Mobile Ulna Head Implant for Transverse Load Distribution
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Solution Overview
Problem
Partial ulna head implants fail to effectively distribute transverse loads during forearm rotation, leading to decalcification of the ulna head and weakening of surrounding ligaments due to the transmission of these loads to the implant stem, rather than the remaining ulna and ligaments.
Innovation Solution
A partial ulna head implant with a mobile hemispherical head made of pyrocarbon, connected to a rod that is held in place by elastic deformation, allowing transverse translation and reducing wear by distributing loads back to the ulna and ligaments, while being secured by the triangular ligament and ulnocarpal ligaments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the head of the implant is rigidly fixed to the rod, then the implant stability is improved, but the transverse loads are transmitted to the stem causing decalcification of the ulna head
Solution Approach 1:
The head of the implant is made mobile relative to the rod through a clearance between the stud and the head, allowing transverse translation. This dynamic design enables the head to move and come to rest against the remaining ulna head or surrounding ligaments during patient movements, thereby transmitting transverse loads to these structures rather than to the rod, preventing decalcification while maintaining implant stability through the triangular ligament and ulnocarpal ligaments
2Object-affected harmful factors
If the head of the implant is made mobile relative to the rod, then the load distribution is improved, but the implant complexity increases
Solution Approach 1:
The implant is divided into distinct functional components: a head for load transmission, a rod for positioning, and a stud connecting them with intentional clearance. This segmentation allows the head to move independently relative to the rod, enabling load distribution to surrounding structures while keeping each component simple in design
Solution Approach 2:
The stud acts as an intermediary element between the head and rod, with its axis parallel but not coincident with the rod axis. The clearance between the stud and head creates a mechanical mediator that allows controlled transverse movement while maintaining connection, simplifying the overall structure compared to more complex joint mechanisms
3Ease of manufacture
If the rod is held by elastic deformation, then the ease of placement is improved, but the holding strength is reduced
Solution Approach 1:
The rod's holding mechanism utilizes elastic deformation, changing the mechanical parameter from rigid fixed to flexible elastic. This allows the rod to be easily inserted and held in place through elastic recovery, while the overall implant stability is maintained by the strong triangular ligament and ulnocarpal ligament attachments that compensate for the reduced holding strength of the elastic deformation mechanism
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
This design maintains the natural load distribution on the ulna and ligaments, preventing decalcification and ligament weakening, while allowing easy placement and adjustment of the implant, ensuring the stability and functionality of the ulna head during pronation and supination.
Implementation Method 1
The rod 2 is for example secured to a stud engaged in a bore of the head, the mobility in transverse translation of the head relative to the rod being obtained by a clearance between the stud and the head
Implementation Method 2
to prevent the head of the implant from wearing out during its movements relative to the holding element or from wearing out the neighboring bones, said head is made of pyrocarbon and its outer surface is polished
Data Source
Figure 1
Figure 2
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AI summary
The invention relates to an implant, especially a partial implant of the head of the ulna, said implant comprising a head (1) for replacing at least one lateral articular part of a bone receiving transversal loads, and a holding element (2) which is connected to the head (1) and is to be fixed to the bone. Said implant is characterised in that the head (1) is mobile in translation in relation to the holding element (2) in at least one direction which corresponds to a direction of the transversal loads when the implant is in place in the patient.