Using Novel Segmentation Technology to Define Safe Corridors for Minimally Invasive Posterior Lumbar Interbody Fusion

Introduction: There has been a rise in minimally-invasive methods to access the intervertebral disc space posteriorly given their decreased tissue destruction, lower blood loss, and earlier return to work. Two such options include the percutaneous lumbar interbody fusion (percLIF) through Kambin’s Triangle and the endoscopic trans-facet approach. However, without accurate pre-operative visualization, these approaches carry risks of damaging surrounding structures, especially the nerve roots. Using novel segmentation technology, our goal was to analyze the anatomic borders and relative sizes of the safe triangle, trans-Kambin, and the trans-facet corridors to assist surgeons in planning a safe approach and determining cannula diameters.

Methods: The areas of the safe triangles, Kambin’s, and trans-facet corridors were measured using commercially available software. For each approach, the exiting (ENR), traversing nerve roots (TNR), theca, disc, and vertebrae were manually segmented on 3D T2- SPACE MRI via a region-growing algorithm. The triangles’ borders were delineated ensuring no overlap between the area and the nerves.

Results: A total of 11 patients (65.4 ± 12.5 years, 33.3% female) were retrospectively reviewed. The Kambin’s, safe, and trans-facet corridors were measured bilaterally at the operative level. The mean area (124.1 ± 19.7 mm2 vs. 83.0 ± 11.7 mm2 vs. 49.5 ± 11.4 mm2) and maximum permissible cannula diameter (9.9 ± 0.7 mm vs. 6.8 ± 0.5 mm vs. 6.05 ± 0.7 mm) for the trans-facet triangles were significantly larger than Kambin’s and the traditional safe triangles, respectively (p < 0.001).

Conclusion : We identified, in 3D, the borders for the trans-facet triangle: the TNR extending until the caudal pedicle as the base, the theca as the height, and the ENR as the hypotenuse. These results illustrate the utility of pre-operatively segmenting anatomic landmarks, specifically the nerve roots, to help guide decision-making when selecting the optimal operative approach.