The efficacy of bilateral intervertebral foramen block for pain management in percutaneous endoscopic lumbar discectomy

Abstract Background: Compared with open lumbar microdiscectomy, percutaneous endoscopic lumbar discectomy (PELD) has the advantages of remarkable preservation of paravertebral structures, less bleeding, shorter operation time and fewer complications, it is a common method for the treatment of lumbar disc herniation (LDH). Local anesthesia is recommended during PELD. However, intraoperative pain is sometimes difficult to control satisfactorily. The efficacy of bilateral intervertebral foramen block (IFB) for pain management in PELD remains unclear. Therefore, this regimen is utilized in a randomized controlled trial for the assessment the safety and effectiveness of bilateral IFB for PELD pain control. Method: This is a single center and randomized controlled trial which will be implemented from September 2020 to September 2021. This research protocol is in accordance with the items of the Standard Protocol for Randomized Trials, which was authorized through the Ethics Committee of Huzhou Central Hospital & Affiliated Centre Hospital of Huzhou University (HZCH0465-0864). 100 participants who undergo PELD will be analyzed. Inclusion criteria contains1. patients diagnosed with LDH undergoing PELD;2. people between the ages of 18 and 75;3. consistent imaging evidence of herniation at a same level (CT or MRI);4. receive conservative treatment for 2 months. The exclusion criteria contains:1. patients with the history of severe renal and hepatic dysfunction;2. more than 1 responsible level3. LDH combined with other spinal diseases needing advanced surgical treatment (such as fracture, spondylolisthesis, lumbar spinal stenosis, tumor, etc.);4. Patients have mental illness that will prevent their willingness to participate in the study. Patients will be randomly divided into bilateral IFB group (with 50 patients) and local infiltration analgesia group (with 50 patients). Primary outcomes are pain score at different time points. The secondary outcomes are the operative time, radiation exposure time, length of hospital stay and postoperative complications. All the analysis is implemented through applying the IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, NY, USA). Results: The clinical outcome variables between groups are illustrated in the Table 1. Conclusion: This investigation can offer a reliable basis for the effectiveness and safety of IFB in treating the PELD pain. Trial registration: This study protocol is registered in Research Registry (researchregistry5985).


Introduction
Lumbar disc herniation (LDH) is a familiar cause of lower extremity radiation pain and low back pain and conservative treatment can improve symptoms of most cases. [1,2] About 80% of the patients suffered from sciatica caused by LDH, which imposes heavy burden on society, families, and individuals. [3,4] In these cases, 10% to 20% of the patients received conservative treatment, but the pain continued, and surgery should be considered. [5] Compared with open lumbar microdiscectomy, percutaneous endoscopic lumbar discectomy (PELD) has the advantages of remarkable preservation of paravertebral structures, less bleeding, shorter operation time, and fewer complications, it is a common method for the treatment of LDH. [6,7] For patients with LDH undergoing surgery with spinal anesthesia or general anesthesia, it is hard to detect the accidental injury of the cauda equina nerve and nerve root due to sensory blockade. [8] Although local anesthesia is recommended during PELD for avoiding nerve root injury, intraoperative pain is sometimes difficult to control satisfactorily under local anesthesia only, [9,10] especially during the process of foraminoplasty, working channel insertion, and nucleus pulposus removal.
Severe pain during foraminoplasty and working channel insertion is considered to originate from the posterior longitudinal ligament. A local intervertebral foramen block (IFB) can block homolateral sinuvertebra nerve and spinal nerve located in the neuroforamen. Our preliminary research has indicated that IFB was associated with improved outcomes in terms of postoperative pain and opioid consumption. However, due to the small sample size and poor study design, the efficacy of bilateral IFB for pain management in PELD remains unclear. Therefore, this regimen is utilized in a randomized controlled trial for the assessment the safety and effectiveness of bilateral IFB for PELD pain control. We assume that that IFB is effective and safety in reducing postoperative pain in PELD.

Study design
This is a randomized controlled, single center trial which will be implemented from September 2020 to September 2021. This research protocol is in accordance with the items of the Standard Protocol for Randomized Trials, which was authorized through the Ethics Committee of Huzhou Central Hospital & Affiliated Centre Hospital of Huzhou University (HZCH0465-0864), and it has been registered in the research registry (researchregis-try5985). All patients had signed consent forms before the surgery.

Population and randomization
100 participants who undergo PELD will be analyzed. In the random envelope, all patients are assigned a random number via using the random number (Table 1), and the result of allocation are hidden. Patients will be randomly divided into bilateral IFB group (with 50 patients) and local infiltration analgesia group (with 50 patients). Inclusion criteria contains 1. patients diagnosed with LDH undergoing PELD; 2. people between the ages of 18 and 75; 3. consistent imaging evidence of herniation at a same level (CT or MRI); 4. receive conservative treatment for 2 months.
The exclusion criteria contains: 1. patients with the history of severe renal and hepatic dysfunction; 2. more than one responsible level 3. LDH combined with other spinal diseases needing advanced surgical treatment (such as fracture, spondylolisthesis, lumbar spinal stenosis, tumor, etc.); 4. Patients have mental illness that will prevent their willingness to participate in the study.  Table 1. After 2 to 3 ml of 0.3% ropivacaine is infiltrated into the local skin, the selected skin entry point is pierced with an 18-gauge needle, and the track is anesthetized with 8 to 10 ml of 0.3% ropivacaine. The facet joint is anesthetized with 3 to 5 ml of 0.3% ropivacaine when the needle arrives at SAP. The following surgical procedures, such as removal of nucleus pulposus, insertion of working channel, and foraminoplasty, are the same as the procedures of conventional PELD. In case of lateral and anteroposterior fluoroscopy, 18-gauge is inserted into contralateral monosegmental intervertebral foramen. 2.5 ml of 0.3% ropivacaine is infiltrated into the contralateral intervertebral foramen for the free anesthesia. Subsequently, patients receive the traditional local anesthesia with 0.3% ropivacaine, which is the same as those of the local anesthesia group for SAP anesthesia, trajectory and homolateral skin. Then adjust the needle the homolateral monosegmental intervertebral foramen. A total of 2.5 ml of the 0.3% ropivacaine is infiltrated into the homolateral intervertebral foramen to conduct the sensory-motor dissociation anesthesia. The following surgical procedures is the same as the procedures of conventional PELD.

Outcome measures
Primary outcomes are pain score at different time point. Visual analog scale (VAS) is used to assess the pain (10: the maximum possible pain and 0: absent pain). [11] The secondary outcomes are the operative time, radiation exposure time, length of hospital stay, and postoperative complications. The radiation exposure time is obtained from the G-arm computer at the end of each procedure. Oswestry Disability Index (ODI) [12] is also recorded at 7 days, 12 weeks, and 1 year postoperatively.

Statistical analysis
All data are recorded into the Microsoft Excel 2010, and then they are analyzed via applying the IBM SPSS Statistics for Windows, version 20 (IBM Corp., Armonk, NY, USA). Afterwards, all the data are expressed with appropriate characteristics such as mean, median, standard deviation as well as percentage. Continuous and categorical variables are analyzed using x 2 -tests and independent t tests, respectively. Intention-totreat analysis is used for the outcome assessments. When P value <.05, it is considered to be significant in statistics.

Results
The clinical outcome variables between groups are shown in Table 1.

Discussion
To the best of our knowledge, this is the first randomized controlled trial to assess the safety and effectiveness of bilateral IFB for PELD pain control. LDH is a common orthopedic disease and a worldwide health problem characterized by low-back and radiating pain. [13,14] PTED has become one of the optimal clinical treatments for LDH due to the advantages of minimal invasion, less blood loss, and rapid recovery. [15,16] Surgery and anesthesia are associated with a stress reaction, immunosuppression, and postoperative pain, which prolong hospital stays and increase the economic burden of patients. [9] Appropriate anesthesia is important to achieve improved clinical outcomes. [17] The lack of a definitive "gold standard" and various programs of anesthesia method during operation indicate that there is much room for improving the perioperative pain control. Recently, IFB is popular used in PELD. However, if conducted unilateral IFB only, satisfactory and instant distribution of local anesthetic to the opposite side usually could not be obtained, due to the mass effect of herniated nucleus pulposus, spinal stenosis, intraspinal adhesion, different puncture site and other factors. Therefore, bilateral IFB is recommend for intraoperative pain management in PELD. Considering that the sample size is small. Our findings must be replicated in more research centers and in larger samples, and evaluate over longer periods of follow-up, before final conclusions can be drawn.

Conclusion
This investigation can offer a reliable basis for the effectiveness and safety of IFB in treating the PELD pain.