The Importance of Image Guidance in Common Spine Interventional Procedures for Pain Management: A Comprehensive Narrative Review

Abstract

Introduction

Image-guided spinal injections are commonly performed by pain physicians and supported by literature. A recent survey showed that half of the Canadian providers still perform landmark-guided injections. This comprehensive review aims to describe the evidence supporting imaging modalities (fluoroscopy, computed tomography (CT) and ultrasound) in improving the accuracy and safety in several commonly performed spine injections. Relevant anatomy and pitfalls of landmark-guided injections are also discussed.

Methods

An extensive literature search was conducted in PubMed, Medline and Embase databases, complemented by a manual search. Search terms included all spine interventions and imaging modalities.

Results

Literature shows that incorrect needle placement without imaging guidance can reach 50% in caudal, 30.4% in lumbar interlaminar and 53% in cervical interlaminar epidural steroid injections. Lumbar and cervical transforaminal steroid injections require imaging to identify intravascular or intradiscal needle placement; misplacement rates can be as high as 20% at cervical, 8% at thoracic, 6–15% at lumbar and 16.5–21% at sacral levels. Imaging techniques for sacroiliac joint steroid injections are superior to non-imaging techniques, while medial branch blocks and facet joint injections require image guidance.

Conclusion

Image guidance is a mandatory requirement when performing spinal procedures for pain management. Fluoroscopy enhances the safety and accuracy of spinal injections, with stored images benefiting patient records. Ultrasound also has an increasingly important role either alone or with fluoroscopy. CT is also effective but with limited accessibility.

Key Summary Points

Image guidance enhances the accuracy and safety of spinal injections.

Landmark-based techniques have high misplacement rates, risking complications.

Fluoroscopy is the gold standard for spinal procedures, with real-time guidance.

Ultrasound offers a radiation-free alternative but requires expertise.

Regulatory bodies mandate imaging to improve patient safety and outcomes.

Introduction

Globally, lower back and neck pain are a major public health problem with high prevalence, incidence and years lived with disability [1, 2]. According to the Global Burden of Disease, in 2020, low back pain affected 619 million people around the world, with a projection of 843 million prevalent cases by 2050 [1]. Neck pain affected 203 million people; the global age-standardized prevalence of neck pain was estimated to be 2450 per 100,000 people, while the years lived with disability were estimated at 244 per 100,000 people [2].

Image-guided spinal injections are commonly performed in symptomatic patients to decrease pain severity, confirm the pain source, and delay or avoid surgery [3]. Epidural steroid injections have been mentioned as a treatment option since 1901 [4–6] and became a fundamental treatment for low back pain and sciatica in the 1970s [3]. Image guidance for spine injections was introduced around the 1980s and undoubtably offered more accuracy over the landmark-based approaches even for experienced physicians [7]. By utilising fluoroscopy, the interventionist can determine the accuracy of needle placement and understand the pattern of injectate flow [3]. Additionally, a targeted injection can improve the effectiveness while the steroid dose can be decreased, minimising its potential short- and long-term side effects [8, 9]. Image guidance has also allowed an expansion of procedures, including nerve root blocks, facet joint injections, sacroiliac joint injections and injections for spondylolisthesis secondary to pars interarticularis defects. Image guidance can also facilitate the epidural injections that are performed via the caudal, interlaminar or transforaminal route [10].

Although the importance of fluoroscopic guidance for epidural steroid injections has been clearly emphasized a few decades ago [11], many clinicians still perform this technique “blindly” [12]. A recent survey in Canada revealed that only 52% of providers are performing spine interventions under image guidance [13]. Besides fluoroscopy, other imaging modalities such as computed tomography (CT) and ultrasound (US) have been adopted for image-guided spine intervention [12, 14]. The rationale of using imaging equipment for spine interventions is aiming towards the improvement of accuracy and the enhancement of safety.

Numerous reviews on the importance of imaging in spine interventions have been published. To our knowledge, no single review comprehensively covers all imaging modalities (US, fluoroscopy and CT scan) in those commonly performed spine interventions. Furthermore, none of those previous reviews explored the reasons behind the failure of the conventional loss of resistance method in patients with spine pathology. The objective of this comprehensive review is to assess the use of various imaging equipment (fluoroscopy, CT scan and US) in improving the accuracy and safety in different commonly performed spine injections. The anatomy pertinent to the understanding of the pitfalls of landmark-guided injection is also discussed.

Methods

We performed an extensive literature search in PubMed, Medline and Embase databases as well as a manual search for additional references from the most recent reviews and additional sources of primary literature, as well as references cited by relevant articles considering publications up to July 2024. The search terminology included all spine interventions and different imaging modalities.

All searches used a combination of the following research keywords: (“epidural injection” OR “epidural steroid” OR “caudal” OR “nerve root” OR “dorsal root ganglion” OR “transforaminal” OR “facet joint” OR “medial branch” OR “zygapophyseal joint” OR “sacroiliac joint” OR “spinal injection”) AND ((“fluoroscopy” OR “X-ray”) OR (“blind or landmark”) OR (“CT” or “Computed Tomography”)). Only full-length original articles were accepted, and the search was limited to English-language publications. All retrieved articles were reviewed by title, abstract, and the article itself when its content was not clearly indicated by the title and abstract. The inclusion criteria were as follows:

1. The article referred to commonly performed chronic pain spine interventions.

2. Authors were comparing landmark-based (or “blind”) technique with imaging modalities or different imaging modalities.

This article is based on previously conducted studies; therefore, no ethical approval was required. SANRA (Scale for the Assessment of Narrative Review Articles) criteria were followed [15]. The PRISMA statement was used for the presentation of our search strategy [16].

Results

The initial search returned 2278 results, with 562 articles eligible. After reviewing those articles, we found that only 30 were relevant for inclusion (Fig. 1). The results of the analysis are divided into three sections: (i) the accuracy of the spine interventions with fluoroscopy, (ii) the accuracy of US- and CT-guided spine interventions and (iii) the anatomic basis for the failure of the landmark-guided technique.

Fig. 1.

PRISMA 2020 flow diagram for new systematic reviews which included searches of databases and registries only

Accuracy of Landmark- Versus Fluoroscopy-Guided Spinal Pain Procedures

The first published paper exploring the accuracy of landmark-based epidural injections was published in 1980 [17]. Since then, many authors have published their studies describing the accuracy and effectiveness of their techniques, comparing different imaging methods either with one another or with landmark-based approaches. With a systematic approach, we have identified those studies and present them in this review (Tables 1, 2, 3).

Table 1.

Landmark-based epidural steroid injections (caudal and lumbar)

Author (year)	Study type	Spinal level	Total no. of procedures	Needle insertion technique	Incorrect needle placement (assessed with fluoroscopy)	Intravascular needle placement (assessed with fluoroscopy)
Renfrew et al. (1991) [7]	Prospective	Caudal epidural	316	Landmark based	52.3% by inexperienced staff (less than 10 blocks) 46.4% by medium experienced staff (10–50 blocks) 38.3% by experienced staff	9.2%
White et al. (1980) [17]	Prospective	Caudal epidural	304 both caudal and lumbar (not specified how many of these were caudal)	Landmark based	25%	6.4%
Lewis et al. (1992) [18]	Prospective	Caudal epidural	26	Landmark based	27%	Not assessed
Stitz et al. (1999) [19]	Prospective	Caudal epidural	54	Landmark based	25.90%	3.7%
Barham et al. (2010) [20]	Prospective	Caudal epidural	137	Landmark based	Overall, 26% (consultants 24%, middle grade surgeons 27%)	1.5%
Feroz et al. (2022) [21]	Prospective	Caudal epidural	421	Landmark based	21.5% (first attempt incorrect 34.5%)	4%
Naidoo et al. (2017) [22]	Prospective	Caudal epidural	252	Landmark based	0%	Not assessed
Price et al. (2000) [23]	Prospective	Caudal epidural	100	Landmark based	36%	5%
White et al. (1980) [17]	Prospective	Lumbar epidural	304 both caudal and lumbar (not specified how many of these were caudal)	Landmark based	30.4%	0%
Price et al. (2000) [23]	Prospective	Lumbar epidural	100	Landmark based	7%	0%
Mehta et al. (1985) [24]	Prospective	Lumbar epidural	100	Landmark based	17%	Not assessed
Fredman et al. (1999) [25]	Prospective	Lumbar epidural	48	Landmark based	8.3%	Not assessed
Bartynski et al. (2005) [26]	Retrospective	Lumbar epidural	74	Landmark based	26%	Not assessed
Alemo et al. (2010) [27]	Prospective	Lumbar epidural	371	Loss of resistance (LOR) and fluoroscopy	12.3%	Not assessed
Liu et al. (2001) [28]	Prospective	Lumbar epidural	100	Landmark based	8%	Not assessed

Table 2.

Fluoroscopically guided transforaminal epidural injections and comparison among DSA, real-time fluoroscopy, anteroposterior and oblique approach

Author (year)	Study type	Spinal level	Comparing techniques	Total no. of procedures	Intravascular needle placement/intradiscal (assessed with fluoroscopy)	Comments
Nahm et al. (2010) [34]	Prospective	All levels (sacral, lumbar, thoracic, cervical)	No	2145 injections on 1088 patients	Overall incidence of intravascular injection = 10.5% (226/2145)  Cervical = 20.6% (28/136)  Thoracic = 8.2% (23/280)  Lumbar = 6.1% (64/1056)  Sacral = 16.5% (111/673)
Furman et al. (2003) [35]	Prospective	Cervical	No	337 patients (504 cervical transforaminal epidurals)	19.4%	Positive flash or blood aspirate to predict intravascular injections was only 44.7% sensitive Flash or blood aspiration was 97.9% specific A negative flash or blood aspiration is unreliable, a positive flash or blood aspiration reliably predicts a vascular injection, and the needle tip should be repositioned
Hong et al. (2013) [36]	Prospective	Lumbar	No	251 TFESIs in 219 patients	Total intravascular: 15.5% (39/251)  Simultaneously vascular and epidural injection: 12.7% (32/251)  Intravascular injection only 2.8% (7/251) Intradiscal: 2.3% (6/251)  Five intradiscal injections occurred at the L4–5 level and one at the L5–S1 level	The sensitivities for detecting intravascular access via aspiration or static fluoroscopic image with contrast were 20.5% and 51.2%, respectively
Furman et al. (2000) [37]	Prospective	Lumbar and sacral	No	670 patients (761 lumbosacral TFESIs)	11.2% overall rate (21.3% S1; 8.1% lumbar)
Manchikanti et al. (2004) [38]	Prospective	Lumbar and sacral	No	100	Total intravascular placement of the needle was noted in 22% of the procedures, whereas negative flashback and aspiration was noted in 5% of the procedures	Epidural filling  Ventral seen in 88% of the procedures  Dorsal noted in 9% of the procedures Nerve root filling seen in 97% of the procedures
McLean (2009) [40]	Retrospective	Cervical	Real-time fluoroscopy and DSA	177 injections on 134 subjects	Detection without DSA: 17.9% Detection by adding DSA to the real-time fluoroscopy: 32.8% (P = 0.0471)
Jeon and Kim (2018) [41]	Prospective	Cervical	Real-time fluoroscopy and DSA	137 cervical transforaminal epidural injections on 128 patients	Detection without DSA: 30.7% Detection by adding DSA to the real-time fluoroscopy: 34.3% (P > 0.05)	The detection rate of real-time fluoroscopy was not statistically different compared to that in DSA
El Abd et al. (2014) [42]	Prospective	41 cervical (18.47%) 113 lumbar (50.9%) 68 sacral (30.36%)	Blood aspiration, real-time fluoroscopy and DSA	222 transforaminal epidural injections on 150 patients	In 11 transforaminal epidural injections blood aspiration was obtained (4.95% of all injections)  3 (1.3%) cervical  4 (1.8%) lumbar  4 (1.8%) sacral Live fluoroscopy during contrast injection detected 46 (20.72%) intravascular flow patterns  7 (3.1%) cervical  17 (7.6%) lumbar  22 (9.9%) sacral DSA identified an additional 5 intravascular injections after all previous steps had resulted in negative vascular penetration signs, which accounted for 2.25% of all injections
Lee et al. (2010) [43]	Prospective	Lumbar	Real-time fluoroscopy and DSA	87	Using DSA guidance overall rate of intravascular injection was 23% (n = 20) Transforaminal epidural injections at S1 had an intravascular injection rate of 40.7% (n = 11) compared with 15.0% (n = 9) for all the lumbar injections	Ability of flash or positive blood aspiration to predict vascular injection (compared to DSA)  Sensitivity = 25.0%,  Specificity = 100%, Ability of the live fluoroscopic guidance to predict vascular injection (compared to DSA)  Sensitivity = 60.0%,  Specificity = 100%
Kim et al. (2013) [44]	Prospective	Lumbar and sacral	Real-time fluoroscopy and DSA	732 injections performed on 348 patients	8.1% (59/732) and 10.5% (77/732) of injections were interpreted as intravascular during fluoroscopy alone and digital subtraction, respectively, p = 0.13	No statistically significant benefit of DSA compared with unprocessed fluoroscopy
Hong et al. (2014) [45]	Prospective	Lumbar	Real-time fluoroscopy and DSA	249 fluoroscopically guided TFESI	Overall incidence of intravascular injection was 12.4% (31/249) Real-time fluoroscopy failed to detect 9 cases of intravascular injections that were subsequently detected by DSA (real-time fluoroscopy sensitivity, 71.0%)	DSA is superior to real-time fluoroscopy for detecting intravascular injections
Park and Kim (2019) [46]	Prospective		Real-time fluoroscopy and DSA	316 patients in 218 enrolled participants 56 injections (17.7%) at cervical levels 31 (10.0%) at thoracic levels 135 (42.7%) at lumbar levels 94 (29.7%) at sacral levels	Positive intravascular injection in real-time fluoroscopy + DSA = 36 Negative intravascular injection in real-time fluoroscopy and positive on DSA = 9	Real-time fluoroscopy missed 9 cases of intravascular injection (2 at cervical, 1 at thoracic, 3 at lumbar and 3 at sacral levels) that were detected using DSA (real-time fluoroscopy sensitivity, 80.0%)
Hong et al. (2021) [47]	Prospective randomized trial	S1	Anteroposterior versus oblique view	147 patients	The incidence rate of intravascular injection in the anteroposterior view group was 24.2% (24/99), whereas that of intravascular injection in the oblique view group was 10.1% (17/99, P = 0.008) Reduced incidence rates of intravascular injection and reduced foramen passage time with the use of oblique view method during S1 TFESI
Kim et al. (2015) [48]	Prospective randomized trial	S1	Anteroposterior versus oblique view	201 procedures 99 with anteroposterior 102 with oblique view approach	Anteroposterior view  Epidural and vascular (17%)  Vascular only 12% Oblique view  Epidural and vascular (8%)  Vascular only 3%	Anteroposterior versus oblique view approach

DSA digital subtraction angiography, TFESI transforaminal epidural steroid injection

Table 3.

Sacroiliac joint injections

Author (year)	Study type	Imaging method	Total no. of patients	Outcome	Comments
Rosenberg et al. (2000) [53]	Prospective, double-blind	Blindly placed and CT scan assessed	39 SI joints in 33 patients	Non-image-guided: 22% (8/37) intra-articular	32% non-image-guided were extra-articular 46% within 1 cm from the joint
Hansen et al. (2003) [54]	Prospective	Blindly placed and fluoroscopy assessed	60	Accurate placement of SI joint injections is successful without fluoroscopy in only 12%	Posterior superior iliac spine was found to be a poor indicator of SI joint anatomic access
Cohen et al. (2019) [55]	Randomized controlled study	Landmark and fluoroscopy	125  64 fluoroscopically guided  61 landmark-guided	Fluoroscopically guided injections provide greater intermediate-term benefit in some patients	These differences are modest and accompanied by large cost differences

CT computed tomography, SI sacroiliac

Epidural Steroid Injections

Caudal Epidural Steroid Injections

We identified eight prospective studies [7, 17–23] assessing the accuracy of the blindly performed caudal epidural injections. The methodology of all involved a fluoroscopic image with contrast applied following the blind insertion of the needle to confirm the correct placement of the needle. As presented in Table 1, the rates of the incorrect needle placement varied significantly among the studies from 0% to more than 50% (median 25.5%). As expected, it also varied amongst clinicians with different level of experience (as explored in two studies [7, 20]—see Table 1). The intravascular needle placement also varies among the studies from 1.5% to 9.2% (median 4.5%).

Lumbar Interlaminar Epidural Steroid Injection

Similarly, Table 1 includes seven studies [17, 23–28] that assessed epidural injections at the lumbar level. The rates of incorrect needle placement and unintended intravascular placement are seen in Table 1. It is evident that the former rate also ranges between studies (7–30.4%, median 12.3%) and can be as high as one in three injections [17]. The intravascular needle placement rate was assessed in only two studies [17, 23] and no cases were identified in either (Table 1).

Cervical Interlaminar Epidural Steroid Injections

No studies directly comparing the landmark with the fluoroscopic technique were identified. Stojanovic et al. assessed the number of loss of resistance (LOR) attempts required to achieve adequate epidural contrast spread, which is the gold standard to confirm the needle placement in the epidural space [29]. In this study a very high rate of false LOR was identified (53%) and, in some cases, even a third or a fourth attempt was required for the needle to reach the epidural space [29]. This is understandable given the discontinuation of ligamentum flavum at cervical levels [30, 31]. Other confounding factors, while using the LOR technique, can be cysts in interspinous ligaments, the paravertebral muscles, the thoracic paravertebral spaces, and intermuscular planes (such as the dorsal thoracolumbar ligament) [32]. Additionally, the spread of the contrast was unilateral in 51% of the cases, while in 28% of the cases the spread was ventral, emphasizing the importance of the use of fluoroscopy for patients with unilateral pain [29].

Another study showed that the use of contrast media in the cervical area is of utmost importance as its spread can show different patterns, while the extent of dispersion can be variable and unpredictable. Gill et al. suggested that the contralateral oblique view provides clear confirmation of epidural spread, while the antero-posterior (AP) view is an excellent view to measure both the craniocaudal and foraminal spread [33]. At low volumes of contrast, the AP view seems to provide the best estimate of the likelihood that the injectate will reach the pain-generating pathology and is considered the optimal for this purpose [33].

Lumbar and Cervical Transforaminal Steroid Injection

Transforaminal injections can only be performed with image guidance for two reasons: there is no established safe landmark-guided method to direct the needle to the foramen; and the high prevalence of vessels, potentially providing vascular support to the spinal cord, in the proximity of the nerve roots in the foramen. Table 2 shows prospective studies that evaluated the risk of intravascular [34–38] and intradiscal [36] needle placement while performing fluoroscopically guided transforaminal injections. The risk of intravascular injection varies amongst the spinal levels and amongst the included studies. At the cervical level it was documented as approximately 20% [34, 35], in the thoracic region around 8% [34], at the lumbar levels it ranged from almost 6% [34] to 15% [36] and at the sacral level from 16.5% [34] to 21% [37]. One study reported a rate of intradiscal needle insertion of 2.3% [36].

To improve the safety of the injection, several techniques may be employed. Real-time fluoroscopy, digital subtraction angiography, and oblique views may provide various safety advantages, including improved needle guiding, better imaging of anatomical structures and a lower risk of procedural complications, when performing epidural injections [39–48].

Real-time fluoroscopy provides continuous viewing of needle insertion and contrast distribution, allowing for quick modifications to improve accuracy and reduce complications. Real-time fluoroscopy also lowers the risk of unintentional dural puncture, nerve damage and vascular trauma by ensuring accurate needle insertion in the epidural space [39].

Digital subtraction angiography (DSA) improves vascular structure imaging by removing background structures, resulting in improved clarity and definition of the epidural space. This technique includes acquiring images before and after contrast injection, then subtracting the pre-contrast image from the post-contrast image to highlight vascular structures. This approach helps to identify vascular abnormalities and reduces the danger of unintended vascular puncture during epidural treatments. DSA helps to avoid unintentional vascular injections, lowering the risk of haematoma development, arterial embolization and other vascular problems [39, 41]. It is important to point out that DSA cannot reliably confirm intra-arterial placement [49].

Oblique fluoroscopic images, by tilting the fluoroscopic C-arm, give additional viewpoints on needle trajectory and contrast spread, allowing for better visibility of the epidural area from various angles. These views can assist in confirming adequate needle insertion in the epidural area and highlight potential issues such as nerve impingement or intravascular injection. In general, this view improves procedural accuracy and lowers the risk of complications; it is particularly useful for the S1 level as seen in Table 2 [50].

Many studies compared the aforementioned techniques as seen in Table 2.

Live fluoroscopy has been deemed better than the static images, as the interpretation of the latter may miss up to 57% of the vascular injections [51]. DSA is not a panacea for preventing adverse outcomes during the performance of neuraxial procedures. Although not all studies identify the advantages of DSA [41], most studies find a clinically and statistically significant difference (see Table 2). Some disadvantages of this method are that DSA is limited by motion artifacts and the images are subject to human interpretation. Any motion between the initial scout film and subsequent images is detected as a change, impeding the subtraction process, and causing degradation of image quality. Thus, utilisation of this technology does not negate the potential for human error nor the potential for patient injury. DSA may provide greater sensitivity and specificity, but the exact limits of detection are unclear, and the safety profile is neither fully characterized nor validated [52]. One significant drawback of DSA is that it may substantially increase exposure to ionizing radiation, comparable to computed tomography angiography (CTA). The routine use of DSA is not warranted on the basis of current medical evidence [52].

Sacroiliac Joint Steroid Injections (SIJ)

Table 3 presents three studies [53–55] supporting that imaging techniques for SIJ are superior to non-imaging techniques. Without image guidance, the misplacement of needle is unacceptable (78–88%), while fluoroscopically guided injection results in not only superior accuracy but also better intermediate-term outcome [55].

Medial Branch Block and Facet Joint Injections

Although facet joint injections and medial branch blocks are commonly performed under imaging techniques (fluoroscopy, CT or US), blind techniques for lumbar levels have also been described [56]. To date, we did not identify any published paper to assess the accuracy of the landmark-based technique for facet injections. Furthermore, considering that the medial branches are deep in location, of small calibre and in close proximity to the nerve root, a blind technique is not recommended according to all current consensus guidelines. Currently, fluoroscopy is the gold standard for facet joint and medial branch blocks and is either recommended or required by multiple insurance companies [57]. The Spine Interventional Society guidelines also state that fluoroscopy is mandatory for the conduct of lumbar medial branch blocks’ as it provides an overview of the bony anatomy as well as the ability to confirm contrast spread [58]. CT guidance may be an alternative; however, it is not currently recommended as the imaging method of choice [57].

Accuracy of Identification of Level of Spine

Different to the context of regional anaesthesia, correct identification of the spine level corresponding to the spinal pathology is important. Without imaging, identification of the level of spine relies on the anatomical landmarks such as Tuffier’s line, the tenth rib line as well as posterior superior iliac spine. One study assessing the accuracy in 60 patients showed that the true level was noted in 48.33% when using Tuffier’s line, 53.33% when using the 10th rib line and 65% of cases when using the posterior superior iliac spine [59]. Another study examining the anatomical landmark for lumbar puncture (L4–L5 intervertebral space or L4 vertebra) reported that there was concordance of intervertebral space identification in 64% of the cases (78/122) as confirmed by US [60]. For the cervicothoracic intervertebral spaces one study showed that the level identification may deviate in up to 58% of cases [61]. The reason behind the poor accuracy is obvious as the recognition of the bony landmark is merely contingent on the tactile sensation, which can be severely hampered with increasing depth of the subcutaneous layer.

Use of CT and Ultrasound Guidance: Comparison with Fluoroscopy

Ultrasound

Facet Joint or Medial Branch Block

A comprehensive review comparing US with CT and fluoroscopy reported that US guidance for injection of the cervical facet joints and their innervating nerves had reasonable accuracy (78–100%) with shorter procedural time compared to fluoroscopy or CT guidance, while offering comparable pain relief [62]. The same review found the accuracy of US-guided lumbar facet joint intra-articular injections to be 86–100%, more reliable than medial branch blocks (72–97%), with analgesia similar to that from fluoroscopy- and CT-guided blocks [62]. However, those conclusions need to be interpreted with care. Firstly, the US-guided procedures are skill dependent and a number of those studies are from specialized centres where a high number of US-guided spine injections are performed [63]. A recent meta-analysis showed that US-guided lumbar medial branch blocks and facet joint injections are associated with a significant risk of incorrect needle placement (7–14% among the studies), as confirmed by fluoroscopy or CT [64]. A recent cadaveric study on the accuracy of cervical medial branch block under US guidance even revealed that the accuracy was less than 79% [65]. Secondly, the success rates also depend on the patients’ body build. Early studies included patients with low body mass index (BMI) [66, 67]. However, when US-guided spine procedures were applied in patients with obesity (BMI > 30), the success rate dropped to 62%. Thirdly, these procedures are more challenging for deeper targets (e.g. lower cervical levels, L5 dorsal ramus) [68]. US technical limitations and individual patient factors also contribute to the risk of incorrect needle placement. The use of US may be indicated in a certain clinical setting or selected clinical scenarios where avoiding radiation exposure is a key outcome [64] or not accessible.

Epidural Steroid Injection

The current literature also supports that US-guided transforaminal epidural injection is an effective procedure with the equivalent efficacy to fluoroscopy-guided injections [62]. One recent meta-analysis supported that US-guided epidural injections are comparable to fluoroscopic guided injections regarding pain control and functional improvement, offering a decreased risk of inadvertent vascular puncture [69]. Another meta-analysis, though, supported that fluoroscopy-guided injections led to better functional status compared to the US-guided blocks [70]. In terms of effectiveness in treating back pain and complications, no difference was identified [70].

Again, it is important to recognize that the part of neurovascular structures within the bony component of vertebrae cannot be visualized by the US. That means that US cannot monitor the intravascular injection in the foraminal area as well as the transforaminal and epidural spread of the injectate, all of which is made possible by fluoroscopy with contrast.

CT Guidance

The use of CT for spinal injections is practiced in some pain centers but is not widespread. One prospective cohort study compared fluoroscopy-guided to CT-guided transforaminal epidural steroid injections and showed similar results at 3 months in both groups (P = 0.511) [71]. CT allows direct visualization of the nerve root and the needle tip, as well as of the distribution pattern of the injected contrast [12].

In addition to the accessibility of the CT machine across the intervention community, radiation dose is a limiting factor. Kamp et al. reported ten times higher radiation dose for patients who received CT-guided spinal procedures when compared to that from fluoroscopy-guided procedures [72]. In the same retrospective study, higher discharge rate and a lower procedural cost were reported [72]. Investigators have explored a low-dose protocol, limited in one or two spinal segments [12]. To support this, another study showed that ultralow-dose CT-fluoroscopy for image-guided lumbar spine epidural steroid injections can offer lower radiation dose compared to the fluoroscopy-guided technique. Ultralow-dose CT-fluoroscopy omits a planning CT scan, utilises CT-fluoroscopy and minimises radiation dose parameters [73]. The radiation dose is an important parameter for clinicians. Dietrich et al. showed that fluoroscopy-guided lumbar spinal injections resulted in lower radiation exposure for participants but higher radiation exposure for physicians when compared with CT-guided injections [74]. This is not surprising as the position of the provider needs to be in close proximity to the patients during the fluoroscopy procedure.

Anatomic Basis for Importance of Image Guidance

While it is clear that the transforaminal approach requires image guidance, practice survey suggests that interlaminar epidural steroid injection is frequently performed without image guidance even in developed countries [75]. Image guidance allows accurate delivery of injectate to the epidural space. In general, there are two reasons why the interlaminar epidural medication is delivered to the wrong location with the traditional LOR technique: failure to detect the wrong location outside the epidural space, and failure to detect the intravascular spread.

Traditionally, the epidural procedure is performed with loss of air/saline resistance technique [76]. The premise of this haptic technique is contingent on the dramatic drop in resistance in the epidural space relative to that inside the ligamentum flavum. The sensitivity of LOR in the lumbar area is 99% but with a specificity of 27% [28]. Risks of false LOR have been reported between 8% and 30% [17, 26, 28]. This can be related to the experience (e.g. failure to recognize the needle in paraspinal muscle) or equipment (smaller gauge epidural needle). Even in experienced hands, there are a few anatomic reasons accounting for the injectate found in the wrong place.

False Localization with LOR Method

Interspinous Ligament and Ligamentum Flavum

Once the needle is in the interspinous ligament, it gives the tactile feeling of high resistance to the procedure provider because of the solid architecture of fibres in the ligament. However, multiple anatomic studies revealed that two-thirds of interspaces had at least one gap in the lumbar interspinous ligament (LISL) filled with adipose tissue [77–79]. The observed gaps approached the dimensions of an epidural needle orifice. This can give the provider a false sense of LOR.

Once the needle passes through the interspinous ligament, it pierces the ligamentum flavum, which typically fuses in the midline to a variable degree in the lumbar spine [80]. Presence of midline gap is uncommon in the lumbar spine [81] and may account for the false LOR. In the cervical spine, the ligamentum flavum is more frequently discontinuous [82], resulting in very high rate of false LOR [29].

Retrodural Space of Okada

The retrodural space of Okada (RSO) is a potential space posterior to the ligamentum flavum that allows communication with bilateral facet joints. A recent detailed anatomic and radiologic investigation identified that 5.9% of attempted lumbar epidural steroid injections were into the RSO [83]. This RSO is situated between the ligamentum flavum and interspinous ligament and is another anatomic reason contributing to the false LOR.

Intravascular Placement of Injectate

In addition to the false localization of the needle, the other cause of failure is the intravascular spread. The interlaminar and foraminal space for lumbar or cervical intervention is populated with a rich network of vessels. The spinal cord receives arterial supplies from three vertical systems (one anterior and two posterolateral spinal axes) anastomosed by a horizontal perimedullary plexus [84]. At each spinal level, the system is also supported by radiculomedullary arteries from subclavian and vertebral arteries (cervical region), and thoracic and lumbar collaterals of the aorta (thoracic and lumbar region). In addition, there is a venous plexus in the epidural space. The veins are large and valveless, and anastomosed with the venous cavae as the posterior drainage network. The diameter can be influenced by the intra-abdominal pressure [85] or the thickness of the epidural fat [86].

Negative aspiration does not guarantee the placement of needle outside the vessels. A study examining the risk of intravascular injection following an apparent negative aspiration showed the risk of intravascular injection in epidural steroid injection (ESI) as follows: cervical transforaminal ESI, 26%; cervical interlaminar ESI, 9%; lumbar transforaminal ESI, 8%; and lumbar interlaminar ESI, 2% [87]. Image guidance with contrast injection, either by real-time fluoroscopy or DSA, is crucial in detection of the intravascular injection.

Discussion

The localization of epidural space by conventional loss of air or saline resistance without imaging is known for the lack of specificity in literature. It relies on the objective tactile judgement of the provider which can be influenced by experience, the nature of the needle tip material and the size of the epidural needle. Even in experienced hands, certain anatomic variations can result in false LOR, leading to failure of the delivery to the epidural space. In addition, the medication can be administered in the intravascular space. Imaging guidance with contrast helps to improve the specificity of the epidural steroid injection. Without imaging, the reliability of injection into the sacroiliac joint and facet joint/nerves is unacceptable. Despite that, many physicians in Canada practise spinal interventions without imaging and that needs to be changed. A welcomed advancement is the recent practice standard established by the College of Physicians and Surgeons of Ontario (CPSO), a regulatory agent for physicians, which mandated the use of imaging guidance for the practice of spine interventions (reference below). Furthermore, a national spine intervention guideline for spine intervention in Canada is under preparation to determine the safety standard of spine intervention [88].

In addition to the accuracy, the other important reason for the use of imaging is to enhance safety by avoiding placement of needle in the wrong place. The Work Group on Infection Prevention from World Institute of Pain (WIP), involving four stakeholder pain societies from Belgium, the Netherlands, and Luxembourg (Benelux), reviewed the literature on neurological complications after epidural corticosteroid injections. These adverse effects are being reported mainly in the cervical region, possibly due to the dense vascularization, but also in the lumbar, and less commonly in the thoracic region [89]. The mechanisms involved are direct damage of the spinal cord or its arterial supply, neurotoxic effects of the injectate (preservatives/ solvents) or embolization, mainly caused by particulate steroids, which may result in ischemia [89]. The unintentional spread of the injectate outside of the target, most commonly the epidural space, can cause significant side effects. As a result of the anatomy of the subdural space, as it is larger in the cervical region, there is a greater risk of subdural injection, resulting in a slow onset respiratory depression [89]. An accidental intra-arterial injection of particulate corticosteroids can cause clusters or aggregates of the corticosteroid and remotely create an embolus, causing a stroke at the cervical level or a spinal cord infraction that can lead to serious and permanent limitations, disability or death [89]. Likewise, an unintentional intrathecal spread of the corticosteroid can lead to serious complications such as cerebral haemorrhage, meningitis, cauda equina syndrome, progressive muscle weakness, bladder dysfunction, and paresthesias [89]. Unwanted injection in the intervertebral disc is also not uncommon (0.17–2%), especially during transforaminal approach despite an optimal placement of the needle [90]. All these emphasize the importance of precise needle insertion and those complications can be largely prevented by proper image-guided techniques. Future research directions should focus on further advancing imaging technologies and potentially integrating artificial intelligence-assisted image guidance to enhance precision and safety.

Limitations

This review does not discuss all the spinal procedures performed in a pain clinic. Additionally, not all procedures have been published as landmark based. Safety is also dependent on the injectate (e.g. particulate or non-particulate steroid) which is not discussed in this review. Importantly the variability in operator experience and study methodologies may affect reported accuracy rates.

Conclusion

Image guidance is a mandatory requirement in commonly performed spinal procedures for pain management. Traditionally, the use of fluoroscopy increases the safety and accuracy of the injections and can be supported by DSA and oblique views for further improvement of the safety. US guidance also has a role and is increasingly utilised for specific procedures to further increase safety and enhance accuracy. Importantly, US can be combined with fluoroscopy and just before the steroid injectate to administer contrast, to further aid safety and determine the spread of the solution. The fluoroscopic image can be then stored in the patient’s records. CT can also be utilised. Here the advantage is a more detailed anatomy; however, CT requires a more advanced hospital setting and possibly the use of it is accompanied by increased doses of radiation, depending on the protocol used. Current guidelines recommend the use of any of the above and promote proper image saving for future reference.

Author Contributions

Philip Peng conceived the research idea and helped draft and revise the manuscript. Martina Rekatsina helped draft and revise the manuscript. Both authors meet all authorship criteria: substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; and drafting the article or revising it critically for important intellectual content.

Funding

No funding or sponsorship was received for this study or publication of this article.

Declarations

Conflict of Interest

Martina Rekatsina is an Editorial Board member of Pain and Therapy. Martina Rekatsina was not involved in the selection of peer reviewers for the manuscript nor any of the subsequent editorial decisions. Philip Peng has received equipment support from Sonosite Fujifilm Canada. Philip Peng is also Steering Committee chair in the development of Spine Intervention Guidelines.

Ethical Approval

This article is based on previously conducted studies and does not contain any new studies with human participants.