Subsidence of Center or Off-Center Posterior Lumbar Interbody Fusion and Transforaminal Lumbar Interbody Fusion Cages

Lumbar interbody fusion cages have been widely used to restore spine alignment. However, it has been speculated whether a single long transforaminal lumbar interbody fusion cage is as effective as a pair of short posterior lumbar interbody fusion cages in preventing excessive subsidence, and how much posterior and transforaminal lumbar interbody fusion cages subside if they are placed off the center of the endplate towards the epiphyseal ring. Thus, in this study finite element models of the lumbar interbody fusion cages and the vertebrae, including the endplate and the epiphyseal ring, were created, and finite element simulations were conducted to estimate the subsidence of a pair of posterior lumbar interbody fusion cages and a single transforaminal lumbar interbody fusion cage not only placed at the center of the endplate but also placed off-center. The finite element simulation results indicated that a long transforaminal lumbar interbody fusion cage was equally or more effective in reducing subsidence compared to a pair of posterior lumbar interbody fusion cages. Furthermore, the results also showed that both posterior and transforaminal lumbar interbody fusion cages resulted in less subsidence when placed off-center and closer to the epiphyseal ring.