MATERIAL and METHODS: The study included 15 fresh human cadavers. The soft tissues were removed at the T12-L1 level and bony tissues, were exposed including the transverse processes. The bilateral facets and pars interarticulares at this level were resected revealing the foraminal anatomy and exiting roots. The anatomical structures constituting the triangular safe working zone (TSWZ) were explored. The nerve root length, nerve root width, nerve root angle, TSWZ height, and base of TSWZ base, nerve root width, nerve root angle and disc height were recorded.

RESULTS: The root length is the hypotenuse of the TSWZ between the axilla of the exiting root and the lateral margin of the pedicle, and the mean root length was 14.94 ± 2.45 mm. The dural height is the interval between the axilla of the exiting nerve root axilla and the superior end plate of the caudal vertebra, and the mean of the dural height was 10.95 ± 1.74 mm. The base of TSWZ is the distance between the lateral margin of the dural sac and the medial margin of the exiting root, and the mean measurement for the base measurement was 11.83 ± 2.26 mm.

CONCLUSION: According to the results data from our cadaveric study, we believe that Kambin’s triangular working zone is a safe area to consider for the endoscopic transforaminal approach at the T12-L1 level, especially for paramedian and foraminal disc herniations. Keywords : T12-L1 level, Endoscopic transforaminal approach, Triangular safe working zone, Cadaver