Background Previous clinical and basic research of axial lumbar interbody fusion (AxiaLIF) all focused on the L5/S1.However,there is no data on the feasibility of this approach for the fusion of both L4/5 and L5/S1.This study aimed to explore whether transsacral axial interbody fusion is a candidate for the fusion of both L4/5 and L5/S1.Methods The subjects (n=40) underwent lumbosacral magnetic resonance imaging (MRI).The median sagittal MRI images were analyzed and five measurement markers were defined as follows:the center of the L4/5 disc (A),the center of the L5/S1 disc (B),the anterior margin of the S1/2 space (C),the sacrococcygeal junction (D),and the coccygeal tip (E).The measurement markers were connected each other to produce nine lines (AB,AC,AD,AE,BC,BD,BE,CD and CE) as the reference lines for surgical approaches.The distance between each reference line and the anterior and posterior margins of the L4,L5 and S1 vertebral bodies were measured to determine the safety of the respective approaches.Results Twenty subjects were capable of finding one reference line to fuse both L4/5 and L5/S1 via transsacral axial interbody fusion approach.The surgical approach reference line was AE or CE line.In the other 20 subjects,it was failed to find a reference line which met the safety criteria for fusing both L4/5 and L5/S1.Conclusions About half of subjects were capable of finding a suitable AxiaLIF reference line to fuse both L4/5 and L5/S1.In some subjects,it was difficult to find a suitable AxiaLIF reference line to fuse both L4/5 and L5/S1.