Ceramic Femoral Resurfacing Head With Anti-Rotation Fixation
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Solution Overview
Problem
Conventional metal-on-metal femoral resurfacing hip prostheses produce metal ions that can cause adverse health effects and have a risk of detachment from the bone cement, leading to potential failure and bone resorption.
Innovation Solution
A ceramic femoral resurfacing head prosthesis with a ceramic convex outer contact surface, a concave inner fixation surface with increased inner-land area, and a shorter ceramic stem, featuring a two-part angular transition and anti-rotation elements to enhance adhesion and reduce stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal-on-metal femoral resurfacing prosthesis is used, then the prosthesis provides structural strength and durability, but metal ions are produced that can cause adverse health effects
Solution Approach 1:
The patent changes the material composition parameter by replacing metal with ceramic materials. The ceramic femoral head and acetabular cup are formulated with specific ceramic compositions (e.g., alumina, zirconia, or composite ceramics) that provide the necessary mechanical strength and wear resistance without producing harmful metal ions, thus resolving the contradiction between durability and harmful ion production
Solution Approach 2:
The patent employs composite ceramic materials that combine different ceramic phases or ceramic with bonding agents to achieve both the required mechanical strength for prosthesis durability and the biocompatibility that prevents harmful ion production. The composite structure allows optimization of both strength and chemical inertness
2Reliability
If a conventional metal femoral resurfacing head prosthesis is used, then the prosthesis provides adequate fixation, but there is a risk of partial or total detachment from the bone cement
Solution Approach 1:
The patent applies local quality by creating specific surface features and geometric configurations at the fixation interface. The ceramic prosthesis includes engineered surface roughness, porous coatings, or geometric interlocking features at the bone cement interface that locally enhance adhesion and mechanical interlocking, preventing detachment while maintaining overall fixation stability
Solution Approach 2:
The patent utilizes optimized spherical curvature of the femoral head and corresponding acetabular cup geometry to distribute contact stresses uniformly across the articulation surface. This curved geometry prevents stress concentration that could lead to fixation failure, while the precise spherical fit enhances the mechanical interlocking with bone cement, reducing detachment risk
3Reliability
If the inner-land area of the femoral resurfacing head is increased to maximize bone volume, then bone resorption from stress shielding is minimized, but the stem length must be reduced
Solution Approach 1:
The patent resolves the length contradiction by transitioning to ceramic materials with superior specific strength (strength-to-weight ratio). The ceramic stem can achieve the required mechanical strength with reduced dimensions, allowing the inner-land area to be maximized for stress distribution and bone preservation, while the shortened stem still provides adequate fixation through the ceramic material's inherent strength properties
4Object-generated harmful factors
If a ceramic femoral resurfacing head prosthesis is used, then metal ion production is minimized and wear is reduced, but ceramics are brittle and fracture can be unpredictable
Solution Approach 1:
The patent employs composite ceramic materials such as zirconia-toughened alumina (ZTA) or alumina-reinforced zirconia that combine the wear resistance and chemical inertness of ceramics with enhanced fracture toughness. The composite structure includes phases that can deflect or arrest crack propagation, making the ceramic prosthesis more resistant to unpredictable fracture while maintaining the benefits of low metal ion production and reduced wear
Solution Approach 2:
The patent incorporates design features that preemptively address potential fracture risks through optimized geometry, such as eliminating sharp corners and stress concentration points, and incorporating gradual transitions in thickness. The prosthesis design anticipates potential failure modes and incorporates features that cushion against stress concentrations before they can initiate catastrophic fracture
Data Source
AI summary
A ceramic femoral resurfacing head prosthesis (110) comprises a ceramic convex outer contact surface (112) engagable with an acetabulum of a patient or an acetabular cup prosthesis and a concave inner fixation surface (114) having an inner-land portion (128), the ceramic convex outer contact surface (112) and the concave inner fixation surface (114) extending to intersect each other at a rim (116). A ceramic stem (120) projects from the concave inner fixation surface (114), and is adapted to be received by a stem bore. The concave inner fixation surface (114) includes a skirt (134) which is cylindrical or substantially cylindrical, or frusto-conical or substantially frusto-conical, and at least one circumferentially elongate recess (136) at the skirt (134).