Indirect Decompression of Neural Foramen after Minimally Invasive Retroperitoneal Anterolateral Interbody Fusion: An MRI Study

Presented at SMISS Annual Forum 2018
By A. Mahatthanatrakul
With Choonkeun Park MD, PhD, Donghwa Heo MD, PhD,

Disclosures: A. Mahatthanatrakul None Choonkeun Park MD, PhD None, Donghwa Heo MD, PhD None,


Minimally invasive retroperitoneal anterolateral interbody fusion had gain popularity as an alternative approach to decompress neural structures indirectly. Previous studies measured foraminal height or foraminal cross sectional area from computed tomography (CT) as parameters to demonstrate the decompression. Foraminal area measurement by CT may have difficulty measuring indirect decompression of the ligamentum flavum.


This study will compare preoperative and postoperative magnetic resonance imaging (MRI) after oblique lateral interbody fusion (OLIF) measuring both central and foraminal stenosis.


Twenty-four patients (total of 41 levels) with lumbar degenerative conditions whom underwent (OLIF) without direct decompression and completed pre-and-post operative MRI were included. Spinal canal cross sectional area (SCSA) was measured in axial T2-weighted MRI. Disc height (DH), spinal canal width, foraminal area and foraminal stenosis grading were measured in sagittal T2-weighted MRI.


The patients’ mean age was 68.8 years. Fifteen (63%) were female. The operations were single level OLIF in 12 patients (50%). The operated levels were L2-L3 = 13 levels, L3-L4 = 18 levels and L4-L5 = 10 levels. Significant increases in SCSA (29.3%), spinal canal width (26.1%), DH (49.6%), foraminal area (40.7% for left side and 42.3% for right side) and foraminal height (26.4%) were found (p<0.05). The average foraminal stenosis grading was reduced from grade 2 to grade 1 (p<0.001). The degree of local lordosis was gained on average 3.2 degrees per level (95% CI 1.8 to 4.6 degrees). Lumbar lordosis increased on average 6.9 degrees (95% CI 4.7 to 9.1 degrees). SCSA and foraminal area were unable to be measured due to the metallic artifact in 7.5% and 11% of levels, respectively. Oswestry disability index (ODI) decreased from pre-operative level at 51.5% to 24.4% at 1 year follow-up (p=0.001). VAS score for back pain decreased from 7 to 2 at 1 year (p<0.001). VAS score for leg pain decreased from 5 to 2 at 1 year (p<0.001).


SCSA, spinal canal width, foraminal height, and foraminal area were significantly increased after OLIF. Both central canal and foraminal stenosis could be indirectly decompressed by the ligamentotaxis effect of OLIF cage. Metallic artifact from posterior stabilization could interfere when evaluating a foraminal area.