Bottom-Loading Bone Anchor Assembly With Drag Ring Stabilization
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Solution Overview
Problem
Existing bone anchor assemblies face challenges with maintaining desired angular orientation between the receiver member and shank during assembly, particularly in bottom-loaded configurations, which can lead to cumbersome surgical procedures and increased assembly size due to the need for larger receiver members to accommodate larger shanks.
Innovation Solution
The use of a drag retaining ring that is advanced proximally into the receiver member, seating the shank head and exerting a radially inward drag force to maintain the desired position of the receiver member relative to the shank, allowing for polyaxial movement while preventing unintended movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bottom-loaded configuration is used to accommodate larger diameter shanks, then the bone anchor assembly can handle larger shank diameters, but the receiver member size and profile increase
Solution Approach 1:
The retaining ring is nested within the receiver member, with the ring's outer surface fitting into a groove formed in the receiver member. This nesting arrangement allows the retaining ring to be contained within the receiver member's profile, preventing increase in overall assembly size while still providing the necessary retention function for larger diameter shanks
Solution Approach 2:
The receiver member is segmented into functional zones: a groove region that receives the retaining ring and a rod receiving region. This segmentation allows the receiver member to accommodate additional components (retaining ring) without increasing overall profile, as the retaining ring occupies a dedicated segment within the existing structure
2Adaptability or versatility
If polyaxial movement freedom is provided between receiver member and shank, then alignment flexibility is improved, but maintaining desired angular orientation becomes difficult during provisional positioning
Solution Approach 1:
The system transitions from a static fixed-position arrangement to a dynamic system where the retaining ring can slide along the shank's outer surface. This dynamic arrangement allows free movement during alignment (when drag force is insufficient) and automatic stabilization when positioning force exceeds drag force, providing both flexibility and stability
Solution Approach 2:
The drag force parameter of the retaining ring is specifically tuned to be greater than the weight of the receiver member. This parameter change ensures that once the receiver member is positioned at the desired location, the drag force is sufficient to counteract gravitational forces and prevent unintended movement, while still allowing intentional repositioning when needed
3Reliability
If additional components are added to retain the shank within the receiver member, then shank retention is improved, but the assembly complexity increases
Solution Approach 1:
The retaining ring serves multiple functions simultaneously: it retains the shank within the receiver member, provides drag force to prevent unintended movement, and is contained within the groove of the receiver member to maintain profile. This multi-functionality reduces the need for separate components for each function
Solution Approach 2:
The retaining ring combines the retention function and the positioning stabilization function into a single component. Rather than having separate mechanisms for retaining the shank and preventing movement, these functions are merged into the drag-retaining ring's integrated design
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 drag retaining ring enables a reduced assembly profile and common assembly procedure across various surgical procedures, ensuring the receiver member remains in the desired position relative to the shank, facilitating easier and more precise surgical implantation.
Implementation Method 1
The walled portion can contact the head of the shank and exert a radially inward drag or friction force on the shank head in resistance to unintended movement
Data Source
Figure 1A~1B
Figure 2
Figure 3~4
AI summary
Bottom-loading bone anchor assemblies and components thereof are disclosed that have a reduced profile and can be utilized with bone screws of various size. A bone anchor assembly (200) of the present disclosure includes a receiver member (206), a drag retaining ring (204), and a shank (202). The retaining ring and shank can be inserted proximally into a bore of the receiver member. The drag ring can have a base and a walled portion extending proximally therefrom. The drag retaining ring can be disposed in a groove of the receiver member with the base forming a seat for the shank head that can hold the shank within the receiver. The walled portion of the drag retaining ring can impart a drag force on the shank head seated in the base to prevent unintended movement between the shank and the receiver member.