Bone Anchor Compression Member Segmented Gripping Features
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Solution Overview
Problem
Traditional bone anchor systems face issues with slippage due to reduced contact surface area when the shaft is positioned at an angle, compromising the effectiveness in correcting spinal deformities.
Innovation Solution
A bone anchor assembly with a compression member having a distal end with gripping features such as inner cylindrical, conical, or spherical surfaces with grooves, providing greater friction and preventing movement of the bone anchor relative to the receiver member, even when oriented at an angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compression member with a distal surface formed as a negative of the head is used, then the bone anchor can be secured at a fixed angle to the rod-receiving member, but the contact surface area is reduced when the shaft is positioned at an angle, increasing the risk of slippage
Solution Approach 1:
The distal end of the compression member is divided into multiple gripping features including teeth with crests, grooves, and contact surfaces that segment the contact area into multiple localized gripping zones. This segmentation allows the compression member to maintain secure engagement with the bone anchor head even when positioned at angles, preventing slippage while preserving fixation reliability.
Solution Approach 2:
The compression member incorporates localized gripping features such as teeth with sharp crests and grooves at specific locations on the distal end. These localized structures provide enhanced friction and contact area precisely where needed to prevent slippage, while the overall design maintains the fixed angle securing function. The local quality enhancement addresses the contact area reduction issue without compromising the primary fixation function.
2Ease of manufacture
If the compression member is designed with simplified geometry, then manufacturing is easier, but the frictional grip on the bone anchor head is insufficient, leading to potential slippage
Solution Approach 1:
The compression member is pre-formed with integrated gripping features including teeth, crests, and grooves during the manufacturing process. These features are created in advance through molding or machining operations, allowing the compression member to be manufactured as a single integrated component. The preliminary formation of these gripping features ensures sufficient frictional grip is built into the design without requiring complex assembly steps, balancing manufacturability with anti-slippage reliability.
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 enhanced frictional grip of the compression member ensures the bone anchor remains securely fixed at the desired angle, reducing the risk of slippage and maintaining effective spinal alignment.
Implementation Method 1
the distal end grips the head portion of the bone anchor with greater friction as compared with a distal end formed as a negative of the head portion of the bone anchor
Data Source
AI summary
Various exemplary methods and devices are provided for fixing bone anchors to bone. In general, the methods and devices can allow for a bone anchor to be fixed to a bone at a desired angle to a receiver member. In an exemplary embodiment, a bone anchor assembly is provided that includes a bone anchor configured to engage bone, a receiver member that polyaxially seats a spherical head of the bone anchor, and a compression member seated within the receiver member, proximally of the head of the bone anchor. The compression member can have a distal end with gripping features thereon configured to create at least one line contact and/or one band contact with the head of the bone anchor, thus providing a firm grip on the head of the bone anchor and reducing a risk of slippage of the bone anchor with respect to the receiver member.