Chronic low back pain is a common disorder in pain clinics, and degeneration of the small joints of the lumbar spine is the main cause. In 1933, Ghormly began to use the term “facet syndrome” to describe chronic low back pain caused by degeneration of the small joints of the lumbar spine. The main manifestations are: limited pressure pain in the lumbar paraspinal area, increased back pain when the load on the small joints is increased (e.g., bending), and no nerve root pulling symptoms on the straight leg raise test. Since the small joints of the lumbar spine are innervated by the posterior medial branch of the lumbar spinal nerve, they are now mostly treated with posterior medial branch of the spinal nerve block or radiofrequency disruption based on it. The posterior medial branch block of the lumbar spinal nerve requires the injection of drugs into the junction of the superior articular process and the root of the transverse process of the corresponding small joint. To ensure the accuracy of the block, X-ray guidance is generally required, but pain clinics are often not equipped with X-ray fluoroscopy, making it difficult to perform posterior medial branch blocks. Since 1989, our department has been using isometric lumbar spine radiographs to guide the posterior medial branch block of the lumbar spinal nerve in outpatient clinics for the treatment of lumbar microarthrosis syndrome, and has achieved good results. In this study, recent patients were selected to observe the effect of this method in the treatment of lumbar small joint syndrome. Data and methods General data Sixty patients, 32 men and 28 women, aged 36 to 52 years, weighing 57 to 74 kg and 155 to 178 cm tall, were clinically diagnosed with lumbar microarthrosis syndrome, and the diagnostic criteria for microarthrosis syndrome were: (1) chronic low back pain, which may be associated with hip and thigh pain but does not exceed the knee joint; (2) limited pressure pain next to the lumbar spine; (3) lumbar hyperextension, hyperflexion, lateral flexion or rotation (4) No nerve root pulling symptoms on straight leg raise test; (5) No abnormal sensation, reflex and muscle strength of lower limbs; (6) Exclude low back pain caused by internal disorders. Patients with coagulation disorders, diabetes mellitus, peptic ulcers, malignant tumors, infections, psychosomatic diseases, nerve root symptoms and segmental lumbar instability were excluded. The enrolled patients were randomly divided into treatment group (Group B) and control group (Group C), with 30 cases in each group. The distance between the superior articular process of the small joint corresponding to the posterior medial branch of the lumbar spinal nerve to be blocked and the junction of the superior articular process of the small joint with the corresponding transverse process root, and the distance between the adjacent spinous process (or spinous process gap) and the approximate depth of needle entry were measured on both sides. The patient is placed in a prone position without a pillow under the abdomen. The lumbar spine spines are traced with a marker, and the patient’s back is marked accordingly according to the above measurements to determine the point of needle insertion. The puncture depth marker was placed at the proposed depth of entry + 1 cm with the usual sterile towel. After local anesthesia, a 22 G lumbar puncture needle is inserted vertically into the skin and the needle is slowly advanced until the bone is touched. If the bone was not touched at the depth marker, the puncture needle was backed off to the subcutaneous level, and the needle was reintroduced with a slight adjustment of the direction of advancement to the cephalad or caudal side until the bone was touched. The patient has a “swelling sensation” that radiates downward. After the return of blood and cerebrospinal fluid, the drug was injected. All patients were administered by the same pain physician with extensive experience in posterior medial branch block of the lumbar spinal nerve. 1％ lidocaine hydrochloride (containing 1 ml of compound betamethasone injection + 500 μg of methylcobalamin injection), 2 ml per site, was used in group B. 1％ lidocaine hydrochloride was used in group C. The total amount of lidocaine hydrochloride in patients did not exceed 100 mg. Observation index A pain physician who was not involved in this study independently evaluated the overall pain, lower back extremity pain VAS scores and angles of lumbar flexion, posterior extension and lateral flexion in both groups before, 5 min, 1 week, 2 weeks and 4 weeks after the block, respectively, and recorded the presence of inadvertent subarachnoid space, skin bruising, hematoma, infection, during and after the block, Complications such as nerve injury occurred. Statistical analysis All measurement data were expressed as mean ± standard deviation ( ± s), and SPSS 13.0 was applied for statistical analysis. One-way ANOVA and paired t-test were used for intra-group comparison, and two-way ANOVA was used for inter-group comparison, and P< 0.05 was considered significant difference. Results The differences in sex ratio, age, height, weight and body mass index between the two groups were not significant (P> 0.05). All patients operated smoothly. The VAS scores were not significantly different between the two groups before the block, and the VAS scores at 5 min after the block were significantly lower and the lumbar mobility was significantly higher than the pre-block basal values (P< 0.05). the VAS scores and lumbar mobility at 1, 2 and 4 weeks after the block in group C were not significantly different from those before the block (P> 0.05), and the VAS scores in group B were significantly lower and the lumbar mobility The VAS score and lumbar mobility in group B at 5 min after block were similar to those in group C, but the VAS score at 1, 2 and 4 weeks after block was significantly lower and the lumbar mobility was significantly higher than that in group C (P< 0.05). No complications such as subarachnoid injection, hematoma, or infection occurred in either group. The VAS scores and lumbar mobility before and after block in both groups are shown in Table 1. DISCUSSION I. About the anatomy of the posterior medial branch of the lumbar spinal nerve After the L1-L4 lumbar spinal nerve exits the intervertebral foramen, its posterior branch emanates at a right angle and travels posteriorly and downward along the anterolateral margin of the superior articular process of the inferior vertebral body, and divides into the medial and lateral branches at the junction of the superior articular process and the transverse process. The lateral branch travels outward, slightly posterior and downward below the transverse process; the medial branch continues to travel posterior and downward along the lateral aspect of the posterior border of the superior articular process and enters a “fibrous canal”. The anterior wall of this canal is the posterior surface of the transverse process, the medial wall is the mastoid process, the lateral wall is the paramedian process, and the posterior wall is the paramedian ligament. While it was thought that the posterior medial branch of the spinal nerve travels close to the external surface of the mastoid process, recent anatomical studies have confirmed that the posterior medial branch does not travel close to the external surface of the mastoid process, but close to the internal surface of the paramedian process, with the vessels located medial to the medial branch [6]. The posterior branch of the L5 spinal nerve emanates and travels posteriorly at the base of the notch formed by the superior articular process of S1 and the sacral wing and gives off two branches. The medial branch goes inward around the lateral aspect of the lumbosacral tuberosity; the lateral branch converges downward into the posterior branch of the S1 spinal nerve. According to the anatomy of the posterior medial branch of the lumbar spinal nerve, the “bony fiber canal” between the mastoid process and the paramedian process is the fixed site of the medial branch, which is located in the posterior-lateral part of the bony fiber canal, near the paramedian process. Therefore, theoretically, the medial side of the mastoid process should be used as the target of the posterior medial branch block. However, in practice, the determination of the block target is subject to the constraints of the operating conditions. The collateral prominence is difficult to discern on X-ray images, and thus cannot be the target of posterior medial branch block under fluoroscopic guidance. Therefore, the junction of the superior articular eminence and the root of the transverse process was used as a target for posterior medial branch block of the L1-L4 spinal nerve in this study. This is consistent with Bogduk’s view and is currently the prevailing practice for X-ray guided posterior medial branch blocks of the L1-L4 spinal nerve. If a CT-guided block of the posterior medial branch of the L1-L4 spinal nerve is performed, the medial aspect of the paramedian process should be used as the target point to improve the accuracy of the block because the paramedian process is clearly discernible on CT images. It should be clear that the target of the X-ray guided block is actually located near the bifurcation of the posterior medial and posterior lateral branches of the lumbar spinal nerve. In the strictest sense, the posterior medial branch is not selectively blocked here, but rather the entire posterior branch. In addition, because of its proximity to the intervertebral foramen, there is a risk that the drug will enter the foramen and block the anterior spinal nerve branch, which is especially important in the case of anhydrous ethanol disruption. The posterior branch of the L5 spinal nerve is divided into medial and lateral branches at the posterior half of the notch formed by the superior articular process of S1 and the sacral wing, which is easily recognized on CT and X-ray images and can be used as a bony landmark for CT or X-ray guided block of the posterior branch of the lumbar spinal nerve. It should be noted that drug injection in this notch also does not selectively block the posterior medial branch of the L5 spinal nerve. The key to a successful block with radiographic guidance is to establish a one-to-one correspondence from the image to the patient’s body landmarks. Under outpatient conditions, the palpable body surface landmarks on the patient’s back are the iliac crest and the spinous process (spinous process gap), which are key to establishing the image-body surface correspondence. Based on the spinous process gap corresponding to the line connecting the highest points of the iliac crest, the corresponding spinous process gap can be easily identified in the patient. Using this as a basis, it should not be difficult to determine the other spinous processes (spinous gaps) of the lumbar spine. The spinous process (spinous interspace) is the baseline for radiographic measurements, which is located in the middle of the patient’s back and is easy to locate, and is the bridge from the radiographic measurements to the patient (Figure 1). Only when an accurate image-patient correspondence is established can the accuracy of block access be fundamentally ensured. In addition, because the patient’s abdomen is not padded with pillows during the lumbar frontal and lateral radiographs, the patient’s abdomen is also not padded with pillows during the block operation, which is different from the operation under X-ray fluoroscopy. IV. Regarding the results of this study, both groups obtained satisfactory pain relief and improvement of lumbar spine function at 5 min after block without significant differences, but at 1, 2 and 4 weeks after block, the pain level and lumbar spine function in group C returned to the pre-block level, while group B still maintained the treatment effect at 5 min after block. This indicates that posterior medial branch block of lumbar spinal nerve can effectively relieve the pain and improve the function of lumbar spine in patients with lumbar microarthrosis syndrome. Compound betamethasone, as a compound of soluble betamethasone ester and microsoluble betamethasone ester, has a strong anti-inflammatory effect and a long duration of action, which can effectively prolong the duration of action of the posterior medial branch block. In addition, since the small joints are doubly innervated by the posterior medial branch of the spinal nerve at the corresponding and superior levels, the treatment should block the posterior medial branch of the spinal nerve at both the corresponding and superior levels. V. Limitations of this study The effectiveness of radiographically guided posterior medial branch block of the lumbar spinal nerve in the treatment of lumbar subtalar syndrome was observed at the therapeutic level in this study. In the absence of X-ray fluoroscopy in outpatient clinics, it is an effective means to improve the accuracy of the block and the outcome of treatment. However, it is still essentially a “blind” operation and is not suitable for treatments that require high block accuracy, such as diagnostic blocks, anhydrous ethanol disruption, and radiofrequency disruption. These treatments still need to be performed under X-ray guidance. In addition, due to the limitations of this study, only the effectiveness of X-ray film-guided posterior medial branch block of the lumbar spinal nerve was observed, and a comparative study with X-ray fluoroscopic manipulation is needed regarding the anatomical accuracy of this method. In conclusion, the results of this study suggest that X-ray film-guided posterior medial branch block of the lumbar spinal nerve is an effective method for the treatment of lumbar subtalar syndrome in the absence of X-ray fluoroscopic equipment in outpatient clinics.