Dynamic biomechanical examination of the lumbar spine with implanted total disc replacement using a pendulum testing...

Area of Science:

• Biomechanical analysis of spinal implants
• Orthopedic biomechanics
• Spinal fusion alternatives

Background:

• Pendulum testing system applies physiological compressive loads to functional spinal units (FSUs) without motion constraint.
• Energy absorption of FSUs can be quantified by the number of cycles to equilibrium during pendulum testing.

Purpose of the Study:

• To evaluate dynamic bending stiffness and energy absorption of lumbar FSUs.
• To compare biomechanical properties of intact FSUs versus those with total disc replacement (TDR) under simulated physiological motion.

Main Methods:

• Biomechanical investigation using five human lumbar cadaveric FSUs.
• Testing on a pendulum system with axial compressive loads (181 N to 488 N) before and after Synthes ProDisc-L TDR implantation.
• Assessment of motion in flexion, extension, and lateral bending, recording cycles to equilibrium and calculating bending stiffness.

Main Results:

• TDR constructs absorbed more energy, reaching equilibrium in fewer cycles than intact FSUs at higher compressive loads (P < 0.05).
• Dynamic bending stiffness significantly increased with load in both intact and TDR FSUs (P < 0.001).
• Intact FSUs demonstrated significantly greater bending stiffness than TDR constructs across all tested compressive loads (P < 0.05).

Conclusions:

• Lumbar FSUs with TDR exhibit reduced stiffness but enhanced energy absorption under cyclic loading.
• These biomechanical findings provide valuable data on the behavior of motion-preserving devices under simulated physiological conditions.
• Further research is needed to fully understand the clinical implications of these biomechanical changes.