Posterior lumbar nerve entrapment is also known as posterior lumbar nerve branch osteofibular canal syndrome. It is a non-specific lower back pain (LBP). About 8% to 15% of LBP is caused by posterior lumbar nerve entrapment. Therefore, this disease is seen to be common and frequent in clinical practice. We found that approximately 15% to 20% of patients had poor outcomes or recurrent episodes when we used acupuncture to release the third lumbar transverse process syndrome in the clinic. It was only after repeated thought and review of the literature that we found that in some cases of recalcitrant third lumbar transverse process syndrome, those who were left with low back pain even after release of the scarred soft tissue at the tip of the third lumbar transverse process may have signs and symptoms caused by the posterior branch of the lumbar nerve entrapment. For a long time, the advent of CT imaging technology has enabled us to have a clear understanding of disc herniation and degeneration of the lumbar spine and small joints, etc., and the level of diagnosis has gradually improved. However, there is a lack of robust diagnosis of the pathways of nerve root circulation inside and outside the spinal canal and the adjacent relationship with the surrounding bone and soft tissue. The advent of spiral CT has made three-dimensional reconstruction techniques possible. Today, we are able to image the examined internal and external nerves at any angle and level, and to display the longitudinal direction of nerve pathways at the same level through reconstruction techniques. Therefore, the maturation of CT 3D reconstruction technology has made it possible to image and diagnose the posterior branch of the lumbar nerve at the site of entrapment. This provides a credible basis for the diagnosis of the disease. The anatomical study of the posterior branch of the lumbar nerve was first described in the paper “Anatomy of the posterior branch of the lumbar nerve and its clinical significance” by Miao Hua and other scholars in the 15th issue of the Journal of Anatomy in 1984 [1]. Since then, many scholars have conducted anatomical studies on the path of the posterior branch of the lumbar nerve and the structure of the bony fiber canal. The posterior branch of the lumbar nerve is divided from the intervertebral foramen and travels posteriorly through the posterior branch of the lumbar nerve, passing through the bony fiber foramen and traveling with small arteries and veins, and is divided into medial and lateral branches after exiting the foramen. The medial branch runs diagonally posterior to the root of the supra-articular process of the inferior vertebrae, and then turns downward through the papillae and inter-articular fibrous canal to the back of the vertebral arch, crossing one to three vertebrae and distributing to the structures on the medial side of the intervertebral joint column (i.e., the area caught by the line between the inner and outer edges of the intervertebral joint). This structure includes: interspinous muscle, multifidus muscle, ligamentum flavum, intervertebral joint capsule, supraspinous ligament, interspinous ligament, and periosteum. The posterior medial branch of the 5th lumbar nerve branches out through the bony sulcus of the sacral wing, turns posteriorly and medially downward, and reaches the lateral aspect of the middle sacral crest via the bony fiber canal, terminating in the multifidus muscle. The lateral branch is further divided into a muscular branch and a cutaneous branch. The posterior lateral branch of the lumbar nerve enters the erector spinae muscle and divides into the terminal branch and innervates the erector spinae muscle as the muscular branch, and the one that penetrates the erector spinae muscle to reach the subcutaneous branch as the dermal branch, which will reach the buttocks or even the lower limbs and form the superior gluteal cutaneous nerve. 2, the posterior branch of the lumbar nerve fiber canal composition and longitudinal and transverse diameter of the posterior branch of the lumbar nerve nerve trunk, at the exit of the nerve root canal through the bone fiber canal called the posterior branch of the lumbar nerve bone fiber canal. The canal is located below the external opening of the intervertebral canal (foramen) and opens posteriorly, perpendicular to the direction of the intervertebral foramen. It consists of four walls: the upper is the sickle margin of the intertransverse process ligament, the lower is the superior margin of the transverse process of the inferior vertebrae, the medial is the bone surface between the outer margin of the superior articular process of the inferior vertebrae and the root of the transverse process, and the lateral is the medial margin of the intertransverse process ligament. Since the posterior branch of the lumbar nerve has to pass through the intertransverse fibrous canal first during its journey, the ligaments and bone wall of this canal can be the anatomical factors for the posterior branch to be compressed: ① the ligaments forming the wall of the canal are dense and inelastic; the inner edge of the intertransverse ligament is curved around the posterior branch of the nerve from top to bottom. ②The bony fiber canal of the posterior branch of the lumbar 5 nerve is bony walled internally, inferiorly and externally. (iii) When stress injury causes bone proliferation and degeneration of the canal wall, and ligament injury causes scar adhesion formation, it will inevitably cause canal narrowing and nerve entrapment [4]. Clinical understanding of posterior lumbar nerve entrapment 1. etiology ① chronic strain injury; ② acute sprain injury; ③ post-traumatic sequelae; ④ spinal rotation displacement after lumbar synostosis. 2. Main clinical manifestations ①History: history of trauma or postural bending and weight-bearing with rotational movements. ②Signs and symptoms: lower back pain (involving pain in nature); finger pain in the lower back (finger pain area outside the lumbar intervertebral foramen, also in the posterior branch nerve distribution area, i.e. radiating pain area), but no pressure pain or pressure pain is not obvious, no percussion pain; rest pain; limitation of activities. Straight leg elevation and strengthening test (-). 3. Diagnosis ① Analysis based on the history of trauma and limitation of activity. ② lower back pain, finger pain and finger pain site, no pressure pain or pressure pain is not obvious. ③ At the exit of the posterior branch of the lumbar nerve equivalent to the bone fiber canal, the closure treatment is effective. ④Lumbar spine radiographs, other diseases can be excluded. ⑤ 3D CT reconstruction of the lumbar nerve. 4. Differential diagnosis ①Lumbar disc herniation: radicular pain with compression of the corresponding segmental spinal nerve at the herniated site; straight leg raise test (+), thoracic cushion pillow test (+), scoliosis test (+). (ii) Third lumbar transverse process syndrome: pressure pain in the body projection of the third lumbar transverse process (+). (③) supraspinous interspinous ligament injury: local pressure pain is obvious. ④ discogenic lower back pain; ⑤ lumbar spinal stenosis; ⑥ sacroiliac arthropathy; ⑦ lumbar muscle strain; ⑧ spinal tumor, tuberculosis, spinal cyst, etc. 5.Treatment ①Closure therapy; ②Low temperature cryotherapy; ③Radiofrequency thermal coagulation therapy; ④Posterior branch dissection; ⑤Needle knife release; ⑥Triple oxygen therapy. Clinical significance of CT 3D reconstruction of lumbar nerve roots 1.The nerve roots and the continued nerve trunk can be accurately identified, which overcomes the difficulty of identification caused by conventional CT and MR which only show the nerve in transverse or oblique section. 2. It can show the overall shape of the nerve. Three-dimensional reconstruction can observe the morphological manifestations of the nerve starting and ending points and its course, which is more informative, realistic, specific and reliable than that covered by a single cross-section. 3.Three-dimensional reconstruction can extend the nerve roots and the continuing nerve trunks and branches, so as to facilitate the acquisition of more information on the route of travel. 4.It can show the anatomy of the nerve path. In short, there are certain characteristic anatomical structures around the nerve path and they appear at a constant level in the reconstruction, and this characteristic anatomical pattern is called “signpost”. This “signpost” is useful for finding the ideal anatomical level during reconstruction, and for detecting abnormalities in nerve variants or lesions. 5. Quantitative analysis of nerve roots or trunks. For example, the thickness, length, direction, angle, and distance from the surrounding adjacent tissues can be measured. Application experience Previous clinical diagnosis of posterior lumbar nerve branch entrapment is difficult to distinguish due to the lack of specific diagnostic basis, which often makes this disease included in many conditions of lower back pain. In terms of treatment, the exact site of the entrapment can only be inferred from the painful area or painful point closure, therefore, there are many problems such as blind treatment and poor localization. In conclusion, despite the anatomical structural features of posterior lumbar nerve entrapment, clinical understanding of it is still relatively superficial and even controversial. In our hospital, CT 3D reconstruction of suspected cases of posterior lumbar nerve branch entrapment has been performed since the second half of 2006, and it was found that the majority of patients had varying degrees of entrapment of the lumbar nerve root (intradural) or posterior lumbar nerve branch (extradural), manifested by thickening of the nerve, or uneven thickness, proliferation of adhesions and uneven density of the perineural tissue, local bone hyperplasia causing nerve displacement, narrowing of the bone fiber canal, and other pathological morphologic changes. These morphological changes in the nerve images suggest that we should look for some causal relationship between the imaging diagnosis and clinical manifestations, i.e., the appearance of symptoms and signs can be found from the 3D reconstructed imaging changes, and the imaging changes in turn can guide and corroborate the clinical diagnosis. After preliminary statistics, the compliance rate between image diagnosis and clinical diagnosis is as high as 95.7%, so it is presumed that the credibility of this new diagnostic technique is relatively high. However, further work is needed to determine whether it can be used as an accepted diagnostic standard. The emergence of 3D CT reconstruction of the lumbar nerve has provided reliable imaging evidence for the diagnosis of posterior lumbar nerve entrapment, and although the standardization of this diagnosis needs to be improved, it has provided a new approach and method for clinical diagnosis and treatment. Based on the imaging diagnosis, we were able to peel off and release the adherent bony fibular canal with needle knife under CT guidance, so that the posterior branch entrapment was then released or became effective. The needle knife technique achieves precise localization, resulting in more optimal efficacy and fewer points of treatment damage, with good social and economic benefits.