Quantitative analysis of indirect decompression in extreme lateral interbody fusion and posterior spinal fusion with a percutaneous pedicle screw system for lumbar spinal stenosis.

BACKGROUND: The authors sought to quantify the results of clinical and radiological analyses of extreme lateral interbody fusion (XLIF) plus percutaneous pedicle screw (PPS) fixation for patients with lumbar spinal stenosis (LSS) by focusing on the distinct mechanism of indirect decompression.
METHODS: Data obtained from a total of 37 patients with 47 surgical sites were retrospectively analyzed. Clinical outcomes for all patients were evaluated using the Japanese Orthopaedic Association (JOA) score and the improvement rate of the JOA score. Preoperative and postoperative magnetic resonance images were used to measure the transverse areas of both the dural sac (DS area) and ligamentous flavum (LF area) in the axial sections and the length of the intervertebral disc bulge (DB length) in sagittal sections. Then, the rate of change (RC) of the DS area (RC-DS), the RC of the LF area (RC-LF), and the RC of the DB length (RC-DB) from the preoperative period to the postoperative period were calculated. Furthermore, we divided all surgical sites into the small expansion group (SE group; RC-DS <150%) and large expansion group (LE group; RC-DS ≥200%) according to the degree of RC-DS.
RESULTS: Preoperative clinical symptoms improved significantly after surgery for all patients regardless of whether the RC-DS was large or small. RC-DS, RC-LF, and RC-DB were approximately 203%, 74%, and 37%, respectively. Moreover, we found that the bulging was significantly shorter in the LE group than in the SE group, although there was no difference in the RC-LF between the LE group and SE group.
CONCLUSIONS: We suggest that indirect decompression after XLIF is particularly influenced by the degree of reduction in DB.