The protocol for the study underwent review and approval by the Clinical Research Ethics Committee of Thammasat University, with registration number MTU-EC-OO-OT-1-044/60. Written informed consents were obtained from the patients. We conducted a non-randomized prospective longitudinal therapeutic cohort study on patients exhibiting symptoms of lumbar radiculopathy, who visited Thammasat University Hospital from the beginning of April 2017 to the end of December 2021. The following are the inclusion criteria: patients must be 18 years old or older and must have radiculopathy (pain, numbness, or weakness) that radiates down their lower extremities more than their back pain. The symptoms must have lasted for less than 3 months in total. All participants must have received a diagnosis of either lumbar disc herniation or spinal stenosis, including grade I spondylolisthesis without spinal instability, from orthopedic spine specialists who confirmed the diagnosis using magnetic resonance imaging or computed tomography myelogram. The need for ESI was not greater than two levels and was confirmed by spine specialists.

Patients who had undergone spinal surgery previously, those with traumatic back pain, and those with back pain caused by diseases other than those mentioned were excluded. Patients with sequestered lumbar disc herniation, severe anatomical distortion, metastatic tumor, cauda equina syndrome, or conus medullaris syndrome, and patients with progressive neurodeficits were excluded from the study. Women who are pregnant or lactating, individuals with a history of or potential for adverse reactions to contrast, those taking anticoagulants or antiplatelets, and individuals with poorly controlled underlying diseases such as diabetes and hypertension are among those excluded from participation. Patients who experienced complications from treatment, those who required surgical intervention, and those who did not return for follow-up after treatment were implicitly excluded from the study.

All participants were divided into two groups: the non-contrast group (NC group) and the contrast group (C group). All participants were assessed using a Numerical Rating Scale (NRS) before treatment, as well as at 5 minutes, 2 hours, 2 weeks, and 2 months after treatment [12,13]. Evaluation done by the Thai version of the Oswestry Disability Index (ODI) [14] prior to treatment and 2 weeks and 2 months after treatment. All ESIs without contrast were performed by the orthopedic spine specialist, while ESIs with contrast were performed by two orthopedic spine specialists (R.A., K.S.). For the steroid preparation, triamcinolone acetonide (TA) 40 mg/mL with 1% lidocaine was used. A single 1 mL (40 mg) dose of TA was administered for patients requiring no more than two sites of ESIs. For patients requiring three or four sites of ESIs, a 2 mL (80 mg) dose of TA was given. TA was mixed with 1% lidocaine at a ratio of 2 mL per location of ESI.

All ESIs were performed using the transforaminal approach with patients positioned in a prone position on a radiolucent table. The procedure was carried out with the aid of uniplanar fluoroscopic guidance to precisely position the needle just below the pedicle of the required level. Local anesthetic was administered at the marked area for all cases. The dosage used was 1 mL of TA and 1% lidocaine. In NC group, a 9 cm, 23G Quincke spinal needle (Becton Dickinson S.A., Madrid, Spain) was inserted vertically toward the pedicle targeting the safe triangle [15]. This triangle is defined by the pedicle as the superior border, the lateral border of the vertebral body as the lateral border, and the outer margin of the spinal nerve as the inferior border. The needle should be positioned below the pedicle and to the side of the line that connects the centers of the pedicles. At the L5–S1 level, the needle tip is positioned below the L5 pedicle and slightly to the side of the lamina’s outer edge. The needle’s position was verified using an anterior-posterior view with fluoroscopy (Fig. 1), taking into account the presence of provocative pain. As the needle touches the nerve root sheath, the patient feels tingling sensations in their foot and a sharp, stabbing pain in their leg [16]. The solution, consisting of 2 mL of TA (40 mg/mL) and 1% lidocaine, was slowly injected at each necessary position.

In C group, the position of a 9 cm, 23G Quincke spinal needle was also checked under fluoroscopy. The key is to position oneself within the safe triangle on the anterior-posterior view, which is located above the intervertebral neural foramen or under the pedicle on the lateral view. After injecting 0.5 to 1 mL of Iohexol (300 g/mL, Omnipaque; Patheon Italia S.p.A., Monza E Brianza, Italy), the fluoroscopy was used to obtain anterior-posterior and lateral views to confirm the needle’s position. After confirming the needle’s position in the epidural space, a 2 mL solution of TA solution (40 mg/mL) and 1% lidocaine was slowly injected. The procedure was repeated at every planned position. Each patient underwent NRS evaluation at 5 minutes and 2 hours following the procedure. All patients were monitored for a minimum of 4 hours following the procedure to detect any potential complications.

All patients will receive the same pain control medication, which includes non-steroidal anti-inflammatory drugs, muscle relaxants, and gabapentinoids. The patients were scheduled for appointments at the outpatient clinic every 2 weeks and 2 months. If patients showed any signs of complications, they would receive appropriate treatment as necessary.

According to previous studies [17,18], the mean weight of ODI score in herniated nucleus pulposus and sciatica pain was 44.65 [17], with a standard deviation of 15 [18]. A two-sample test of equality of means [19], with a power of 80% and a 5% significance level, was used to detect the difference in ODI scores at 10, resulting in a sample size of 36 patients per arm. Standard descriptive statistics were calculated. The Student t-test and Mann-Whitney U test were used to analyze the differences in preoperative NRS, preoperative ODI, operation time, and fluoroscope dosage between the two groups. A Pearson’s chi-square test was conducted to analyze the variations in the frequency of ages, diagnoses, and levels of injection. The repeated analysis of variance test was conducted to analyze the variations between the postoperative NRS (5 minutes, 2 hours, 2 weeks, and 2 months) and postoperative ODI (2 weeks and 2 months). All analyses were two-sided, and a p-value less than 0.05 was considered statistically significant.

The Numerical Rating Scale (NRS) was assessed prior to the procedure and at 5 minutes, 2 hours, 2 weeks, and 2 months post-procedure. There is no significant difference in baseline NRS between the two groups (p-value of 0.49). At the 5-minute interval, both groups experienced a 55% decrease in NRS score compared to baseline. The C group (contrast) demonstrated a statistically significant decrease in NRS score (3.39±1.54) compared to the NC group (non-contrast; 3.86±0.72) with a p-value of 0.039. After 2 hours, both groups experienced a reduction in NRS of approximately 70% from baseline. However, there was no significant statistical difference between the two groups, although the C group had a slightly lower NRS (2.53±0.74 versus 2.54±0.74) with a p-value of 0.98. Two weeks after the procedure, it was observed that the NRS score had slightly increased, with an NRS of 3.52±1.24 in the NC group and 3.53±1.13 in the C group. There was no significant statistical difference between the two groups, with a p-value of 0.947. After 2 months, the NRS in the NC group (3.2±0.86) was slightly lower than in the C group (3.55±1.11), but this difference was not statistically significant (p=0.059) (Table 2, Fig. 2).

The ODI was assessed as a baseline prior to the procedure, and then again at 2 weeks and 2 months after the procedure. The C group had a lower ODI compared to the NC group at all three evaluation time points (baseline, 2 weeks, and 2 months), with a mean of 40.18±7.54 versus 41.32±5.90 (p-value of 0.359), 23.5±6.67 versus 24.26±6.52 (p-value of 0.534), and 22.75±6.61 versus 23.19±6.15 (p-value of 0.706), respectively. However, these differences were not statistically significant. Data from both groups showed a significant improvement in ODI after the procedure at 2 weeks and 2 months compared to baseline, with a mean increase of 17 units (p<0.001) (Table 3, Fig. 3).

After calculating the duration of each procedure from when the patient entered to when they left the operating room, it was found that the NC group had a significantly shorter procedural time. The mean time for the NC group was 20.96±4.90 minutes, while the C group had a mean time of 23.73±4.72 minutes, with a p-value of 0.002. When considering the number of lumbar levels, the NC group had a significantly shorter procedural time of approximately 4 minutes per level compared to the C group (12.58±3.30 minutes versus 16.70±5.94 minutes, p=0.0001).

Considering the amount of radiation exposure in each procedure, it was found that the NC group had a lower fluoroscopic dosage compared to the C group (3.62±1.66 mGy versus 5.32±2.74 mGy, p=0.0001). While analyzing the number of lumbar levels, it was found that the NC group had a 40% lower fluoroscopic dosage than C group (2.00±0.52 mGy compared to 3.45±1.36 mGy, p<0.0001) (Table 4 and Figs. 4, 5).