This retrospective cohort analysis included a total of 72 patients with unilateral lumbosacral radiculopathy caused by single-level LDH. In the present study, forty-one patients with LDH underwent PTED, and the other 31 patients underwent traditional discectomy described by Caspar with or without laminotomy (Table 1) . All patients were recruited in SongJiang district central Hospital from December 2017 to March 2019. The study protocol was approved by Human Ethics Committees (Songjiang district central hospital, Shanghai, China; SJ2017-KY032). All subjects gave informed consent.
The inclusion criteria for patients with LDH includes [13, 14] (1) low back discomfort with referral of pain or paresthesias into a single lower limb following an L4/L5/S1 distribution pattern; (2) lumbosacral magnetic resonance imaging (MRI) or computer tomography (CT) that demonstrated unilateral L4/L5/S1 nerve root compression by herniated disc at the L3/4, L4/L5 or L5/S1 level; (3) conventional electrophysiologic studies including normal sensory nerve conduction studies and a needle EMG revealing the presence of disease only on the involved side of abnormal spontaneous activity and/or changes in motor unit action potential in muscles that were innervated by the involved L4/L5/S1 root. (4) Surgical findings of unilateral compressed herniated discs at the L4/L5/S1 root on the involved side. (5) Postoperative drain for 3 days. The exclusion criteria for patients with LDH includes previous spinal surgery, polyneuropathies, plexopathies, focal neuropathies, muscle disorders, cauda equina syndrome, scoliosis, spondylolisthesis, vertebral fractures, and other spinal pathologies. Furthermore, patients with incomplete medical records or lost to follow-up were excluded.
All patients underwent open discectomy performed by the same spine surgeon experienced in this technique. After the general anesthesia, the patient is placed in a knee-chest position, and intervertebral segment to treat is located by a positioning needle under the C-arm fluoroscopy. After performing a paramedian 3- to 4-cm skin incision, a unilateral interlaminar approach is used, and the superior facet is partially removed if needed to provide a good view of the involved nerve root. A small annular incision is performed to remove the herniated disc part before smoothly extracting the mobile disc fragments. The intervertebral space is cleaned by suction without any excessive curettage. Afterwards, the canal is inspected to ensure that there is no more detached disc fragment and that the nerve root is freely mobile after decompression.
Percutaneous transforaminal endoscopic discectomy:
All patients underwent PTED performed by the same spine surgeon experienced in this technique. The PTED procedure was performed in the prone position using C-arm fluoroscopy under general anesthesia, and the positioning needle trajectory was planned on the preoperative MRI/CT to target the intervertebral foramen. The needle was introduced 10-13 cm lateral to the midline, with the transit corridor in Kambin’s triangle, and C-arm fluoroscopy was used during needle introduction to validate correct positioning. Then, Sequential reamers (joimax, Irvine, California, USA) were used to enlarge the neural foramen by removing the ventral aspect of the superior facet. The cannula and endoscope were then introduced, and herniated disc material was removed using endoscopic forceps under cold saline irrigation.
A drainage tube was placed for 72 hours. Antibiotics were given at postoperative 48 hours to prevent infection, and both hormone and non-steroidal anti-inflammatory drugs were not used in all patients in this study after operation. After one day of bed rest, the patients were allowed to walk with the protection of a waist brace. When the patients presented with postoperative reactive pain, the non-steroidal anti-inflammatory drugs were used until the Numerical Rating Scale（NRS）scores are lower than 3.
Assessment of pain:
Lower limb pain in all patients with LDH were measured by NRS scores before and 1 day after operation, and the NRS scores was further evaluated in the patients with reactive pain. In this study, the reactive pain was defined as preoperative pain relief after surgery followed by the recurrence pain at the primary site or other sites in lower limbs, and NRS score of this recurrence pain should increase at least 2 points compared to postoperative initial pain. NRS scores is a continuous scale composed anchored by a score of zero, indicated no pain, and a score of 10, represented the worst pain.
Assessment of venous blood and drainage fluid samples:
Venous blood samples were obtained before surgery and on the first, third, and sixth days after operation, and the wound drainage fluid was collected from first to third day after operation. The blood samples were collected and immediately centrifuged at 3000rpm for 10min, and they were then stored at -20°C until assayed. The drainage fluid samples were collected and immediately centrifuged at 1500rpm for the first 15min and 3000rpm for the second 15min, and they were then stored at -80°C until assayed. For the blood samples, white blood cell (WBC) count, interleukin-6 (IL-6), C-reactive protein (CRP) and creatine kinase (CK) were measured. In the drainage fluid samples, both interleukin (IL)-1β and IL-6 were measured.
Both IL-1β and IL-6, as well as CRP, were analyzed by the enzyme-linked immunosorbent assay (ELISA) according to the protocol provided by the manufacturer (R&D Systems, Inc., USA). Take out the EP tube and thaw at room temperature. The kit includes sample hole, standard sample hole and blank hole. The standard holes were continuously dripped with 50 μL of standards with different concentrations, and the sample hole first add 10 μL of the sample to be tested, then add 40 μL of sample diluent. Except for the blank hole, first drop 100 μL of detection antibody labeled with horseradish peroxidase (HRP) into the standard hole and sample hole, seal the reaction hole with a sealing film, and incubate in a constant temperature box (37 ℃, 60 min); after discarding the liquid, blot dry with absorbent paper, fill up the washing liquid in each well, let stand for 1 min, shake off the washing liquid, blot dry with absorbent paper, repeat 5 times, wash buffer and distilled water Prepared at a ratio of 1:19; add 50 μL of A and B substrates to each well, and incubate in the dark at 37°C for 15 min. After adding 50 μL of stop solution to each well, measure the optical density of each well at the wavelength of 450 nm within 15 minutes, and obtain the concentration according to the kit instructions. The detection limits of this assay were 0.19 pg/ml for IL-6, 0.3 pg/ml for IL-1β and 0.10 mg/dl for CRP.
The measurements were analyzed using SPSS version 18.0 (IBM, USA). Measurements between the cases in two patient groups were compared by the independent t-tests, and the same statistical method was also used to analyze the measurements between the cases with or without reactive pain in both patient groups. The frequencies of postoperative reactive pain between two patient groups were compared by chi-square tests. The correlations between both duration and extent of reactive pain and inflammation related markers in both blood and drainage fluid samples were analyzed by Pearson correlation coefficient analysis. In all instances, a P-value < 0.05 was considered significant.