Modular Screw Apparatus for Orthopedic Shell Stability
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Solution Overview
Problem
The existing shell and liner systems in arthroplasty procedures often detach during trial reduction or implantation due to off-axis torquing, material fatigue, or improper design, leading to instability and increased surgery time.
Innovation Solution
A modular screw apparatus with a female and male component configuration that includes a press or snap fit connection, and can be fused using electron beam welding, allowing rotation and providing a radially extending flange to withstand off-axis forces, thereby enhancing fixation and preventing detachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional attachment mechanism is used to connect the liner to the shell, then the assembly is simple to manufacture, but the connection fails under off-axis torquing and material fatigue causing detachment
Solution Approach 1:
The modular screw is divided into two separate components: a first component with a threaded portion that engages the shell, and a second component with a head that engages the liner. This segmentation allows each component to be optimized for its specific function - the threaded portion resists off-axis torquing through threaded engagement with the shell, while the head portion provides a bearing surface for the liner. The segmented design eliminates the detachment problems of traditional single-piece attachment mechanisms while maintaining manufacturing feasibility through separate fabrication and assembly of the two components.
Solution Approach 2:
The second component of the modular screw is positioned within a cavity of the first component, creating a nested configuration. The head of the second component sits within the cavity of the first component, with the bearing surface of the head engaging the liner from the inside. This nesting arrangement allows the modular screw to withstand off-axis forces while maintaining a compact structure that does not significantly increase the overall device complexity.
2Strength
If a modular screw with two components is used to withstand off-axis forces, then the stability and reliability improve, but the manufacturing process becomes more complex
Solution Approach 1:
By segmenting the screw into two components with distinct functions, each component can be manufactured using optimized processes for its specific requirements. The threaded portion can be manufactured with precise threading to engage the shell, while the head portion can be manufactured with a smooth bearing surface for liner engagement. This segmentation actually simplifies manufacturing by allowing each component to be produced independently with specialized processes, then assembled through straightforward threading and positioning.
3Adaptability or versatility
If the modular screw allows rotation relative to the liner, then the range of motion assessment is improved, but the fixation stability may be compromised
Solution Approach 1:
The modular screw is designed with controlled rotational capability - the second component can rotate relative to the liner within the cavity, allowing for dynamic movement assessment during trial reduction procedures. However, the threaded engagement of the first component with the shell and the bearing surface engagement with the liner provide sufficient constraint to maintain fixation stability. This dynamic design allows the system to accommodate necessary movements while preventing pathological detachment, resolving the contradiction between motion assessment and fixation stability.
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 modular screw apparatus improves the stability of the shell and liner system during trial reduction, reducing the risk of detachment and minimizing surgery time by providing increased fixation and withstanding off-axis torquing forces.
Implementation Method 1
the male component and the female component can be fused together using electron beam welding
Data Source
AI summary
An orthopedic instrument comprises a shell configured to be inserted into a cup-shaped site, a liner configured to be received within a cavity of the shell, wherein the liner has an aperture and a mating feature adjacent to the aperture, and a modular screw configured to be received within the aperture of the liner. The modular screw can include a first component that is positionable adjacent to a first side of the mating feature and a second component that is positionable adjacent to a second side of the mating feature. When assembled, the modular screw can be configured to rotate relative to the liner.