Intramedullary Rod With Wedge Expanders for Bone Stress Distribution
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Solution Overview
Problem
Existing intramedullary fixation devices often cause high stress in specific bone areas, leading to potential damage or fractures due to uneven stress distribution and point contact, which can result in undesired bone remodeling.
Innovation Solution
A rod with wedge bolts and expanders that allow for controlled radial peripheral deformation, ensuring even stress distribution along the intramedullary canal through a central screw, with adjustable geometric parameters to optimize stress transmission and bone apposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid rods are percussed into the bone or threads are machined in the intramedullary canal, then fixation strength is improved, but bone damage and fractures occur
Solution Approach 1:
The patent changes the fixation mechanism from rigid mechanical insertion (percussion or threading) to controlled elastic expansion. The intramedullary rod is designed with elastic properties that allow it to expand radially after insertion, creating friction-based fixation without damaging the bone. This parameter change from rigid to elastic behavior resolves the contradiction between achieving strong fixation and avoiding bone damage.
2Strength
If retractable flanges or balls are used to expand the rod, then fixation is improved, but point stress concentrates on the bone wall
Solution Approach 1:
The patent applies homogeneity by designing the intramedullary rod with uniform elastic properties along its entire length, allowing for even radial expansion. This creates homogeneous stress distribution across the bone wall rather than concentrated point stress. The elastic material deforms uniformly, ensuring that the load is distributed evenly along the intramedullary canal, preventing localized bone damage.
3Strength
If the rod is made rigid to ensure structural stability, then mechanical strength is improved, but stress damping is reduced and bone apposition is hindered
Solution Approach 1:
The patent changes the material parameter from rigid to elastic, allowing the rod to exhibit both structural stability and stress damping. The elastic material can deform under load, providing stress damping that promotes bone apposition, while maintaining sufficient structural integrity through controlled expansion and friction-based fixation. This parameter change resolves the contradiction between rigidity and stress damping.
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 solution effectively reduces stress concentration, promotes homogeneous stress and deformation transmission, and facilitates easier implantation and extraction, enhancing bone health and stability without causing excessive bone growth or resorption.
Implementation Method 1
a single element is used which is radially deformed
Implementation Method 2
the behaviour of both of them being different. The flanges or balls move outwardly by the action of the central conical elements
Data Source
Figure 1~3
Figure 2A~2C
Figure 4
AI summary
Intramedullary fixation device, having an intramedullary rod (2) which is provided for insertion thereof into a bone (1) and consists of a central screw (4) having a first free end comprising a stopper (7) and a second free end with a pre-tensioning nut (8), an alternating series of expanders (3) and bolts (5) being arranged in between, the bolt surfaces in contact with the expanders (3) having a wedge shape. The bolts (5) or expanders (3) may have no, or one or more variations in the dimensions of the different geometric parameters, in accordance with the adjacent expanders, along the length of the implant, and the central screw (4) may have a variable cross section. The device may have different additional components, such as an osteotomic base (9) for fixation of the musculature. The device promotes maximum nailing limited between these elements and produces a controlled peripheral radial deformation.