Minimally Invasive Screw Extension Assembly for Spinal Rod Alignment
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Solution Overview
Problem
Spinal surgeons face difficulties in aligning and seating fixation rods within slotted rod receiving implants, particularly when correcting preexisting misalignments, due to the complexity of positioning and securing the rods during vertebral corrective surgery.
Innovation Solution
A screw extension assembly comprising an inner slotted shaft with deflectable leg extensions and an outer shaft, along with a removable nut and locking mechanism, which allows for easy alignment and secure seating of fixation rods within the slotted rod receiving implants, facilitating corrective spinal alignment and support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional rod placement tools are used, then the fixation rod can be seated in the slotted implant, but the alignment precision and ease of operation deteriorate when correcting preexisting misalignments
Solution Approach 1:
The assembly employs nested shafts where an inner shaft is positioned within an outer shaft. The inner shaft contains slotted distal end portions with deflectable leg extensions that engage the implant, while the outer shaft provides additional structural support and alignment features. This nested configuration enables precise alignment through the inner shaft's engagement mechanisms while the outer shaft maintains overall structural integrity and facilitates ease of operation.
Solution Approach 2:
The deflectable leg extensions on the inner shaft provide dynamic adaptation capability. These legs can deflect to engage with the grooves on the implant surface, allowing the assembly to adapt to slight variations in implant positioning while maintaining precise alignment. The dynamic nature of the deflectable legs enables automatic adjustment during the rod seating process, improving both alignment precision and ease of operation.
2Stability of the object's composition
If the rod is securely fixed into the implant, then the spinal alignment stability improves, but the device complexity increases due to multiple components
Solution Approach 1:
The assembly merges multiple functions into a integrated structure. The inner and outer shafts are combined to provide both engagement and support functions. The deflectable leg extensions are integrated into the inner shaft rather than being separate components. The set screw mechanism is incorporated directly into the assembly structure. This merging approach achieves secure fixation and spinal alignment stability while minimizing the number of separate parts, thereby reducing overall device complexity.
Solution Approach 2:
The assembly exhibits multi-functionality where the inner shaft serves both as a structural support element and as an engagement mechanism through its deflectable legs. The outer shaft provides both structural support and alignment guidance. The set screw mechanism simultaneously secures the rod and maintains the engagement of the deflectable legs. This multi-functional design achieves stable spinal alignment without requiring numerous specialized components, thus reducing device complexity.
3Ease of operation
If the deflectable leg extensions are used to engage the implant, then the ease of clipping onto the implant improves, but the manufacturing precision requirements increase
Solution Approach 1:
The deflectable leg extensions utilize elastic deformation as a key parameter change mechanism. By designing the legs with appropriate material properties and geometric dimensions, they can deflect under minimal force to engage the grooves on the implant surface. This parameter-based approach allows for easy clipping operation while the manufacturing precision requirements are concentrated on the critical engagement surfaces and groove geometries, rather than requiring high precision throughout the entire component.
Data Source
AI summary
A screw extension assembly for use in minimally invasive spinal surgery, the assembly has an inner slotted shaft and an outer shaft, a rod reducer and a removable nut. The combination when assembled is configured to move a spinal fixation rod into a slotted rod receiving spinal implant where it is seated and affixed thereto. The screw extension assembly further has a locking knob rotationally coupled to a proximal end of the outer shaft, wherein the inner shaft has one or more cam grooves and the locking knob has a pin extending into and guided by said cam groove causing the outer shaft to translate longitudinally upon rotation of the locking knob relative to the inner shaft toward an engaged position locking the deflectable legs in the coupled position to the slotted rod receiving implant.