Bone Screw Thread Geometry for Safer Lateral Mass Fixation
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Solution Overview
Problem
Existing spinal implants face challenges in providing secure fixation while minimizing the risk of vertebral artery or nerve root injury during minimally invasive procedures, particularly in cervical and thoracic regions, due to inadequate design ratios and thread configurations.
Innovation Solution
A bone screw with a length-to-major diameter ratio of less than 2.0 and a major-to-minor diameter ratio greater than 2.0, featuring a thread pitch of greater than 1.0 mm, thread depth, and a thread depth-to-base-width ratio of about 5, designed for minimally invasive lateral mass screw placement, which includes a thread configuration that disrupts and cuts tissue to enhance holding power and minimize tissue damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bone screw with length-to-major diameter ratio greater than 2.0 is used, then the screw provides sufficient structural strength, but the risk of vertebral artery or nerve root injury increases during minimally invasive procedures
Solution Approach 1:
The patent changes the geometric parameters of the bone screw by reducing the length-to-major diameter ratio to less than 2.0, which allows the screw to engage more effectively in the limited space of cervical and thoracic lateral masses while reducing the risk of injury to surrounding neurovascular structures
2Strength
If a bone screw with major-diameter-to-minor diameter ratio less than or equal to 2.0 is used, then the screw structure is simpler, but the pullout strength is insufficient
Solution Approach 1:
The patent optimizes the thread geometry by specifying a major-diameter-to-minor diameter ratio greater than 2.0, which creates a more aggressive thread profile that enhances bone engagement and pullout strength while maintaining compatibility with minimally invasive insertion techniques
3Strength
If a bone screw with pitch less than or equal to 1.0 mm is used, then the thread engagement is denser, but the tissue disruption increases and holding power is reduced
Solution Approach 1:
The patent specifies a pitch greater than 1.0 mm, which reduces the number of threads per unit length and minimizes tissue disruption during insertion while maintaining adequate bone engagement through the optimized thread depth and profile, thereby improving holding power in minimally invasive procedures
Data Source
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AI summary
A bone screw has a first portion including a head. A second portion includes a threaded shaft having a length and a major diameter. The shaft includes a length-to-major diameter ratio of less than about 2.0. The thread has a minor diameter and includes a major-diameter-to-minor diameter ratio of greater than about 2.0. The shaft further has at least one thread including a pitch of greater than about 1.0 mm and defining a pitch cavity for disposal of tissue. Systems and methods of use are disclosed.