Does osteoporosis affect the adjacent segments following anterior lumbar interbody fusion? A finite element study.

BACKGROUND Adjacent segmental degeneration (ASD) is one of the common complications following anterior lumbar interbody fusion (ALIF). Osteoporosis is becoming increasingly prevalent in elderly population. The patients undergoing ALIF may suffer from osteoporosis with age. However, the influence of osteoporosis on ASD after ALIF remains unclear. METHODS Three finite element models of L3-S1 segment including one healthy model, one ALIF model, and one ALIF with osteoporosis model were used for analysis. The ALIF was simulated at L4-L5 segment. Based on a hybrid test method, the models were imposed with a preload of 400N and an adjusted moment in flexion, extension, lateral bending, and axial torsion. The intradiscal pressure (IDP), shear stress on annulus fibrosus, and range of motion (ROM) at L3-4 and L5-S1 levels were calculated and compared. RESULTS In each direction, the maximal values of IDP and shear stress on annulus fibrosus at L3-L4 and L5-S1 segments were found in the ALIF model, and the minimal values were found in the healthy model. At L3-L4 and L5-S1segments, the maximal values of ROM in most directions were found in the ALIF model, followed by ALIF with osteoporosis model, and the minimal values were found in the healthy model. However, the maximal value of ROM at L5-S1 in axial torsion was found in ALIF with osteoporosis model. CONCLUSIONS Osteoporosis may mitigate the adverse influence of anterior lumbar interbody fusion on adjacent segments.