Comparison of posterior versus transforaminal lumbar interbody fusion using finite element analysis. Influence on adjacent segmental degeneration.

OBJECTIVES To compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on adjacent segment degeneration (ASD). METHODS The study was carried out in the Traumatology and Orthopedics Laboratory, Department of Traditional Chinese Medicine, Medical School, Jinan University, Guangzhou, China, between December 2013 and November 2014. A normal, healthy finite element model of L3-5 was developed, a PLIF and a TLIF model were modified from the normal model, and interbody fusions were performed in the L4-5 segment. An 800 N compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending, and axial rotation were imposed on the L3 superior endplate. Intradiscal pressure and intersegmental rotation in L3-4 were investigated. RESULTS The values of intradiscal pressure and intersegmental rotation in the PLIF or TLIF model were higher than those in the normal, healthy model, but the values in the TLIF model were relatively lower than those in the PLIF model in all directions.  CONCLUSION Posterior lumbar interbody fusion has more adverse influence on the superior adjacent segment than TLIF.