When the safe triangle is unsafe: volumetric magnetic resonance imaging root mapping for patient-specific assessment of Kambin’s triangle before transforaminal lumbar disc procedures
Year: 2026
Type: article
Study design: Observational Study
Abstract: Background: Kambin's triangle is a useful geometric model for lumbar transforaminal access, but the clinically usable corridor is patient specific because the exiting nerve root, dorsal root ganglion (DRG), traversing neural structures, anatomic variants, and disease-related displacement may alter the contemplated path. We evaluated volumetric magnetic resonance imaging (MRI) root mapping as a method for characterizing nerve-root anatomy relevant to patient-specific transforaminal trajectory planning. Methods: This retrospective descriptive MRI-anatomy study analyzed 76 selected patients who underwent volumetric 3D T2-weighted MRI root mapping between March 1, 2022 and March 12, 2026 during evaluation of symptomatic lumbar levels before contemplated transforaminal or percutaneous disc access. Sixteen earlier contrast-assisted cases are mentioned only as historical technique-development context and were not included in the MRI analysis. Multiplanar, oblique, and curved reconstructions were reviewed collaboratively by a radiologist with musculoskeletal/spine imaging involvement and the operating surgeon/radiology team. Trajectory assessment distinguished anatomically favorable, borderline, and unfavorable/high-risk relationships, including dimensional incompatibility and direct neural trajectory conflict. Results: Nine of the 76 patients (11.8%) demonstrated one of the two predefined nerve-root findings relevant to the intended transforaminal trajectory. Four unique patients had double or variant nerve roots occupying the intended Kambin corridor. Five additional unique patients had displacement of the exiting nerve root into the planned cannula trajectory; three were considered unfavorable/high-risk and two borderline. The two groups did not overlap. The abnormalities were identified at L4-5 in five patients, L5-S1 in three, and L3-4 in one. The remaining 67 patients did not demonstrate either predefined finding and are not interpreted as a validated safe comparator group. None of the nine relevant cases generated a material disagreement regarding the root-course abnormality or its relationship to the contemplated trajectory. Conclusions: Volumetric MRI may identify patient-specific neural anatomy relevant to transforaminal trajectory and route planning. Its contribution is trajectory-oriented visualization rather than proof of procedural safety or diagnostic superiority over routine MRI. The observed frequency in this selected symptomatic-level cohort is descriptive and should not be interpreted as the population prevalence of aberrant nerve-root anatomy.
Source: Journal of Spine Surgery
Language: English
Subfield: Orthopedics and Sports Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W7223809721