Sequential MRI Changes After Lateral Lumbar Interbody Fusion in Spondylolisthesis with Mild and Severe Lumbar Spinal Stenosis

Abstract

Objective: We assessed the sequential magnetic resonance imaging changes of indirect neural decompression after minimally invasive lumbar lateral interbody fusion (LIF) combined with posterior percutaneous pedicle screw (PPS) fixation for degenerative spondylolisthesis (DS) according to the severity of preoperative lumbar spinal stenosis.

Methods: A total of 43 patients (mean age, 68.7 years; 16 men and 27 women) with DS who had undergone LIF and closed reduction with PPS fixation were enrolled. The intervertebral levels were divided into the moderate stenosis (MS) group (preoperative cross-sectional area [CSA] of the thecal sac >50 mm²) and severe stenosis (SS) group (CSA ≤50 mm²). The CSA, ligamentum flavum thickness, and diameter of the thecal sac at the affected level were measured on cross-sectional magnetic resonance images at baseline, immediately postoperatively, and 2 years postoperatively.

Results: For the 31 and 29 intervertebral levels in the MS and SS groups, the mean CSA at baseline, immediately postoperatively, and 2 years postoperatively was 76.9 mm² and 35.8 mm², 104.3 mm² and 81.4 mm², and 130.9 mm² and 105.7 mm², respectively. The mean ligamentum flavum thicknesses at 2 years postoperatively became thinner than that immediately after surgery in both groups (P < 0.01). The mean diameter of the thecal sac at 2 years was longer than that immediately after surgery in both groups (MS group, P < 0.05; SS group, P < 0.01) The expansion ratio of the CSA at 2 years postoperatively was significantly greater in the SS group than that in the MS group (P < 0.01).

Conclusions: Sequential enlargement of the spinal canal was obtained by the thinning of the ligamentum flavum after LIF and PPS fixation in patients with DS with both mild and severe stenosis. The effect of indirect neural decompression was equivalent even in those with severe lumbar spinal stenosis.

Keywords: Cross-sectional area; Degenerative spondylolisthesis; Indirect neural decompression; Lateral lumbar interbody fusion; Ligamentum flavum; Lumbar spinal stenosis; Percutaneous pedicle screw; Sequential change; Severe stenosis; Surgical outcome; Thecal sac.