High Demand Loading Conditions and Their Effect on Polyethylene Stresses in Lumbar Total Joint Replacement: Implications for Spine Wear Protocols.

The study aimed to compare contact stresses for a novel lumbar total joint replacement (LTJR) during a standardized duty cycle with elevated loading conditions. A finite element model (FEM) of an LTJR was developed, verified, and validated using the ASME V&V40 standard. Simulations were performed using LS-Dyna. Increasing the axial loading for the 95th percentile male generally resulted in an increase in the peak contact pressures throughout the duty cycle. Specifically, contact pressure reached a maximum of 37.6 MPa. Despite this increase, the polyethylene peak contact stresses remained considerably lower than values previously documented during impingement. For 95th percentile male loading, the bearing mechanics of the LTJR design remained reasonably consistent with the 50th male loading scenario. Contact between the superior and inferior components remained confined to the intended hemispherical bearing surfaces, without evidence of impingement. The contact stresses in elevated loading scenarios fell below the levels associated with impingement loading. The polyethylene bearing stresses indicate that relative risks of wear and surface damage, including pitting, delamination, and fracture associated with a 95th percentile male, will be lower relative to the conditions from impingement testing. Clinical Significance: Our in silico approach to exploring elevated boundary conditions for spine wear testing will facilitate future test method development.