Experimental Study of Failures of the Rigid Spinal Posterior Fixation System Under Compressive Load Conditions: A...

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Spinal Biomechanics

Background:

• Spinal fusion surgery biomechanics and instrumentation failure are widely studied.
• Existing research lacks focus on axial compressive loads in spinal biomechanics.
• Understanding load sharing is crucial for spinal instrumentation.

Purpose of the Study:

• To investigate the biomechanical effects of axial compressive loads on pedicle screw instrumentation in lumbar vertebrae.
• To quantify strain in pedicle screw rods and intradiscal pressure under load.
• To calculate stress distribution and load sharing between the spine and instrumentation.

Main Methods:

• Axial compressive load tests were conducted on human cadaveric lumbar vertebrae specimens.
• Pedicle screws (PS) were used for fixation.
• Strain gauges and pressure sensors measured rod strain and intradiscal pressure.

Main Results:

• Bending stress in the pedicle screw rod was over 10 times the compression stress, concentrating on one rod.
• Rod deformation exhibited kyphotic behavior, contrasting with the lumbar spine's lordotic behavior.
• The stress shielding rate was approximately 40%.

Conclusions:

• The study provides foundational data for developing and validating numerical simulations of spinal implants.
• Findings are essential for predicting and understanding spinal implant dislodgement and failure mechanisms.
• This research contributes to improving the design and performance of spinal instrumentation.