Monoaxial Screw Conversion Instrument for Spinal Fixation
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Solution Overview
Problem
Current spinal fixation systems face difficulties in aligning and seating rods into the receiving member of fixation devices due to the positioning and rigidity of vertebrae, particularly in minimally invasive procedures where polyaxial screws are converted to monoaxial screws for deformity correction, but existing methods cannot facilitate this conversion intraoperatively without compromising rod placement.
Innovation Solution
The development of devices and methods that allow for the selective and reversible conversion of polyaxial screws to monoaxial screws during spinal surgery, using an outer and inner component configuration that translates longitudinally to apply a distal force to the polyaxial screw, enabling manipulation and alignment of vertebrae without preventing the passage of spinal fixation elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyaxial screws are used to facilitate positioning of the fixation rod, then ease of operation is improved, but the ability to manipulate vertebrae for deformity correction is compromised
Solution Approach 1:
The receiving member is designed with dynamic characteristics, allowing it to transition between a polyaxial state (permitting multi-directional movement for rod insertion) and a monoaxial state (restricting movement to facilitate vertebrae manipulation). This dynamic reconfiguration enables the same component to serve multiple functional requirements during different stages of the surgical procedure.
2Adaptability or versatility
If polyaxial screws are converted to monoaxial screws for deformity correction, then adaptability is improved, but rod placement capability is compromised
Solution Approach 1:
The system performs preliminary action by converting the receiving member to a monoaxial state before rod placement to enable deformity correction. After the vertebrae are properly positioned and deformities corrected, the receiving member is then converted back to a polyaxial state, which facilitates subsequent rod insertion and seating.
3Reliability
If closure mechanism is used to lock polyaxial screw, then reliability is improved, but ease of operation is worsened due to top-down insertion requirement
Solution Approach 1:
The closure mechanism is designed to advance in a direction opposite to conventional top-down insertion. By inverting the insertion direction, the mechanism can effectively lock the polyaxial screw while accommodating minimally invasive approaches and deformity correction procedures, thereby maintaining reliability without compromising ease of operation.
Data Source
AI summary
Devices and methods for selectively converting polyaxial bone screws into monoaxial screws are described herein. In one embodiment, a spinal screw extension instrument is provided having an outer component configured to engage a receiving member of a polyaxial screw. The instrument further includes an inner component disposed within an inner lumen of the outer component and configured to translate longitudinally relative to the outer component such that the inner component can apply a distal force to a compression member of the polyaxial screw disposed within a distal portion of the receiving member to thereby convert the polyaxial screw to a monoaxial screw.