Interbody Spacer Material Properties and Design Conformity for Reducing Subsidence During Lumbar Interbody Fusion.
J Biomech Eng. 2017 Mar 23;:
Authors: Chatham LS, Patel VV, Yakacki CM, Carpenter RD
One major complication with lumbar spinal fusion surgery is subsidence, in which the interbody spacer penetrates the vertebral endplates. Towards reducing the risk of subsidence, the objective of this study was to investigate the effects of interbody spacer material and design on the stress in the lumbar spine after interbody fusion. A finite element model of the L4-L5 motion segment was developed from computed tomography images of a cadaveric lumbar spine. A spacer, pedicle screws, and posterior rods were incorporated into the model, and the system was loaded under axial compression. Polyetheretherketone (PEEK), titanium, poly(para-phenylene) (PPP), and PPP with simulated 70% porosity were used as the spacer material to quantify the effects on stress in the system. A standard spacer design was compared with a custom design that conformed to the vertebral endplate anatomy. Experimental testing of a cadaveric specimen was used to validate the model’s results. There were no large differences in stress levels (< 3%) at the bone-spacer interfaces or posterior rods when PEEK was used instead of titanium. The porous PPP spacer produced an 8-15% decrease in stress at the bone-spacer interfaces and posterior rods. The custom spacer significantly decreased (> 37%) the stress at the bone-spacer interfaces for all materials tested, with 70% porous PPP resulting in the lowest overall stress at the bone-spacer interfaces. The results demonstrate the potential for more compliant materials and conforming geometry to reduce stress on vertebral endplates, thereby decreasing the risk of subsidence.
PMID: 28334320 [PubMed – as supplied by publisher]