Intraoperative Myelography in Minimally Invasive Decompression for Degenerative Lumbar Spinal Stenosis

Study Design: A retrospective comparative series study. Objective: To develop an intraoperative myelography protocol and determine its value on the treatment results in microendoscopic decompressive laminotomy (MEDL) for degenerative lumbar spinal stenosis. Summary of Background Data: The MEDL is a minimally invasive but technically demanding technique for decompressing spinal stenosis. An intraoperatively assessing method for adequate decompression is lacking, but may be helpful and has positive value on the treatment results. Methods: Forty consecutive degenerative lumbar spinal stenosis patients receiving MEDL were included in this study. The earlier 20 patients received MEDL without myelography (the traditional group); the later 20 patients received MEDL with the myelography protocol (the myelography group). An additional intraoperative myelography was performed in the myelography group to help localizing the stenosis before decompression and verifying adequate decompression after decompression. Any residual filling defects identified in the postdecompression myelogram were considered signs of inadequate decompression and additional decompression was performed until they resolved. Results: Inadequate decompression was identified in 4 of 20 patients in the myelography group, but none in the traditional group. Both groups had significant improvement after surgery. However, the myelography group had significantly better results with lower 6-month Oswestry Disability Index (ODI) (6 vs. 10, P = 0.049), more ODI improvement (44 vs. 28, P = 0.009), higher Japanese Orthopedic Association (JOA) scores (27.5 vs. 24, P = 0.043), a higher JOA improvement rate (92.8% vs. 73.2%, P = 0.013), and greater decompression effect (56.8% vs. 41.4% cross-sectional dural area, P = 0.024). The myelography group also had a higher proportion of patients to have "significant ODI improvement," " JOA success," and " JOA good-to-excellent results." There were no myelography-related complications. Conclusions: The intraoperative myelography protocol provides a simple method to precisely localize the stenosis and verifies the adequacy of decompression; hence, improves the treatment result of MEDL.