Anatomical and pathophysiological basis For the etiology of low back pain, in addition to intervertebral disc herniation and spinal stenosis, in recent years, the lumbar spinal canal outside the anatomical structure of the lumbar nerve root and the lumbar nerve posterior branch of the lumbar nerve compression is more and more attention by scholars. The lumbar nerve roots emanate from the spinal cord, and when they exit the dural sac, the anterior and posterior roots reside in the intrinsic root sheaths, and then the root sheaths are renewed as the nerve sheaths distal to the external orifices of the intervertebral canals, and the nerve roots travel obliquely toward the front and downward. After the lumbar nerve roots leave the dural sac, they travel diagonally downward to the intervertebral foramen and pass through a narrow bony-fibrous channel called the lumbar neural root canal, which consists of the lateral saphenous fossa and the intervertebral foramen that extends anteriorly and posteriorly. The lumbar nerve root canal is wide on the inside and narrow on the outside, and is slightly flattened anteriorly and posteriorly, like a funnel with a small mouth facing outward. The outer part of the lateral saphenous fossa is the vertebral arch root, the posterior wall is the top of the superior articular process, the vertebral plate, and the ligamentum flavum, and the anterior part is the bottom of the vertebral body which is formed by the posterior and posterior lateral parts of the upper and lower vertebral bodies and the neighboring intervertebral discs. The upper and lower boundaries of the intervertebral foramina were the pedicles, and the bottom part was the posterior inferior margin of the upper vertebra, the intervertebral disc, and the posterior superior margin of the lower vertebral body, respectively, and the top part was formed by the ligamentum flavum, which was followed by the articular synchondrosis. The lumbar nerve channel cavity maintains a certain spatial ratio between the lumbar nerve root and the lumbar nerve root. When the normal spatial proportionality is changed, the lumbar nerve root will be compressed in a certain part of the channel and symptoms will appear. The pathophysiologic basis of radicular pain is not fully understood. Under the effect of long-term inflammatory stimulation, chronic strain injury, herniated disc, hypertrophy of ligamentum flavum, hyperplasia of small joints, etc., bony or non-bony stenosis occurs in a certain part of the lumen wall of the nerve channel, resulting in the narrowing of the ratio between the lumen and the space of the nerve root, and the nerve root is compressed. Mechanical compression of the nerve root can increase the permeability of the capillaries in the nerve, leading to edema formation, causing changes in nerve conduction and decreasing the nutritional support for the spinal nerve root, resulting in nerve damage and functional changes. In addition to pain caused by mechanical compression, chemical inflammation of the nerve root also plays an important role. This is evidenced by the fact that chemical analgesics such as phospholipase A2, substance P, and calcitonin-related factor were found to be significantly increased in the tissues surrounding the painful nerve roots.SNRB directly injects local anesthetics and steroids into the peripheral area of the nerve roots, and it is generally believed that local anesthetics can temporarily relieve pain by reducing the nociceptive afferents of the inflamed tissues, or achieve long-term analgesic effects by blocking the sustained nerve activity that produces pain. Long-term analgesic effect. Further research found that adding steroids to local anesthetics has a better analgesic effect, probably because glucocorticoids have anti-inflammatory and immunosuppressive effects by inhibiting prostaglandin synthesis, on the one hand, reducing the release of inflammatory mediators and immune substances, thus reducing the stimulation and sensitization of injury receptors, on the other hand, reducing the congestion and edema of the nerve root, indirectly playing the role of mechanical decompression, increasing the blood supply to the nerve root, thus achieving the therapeutic effect of the nerve root. Indications and contraindications Indications and contraindications Adaptation There are many reasons for spine-related pain, the common ones are bulging intervertebral discs and mechanical compression caused by degenerative changes of the spine, in addition to fractures, infections, tumors, spinal postoperative period, or the result of the combined effect of many factors. In some patients, the imaging findings do not coincide with clinical symptoms and signs, in which case diagnostic selective nerve root block is a reliable means of finding the diseased nerve root. The indications for diagnostic selective nerve root block include: (1) atypical low back pain; (2) inconsistency between imaging and clinical manifestations; (3) uncertain or ambiguous EMG and MRI findings; (4) abnormal nerve distribution, such as nerve root union or bifurcation variant; (5) atypical low back pain after lumbar spine surgery; and (6) patients with migrated vertebrae. When the exact source of low back pain is not clear from the above clinical or imaging tests, and when a pre-surgical outcome assessment is needed, selective nerve root blocks can be used to clarify whether the pain is coming from that nerve root and to predict the outcome of surgical treatment. There are many indications for therapeutic lumbar nerve root blocks, with patients with radicular pain being the primary indication, and recent MRI or CT findings ruling out disc prolapse or tumor as the cause of radicular pain. Patients with radicular pain who are considered for SNRB include: (1) those with unclear or only minor abnormalities on imaging; (2) those with multisegmental disc pathology on imaging but do not yet require surgical intervention; (3) those with unexplainable and complex pain that reappears after surgery; (4) those with uncertainty on neurological examination; and (5) patients with radicular pain who require short-term pain relief, such as patients with prolapsed discs who require preoperative analgesia. Contraindications to SNRB are the same as other percutaneous puncture procedures, including: ① abnormal coagulation function; ② severe allergic reaction to any of the components of the injection solution; ③ systemic infection or skin infection at the puncture site.