A total of 1,100 patients who had been diagnosed with single-segment LDH by X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) and underwent lumbar discectomy with IFD or TELD between January 2012 and December 2017 in our hospital were included in this study. All patients underwent formal conservative treatment, including bed rest, lumbar traction, physical therapy and oral nonsteroidal anti-inflammatory drugs for 3 months. Patients with an inadequate response to treatment were then treated with surgery. Other inclusion criteria were that the herniation site was L3/4, L4/5 or L5/S1 herniation and that the herniation type was posterolateral, central, paracentral or extreme lateral herniation. The exclusion criteria were as follows: (1) obvious lumbar instability evident on X-ray, (2) central stenosis confirmed by CT or MRI, (3) severe ossification of the posterior longitudinal ligament, (4) large posterior central herniation, (5) unconsciousness or inability to adhere to the treatment, (6) refusal to sign the informed consent form, (7) a lumbar deformity or tumour, (8) infection at the surgical site, and (9) severe liver and kidney dysfunction or cardiovascular or cerebrovascular disease. Patients were divided into two groups: Group A underwent IFD and Group B underwent TELD.
Each patient in Group A was placed in the prone position under general anaesthesia. A 4–6 cm posterior midline incision was made with the deteriorating segment positioned in the centre. The lumbar fascia was exposed, and the attachment of the spinalis muscle was cut near the spinous process so that the supraspinous and interspinous ligaments were preserved. The soft tissue behind the laminae was stripped to reveal the intervertebral space, upper and lower lamina and small joints. A laminar rongeur was used to remove the ligamentum flavum between the lamina and small portions of the upper and lower lamina adjacent to the deteriorating segment; thus, interlaminar fenestration was performed. A neuroexfoliator was used to separate and gently retract the nerve root, revealing the intervertebral disc. The fibrous ring was cut, and the nucleus pulposus was removed with dedicated forceps. The incision was closed [4, 12].
Each patient in Group B was placed in the lateral recumbent position. C-arm X-ray was used to locate the surface projection of the intervertebral space of interest. An entry point was made 12–14 cm from the posterior midline of the spine at the level of the disc. Local anaesthesia was administered (1% lidocaine). A puncture needle was slowly advanced to the fibrous ring in the intervertebral space and positioned at the outer edge of the superior articular process. It was located lateral to the intervertebral space near the upper edge of the lower vertebra. One millilitre of methylene blue was injected into the intervertebral disc for contrast radiography. A guidewire was inserted, and X-ray was used to confirm that the tip of the guidewire had crossed the articular process and then the puncture needle was withdrawn. An 8 mm incision was made at the entry point. The cannulas were passed from thin to thick along the guidewire, and the superior articular process was partially removed with a ring drill. The working cannula was then inserted into the epidural space. A transforaminal endoscope (TESSYS® [transforaminal endoscopic spine system], joimax® GmBH, Germany) was inserted, and the degenerative, blue-stained intervertebral disc was removed. Part of the nucleus pulposus was ablated by a radiofrequency electrode (Ellman, USA). The spinal canal was assessed carefully, and the nerve root was detached. After the wound was rinsed, the fenestrated fibrous ring was repaired by electrocoagulation. The working cannula was then removed, and the incision was closed .
Patients were asked to perform straight leg raises in bed on the same day after surgery, and off-bed training with lower back braces was initiated two days later for Group A patients, or one day later for Group B patients.
Patients were asked to use the Visual Analogue Scale (VAS)  to rate the severity of the pain in their lower back and legs before surgery, 1 month after and at the final follow-up appointment. A score of 0 points corresponded to no pain; 1 to 3 points, to slight pain; 4 to 6 points, to obvious pain that affected sleep but was still tolerable and 7 to 10 points, to intense, unbearable pain. Functional changes were evaluated using the ODI , which has 10 questions on the severity of pain, ability to perform self-care, lifting objects, walking, sitting, standing, sleeping, social life and travel. There are six response options for each question, and the highest score for each question is 5 points. The lower the score was, the better the postoperative recovery. The MacNab criteria  were used to evaluate surgical efficacy. Patient outcomes were graded as excellent, good, fair or poor, representing no symptoms, mild symptoms and slight limitations in mobility, improved symptoms but large limitations in mobility and unimproved or even worsened symptoms, respectively. The excellent and good rate was calculated as follows: (excellent + good)/total cases × 100%.
SPSS 19.0 (SPSS, IL, USA) software was used for the statistical analyses. Measurement data are expressed as the mean ± standard deviation (x ± s). Comparisons between groups were performed by one-way analysis of variance and t-tests. Comparisons of the count data, as well as the ‘excellent’ and ‘good’ rates between the two groups, were performed using the x2 test. P < 0.05 indicated a significant difference.