Spinal Deformity Correction via Uni-Planar Screw Angular Limits
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Solution Overview
Problem
Existing spinal deformity correction techniques often fail to address all three primary planes of correction (coronal, sagittal, and axial) effectively, leading to issues like 'Flatback Syndrome' and 'Rotational Trunk Shift', as they do not adequately manage axial balance.
Innovation Solution
A system utilizing uni-planar or polyaxial pedicle screws with derotation tubes and restraint sleeves allows for simultaneous correction of all three planes, providing a rigid and quick assembly method with controlled derotation capabilities, including a fastening system with limited angular displacement and alignment systems using U-shaped saddles and locking cap assemblies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional spinal fusion constructs (Harrington rod, Cotrel-Dubousset technique) are used, then coronal and sagittal plane correction is achieved, but axial plane balance is not addressed leading to rotational trunk shift
Solution Approach 1:
The spinal fusion construct is segmented into modular components: pedicle screws with polyaxial capability, separate derotation elements (such as derotation rods or cables), and connection elements. This segmentation allows independent optimization of each component for its specific function while maintaining overall system versatility for correcting all three planes of deformity.
Solution Approach 2:
The spinal fusion construct incorporates multi-functional elements that can address coronal, sagittal, and axial plane deformities. For example, polyaxial pedicle screws provide both structural support for coronal/sagittal correction and serve as anchor points for derotation elements, eliminating the need for separate specialized hardware for each plane.
2Manufacturing precision
If curved rods are rotated 90 degrees to match spinal deformity convexity and concavity, then coronal and sagittal balances are corrected, but axial unbalanced vertebra remains uncorrected
Solution Approach 1:
The construct incorporates dynamic derotation elements that can be adjusted and tightened progressively during surgery to achieve optimal axial alignment. Derotation cables or rods can be tensioned in stages, allowing the surgeon to dynamically adjust the derotation force applied to each vertebra while maintaining coronal and sagittal corrections.
Solution Approach 2:
Intermediary derotation elements (such as derotation rods connecting adjacent pedicle screws, or cables passing through the spinal canal) are introduced as mediators to transmit rotational corrective forces. These intermediaries enable axial plane correction without compromising the precision of coronal and sagittal alignment achieved by the primary rod construct.
3Stability of the object's composition
If rigid constructs are used to provide stability, then spinal alignment is maintained, but assembly time increases and surgical efficiency decreases
Solution Approach 1:
The polyaxial pedicle screws are pre-assembled with derotation elements and connection hardware before insertion into the vertebrae. This preliminary assembly allows the surgical team to prepare rigid, stable constructs in advance, reducing intraoperative assembly time while maintaining the stability needed for precise spinal alignment.
Solution Approach 2:
The construct incorporates dynamic locking mechanisms that allow for progressive tightening and stabilization. Elements such as progressive collapse cages or adjustable locking screws enable the construct to achieve final rigid stability through controlled, staged tightening rather than requiring all components to be fully assembled and locked simultaneously, thereby improving surgical efficiency.
Data Source
AI summary
A spinal alignment system can include a rod and a plurality of uniplanar screw assemblies that include a screw, a cap, and a housing. The screw and cap can be configured such that the relative angular displacement between the screw and the cap is limited to a first limit angle in a first plane and to a second limit angle in a second plane that is perpendicular to the first plane, the second limit angle being larger than the first limit angle. The housing can be coupled to the cap and configured to maintain the cap in proximity with the head of the screw. The housing can have two elongated elements forming a U-shaped saddle. The alignment system can also include a plurality of locking cap assemblies that capture the rod within the U-shaped saddle and are tightened to fixedly couple the rod to the respective uniplanar screw assemblies.