Variable Inclination Humeral Head Prosthesis
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Solution Overview
Problem
Current shoulder arthroplasty systems lack the ability to provide variable inclination and version of the humeral head component, leading to component malposition and increased inventory needs, with existing methods being cumbersome or difficult to implement.
Innovation Solution
A joint prosthesis system that includes a stem or stemless device with an adapter and mounting stud, allowing for adjustable inclination and version of the prosthetic tray with respect to the stem, using a semi-spherical surface and taper lock mechanism for precise alignment and secure fitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple humeral stems with fixed inclination angles are manufactured, then the inclination range is covered, but inventory requirements increase significantly
Solution Approach 1:
The humeral head component is separated from the stem, allowing independent adjustment of inclination angle. The modular design enables the head to be positioned at various angles relative to the stem using a set screw mechanism, eliminating the need to manufacture multiple stemmed components with fixed inclinations.
Solution Approach 2:
The humeral head component is made adjustable rather than fixed. A set screw mechanism allows the inclination angle to be modified intraoperatively, transforming a static component into a dynamic one that can adapt to different anatomical requirements without increasing inventory.
2Adaptability or versatility
If a set screw is used to lock inclination angle, then adjustability is achieved, but the set screw becomes a weak link problematic during removal
Solution Approach 1:
A polyaxial collar is introduced as an intermediary component between the humeral head and the stem. The collar receives the head and provides the adjustment mechanism, while the set screw locks the collar at the desired angle. This distributes the functional load and reduces stress concentration on the set screw itself.
Solution Approach 2:
The adjustment and locking function is separated from the primary load-bearing path. The set screw only needs to maintain positional orientation rather than bear mechanical loads, as the collar and stem interface handle the structural forces.
3Adaptability or versatility
If a lateral opening in the humeral stem is used to fix inclination, then adjustment is possible, but stem removal becomes impossible without removing the humeral head
Solution Approach 1:
The humeral head assembly is completely separated from the stem, with each component able to be removed independently. The head attaches to the stem via the modular interface with collar and set screw, allowing the head to be detached without affecting the stem implantation.
Solution Approach 2:
The fixation mechanism is extracted from the stem itself and placed in the head assembly. The lateral opening concept is replaced by a self-contained adjustment mechanism in the head that does not compromise stem integrity or removal.
4Manufacturing precision
If complex assembly with locking mechanism is used, then inclination is fixed, but the assembly process requires more than ten steps and reduces flexibility
Solution Approach 1:
The adjustment and locking functions are combined into a single set screw mechanism. One screw simultaneously controls both the inclination angle adjustment and the locking function, reducing the number of separate steps required compared to multi-component locking systems.
Solution Approach 2:
The system allows dynamic adjustment during assembly. The set screw can be positioned at any point along its threaded path to achieve the desired inclination angle, providing continuous adjustment rather than discrete angular positions, which simplifies the assembly process.
Data Source
AI summary
Methods and devices are disclosed for joint (e.g., shoulder) arthroplasty, including for reverse joint arthroplasty. In one aspect, there is provided a trial device for determining inclination, offset, and/or version of a prosthetic tray with respect to a prosthetic stem or stemless implant. In another aspect, there is provided a joint (e.g., shoulder) prosthesis, which allows for variable offset, inclination or version or any combination thereof. In another aspect, there is provided a method for setting an offset or inclination angle or a version angle or any combination thereof of a prosthetic tray with respect to a stem or stemless device implanted or to be implanted in a bone of a joint (e.g., shoulder) by matching the corresponding offset or version or inclination or any combination thereof to a trial device.