Intramedullary Space-Truss Implants for Stress-Shielding Control
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Solution Overview
Problem
Total hip replacement surgeries often result in periprosthetic osteolysis due to adaptive bone remodeling caused by stress shielding from implants, leading to implant loosening and failure.
Innovation Solution
An intramedullary implant with a space truss structure that distributes stress evenly through the bone by using a web structure composed of struts and nodes, applying microstrain and osteogenic responses to promote bone integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal stem implant is inserted into the bone, then the mechanical strength and load-bearing capacity are improved, but stress shielding occurs causing reduced load on proximal bone leading to osteolysis and implant loosening
Solution Approach 1:
The implant stem is segmented into multiple regions with varying structural characteristics. The proximal portion includes porous coating and reduced rigidity features, while the distal portion maintains higher strength. This segmentation allows differential stress distribution - the proximal segment transfers load to bone to prevent osteolysis, while the distal segment provides overall structural support.
Solution Approach 2:
Different portions of the implant stem are given different local properties. The proximal portion has porous coating and reduced rigidity to promote bone ingrowth and stress transfer, while the distal portion has solid construction for load bearing. This local quality differentiation resolves the contradiction by making each region optimized for its specific function.
2Strength
If the implant material is made harder than natural bone, then the load-bearing capacity is improved, but adaptive bone remodeling occurs causing stress shielding and osteolysis
Solution Approach 1:
The rigidity parameter of the implant is changed along its length. The proximal portion has reduced rigidity through porous coating and structural modifications, while the distal portion maintains higher rigidity. This parameter gradient allows the implant to be stronger overall while preventing stress shielding at the critical proximal region where bone remodeling occurs.
3Strength
If the stress distribution is concentrated on the distal femur, then the implant strength is improved, but the proximal bone experiences reduced load leading to bone loss and implant loosening
Solution Approach 1:
The implant design creates dynamic stress distribution through its proximal portion features including porous coating and reduced rigidity. These features enable the implant to adaptively transfer loads to the proximal bone during physiological loading, maintaining bone density and preventing osteolysis while the distal portion provides overall structural strength.
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 implant reduces implant loosening by evenly distributing stress, promoting bone growth and integration, thereby enhancing long-term stability and reducing failure risks.
Implementation Method 1
a diameter and/or length of the struts and/or density of the space truss are predetermined such that when the space truss is in contact with the bone structure at least a portion of the strain on the intramedullary rod is distributed through the space truss to the bone
Implementation Method 2
at least a portion of the struts create a microstrain, that is transferred to the adherent osteoblasts, bone matrix, or lamellar tissue
Implementation Method 3
creating an osteogenic response
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
Various embodiments of implant systems and related apparatus, and methods of operating the same are described herein. In various embodiments, an intermedullary implant for interfacing with a bone structure includes a web structure, including a space truss, configured to interface with human bone tissue. The space truss includes two or more planar truss units having a plurality of struts joined at nodes. Implants are optimized for the expected stress applied at the bone structure site.