Flexible Spinal Rod Load Distribution to Reduce PJK
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Solution Overview
Problem
The incidence of proximal junctional kyphosis (PJK) and adjacent level failure in spinal fixation surgeries is high due to the structural rigidity of traditional spinal rods, leading to increased morbidity and the need for additional surgeries, especially when lumbar lordosis and thoracic kyphosis are not properly restored post-surgery.
Innovation Solution
A spinal construct with a flexible member that transitions load from a rigid portion to the patient's anatomy, reducing the load on uninstrumented vertebral levels by using a fixation member with a head and shank, where the flexible member is secured to the vertebra using an inserter system that includes a handle and tubular member, allowing for adjustable tension to accommodate movement while limiting kyphotic movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional rigid spinal rods are used for fixation, then structural stability is improved, but the incidence of proximal junctional kyphosis and adjacent level failure increases due to excessive load on uninstrumented vertebral levels
Solution Approach 1:
The patent changes the mechanical parameter of the spinal rod from rigid to flexible by using a flexible member that can bend and deform. This flexible spinal rod maintains structural stability while reducing the transmission of excessive loads to uninstrumented vertebral levels, thereby decreasing the incidence of proximal junctional kyphosis and adjacent level failure.
Solution Approach 2:
The patent employs composite construction by combining the flexible spinal rod with rigid fixation components (screws, connectors) at specific levels. This creates a hybrid system where the flexible rod provides load distribution and stress reduction, while the rigid components ensure stable anchorage at instrumented levels, resolving the contradiction between overall stability and localized stress reduction.
2Stability of the object's composition
If rigid spinal fixation constructs are used, then immediate post-surgical stability is improved, but the need for additional corrective surgeries increases due to failure to accommodate spinal movement and maintain sagittal balance
Solution Approach 1:
The patent transitions from a static rigid rod to a dynamic flexible rod that can adapt its configuration in response to spinal movements and loading conditions. The flexible member allows controlled deformation to accommodate physiological spinal motion while maintaining sagittal balance, preventing the need for additional corrective surgeries.
Solution Approach 2:
The flexible spinal rod changes its mechanical parameters (bending stiffness, curvature) in response to applied loads and spinal positioning requirements. This allows the construct to maintain immediate post-surgical stability while adapting to maintain proper sagittal balance, thereby reducing the need for additional corrective procedures.
3Reliability
If flexible members are used to reduce load on adjacent levels, then the incidence of PJK is reduced, but the structural rigidity of the construct is decreased
Solution Approach 1:
The patent optimizes the flexibility parameter of the spinal rod by selecting materials and cross-sectional geometries that provide appropriate bending compliance. The flexible rod has controlled stiffness characteristics that allow it to reduce load transmission to adjacent levels while maintaining sufficient structural rigidity to provide stable fixation and support spinal alignment.
Data Source
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AI summary
A system for securing a flexible member to a vertebra includes a flexible member, a fixation member, and an inserter. The flexible member includes two ends. The fixation member includes a head and a shank that defines a longitudinal axis of the fixation member. The head defines a slot that passes through the head orthogonal to the longitudinal axis. The slot receives a portion of the flexible member. The inserter includes a handle and a tubular member that has proximal and distal end portion. The proximal end portion is attached to the handle and the distal end portion extends from the handle. The tubular member defines a passage between the proximal and distal end portions. The distal end portion includes a couple for receiving the head of the fixation member with the portion of the flexible member received in the slot of the flexible member.