instruments featuring forceps-like jaws with a pivot mechanism, opposing protrusions, and a cross-pin or foot feature that securely engage with receivers, incorporating a stopping mechanism to limit clamping force and maintain a locked position without additional force on the receiver, allowing for precise rod reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If traditional rocker reducer instruments are used to reduce the rod into the receiver, then the rod reduction force can be applied, but the instrument causes slippage and applies excessive compressive force to the receiver
Solution Approach 1:
The instrument is divided into separate functional components: engagement features (protrusions and recesses) that secure the instrument to the receiver, and application features (rocker arm and cross-pin) that deliver reduction force to the rod. This segmentation allows the engagement and force application functions to be optimized independently, preventing slippage while controlling compressive force.
Solution Approach 2:
The cross-pin acts as an intermediary element between the rocker arm and the rod, providing a controlled interface for force transmission. The cross-pin engages with the rod at a specific point, allowing the rocker arm to apply reduction force while the pin itself mediates the force transmission to prevent direct compression of the receiver.
2Reliability
If the instrument is designed to securely engage the receiver, then slippage is prevented, but excessive clamping force is applied to the receiver
Solution Approach 1:
The engagement features (protrusions and recesses) are designed with specific geometric characteristics that concentrate the engagement force at discrete points rather than distributing it uniformly. The protrusions engage with corresponding recesses in the receiver, creating localized contact points that secure the instrument while the distributed nature of multiple contact points prevents excessive force at any single location.
Solution Approach 2:
The instrument design incorporates the stopping mechanism and cross-pin configuration beforehand to prevent excessive clamping force from being applied to the receiver. The geometric constraints built into the instrument structure ensure that even when the instrument is fully closed, the receiver is not subjected to harmful compressive forces.
3Reliability
If manual clamping force is maintained to secure the instrument, then engagement is sustained, but the user must continuously apply force increasing operation complexity
Solution Approach 1:
The instrument's engagement mechanism is designed to be self-sustaining through the geometric interlocking of protrusions and recesses. Once the instrument is closed onto the receiver, the engagement features automatically maintain the secure connection without requiring continuous manual force application. The ratcheting mechanism further enhances this by providing a self-locking action that maintains engagement with minimal user input.
Data Source
AI summary
Example rocker reducer instruments securely engage a receiver that is implanted in a vertebra of the spine and move a spinal fixation element, such as a rod, into a channel formed in the receiver. Example instruments pivot around their contact point with the receiver and a cross-pin or foot feature on the instrument makes contact with the spinal rod and applies a downward force to reduce the rod into the receiver. Further, example instruments can contain a stopping mechanism to limit the amount of compressing force applied to the receiver while maintaining the instrument in a rigid, closed position.