Cannulated Compression Screw With Dynamic Tension Member
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Solution Overview
Problem
Existing bone screws and fasteners fail to provide sufficient fixation and strength against bending loads, multi-axial forces, and off-axis loading scenarios, leading to loosening and reduced pressure over time, which hampers bone healing and osteogenesis.
Innovation Solution
A bone screw design featuring a distal member with bone-engaging threads, a proximal member that slidably engages the distal member, and a tension member that elongates to urge the distal member towards the proximal member, providing improved fixation and compression through a length limiting mechanism and a pre-stretch driver system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing bone screws and fasteners are used, then initial fixation is provided, but fixation strength and pressure decrease over time due to subsidence, resorption, motion, and loosening
Solution Approach 1:
The bone screw incorporates a tension member that can dynamically adjust its length to maintain compression force. The tension member transitions from a relaxed state to an elongated state as the bone screw shortens due to subsidence or bone resorption, thereby maintaining continuous compressive force on the bone interface throughout the healing process.
Solution Approach 2:
The invention changes the physical state of the tension member from relaxed to elongated as needed. When the bone screw shortens due to subsidence or bone resorption, the tension member elongates to maintain the compression force, effectively changing its length parameter to compensate for the shortening of the bone screw and maintain reliable fixation.
2Strength
If existing bone screws are used, then bone fixation is provided, but bending loads and multi-axial forces cause loosening and failure over time
Solution Approach 1:
The bone screw is divided into distinct functional segments: a proximal portion with a first thread pitch, a distal portion with a second thread pitch, and a tension member. This segmentation allows each portion to perform its specific function - the proximal portion engages the near bone, the distal portion engages the far bone, and the tension member maintains compression - thereby improving overall fixation stability against multi-axial forces.
Solution Approach 2:
The bone screw combines different thread pitch configurations in a single device, creating a composite structure with varying mechanical properties along its length. The proximal and distal portions have different thread characteristics optimized for their respective locations, while the tension member provides elastic compliance, creating a composite fixation system that resists bending loads and multi-axial forces more effectively than uniform screws.
3Duration of action of stationary object
If a tension member is added to provide continuous compression, then pressure maintenance is improved, but device complexity increases
Solution Approach 1:
The tension member is integrated within the hollow body of the bone screw, merging the compression maintenance function with the structural body. The tension member's proximal end is attached to the proximal portion and its distal end is attached to the distal portion, combining multiple functions (structural support, compression application, and length adjustment) into a single integrated device rather than separate components.
Solution Approach 2:
The tension member is nested within the hollow body of the bone screw. The hollow body serves as the outer structure that engages with the bone, while the tension member is contained within this hollow structure, allowing the compression mechanism to be embedded within the main body without requiring additional external components or increasing overall device complexity.
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 bone screw maintains effective compression and stabilization between bone portions, enhancing bone healing and fusion by resisting subsidence and motion-induced loosening, while the tension member's superelastic properties ensure consistent compressive force over time.
Implementation Method 1
a tension member. The tension member may have a proximal end coupled to the proximal member, and a distal end coupled to the distal member such that, in response to motion of the distal member away from the proximal member, the tension member elongates and urges the distal member to move toward the proximal member
Data Source
AI summary
A bone screw may be insertable into a bone. The bone screw may have a distal member with bone-engaging threads, a proximal member configured to slidably engage the distal member, and a tension member with a proximal end coupled to the proximal member, and a distal end coupled to the distal member such that, in response to motion of the distal member away from the proximal member, the tension member elongates and urges the distal member to move toward the proximal member.