Polyaxial Bone Anchor Locking Cap Single-Tool Clamping
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Solution Overview
Problem
Current bone anchor systems for spinal fixation are cumbersome and time-consuming due to difficulties in aligning spinal rods with U-shaped channels, often requiring multiple surgical tools and resulting in instability during the clamping process.
Innovation Solution
A polyaxial bone anchor with a locking cap that includes a main body, set screw, and saddle, allowing for simplified clamping of the spinal rod and anchor member using a single tool, with features like preloaded set screws and dovetail connections to secure the rod and anchor member in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a set screw or fastener is used to clamp the spinal rod and anchor member, then the rod and anchor member can be secured in place, but the clamping process is time-consuming and may result in the rod or anchor member moving out of position before clamping is completed
Solution Approach 1:
The locking cap is designed with a preloaded set screw that is initially positioned to engage the spinal rod. The preloaded condition means the set screw is already under compression force, ready to clamp immediately when the locking cap is installed, eliminating the need for gradual tightening and reducing the risk of movement during the clamping process
Solution Approach 2:
The locking mechanism is divided into separate functional components: the locking cap that provides structural support and guidance, the set screw that provides the clamping force, and the saddle that distributes the load. This segmentation allows each component to be optimized for its specific function and enables rapid assembly without complex adjustment procedures
2Manufacturing precision
If multiple surgical tools are used to position and clamp the spinal rod and anchor member, then precise positioning can be achieved, but the complexity of the procedure increases
Solution Approach 1:
The locking cap is designed to perform multiple functions with a single component: it guides the set screw into proper engagement, provides the clamping force through the preloaded set screw, and secures the spinal rod in the correct position. This multi-functionality eliminates the need for multiple specialized tools and simplifies the surgical procedure while maintaining positioning accuracy
Solution Approach 2:
The locking cap acts as an intermediary device that bridges the gap between the spinal rod and the anchor member. It provides a standardized interface that ensures proper alignment and positioning while simplifying the connection process, eliminating the need for multiple adjustment tools that would otherwise be required to achieve the same result
Data Source
AI summary
A bone anchor (100) for attaching a rod (108) to a bone has an anchor member (106) for attachment to the bone and an anchor head (104) having a U-shaped opening for receiving the rod. The bone anchor also includes a locking cap (102) that has a main body (900) and a set screw (1000). Advantageously, in one embodiment the locking cap preferably is designed such that a single tool can be used to lock the locking cap in place on the anchor body preferably with a 90° turn and preferably then drive the set screw to clamp the rod. The locking cap also preferably non-threadingly engages the anchor body. The anchor body preferably has an inclined surface on its top surface which elastically deflects extending tabs on the main body to secure the locking cap to the anchor body. A method of implantation and assembly of the bone anchor are also described.