Deformable Threaded Locking Structures for Bone Plates
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Solution Overview
Problem
Variable-angle locking screws tend to cause cross-threading within locking holes due to misalignment of screw head threads with internal threads, reducing the interference fit and mechanical strength at the locked interface.
Innovation Solution
The design incorporates locking structures with complimentary thread geometries, featuring a stronger screw head thread profile interfacing with a more malleable plate hole thread profile, and adjusted edge geometries to minimize mechanical interference at angulated screw orientations, ensuring enhanced control over thread deformation and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable-angle locking screws are used to lock at angulated orientations, then versatility of locking orientations is improved, but cross-threading occurs reducing mechanical strength
Solution Approach 1:
The patent modifies the thread geometry parameters by creating an asymmetric thread profile where the leading flank has a different angle than the trailing flank. This parameter change allows the screw to accommodate angular misalignment during insertion while maintaining proper thread engagement, thereby preventing cross-threading and preserving mechanical strength at angulated orientations
Solution Approach 2:
The asymmetric thread profile is designed in advance to anticipate and compensate for potential misalignment issues. The geometry is pre-configured with a more acute leading flank angle that facilitates initial thread engagement even when the screw is inserted at an angle, preventing cross-threading before it can occur
2Strength
If screw head threads are made stronger to enhance locking, then mechanical strength is improved, but alignment with internal threads becomes more difficult causing cross-threading
Solution Approach 1:
The patent applies asymmetry to the thread profile by creating different flank angles on opposite sides of the thread. The leading flank has a more acute angle that facilitates easier engagement and alignment with the internal threads, while the trailing flank maintains sufficient strength. This asymmetric design allows the stronger thread to align more easily with the internal threads, preventing cross-threading while maintaining mechanical strength
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A bone plate (4) includes a plate (5) body defining an upper surface (18), an opposed bone-facing surface, and a combination hole (90) comprising a locking hole (6) and a compression hole (92) that intersect one another and each extending from the outer surface to the bone-facing surface. The locking hole and the compression hole extend away from each other along a longitudinal axis. The plate body further defines a locking surface (24a) that defines the locking hole, and a second surface (24b) that defines the compression hole. The locking surface further defines a plurality of columns (26) sequentially located about a central axis (22) of the locking hole, a plurality of recesses (28) located, respectively, between at least some of the columns, and plate threads (9) that traverse each of the columns. Crests (56) of the plate threads extend linearly from a first side of each column to a second side of each column.