Curved Intramedullary Nail Decoupling Mechanism
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Solution Overview
Problem
Straight intramedullary nails are operationally complex due to physiological curvatures of long bones and can weaken cortical bone, with existing adjustment mechanisms prone to breaking under bending moments caused by curvature, limiting their use and functionality.
Innovation Solution
A curved intramedullary nail design with a decoupling mechanism between the rod and adjustment components to prevent transmission of bending moments, allowing for reliable adaptation to bone curvature and high load-bearing capacity, featuring a joint and threaded elements that enable incremental length adjustment without damaging the mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a curved intramedullary nail is used to adapt to physiological bone curvature, then ease of insertion and load-bearing capacity are improved, but bending moments are transmitted to the adjustment mechanism causing component breakage
Solution Approach 1:
The intramedullary nail is divided into separate functional segments: a curved rod for bone adaptation and a separate adjustment mechanism with straight screws. The joint connects these segments while allowing relative movement, isolating the adjustment mechanism from curvature-induced bending moments.
Solution Approach 2:
A joint acts as an intermediary element between the curved rod and the adjustment mechanism. This joint permits the rod to follow physiological curvature while preventing direct transmission of bending moments to the straight screw components of the adjustment mechanism.
2Reliability
If straight intramedullary nails are used, then adjustment mechanism reliability is maintained, but surgical complexity increases due to physiological curvatures of long bones
Solution Approach 1:
The nail system is segmented into a curved rod portion for insertion and a separate adjustment mechanism. This allows the rod to be pre-formed to match physiological curvature for easy insertion, while the adjustment mechanism remains simple and reliable for postoperative length modification.
Solution Approach 2:
The rod is designed with a curved configuration matching the physiological curvature of long bones, enabling straightforward insertion without requiring complex surgical manipulation. The curvature is maintained in the rod while the adjustment mechanism remains separate and accessible.
3Strength
If the rod is curved to match bone anatomy, then load-bearing capacity is improved, but curvature-related stresses damage the adjustment mechanism components
Solution Approach 1:
The load-bearing function is assigned to the curved rod, while the adjustment mechanism is separated and designed to handle only axial forces. The joint connection allows the rod to bear curvature stresses without transmitting these moments to the adjustment mechanism components.
Solution Approach 2:
The adjustment mechanism is extracted from the curved rod structure and positioned as a separate component. This extraction removes the adjustment mechanism from the path of curvature-induced bending moments, protecting it from damage while maintaining the rod's load-bearing capability.
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
In a curved intramedullary nail for connecting two parts of a bone, with a tube for fastening to the first bone part, with a rod arranged inside the tube, which rod has a fastening portion protruding from the tube for the purpose of fastening to the second bone part, and with an adjustment mechanism arranged inside the tube, which adjustment mechanism can be actuated by repeated relative rotation movements between the rod and the tube, wherein the rod can be driven out of the tube or driven into the tube by actuation of the adjustment mechanism, a decoupling between the rod and at least one component of the adjustment mechanism is provided, which prevents the transmission of curvature-induced bending moments to the component.