P40. Indirect effect on adjacent segment after minimally invasive transforaminal lumbar interbody fusion

Abstract

<h3>BACKGROUND CONTEXT</h3> MIS-TLIF is an alternative treatment for degenerative spine disease, which aims to decompress and stabilize the most stenotic level correlating with clinical symptoms, while sparing the less severe adjacent segments. According to previous studies, interbody fusion was reported to not only affect the fused level, but also the adjacent segments. These effects might cause changes in canal dimensions at the adjacent segments, leading to unsatisfactory postoperative symptoms. <h3>PURPOSE</h3> The goal of this study was to compare the dural sac area and other canal dimension parameters on MRI at the adjacent segments before and after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF), including the change in segmental and regional parameters measured on plain radiograph. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study King Chulalongkorn Memorial Hospital. <h3>PATIENT SAMPLE</h3> Patients who underwent MIS-TLIF at L4/5 level in King Chulalongkorn Memorial Hospital The indications for surgery were spinal canal stenosis, herniated nucleus pulposus, and spondylolisthesis grade 1-2. <h3>OUTCOME MEASURES</h3> MR image parameters: dural sac area (DSA), sagittal spinal AP diameter (SAPD), ligamentum flavum area (LFA), ligamentum flavum thickness (LFT), foraminal area (FA), foraminal height (FH), at the adjacent segments of fused level. Standing lateral plain radiograph: disc height (DH), segmental angle (SA) of adjacent segments and fused level lumbar lordosis (LL) <h3>METHODS</h3> Forty-four patients who underwent MIS-TLIF at L4/5 level were examined. The indications for surgery were spinal canal stenosis, herniated nucleus pulposus, and spondylolisthesis grade 1-2. We reviewed their standing plain radiograph and MR image parameters, including dural sac area (DSA), sagittal spinal AP diameter (SAPD), ligamentum flavum area (LFA), ligamentum flavum thickness (LFT), foraminal area (FA), foraminal height (FH), disc height (DH), segmental angle (SA), and lumbar lordosis (LL) at the adjacent segments of fused level. Disc height and segmental angle at fused level was also reviewed. All parameters were compared before, and 3 months postoperatively. <h3>RESULTS</h3> The mean (SD) pre- and postoperative DSA at upper adjacent segment was 125.12 (35.72) and 133.17 (35.07) mm2, while pre- and postoperative DSA at lower adjacent segment was 103.58 (44.32) and 117.66 (46.34) mm2 respectively. The postoperative DSA significantly increased in the upper (mean change 8.05 (95%CI 4.44-11.66) mm2, P <0.001) and lower (14.08 (95%CI 9.47 – 18.69) mm2; P <0.001) adjacent segments. Eleven (25%) and 22 (25%) patients had preoperative upper adjacent segment areas <100 mm2 and ≥100 mm2respectively. The mean change in DSA was greater in patients with preoperative DSA <100 mm2 versus ≥100 mm2, but the difference was more pronounced in the upper versus the lower adjacent segment (4.3 (95%CI -4 to 12.7) mm2; P = 0.30 versus 1.1 (95%CI -8.3 to 10.4); P = 0.82, respectively). Significant increases in SAPD were also seen in both upper (0.85 (95%CI 0.45 to 1.25 mm; P <0.001) and lower (0.66 (95%CI 0.34 to 0.97) mm; P<0.001) adjacent segments. LFT significantly decreased in the lower adjacent segment (-0.37 (95%CI -0.62 to -0.11) mm; P=0.006); a small but non-significant decrease was also observed in the upper adjacent segment (-0.1 (95%CI -0.37 to 0.17) mm; P=0.47). No other significant changes in other canal dimensions were noted. <h3>CONCLUSIONS</h3> Adjacent segment DSA increased significantly after MIS-TLIF. In addition, other parameters representing canal dimension (SAPD, LFT) also significantly changed after the operation. Further studies are needed to assess the relationship between these changes and postoperative clinical outcomes. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.