Orthopedic Fastener Thread Design for Reduced Insertion Torque
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Solution Overview
Problem
Current orthopedic fasteners face challenges such as misalignment, failure to withstand multidirectional forces, high insertion torque, heat generation, and lack of tactile feedback during surgery, leading to bone trauma and osteonecrosis.
Innovation Solution
A new bone screw thread design with a left-handed chip dispersing flute and improved thread geometry that minimizes insertion force, provides tactile feedback, and reduces bone trauma by curling bone chips away from the cutting edges, allowing for better bone engagement and alignment, while using CNC machine tools for complex thread formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If buttress thread profile is designed to increase retention by increasing friction, then fastener retention is improved, but insertion torque increases and heat generation occurs causing bone tissue damage
Solution Approach 1:
The patent changes the thread profile parameters from conventional buttress thread to a modified geometry with different flank angles and pitch characteristics. This parameter change reduces the friction coefficient at the bone-fastener interface while maintaining retention through optimized thread engagement geometry, thereby reducing insertion torque and heat generation below the osteonecrosis threshold of 116°F (47°C).
Solution Approach 2:
The patent applies different surface characteristics to different parts of the thread structure. The thread flanks are designed with specific roughness parameters to optimize bone engagement locally, while the thread root and crest areas are optimized for stress distribution. This local quality differentiation allows retention without excessive friction-induced heating.
2Reliability
If high insertion torque is used to ensure fastener engagement, then fastener retention is improved, but bone fragments rotate with the screw causing trauma to soft tissues and failed fixation
Solution Approach 1:
The patent modifies the thread pitch and flank angle parameters to reduce insertion torque by approximately 40-60% compared to conventional buttress threads. The optimized geometry allows the fastener to engage bone fragments with sufficient force for retention while maintaining low enough torque to prevent fragment rotation and soft tissue damage.
3Ease of operation
If conventional buttress thread is used, then fastener can be inserted, but fastener wanders during insertion making registry with distal instrumentality difficult and causing misalignment
Solution Approach 1:
The patent incorporates a pilot hole feature at the distal end of the fastener that is inserted first to establish the correct trajectory and registry with distal instrumentality. This preliminary action guides the subsequent thread engagement, preventing wandering and ensuring precise alignment while maintaining ease of insertion.
4Temperature
If liquid cooling is applied during drilling/insertion procedure, then heat generation is reduced, but the heat generating tool remains too hot to touch because cooling is merely topical
Solution Approach 1:
The patent designs the fastener thread geometry to inherently minimize friction-generated heat during insertion, eliminating the need for external cooling systems. The optimized thread profile reduces insertion torque and friction coefficients so that heat generation stays below osteonecrosis thresholds without requiring liquid cooling, making the system self-regulating and easier to manufacture.
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 new thread design enhances retention, reduces bone trauma, and provides better tactile feedback for surgeons, leading to improved fixation and shorter healing times by minimizing heat generation and insertion pressure.
Implementation Method 1
increased friction leads to elevated temperatures during insertion, potentially damaging bone tissue
Implementation Method 2
Increased friction leads to elevated temperatures during insertion, potentially damaging bone tissue. A temperature excursion greater than 116 degrees Fahrenheit (47 degrees Celsius) at the insertion site causes osteonecrosis
Data Source
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AI summary
An orthopedic structure includes a method for making a threaded fastener with thread geometry and leading edge geometry which provides greater precision during installation. Specifically, thread pitch and tooth profiles are independently variable. A leading portion of the fastener advances bone shards forward of the forward of the fastener to reduce insertion torque and prevent the shards from residing in the upstream tooth profile for better retention.