At present, open disc removal and microendoscopic discectomy (MED) are the two main modalities of surgical treatment for lumbar disc herniation (LDH), and both of them have a certain recurrence rate [1, 2]. In China, the reoperation rate of lumbar disc reaches 2.0%~9.2% [1], and the recurrence rate after minimally invasive nucleus pulposus removal (MED) is reported to be 4%~11% in foreign countries [2], and the reasons for the symptomatic recurrence of LDH after MED need to be explored. This paper compares the efficacy of MED and open disc removal for LDH and analyzes the reasons for reoperation in each case. Clinical data 1.General data From January 2000 to January 2006, a total of 1,862 cases of single-segment LDH were diagnosed and operated by clinical examination, CT or MRI, 1,091 cases were male and 771 cases were female, aged 14-60 years old, the average age was 39.4 years old. 1,276 cases were treated by MED, and 586 cases were treated by open disc extraction. After the operation, according to the routine anti-inflammatory, dehydration, prevention of infection, symptomatic treatment, outpatient follow-up of a total of 1,518 cases, follow-up time of 8 to 60 months, the average 39.2 months, of which 1,059 cases in the MED group and 459 cases in the open group. 2. Criteria 2.1 Inclusion criteria The selection criteria were age 60 years, single-segment disc herniation, no previous surgery; all cases were diagnosed by CT, MRI and ineffective conservative treatment for more than 3 months. 2.2 Exclusion criteria: Combination of lumbar spinal stenosis, lumbar tumor, tuberculosis, lumbar spondylolisthesis, intervertebral instability, history of lumbar spine fracture, multisegmental disc herniation, bilateral disc herniation, extreme lateral herniation, giant free herniation, and lumbar surgery history. 2,3 The modified Macnab efficacy evaluation criteria were used: excellent: pain disappeared, no motor dysfunction, and resumed work and activities; good: occasional pain, main symptoms disappeared, muscle strength was normal, straight leg raising test (-), and could engage in light work; OK: symptoms improved, but still have pain, and could not work; poor: there were signs of nerve compression, and further surgical treatment was needed. Results: 1,518 cases were followed up. 91.31% of the MED group and the open group were satisfied with the most recent postoperative follow-up (those with good Macnab score). Discussion: The efficacy of MED and open nucleus pulposus removal was evaluated after 8-60 months of follow-up. 91.3% (967/1059) and 93.2% (428/1059) of the MED group and the open group were satisfied with the most recent postoperative follow-up (those with good modified Macnab score) respectively. 93. 2% (428/459), with no significant difference (P>0. 05); there was no significant difference in the time of initial surgery between the two groups (P>0. 05); intraoperative bleeding, hospitalization time, and return to work were significantly less in the MED group than in the open group (P<0.05), but the hospitalization cost of the former was higher than that of the open group (P<0.05).The average intraoperative blood loss in the MED group was 40. 2m,l Postoperative routine placement of rubber sheet drainage, drainage is often negligible; open group average intraoperative blood loss. The average blood loss in the open group was 112.7m,l and the average postoperative drainage was still 62.9m,l so the total blood loss was about 170ml on average.The time to return to work was about 6 weeks in the MED group and 3 months in the open group,and the time to return to physical activities was a little bit later in the open group,which showed that both groups achieved good therapeutic effects.MED has the advantages of small trauma,less bleeding,short hospitalization time,fast postoperative recovery,and the patients can return to work as soon as possible,but the advantages of hospitalization are not as good as those in the open group,but the patients can return to work as soon as possible. MED has the advantages of less trauma, less bleeding, shorter hospitalization time, quicker recovery after surgery, patients can resume work as soon as possible, but the cost of hospitalization is slightly higher. At present, the recurrence rate after lumbar disc removal surgery is reported to be 2%~9.12% [1]. The reoperation rate after lumbar disc removal is reported to be 2%~11% in foreign countries[3]; the reoperation rate after minimally invasive disc removal is about 4%~11%[2].The reoperation rate of MED group and open group are both lower, 6.89% and 2.61% respectively, and the difference between the two groups is significant (P<0.05).The reoperation time of MED group is 7 days~8 months, with an average of 5.6 months, while the reoperation time of open group is 6~60 months, with an average of 6.6 months and 6.6 months. ~In the MED group, the recurrence time was 7 days to 8 months, with an average of 5.6 months, while in the open group, it was 6 days to 60 months, with an average of 31.2 months, with a significant difference (P<0.05). The MED group had an earlier recurrence of symptoms, mainly due to the failure to relieve lateral recess stenosis and in situ recurrence, while the open group had a later recurrence of secondary stenosis, and neuronal root adhesion. In our opinion, the causes of symptomatic recurrence after nucleus pulposus removal exist in the whole process of treatment, including preoperative, intraoperative and postoperative factors. 2.1 Diagnostic error is the main preoperative factor for recurrence. Lumbosacral spine tuberculosis, tumor, lumbar spondylolisthesis, sacroiliac and hip joint lesions, pyriformis syndrome, lumbosacral radiculitis, nerve root cysts, neurofibromas or nerve sheath tumors need to be differentiated from LDH. We emphasize the strict preoperative physical examination, to grasp the difference between the radicular pain of LDH and other low back pain, especially the hip pain and calf pain and foot pain is not obvious, we should make the pear-shaped muscle tension test, the 4-word test, the oblique trigger test, the pick-up test, etc., and combined with the corresponding imaging data, generally not easy to misdiagnose. 2.2 Positioning error is an important intraoperative factor in the failure of myelomeningocele removal. Variations in spinal anatomy may make intraoperative localization difficult. Shen Chengda[4] reported that in the treatment of LDH with MED, intraoperative C-arm X-ray localization was performed, but the localization error rate still reached 1.1% (5/456). When we performed open discectomy or MED, we used intraoperative localization in all cases, and even repositioned the disc when there was a doubt about the disc space, and no localization error occurred. Therefore, intraoperative X-ray localization should be performed when no obvious disc herniation is detected intraoperatively to avoid localization errors. However, blind exploration of the upper and lower intervertebral spaces is not recommended to minimize trauma and the possibility of postoperative nerve root adhesion. 2,3 Incomplete removal of the nucleus pulposus, resulting in postoperative herniation in situ, is another intraoperative factor for recurrence. The intervertebral disc is an important structure to maintain the stability of the lumbar spine. Surgical injury to the posterior column structure, fibrous annulus tension and the integrity of the nucleus pulposus were destroyed, and the strong unity between the intervertebral disc and the upper and lower vertebral bodies was destroyed. The potential sagittal instability of the lumbar motion segments is the main reason for the recurrence of low back pain in the same interval [5]. In young patients, the degeneration of nucleus pulposus is mild, and if the nucleus pulposus is not removed enough during the operation, the postoperative degeneration will be accelerated; because of the poor blood supply of the annulus fibrosus, the postoperative healing is slow, and the degenerated nucleus pulposus will be protruded from the original position under the action of the traumas and other factors. Zeng Yan et al[6] reported that there were 56 cases of recurrent LDH, and 38 cases were in situ disc prolapse, accounting for 67.9%. We found that this situation was more frequent in the MED group, with 14 cases of incomplete nucleus pulposus removal and 8 cases of undetected free herniation, totaling 22 cases, accounting for 30.1% of the total number of recurrences in the MED group, whereas neither of these two situations occurred in the open group. 2,4 Combined lateral saphenous fossa stenosis was the main cause of recurrence after nucleus pulposus removal. The lateral saphenous fossa is the narrowest part of the spinal canal, which is the nerve root channel; the smaller the sagittal diameter and the larger the transverse diameter, the narrower the spinal canal is.The sagittal diameter of the lateral saphenous fossa of L5 was 5.20±1.24 mm on the right, and 4.98±1.40 mm on the left, and the transverse diameter was 3.18±1.37 mm on the right, and 3.52±1.42 mm on the left; because the foramen of L5 was in the form of a trilobed shape, the lateral saphenous fossa was obvious, the small sagittal diameter was the smallest one which could reach to 2 mm and the supraspinatus synostosis of L5 was the smallest one, the smallest one could be 2 mm and the smallest one could reach to 2 mm. Because the L5 foramen is trilobed, the lateral saphenous fossa is obvious, and the sagittal diameter is small, with a minimum of 2 mm. Chen Limin et al [8] reported that the combined spinal stenosis and neural root canal stenosis in 11 cases, accounting for 50% of the recurrent LDH in this group, was the main cause of recurrence.Burton et al [9] reported that the lateral saphenous fossa stenosis accounted for 56% of the LDH reoperation patients. Postoperative secondary nerve root channel stenosis is an important cause of intractable low back pain and an important pathologic change in secondary surgery, and prophylactic lateral saphenous fossa enlargement has been advocated to improve the long-term efficacy of reoperation [10]. Among the reoperation patients, 33 cases of MED group failed to release the lateral saphenous fossa stenosis, accounting for 45.2% of the total number of recurrences in the group, and 2 cases of the open group accounted for 41.2% of the total number of recurrences in the two groups, which was the primary reason for reoperation. As a result, the lateral saphenous stenosis can not be relieved completely, and the recurrence rate after surgery is relatively high. Of course, with the skillful operation of minimally invasive techniques, the number of lateral saphenous fossa stenosis not relieved has decreased significantly, and MED has even been successfully used in the treatment of spinal stenosis. In the open group, the recurrence rate was relatively low due to the larger area of nerve root and dural sac exposed during the operation, more disc tissues removed, and more adequate decompression of the nerve root canal and lateral saphenous fossa. 2,5 Postoperative adjacent disc herniation is one of the complications after nucleus pulposus removal. Among the 85 cases in this group, there were 5 cases of postoperative adjacent disc herniation in the MED group and 2 cases in the open group, accounting for 8.24%. It was found that excessive resection of the posterior lumbar spine structures weakened or disappeared its role in limiting excessive lumbar spine activities, increased stress in the preserved part, accelerated degeneration, leading to lumbar spine instability, and increased the chances of intervertebral disc prolapse[11].Kirkaldy-Willis[12] pointed out that the two posterior small joints and the anterior discs constitute the triple-joint complex, which plays an important role in the stability of the spinal column. Degeneration, trauma, or medical injury can cause this complex to be involved, affecting the stability of the spine. In this group, there were 5 cases of lumbar segmental instability after surgery, but no lumbar spondylolisthesis. Reoperation for recurrent LDH can achieve good results after solving the two problems of decompression and stabilization at the same time. Zeng Yan et al[6] treated 56 cases of recurrent LDH with posterior decompression, discectomy, transverse process or intervertebral bone grafting, and pedicle screws for internal fixation, and the average improvement rate after surgery was 70.7% according to the JOA score. Among the cases in this group, there were 73 cases of re-operation in the MED group, in which the nucleus pulposus was not sufficiently removed during the operation, and there were 14 cases of in situ protrusion, of which 3 cases were repaired by MED with no difficulty; the other 11 cases were combined with lateral saphenous fossa stenosis, so the second operation was performed by open-window nucleus pulposus removal; the 5 cases of neighboring herniated discs were treated by MED; the 8 cases of free nucleus pulposus protrusion were not detected by the initial operation, so the second operation was performed by hemi-discectomy; and the 5 cases of adjacent disc protrusion were treated by MED; the 8 cases of free nucleus pulposus hernia not detected during the initial operation, so the second operation was performed by hemi-discectomy. In 41 cases of combined lateral saphenous stenosis which was not relieved by the initial surgery and led to the recurrence of symptoms, the second surgery was performed by enlarged open nucleus pulposus removal in 18 cases, hemilaminectomy in 13 cases, intervertebral implant fusion with hemilaminectomy and unilateral pedicle screw fixation in 2 cases; 2 cases of neurogenic adhesion were performed by hemilaminectomy, transverse implant fusion and unilateral pedicle screw internal fixation; 3 cases of lumbar instability were performed by total discectomy, intervertebral implant fusion and internal fixation; 3 cases of total discectomy, intervertebral implantation, and internal fixation in 3 cases; 3 cases of lumbar instability were treated by MED. In 3 cases of lumbar instability, total laminectomy, intervertebral implant fusion and bilateral internal fixation were performed; in 8 cases of intervertebral discitis, anterior disc removal and implant fusion were performed. The immediate effect was good, but the long-term effect is yet to be observed. There were 12 cases of reoperation in the open group, which were often combined with various reasons. The cases of reoperation included: nerve root adhesion and disc herniation of adjacent segments, 2 cases of hemilaminectomy with nucleus pulposus removal and 1 case of anterior disc removal; 2 cases of recurrence of lateral saphenous fossa stenosis and dural sac narrowing, 2 cases of hemilaminectomy, intertransverse fusion, and unilateral pedicle screw fixation; and 2 cases of lumbar spinal instability, secondary spinal stenosis, nerve root adhesion, dural sac narrowing, and postoperative lumbar spinal stagnation, with nerve root adhesion. Postoperative lumbar instability, secondary spinal stenosis, nerve root adhesion, and dural sac narrowing were treated with total laminectomy and intervertebral implant fusion and internal fixation in 4 cases; 4 cases of intervertebral discitis were treated with anterior disc removal and implant fusion. Previously, it was thought that if LDH recurred after MED, the best way to reoperate was to remove the nucleus pulposus through an interlaminar window.Isaacs et al.[13] reported that MED was successful in the treatment of recurrent LDH, and there was no significant difference in the amount of surgical blood loss, operative time, complications, and length of hospitalization compared with the initial MED, so the efficacy of MED in the treatment of recurrent LDH was comparable to or better than that of conventional surgery. We treated 3 cases of recurrent LDH in the MED group and 1 case of recurrent LDH in the open group with MED, and we paid attention to the gradual loosening of adhesions from the upper edge of the vertebral plate during the operation, so that the nerve roots were not easily damaged. The working channel was positioned at the junction of the vertebral plate and articular process in the nerve root plane, and care was taken to make sure that it was slightly more lateral than the initial approach, so that good decompression of the nerve root and scar release could be achieved endoscopically. Localized nerve root adhesion and scar formation after disc removal is considered a contraindication to posterior surgery. Currently, some scholars advocate anterior surgery to remove the herniated disc and scar tissue and release the nerve root. We performed anterior disc removal and nerve root release surgery for one case each in the MED group and the open group, and the results were good. 4. Methods of preventing recurrence Some scholars have improved the surgical methods to prevent and reduce the recurrence of LDH after Nucleus pulposus removal.Mastronardi et al[14] embedded ORC (oxidized regenerative cellulose) into the intervertebral space after minimally invasive disc removal in a total of 158 cases, with a minimum of 18 months follow-up, and the total recurrence rate was 3.35%. The overall recurrence rate was 3.35%. This is considered to be a safe and effective method to reduce the recurrence of postoperative LDH, but the long-term results have yet to be confirmed.Suda et al.[15] found that preoperative segmental kyphosis of >10° in the flexion position and/or posterior slip of >10% in the extension position were the high-risk factors for postoperative lumbar disc removal, and they were the indications for spinal fusion. It is believed that preoperative flexion-extension radiographs can predict the recurrence rate after LDH. We routinely took dynamic radiographs of patients with suspected preoperative lumbar instability to exclude lumbar instability, isthmic fracture, or lumbar spondylolisthesis, and performed lumbar fusion in these patients, which reduced the recurrence rate in the MED and open groups. At the same time, careful physical examination and imaging examination can eliminate misdiagnosis; strict control of surgical indications can avoid unnecessary surgery; adopt the most appropriate treatment according to the condition, and try to use less traumatic surgical procedures, such as MED, X-Tube, METRx, and lateral approach microscopic nucleus pulposus removal; careful operation can reduce the misinjury; preoperative and intraoperative localization can eliminate the localization error; and carefully explore the nerve root and try to release the nerve stenosis and the lateral saphenous fossa, so as to reduce the recurrence rate of the MED and open group. Careful exploration of the nerve root, try to release the lateral saphenous fossa stenosis and nerve root canal stenosis; place negative pressure drainage tube after surgery to reduce the scar formation caused by local hematoma; emphasize the postoperative lumbar dorsal muscle functional exercise to stabilize the lumbar spine.