Objective: To study the relationship between the relative dural sac cross-sectional area (RDCA) and shape of the dural sac in the lumbar spinal stenosis patients and outcomes after bipotal endoscopic spine surgery (BESS).
Materials and Methods: This was a retrospective cohort study which included the population of patients diagnosed with lumbar spinal stenosis whom underwent BESS at HRH MSMC from the period of May 2014 to April 2019. RDCA and shape of the dural sac were evaluated with pre-operative MRI. RDCA and morphological grade were reported as percentage and Schizas scale (A, B, C, D) respectively. The Oswestry Disability Index (ODI) and visual analog score (VAS) in leg pain were our primary outcome on the present study and the data were collected before the operation and one yerar after the procedure.
Results: A total of 128 patients (160 levels of surgery) underwent BESS for lumbar spinal stenosis. There were an association between RDCA and morphological grading. Severe morphological grading was associated with decreased in RDCA measured from the MRI. There were improvement of ODI and VAS in the all groups of radiographic grading. And clinical improvement was increased but not significantly in the person who had RDCA less than 50% (p-value >0.05).
Conclusion: The MRI-based morphological grading and RDCA were associated with good surgical results after BESS regarding their association with baseline and 12-month follow-up. There are numerous patients who achieved greater surgical outcome of the reduction of ODI and VAS especially in RDCA less than 50%. RDCA <75% and Schizas B, C, D. RDCA represented the preferred method for assessing the extent of spinal stenosis. This evidence was difference from the former reports that morphologic classification grade B had likelihood of a positive outcome after BESS.

Keywords: Dural sac cross-sectional area; Morphological grading; Spinal stenosis; Endoscope; Biportal endoscope; Relative