Sensitivity of Lumbar Total Joint Replacement to Axial and Coronal Plane Misalignment Using Computational Modeling.

Area of Science:

• Biomechanical engineering
• Spinal surgery
• Implant design

Background:

• Component misalignment during lumbar total joint replacement (LTJR) can impact bearing surface interactions.
• Investigating misalignment is crucial for understanding implant performance and longevity.

Purpose of the Study:

• To computationally investigate the effects of clinically relevant misalignment scenarios on LTJR performance.
• To evaluate polyethylene stresses and contact mechanics under various malpositioning conditions.

Main Methods:

• Validated finite element models (FEM) of LTJR and the lumbar spine (L3-L5) were used.
• Misalignment was simulated by adjusting axial plane convergence, anterior-posterior offset, and coronal plane tilt.
• Analyses under simulated bending conditions assessed contact pressures and von Mises stresses.

Main Results:

• Coronal plane tilt significantly affected stress magnitude and distribution.
• Increasing anterior-posterior offset altered stress patterns on the affected component.
• Axial plane convergence angle had minimal impact on overall stress.

Conclusions:

• Polyethylene stresses remained below impingement levels across all simulated misalignment scenarios.
• Contact areas stayed within intended bearing surfaces, indicating no impingement.
• LTJR demonstrated reasonable insensitivity to misalignment under simulated bending conditions.