Low back pain is one of the common orthopedic surgical diseases, of which lumbar degenerative disc disease, lumbar spondylolisthesis and various segmental instability are the common causes of low back pain. Posterior lumbar decompression + fixed fusion is the most commonly used procedure for treatment. Vertebral fusion includes posterior posterolateral fusion, interbody fusion, etc. The Threaded Fusion Cage (TFC) is a horizontal cylindrical intervertebral fusion device, mainly used in the treatment of lumbar degenerative diseases, and lumbar spondylolisthesis, etc. The TFC appeared in the late 1980s and its use has increased significantly in the last decade [1].The principles of TFC for lumbar degenerative diseases include. Direct increase in intervertebral space height, small joint repositioning, and increase in nerve root canal volume to achieve neurological decompression [2].2. Self-stabilizing effect: implantation of TFC causes tension in the intervertebral disc fibrous ring and anterior and posterior longitudinal ligaments, and these soft tissue tensions in turn help stabilize the TFC, i.e., bracing-tension band effect [3].3. Internal fixation at the intervertebral interface: intervertebral fusion of the interbody fusion device between the vertebral bodies in the maximum weight-bearing axis of the spine. A three-dimensional super-stationary structure is formed between the two vertebral bodies and the fusion device, thus providing adequate bending, support, and slip resistance. In recent years, the use of TFC has decreased year by year due to the availability of other intervertebral fusion materials. With regard to the efficacy of TFC in the treatment of degenerative lumbar spine diseases, there are few reports of medium- and long-term efficacy observations. Therefore, this paper focuses on the mid- and long-term efficacy of TFC for lumbar degenerative diseases and related complications by counting the surgical cases of TFC for lumbar degenerative diseases in our hospital in the past 10 years. I. Materials and methods 1. Subjects: The cases in this group were surgical cases of TFC for lumbar degenerative diseases in our hospital from March 1997 to March 2002, and each patient was operated for single-segment lesions. The surgeries were all performed by the same group of surgeons in our department with skilled surgical techniques. 2. Study methods: 2.1 Surgical methods: After general intravenous anesthesia, prone position on the spinal table, a median lumbosacral incision was made and conventional posterior decompression was performed. If the preoperative diagnosis was lumbar spondylolisthesis II°, four R-F pedicle nails were driven into the lateral aspect of the articular process of the corresponding lesion vertebra to reset it. In the case of simple lumbar disc herniation, the disc is removed directly. The posterior longitudinal ligament at the joint space is incised, the appropriate type of sleeve is placed in the joint space, drilled, tapped, the appropriate type of TFC is placed, and the posterior plate is crushed and implanted into the Cage with a cap. Rinse, place gelatin sponge in the epidural, place one negative pressure drainage tube, and suture the incision layer by layer. 2.2 Postoperative treatment: postoperative antibiotics were routinely applied for 3 days to prevent infection, and Micropulse was administered intramuscularly for nutritional nerve treatment. The drainage tube was removed 1~2 days after surgery. After the drainage tube was removed, functional exercises for the lumbar back muscles were started, and the stitches were removed and discharged two weeks after surgery, and a rigid lumbar support club was worn for 3-6 months. 2.3 Outcome assessment: The inpatient medical records were reviewed to find out the number of days of hospitalization, operation time, blood transfusion, source of bone graft, type and number of intervertebral fusion devices, application of pedicle nail, intraoperative complications, and preoperative lumbar JOA score, and the preoperative lesioned intervertebral space height was measured by X-ray (the intervertebral space height was measured by taking the anterior edge of the vertebral body, posterior edge of the vertebral body, and midpoint of the vertebral body on the lateral X-ray of the lumbar spine). (The intervertebral space height is measured by taking the average of the three on the lateral lumbar X-ray). All cases were booked by telephone and followed up in our outpatient clinic. The follow-up included two aspects: 1. JOA score of the lumbar spine at the time of follow-up and calculation of the postoperative improvement rate, postoperative improvement rate = (JOA score at the time of follow-up – preoperative JOA score) / (29 – preoperative JOA score). 2. Lateral and frontal X-rays of the lumbar spine were taken at the time of follow-up to measure the height of the diseased intervertebral space, the fusion of the diseased segment, the subluxation and displacement of the Cage, and the degeneration of the adjacent vertebrae (ASD). situation. The criteria for fusion: (i) no visible activity or intervertebral motion less than 3 degrees on power images; (ii) no translucent zone around the fusion; (iii) minimal loss of intervertebral height; (iv) no visible fusion, implant, or vertebral fracture; (v) no signs of sclerosis of the implant bed or implant mass; and (vi) bone visible in the fusion [4]. However, since only the frontal and lateral X-rays of the lumbar spine were taken in this study, and no hyperextension-hyperflexion dynamic X-rays were performed, intervertebral fusion was considered to have been achieved as long as 2-6 items were satisfied in the judgment. 3. Data processing: All data were statistically processed by SPSS, and the mean ± standard deviation was used to express the preoperative and follow-up JOA scores, operative time, preoperative and follow-up intervertebral space height, and Cage subluxation displacement distance. The differences in JOA scores at preoperative follow-up and the differences in interbody height at preoperative follow-up were analyzed by paired t-test, and the effects of the application of pedicle nailing or not, different bone graft sources, and the number of Cages on the fusion rate were analyzed by X2 test. II. RESULTS 1. General information: There were 84 patients in this group, 48 males and 36 females; age ranged from 27 to 67 years, with an average of 46.29±7.18 years. A total of 50 patients completed the follow-up, with a follow-up rate of 59.5%. Of these 50 cases, 27 were male and 23 were female; age ranged from 27 to 64 years, with an average of 46.29±7.18 years. Etiology: lumbar disc herniation accounted for 40 cases (80%); lumbar spondylolisthesis 10 cases (20%). All cases underwent posterior lumbar decompression + TFC interbody fusion, and 5 of them were repositioned and fixed with RF pedicle nail due to lumbar spondylolisthesis II°. One case died in an accident, which could not be counted as medium- and long-term follow-up because its follow-up time did not reach 5 years, so it was excluded from the following statistics. 2. Surgical safety analysis: 49 patients were hospitalized for 17-54 days, with a mean of 31.76±9.28 days. The operative time was 2-6 hours, with an average of 3.00±0.94 hours. No serious complications such as cardiac infarction, cerebral infarction, multiple organ failure, hemorrhagic shock, or death occurred in all patients during the perioperative period. Intraoperatively, 1 Cage was used for implant fusion in 12 cases (24.5%) and 2 Cages were used for implant fusion in 37 cases (75.5%). Five patients were fixed with RF nails (10.2%), and the rest were fixed with TFC self-stabilization. For the bone graft source, 7 patients had an autologous iliac bone graft fusion (14.3%) and 42 patients had an autologous spinous and laminar bone graft fusion (85.7%). For the Cage model, 12*21 was used in 2 patients (4.1%), 14*21 in 39 patients (79.6%), and 16*21 in 8 patients (16.3%). 3. Symptom relief: preoperative JOA score of 5-25 in the follow-up cases, with a mean of 15.94±4.87; JOA score of 7-29 at follow-up, with a mean of 27.12±3.80. Using a paired t-test, the JOA scores at follow-up were statistically different from the preoperative JOA scores (t=12.5, p=0.000). Postoperative improvement rate at follow-up -144%-100%, mean 83.7%. 4. X status at follow-up: the preoperative lesioned segment intervertebral foraminal height was 0.30-1.30 cm in 49 cases, with a mean of 0.85±0.22 cm; the corresponding lesioned segment intervertebral height at follow-up was 0.58-1.64 cm, with a mean of 0.95±0.22 cm, and there was a significant difference between the two (t=3.67, p=0.001). Fusion did not occur in eight cases, and interbody fusion was achieved in the remaining cases, with a fusion rate of 83.7%. There was no significant difference in the fusion rate between the group with and without the pedicle nail (Fisher exact test p>0.05). There was no significant difference in the fusion rate between different bone graft sources (X2=1.602, P>0.05), and no significant difference in the fusion rate of unilateral and bilateral Cages (Fisher exact test P>0.05). 12 cases had vertical displacement of the Cage, with an incidence of 24.5% and a mean displacement of 0.06±0.13 cm. 6 of them had Cage subsidence (0.1- 0.5 cm, mean 0.5 cm). 0.5cm, mean 0.32±0.17cm) and 6 cases had upward Cage displacement (0.1-0.3cm, mean 0.18±0.10cm). No left-right or anterior-posterior lateral displacement of the Cage occurred in all 49 patients. Adjacent vertebral degeneration (ASD) occurred in 9 cases, and the incidence of ASD was 18.4%. 5. Analysis of complications and residual symptoms: In terms of complications, one case had cauda equina injury and postoperative anal sphincter dysfunction; one patient developed a lumbar abscess three years after surgery and was reoperated to clear the abscess and drain it; one case had nerve root compression during Cage placement due to improper nerve root protection during surgery. In terms of residual symptoms, two cases had reduced muscle strength of the affected limb (incidence 4.1%), which slightly affected walking; four cases had numbness and pain of the affected limb (incidence 8.2%), of which two cases had occasional numbness and pain and two cases had frequent numbness and pain, which seriously affected daily life; six cases had lumbar discomfort (incidence 12.2%), but all of them had occasional attacks. Except for one case of cauda equina injury and two cases of severe numbness mentioned above, all other 46 patients resumed their preoperative working life after surgery. Chronic low back pain is one of the common clinical symptoms in orthopedic surgery, and degenerative diseases of the lumbar spine (including lumbar disc herniation, lumbar spondylolisthesis, lumbar spinal stenosis, segmental instability, etc.) are the most common causes of chronic low back pain. Surgical treatment of degenerative lumbar spine diseases, on the other hand, includes minimally invasive approaches, artificial prosthesis replacement and spinal decompression fusion. There are many spinal fusion procedures, each with its own advantages and disadvantages, and the surgical results and fusion rates reported in the literature vary. In our department, posterior lumbar decompression + posterior TFC interbody fusion was used in all cases. There are many types of intervertebral fusion devices. The TFC is a representative of horizontal cylindrical titanium interbody fusion, which is designed to increase the height of the intervertebral space by 1. directly increasing the height of the intervertebral space, 2. the tension band effect, and 3. the internal fixation of the intervertebral interface. Many studies have shown a significant increase in intervertebral foraminal volume after placement of a spinal interbody fusion. The significant increase in the intervertebral space height of the diseased segment at the follow-up of our patients suggests that TFC implantation did increase the nerve root space and maintain the effect of posterior neural decompression. No anterior-posterior or lateral displacement of the Cage was found in the follow-up cases, indicating the existence of a good self-stabilizing effect of the TFC. the higher incidence of vertical displacement of the Cage (24.5%) may be related to the inconsistency of the elastic modulus of the TFC and the cancellous bone of the vertebral body, combined with the fact that the TFC has a thread with a strong shear force. Many studies and other studies have shown that fusion rates of more than 90% can be achieved with TFC alone and are thought to provide adequate biomechanical stability of the spine. However, many scholars have raised objections in recent years. It is now believed that TFC implantation significantly improves the stability of the spine in all directions except rotation and posterior extension. From the follow-up cases in this paper, the fusion rate was high in 49 cases (83.7%), which basically led to the stabilization of the spinal lesion segments. Although the ex vivo test showed that TFC supplemented with pedicle screw fixation resulted in stronger fixation, this trial showed that there was no significant difference in the fusion rate between patients with and without the pedicle nail, and that the RF pedicle nail only served to reset the lumbar spine slip during surgery and had no effect on the fusion rate. The incidence of ASD was 18.4% in all cases. The author believes that the occurrence of ASD is not only related to fusion, but also to the patient’s own aging, the change in the total elastic modulus of motion of the segment caused by TFC implantation, and the work status of the patient, which needs to be confirmed by further studies. Since there was no significant difference in the fusion rate between the three bone graft sources used in this procedure, the author believes that all three bone graft sources can be used, depending on the amount of intraoperative spinous bone and the amount of bone graft required. Many papers have reported that TFC for lumbar degenerative disease has achieved good recent results, but there is a lack of long-term follow-up. In this paper, we conducted medium and long term follow-up of our TFC treatment for lumbar degenerative disease cases, and the JOA score increased significantly at the time of follow-up, and the average postoperative improvement rate was 83.7%, so the surgical efficacy was obvious, and only one patient had symptoms of cauda equina compression at the time of follow-up, and two cases were left with numbness and pain in the affected limbs, which affected life. Even after prolonged observation most patients did not have recurrence of symptoms. Complications of interbody fusion include nerve root or cauda equina injury, dural tears, cortical penetration by the arch, infection, and fracture of the internal fixation. In one of the follow-up cases, the nerve root was not properly protected during surgery, and the nerve root was squeezed during Cage placement. At the time of follow-up, the patient had only mild lower extremity numbness. 3 years after surgery, one patient developed a right lumbar abscess, which was removed by incision and drainage, and the RF pedicle nail was removed and healed after the application of antibiotics. No internal fixation fracture occurred in this observation follow-up case. It has been shown that for the TFC to be firmly fixed in the upper and lower endplates of the lower lumbar spine, the diameter of the TFC must be greater than 14 mm, but in our follow-up cases, two patients with a TFC diameter of 12 mm achieved excellent postoperative results, with a significant increase in the intervertebral space height, fusion of the intervertebral space, no displacement of the Cage, and no ASD. The size of the intervertebral space of the diseased segment should be accurately measured before surgery according to the actual needs. An oversized Cage is difficult to install and requires excessive resection of the posterior spinal tissue, which can affect spinal stability. A too-small Cage cannot be firmly fixed between the adjacent upper and lower vertebral bodies, which may lead to Cage displacement and affect the interbody fusion effect. In conclusion, posterior lumbar decompression + TFC interbody fusion for lumbar degenerative disease is safe, and after long-term follow-up, it shows positive postoperative efficacy, significant increase in interbody height and long-term maintenance, insignificant Cage displacement, high interbody fusion rate, low incidence of adjacent vertebral degeneration, and fewer surgical complications, and remains a trusted interbody fusion procedure for the lumbar spine.