Frangible Region in Surgical Instrument Torque Control
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Solution Overview
Problem
Surgical instruments and bone fasteners often break during spinal surgeries due to excessive torque, leading to fragments remaining in the body and difficulty in removal, especially in confined spaces like the spine, causing safety and retrieval issues.
Innovation Solution
Incorporating a frangible region on surgical instruments, such as drivers, that breaks at a predetermined torque lower than the ultimate torque of the instrument and bone fastener, allowing for easy removal of the broken piece and providing visual indicia for wear detection to prevent failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the surgical instrument is designed with high strength to withstand torque during implantation, then the instrument can transmit sufficient torque to secure the bone fastener, but the instrument may break and fragment into the treated region when excessive torque is applied
Solution Approach 1:
The surgical instrument is divided into distinct segments: a proximal portion, a frangible region, and a distal portion. The frangible region is specifically designed with reduced structural integrity (through features like reduced wall thickness, material differences, or geometric discontinuities) so that it acts as a predetermined failure point. This segmentation allows the instrument to transmit torque effectively through the stronger proximal and distal portions while the frangible region serves as a safety mechanism that breaks before catastrophic failure of the entire instrument occurs.
2Reliability
If the surgical instrument is made robust to prevent breaking, then instrument reliability is improved, but removal of broken portions becomes difficult when failure occurs in confined surgical sites
Solution Approach 1:
The frangible region is pre-engineered with specific geometric features (such as reduced cross-section, material variations, or stress concentration points) that create a predetermined failure point. This preliminary design ensures that when excessive torque is applied, the instrument will break at the frangible region rather than at other critical locations. The break is designed to occur in a controlled manner that leaves a manageable proximal portion attached to the bone fastener and a distal portion that can be easily removed from the surgical site.
3Ease of operation
If the frangible region is positioned closer to the distal end to facilitate removal, then ease of removal is improved, but the visual inspection capability before the frangible region is reduced
Solution Approach 1:
The frangible region incorporates localized geometric or material differences that create visual indicators of wear and potential failure. These may include variations in surface texture, color, cross-sectional geometry, or the inclusion of visual markers that allow the surgeon to inspect the frangible region before and during the procedure. This local quality enhancement enables detection of wear patterns without requiring the frangible region to be positioned at the extreme distal end, thus balancing both inspection capability and ease of removal.
Data Source
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AI summary
A surgical instrument for implanting a bone fastener is provided. The surgical instrument comprises an elongated body (24) having a frangible region (34) and a distal end (30) adjacent to the frangible region. The distal end of the surgical instrument is configured to engage the bone fastener. The bone fastener is less frangible than the frangible region of the elongated body of the surgical instrument. Kits and methods are also disclosed.