Bone Fixation Plate Thread Geometry for Variable-Angle Locking
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Solution Overview
Problem
Existing polyaxial bone plate systems are cumbersome and prone to component loss during surgery, and they do not adequately prevent relative motion between the screw and the bone fixation plate, especially when the screw is oriented at non-perpendicular angles.
Innovation Solution
A bone fixation plate with passages defined by inner walls featuring a mismatched thread profile between the screw head and the plate, allowing variable angle locking through sacrificial engagement and a convergent surface to prevent further advancement, facilitating off-axis insertion and secure anchoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bushing or expandable ring is used to lock the screw angle, then variable angle locking is achieved, but the number of components increases making the system cumbersome and prone to component loss
Solution Approach 1:
The patent merges the locking mechanism directly into the plate hole structure by forming threaded inner wall portions with mismatched thread profiles. The bone screw head threads engage with these mismatched threads to lock the screw at a variable angle relative to the plate, eliminating the need for separate bushings or expandable rings. This integration reduces component count while maintaining variable angle locking capability.
2Adaptability or versatility
If a bushing is rotatable within the plate hole to allow variable angulation, then screw orientation flexibility is improved, but the system becomes more complex and manipulation during surgery becomes tedious
Solution Approach 1:
The plate holes are pre-formed with threaded inner wall portions that have mismatched thread profiles during manufacturing. This preliminary preparation allows the bone screw to be directly inserted at various angles without requiring rotation of bushings or other intermediate components during surgery. The mismatched threads are designed in advance to engage the screw head threads and lock the desired angle automatically.
3Adaptability or versatility
If known polyaxial systems use multiple components for angle locking, then variable angle capability is achieved, but relative motion between screw and plate is not sufficiently prohibited
Solution Approach 1:
The patent employs asymmetric mismatched thread profiles on the inner wall portions of the plate holes. The first, second, and third threaded inner wall portions have different thread pitches or thread profiles that do not match the bone screw head threads. This asymmetry creates a mechanical interference that prevents the screw from rotating or moving relative to the plate after insertion, while still allowing variable angle positioning during insertion.
Data Source
AI summary
A bone fixation system for reconstruction and/or trauma treatment of bones, the bone fixation plate comprising: a bone fixation plate configured and dimensioned for application to a patient's bone, the bone fixation plate comprising an in-use upper surface and an in-use lower surface with at least one opening formed on the upper and lower surfaces to form a passage extending from the upper surface to the lower surface; each passage being defined by inner walls extending from the upper surface to the lower surface, the inner walls having a height extending between the upper surface and the lower surface, the inner wall further comprising: a threaded inner wall portion extending from the upper surface towards the lower surface, the threaded inner wall portion having threads with a thread pitch (PW); and a non-threaded lower inner wall portion extending from a lower part of the threaded inner wall portion towards the lower surface of the bone fixation plate; and at least one bone screw with a threaded screw head having threads with a thread pitch (PH) for engaging and interfacing with the threaded inner wall for variable angle anchoring of the threaded screw head during use.