Medical Screw Reverse External Thread for Easy Extraction
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Solution Overview
Problem
The existing medical screws with reverse internal threads face difficulties in withdrawal due to foreign substances like callus adhering to the head portion, making it troublesome to engage the operating jig and remove the screw quickly during surgical operations.
Innovation Solution
A medical screw with a reverse external thread portion on its head perimeter allows easy removal of foreign substances, and a withdrawal operating jig with a reverse internal thread engages with this external thread for efficient screw extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reverse internal thread portion is formed inside the head portion for easy withdrawal, then the screw can be pulled out by rotating in reverse direction, but foreign substances like callus adhering to the head portion make it difficult to engage the operating jig
Solution Approach 1:
The patent inverts the traditional internal thread design by forming a reverse external thread portion on the outer periphery of the head portion instead of an internal thread inside the head. This inversion allows the withdrawal operating jig to engage with the external thread from the outside, making it possible to remove callus and other foreign substances that would otherwise obstruct engagement with an internal thread structure.
2Strength
If the screw is screwed into the bone firmly for stable fixation, then the fracture site is securely joined, but the screw becomes difficult to withdraw after several months when callus is generated
Solution Approach 1:
The patent employs asymmetry by creating a reverse external thread portion on the head that rotates in the opposite direction to the main screw thread. The main screw thread portion screws into the bone in a clockwise direction for secure fixation, while the reverse external thread portion on the head allows withdrawal by rotating counterclockwise, enabling easy removal after the fracture has healed.
3Ease of operation
If the head portion is exposed for easy engagement of operating jig, then the screw can be manipulated easily, but foreign substances can adhere to the head portion causing operational difficulties
Solution Approach 1:
The patent extracts the thread structure from the internal cavity of the head and places it on the external periphery of the head as a reverse external thread portion. This extraction allows the operating jig to engage with the thread from the outside, making it easier to remove any adhering foreign substances like callus during the engagement process, thereby maintaining ease of operation.
Data Source
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AI summary
A medical screw which can be withdrawn easily from a fracture site in which the medical screw is screwed in is provided. A reverse external thread portion 11h formed in a reverse direction to a direction of a thread of a screw thread portion 11b of a distal end portion 11a is provided on an outer periphery of a head portion 11e of a medical screw 11, and a reverse internal thread portion 14a provided at a front end portion of a rod-shaped member of a withdrawal operating jig 14 is engaged with the reverse external thread portion 11h by rotating in a reverse direction to a direction of a thread of the screw thread portion 11b, whereby the screw 11 and the withdrawal operating jig 14 are unified. Furthermore, the withdrawal operating jig 14 is rotated in a reverse direction to the direction of screwing in of the screw 11, so that the screw 11 is pulled out of the body by being loosened and withdrawn from a fracture site D.