Orthopedic Set Screw Torque Control for Spinal Rod Fixation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing orthopedic tools face challenges in applying the right amount of torque to set screws during spinal surgery, particularly when attaching a spinal rod to a pedicle screw, which can lead to issues like screw loosening and implant breakage.
Innovation Solution
A method and orthopedic implant kit with dual torque limiting mechanisms are introduced, allowing for a first torque level for initial attachment and a higher second torque level for final fixation, using handles with integrated or separate torque limiting/indicating features to ensure precise torque application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single torque level is applied to the set screw, then the attachment process is simple, but it risks screw loosening or implant breakage due to insufficient or excessive torque
Solution Approach 1:
The torque application process is segmented into two distinct stages with two different torque levels. The first torque level (e.g., 5-15 Nm) is applied during initial rod reduction and set screw engagement, while the second torque level (e.g., 15-30 Nm) is applied for final rod-to-screw fixation. This segmentation allows each stage to receive the appropriate torque without risking loosening or breakage, resolving the contradiction between reliability and simplicity.
Solution Approach 2:
The torque control mechanism transitions from a static single-torque design to a dynamic multi-torque system. The torque limiting mechanism is configured to provide different torque limits at different stages of the tightening process, enabling the system to adapt torque output based on the operational phase, thereby improving reliability while maintaining manageable complexity.
2Strength
If high torque is applied to ensure secure fixation, then implant stability is improved, but the risk of implant breakage increases
Solution Approach 1:
The first torque level is applied as a preliminary action to achieve initial rod reduction and set screw engagement before applying the higher second torque level. This preliminary tightening ensures proper positioning and gradual load distribution, allowing the implant components to settle into their final configuration before maximum torque is applied, thereby reducing the risk of sudden breakage while achieving secure fixation.
Solution Approach 2:
The torque parameter is changed in two distinct steps rather than applied at a single high level. The torque limiting mechanism is configured with two different torque thresholds, allowing the operator to progressively increase torque from a lower initial level to a higher final level. This parameter progression ensures that fixation strength is achieved without exceeding the breakage threshold of implant components.
3Measurement precision
If multiple torque levels are applied for precise fixation, then surgical precision is improved, but the operation time increases
Solution Approach 1:
The torque limiting mechanism is designed to automatically enforce the two-torque-level protocol without requiring complex external control systems. The mechanical torque limits self-regulate the applied torque at each stage, providing precision through inherent mechanical constraints rather than electronic sensors or complex control algorithms. This self-limiting design achieves precise torque application while minimizing additional operational complexity and time.
Data Source
AI summary
An orthopedic implant kit for tightening a set screw to a head of a pedicle screw for holding a spinal rod to the pedicle screw, the kit including a screw extender for holding the head of the pedicle screw, a set screw driver for engaging with the set screw to threadably tighten the set screw to the head of the pedicle screw, a first torque limiting mechanism for limiting a torque between the set screw driver and the screw extender to a first torque value or a first torque indication mechanism for indicating that the first torque has been reached, and a second torque limiting mechanism for limiting a torque between the set screw driver and the screw extender to a second torque value, the second torque value being higher than the first torque value.