General Session: MIS-1
Presented by: S-J. Park - View Audio/Video Presentation (Members Only)
S-J. Park(1), C-S. Lee(1), S-S. Chung(1), J-H. Kim(1), J-S. Kim(1)
(1) Samsung Medical Center, Sungkyunkwan University, School of medicine, Orthopedic Surgery, Seoul, Korea, Republic of
Study Design: Radiographic analysis using prospectively collected data.
Objective: To evaluate the effect of indirect decompression on the canal size for central spinal stenosis and to provide the cut-off value of cross-sectional area of thecal sac (CSA) for additional decompression.
Summary of Background Data: Despite a number of studies regarding successful indirect decompression, how much the stenotic central canal can be decompressed indirectly by lateral lumbar interbody fusion (LLIF) has not been clearly determined.
Methods: Seventy-two stenotic levels with CSA less than 100mm2 were analyzed for 35 patients. All surgeries were performed in two stages. Magnetic resonance imaging (MRI) was obtained three days after LLIF, and then the decision was made whether additional decompression would be performed or not during the subsequent posterior fixation surgery. Regression analysis was performed to assess the factors affecting the postoperative CSA. The cut-off value of CSA for those who needed additional decompression was calculated by a formula using correlation analysis.
Results: The mean CSA increased from 78.7 mm2 to 104.9 mm2 with a mean increase ratio of 41.1%. Regression analysis showed that the preoperative CSA was a single independent factor affecting postoperative CSA (β=0.835, p< 0.001). When submitted to the correlation test, the following formula was found: Postoperative CSA = 0.87 x preoperative CSA + 36.5. Additional decompression was performed for 16 of the 72 levels. The mean preoperative CSA in the decompression group was significantly lower than that in the group that did not receive decompression (52.3 mm2 vs. 86.3 mm2). A CSA of 70mm2 was estimated to be the cutoff value which might require additional posterior decompression.
Conclusion: Preoperative CSA was a single independent factor affecting postoperative CSA. Additional posterior decompression should be considered for spinal stenosis of patients with a CSA value less than 70mm2 when a single-stage anterior-posterior surgery is planned.