Triângulo de segurança lombar : estudo comparativo das incidências coronais e oblíquas em ressonância nuclear magnética 3 tesla

Abstract

Introduction: Minimally invasive surgery, through the safer access corridor to the intervertebral disc (safety triangle or Kambin's triangle), associated with the improved quality of preoperative images (nuclear magnetic resonance - NMR) provides surgeries with minimal technical damage and fast recovery. Although the surgical approach is oblique, NMR images are usually obtained from axial, sagittal, and coronal planes. Thus, the oblique plane can contribute to a better analysis of the safety triangle and the location of the dorsal root ganglion. Objectives: Compare the area and measures of the safety triangle and the location of the dorsal root ganglion in the safety triangle obtained in coronal and oblique planes in the L2-L3/L3-L4/L4-L5 levels in patients submitted to 3 Tesla NMR. Methods: An observational study with a convenience sample including 210 patients over 18 years old, obtained from the records of 3 Tesla lumbar spine NMR scan and performed at the Brain Institute of Rio Grande do Sul (InsCer) from December 2017 to December 2020. Scans with lumbar spine anomalies were excluded. The demographic variables studied were sex, age group, and radiological variables obtained from NMR images [dimensions/location assessed: height of the safety triangle (mm)= formed by the lateral edge of the dura-mater; base of the safety triangle (mm)= formed upper plateau of the lower vertebra; hypotenuse of the safety security (mm)= formed by the corresponding nerve root; safety triangle area (mm3); dimensions and location of the ganglion in the safety triangle (mm)]. Data collection was obtained by a single researcher, on the right side, through reconstruction in maximum intensity projection, with an increase of 0.5 mm, thickness of 5 mm and inclination of 30 degrees in the oblique plane. Results: The mean age of the sample was 45.5±13.3 years (18-98 years), most female (57.1%). The mean of the dimensions, as well as the area, gradually increased from L2 to L5 in both planes. Women had significantly lower values in 19 of the 21 dimensions obtained in the coronal plane and in 17 dimensions obtained in the oblique plane in relation to male sex. Regarding the age group, only 5 of the 42 dimensions obtained with coronal and oblique planes were significantly higher in the 40-65 years age group compared to the 18-39 years age group. The mean area of the safety triangle was lower in the oblique plane compared to coronal plane in all studied levels. From the seven dimensions of the safety triangle obtained for each level of the lumbar spine, six were significantly smaller in the oblique plane in relation to the coronal plane. The smallest ganglion dimension was the only dimension that showed no difference. Conclusion: The dimensions of the safety triangle in the oblique plane were smaller concerning the coronal plane. Therefore, the oblique plane of NMR images was indicated as an important tool in the preoperative assessment, as it represents the most reliable surgical access corridor to the disc, increasing the safety of these procedures.