Segmented Threaded Rod for Implantable Bone Adjustment
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Solution Overview
Problem
Current implantable reconfigurable bone adjustment devices face failures due to stress concentrations at the junction of the threaded rod and driver, leading to inadequate bone adjustment performance.
Innovation Solution
The implementation of a reconfiguration assembly that includes a drive mechanism with a driver and a threaded rod, where the driver is operable to controllably rotate, and the junction is designed to reduce applied stresses through offset axes of rotation, dynamic joints, and segmented threaded rods with varying diameters to distribute forces and alleviate bending moments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the threaded rod is rigidly affixed to the driver structure, then the drive mechanism can achieve controlled rotation of the threaded rod, but stress concentrations occur at the junction leading to device failure
Solution Approach 1:
The threaded rod is divided into multiple segments with varying diameters rather than being a uniform structure. The proximal segment has a first diameter, the intermediate segment has a second diameter, and the distal segment has a third diameter. This segmentation allows the structure to better distribute stresses and bending moments along its length, reducing stress concentration at the critical junction with the driver while maintaining the ability to transmit rotational force for controlled bone adjustment.
Solution Approach 2:
Different segments of the threaded rod are given different local properties through varying diameters. The proximal segment near the driver has one diameter configuration, the intermediate segment has another, and the distal segment has a third. This local quality variation optimizes the structural response to different loading conditions at different locations, with each segment's diameter tailored to the specific stress and bending moment requirements at that position.
2Adaptability or versatility
If the threaded rod engages device components to achieve dimensional modification, then bone adjustment function is achieved, but substantial forces and bending moments are imposed on the threaded rod junction
Solution Approach 1:
The threaded rod is segmented into multiple sections with different diameters to handle varying force requirements along its length. The proximal segment with the first diameter is positioned to handle forces near the driver junction, the intermediate segment with the second diameter handles mid-section forces, and the distal segment with the third diameter handles forces at the bone engagement point. This segmentation allows the structure to adapt to the force distribution pattern while maintaining bone adjustment functionality.
Solution Approach 2:
The diameter parameter of the threaded rod is changed along its length rather than remaining constant. By varying the diameter parameter from proximal to distal segments, the structural stiffness and strength characteristics are optimized to match the force and bending moment distribution, enabling the device to handle substantial forces while reducing stress concentration at the driver junction.
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
This design effectively reduces stress concentrations and enhances the durability of the device, allowing for controlled and efficient bone adjustments by isolating forces away from the junction, thereby preventing device failure and ensuring consistent performance.
Implementation Method 1
a threaded rod having a proximal end operatively coupled to the driver at a junction so that rotation of the drive mechanism rotates the driver, which rotates the threaded rod
Data Source
AI summary
A reconfigurable bone adjustment device (1, 101, 201) includes a first member (10,110, 210, 1010) configured for attachment to a first bone fragment, a second member (20, 130, 230, 1030) configured for attachment to a second bone fragment and a reconfiguration assembly (2, 102, 401, 501, 601, 701, 801, 901, 1020) configured to move the second member relative to the first member. The reconfiguration assembly includes a drive mechanism (50, 150, 250, 440, 540, 640, 740, 840, 940, 1050) and a threaded rod (70, 170, 245, 470, 570, 670, 770, 870, 970, 1070, 1170) operatively coupled to the drive mechanism so that rotation of the drive mechanism rotates the threaded rod. The reconfiguration assembly operates to reduces stresses, forces, bending moments and/or eccentric moments on a junction and/or by configuring the junction in a manner whereby one of more of the forces, is isolated away from the junction.