Abstract: BACKGROUND: The clinical application of stand-alone oblique lateral interbody fusion is greatly affected by the bone mineral density of patients, but there is no relevant report on the specific bone mineral density at home and abroad.
OBJECTIVE: To compare the biomechanical performance of an oblique lateral interbody fusion cage among different bone density models.
METHODS:  Based on the CT data of healthy adult male volunteers, there were L3-S1 normal control finite element model (M0 group), the normal bone mineral density (T value>-1.0 SD) L4-5 stand-alone oblique lateral interbody fusion finite element model (M1 group), osteopenia (-2.5 SD<T value<-1.0 SD) L4-5 stand-alone oblique lateral interbody fusion finite element model (M2 group) and osteoporosis (T value≤-2.5 SD) L4-5 stand-alone oblique lateral interbody fusion finite element model (M3 group). A motion torque of 10 N•m was applied on the surface of the L3 vertebra to simulate the biomechanical properties of the lumbar spine under six working conditions of the human body and to evaluate the range of motion of the L4-5 segments and the stress distribution of the bony endplate and cage. 
RESULTS AND CONCLUSION: (1) Under the same working conditions, compared with the M0 group, range of motion of the L4-5 segments of the M1, M2, and M3 groups all decreased, and the M3 group had the largest reduction. (2) Under the conditions of flexion, extension, and lateral bending, compared with the M0 group, the bony stress of the M1, M2, and M3 groups all increased significantly. Under the left and right rotation, compared with the M0 group, the bony endplate stress of the M1, M2, and M3 groups increased to different degrees. Under the same conditions, compared with the M1 group, the bony endplate stress in the M2 group was not significantly decreased, and the bony endplate stress in the M3 group was significantly increased. (3) Compared with the M1 group under the same working conditions, the cage stress in the M2 group was not significantly decreased, and the cage stress in the M3 group was increased significantly. (4) The results suggest that there is a risk of cage subsidence in patients with osteoporosis who undergo stand-alone oblique lateral interbody fusion surgery. For patients with bone mineral density T value>-2.5 SD, stand-alone oblique lateral interbody fusion surgery can improve biomechanical stability.

Key words: biomechanical test, finite element analysis, lumbar vertebra, oblique lateral interbody fusion, subsidence, bone mineral density