Dual-Modulus Hip Stem Structure for Reduced Stress Shielding
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Solution Overview
Problem
Metallic femoral prostheses with high elastic modulus shield the bone from stress, leading to inadequate bone remodeling and potential implant failures due to mismatch in elastic properties between the prosthesis and the patient's bone.
Innovation Solution
An orthopaedic prosthesis comprising a metallic foam shell with a low elastic modulus and a metallic core with a high elastic modulus, where the foam shell engages the patient's femur and the core receives the femoral head component, reducing stiffness and promoting bone integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metallic stem component with high elastic modulus is used, then the strength and load-bearing capacity of the prosthesis is improved, but the bone tissue is shielded from stress leading to inadequate bone remodeling
Solution Approach 1:
The stem component is segmented into a metallic core and a foam shell layer, with each segment serving a distinct function. The metallic core provides strength and load-bearing capacity, while the foam shell layer transmits stress to the bone tissue to promote remodeling. This segmentation resolves the contradiction by separating the conflicting requirements of strength and bone stimulation into different spatial zones.
Solution Approach 2:
The prosthesis employs a composite structure combining metallic material (high elastic modulus) and foam material (low elastic modulus). This composite design allows the metallic core to provide necessary mechanical strength while the foam shell layer provides stress transmission to the bone, simultaneously satisfying both the strength requirement and the bone remodeling requirement.
2Stability of the object's composition
If a metallic stem component with high elastic modulus is used, then the structural integrity of the prosthesis is improved, but stress shielding occurs causing potential implant failures
Solution Approach 1:
Different regions of the stem component are assigned different material properties: the metallic core maintains high elastic modulus for structural integrity, while the foam shell layer has low elastic modulus to allow stress transmission. This local differentiation of material quality eliminates stress shielding in the regions where bone contact occurs, while preserving overall structural integrity.
Solution Approach 2:
The foam shell layer acts as an intermediary between the metallic core and the bone tissue. It transmits mechanical stress from the core to the surrounding bone, preventing stress shielding while the core maintains structural integrity. This intermediary layer resolves the harmful effect of stress shielding without compromising the overall structural stability.
3Reliability
If the foam shell thickness is increased to reduce stiffness, then bone remodeling is promoted, but the overall strength of the prosthesis decreases
Solution Approach 1:
The prosthesis is divided into functional segments: the metallic core segment provides strength and stiffness, while the foam shell segment provides compliance and stress transmission. This segmentation allows optimization of each segment's thickness independently, promoting bone remodeling through adequate foam layer thickness without compromising overall strength through the reinforcing metallic core.
Solution Approach 2:
The composite structure of metallic core and foam shell allows the system to achieve an optimal balance between strength and compliance. The metallic core compensates for the reduced stiffness of the thicker foam shell, maintaining overall prosthesis strength while the foam layer promotes bone remodeling through stress transmission.
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 combination of low modulus foam shell and high modulus core reduces stress shielding, enhancing bone remodeling and implant stability, thereby improving the longevity and effectiveness of the hip replacement surgery.
Implementation Method 1
The foam shell includes a sheath and a cover layer. The metallic core includes a neck positioned proximal of the sheath, the neck being configured to receive a femoral head component, a first core segment positioned in the sheath, and a second core segment positioned distal of the sheath. The cover layer of the foam shell extends distally from the sheath, and the cover layer engages only a lateral surface of the second core segment.
Implementation Method 2
The metallic core includes a neck positioned proximal of the sheath, the neck being configured to receive a femoral head component, a first core segment positioned in the sheath, and a second core segment positioned distal of the sheath.
Data Source
AI summary
An orthopaedic prosthesis for use in a hip replacement surgery. The orthopaedic prosthesis includes a metallic foam shell and a metallic core. The metallic core includes a neck configured to receive a femoral head component and a stem extending through the metallic foam shell.