Cannulated Bone Screw Channels for Uniform Cement Anchorage
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Solution Overview
Problem
Existing bone screws face challenges in securely anchoring in bone defects due to loosening and pull-out, particularly with the uneven distribution of bone cement, which affects the mechanical strength and stability of the repair site.
Innovation Solution
A cannulated bone screw design with a cylindrical screw body featuring a longitudinal interior channel and multiple delivery channels along helical grooves, allowing for uniform distribution of a flowable medium like bone cement, combined with a bone screw manifold and washer for enhanced fixation and compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of delivery channels or ports in the screw body is increased to improve bone cement distribution, then the distribution of bone cement is improved, but the mechanical strength of the bone screw is weakened
Solution Approach 1:
The screw body is divided into multiple threaded portions (first, second, and third threaded portions) with different numbers and distributions of delivery channels. The first threaded portion has a first number of delivery channels, the second threaded portion has a second number of delivery channels, and the third threaded portion has a third number of delivery channels, where the first number is greater than the second number, and the second number is greater than the third number. This segmentation allows optimized bone cement distribution in different regions while maintaining structural integrity.
Solution Approach 2:
Different regions of the screw body have different channel densities tailored to local requirements. The proximal region (first threaded portion) has higher channel density for better cement distribution near the head, while the distal region (third threaded portion) has lower channel density to maintain strength in the critical load-bearing area. Each threaded portion has delivery channels spaced at specific intervals (e.g., 2-4 mm in first portion, 4-6 mm in second portion, 6-10 mm in third portion).
2Reliability
If bone cement is used to fill the hole before screw installation to prevent loosening, then the likelihood of screw loosening is reduced, but the even distribution of bone cement along the screw length is challenging
Solution Approach 1:
The delivery channels are pre-formed in the screw body during manufacturing, preparing the pathway for bone cement distribution before the actual implantation. This allows the screw to actively distribute cement as it is being installed, rather than relying on passive filling after installation.
Solution Approach 2:
The delivery channels act as intermediaries that guide and distribute bone cement from the proximal end to the distal end of the screw body. The channels ensure uniform distribution of cement along the entire length of the screw, preventing clumping or uneven deposition that would occur with direct filling methods.
3Strength
If solid screws are used with bone cement to increase initial stiffness and strength, then the initial stiffness and strength of the repair is increased, but loosening of the screw at the repair site is not significantly decreased
Solution Approach 1:
The screw utilizes fluid dynamics principles to distribute bone cement through its delivery channels. The flowable bone cement is pumped through the channels under controlled pressure, ensuring uniform distribution along the screw length and into the surrounding bone, creating a reliable mechanical interlock that prevents loosening.
Solution Approach 2:
The screw creates a composite structure by distributing bone cement through multiple delivery channels into the surrounding bone tissue. The combination of the metallic screw body, the flowable bone cement, and the native bone creates a composite fixation system that provides both initial strength and long-term stability by preventing loosening through uniform cement distribution.
Data Source
Figure 1
Figure 2A~2C
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AI summary
The invention features improved bone screws, a delivery manifold for delivering a flowable medium to a bone screw, and washers for use with the bone screw to provide compressive fixation. The invention also features methods of treatment using the bone screws, washers, and/or delivery manifold, and kits that include the same.