Abstract

INSTITUTION WHERE THE STUDY WAS REALIZED: Institute of Orthopaedics and Traumatology and Morgue of São Paulo University Teaching Hospital (Hospital das Clinicas) – Medicine College of São Paulo University Study Design. The triangular safe zone of L2-S1 was investigated by anatomic dissection of 100 foraminal levels in 14 human male cadaver spines.Objectives. The goal was to best understand the triangular safe zone of Mirkovic et al. (1995) and to determine the boundaries, the format, the dimensions and the largest safe working cannula diameter.Summary of Background data. Working cannula are used in percutaneous lumbar procedures. Mirkovic et al. defined triangular safe zone and determined the optimal cannula size and point of insertion in 1995. Based in their study, we decided to study the anatomy of lumbar foraminal zones applied in percutaneuos procedures.Methods. Triangular safe zone dimensions from L2-L3 to L5-S1 were determined as was the inscribed circle (IC) diameter. IC was the maximal cannula size that can be placed within the safe zone.Results. The height of triangular safe zone was formed by the lateral border of the thecal sac, not corresponding to the medial pedicular border; the base, by superior endplate of the inferior vertebra; and the hypotenuse by the spinal nerve. The average dimensions determined were: width 13.41 mm, height 21.68 mm, and hypotenuse 25.49 mm. The triangle formed like this is totally different from that described previously in the literature. In higher lumbar vertebrae (L2-L3 and L3-L4) approximately right-angled triangular safe zones were delineated, whereas in lower lumbar vertebrae (L4-L5 and L5 e S1), obtuse-angled triangular safe zones were delineated. Conclusion. the triangular safe zone admits progressively larger external diameter working cannula from L2-L3 to L5-S1.