Analysis of Temporal Changes in Dural Sac Morphology After XLIF Indirect Decompression

STUDY DESIGN: Retrospective study. OBJECTIVE: To investigate temporal changes in dural sac morphology after extreme lateral interbody fusion (XLIF) indirect decompression for central lumbar spinal stenosis and to study the factors influencing the changes. METHODS: The morphology of the dural sac was categorized into 4 grades (A, minor; B, moderate; C, severe; and D, extreme) by partially modifying Schizas classification (m-Schizas). The study involved 38 patients and 47 intervertebral spaces treated with indirect decompression (grade C or D). We evaluated m-Schizas before surgery, immediately after surgery, and at final follow-up. We performed a statistical analysis on the risk factors of grade C or D stenosis (poor morphological improvement) at final follow-up. The factors evaluated were preoperative dural sac cross-section area (CSA), diagnosis, cage size, location of cage insertion, locked facets, bony lateral recess stenosis, end plate injury, and changes in the posterior disc height (PDH) and disc angle (DA). RESULTS: On morphological evaluation, improvement to grade A or B was seen in 10 intervertebral spaces (21.2%) immediately after the surgery, and improvement was achieved in 38 intervertebral spaces (80.8%) at final follow-up. The risk factor of poor morphological improvement was found to be small preoperative dural sac CSA (odds ratio 1.32, P < .002). CONCLUSIONS: After XLIF indirect decompression, the morphological improvement of the dural sac was remodeled with time and further expansion was seen in many patients. However, the study suggested that sufficient morphological improvement may not be achieved in spinal stenosis whose preoperative state is severe.