Fig. 3

(A, B, C)The skin entry point was determined by the intersection of imaginary line 1 and line 2. line 1 was drawn on the AP Ferguson view that crosses the transverse disc plane from the center of the upper endplate of the inferior vertebra to the tip of superior articular process(SAP). on the lateral C-arm view, line 2 was drawn on the lateral skin that projects at the lower third of the foramen (posterior edge of superior endplate of caudal vertebra to the tip of superior articular process)