Seventy-eight lumbar nerve roots were injected in the patients that underwent SNRB under fluoroscopic guidance. The accuracy of needle-tip on each lumbar nerve root under ultrasound guidance with fluoroscopic confirmation ranged from % to %. Mean of the accuracy of needle-tip under ultrasound guidance comparing with subsequently fluoroscopic confirmation was % while 95% CI ranged from to %. The age older than 65 years old was significantly associated with the poor accuracy under ultrasound guidance (p-value = ).
SDR begins with a 1- to 2-inch incision along the center of the lower back just above the waist. An L1 laminectomy is then performed: a section of the spine's bone, the spinous processes together with a portion of the lamina, are removed, like a drain-cap, to expose the spinal cord and spinal nerves underneath. Ultrasound and an x-ray locate the tip of the spinal cord, where there is a natural separation between sensory and motor nerves. A rubber pad is then placed to separate the motor from the sensory nerves. The sensory nerve roots, each of which will be tested and selectively eliminated, are placed on top of the pad, while the motor nerves are beneath the pad, away from the operative field.
In an SNRB, the nerve is approached at the level where it exits the foramen (the hole between the vertebral bodies). The injection is done both with a steroid (an anti-inflammatory medication) and lidocaine (a numbing agent). Fluoroscopy (live X-ray) is used to ensure the medication is delivered to the correct location. If the patient’s pain goes away after the injection, it can be inferred that the back pain generator is the specific nerve root that has just been injected. Following the injection, the steroid also helps reduce inflammation around the nerve root.