Usefulness of 3D CT/MRI Fusion Imaging for the Evaluation of Lumbar Disc Herniation and Kambin’s Triangle

Study design: Prospective study. Objective: The aim of this study is to visualize the morphology of a lumbar herniated disc and Kambin’s triangle in three dimensions (3D) based on preoperative CT/MRI fusion images. Methods: CT/MRI fusion images of 23 patients (10 males and 13 females; mean age 58.2 years) were used to evaluate Kambin’s triangle, which is created between the superior articular process (SAP), exiting nerve root (ENR), inferiorly by the superior endplate of the lower lumbar vertebra and dural canal medially at 60 degree and 45 degree endoscopic approach angles. The percentage of the safe usage of transforaminal endoscopic approach was evaluated to utilize a 5 mm dilater without partial facet resection in the fusion image. The 3D lumbar nerve root sleeve angulation (3DNRA), which is the angle between the axis of the thecal sac and the nerve root sleeve, was calculated. The herniated discs were also visualized in the CT/MRI fusion image. Results: The 3DNRA became smaller from L2 to S1. The L2 3DNRA was statistically larger than those of the other root, and the S1 3DNRA was significantly smaller than the others (p < 0.05). (L2, 41.0°; L3, 35.6°; L4, 36.4°; L5, 33.9°; and S1, 23.2°). The SAP-ENR distance at 60° was greatest at L4/5 (5.9 mm). Possible needle passages at 60° to each disc level were 89.1% at L2/3, 87.0% at L3/4 and 84.8% at L4/5. However, the safe 5 mm dilater passage at 60° without bony resection to each disc level were 8.7% at L2/3, 28.3% at L3/4 and 37.0% at L4/5. The 60° corridor at L2/3 was the narrowest (p < 0.01). All herniated discs were visualized in the fusion image and the root compression site was clearly demonstrated especially with foraminal/extraforaminal herniations. Conclusion: The 3D lumbar CT/MRI fusion image enabled a combined nerve-bony assessment of Kambin’s triangle and herniated disc. A fully endoscopic 5 mm dilater may retract the exiting nerve root in more than 60% of total cases. This new imaging technique could prove to be very useful for the safety of endoscopic lumbar disc surgery.