Intracorporeal Lengthening Device With Threaded Rod And Connecting Nut
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Solution Overview
Problem
Existing bone lengthening and transport devices are bulky, difficult to miniaturize, painful, and require repeated surgeries for spinal deformity correction, with limitations in curved or constrained spaces, and lack the ability to perform both distraction and compression independently.
Innovation Solution
A new intracorporeal lengthening device with adjustable length, featuring a threaded rod, control shaft, and flexible transmission shaft, allowing for adjustable movement and operation in curved spaces, capable of both distraction and compression without the need for external sealing or complex gear systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external fixators are used for bone lengthening, then bone elongation can be achieved, but infections and discomfort for daily life occur
Solution Approach 1:
The invention extracts the lengthening function from external fixators and relocates it inside the body through an intramedullary nail. The active components (threaded rod, connecting nut, transport part) are contained within the bone marrow cavity, removing the need for external structures that cause infection and discomfort while maintaining the bone elongation capability through internal mechanical action.
Solution Approach 2:
The invention employs a nested structure where the threaded rod is received within the intramedullary nail cavity, the connecting nut moves along the threaded rod, and the transport part is guided within the nail. This nested arrangement allows all lengthening components to be contained within the bone, eliminating external fixators and their associated harmful effects.
2Length of moving object
If ratchet systems are used in bone transport nails, then bone transport can be achieved, but the devices become bulky and difficult to miniaturize
Solution Approach 1:
The invention extracts the ratchet mechanism from the system and replaces it with a threaded rod and connecting nut assembly. This elimination of the ratchet system removes bulky components and reduces the overall number of parts, enabling miniaturization of the intramedullary nail while maintaining unidirectional transport capability through the self-locking nature of the threaded connection.
Solution Approach 2:
The threaded rod serves multiple functions: it provides the mechanical interface for the connecting nut, enables unidirectional movement through its self-locking property, and acts as a guide for the transport part. This multi-functionality reduces the need for separate components that would be required in a ratchet system, simplifying the overall device structure.
3Reliability
If gears and threads are used on elongation rods, then lengthening can be achieved, but sealing against biological materials becomes technically delicate and sterilization is limited
Solution Approach 1:
The invention extracts the gear mechanism from the system and replaces it with a threaded rod and connecting nut assembly. This eliminates the need for complex gear teeth and sealing interfaces, allowing the use of simple cylindrical components that can be easily sterilized by standard methods without compromising sealing or functional reliability.
Solution Approach 2:
The invention applies threading only where mechanically necessary (on the rod for nut engagement) rather than on all rotating surfaces. This localized threading reduces the total surface area requiring sealing and simplifies the sealing requirements, making sterilization more flexible while maintaining reliable mechanical connection at the critical interface between the rod and connecting nut.
4Strength
If threaded rods are used in highly stressed fatigue applications, then lengthening can be achieved, but the life of the implant is limited or over-sizing is required which makes it bulky
Solution Approach 1:
The invention applies preliminary protective measures by providing a smooth transition zone at the end of the threaded rod that receives the connecting nut. This design feature prevents stress concentration and fatigue initiation at the critical thread-root interface, extending the fatigue life of the rod without requiring increased diameter, thus maintaining a compact device size while improving strength.
5Productivity
If known distractors are used for spinal deformity correction, then deformity correction can be achieved, but repeated surgeries are required which increase difficulties, costs and risks
Solution Approach 1:
The invention employs a dynamic lengthening mechanism where the connecting nut can be rotated along the threaded rod to adjust the distance between the first and second parts of the intramedullary nail. This allows continuous or staged lengthening of the spinal construct without requiring surgical removal and reinstallation of the device, reducing the number of surgeries needed while maintaining the ability to correct deformities progressively.
6Volume of moving object
If intracorporeal devices are made compact, then implantation in curved spaces is possible, but the ability to perform both distraction and compression independently is lost
Solution Approach 1:
The invention creates a compact intramedullary nail that can perform both distraction and compression functions through the threaded rod and connecting nut mechanism. By rotating the connecting nut in opposite directions, the device can either lengthen (distraction) or shorten (compression) the distance between the first and second parts, providing bidirectional adjustment capability within a compact form factor suitable for curved spinal spaces.
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 device is compact, painless, and can be operated manually, providing adjustable lengthening and compression capabilities in curved or constrained spaces, reducing the need for repeated surgeries and improving patient comfort and surgical efficiency.
Implementation Method 1
a rod comprising at least one thread, called a threaded rod, pivotally mounted relative to the reference part
Implementation Method 2
drive means connecting the control shaft to the threaded rod
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A device for moving tissue inside the body, in particular bone tissue, may include a reference part, a transport part which is slidably mounted relative to the reference part; a threaded rod pivotably mounted relative to the reference part, a control shaft, driving means connecting the control shaft to the threaded rod, a connecting nut between the transport part and the threaded rod, the connecting nut being mounted onto the threaded rod and being rotatably guided relative to the reference part, and means for converting the movement of the connecting nut along the threaded rod into a movement of the transport part relative to the reference part. In order to limit the longitudinal translation of said threaded rod relative to the reference part, a first abutment and a second abutment rigidly connected to the threaded rod respectively cooperate with a first bearing and a second bearing, these bearings being rigidly connected to the reference part and being placed at a distance from one another between the abutments. The connecting nut is movable along the threaded rod between the first bearing and second bearing.