Age-Related Stability for Artificial Disc Fixators Inserted into a Lumbar Vertebra: Finite Element Analysis

The objective of this research was to analyze age-related stability at 20, 40, 60, and 80 years of age for two artificial disc fixators inserted into the L3 lumbar vertebra after total disc replacement (TDR) surgery. To precisely analyze the lumbar vertebra, elastic moduli of the cortex verified by load contributions between two materials were used. The stress shielding problem was solved using a p-element. For a wedge-type of Charite III and a plate-type of ProDisc L, these two models and the aging L3 lumbar were created. Decreasing disc loads applied to the aging vertebra. Based on this, load-analysis of the trabecular bone for supporting the artificial disc with fixators was performed every 20 years. The results showed as follows: 1) The ultimate loads resulting in maximal stresses and strains of the plate shape after TDR showed a reduction of about 72 and 79%, respectively, compared with healthy vertebral bodies; 2) The decreasing width of the physiological loads greatly influenced the increase and decrease of stress and strain; 3) Both fixtators were involved in low back pain and were limited to less than 800 N at 80 years old; therefore, it was predicted that continued treatment would be needed.