Efficacy and safety of ultrasound-guided caudal epidural steroid injection in patients with low back pain and sciatica

Abstract

BACKGROUND:

Fluoroscopy-guided caudal epidural steroid injection (EDSI) is an option for conservative treatment of low back pain and sciatica; however, repeated exposure to radiation is a concern. With the blind technique, the needle misplacement rate is 30%; hence, ultrasound-guided caudal EDSI is a favored option.

OBJECTIVE:

To determine the efficacy of ultrasound-guided EDSI for low back pain and sciatica.

METHODS:

One hundred and ten patients with low back pain and sciatica who were unresponsive to conservative treatment, were prospectively recruited. Ultrasound-guided caudal EDSI was administered at 0, 3, and 6 weeks. Visual Analog Scale (VAS) score was recorded at 0, 2, 4, 12, and 24 weeks. Patients completed the Roland-Morris Disability Questionnaire (RMDQ) at pre-injection and 24 weeks post-injection.

RESULTS:

VAS was significantly reduced at 2, 4, 12, and 24 weeks ( $p<$ 0.01). At 2, 4, 12, and 24 weeks after injection, 20%, 26%, 74%, and 83% of patients displayed $>$ 50% VAS reduction, respectively. The mean pre-injection RMDQ score was 15 and that post-injection at 24 weeks was 7 ( $p<$ 0.01). The majority of patients had $>$ 50% reduction in the RMDQ score.

CONCLUSIONS:

Ultrasound-guided EDSI was safe and efficacious for low back pain and sciatica treatment at the intermediate follow-up.

Keywords

Low back pain sciatica epidural injection ultrasound

1. Introduction

Low back pain is defined as pain localized below the costal margin and above the inferior gluteal fold, while the term sciatica is described as an irritation or compression of the sciatic nerve that causes radiating pain originating in the lower back and traveling through the buttock and down the back of the lower leg. Low back pain and sciatica are the most and third most common causes of disability, respectively, in the general population below and above 45 years of age [1]. The most common causes of low back pain and sciatica among the elderly population are intervertebral disc diseases and spinal canal stenosis. With age, disc degeneration leads to a loss of segmental height combined with disc protrusion, hypertrophy of the facets, and development of bony spurs of the vertebral endplates, which can lead to narrowing of the spinal canal and the neural foramina [2]. These can structurally pinch or compress the nerve root and may include biochemical factors due to inflammatory process [3, 4]. This pathophysiological process can lead to incapacitating back pain and sciatica [5]. Conservative treatments to mitigate pain and regain function are the mainstay treatment. Epidural steroid injection (EDSI) therapy has been commonly used in the conservative treatment of low back pain and sciatica. Initially reported by Robecchi and Capra [6] and Lievre et al. [7] in the early 1950s, it has gained more popularity in recent years.

A previous study demonstrated a 50% reduction in the Visual Analog Scale (VAS) score for 35% of patients and functional improvement of 2 points on the Roland-Morris Disability Questionnaire (RMDQ) as a result of caudally placed fluoroscopy-guided EDSI [8]. However, repeated exposure to ionizing radiation is a concern for physicians and patients of reproductive age, and fluoroscopy and contrast agent injection may not be possible in all settings. Ultrasound has become more popular among all specialties of clinical practice given the ease of use, availability, and no risk of radiation exposure to the patient and operator. The sacral cornua and sacral hiatus can be easily located on an ultrasonogram [9]. Hence, ultrasound-guided caudal approach EDSI is a good option for epidural administration in an outpatient setting. A previous retrospective study found that ultrasound-guided EDSI was effective for providing pain relief in patients with lower lumbar radicular pain [10], but only one study reported on the safety of this procedure [11]. To the best of our knowledge, there are no published studies that evaluated the efficacy and safety of this procedure among patients with both low back pain and sciatica. This study thus aimed to determine the efficacy of ultrasound-guided caudal approach EDSI among patients with both low back pain and sciatica, by comparing the improvement in pain and function pre- and post-injection. The treatment adverse effects were also evaluated.

2. Materials and methods

2.1 Patients

This prospective study entailed 110 patients with both low back pain and sciatica. After explanation of the possible consequences, all participants signed an informed consent form for treatment with caudal epidural injections. The inclusion criteria were $>$ 18 years of age and failed conservative treatment with medication and physical therapy for $\geqslant$ 3 months. Patients with a bleeding disorder, signs of infection, progressive motor deficit, cauda equina syndrome, and history of previous lumbar surgery were excluded. The only drugs allowed for pain control in this study were acetaminophen ( $<$ 1000 mg per day) and diclofenac ( $<$ 50 mg per day) for 5 to 7 days per month, the same doses previously prescribed during conservative treatment. The diagnosis was confirmed and the severity determined using magnetic resonance imaging. Herniated nucleus pulposus was defined as a displacement of the disc component beyond the limits of the intervertebral disc space [12]. Spinal canal stenosis was defined as an abnormal narrowing of the spinal canal, where the anteroposterior diameter of the osseous spinal canal was $<$ 12 mm at the level of the endplate [13]. Spondylolisthesis was defined as an anterior displacement of one vertebral body over the other because of the presence of an osseous defect in the posterior neural arch [14]. Pre-injection history, physical examination, and VAS and RMDQ scores were obtained. Ultrasound-guided caudal approach EDSI was administered to every patient by two experienced physicians at 0, 3, and 6 weeks. Patients were followed up until 24 weeks. VAS was recorded at 2, 4, 12, and 24 weeks while the RMDQ was recorded at 24 weeks post-injection. Physicians who evaluated the post-injection VAS and RMDQ were different from those who performed the evaluation before injections and blinded to the treatment. Participants who had a complete response to treatment (VAS score $=$ 0) after the first or second injection were excluded from the analysis.

2.2 Ultrasound-guided caudal approach EDSI

The patients were placed in a prone position. We used the Sonosite M-turbo ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ ultrasound system with a linear probe at 13–6 Hz. Ultrasonography was performed to identify the sacral hiatus and canal (Fig. 1). Diameter of the sacral hiatus was measured as the distance between the two cornua of the sacrum. After identification of the sacral hiatus and skin preparation, the injection site was infiltrated with 2 mL of 1% xylocaine. A 20-gauge (3.5-inch) spinal needle was inserted and advanced under longitudinal sonographic guidance of the sacral canal. After confirming the needle tip position, a lock extension tube was connected to the spinal needle and 15 mL of 1% Xylocaine mixed with 40 mg of Triamcinolone acetonide infiltrated into the epidural space under real-time sonographic guidance. The epidural needle was withdrawn, and the patient placed in supine position.

Figure 1.

Ultrasound presentation of the sacral hiatus A: the short axis view through the sacral cornua (SC): the epidural space is located between the sacrococcygeal ligament (solid arrow) anteriorly and the sacrum (arrowhead). B: the long axis view through the middle of the hiatus.

2.3 Statistical analysis

VAS and RMDQ scores and their reduction were calculated and compared to baseline scores using the Wilcoxon signed-rank test. Baseline characteristics including gender, age, body mass index (BMI), marital status, area of residence, and diagnosis type are shown as mean $\pm$ SD and percentage as appropriate. The reduction in VAS scores was dichotomized using a threshold of reduction at 50%. Logistic regression was used to determine the association between baseline characteristics and unsuccessful pain relief (score reduction $<$ 50%). All analyses were performed using STATA software version 16 (Stata Corp, College Station, TX, USA). This study was approved by the Research Ethics Committee of Faculty of Medicine, Chiang Mai University.

3. Results

3.1 Demographic data

Among the 110 patients who received ultrasound-guided caudal EDSI, 22 (20%) were men and 88 (80%) were women. The mean age was 63 years. Mean height, weight, and BMI were 156 cm, 59 kg, and 23.43 respectively (Table 1). There were no participants with a VAS score of 0 after the first or second injection, and therefore, all 110 participants were included in the analysis. There were no participants lost to follow-up.

Table 1
Baseline characteristics of the patients

		Value $N=$ 110
Gender	Male, $n$ (%)	22 (20%)
	Female, $n$ (%)	88 (80%)
Age (year)	Mean $\pm$ SD	63 (55–71)
Weight (kg)	Mean $\pm$ SD	59 (53–65)
Height (cm)	Mean $\pm$ SD	156 (153–160)
BMI	Mean $\pm$ SD	23.43 (21.78–25.78)
Marital status	Single, $n$ (%)	4 (4%)
	Married, $n$ (%)	83 (75%)
	Divorced, $n$ (%)	5 (5%)
	Widowed, $n$ (%)	18 (16%)
Area of residence	Urban, $n$ (%)	61 (55%)
	Rural, $n$ (%)	49 (45%)
Diagnosis	HNP, $n$ (%)	9 (8%)
	SCS, $n$ (%)	88 (80%)
	Spondylolisthesis, $n$ (%)	13 (12%)

BMI $=$ body mass index, HNP $=$ herniated nucleus pulposus, SCS $=$ spinal canal stenosis.

Table 2

Proportion of pain reduction after injection

Pain reduction	$n$ (%) reduction in VAS after injection				$n$ (%) reduction in RMDQ after injection
	Week 2	Week 4	Week 12	Week 24	Week 24
No reduction	2 (2)	0 (0)	2 (2%)	2 (2)	7 (6)
Less than 50% reduction	86 (78)	69 (72)	27 (24)	17 (15)	45 (41)
At 50% reduction or more	22 (20)	41 (26)	81 (74)	91 (83)	58 (53)

VAS $=$ visual analog scale, RMDQ $=$ Roland-Morris Disability Questionnaire.

Table 3

Odds ratio and 95% confidence interval demonstrated effect of age, HNP, SCS, spondylolisthesis, living with partner, rural and BMI on unsuccessful pain score reduction ( $<$ 50%) at 24 weeks after injection

	VAS			RMDQ
	OR	[95% CI]	$P$ value	OR	[95% CI]	$P$ value
Female	0.92	0.27–3.12	0.900	1.10	0.43–2.80	0.849
Age (year)	0.98	0.94–1.02	0.237	0.97	0.94–1.00	0.078
Age $\geqslant$ 60	0.47	0.17–1.28	0.140	0.43	0.19–0.98	0.045
BMI	0.01	0.87–1.17	0.873	0.94	0.88–1.10	0.786
HNP	1.57	0.18–13.86	0.684	2.33	0.40–13.61	0.346
SCS	1.13	0.23–5.63	0.881	0.97	0.30–3.13	0.962
Spondylolisthesis	0.86	0.17–4.22	0.848	0.95	0.30–3.03	0.931
Living with partner	7.2	0.91–56.74	0.061	2.15	0.87–5.33	0.099
Rural	2.50	0.90–6.95	0.079	0.54	0.25–1.15	0.111
Baseline pain	0.76	0.48–1.19	0.230	1.22	0.85–1.76	0.277

BMI $=$ body mass index, OR $=$ Odds Ratio, 95% CI $=$ 95% confidence interval, VAS $=$ visual analog scale, RMDQ $=$ Roland-Morris Disability Questionnaire, HNP $=$ herniated nucleus pulposus, SCS $=$ spinal canal stenosis.

Figure 2.

Wilcoxon signed rank test chart demonstrated significant reduction in VAS compared at pre-injection and post-injection at 2, 4, 12, and 24 weeks.

3.2 VAS and RMDQ

VAS scores at 0, 2, 4, 12, and 24 weeks post-injection are shown in Table 2. The mean VAS score before injection was 7, while that at 12 and 24 weeks was 3. Significant reduction in VAS scores was observed 2, 4, 12, and 24 weeks after injection ( $p<$ 0.01) (Fig. 2). The proportion of patients who had successful pain reduction, defined as a $>$ 50% reduction in pre- and post-injection VAS scores, were 20%, 26%, 74%, and 83% at 2, 4, 12, and 24 weeks, respectively, after injection (Table 2). There was a significant reduction in RMDQ scores; the mean RMDQ score was 15 at pre-injection and 7 post-injection at 24 weeks ( $p<$ 0.01) (Fig. 3). Fifty-three percent of the patients experienced a $>$ 50% reduction in the RMDQ score (Table 2).

Figure 3.

Wilcoxon signed rank test chart demonstrated significant reduction in RMDQ compared at pre-injection and post-injection at 24 weeks.

3.3 Factors influencing pain reduction

Age, marital status, area of residence, diagnosis type, BMI, and duration of symptoms had no association with reduction in VAS scores; however, age $>$ 60 years was associated with a greater reduction in RMDQ scores ( $p=$ 0.045) (Table 3).

3.4 Complications

Four patients experienced dizziness and nausea after the first injection, but resolved spontaneously. No major serious complications occurred during this study.

4. Discussion

Degenerative spine diseases including disc degeneration, spinal canal stenosis, and degenerative spondylolisthesis are common causes of low back pain and sciatica [15]. Epidural steroid injection is commonly administered for pain relief and functional improvement. The results of this prospective study wherein caudal epidural steroids were administered using ultrasound-guided injections in patients with low back pain and sciatica, demonstrated significant improvement in all parameters at the 24-week follow-up. More than 50% reduction in VAS scores was observed in 83% of the patients and $>$ 50% reduction in RMDQ scores in 53% of the patients. Age $>$ 60 years influenced the RMDQ score; the highest reduction in RMDQ score was experienced by this age group. This may be because people in this age group are typically retired.

Several studies show that low back pain and sciatica result from mechanical compression and chemical irritation of the nerve root [16, 17]. EDSI inhibits the inflammatory mediator phospholipase A2, which is a precursor of E2 prostaglandins, which reduce the permeability of capillaries and inhibit neurotransmitters via nociceptive C-fibers [18, 19], lowering spinal canal adhesion by the volume effect of the injection. Three common approaches for epidural steroid injection are interlaminar, transforaminal, and caudal. The most common approach for all indications in anesthesia is the interlaminar approach. Previous studies revealed superior results with the bilateral transforaminal approach compared to the interlaminar approach in reduction of the Roland-5-point pain scale scores and an increased patient satisfaction index [18]. A double-blind study demonstrated significant short-term and long-term pain relief using the caudal approach EDSI among patients with chronic low back pain and sciatica [20], while a systematic review reported better results in terms of efficacy of the caudal approach compared to the interlaminar approach [21]. Accurate needle placement into the epidural space is crucial. There are several methods for detection of the sacral hiatus and confirmation of correct needle position. The most common clinical landmark to identify the sacral hiatus is palpation of both sacral cornua and identification of the soft spot in between. The physician can feel the resistance of the sacrococcygeal ligament and the “pop” sound when the needle advances into the epidural space. The whoosh test to confirm the correct needle placement inside the epidural space involves the injection of 2 mL of air. The physician will feel no air under the skin if the needle is in the proper position. However, with no imaging guidance, only 64% to 74% of caudal epidural injections were observed to be correctly placed within the epidural space [22, 23]. Klocke et al. first described the successful use of ultrasound to identify correct caudal epidural steroid injection in an obese patient [24]. The avoidance of a potential radiation hazard makes the use of ultrasound-guided EDSI an accepted alternative approach.

Our study is in line with several previous studies. A previous systematic review and meta-analysis by Liu et al. demonstrated reduction in pain and functional improvement among patients with lumbosacral radicular pain treated with caudal epidural steroid injection [25]. Manchikanti et al. also reported significant pain relief in 76% cases of lumbar disc herniation and radiculitis, with over 50% reduction in pain after caudal EDSI [26]. Waldman et al. reported that caudal EDSI treatment for patients with a herniated lumbar disc indicated a significant reduction in combined VAS scores for 63% of the patients at 6 weeks, 67% at 3 months, and 71% at 6 months [27]. Ibrahim et al. also reported that ultrasound-guided caudal EDSI led to significant pain reduction and improved nerve function in patients with chronic radicular low back pain [28]. Another study by Park et al. revealed successful results of ultrasound-guided caudal EDSI in patients with lower lumbar radicular pain ( $>$ 50% improvement in the verbal numeric pain scale) among 53.4% of the patients [10].

Ultrasound-guided caudal EDSI has some limitations. An incorrect injection site causes low treatment effectiveness. In the study by Chen et al., patients with a closed sacral canal and a sacral hiatus diameter in the range of 1.5 mm as detected by ultrasound experienced a high rate of failure of caudal EDSI [9]. The major limitation of ultrasound-guided caudal EDSI is accidental intravenous injection, which can occur in approximately 5–9% of cases [22, 23] and cannot be detected during real time ultrasound-guided EDSI. Our study also reported four patients who experienced nausea and dizziness after the injection, which may be due to inadvertent intravenous injection.

Our study has some limitations. First, although prospective, the study was not a randomized controlled trial. However, the study participants were similar in terms of baseline characteristics due to our rigorous inclusion and exclusion criteria. Second, the duration of follow up was short.

5. Conclusions

Ultrasound-guided EDSI is feasible and efficacious for the treatment of low back pain and sciatica at the intermediate follow-up (2 to 24 weeks) with no serious complications.

Footnotes

Conflict of interest

None to report.

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