Anatomical assessment of the Kambin's triangle for percutaneous posterolateral transforaminal endoscopic surgery of lumbar intervertebral discs: a magnetic resonance imaging based study

The aim of the present study was to utilize magnetic resonance imaging (MRI) as a noninvasive tool for evaluation of the Kambin's triangle safe zone. Lumbar MRIs of 67 healthy subjects were analyzed. On the coronal plane, the distance from the superior endplate to the nerve root exiting from the dura (distance a), the distance from the lateral aspect of the dura to the medial aspect of the nerve root (distance b), and the angle between the nerve root and plane of the corresponding disc (angle α) was measured. On the axial plane, the vertical distance from the upper facet surface to the exiting nerve root and root-disc distance was also measured. On the sagittal plane, foraminal height, diameter, nerve root-disc distance, and nerve root-pedicle distance were measured. On the coronal plane, right and left α angle was 50.78±4.43 (range, 48.52-51.84 degrees) and 51.07±4.08 (range, 49.25-51.91) degrees, respectively. Distance of right 'a' was 17.86±3.86 mm (range, 10.56-24.84 mm) and left 'a' was 18.03±3.73 mm (range, 10.98-24.82 mm), distance of right 'b' was 15.57±2.61 mm (range, 10.54-20.70 mm) and left 'b' was 15.46±2.68 mm (range, 10.93-19.23 mm). All these measurements increased as the spine level went down. Foraminal height and diameter decreased caudally. Nerve root-facet distance did not show change as the level went down. The study indicated that radiologic measurement is feasible to evaluate the anatomy of the Kambin's triangle. At lower lumbar levels, the exiting nerve root is at risk of injury.