Objectives:

We assessed the sequential magnetic resonance images (MRI) changes of indirect neural decompression after minimally invasive lateral lumbar 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:

Forty-three patients (mean age: 68.7 years, male: 16, female: 27) with DS who underwent LIF and closed reduction with PPS were enrolled. Intervertebral levels were divided into the moderate stenosis group (M group; preoperative cross-sectional area [CSA] of the thecal sac > 50mm²) and severe stenosis group (S group; CSA ≤ 50mm²). CSA, ligamentum flavum thickness, and the diameter of the thecal sac at the affected level were measured on cross-sectional MRI at baseline, immediately after operation, and 2 years postoperatively.

Results:

Of the 31 and 29 intervertebral levels in the M and S groups, the mean CSA at baseline, immediately after operation, and 2 years postoperatively were 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 those immediately after surgery in both groups (P<0.01). Mean diameters of the thecal sac at 2 years became longer than those immediately after surgery in both groups (M group: P<0.05, S group: P<0.01) The expansion ratio of CSA at 2 years postoperatively was significantly higher in the S group than that in the M group (P<0.01).

Conclusions:

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