How to insert a more suitable ATP-OLIF51 cage?: A radiological study compared L5/S1 endplate to L4/5 endplate

The purpose of this study was to investigate if the parameters of the L5/S1 endplate are consistent with the L4/5 endplate, to explore the more optimal location of the cage, and to design a new L5/S1 cage in anterior to psoas-oblique lateral interbody fusion (ATP-OLIF). A total of 120 individuals with low back pain were retrospectively studied, with all participants undergoing lumbar CT from L4 to S1. On the endplate plane, the anterior, middle, and posterior transverse diameters, as well as the sagittal diameter, were measured. Disc height and segmental lordosis angle were assessed in the middle sagittal plane of L4/5 and L5/S1. All parameters were measured with the picture archiving communication system. For middle sagittal plane parameters, L5/S1 had a substantially higher segmental lordosis angle compared to L4/5 (P < .01). For endplate plane parameters, S1 superior endplate had significantly smaller sagittal, middle, and posterior transverse diameters than L5 superior endplate (P < .01), larger anterior transverse diameter than L5 superior endplate (P < .01), and smaller sagittal, middle, and posterior transverse diameters than L5 inferior endplate (P < .05). The L5 inferior endplate had considerably lower sagittal, middle, and posterior transverse diameters compared to the L4 inferior endplate (P < .01). The anterior transverse diameter of the S1 superior endplate was significantly greater than the posterior transverse diameter (P < .01), while the anterior transverse diameters of the L5 superior and L4 inferior endplates were significantly smaller than the posterior transverse diameter (P < .01). The L5/S1 endplate's specifications differ from those of the L4/5 endplate. ATP-OLIF in L5/S1 requires a cage with a significant lordosis angle and a narrow posterior transverse diameter. It may be safer to situate the cage anteriorly. These findings are important for anatomical study, the design of the ATP-OLIF51 cage, and the scientific planning of spinal surgery.