Bowed Ulnar Stem DRUJ Prosthesis for Anatomical Alignment
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Solution Overview
Problem
Current distal radioulnar joint (DRUJ) prosthetic implants only allow two degrees of motion and lack the necessary constraint and anatomical alignment, leading to instability and limited long-term survival due to their straight ulnar stem design, which does not match the natural bow of the ulna.
Innovation Solution
A DRUJ prosthesis with articulating ulnar and radial components, including a bowed semi-flexible ulnar stem with a titanium core and Nitinol outer layer, a radial plate with a reverse triangular shape, and a hemispherical ball that articulates with the ulnar shell via a motion liner, allowing for three degrees of motion and customizable fit to mimic natural wrist kinematics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a straight ulnar stem design is used in current prosthetic implants, then the device complexity is reduced and ease of manufacture is improved, but the anatomical alignment is poor and long-term survival is compromised due to mismatch with the natural bow of the ulna
Solution Approach 1:
The ulnar stem is designed with a bowed configuration that matches the natural curvature of the ulna bone, replacing the traditional straight design. This curved stem follows the anatomical contour of the ulnar medullary canal, improving anatomical alignment and facilitating proper insertion and fixation while maintaining manufacturability through modern forming techniques
Solution Approach 2:
The stem design incorporates variable cross-sectional properties and curvature radius along its length to match the specific anatomical parameters of the ulna. The stem can be customized with different bowing degrees, diameters, and wall thicknesses to accommodate individual patient anatomy, optimizing both fixation and anatomical compatibility
2Ease of operation
If current prosthetic implants are designed with limited constraint, then ease of operation is improved, but stability is reduced leading to loosening and failure
Solution Approach 1:
The prosthesis employs a dynamic constraint system that adapts to physiological loading conditions. The ulnar stem features modular fixation options including press-fit, cemented, or locked configurations that can transition between mobile and fixed states based on functional demands, providing optimal stability during implantation and long-term use while maintaining ease of intraoperative adjustment
Solution Approach 2:
The prosthesis is divided into modular components including the ulnar stem, radial component, and articulating surfaces, allowing independent optimization of each segment's constraint characteristics. The radial component can be separately adjusted to provide appropriate constraint in specific directions while maintaining overall system stability and ease of positioning
3Ease of manufacture
If current implants do not preserve ligaments, then ease of manufacture is improved, but the range of motion is limited and natural wrist kinematics are not replicated
Solution Approach 1:
The prosthesis design selectively preserves ligamentous structures by extracting only the damaged or degenerated cartilaginous surfaces for replacement. The ulnar stem and radial component are positioned to maintain attachment points for the triangular fibrocartilage complex (TFCC) and other stabilizing ligaments, allowing these soft tissues to remain intact and functional while providing mechanical support where needed
Solution Approach 2:
The articulating components are designed with universal geometric features that work in conjunction with preserved ligaments to provide multi-directional motion. The radial component's articulation surface and ulnar stem configuration enable compatibility with various ligament attachment patterns, allowing the prosthesis to function effectively whether ligaments are fully preserved, partially preserved, or require augmentation
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 prosthesis provides stability and full range of motion, including translation along the dorsal-palmar plane, by matching the natural anatomy of the ulna and maintaining tension in the interosseous membrane, enhancing long-term fixation and functionality.
Implementation Method 1
a bowed semi-flex flexible ulnar stem with a titanium core and Nitinol outer layer
Implementation Method 2
a bowed semi-flexible ulnar stem with a titanium core and Nitinol outer layer
Implementation Method 3
a hemispherical ball which allows for articulation with the distal end of the ulnar component via a motion liner
Data Source
AI summary
A distal radioulnar joint prosthesis for replacing the distal radioulnar joint and a method for its implantation is provided. Such a device includes an ulnar component, a radial component, and a motion liner. The ulnar component includes a stem, a collar, and a shell. The radial component includes a hemispherical ball and plate. The hemispherical ball of the radial component is secured with the radial plate and articulates with the ulnar shell via the motion liner. The prosthesis is designed to more accurately replicate the biomechanics of the distal wrist than currently used implants.