Safety Coupling Shear Pin for Orthopedic Knee Implant
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Solution Overview
Problem
The strong connection between the transition adapter and natural bone can lead to fractures under extreme force loads, particularly torsional moments, which can cause spiral fractures or femoral neck fractures, and existing solutions are costly and complex.
Innovation Solution
A disengaging safety coupling with a shear pin mechanism that slips when a maximum torsional moment is exceeded, preventing the transmission of high torsional forces to the femoral stump, and allowing manual reactivation after the event, with adjustable settings for the maximum moment value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the connection between the transition adapter and natural bone is made strong to ensure stable fixation, then the stability and integration of the implant is improved, but the risk of fractures under extreme torsional loads increases
Solution Approach 1:
The patent introduces a safety coupling as an intermediary element between the first coupling part (connected to bone) and the second coupling part (connected to exoprosthesis). This safety coupling includes a shear pin that acts as a mediator to protect the bone-implant connection by allowing controlled failure before the strong bone connection is compromised.
Solution Approach 2:
The safety coupling with shear pin is designed to fail beforehand under extreme torsional loads, cushioning the protective effect against the strong bone-implant connection. The shear pin is positioned to fail at a predetermined torque level, preventing higher forces from reaching the bone interface.
2Object-affected harmful factors
If a predetermined breaking point is designed into the prosthesis to prevent femoral stump fractures, then the protection against extreme loads is improved, but the device complexity and cost increase
Solution Approach 1:
The patent extracts the safety function from the main prosthesis structure and places it in a separate, dedicated safety coupling component. The shear pin is a simple, isolated element that can be easily replaced, separating the complex exoprosthesis from the simple sacrificial safety element.
Solution Approach 2:
The shear pin is designed as a cheap, replaceable component that may fail under extreme loads. Instead of making the entire prosthesis complex and expensive with built-in breaking points, a simple disposable shear pin provides the necessary protection.
3Object-affected harmful factors
If the shear pin is designed to shear at a specific torque to protect the bone connection, then the protection against spiral fractures is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent allows adjustment of the shear pin's material properties and geometric parameters (diameter, length, material strength) to achieve the desired shear torque. By changing these parameters, the same simple shear pin design can protect against different load levels without requiring complex manufacturing precision.
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
Prevents spiral fractures by allowing the exoprosthesis to rotate without transmitting excessive torsional moments to the femoral stump, with adjustable settings and cost-effective maintenance by replacing shear pins.
Implementation Method 1
The central function of the safety clutch is performed by the at least one shear pin. This is designed in such a way that it shears off after the maximum value of the torsional moment is exceeded
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a connection adapter between a rigid transcutaneous implant, which can be anchored intracorporeally in a femoral stump, and a part of an extracoporeal orthopaedic knee joint, said connection adapter comprising a first coupling part (1) for connection to the transcutaneous implant and a second coupling part (2) for connection to the knee joint, wherein the second coupling part (2) can be connected releasably to the first coupling part (1), wherein a safety coupling (3) is arranged in the interior of the second coupling part (2) and transfers a torsional moment between the first coupling part (1) and the second coupling part (2) and slips through when an adjustable maximum value of the torsional moment is exceeded.