This prospective cohort study was approved by the Ethics Committee of West China Hospital, Sichuan University and was registered with the Chinese Clinical Trial Registry (ChiCTR1800019551). The study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants prior to surgery.
Here, except for 2 patients who refused to participate in the study and 2 patients with controversial diagnosis, 69 patients with single-level LLSC stenosis, simultaneously occurring in both zones 1 and 2 from November 2018 to April 2019, were enrolled. All of the included patients underwent DPLF–PELD performed by one endoscopic spine surgeon (KQQ). Table 1 presents the characteristics of 69 patients. LBP, muscle weakness of the lower limbs, extremity radiating pain with/without gluteal pain, and neurogenic intermittent claudication were observed in 5 (7.2%), 1 (1.4%), 62 (89.8%), and 53 (76.8%) patients, respectively. No patients had a history of surgeries.
Inclusion and exclusion criteria
The study included the following patients: (1) Those who manifested a single nerve root symptom, such as single-side extremity pain, numbness, or weakness with or without LBP. (2) Those who possessed full preoperative radiological information. The method of distinguishing the stenotic zone has been described in a previous study (figure 1). Stenosis in zone 1 was diagnosed by sagittal T2-weighted MRI scans through the paracentral region: the anteroposterior distance measured less than 1 mm. Stenosis in zone 2 was diagnosed by axial bone window CT scans, which showed that the anteroposterior distance in the lateral recess region was less than 3 mm. The radiological diagnosis should be related to clinical symptomatology. The preoperative blocking of the nerve root could be applied in some intractable cases. (3) Those who presented with obvious symptoms (preoperative leg pain visual analog score [VAS] score over 6) after over three months of ineffective conservative treatment. (4) Those who provided informed consent for our study and agreed to attend all required follow-up visits.
The study excluded the following patients: (1) those with lumbar segmental instability indicated by preoperative lumbar flexion-extension x-rays; (2) those who were diagnosed with lumbar central canal stenosis; (3) those who were diagnosed as having a pure lumbar disk herniation; (4) those with a high-grade lumbar spondylolisthesis with multilevel spinal stenosis or other deformity; (5) those exhibiting a high iliac crest, with the peak of the iliac crest surpassing the lower quarter of the L4 vertebral body, hindering puncture at L5/S1; and (6) those with any type of surgical contraindication.
In order to minimize the selection bias, in addition to strictly grasping the inclusion and exclusion criteria, three observers (WY, DMY and WH) simultaneously judged the stenosis area of each patient through preoperative CT and MRI imaging data. Each observer was blinded to the patient. The patient will be included in the study only when all three observers judged that the stenosis occurred in both zones 1 and 2. This method is similar to the reliability test in our previous study.
Special surgical tools
Specially designed depth-limited trephine for foraminoplasty (ZL 201621149959.2): consisted of a trephine, handle, and stopper (figure 2). The saw tooth of the trephine was no different from the traditional trephine. The diameter of the trephine had various sizes: 6.5 mm, 7.5 mm, and 10 mm. However, the total length of the trephine is identical at 243 mm. At the proximal end of the trephine, 17 circular grooves are designed. The first groove is 165 mm away from the distal end of the trephine, and there is an interval of two mm in the next adjacent grooves. The depth of foraminoplasty was accurately controlled and limited by the stopper located in the trailing end of the trephine. The stopper is locked in one of the grooves, thus preventing the advancement of the trephine. The exact foraminoplasty depth required can be adjusted based on the stopper location. The handle can be easily assembled and disassembled from the trephine.
All DPLF–PELD procedures employed by the author were essentially a classic THESSYS technique popularized by Hoogland. The entire procedures were performed under local anesthesia, with the patient in the prone position on a radiolucent table, using C-arm fluoroscopy. A 1.6 mm Spinal Guiding Cannulas (SPINENDOS, Germany) was inserted into the safe zone of Kambin’s triangle. The puncture point was 12 ± 2 cm from the midline, according to the size of the body and surgical level, and 2–5 cm from the horizontal line of the target intervertebral disk. After infiltrating 15–20 ml of 0.5% lidocaine into the subcutaneous soft tissue, around the SAP, and intervertebral foramen, the needle was replaced with a 0.7-mm-diameter guiding wire. A dilator 2-channel (7.0-, 6.3-, or 5.3 mm-diameter) was passed over the guiding wire under fluoroscopic control. A trephine protection tube (6.5-, 7.5-, or 8.5-mm-diameter) was introduced over the obturator until it was situated in the proper position. The depth-limited trephine designed by us (6.5-, 7.5-, or 8.5-mm-diameter, selected based on pathologic conditions) was used to perform two-time foraminoplasty, which was facilitated by changing the trajectory of the trephine, to aim for different compressive portions. The details of the two foraminoplasty procedures are shown in table 2 and figure 3.
In the first foraminoplasty, the scale of the resection could be slightly adjusted, based on different pathologic conditions. After the first foraminoplasty, a radiofrequency probe was endoscopically used (working tube with an elevator tip, ID 7.2 mm, OD 8.0 mm, and L178 mm; spinal endoscope, 30° direction of view, WC 3.75 mm, OD 6.3 mm, and WL 181 mm) to control bleeding and to adequately expose bony structures by resecting any adherent soft tissue. The margin of exposure should run from the upper-ventral surface of the SAP to the lower-ventral surface of the SAP and upper surface of the pedicle. Next, a 1.5-mm Kirschner wire was inserted into the aiming site. After removing the spinal endoscope, the second foraminoplasty was then performed, after positioning the trephine protection tube over the Kirschner wire and adjusting its tip to embrace the ventral-basal aspect of the SAP. In some severe stenosis cases, to prevent injury to the nerve roots, we only inserted the trephine into the three quarters of the SAP, thus breaking the involved SAP, instead of performing a complete resection by the trephine. For the two foraminoplasty procedures, the trephine needed to be underdraught, thus aiming to resect more of the SAP. The order of the two steps can be adjusted according to different situations.
In the following step, the trephine protection tube was replaced with the working tube with an elevator tip. High-speed drilling was then used to resect the remaining hypertrophied SAP or IAP as needed. The working tube was adjusted to completely remove decompressive factors: the hypertrophied ligamentum flavum, facet joints, and anterior herniated disk. To reduce the recurrence rate of lumbar disk herniation (LDH), we did not perform discectomy (only decompress dorsal compressive factors) for patients whose annulus was not damaged. The compressed nerve root was decompressed and explored from the distal end to near-end, especially at the attachment point of the annulus. The surgeon could see and mobilize both the traversing nerve root and the exiting nerve root under endoscopic visualization. Free movement of the dural sac and nerve root could be a sign of complete decompression. Epidural bleeding was controlled with a radiofrequency probe under saline irrigation.
For each operation duration, times of intraoperative C-arm fluoroscopy use and any complications were recorded. Every patient was asked to wear lumbar protection devices for two to four weeks after the operation, and to take muscle function exercise the initial two weeks following the surgery.
Outcomes were evaluated via follow-up interviews (WY) who was blinded to each patients at three months and a final follow-up post-surgery. We used LBP, leg pain VAS, and Oswestry disability index (ODI) to evaluate the outcomes of surgery. Function outcomes were assessed using the modified Macnab criteria. All patients routinely underwent 3D-reconstructive CT scans two days after the operation as well as MRI and CT scans after three months to confirm complete decompression. In the final follow-up, patients underwent CT to confirm no recurrence of LLSC stenosis, and flexion-extension x-rays to observe for lumbar stability. All patients’ postoperative radiological exams are permitted to be discharged.
Sample size calculation
Calculation of the required sample size for this study is not constructive. This study is a case series based on the assumption that for introducing and acquiring experience in a new operative technique. We ultimately included 69 cases in the study though a sample size of 30 patients is enough according to previous reports.
Statistical analysis was performed with SPSS 23 software (SPSS Inc., Chicago, IL). Preoperative and postoperative (three-month and final follow-up) VAS and ODI scores (calculated as mean ± standard deviations) were analyzed with analysis of variance (ANOVA). Here, p < 0.05 was considered the threshold for significance.