Hybrid Bone Fixation Element With Expandable Stent
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Solution Overview
Problem
Conventional bone screws primarily engage the cortical outer portion of bones, with little to no purchase in the softer cancellous inner portion due to its softness, leading to inadequate fixation strength.
Innovation Solution
A hybrid bone fixation element featuring a threaded cortical contacting portion and an expandable non-threaded stent distal portion that expands within the cancellous inner portion, enhancing purchase strength by increasing the radial diameter and surface area of contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional bone screw with threads is used to engage the cortical outer portion of the bone, then the screw can be inserted and secured in the cortical bone, but the purchase strength is insufficient because the threads cannot effectively engage the softer cancellous inner portion
Solution Approach 1:
The bone fixation element is divided into two distinct functional segments: a proximal threaded portion for engaging cortical bone and a distal expandable portion for engaging cancellous bone. This segmentation allows each portion to be optimized for its specific bone type, with the threaded portion providing secure cortical engagement and the expandable portion providing radial expansion force for cancellous bone purchase.
Solution Approach 2:
Different portions of the bone fixation element have different structural properties tailored to their specific engagement requirements. The proximal portion has threads for cortical bone engagement, while the distal portion has an expandable structure for cancellous bone engagement. This local differentiation of quality allows optimal performance in each bone type without compromise.
2Reliability
If the bone screw is designed to threadably engage the cortical outer portion, then secure fixation in cortical bone is achieved, but the softer cancellous inner portion provides little to no purchase due to its softness
Solution Approach 1:
The distal portion of the bone fixation element is designed to change shape dynamically during insertion and activation. It transitions from a compressed delivery configuration that allows easy insertion through the cortical bone to an expanded configuration that engages the cancellous bone with radial force, thereby achieving reliable fixation in the softer bone tissue.
Solution Approach 2:
The expandable portion undergoes parameter changes in its radial dimension during deployment. It transitions from a small radial diameter in the delivery configuration to a larger radial diameter in the expanded configuration, increasing its engagement surface area and purchase strength in the cancellous bone while maintaining reliability.
3Strength
If an expandable stent is added to engage the cancellous inner portion, then purchase strength in cancellous bone is improved, but the device complexity increases due to the additional components and expansion mechanism
Solution Approach 1:
The expandable stent is integrated with the threaded bone screw to form a single unified bone fixation element. The distal expandable portion is coupled to the proximal threaded portion, combining two functional elements into one device that can be inserted and activated as a single unit, thereby reducing overall system complexity while maintaining enhanced purchase strength.
Solution Approach 2:
The bone fixation element combines multiple functions in a single device: the proximal threaded portion provides cortical bone engagement while the distal expandable portion provides cancellous bone engagement. This multi-functionality allows the single device to address both bone types effectively without requiring separate components or procedures.
Data Source
AI summary
The present invention is directed to a hybrid bone fixation element including a threaded proximal cortical bone contacting portion for threadably engaging the cortical portion of a human bone and a non-threaded expandable distal collections portion for engaging the cancellous portion of the human bone. The hybrid bone fixation element can be used, for example, as a pedicle screw, a bone screw or in any other type of bone fixation application.