Modular Endoprosthesis Stem and Head for Femoral Stump Load Transfer
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Solution Overview
Problem
Conventional prostheses for femoral stumps often cause pain and instability due to inadequate load distribution, leading to reluctance in weight-bearing and suboptimal walking behavior, as they rely on the tuber for support rather than the femoral bone, and existing implants struggle to mimic natural force distribution effectively.
Innovation Solution
An endoprosthesis with a separable shaft and head section, featuring a distal recess and integral connecting pin, allows for optimal load transfer from the external prosthesis to the femoral bone, reducing pressure on the tuber and improving walking sensation, while being adaptable to individual anatomy through a set of interchangeable components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional prostheses use a funnel or shaft pulled over the thigh stump with tuberosity support, then the prosthesis structure is simple and easy to manufacture, but the tuberosity experiences excessive pressure causing pain and instability
Solution Approach 1:
The prosthesis is divided into separate modular components: a stem section inserted into the medullary cavity, a head section with support surface, and an intermediate section with connecting elements. This segmentation allows the load-bearing functions to be distributed appropriately - the stem transfers forces to the femur while the head section's support surface distributes loads to the distal femoral end face, eliminating tuberosity pressure points
Solution Approach 2:
The head section with its support surface acts as an intermediary element between the external prosthesis and the femoral bone. This intermediate structure transfers and distributes forces from the external prosthesis through the support surface to the distal end face of the femur, preventing direct concentration of forces on the tuberosity
2Object-affected harmful factors
If implants are inserted into the femoral stump to shift force transmission from tuberosity to femur, then the load distribution improves, but the patient's sensory perception does not resemble natural sensation before amputation
Solution Approach 1:
Different sections of the prosthesis have specialized local properties optimized for their specific functions: the stem section has surface characteristics for bone integration, the intermediate section provides precise angular orientation, and the head section features a support surface with specific geometry to mimic natural force distribution patterns, collectively restoring natural sensory feedback
Solution Approach 2:
The prosthesis incorporates dynamic alignment capabilities through the intermediate section's angular orientation relative to the stem section's longitudinal axis. This allows the prosthesis to adapt to natural movement patterns and force vectors during gait, creating dynamic sensory feedback that resembles pre-amputation conditions
3Ease of manufacture
If a single integrated prosthesis design is used, then manufacturing is straightforward, but adaptability to individual patient anatomy is limited
Solution Approach 1:
The prosthesis is designed as an assembly of standardized modular components (stem sections, intermediate sections, head sections) that can be combined in various configurations. Each module is manufactured to precise specifications, allowing flexible adaptation to different patient anatomies through selective combination rather than custom manufacturing of each component
Solution Approach 2:
The modular components are designed with universal interfaces and standardized geometries that allow the same basic modules to serve multiple patients with different anatomical requirements. The stem sections, intermediate sections, and head sections can be combined in various orientations and configurations to accommodate individual anatomical variations while maintaining manufacturing efficiency
Data Source
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AI summary
An endoprosthesis (10) for a long bone, in particular for a femoral stump, is disclosed, comprising a stem (12) and a head (14) attachable to it. The stem is designed to be inserted into the medullary cavity of the long bone. The head has a support surface (40) molded onto it, designed to support a distal end face of the long bone when the endoprosthesis is implanted. The head and stem are joined by inserting an integral connecting pin (42) of the head into a distal recess in the stem that is open towards its distal end. Furthermore, an endoprosthesis set comprising a number of different stems and heads is disclosed, wherein the recesses and connecting pins are shaped such that each stem can be connected to each head.