Does the position of cage affect the clinical outcome of lateral interbody fusion in lumbar spinal stenosis?

Abstract

Background: Lateral interbody fusion (LLIF) decompress the neural elements indirectly by increasing the height of disc, instead of resecting the disc or osteophytes herniated to the canal. When performing LLIF, the position of interbody cage is quite important for the outcome of decompression. This study aims to identify the ideal cage position in LLIF and to investigate if the posterior instrumentation would affect the indirect decompression. Methods: This is a retrospective study. Patients underwent 2-stage surgeries: stage I was LLIF and stage II was percutaneous pedicle screws fixation after 1 week. Anterior disc height (ADH), posterior disc height (PDH), left and right foraminal height (FH) and segmental angle (SA) were measured on lateral CT reconstructions. The cross-sectional area of the thecal sac (CSA) was determined by the outlined area of the thecal sac on a T2-weighted axial MRI. The patients were subgroups according to the cage position: the anterior (cage located at the anterior 1/3 of disc space) and posterior groups (cage located at the posterior 2/3 of disc space). P-values <0.05 were considered significant. Results: This study included 46 patients and 71 surgical levels. After stage I LLIF, significant increase in ADH, PDH, bilateral FH was found in both 2 subgroups, as well as the CSA (all p<0.01). SA increased 2.84±3.2° in anterior group after stage I LLIF and increased 0.81±3.1° in posterior group (p=0.013). After stage II surgery, SA was similar between anterior and posterior group (p=0.20). CSA showed no difference between the 2 groups. Conclusion: The anteriorly placed cage may provide better improvement of anterior disc height and segmental angle after stand-alone LLIF surgery. After the second stage posterior instrumentation, the cage position would not affect the segmental angle or foraminal height.