Radiographic measurement for transforaminal percutaneous endoscopic approach (PELD)

A radiographic study to analyze the working zone and relationship of the nerve root to their corresponding intervertebral disc for transforaminal percutaneous approaches.

100 MRIs of transverse and sagittal views of 37 males, 63 females (average age 45 years), 50 MRIs of coronal views of 22 males, 28 females (average age 42 years), and 100 X-rays, 46 males, 54 females (average age of 44 years) were used for image analysis. All radiologic measurements were obtained independently by two experienced radiologists. On sagittal plane, foraminal height, foraminal diameter, nerve root-disc distance and nerve root-pedicle distance were measured. On transverse plane, foraminal width, nerve root-disc distance, nerve root-facet distance and target angle (J°) were analyzed at the superior (s) and inferior (i) margin of the disc. On coronal plane, nerve root-disc distance and nerve root-pedicle distance were measured at the medial, middle and lateral borders of the pedicle.

Sagittal plane; foraminal height and diameter decreased caudally. Transverse plane; foraminal width was larger at the superior margin of the disc. Nerve root-disc distance decreased caudally. The nerve root lied dorsal to the disc at L2-L3 and L3-L4, whereas at L4-L5 and L5-S1 it lied ventrally. Nerve root-facet distance was shortest at the superior margin. Target angles (Js°, Ji°) at L2-L3 and L3-L4 were wider at their superior margin than at their inferior margin. Coronal plane; nerve root-disc distance increased from L2-L3 to L5-S1 whereas nerve root-pedicle distances decreased, thus coursing more vertically.

At lower lumbar levels the exiting nerve root is at risks of injury. Hence, it is advised to enlarge the foramen for safe passage of endoscopic instruments and to minimize the possibility of nerve injury.