Can unilateral-approach minimally invasive transforaminal lumbar interbody fusion attain indirect contralateral decompression? A preliminary report of 66 MRI analysis

Few studies have measured the amount of indirect decompression at the contralateral neural foramen after unilateral-approach minimally invasive transforaminal lumbar interbody fusion (MITLIF). This study examined the amount of intraoperative indirect decompression at the contralateral neural foramen after a unilateral-approach MITLIF in patients with bilateral foraminal stenosis. From February 2009 to October 2012, 66 consecutive patients with bilateral foraminal stenosis underwent unilateral-approach MITLIF and postoperative magnetic resonance imaging (MRI). Direct decompression was performed at the central canal and approach-side neural foramen, while indirect decompression using cage distraction was pursued at the contralateral neural foramen. Qualitative parameters of the central canal (dural sac morphology) and neural foramen (foramen morphology) were analyzed using pre- and post-operative MRI. Quantitative measurement on the central canal (dural sac cross-sectional area) and neural foramen (foramen height and width) were also measured. A total of 69 intervertebral levels in the 66 patients were analyzed. Qualitative parameters of the central canal and contralateral neural foramen improved significantly after unilateral-approach MITLIF (both P < 0.001). The mean dural sac cross-sectional area increased from 51.1 +/- A 28.8 to 84.8 +/- A 30.2 mm(2) (P < 0.001). The mean preoperative contralateral foramen height, maximum foramen width, and minimum foramen width were 11.8 +/- A 2.0, 4.9 +/- A 1.5, and 1.5 +/- A 0.7 mm, respectively, and these values increased postoperatively to 14.7 +/- A 2.5, 6.5 +/- A 1.8, and 2.4 +/- A 1.0 mm, respectively (all P < 0.001). Quantitative and qualitative parameters of the central canal and contralateral neural foramen increased significantly after unilateral-approach MITLIF.