Polyaxial Bone Anchor Angulation Mechanism
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Solution Overview
Problem
Existing polyaxial bone anchors have limited angulation, making it difficult for surgeons to align spinal rods with anchor heads due to the curvature of the spine and varying vertebrae sizes, restricting flexibility in spinal fixation and stabilization.
Innovation Solution
The development of polyaxial bone anchors with enhanced angulation capabilities, allowing the pedicle screw or hook to rotate up to 50° from the central axis, facilitated by a collet or spherical locking element that can pivot within the anchor head, providing increased flexibility in aligning spinal rods during surgery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If typical polyaxial bone anchors with 30° angulation are used, then the device structure remains simple, but the alignment flexibility with spinal rods is insufficient due to spine curvature and vertebrae size variations
Solution Approach 1:
The patent implements a dynamic angulation mechanism where the anchor member can rotate relative to the anchor head within a conical space of up to 50° from the central axis. This dynamic capability allows the surgeon to align the spinal rod with the U-shaped channel after the anchor member is inserted into the vertebra, accommodating spine curvature and vertebrae size variations without requiring complex pre-alignment procedures.
Solution Approach 2:
The patent introduces an additional rotational degree of freedom by allowing the anchor member to pivot within the anchor head. This transforms the fixed-axis insertion into a multi-dimensional positioning capability, where the anchor member can orient itself in multiple directions within the conical space, thereby improving alignment flexibility without significantly increasing overall device complexity.
2Measurement precision
If increased angulation capability is provided, then the alignment precision and positioning flexibility improve, but the structural complexity of the anchor head and locking mechanism increases
Solution Approach 1:
The patent employs a conical space geometry to define the angulation limits of the anchor member. The central axis and conical boundaries provide a natural geometric constraint that guides the rotation and positioning of the anchor member. This geometric approach simplifies the control of angulation while maintaining precision, as the conical space inherently limits the rotation to the desired 50° range without requiring complex mechanical stops or guides.
3Reliability
If multiple screws or hooks with multiple spinal rods are used to achieve proper alignment, then the fixation stability improves, but the surgical procedure complexity and time increase
Solution Approach 1:
The patent allows the anchor member to be inserted into the vertebra first, establishing a secure fixation point before the spinal rod is aligned and attached. This preliminary insertion of the anchor member with its subsequent angulation capability eliminates the need for pre-alignment procedures, allowing the surgeon to work sequentially from insertion to alignment to fixation, thereby reducing surgical procedure time while maintaining fixation stability.
Data Source
AI summary
A polyaxial bone anchor has a locking element shaped and configured to allow an anchoring member (e.g., a screw or hook) to polyaxially rotate at large angles about a central axis of the bone anchor before compression locking the anchoring member within an anchor head.