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Biomechanical analysis of a novel, triangular spinal fixation system
Jacob Mazza1, Jill Serbousek2, Richard G Fessler1
1Department of Neurosurgery, Rush University Medical Center, Chicago, IL, United States.
Background:
Pedicle screw fixation is a mainstay surgical technique for providing posterior stability to the spinal column, and consists of screws, rods and set caps. These components are prone to failure in various ways, but developing fixation systems with fewer components at risk of malfunction may limit construct failures. Utilizing a rod-less, triangular design, the novel system is intended to optimize construct strength while minimizing points of failure. This study aims to characterize the biomechanical performance of a novel posterior spinal instrumentation construct compared to traditional pedicle screw fixation.
Methods:
The ASTM (American Society for Testing and Materials) F1717 protocol for static compression bending, static torsion, and dynamic compression bending was followed. Biomechanical data for six (6) novel constructs were collected and compared to three (3) predicate traditional pedicle screw and rod constructs. Testing was performed to failure for each biomechanical test, and all mechanisms of failure were recorded.
Results:
In static compression bending, the average stiffness and displacement across all novel systems tested were 111±9.2 N/m and 4.2±0.5 mm, respectively as compared to predicate constructs which were 50±2 N/m and 18±6 mm, respectively. Static torsion testing showed that the novel systems, on average, required 21±1.7 N/m to rotate 1°-four times greater force than predicate systems. In dynamic compression bending, four novel constructs successfully reached runout at 5,000,000 cycles with a maximum applied force of 250 N. Predicate constructs were not able to tolerate loads greater than 160 N.
Conclusions:
The novel spine fixation system demonstrated superior biomechanical performance compared with predicate constructs in all testing completed. The novel construct was stiffer, displaced less, and required approximately four times as much torque to rotate the construct by a single degree compared with the predicate pedicle screw construct. The applied forces achieved at runout were substantially greater than predicate systems with less intraconstruct motion.