Bone Fixation Plate Spherical Screw Locking Mechanism
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Solution Overview
Problem
Existing bone fixation plates for the cervical spine face challenges such as screw backout, inadequate purchase, and high profile designs, which lead to complications like irritation and abrasion of surrounding tissues, and insufficient ability to accommodate movement of vertebrae during bone graft compression.
Innovation Solution
A bone fixation plate with spherical curvature openings and a locking mechanism that allows screws to be easily and reliably locked in place, preventing backout through a sliding fit and interference points, while maintaining a low profile and accommodating micromotion and bone graft compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long screws are used to achieve sufficient purchase and prevent backout, then screw holding power is improved, but the plate profile increases and screw interference with each other occurs
Solution Approach 1:
The opening in the plate is formed with a spherical curvature that receives the spherical head of the screw. This curved geometry creates an interference fit between the screw head and the opening, preventing screw backout without requiring longer screws or increasing the plate profile. The spherical surfaces provide mechanical interlocking through geometric constraint.
2Strength
If screw length is minimized to prevent screw to plate junction breakage, then hardware failure risk is reduced, but screw purchase in bone becomes insufficient
Solution Approach 1:
The spherical curvature of the opening creates an interference fit with the spherical screw head, providing mechanical retention without requiring long screw lengths. The geometric interference prevents screw backout while allowing the use of shorter screws that are less prone to breakage at the plate junction.
3Stability of the object's composition
If rigid fixation is used to maintain desired spacing between vertebrae, then bone graft compression is prevented, but vertebrae cannot accommodate micromotion during graft healing
Solution Approach 1:
The spherical opening and spherical screw head create a dynamic interface that allows controlled micromotion between the plate and vertebrae during bone graft healing, while maintaining overall spacing stability. The spherical geometry permits small angular adjustments and positional variations without compromising the fixed spacing between vertebral bodies.
Data Source
AI summary
An apparatus for reducing the profile of a bone fixation plate while preventing backing out of screws is disclosed. The plate has at least two openings though which two screws can pass through bony tissue. The apparatus includes at least one section of relief and sections of engagement. As the screw is tightened, it will begin to lag the plate to the bone. When the screw head interferes with the plate at the interference point, there is a slight resistance that insertion forces can overcome. When the screw is advanced further, it snaps into the sliding fit area and is allowed to move freely. The forces that cause the screw to back out from the plate are preferably not strong enough to pass the screw head back past the interference section. At least one of the two openings is configured as an elongated slot to allow the screw to translate in the slot. It may be desirable to include a set screw to help prevent backout.