Intramedullary Nail with Segmented Motion Assembly
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Solution Overview
Problem
Current intramedullary nails face challenges in providing sufficient axial interfragmentary motion for healing, especially in patients who cannot or are unable to bear weight, due to design features that increase torsional stiffness, reducing mechanical stimulation and healing potential.
Innovation Solution
The intramedullary nail system incorporates a fastener with a circular outer surface and a stop that mates with a slot in the nail stem, allowing for controlled axial movement through micro-dynamisation, full-dynamisation, and cross-locking configurations, providing rotational control and reducing material removal while maintaining torsional stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If design features are added to increase torsional stiffness, then torsional stability is improved, but axial stiffness increases which reduces mechanical stimulation for healing
Solution Approach 1:
The intramedullary nail is divided into two functional segments: a proximal locked segment that provides torsional stability through interlocking features, and a distal dynamic segment that allows controlled axial movement through a motion assembly. This segmentation enables the proximal end to resist rotation while the distal end maintains flexibility for mechanical stimulation at the fracture site.
Solution Approach 2:
The nail incorporates a motion assembly with a spring mechanism that transforms the static, rigid structure into a dynamic system. The spring allows controlled axial compression and expansion, enabling the nail to adapt its stiffness characteristics - providing rigidity when needed for torsional stability while allowing movement for axial stimulation during weight-bearing activities.
2Stability of the object's composition
If elastic flexure is relied upon for axial motion, then torsional stability is maintained, but patients unable to bear weight do not achieve sufficient motion for healing
Solution Approach 1:
The motion assembly is designed as a self-contained mechanism within the nail that automatically provides axial motion capability regardless of external loading conditions. The spring mechanism inherently maintains compressive force and allows movement without requiring patient weight-bearing, enabling the system to serve its own function of providing mechanical stimulation independently of user activation.
3Stability of the object's composition
If relative movement between bone screws and apertures is minimized, then torsional instability is reduced, but axial stiffness increases reducing mechanical stimulation
Solution Approach 1:
The nail structure segments the fixation function from the motion function. Bone screws are locked into the proximal segment where they provide torsional stability through minimal relative movement, while the distal segment contains the motion assembly that independently manages axial movement. This spatial segmentation allows each function to be optimized without compromising the other.
Solution Approach 2:
The system transitions from a static connection between screws and apertures to a dynamic system where the motion assembly mediates the interaction. The spring mechanism allows controlled relative movement between structural components, transforming the rigid screw-aperture connection into a flexible system that maintains torsional stability while enabling axial motion for healing stimulation.
Data Source
Figure 1~1(B)
Figure 2~2(C)
Figure 3(A)~3(C)
AI summary
An intramedullary nail system (1) comprising a nail stem (2) having a multi-featured proximal end (3), a distal end (5) and a central conduit (22) configured to accommodate a fastener (4) having a proximal end (7), a distal end (9) and a central shaft (22a), wherein the fastener (4) comprises a stop (8) extending laterally from the proximal end (7) relative to a vertical axis of the fastener (4) and which is configured to matingly engage with an internal wall (3a) of the multi-featured proximal end (3) to provide control over rotational and distal movement of the system (1) when secured with a bone screw.