Fig. 3

a, b Schematic diagram of the inclination of the trephine trajectory in lateral and AP (anterior-posterior) views in the first foraminoplasty. c, d Schematic diagram of the inclination of the trephine trajectory in lateral and AP views in the second foraminoplasty. The cross point of the white solid line is described in the text. e schematic diagram of the two-time percutaneous lumbar foraminoplasty procedure. f schematic diagram of the difference between classical TESSYS technique and double percutaneous lumbar foraminoplasty and PELD (DPLF–PELD) technique