Modular Trapeziometacarpal Prosthesis With Spherical Head
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Solution Overview
Problem
Existing orthopedic joint prostheses, such as trapezio-metacarpal prostheses, often fail to fully replicate the complex movements of joints, leading to instability, dislocation, and uneven stress distribution, particularly in cases of osteoarthritis, due to inadequate kinematics and fixation methods.
Innovation Solution
A modular metacarpal prosthesis design featuring a spherical head with a modular neck in various sizes, a cup with frustoconical zones and circular grooves for secure fixation, and an implant with a congruent friction zone and high friction coefficient, allowing for improved mobility and stress distribution, and the option to switch between total and semi-anchored configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional joint prosthesis with fixed geometry is used, then the structure is simple, but it cannot adapt to complex joint movements leading to dislocation and instability
Solution Approach 1:
The prosthesis is divided into separate modular components: a stem with spherical head, a interchangeable kinematic element, and a cup. This segmentation allows each component to be optimized independently and enables replacement of the kinematic element to match different joint movements without replacing the entire prosthesis.
Solution Approach 2:
The prosthesis incorporates a spherical head that can rotate freely within the cup, allowing dynamic adaptation to various joint movements. The interchangeable kinematic element can be selected or adjusted to match the specific kinematics of the patient's joint, enabling the prosthesis to dynamically adapt to complex movements rather than being fixed in geometry.
2Reliability
If a prosthesis with fixed kinematics is used, then manufacturing is simple, but it does not adapt to real joint movements causing uneven stress distribution
Solution Approach 1:
The spherical head and cup design provides universal compatibility for different joint movements. The standardized interface allows the same basic prosthesis structure to accommodate various kinematic requirements by simply changing the intermediate kinematic element, achieving multi-functionality without complex manufacturing.
Solution Approach 2:
The prosthesis allows changes in kinematic parameters by interchangeably mounting different kinematic elements on the spherical head. This enables adjustment of movement patterns, rotation axes, and stress distribution characteristics without redesigning or remanufacturing the entire prosthesis, simply requiring parameter changes through component selection.
3Reliability
If an unanchored spacer is used, then the implant procedure is simple, but the spacer dislocates and causes premature wear
Solution Approach 1:
The invention merges the benefits of both anchored and unanchored approaches by combining a fixed stem-provides structural stability and anchoring with a mobile cup-allows natural joint movement and stress distribution. This hybrid design prevents dislocation while maintaining the simplicity of the implant procedure, as the cup is easily attachable and detachable on the spherical head.
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
Enhances stability, mobility, and stress distribution across the joint, reducing the risk of dislocation and premature wear, while providing a flexible therapeutic approach for surgeons to adapt to different pathologies.
Implementation Method 1
At least one of the frustoconical zones has circular grooves to prevent tearing
Implementation Method 2
two frustoconical zones of decreasing section in the direction of its introduction into the bone where it is fixed
Implementation Method 3
an outer surface in contact with the bone(s) and/or the surrounding cartilage(s), and having a good coefficient of friction
Data Source
Figure 1~2
Figure 3~5
AI summary
The prosthesis includes a rod (1) to be attached onto one of the metacarpal bones, said rod (1) being equipped to receive, in an articulated manner, either a cupula (2) to be attached onto the trapezium or an implant (3) capable of replacing said trapezium.