Mechanical Peg Prosthesis for Revision Surgery Bone Conservation
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Solution Overview
Problem
Current joint prostheses with porous and solid metal components face challenges in revision surgery due to difficulties in dislodging extensions from bone, leading to excessive bone resection and potential bone pathologies, especially when bone has grown into the extensions, complicating the removal process and requiring more extensive bone removal.
Innovation Solution
A joint prosthesis design featuring a solid metal portion with a chamfered chamber and a porous metal peg, where the peg is mechanically fixed without a metallurgical connection, allowing for easier removal by cutting along the bone-engaging surface and using a trephine saw to dislodge the pegs, conserving native bone and reducing the need for large resections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If porous metal pegs are used to extend into bone for stabilization, then bone ingrowth and fixation are improved, but removal during revision surgery becomes difficult and requires excessive bone resection
Solution Approach 1:
The peg is divided into two distinct segments: a porous metal portion for bone ingrowth and fixation, and a solid metal portion for mechanical retention in the prosthesis. This segmentation allows each portion to serve its specific function optimally while enabling easier removal during revision surgery by separating the bone-engaging porous portion from the prosthesis-connected solid portion.
Solution Approach 2:
The invention extracts the porous metal peg from the solid metal prosthesis body, allowing it to be removed independently during revision surgery. The porous peg can be extracted from the bone without requiring removal of the entire prosthesis, thereby conserving native bone and reducing surgical complexity.
2Strength
If extensions are made of solid metal for structural strength, then mechanical strength is improved, but bone ingrowth capability deteriorates
Solution Approach 1:
The extension is constructed as a composite structure combining porous metal and solid metal materials. The porous metal portion provides bone ingrowth capability and surface area for biological integration, while the solid metal portion provides structural strength and mechanical retention within the prosthesis. This composite approach resolves the contradiction between biological and mechanical requirements.
3Strength
If porous metal pegs are sintered to solid metal base, then connection strength is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention replaces the metallurgical sintering process with a mechanical interference fit system. The tapered peg portion is inserted into a corresponding tapered hole in the solid metal base, creating a secure mechanical connection through friction and geometric interlocking. This mechanical connection system is simpler to manufacture than sintering, as it eliminates the need for high-temperature processing and complex joining equipment.
4Reliability
If pegs are designed to penetrate deep into bone for stabilization, then fixation reliability is improved, but bone loss during revision increases
Solution Approach 1:
The invention introduces a dynamic removal mechanism where the porous peg can be selectively extracted from the bone during revision surgery. The peg is designed with a retention mechanism (tapered fit, set screws, or other fastening methods) that allows controlled removal without requiring extensive bone resection. This dynamic design enables the peg to be removed intact or in pieces, minimizing bone loss while maintaining fixation reliability during the primary implantation.
Data Source
AI summary
An orthopaedic prosthesis for cementless fixation has a solid metal base and porous metal pegs extending out from the base. The pegs are mechanically, rather than metallurgically, fixed to the base. A process for making such a prosthesis is also disclosed.