Multi-layer Acetabular Shell Stiffness Matching
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Solution Overview
Problem
Conventional metal-backed orthopedic components, such as acetabular cups, cause stress shielding, leading to bone atrophy and resorption due to their high stiffness, which is not compatible with natural bone, and require a minimum polymer thickness of 4-6 mm to reduce contact stress, limiting design flexibility and increasing material usage.
Innovation Solution
An orthopedic component with multiple layers, featuring a porous metal outer layer and a biocompatible polymer inner layer, such as PEEK or UHMWPE, to achieve a lower overall stiffness similar to bone, allowing for customization and reduced material usage while maintaining joint stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal-backed acetabular component is used, then structural strength and stability are improved, but stress shielding occurs leading to bone atrophy and resorption
Solution Approach 1:
The patent applies composite materials by combining a metal backing component with a polymer liner layer to create an acetabular cup that balances structural strength with bone-compatible stiffness. The metal backing provides mechanical strength while the polymer layer reduces stress shielding effects, allowing stress distribution more similar to natural bone.
Solution Approach 2:
The patent applies local quality by creating different regions with different material properties within the acetabular component. The metal backing provides high strength where needed for structural support, while the polymer liner provides lower stiffness in the articulating surface region to reduce stress shielding and improve bone compatibility.
2Stress or pressure
If a thick polymer liner (4-6 mm) is used in metal-backed acetabular components, then contact stress is reduced, but material usage and device complexity increase
Solution Approach 1:
The patent applies parameter changes by optimizing the polymer liner thickness to a range of 2-4 mm, which is thinner than the conventional 4-6 mm minimum. This parameter optimization maintains adequate contact stress distribution while reducing polymer material usage and simplifying the device structure.
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
The customized orthopedic component reduces stress shielding, allows for optimal bone retention, and enables thinner polymer layers without increased contact stress, enhancing surgical fit and extending component lifespan through antioxidant stabilization.
Implementation Method 1
molding the inner layer to the bone contacting layer to form at least one of the bone contacting layer, an interdigitation layer, and an inner layer to have the selected thickness
Data Source
AI summary
An orthopedic component having multiple layers that are selected to provide an overall modulus that is substantially lower than the modulus of known orthopedic components to more closely approximate the modulus of the bone into which the orthopedic component is implanted. In one exemplary embodiment, the orthopedic component is an acetabular shell. For example, the acetabular shell may include an outer layer configured for securement to the natural acetabulum of a patient and an inner layer configured to receive an acetabular liner. The head of a femoral prosthesis articulates against the acetabular liner to replicate the function of a natural hip joint. Alternatively, the inner layer of the acetabular shell may act as an integral acetabular liner against which the head of the femoral prosthesis articulates.