An 80-year-old man was referred to our pain clinic for radicular pain of the left lower limb. Just over 6 months previously, he had presented with severe radicular pain in his left leg. Magnetic resonance (MR) images revealed lumbar intervertebral disc protrusion (migrated to the left, L4-5, L5-S1) (Figure 1A and B), lumbar spinal canal stenosis, and degenerative lumbar scoliosis. At that time, he received posterior lumbar decompression interbody fusion plus spinal stabilization (L1-5), and his symptoms disappeared after surgery.
Four months later, the radiating pain in the lateral aspect of the left lower limb and the dorsum of the foot recurred, at the same sites as pre-surgery. The worst visual analogue scale (VAS) was 9/10. He could hardly stand up and walk. Weakness of dorsiflexion and plantarflexion was found in the foot. The lying straight leg raise test was positive, and the Achilles reflex was absent.
The previous medication included oral nonsteroidal anti-inflammatory drugs and physiotherapy, but neither treatment was effective. All the symptoms and physical examinations suggested problems of the L4-5, L5-S1 intervertebral discs, likely due to insufficient surgical decompression, recurrent disc herniation, or foraminal stenosis.
Ultrasound-guided experimental L4 and L5 PVB was then planned for this patient. The difficulty in this case was that the anatomical structure could not be located by body-surface land markers, due to the removal of spinous processes during the prior surgery. In addition, the anatomical structure could not be seen clearly through ultrasound, because of echogenic artifacts due to the surgical instruments, and the disordered fascia and muscle structure due to the surgical incision. Fortunately, on the X-ray film we found that the last-but-one pedicle screw and the terminal of the left rod were just next to the needle pathway we designed for the block, and might be used as markers for the puncture (Figure 1C and D).
The patient was placed lateral with the affected side upward. A convex type transducer (Wisonic Medical Technology, Shenzhen, China) was placed in a longitudinal orientation at the level of L5-S1, 3 cm lateral to the midline. With the probe sliding upward, the pedicle screws and the rods could be identified (Figure 2). Surface landmarks, such as iliac crest and locations for the pedicle screws and the rods were made on the skin. At the caudal side of the last-but-one pedicle screw and terminal of the rod, two lines were drawn perpendicular to the spine.
A paramedian transverse oblique scanning approach with needle in-plane was chosen for the L4 PVB. After proper sterile technique, the gel was applied to the ultrasound transducer. The transducer and cable were covered with a sterile sleeve, and placed along the vertical line with the caudal side of the target pedicle screw. The bone structure and fascia between muscles could not be seen clearly, because of the previous lumbar surgery. The pedicle screw was the most easily recognizable structure for hyperechoic. After local anesthetic (2 mL lidocaine 1%) infiltration to the skin and subcutaneous tissue, a 22G 90-mm needle (TuoRen Medical Instrument Finty, Zhengzhou, China) was inserted in a medial to lateral direction, overstride the pedicle screw, and reached the outboard of the foramen intervertebral (Figure 3). After confirmation of the needle tip with 2 mL normal saline, 5 mL of 0.1% lidocaine mixed with 3 mg betamethasone was injected.
Because of the obstruction of the iliac bone, a paramedian transverse oblique scanning with needle in-plane approach could not be used for L5 PVB. Instead, we chose a paramedian transverse scanning with needle out-plane approach. The transducer was placed along the vertical line with the terminal of the rod, beneath the space between the iliac bone and the nail rod. A hyperechoic area was observed, which was assumed to be L5 paravertebral space. After the puncture point was anesthetized with 2 mL of 1% lidocaine, the needle was inserted towards the hyperechoic area, out the plane of the ultrasound beam in a cephalad-to-caudal direction (Figure 4). Considering that the entire needle with an out-plane approach could not be confirmed by ultrasonography, the depth of the needle tip was referenced according to the previous measurement on the X-ray film. Another 5 mL solution was injected.
After 20 minutes of observation, the patient felt well enough to return home. At the third day after the block, the patient reported that his daily baseline level of pain had diminished to 50% of its original severity. We repeated this procedure every 14 days, three times in total. Three months after the last procedure, his visual analogue scale (VAS) was 2/10, and he could go for walks, and he was satisfied with the extent of pain control.