Does Osteoporosis Affect the Adjacent Segments Following Anterior Lumbar Interbody Fusion? A Finite Element Study

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