The Effect of High-Demand Loading Conditions on Polyethylene Stresses in Total Joint Replacement of the Lumbar Spine...

In this study, we introduce a method for evaluating the effects of high-demand spinal loading on polyethylene stresses in a lumbar total joint replacement (LTJR).

A previously validated finite element model of the lumbar spine was virtually implanted with an LTJR at L5-S1 and subjected to loading generally above the standard in vitro Mode I wear testing. Specifically, three elevated loading conditions were considered: (1) flexion with 50th and 95th percentile male body weights; (2) flexion in combination with axial rotation and lateral bending for 50th and 95th percentile male body weights; and (3) uniaxial torsion under a worst-case load as defined by ASTM F2423.

In all three loading scenarios, bearing contact occurred within the intended spherical articulations, consistent with Mode I in vitro wear testing. No component impingement outside the spherical bearing surfaces was observed. The resulting contact and von Mises stresses, as well as effective plastic strains, remained below those predicted for Mode IV impingement simulations.

This study provides an approach for evaluating the upper biomechanical loading limits for an LTJR design at L5-S1, extending beyond the 50th percentile conditions typically used in standard in vitro testing.