A comparison between remaining and resecting the posterior longitudinal ligament in percutaneous endoscopic transforaminal discectomy for disc herniation: A retrospective cohort study

Nowadays, percutaneous endoscopic lumbar discectomy (PELD) has become a popular surgical option for the management of LDH, On the basis of the approach to the herniation disc materials, PELD could be classied into percutaneous endoscopic transforaminal discectomy (PETD) and percutaneous endoscopic interlaminar discectomy (PEID). During PETD procedure, especially in in-and-out approach, accurate determination of whether the posterior longitudinal ligament is needed resection seems particularly important.In the study, we tried assessing comparative clinical outcome, surgical duration and complications between the two different surgical methods of LDH treated by PETD via inside-and-out approach. MacNab criteria were used to evaluate clinical outcomes. All cases underwent lumbar spine anteroposterior, lateral, exion-extension x-ray, computed tomography (CT), and magnetic resonance imaging (MRI) to conrm the diagnosis and pathological type. Operation time, blood loss, recurrence of LDH and other complication such as dural tear, nerve injury, intervertebral infection, etc. of these two groups were recorded. Clinical evaluation was performed preoperatively, immediately postoperatively, and at each follow-up visit (1 month, 3 months, and nal follow-up). 3 months after surgery, MRI was performed to conrm the nerve root compression was relieved and exion-extension x-ray was used to assess spinal stability. All patients were followed up without loss for at least 24 months.


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Background Lumbar disc herniation (LDH) is a common disease with a reported prevalence of 1-3% and is a major cause of low back pain (LBP) with radiation to the legs [1]. Although conservative treatment has been usually proposed for LDH patients, some patients whose symptoms has not improved with conservative management may still require surgical intervention [2]. Among the operative methods, open lumbar discectomy and fusion is considered to be the gold standard treatment of LDH [3,4].However, the procedure make damage to muscular and ligamentous structures and require prolonged hospital stays and expensive hospitalization cost. Nowadays, percutaneous endoscopic lumbar discectomy (PELD) has become a popular surgical option for the management of LDH, Since the posterolateral nucleotomy technique was rst introduced by Kambin and Gellman [5][6][7] .
On the basis of the approach to the herniation disc materials, PELD could be classi ed into percutaneous endoscopic transforaminal discectomy (PETD) and percutaneous endoscopic interlaminar discectomy (PEID). PETD is more widely used because it can manage all types of LDH theoretically [8]. During PETD procedure, especially in in-and-out approach, accurate determination of whether the posterior longitudinal ligament is needed resection seems particularly important. To our knowledge, there is not much research to cormpare the curative effect of resecting the posterior longitudinal ligament or not.
In this retrospective study, we tried assessing comparative clinical outcome, surgical duration and complications between the two different surgical methods of LDH treated by PETD via inside-and-out approach.

Materials And Methods
From January 2015 to January 2017, a total of 135 symptomatic LDH patients who were treated by PETD resecting the posterior longitudinal ligament (68 patients) or remaining the posterior longitudinal ligament (67 patients) during the surgery were included in this retrospective analysis. This study was conducted with approval from the Ethics Committee of our Hospital. Written informed consent was obtained from all participants. All procedures involving human participants were performed in accordance with the Declaration of Helsinki. Visual analog scale (VAS) score, Oswestry disability index (ODI) and modi ed MacNab criteria were used to evaluate clinical outcomes. All cases underwent lumbar spine anteroposterior, lateral, exion-extension x-ray, computed tomography (CT), and magnetic resonance imaging (MRI) to con rm the diagnosis and pathological type. Operation time, blood loss, recurrence of LDH and other complication such as dural tear, nerve injury, intervertebral infection, etc. of these two groups were recorded. Clinical evaluation was performed preoperatively, immediately postoperatively, and at each follow-up visit (1 month, 3 months, and nal follow-up). 3 months after surgery, MRI was performed to con rm the nerve root compression was relieved and exion-extension xray was used to assess spinal stability. All patients were followed up without loss for at least 24 months.
The inclusion criteria were as follows: (1) symptomatic radiating leg pain with positive straight leg-raising test; (2) CT and MRI suggesting a single level disc herniation correlated with the clinical ndings; (3) signi cant pain refractory to conservative treatment for at least 4 weeks such as bed rest, immobilization, and pain management program; (4) no previous surgical history at the same level. The exclusion criteria were as follows: (1) ank pain as the main symptom; (2) segmental lumbar spinal stenosis or degenerative scoliosis; (3) unstable lumbar vertebrae; (4) rupture of the posterior longitudinal ligament preoperatively (5) high iliac crest or large L5 transverse process which interlaminar approach required; (6) infection, tumor or other pathological conditions.

Operative Technique
All surgeries were performed by the same experienced surgeon. Patients were placed in the prone position on a radiolucent surgery table. Local anaesthesia was selected for monitoring of any intra-operative changes in the patients'symptoms and signs. Prior to surgery, C-arm X-ray uoroscopy was used to con rm the target segment. The surgical puncture point and distance depended on the body type of each patient, and the distance was usually 11-14 cm from the midline. 1% Lidocaine was used from the skin fascia to the surface of the annulus brosus. An 18G needle was inserted into target intervertebral foramen. Anteroposterior uoroscopy con rmed the needle positioned on the medial pedicle edge. Lateral uoroscopy con rmed the needle positioned on the posterior edge of the vertebral body. Then, Endoscope was positioned through a working channel that was inserted via a 0.8-cm skin incision at the entry point of the puncture needle ( Fig. 1) .
Under endoscopy, the posterior longitudinal ligament was usually in the middle of the eld, and the spinal canal is up, the intervertebral disc is down (Fig. 2) .First, pituitary rongeur was used to remove the prominent intervertebral disc under the posterior longitudinal ligament. Next, the working channel was rotated upward to detect residual nucleus pulposus tissue in spinal canal. During the procedure, the posterior longitudinal ligament was resected for some patients (68 cases). Decompression is supposed to su cient when the nerve root has good mobility and the dural sac beat with the heartbeat. Bipolar radiofrequency was used for Annulus ssure coagulation and hemostasis. After endoscopy and working channel were removed, the skin was sutured with a single stitch.
All PETD is daytime surgery at our hospital, and patients were discharged after resting in bed for 1-2 hours postoperatively.1 day later, patients were recommended to begin lumbodorsal muscle exercise and straight leg-raising exercise with a protective belt.

Statistical Analysis
Statistical analyses were carried out using SPSS version 19.0 software (SPSS, Chicago, IL

Results
PETD via inside-and-out approach were performed in all patients. 135 patients were grouped to undergo either of the surgical methods. There were 38 males and 30 females in the group A that resecting the posterior longitudinal ligament (mean age = 52.40 ± 8.73 years) and 35 males and 32 females in the group B that remaining the posterior longitudinal ligament (mean age = 53.50 ± 9.24 years). There were no statistically signi cant differences between the two groups in demographic data such as age, gender, or pain duration (Table 1). In the group A, Surgery was performed at the L3/4, L4/5, and L5/S1 levels in 6 (8. The mean operation time of the group A and the group B respectively, were 82.7 ± 18.5 min and 115.6 ± 24.6 min (P < 0.01). The average blood loss was 12.6 ± 5.5 ml and 14.2 ± 7.3 ml and there was no difference between the two groups. The postoperative VAS scores and ODI were signi cantly higher than those before surgery in two groups (P < 0.01). The differences in the results were not signi cant between the two groups (P > 0.05) ( Table 2). For the modi ed MacNab criteria, the clinical outcome at nal follow-up was excellent in 35 patients, good in 27, and fair in 4, excellent/good ratio is 91.2% in group A and excellent in 33 patients, good in 28, and fair in 5 with an excellent/good ratio of 91.0% in group B. There was no signi cant difference in the excellent/good ratio between the two groups (P > 0.05). In the series of patients, No serious complications, such as dural tear, wound infection or persistent nerve root injury, were observed. There are 4 patients in group A and 5patients in group B developed postoperative dysesthesia. 3 patients (2 in group A, 1 in group B) experienced transient motor weakness. All of whom recovered with conservative treatment from 4 to 12 weeks. There was no signi cant difference in the complication rate between the two groups (P > 0.05). 1 patient in group A and 2 patients in group B had a recurrent disc herniation 3-6 months after surgery. Although the recurrence rate is higher in group B, There was no signi cant difference between the two groups (P > 0.05). The exion-extension x-ray indicated that all cases in none of the patients in either group had increased spinal instability after surgery.

Discussion
For decades, minimally invasive spine surgery has been increasingly popular in treating LDH for multiple advantages compared with the open technique: such as less invasive, decreased blood loss, faster function recovery, shorter length of hospitalization, and lower risk of spinal instability [9][10][11].PETD via inside-and-out approach has become one of the most common minimally invasive spinal surgeries since Yeung et al. developed the spinal endoscopic YESS system in 2002 [7,12].Many studies have indicated that this technique could achieve good results with effective nerve root decompression, low complication rates for most types of LDH [13][14][15][16]. Yeung et al [7] reported 307 cases of LDH treated with the this technique followed-up for more than one year, and the excellent -to -good rate was 89.3%. Similarly, in a study of 219 LDH patients (167 paramedian and 52 central herniations), the clinical outcomes showed the excellent or good rate was 88.1% with PETD via inside-and-out approach.
In the surgical technique, the working channel is rst to be inserted into the disc just underneath the herniated nucleus pulposus, then, the channel is gradually diverted into the spinal canal as decompression progresses. During this procedure, if the posterior longitudinal ligament is found ruptured, the resection is recommended [17]. However, if the posterior longitudinal ligament is intact, whether the posterior longitudinal ligament is needed resection is controversial signi cantly [8].
Theoretically, retaining the posterior longitudinal ligament is bene cial to maintain spinal stability and prevent the reherniation of nucleus pulposus; On the other hand, it might increase the risk of free nucleus pulposus tissues left in spinal canal leading to inadequate decompression.
To our knowledge, no study has assessed the comparative curative effect between the two different surgical methods. In the current study, the results showed both methods had the same satisfactory clinical e cacy with similar complication rate. For the patients in group A, although the posterior longitudinal ligament is not resected, the careful detection underneath the herniated nucleus pulposus and in the spinal canal was made to con rm no residual nucleus pulposus tissues, which guarantee the adequate decompression as in group B. The recurrence rate is higher in group B, however, there was no signi cant difference between the two groups. The exion-extension x-ray indicated that all cases in none of the patients in either group had increased spinal instability after surgery. The reason we think is that the posterior longitudinal ligament is only one aspect of maintaining spinal stability, the supraspinous ligament, interspinous ligament, capsule of facet joint was intact in both methods which play an important role in maintaining the spinal stability. The main difference between the two methods is patients in group B experienced longer operation time which may decrease patients' satisfaction under intraoperative local anesthesia. So, in our opinion, the resection of the posterior longitudinal ligament is unnecessary when the ligament is intact.
The retrospective nature of this study is a limitation. Studies of multicenter, randomized controlled trials should be conducted to compare the clinical e cacy of the two different surgical methods of LDH treated by PETD via inside-and-out approach.

Conclusions
Whether the posterior longitudinal ligament is resected do not make any difference on curative effect in PETD via inside-and-out approach, and remaining the ligament when it's intact is preferred because of its shorter operation time.

Declarations
Availability of data and materials The spinal internal xation devices including pedicle screws, rod, and cage in surgical procedure are available and produced by Weigao Orthopedic, Shandong,China. The patients' data were collected in Chinese PLA General Hospital, the First Medical Center.

Ethics approval and consent to participate
This study was conducted with approval from the Ethics Committee of Chinese PLA General Hospital and was performed in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants.  Intraoperative view. The posterior longitudinal ligament was in the middle (arrow), the top part is spinal canal (black star) and the bottom part is herniation (red star).