Orthopaedic Implant Dynamic Trans-Fixation Slot
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Solution Overview
Problem
Existing orthopaedic implants for bone fractures, such as intramedullary nails, face issues with instability due to 'windshield wiper effect' where the nail translates along the fastener's axis, causing bone instability and pain, and prior solutions that lock fasteners in threaded slots prevent dynamization, limiting the types of fasteners and requiring precise angular orientation.
Innovation Solution
An orthopaedic implant with an elongated slot featuring a retractable projection that slidably fits within a groove of the fastener, preventing sliding along a transverse axis while allowing translation along the longitudinal axis, enabling dynamization without causing rotational motion of the fastener.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If elongated slots are used to allow fastener sliding for dynamization, then bone healing is promoted through stress, but the nail translates along the fastener axis causing windshield wiper effect and bone instability
Solution Approach 1:
The slot is segmented into two functional zones: a threaded engagement zone with transverse threads that prevent transverse translation, and a smooth dynamization zone that allows longitudinal sliding. This segmentation resolves the contradiction by separating the functions of stability and dynamization into distinct spatial regions within the slot structure.
Solution Approach 2:
Different portions of the slot have different surface qualities: the engagement portion has threaded surfaces for transverse constraint, while the dynamization portion has smooth surfaces for longitudinal movement. This local differentiation allows the slot to simultaneously provide stability against transverse translation and enable beneficial longitudinal dynamization.
2Stability of the object's composition
If threaded slots with threaded sidewalls are used to engage fastener threads for preventing translation, then transverse stability is improved, but the nail cannot dynamize and fastener rotation causes severe patient pain
Solution Approach 1:
The slot is divided into a threaded engagement zone for transverse stability and a smooth dynamization zone for longitudinal movement. The threaded portion engages the fastener to prevent transverse translation, while the subsequent smooth portion allows the fastener to slide longitudinally without rotation, eliminating patient pain while maintaining stability.
Solution Approach 2:
Instead of having threads along the entire slot length (which would prevent all translation including longitudinal), the invention inverts the approach by providing threads only in the transverse engagement zone and leaving the longitudinal zone smooth, thereby allowing dynamization while preventing transverse instability.
3Manufacturing precision
If threaded slots are used to lock fasteners, then intraoperative fracture compression is achieved, but the types of fasteners are limited and precise angular orientation is required
Solution Approach 1:
The slot design with threaded engagement zone and smooth dynamization zone can accommodate multiple fastener types including screws, pins, and rods. The threaded portion provides universal engagement capability while the smooth portion allows various fastener geometries to slide during dynamization, enhancing compatibility without sacrificing compression precision.
Solution Approach 2:
The slot transitions from a static threaded engagement zone to a dynamic smooth sliding zone, allowing the fastener to be initially locked in precise angular orientation for compression, then dynamically slide longitudinally during dynamization. This dynamic behavior maintains precision requirements while accommodating different fastener types and orientations.
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 stabilizes the bone by preventing unwanted translation of the nail while allowing dynamization, reducing patient discomfort and accommodating various fastener types without precise angular alignment, thus enhancing fracture healing and implant stability.
Implementation Method 1
the single projection slidably fits within a groove of the fastener to limit sliding of the implant over the fastener along an axis substantially transverse to the long axis and to permit sliding of the implant over the fastener along the long axis
Data Source
Figure 1A
Figure 1B~1C
Figure 2
AI summary
An orthopaedic implant for use with a fastener having at least one of threads and grooves includes a body defining a long axis. The body includes an inner wall defining an elongated slot. The inner wall includes a pair of opposing walls and a single projection disposed on the inner wall. When the fastener is inserted into the slot, the single projection slidably fits within a groove of the fastener to limit sliding of the implant over the fastener along an axis substantially transverse to the long axis and to permit sliding of the implant over the fastener along the long axis.