Self-Drilling Bone Screw for Bicortical Sacral Fixation
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Solution Overview
Problem
Minimally invasive surgical techniques struggle to achieve bicortical purchase of pedicle screws in the sacrum due to the use of blunt-tipped, non-self-drilling screws, which results in weaker unicortical fixation, as they cannot effectively penetrate the distal cortical margin without risking organ perforation and cannot form threads in the cancellous bone without stripping the proximal cortical bone.
Innovation Solution
A self-drilling, self-tapping bone screw with a distal tip that drills and threads into the bone structure as it is installed, allowing for bicortical purchase without the need for a pilot hole, featuring a self-drilling tip with a length equal to or greater than the cortical bone layer to prevent thread stripping and a lead thread that forms internal threads as it penetrates, enabling secure bicortical fixation in both cortical and cancellous bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a blunt-tipped cannulated pedicle screw is used in minimally invasive surgery, then the surgical approach is less invasive, but the screw cannot achieve bicortical purchase and only provides weaker unicortical fixation
Solution Approach 1:
The patent combines the functions of a drill bit and a screw thread into a single self-drilling, self-tapping screw tip. The distal tip includes both cutting edges for drilling through cortical bone and helical threads for engaging bone, merging the previously separate drilling and screwing operations into one integrated component that achieves bicortical purchase through minimally invasive insertion
Solution Approach 2:
The patent changes the geometric parameters of the screw tip by providing a distal tip with specific dimensions - the tip length is at least equal to the cortical bone layer thickness, and the tip diameter is less than the major diameter of the threads. These parameter changes enable the tip to penetrate cortical bone and form threads in cancellous bone without stripping the cortical bone, achieving both minimally invasive insertion and strong bicortical fixation
2Strength
If a pilot hole is drilled through the entire bone structure before inserting a bone screw, then bicortical purchase can be achieved, but the surgical procedure becomes more complex and time-consuming
Solution Approach 1:
The patent merges the pilot hole drilling function and the screw insertion function into a single self-drilling, self-tapping screw. The distal tip with cutting edges drills through the cortical bone to create the pilot hole, while the helical threads simultaneously form internal threads in the cancellous bone, eliminating the need for separate drilling and tapping steps and reducing surgical complexity
Solution Approach 2:
The screw performs its own drilling and thread-forming functions through the self-drilling, self-tapping distal tip design. The cutting edges self-drill through cortical bone, and the helical threads self-tap internal threads in cancellous bone as the screw is inserted, making the system self-sufficient and eliminating the need for separate pilot hole drilling and tapping operations
3Ease of manufacture
If a self-tapping screw forms threads in proximal cancellous bone first, then the threads can be formed easily, but the proximal cortical bone gets stripped when the screw advances further
Solution Approach 1:
The patent changes the dimensional parameters by making the distal tip length at least equal to the cortical bone layer thickness and the tip diameter less than the major diameter of the threads. This ensures the tip penetrates cortical bone completely before threads form, preventing cortical bone stripping while maintaining easy thread formation in cancellous bone
Solution Approach 2:
The distal tip performs preliminary drilling action through cortical bone before the helical threads engage and form internal threads in cancellous bone. This preliminary drilling creates a pilot hole that guides the threads, ensuring threads form easily in cancellous bone without stripping the overlying cortical bone
4Strength
If a sharp-tipped guide wire is used to perforate the distal cortical margin, then bicortical purchase can be achieved, but there is a risk of perforating organs in the pelvis
Solution Approach 1:
The self-drilling distal tip acts as an intermediary that drills through cortical bone in a controlled manner to create a pilot hole, replacing the sharp-tipped guide wire. This intermediary function allows bicortical purchase to be achieved without the risk of uncontrolled guide wire perforation of pelvic organs, as the drilling process is more predictable and controllable
Data Source
AI summary
A self-drilling, self-tapping bone screw is described in which the bone screw has a drill tip free of threads and having a length at least as great as about the thickness of a proximal cortical bone layer, with the drill tip having opposed lands and a helical flute between each of the lands with each of the lands having a cutting edge configured to cut bone as the drill tip is rotated into the bone with the flutes conveying the bone debris away from the drill tip, where a lead thread begins to self-tap internal threads in the proximal cortical bone layer after the drill tip has drilled through the proximal cortical bone layer so as to avoid stripping the threads formed in the bone layer. A method of installation is also disclosed.