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Pain Medicine: Review Article

Is Ultrasound Guidance Advantageous for Interventional Pain Management? A Systematic Review of Chronic Pain Outcomes

Bhatia, Anuj, MBBS, MD, FRCA, FRCPC, FIPP, FFPMRCA, EDRA; Brull, Richard, MD, FRCPC

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doi: 10.1213/ANE.0b013e31828f5ee4
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Recently, there has been increasing interest in the use of ultrasound (US) to guide needle placement for interventional chronic pain management. Compared with traditional anatomical landmark and fluoroscopic guidance, distinct advantages of US guidance include real-time visualization of the needle, target structure, injectate, and surrounding tissues. Proponents of US guidance for interventional chronic pain management cite enhanced accuracy of injection and a reduction in procedure-related complications.1,2 Additionally, the avoidance of radiation exposure as well as ease of portability associated with modern US is an important feature attractive to both pain practitioners and patients alike. In contrast to peripheral nerve blockade for surgical anesthesia and acute pain management where procedure-related characteristics, such as onset and performance time, decidedly favor US guidance over traditional nerve localization techniques,3 the measurement of outcomes after US guidance for chronic pain can be challenging at best. Enthusiasm for the use of US for chronic pain interventions, especially those involving the neuraxis, has been tempered by concerns regarding the inability to visualize intravascular injection and spread of injectate.2 Clinically important efficacy outcomes for chronic pain are measured in months and years rather than minutes and hours, and are thus far less readily quantifiable than those captured in the perioperative period. Furthermore, patients with chronic pain syndromes often suffer from psychological and behavioral pathologies in addition to biomechanical etiologies, which may undermine the reliability of any single randomized trial when considered in isolation. Therefore, to define the effect of US, we reviewed the contemporary literature relating to the performance, efficacy, and safety of US guidance compared with traditional techniques for interventional chronic pain procedures.

METHODS

The authors (AB and RB) systematically searched the electronic database MEDLINE from January 1982 to May 2012 using the following medical subject heading words: “pain management” OR “injection” OR “block” OR “transforaminal” OR “lumbar facet joint” OR “lumbar intraarticular” OR “cervical facet joint” OR “cervical intraarticular” OR “medial branch nerve” OR “cervical nerve root” OR “lumbar nerve root” OR “caudal epidural” OR “sacroiliac joint” OR “ganglion impar” OR “greater occipital nerve” OR “intercostal nerve” OR “suprascapular nerve” OR “ilioinguinal nerve” OR “iliohypogastric nerve” OR “lateral femoral cutaneous nerve” OR “pudendal nerve” OR “piriformis muscle” OR “cervical sympathetic chain” OR “stellate ganglion.” The Boolean operator “and” was used to combine these search results with the term “ultrasound.” All randomized controlled trials (RCTs), case series, and retrospective reviews in the English language involving human subjects (adult patients, volunteers, or cadavers) were eligible for inclusion in the present review. Only studies that compared or validated US against: (1) traditional guidance techniques, such as loss of resistance, mechanical elicitation of paresthesias, peripheral nerve stimulation, anatomical landmarks, fluoroscopy, computed tomography (CT), and magnetic resonance imaging (MRI); (2) resultant sensory changes in the corresponding dermatomal distribution(s); or (3) anatomical dissection (for cadaveric studies) were included. Studies were excluded if at least 1 of the following outcomes was not reported: accuracy of needle placement, pain, analgesic consumption, or functional improvements. Studies describing intraarticular (except facet joint) and trigger-point injections, celiac plexus, superior hypogastric plexus, and endoscopic US procedures (e.g., celiac plexus block) were excluded because of lack of literature comparing US with the current standards of care (anatomical landmarks, nerve stimulation, fluoroscopy, CT guidance) and to focus this review on neuraxial and peripheral neural procedures performed for relieving chronic pain. The reference sections of all articles were manually reviewed for any relevant articles not identified in the original search.

For the purposes of this review, the outcomes sought were divided into the following categories: (1) Performance-related outcomes, including accuracy of needle positioning, resultant sensory block, duration of procedure, number of attempts, identifying the minimum effective volume, patient discomfort during and overall satisfaction with procedure; (2) Efficacy-related outcomes, including objectively recorded pain scores over the short and long terms, physical and emotional state, participants’ rating of global improvement; and (3) Safety-related outcomes, including measurement of radiation exposure and adverse events. The methodological quality of each study was assessed using the Jadad score and/or the Oxford Centre for Evidence-based Medicine Levels of Evidence 2011 levels of evidence.4,5

RESULTS

We identified 46 studies, including 1066 human subjects in total, which fulfilled our inclusion criteria. Among these 1066 subjects, 810 were patients, 134 were volunteers, and 122 were cadavers. (Table 1) Forty-one of these studies were case series, and 5 were RCTs of intermediate or poor methodological quality. Twenty-eight of these studies examined the use of US guidance for neuraxial procedures (Tables 2 and 3), while 18 examined US for peripheral structures (Tables 4 and 5).

Table 1
Table 1:
Subject Profile of Studies Comparing Ultrasound Guidance with Traditional Guidance Techniques for Interventional Chronic Pain Procedures
Table 2
Table 2:
Study Characteristics for Neuraxial Targets
Table 3
Table 3:
Study Outcomes for Neuraxial Targets
Table 4
Table 4:
Study Characteristics for Peripheral Targets
Table 5
Table 5:
Studies Outcomes for Peripheral Targets

Neuraxial Procedures

Injections about the spine are performed to diagnose and/or treat pain largely due to arthritis of the facet joints or nerve root compression. Imaging guidance is mandatory to ensure accurate deposition of the injectate, exclude false positive responses due to blockade of other potential pain generators, and avoid potentially catastrophic unintentional injection into vital radicular arteries that supply the spinal cord.52

Among the 28 studies examining US guidance for neuraxial procedures,6–33 25 used another imaging modality (fluoroscopy/CT/MRI) for anatomical validation.6–14,16–27,30–33 Clinical validation was sought in only 10 of the 28 studies,7,11,14,15,23–25,27–29 and only 9 studies duly recorded pain scores after the neuraxial procedure.14–16,18,19,24,25,27,28 The results of studies investigating US guidance for neuraxial procedures are summarized in Tables 2 and 3.

Cervical Spine Procedures

Facet Intraarticular Injection

Performance.

We identified 1 cadaveric study that evaluated use of US for cervical facet intraarticular injections in which US images of 40 cervical facet joints were captured, and 10 US-guided intraarticular injections were performed.6 US was associated with a success rate of 90% and 100% for identifying the facet joint and intraarticular needle placement, respectively, as confirmed by CT scan.

Efficacy.

No comparative data available.

Safety.

No comparative data available.

Injection of Nerve Supply to Facet Joints

Performance.

We identified 2 case series7,8 and 1 cadaveric study9 that validated US against radiation-based imaging techniques. All 3 studies reported accuracy rates for US-guided needle placement exceeding 80%. Eichenberger et al.7 used US in 14 volunteers to identify and inject the third occipital nerve (TON) with local anesthetic to diagnose the facet joint between the second and third cervical vertebrae as a source of neck pain. Needle position was confirmed by radiograph, and sensory block in the corresponding dermatomes was used as a marker for a successful TON block. The TON was identified in 96% of scans, correct needle position was reported in 82% of patients, and TON was successfully blocked in >90% of patients. Finlayson et al.8 placed needles and injected contrast at the TON and medial branches from the third to sixth cervical levels in 53 patients. Needles were positioned accurately in 80% of attempts, and spread of contrast was acceptable in 95% of injections. Lee et al.9 proposed an US-guided technique for radiofrequency cervical medial branch neurotomy in a study of 5 cadavers. After the sonographic target was defined and identified in the third to the seventh cervical segments in first phase of the study, correct needle placement with US as validated by radiograph was reported in 100% of attempts (17 procedures), and successful neurotomy was confirmed using histopathological diagnosis in 88% of procedures.

Efficacy.

No comparative data available.

Safety.

No comparative data available.

Selective Nerve Root Block

Performance.

We identified 2 studies, 1 in cadavers10 and 1 in patients11 that reported the use of US for identifying and injecting nerve roots in the middle and lower cervical spine. Among 4 cadavers, Galiano et al.10 identified the spinal nerves in 35 of 40 scans, and needles were positioned in close proximity dorsal to the spinal nerve in all 8 attempts as confirmed by CT scan. Narouze et al.11 reported accuracy rates of 100% and 80% for nerve identification and needle placement with US guidance (validated by fluoroscopy), respectively, in a case series of 10 patients.

Efficacy.

In their case series, Narouze et al.11 reported that sensory blockade in the corresponding dermatomal territory was successfully achieved for all cervical nerve root injections. We did not find any studies that reported long-term pain relief with the US-guided injections of steroids around cervical nerve roots.

Safety.

Narouze et al.11 reported that US enabled the detection of blood vessels at the anterior aspect of the foramen in 4 of 10 patients, as well as critical vessels at the posterior aspect of the intervertebral foramina in 2 patients, of which 1 traversed medially into the foramina to most likely form or join a segmental feeder artery. Though no complications were reported, the authors suggested that a needle positioned under traditional fluoroscopic guidance might well have punctured 1 or more of these vessels.

Lumbar Spine Procedures

Facet Intraarticular Injection

Performance.

Two cadaver studies12,13 and 2 clinical RCTs14,15 evaluated the performance of US-guided lumbar facet intraarticular needle placement. In a study of 5 cadavers, Galiano et al.12 imaged 50 lumbar facet joints using US and placed 10 needles into the joint cavity under US guidance. Mean depth and lateral distance from the target as measured by US correlated well with CT measurements, and all needles placed under US guidance were in the correct location as validated by CT. Gofeld et al.13 used US guidance to inject contrast dye into 50 lumbar facet joints in cadavers. Fluoroscopic imaging revealed correct dye placement for 44 of the 50 procedures. The authors were unsuccessful in 4 of 6 injections due to lack of visualization of the intraarticular space with US. In an RCT of 40 patients, Galiano et al.14 compared US guidance with CT guidance for intraarticular lumbar facet joint injections for low back pain (LBP). Needletip placement was deemed accurate in 80% of patients in the US group as verified by CT compared with 100% of patients in the CT group. It was not possible to visualize the facet joint in 2 patients in the US group who had a body mass index (BMI) >28. Finally, Ha et al.15 compared US guidance with fluoroscopy in 105 patients with LBP (see Efficacy, below), but these authors did not validate the position of needles placed using US guidance against another imaging modality.

Efficacy.

Galiano et al.14 and Ha et al.15 each reported a reduction in immediate (within 6 hours), intermediate (at 4–6 weeks), and long-term (at 6 months) pain scores in all their trial participants (40 and 105 participants, respectively) after US-guided injections equivalent to those performed using CT guidance and fluoroscopy, respectively.

Safety.

No comparative data available.

Injection of Nerve Supply to Facet Joints

Performance.

Four studies evaluated the accuracy of US guidance to block the nerve supply to lumbar facet joints from medial branches of dorsal rami by validating the needle position against fluoroscopy or CT imaging.16–19 In the first study, Greher et al.16 used US to scan medial branch nerves innervating facet joints in 20 healthy, nonobese volunteers. In these 20 volunteers, the image quality of key sonographic landmarks was described as “good” in 19 and of “sufficient quality” in 1 morbidly obese subject. In the second phase of this study, Greher et al.16 performed US-guided injections to block these nerves in 1 cadaver and 5 patients with LBP. All 3 needles placed in the cadaver under US guidance were confirmed to be in the correct position by dissection. Among the 5 patients, 25 of 28 US-guided needle placements were accurately positioned as confirmed by fluoroscopy, with the remaining 3 closer than 5 mm to the defined target point. In a separate cadaveric study, Greher et al.17 performed 50 injections of contrast medium around the nerve supply to the lumbar facet joints in 5 cadavers. CT imaging revealed accurate injections in 94% of attempts. Finally, Shim et al.18 performed 101 lumbar medial branch nerve blocks under US guidance in 20 patients with an accuracy rate of 95% as validated by fluoroscopy.

The accuracy of US-guided lumbar medial branch block reportedly decreases at the lower lumbar levels and in patients with BMI >30 kg/m2. Rauch et al.19 found that the accuracy rate decreased to 62% when a US-guided approach for lumbar medial branch blocks was evaluated in obese patients by using fluoroscopy as a comparator. The fifth lumbar (L5) level was reported to be more challenging than the rest because of the acoustic shadowing produced by the bony ilium. The accuracy of US guidance for L5 dorsal ramus block has not yet been evaluated, while the US-guided blockade of the L4 medial branch was found to be less accurate compared with higher lumbar levels in cadavers when accuracy was checked using dissection or fluoroscopy.16,19

Efficacy.

The US-guided approach for lumbar facet medial branch block was reported to be successful (defined as reduction of >50% in pain scores within 30 minutes of injection) in >90% of volunteers and nonobese patients.16,18 Rauch et al.19 found the efficacy rate decreased to 62% when the US-guided approach for lumbar facet medial branch block was performed in obese patients.

Safety.

The rate of aberrant contrast medium spread (14% paraforaminal, 10% epidural, 4% intravascular) with the US-guided techniques was relatively high in Greher et al.’s17 cadaveric study, but the authors used larger (1 mL) than usual (0.5 mL) volumes. Shim et al.18 detected no fluoroscopic evidence of aberrant spread (epidural or paraforaminal space) of the contrast dye when 0.2 mL was injected under US guidance, though the authors reported a rate of intravascular needle placement that was comparable with fluoroscopic-guided injections.

Selective Nerve Root Block

Performance.

Lumbar nerve roots can be especially difficult to visualize with US as the depth of penetration, and the bony structures in the lumbar spine can greatly attenuate the US beam.2 Four studies, 3 cadaveric20–22 and 1 observational,23 investigated the performance of lumbar selective nerve root injections under US guidance. Two of the cadaveric studies used CT20,21, and 1 used fluoroscopy22 for validation of the US-guided injections. A high degree of correlation was found between distances measured by US as confirmed by CT in the cadaveric studies, and all needles were placed within the dorsal third of the intervertebral foramina in the periradicular area. However, the authors of both cadaveric studies did not convincingly visualize the lumbar nerve roots with US and instead used surrogate sonographic bony or ligamentous acoustic shadows to guide their injections.20,21 Gofeld et al.22 injected contrast in the lumbar transforaminal space of 5 cadavers using US guidance followed by validation against fluoroscopy. Contrast was intraforaminal in 42 of 46 injections; the remaining 4 injections (all at the fifth lumbar—first sacral interspace) could not be performed due to bone (iliac crest) obstructing visualization of the transforaminal space.22 Sato et al.23 evaluated US guidance combined with electrical nerve stimulation to facilitate blockade of the fifth lumbar (L5) nerve root in 78 patients. The authors reported an accuracy rate of >95% when confirmed by visualization of perineural contrast spread on fluoroscopy and development of hypesthesia in the corresponding dermatomal distribution. It is noteworthy, however, that these authors performed fluoroscopy before scanning the lumbar spine with US to ensure that the correct level was targeted. The authors also reported that the fifth lumbar (L5) inferior articular process and lack of space between the transverse process of L5 and sacral ala obstructed visualization of the L5 nerve root in 3 of 78 patients.

Efficacy.

Blockade of the fifth lumbar (L5) nerve root in 78 patients using US combined with electrical nerve stimulation was associated with diminished or fully resolved pain in 75 of 78 (96%) patients.23

Safety.

Three of 46 US-guided transforaminal injections in cadavers revealed intravascular spread of contrast on fluoroscopy.22 It is noteworthy that traditional fluoroscopic-guided transforaminal injection is associated with a similar rate of inadvertent intravascular injection.53

Sacroiliac Joint

Performance.

In a study of 10 cadavers, Klauser et al.24 reported that 20 US-guided injections into the sacroiliac joint (SIJ) had an accuracy rate of 80% which, as reported in a follow-up study, could not be improved further when the images obtained from US were fused with previously acquired CT images.25 US guidance for SIJ injection in patients had an accuracy rate varying between 40% (for 20 injections in 14 patients) and 76% (for 60 injections in 34 patients) when needletip position was verified by fluoroscopy26 and MRI,27 respectively.

Efficacy.

Three small case series reported that US-guided injections of steroids into the SIJ can reduce long-term (3–6 months after procedure) pain scores by >75%.24,25,28

Safety.

No comparative data available.

Caudal Epidural Space

Interventional procedures for delivery of drugs into the epidural space through the caudal route pose significant challenges because variations in anatomy can lead to subcutaneous or intravascular injections. Bony landmarks (e.g., sacral cornu and hiatus) can be difficult to identify by palpation or fluoroscopic guidance, especially in obese patients. Indeed, the incidence of misplaced needles inserted using anatomical landmarks (without fluoroscopic guidance) for caudal epidural injections can range from 12.5% in patients with easily palpable landmarks to 66% in patients whose bony landmarks cannot be palpated.54

Performance.

In a series of patients who were obese and/or had difficulty lying prone, Klocke et al.29 reported that preprocedural US imaging for caudal epidural injections provides information that can increase the probability of accessing the caudal epidural space using fluoroscopic guidance. Chen et al.30 reported a 100% accuracy rate for needle placement (as confirmed by fluoroscopy) into the caudal epidural space in 70 patients when US guidance was used. Importantly, however, the needletip could not be visualized after the needle was advanced into the sacral epidural space due to bony acoustic shadowing, thus precluding the identification of a dural tear or intravascular placement. Finally, the color Doppler mode on US has been evaluated as a method to confirm drug injection by detecting unidirectional flow during injection into the caudal epidural space and validated by fluoroscopy. In this setting, US reliably detected injection into the epidural space in 40 of 43 caudal injections.31

Efficacy.

No comparative data available.

Safety.

Significant vascularity in the caudal epidural region may result in intravascular injection,55,56 which is more common in elderly patients as the epidural venous plexus may continue inferiorly in these patients.57 Inadvertent intravascular needletip placement was reported in 1 of 3 patients in whom US was used to guide needle placement for real-time caudal epidural injections.32

Ganglion Impar Block

The ganglion impar is the fusion of the caudal end of the paired sacral sympathetic chains at the anterior aspect of sacrococcygeal joint (SCJ). Blocks of the ganglion impar have been advocated to evaluate and manage visceral or sympathetically maintained pain in the coccygeal and perineal area. Fluoroscopy is commonly used for needle guidance during this procedure, especially for the trans-sacrococcygeal approach, but this technique can be challenging because the SCJ is often not readily visualized on fluoroscopy.

Performance.

In a recent case series, the SCJ was visualized by US in all 15 patients as confirmed by fluoroscopy. However, US could not reliably identify the depth of the needletip or spread of injectate over the anterior surface of the rectum.33

Efficacy.

No comparative data available.

Safety.

No comparative data available.

Peripheral Procedures

Among the 18 studies that examined US guidance for peripheral procedures,34–51 4 studies used fluoroscopy,37,38,40,49 4 evaluated sensory loss in the corresponding dermatomal distribution,35,46,47,49 2 included electrical stimulation,39,45 and 2 used signs of sympathetic blockade for validation purposes.36,37 The results of studies investigating US guidance for peripheral procedures are summarized in Tables 4 and 5.

Greater Occipital Nerve

Local anesthetic blocks of the greater occipital nerve (GON) are frequently performed either to diagnose or treat different types of headaches.2 Anatomic landmarks have been used to localize the GON, but nonimage-guided blocks of the GON tend to require a higher drug volume, thereby increasing the probability of a false positive or negative result.

Performance.

Two different US-guided approaches to GON block were evaluated in a study of 20 cadavers.34 The first approach was at the level of the superior nuchal line while the second was at the level of the second cervical vertebra. Accuracy of injection was evaluated by dye staining of the GON, which was reported to be 80% and 100% for the 2 approaches, respectively.

Efficacy.

Sensory block in the dermatomal distribution of GON at 15 minutes after injection of local anesthetic and steroid using US compared with anatomical landmark guidance was reported in a case series of 45 patients with occipital neuralgia and cervicogenic headache.35 The authors described rapid onset of analgesia after all (22 of 22) the injections in the US group and 20 of 23 patients in the anatomical landmark group. Pain scores at 4 weeks after injection were reported to be significantly lower in US group as compared with the anatomical landmark group (reduction in pain scores by 64% and 42%, respectively).

Safety.

No comparative data available.

Cervical Sympathetic Trunk

Cervical sympathetic trunk (CST) block is performed for a variety of indications including sympathetically mediated pain and ischemia of the upper limb. Anatomical landmark- and fluoroscopy-based techniques can lead to incorrect needle placement due to variability in size and location of bony landmarks as well as the CST itself.58,59 The literature is replete with discussion of potential and reported complications from non–US-guided techniques, including unintended puncture of vertebral artery and esophagus.58,60

Performance.

Surrogate markers of accurate localization for CST blockade include increase in skin temperature, increase in upper limb blood flow, Horner syndrome, and change in skin resistance after injection of local anesthetic.61 A case series (1 of the first on use of US for interventional pain procedures) reported that stellate ganglion block (as evidenced by vasodilation and presence of Horner syndrome) was achieved after all 12 US-guided attempts compared with 11 of 12 attempts for the anatomical landmark group.36 Block onset within 10 minutes was observed in all patients in the US group compared with 10 of 12 patients in the anatomical landmark group. It is noteworthy that larger volumes (8 mL) were used in the anatomical landmark group compared with the US group (5 mL). Accuracy of US guidance for CST blockade was also validated in cadavers and live subjects by dissection and fluoroscopy, respectively, and an injectate volume of 5 mL was found to be adequate for spread from the fourth cervical level to the first thoracic level.37

Efficacy.

No comparative data available.

Safety.

Kapral et al.36 reported neck hematoma formation in 3 of 12 patients who underwent CST using anatomical landmarks, whereas none of the 12 patients in the US group suffered this complication.

Suprascapular Nerve

Suprascapular nerve (SSN) block is performed for the treatment of chronic shoulder pain. SSN block is traditionally performed with either the aid of a nerve stimulator or fluoroscopy, but neither of these aids can ensure accurate perineural deposition of injectate or prevent a pneumothorax that may result from inadvertent anterior positioning of the needle. In addition, the suprascapular notch, which is often used as a radiological landmark, varies in shape and may be absent in up to 8% of the population.62 Such variation in anatomy can pose problems for injection techniques that rely on fluoroscopy for guidance.

Performance.

US is reported to allow visualization of the SSN itself without reliance on the suprascapular notch for nerve localization. A recent case report endorsed the accuracy of US guidance for SSN blockade in 1 cadaver and 1 patient using dissection and fluoroscopy for validation, respectively.38 However, in a case series of 27 patients in which electric current thresholds for stimulation of SSN were used for validation of the US-guided approach in the supraspinous fossa, only 5 patients had stimulating thresholds within the accepted range (between 0.1 and 0.8 mA).39 Siegenthaler et al.40 described a new, more proximal approach in the supraclavicular area of cadavers and volunteers for identifying the SSN with US. This novel US-guided approach was more successful for identifying the SSN compared with the US approach in the supraspinous fossa (81% and 36%, respectively). The authors performed 20 injections of dye around the SSN in 10 cadavers with this new approach and reported that 19 of 20 injections were accurate as confirmed by dissection.40

Efficacy.

Gorthi et al.41 performed a RCT comparing the efficacy of US- versus anatomic landmark-guided SSN blocks in 50 patients. Though both groups showed significant improvement in pain scores immediately after the procedure, patients in the US group maintained lower (45% reduction from baseline) pain scores 1 month after the procedure, while pain scores in the anatomic landmark group had reverted to baseline.

Safety.

Gorthi et al.41 reported 2 cases of arterial punctures and 3 cases of nerve injury with deficits persisting for 2 months in the anatomical landmark group but no complications in the US group. There were no cases of pneumothorax in either of the groups.

Intercostal Nerve

Intercostal nerve (ICN) blockade is often performed to relieve pain from intercostal neuralgia. Pneumothorax and intravascular injection are potential complications of this technique. ICN blocks can be performed using landmark-based techniques, fluoroscopy, nerve stimulation, and US guidance, but US is the only modality that allows visualization of the pleura and intercostal vessels in real-time during needle placement.

Performance.

A recent cadaver study reported that US guidance enabled sufficient spread of dye for ICN block at the midthoracic level with as little volume as 2 mL per side.42

Efficacy.

In a retrospective study of 29 patients with chronic pain, Shankar and Eastwood43 found a similar reduction in pain scores (40%–50%) and duration of pain relief (6–7 weeks) between 12 patients who received US-guided ICN blocks and 27 others who had their ICN blocks performed under fluoroscopic guidance. Patients in both groups received a mixture of local anesthetic (5% tetracaine) and steroid.

Safety.

Shankar and Eastwood43 reported no cases of inadvertent intravascular needle placement when US was used to guide ICN blockade yet 2 cases of inadvertent intravascular needle placement among the 27 patients who underwent fluoroscopic-guided ICN. There were no cases of pneumothorax in either of the groups.43

Ilioinguinal and Iliohypogastric Nerves

Ilioinguinal and iliohypogastric nerve blocks are performed in patients with chronic groin pain after lower abdominal or pelvic surgery. A multitude of landmark-based techniques have been described, and there is a lack of consensus regarding the optimal approach.1 US guidance allows visualization of muscles of the abdominal wall so that the needle may be accurately placed in the fascial expansion between the internal oblique and transversus abdominis muscles where the 2 nerves are located. It has also been suggested that the use of US guidance may help to avoid complications, such as femoral nerve palsy63 and bowel perforation in children;64 however, there is a distinct lack of adult comparative data in the literature.

Performance.

Eichenberger et al.44 reported that the US-guided injection of 0.1 mL dye around the ilioinguinal and iliohypogastric nerves in 37 cadavers accurately stained the nerves in >95% of attempts.

Efficacy.

No comparative data available.

Safety.

No comparative data available.

Lateral Femoral Cutaneous Nerve

Blockade of the lateral femoral cutaneous nerve (LFCN) is used for the diagnosis and management of meralgia paresthetica, a neuropathic pain condition resulting from injury to the LFCN. Traditional techniques for blocking the LFCN, which rely on anatomical landmarks, such as the anterior superior iliac spine, can fail because of the inconsistent relation of the anterior superior iliac spine to the LFCN.1

Performance.

Ng et al.45 investigated the accuracy of needle placement for US guidance compared with anatomical landmarks for blocking the LFCN in cadavers and subsequently in volunteers. Of the 19 needle insertions performed in cadavers using anatomic landmarks, the needle was confirmed by dissection to be in contact with the nerve only once compared with 16 of 19 needles that were in contact with the nerve using US guidance. In the second phase of this study performed in 20 volunteers, the accuracy in locating the LFCN was 80% and 0% for US- and landmark-based techniques, respectively, as confirmed by a nerve stimulator. Another study evaluated volume of local anesthetic required to block the LFCN using US in 10 patients with meralgia paresthetica. Five of these patients had a BMI >30 kg·m−2. Injectate volumes varying from 1 to 8 mL were required to achieve sensory block of the LFCN. The authors acknowledged that they had used 7 to 8 mL for the first 2 patients, but subsequent injections required only 1 to 2 mL.46 In a descriptive study including 1 cadaver and 8 volunteers, injection of 0.3 mL of dye or local anesthetic under US guidance was found to be adequate as confirmed by dye staining of the LFCN and rapid sensory loss, respectively.47

Efficacy.

Tagliafico et al.48 described a series of 20 patients who underwent US-guided injections of local anesthetic and steroid for treatment of meralgia paresthetica. The authors reported a significant reduction in visual analog scale pain scores in all patients at 2 months after the procedure. However, relatively large volumes (9 mL) of injectate were used, and 4 of the 20 patients had required a repeat US-guided LFCN block procedure at 1 week.

Safety.

No comparative data available.

Pudendal Nerve

Pudendal nerve (PN) block is performed for the diagnosis and treatment of pudendal neuralgia. Conventional fluoroscopic-guided techniques for blocking the PN rely on placement of the needletip medial to the ischial spine,65,66 but fluoroscopy does not allow identification of the depth at which the PN courses in the plane between the sacrospinous and sacrotuberous ligaments. An approach to access this interligamentous plane using CT scan has been described,67 but CT scan is not readily accessible and carries the dual risk of unintended puncture of adjacent vessels and exposure to radiation. US may allow direct visualization of the anatomical landmarks in close proximity to the PN, such as the ischial spine, internal pudendal artery, and the sacrospinous and sacrotuberous ligaments while enabling the interventionalist to track the spread of the injectate in real time.

Performance.

US-guided placement of needles for PN block was validated using fluoroscopy to record position of the needletip in relation to the ischial spine in a case series of 17 patients.49 There was a high degree of agreement between the 2 imaging modalities, and injection of local anesthetic was associated with a 100% incidence of sensory block in the perineal area. In a recent crossover study, Bellingham et al.50 evaluated the accuracy of PN blocks performed using US compared with fluoroscopy in 23 patients. Each patient received bilateral PN blocks, one side using US and the contralateral side using fluoroscopy. Both imaging techniques were associated with a success rate of 80% for corresponding PN sensory blockade. However, the US-guided technique required significantly more time to perform compared with the fluoroscopy-guided technique.

Efficacy.

No comparative data available.

Safety.

Bellingham et al.50 reported no differences in frequency of inadvertent sciatic nerve block between US- and fluoroscopic-guided PN block.

Piriformis Muscle

Piriformis syndrome is an uncommon cause of buttock and leg pain. The management of piriformis syndrome includes the injection of the piriformis muscle with local anesthetic and steroids or botulinum toxin. This procedure is usually performed under fluoroscopic guidance.1

Performance.

In a cadaveric study, Finnoff et al.51 reported accurate needletip placement rates of 95% after 10 US-guided piriformis injections compared with 30% after 10 fluoroscopic-guided injections as confirmed by dissection. Notably, the fluoroscopic-guided injections resulted in a 65% incidence of misplaced injectate (into gluteus maximus) as compared with a 5% incidence with US-guided injections.51

Efficacy.

No comparative data available.

Safety.

No comparative data available.

DISCUSSION

Our review of the literature reveals that the utility of US as an alternative to traditional guidance techniques for chronic pain procedures is variable and depends on the specific type of procedure performed. Table 6 presents a summary of the available evidence that supports the use of US as a practical alternative to traditional guidance techniques. However, much of the data supporting the use of US as an alternative guidance technique stem from cadaveric studies, volunteer feasibility studies with relatively small sample sizes, or comparative studies with insufficient blinding, randomization, and/or power to detect significant differences between groups. The translation of results from cadaveric studies into clinical practice is inevitably limited by relatively poor compliance of embalmed cadaveric tissue while the lack of blood flow can complicate provider appreciation of the accuracy, extent, and safety of needle placement and injection.68 The small sample sizes also preclude reliable measurements of complication rates. Finally, most of the patient studies excluded patients with anatomic variations or pathologies. It follows that the results of these studies may not apply to the heterogeneous case mix encountered in routine clinical chronic pain practice.

Table 6
Table 6:
Summary of Evidence in Support of Ultrasound Guidance as a Useful Alternative to Traditional Guidance Techniques for Interventional Pain Procedures

US technology is subject to a number of limitations that likely contribute to the small size and number of published studies, as well as explain the guarded optimism on the part of chronic pain providers. First, the resolution of modern portable US machines is finite. Suboptimal resolution combined with small size targets (medial branches supplying lumbar facet joints) and, frequently, obesity, further reduce image quality. Next, interventionalists familiar with fluoroscopy but new to US require additional training and skill.26 US images are fundamentally different from fluoroscopy because US shows only those structures within the path of the beam, whereas fluoroscopy allows visualization of surrounding areas. Operators may find it easier to convert/reconstruct mental 3-dimensional pictures of the spine from images obtained from fluoroscopy than those obtained from US, which may at least partially explain why US-based techniques tend to require more procedure time. This may improve as experience with US increases. Moreover, US does not illuminate contrast dye to confirm delivery of injectate around or into the area of interest (e.g., spinal nerve root and facet joint, respectively) and to exclude uptake by other anatomical structures such as blood vessels. There is also potential for incorrect spinal level identification during US-guided neuraxial injections. Unlike fluoroscopy, US does not always offer the option of visualizing multiple vertebrae in 1 view.69 This makes correct level identification particularly difficult in patients with altered spinal anatomy from pathology or surgery. Moreover, lumbarization of sacral vertebrae or sacralization of lower lumbar vertebrae may render the identification of the correct vertebral level with US problematic. Finally, certain spinal levels (e.g., interspace between the fifth lumbar and first sacral vertebrae) may be difficult to access with the US beam because of acoustic shadowing caused by the ilium. However, a large iliac crest and prominent transverse processes of the fifth lumbar vertebra can also make fluoroscopy-guided procedures quite challenging.

The Future

Despite the aforementioned shortcomings, US imaging for interventional pain procedures is evolving at a rapid pace. The American, European, and Asian-Australian societies of regional anesthesia and pain medicine have recently released consensus guidelines describing requisite training and skill for the performance of US-guided interventional chronic pain procedures,70 while exciting innovations abound, including virtual reality guidance systems and fusion imaging with other modalities such as CT scanning. Virtual guidance involves acquisition of CT images registered into a virtual world that includes images generated by an US probe tracked in real time, permitting guidance of tracked needles. In experiments with phantoms and cadavers, this guidance system helped achieve a high degree of accuracy for lumbar facet injections.71 Image fusion of real-time US with previously obtained CT scans has also been proposed to guide needle insertion into the cervical and lumbar facet and SIJs.14,25 Finally, there may prove to be a role for combined US and fluoroscopy guidance in certain procedures, such as caudal epidural and ganglion impar injections, where US can help in identifying the initial site for needle insertion while fluoroscopy can then be used to confirm depth and angulation of needle as well as spread of injectate by mixing with contrast.

In conclusion, recent evidence suggests that US guidance may match or improve performance- and safety-related outcomes compared with many anatomic landmark- and fluoroscopic-guided techniques; however, there are presently insufficient data to support improved efficacy for relieving chronic pain in both the short and long terms.

DISCLOSURES

Name: Anuj Bhatia, MBBS, MD, FRCA, FRCPC, FIPP, FFPMRCA, EDRA.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Anuj Bhatia approved the final manuscript.

Name: Richard Brull, MD, FRCPC.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Richard Brull approved the final manuscript.

This manuscript was handled by: Spencer S. Liu, MD.

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