Bone Plate Locking Mechanism for Polyaxial Screw Retention
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Solution Overview
Problem
Standard bone plates and screws face issues with screw backout and inadequate bone purchase due to improper screw positioning, leading to reduced construct strength and potential patient discomfort, necessitating additional surgeries.
Innovation Solution
A bone plate design featuring offset, ramped upper and lower lips around screw holes with a countersink, allowing for polyaxial screw placement and deformation upon insertion, combined with a screw of harder material to secure the screw in place and facilitate various angular orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard bone plate and screw constructs are used, then the bone plate can be affixed to the bone, but the screws tend to back out of plate holes after implantation
Solution Approach 1:
The bone screw hole is segmented into multiple functional zones: an entry portion with first lips for initial screw engagement, a body portion with second lips for lateral engagement, and a countersink for head seating. This segmentation allows different portions of the hole to perform distinct functions - the first lips prevent backout while the second lips enable polyaxial positioning
Solution Approach 2:
The first and second lips are designed to be deformable rather than rigid. When a screw is inserted, the lips deflect elastically to accommodate the screw head and shaft, then maintain continuous contact pressure against the screw. This dynamic behavior allows the lips to adapt to screws at various angles while still preventing backout through elastic retention forces
2Adaptability or versatility
If screws are placed at fixed angles in bone screw holes, then the plate structure is simple, but the ability to achieve proper bone purchase is limited
Solution Approach 1:
Different regions of the bone screw hole have different geometric properties tailored to specific functions. The entry portion has first lips that are optimized for preventing screw backout through elastic deflection, while the body portion has second lips configured for engaging screws at various angles. The countersink provides a specific geometry for head seating. This local differentiation of hole properties enables both versatility and structural efficiency
3Reliability
If threaded plate holes are used to prevent screw backout, then screw retention improves, but the ability to accommodate polyaxial screw placement is reduced
Solution Approach 1:
The invention merges two previously separate functions into a single integrated bone screw hole structure: the first lips provide threaded engagement for preventing backout, while the second lips provide a deformable barrier that engages screws laterally regardless of angle. Both sets of lips work together within the same hole to simultaneously achieve screw retention and polyaxial accommodation without requiring separate components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively prevents screw backout and enables proper bone purchase, enhancing the stability and ease of use of bone plates, reducing the need for additional surgeries and improving patient comfort.
Implementation Method 1
Placement of the bone screw through the bone plate may result in a deformation or deflection of the first and second lips
Implementation Method 2
the first and second lips may include ramped surfaces... Placement of the bone screw through the bone plate may result in a deformation or deflection of the first and second lips
Data Source
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AI summary
A bone plate locking mechanism and methods for utilizing same are disclosed. A bone plate in accordance with the present invention includes a bone screw hole having a plurality of first lips and a plurality of second lips. The first lips are closer to the upper surface than the second lips and the first and second lips are offset around the bone screw hole.