Bio-Flexible Spinal Rod Structure for Fatigue Fracture Prevention
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Solution Overview
Problem
Conventional spinal fixation rods lack elasticity, leading to issues such as difficulty in maintaining natural spinal alignment, increased surgical burden, and fatigue fractures due to concentrated stress at the contact area between the set screw and rod.
Innovation Solution
A bio-flexible spinal fixation apparatus with a rod design featuring a straight part with a flat surface and a coil part positioned eccentrically, combined with a washer to ensure surface contact and uniform load distribution, preventing fatigue fractures and facilitating easier installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional rod with single form and no elasticity is used to connect pedicle screw pikes, then the rod can be manufactured with standard materials like medical titanium, but the rod cannot maintain natural sagittal balance and causes concentration of load on upper or lower segments leading to degenerative changes in adjacent segments
Solution Approach 1:
The rod is divided into multiple segments with different material properties. The first rod segment has higher elasticity to absorb impact and maintain natural motion, while the second rod segment has lower elasticity to provide stable fixation. This segmentation allows each segment to perform its specific function optimally, resolving the contradiction between manufacturability and spinal segment stability.
Solution Approach 2:
The rod is constructed as a composite structure combining materials with different elastic properties. The first rod segment uses a material with higher elasticity (such as nickel-titanium alloy) while the second rod segment uses a material with lower elasticity (such as stainless steel or titanium). This composite material approach enables the rod to simultaneously provide flexibility for natural motion and rigidity for stable fixation.
2Strength
If a rigid rod structure is used for spinal fixation, then the rod provides strong fixation force, but the rod cannot accommodate frequent spinal motions and is prone to fatigue fracture at the contact area between set screw and rod
Solution Approach 1:
The rod is segmented into two parts with different elastic properties. The first rod segment with higher elasticity acts as a cushioning element to absorb repeated loading from spinal motions, preventing stress concentration at the set screw contact area. The second rod segment with lower elasticity provides the necessary fixation strength. This segmentation resolves the contradiction between strength and fatigue resistance.
Solution Approach 2:
The elastic modulus parameter is changed along the length of the rod. The first rod segment has a higher elastic modulus to provide flexibility and absorb impact, while the second rod segment has a lower elastic modulus to provide stable fixation. This parameter change allows the rod to withstand frequent spinal motions without fatigue fracture while maintaining strong fixation force.
3Reliability
If the coil part of the rod is configured with specific eccentricity and inclination to enable natural spinal motion, then the rod can maintain natural sagittal balance, but the rod structure becomes more complex and difficult to install during surgery
Solution Approach 1:
The rod is segmented into a first rod segment with specific eccentricity and inclination configuration to enable natural spinal motion, and a second rod segment with simpler structure for stable fixation. By segmenting the rod, the complex eccentricity and inclination features are concentrated in the first segment where they are most needed for natural motion, while the second segment provides simplified structural support, thus reducing overall installation complexity.
Solution Approach 2:
The first rod segment at the proximal end is configured with specific eccentricity and inclination to maintain natural sagittal balance and accommodate spinal motion. The second rod segment at the distal end has a simpler, more straightforward structure for stable fixation. This local quality differentiation applies the complex configuration only where necessary for natural motion while keeping the rest of the structure simple for easy installation.
4Stability of the object's composition
If a non-elastic rod is used to fix the spine, then the rod provides stable fixation, but the rod cannot accommodate repeated loads from frequent spinal motions and leads to fatigue fracture
Solution Approach 1:
The rod is divided into two segments with different elastic properties. The first rod segment with higher elasticity absorbs repeated loads from frequent spinal motions through elastic deformation, preventing stress concentration. The second rod segment with lower elasticity maintains stable fixation. This segmentation allows the rod to simultaneously provide stability and resistance to repeated loading.
Solution Approach 2:
The rod is constructed as a composite structure where the first rod segment uses a material with higher elasticity to absorb repeated loads and prevent fatigue fracture, while the second rod segment uses a material with lower elasticity to provide stable fixation. This composite material construction resolves the contradiction between fixation stability and resistance to repeated loading.
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 apparatus allows for natural spinal motion, reduces surgical complexity, and prevents fatigue fractures by evenly distributing load, mimicking the body's normal load-sharing mechanism and minimizing adjacent segment degeneration.
Implementation Method 1
a coil part 24 wound to be inclined by a specific angle based on a center separated by a predetermined distance with an eccentricity from a center of the straight part 22
Implementation Method 2
a washer 40 that is integrally coupled to a bottom surface of the set screw 30 and applies a fixed load to the straight part 22 of the rod 20 with uniform sharing
Implementation Method 3
an upper surface of the straight part 22 of the rod 20 makes a flat surface 26
Data Source
AI summary
The present invention relates to a bio-flexible spinal fixation apparatus capable of realizing motions similar to general body mechanical motions during flexion and extension motions after spinal fixation surgery by configuring a center of a coil part of a rod to have a eccentricity at a certain distance from a center line of a straight part and a specific inclination, and conveniently performing an operation of setting a fixing position of the rod during spinal fixation surgery by machining the straight part section of the rod into a flat surface. The present invention includes a screw pike that includes a head part and a screw; a rod that has a straight part and a coil part wound to be inclined by a predetermined angle with an eccentricity from a center of the straight part; and a set screw.