Self-Guiding Orthopedic Fastener Prevents Cross-Threaded Plate Apertures
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Solution Overview
Problem
Existing orthopedic fasteners often experience cross-threading issues when engaging with orthopedic plates, leading to weakened fixation and difficulty in removal, which can damage the plate and render it unusable.
Innovation Solution
A fastener design featuring a single thread profile throughout its length with a thicker plate-engaging portion and a bone-engaging portion of varying diameter, preventing cross-threading by ensuring correct alignment and secure locking without tapering, allowing for easy insertion and removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conical threads are used to self-start threading in the plate aperture, then the fastener can automatically align and begin threading, but cross-threading occurs and weakens the fixation
Solution Approach 1:
The patent changes the thread geometry parameters by using a cylindrical (parallel) thread profile instead of a conical thread profile. This parameter change maintains the self-start capability while preventing cross-threading, as the constant diameter thread engages the female threads more accurately without the progressive diameter increase that causes misalignment in conical threads.
Solution Approach 2:
The patent introduces asymmetry in the thread engagement process by having the male thread engage the female thread at a specific orientation. The thread profile is designed so that the leading edge of the male thread naturally guides itself into the correct alignment with the female thread, creating a self-aligning mechanism that prevents cross-threading while maintaining ease of insertion.
2Ease of operation
If conical threads are used to increase diameter toward the plate portion, then self-start threading is facilitated, but the fastener becomes difficult or impossible to remove and may damage the plate
Solution Approach 1:
The patent changes the geometric parameter of the thread from conical (variable diameter) to cylindrical (constant diameter). This parameter change allows the fastener to be easily inserted while also enabling easy removal, as the constant diameter thread does not create the progressive tightening effect that makes conical threads difficult to remove.
Solution Approach 2:
Instead of using a conical thread that progressively increases in diameter to facilitate insertion (which then makes removal difficult), the patent inverts the approach by using a cylindrical thread with constant diameter. This inversion maintains insertion ease through proper thread profile design while eliminating the removal difficulty associated with conical threads.
3Ease of manufacture
If a single thread profile is used throughout the fastener length, then manufacturing is simplified, but optimized engagement with both bone and plate is difficult to achieve
Solution Approach 1:
The patent applies a single cylindrical thread profile throughout the entire length of the fastener, making the thread universal for both bone engagement and plate aperture engagement. This single thread design simplifies manufacturing while still achieving reliable engagement in both locations through proper thread geometry and the thicker plate-engaging portion that provides structural support.
Solution Approach 2:
While using a single thread profile throughout, the patent applies local quality by varying the shank diameter - the plate-engaging portion has a thicker diameter than the bone-engaging portion. This local variation in thickness allows the single thread profile to function optimally in both engagement locations, maintaining manufacturing simplicity while achieving location-specific optimization.
4Reliability
If the plate-engaging portion has larger diameter than the bone-engaging portion, then secure locking with the plate is achieved, but the transition between portions adds manufacturing complexity
Solution Approach 1:
The patent segments the shank into two distinct portions: a plate-engaging portion with larger diameter and a bone-engaging portion with smaller diameter. This segmentation allows each portion to be optimized for its specific function - the thicker plate portion provides secure locking while the thinner bone portion allows for proper thread engagement in bone tissue.
Solution Approach 2:
The patent incorporates a chamfered step at the transition between the plate-engaging and bone-engaging portions. This preliminary geometric feature facilitates the transition during insertion, guiding the fastener into proper alignment and reducing manufacturing complexity by providing a defined transition zone that is easy to produce.
Data Source
AI summary
A screw fastener for attachment to an orthopedic component such as an orthopedic plate for use in connection with fracture fixation, joint reconstruction or spinal stabilization or fusion is disclosed as having a shank with at least two different shank diameters, one in a plate engaging portion of the shank and one in the bone or other component engaging portion of the shank. At least two of the different shank diameters on the shank include threads, the threads on the two different diameter portions each having substantially the same thread height and pitch. A plate having a threaded aperture, or an adapter having a threaded aperture, is sized such that the threads of the smaller diameter shank portion engage and cooperate with the internal threads of the aperture to correctly align the screw fastener and the implant as the screw fastener is threaded through the implant. The threads on the larger diameter shank portion and the internal threads of the aperture of the implant are sized so that the threads of the larger diameter shank portion are fully engaged with the internal threads of the orthopedic implant.