Conical Stem Interphalangeal Prosthesis for Ligament Preservation
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Solution Overview
Problem
Existing interphalangeal and metacarpal-phalangeal joint prostheses require substantial bone resection and can damage collateral ligaments, leading to joint stiffening and reduced mobility due to their design, which does not accurately mimic the natural joint structure.
Innovation Solution
A distal component with a conical stem portion and a separate head portion that can be snap-fitted together, minimizing bone resection and retaining collateral ligaments, allowing for more natural joint movement and flexibility, while being modular for customizable implant sizes and materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional two-part prosthesis with flat bearing surfaces are used, then articulating contact is achieved, but substantial bone resection is required and collateral ligaments are damaged
Solution Approach 1:
The patent applies spheroidality by providing a prosthesis with a conical stem portion and a head portion where the bearing surface is substantially domed rather than flat. This curved surface configuration allows the prosthesis to articulate within a conical recess in the bone, eliminating the need for extensive flat bone resection and preserving collateral ligaments that would otherwise be damaged by flat-surface prostheses.
2Reliability
If one-piece prosthesis with hinge mechanism are used, then joint replacement is achieved, but long-term joint stiffening occurs
Solution Approach 1:
The patent applies segmentation by dividing the prosthesis into two separate components: a stem portion and a head portion. This segmentation allows the head to rotate freely on the conical stem without the constraints of a hinge mechanism, thereby maintaining natural joint mobility and preventing long-term stiffening while still achieving reliable joint replacement.
3Reliability
If flat bearing surface prosthesis are used, then articulation is achieved, but collateral ligaments are damaged or lost
Solution Approach 1:
The domed bearing surface of the head portion articulates within a conical recess, creating a curved contact path that preserves the attachment points of collateral ligaments. This curved geometry allows articulation to occur without the need for flat bone resection that would otherwise damage or remove these ligaments.
4Ease of manufacture
If substantial bone resection is performed to accommodate flat prosthesis, then prosthesis insertion is enabled, but joint mobility is reduced
Solution Approach 1:
The conical stem and domed head configuration requires only a conical recess in the bone rather than extensive flat resection. This curved geometry enables straightforward prosthesis insertion while preserving surrounding bone and ligament structures, thereby maintaining natural joint mobility.
Data Source
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AI summary
A distal component for an interphalangeal prosthesis suitable for insertion into a proximal end of a distal phalangeal bone, said component comprising: a stem portion (4) shaped to be received within a surgically prepared bore in the proximal end of the distal bone, said stem portion generally tapering inwardly from a proximal to a distal end and having a central longitudinal axis extending from the distal end to the proximal end; and a head portion (5) having an under-surface (7) and an upper-surface (6), the under-surface of which in use will bear on the bone into which the stem is implanted, said head portion extending from the stem portion and being ramped away therefrom at an angle of greater than 90° to the longitudinal axis of the shaft; said upper-surface comprising an articulating surface shaped to enable a cooperating surface on a distal end of a proximal bone forming said joint to articulate there-against.