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Abstract
Introduction XXI century has brought high resolution ultrasound (HRUS) to contemporary interventional pain practice. It has been taken enthusiastically by many practitioners with more reservation from others.
In 2012 it has been only few hundred publications related to ultrasound in pain medicine (USPM) in comparison to more than 2000 dedicated to ultrasound guided regional anaesthesia (UGRA). By 2023 it has been around 1500 articles concerning USPM with around 5000 of UGRA. (Pubmed search- September 2023).
Teaching and training have been thriving around the world. After initiation by dr Barry Nicholls in 2008 author of this abstract has been running RA-UK USPM course in London coming to 16th edition next year. We have been proudly hosting the Faculty who have been pioneering USPM combining clinical expertise with anatomical knowledge: Bernhard Moriggl, Urs Eichenberger, Manfred Greher, Samer Narouze, Philip Peng just to mention a few. We trained few generations of pain physicians by now, some of them becoming faculty of the course and teaching globally.
HRUS opened a new horizon for pain medicine bringing precision, safety, diagnostic potential and as the result, better outcome. Pain medicine has become more interdisciplinary involving radiology, rheumatology, sport medicine, neurology, physiotherapy and other specialities.
HRUS has changed our clinical practice in pain interventions such as stellate ganglion, occipital nerves, cervical roots, peripheral nerves diagnostic, peripheral nerve stimulation(neuromodulation), musculoskeletal including joint injections . For some procedures, especially around lumbar spine, although confirmed by feasibility study, HRUS does not offer advantage over fluoroscopy especially in patients with increased body habitus.
Figure 1 shows author’s classification of clinical applications of ultrasound in interventional pain practice.
There are specific procedures where information from ultrasound and fluoroscopy imaging complements each other making given procedure safer, more precise and less time consuming.
Following are highlights of combined/hybrid techniques: ultrasound and fluoroscopy
Cervical spine Cervical Medial Branch Blocks:
There is plethora of fluoroscopy guided techniques: posterior, lateral, anterior, oblique approach involving multiple x-ray beam adjustment to position the tip of the needle in the middle of articular pillar.
Ultrasound technique described by Siegenthaler et al.1 consist of long axis scan visualising wavy, sinusoid with top being facet joints and bottom waist of articular pillar. Out of plane, anterior to posterior needle direction has been advocated to avoid inadvertent vertebral artery puncture. ‘In Plane ‘approach described by Finlayson et al.2 follows in plane path from posterior to anterior and place the needle on the target at the middle upper part of the waist of articular pillar.
Reversed fluoroscopy/ultrasound techniques has been published by Krol et al.3 and in Ultrasound-guided interventions in chronic pain management.4Patient in prone position, needle entrance under fluoroscopy tunnel view in AP projections form posterior to anterior. Lateral projection assesses advance to the articular pillar of the desired level. Finally, under ultrasound in transverse, short axis view needle is adjusted to rest in final position close to the bone, behind the posterior tubercle, away from the nerve root. Presence of vessels and spread of the injectate is observed directly. Long axis view also confirms accurate needle position.
Figure 2 - Described technique reduces significantly amount of radiation used for each intervention yet easily defines the level of vertebra addressed. Final adjustment with ultrasound allows confident, safe injections and radiofrequency thermal lesion. One entry point can be used for most levels reducing procedure discomfort.
Cervical Nerve Roots Ultrasound guidance allows not only visualise nerve roots leaving foramina but appreciate associated arteries including vertebral artery (VA), other neural structures and to certain extend spread of the solution. Ultrasound identification of the nerve root in question is relatively straightforward once pattern of recognition is followed. Dynamic scanning is required for counting the right level.
Figure 3 - Showing C7 nerve root and VA as a two black (hypoechoic) round structures. Colour doppler shows VA in front of the nerve root Fluoroscopy picture shows spread of the contrast extraforaminal or epidural in AP and lateral projection. Plastic model shows transverse probe position at C7 level.
The course of the nerve within the foramen is only few mm and its often occupies the whole space especially if narrowed. The needle tip position just outside the foramen seems to be safe and effective. Injection pressure monitoring is recommended to detect intraneural needle position and avoid inadvertent spread.5
Thoracic spine Fluoroscopy and HRUS are perfect hybrid technique. Exact level required for interventions and bony landmarks are easily identified by x-ray image. HRUS allows direct needle visualisation reaching the targets: thoracic nerve root, paravertebral space, intercostal nerve, medial branches, costotransverse joint and ligament. Erector spinae fascial plane can be easily targeted if one wishes so.
The main indications for interventions are persistent post-surgical pain (PPSP – post thoracotomy, breast surgery, chest trauma), intercostal neuralgia, postherpetic neuralgia, costotransverse, costovertebral and thoracic facet pain.
Figure 4 - shows diagram of typical targets and US probe position, US images and paravertebral contrast spread with needle on target.
Lumbar Sympathectomy Lumbar sympathetic chain is targeted at anterior-lateral surface of L2 and L3 vertebral body. Fluoroscopy technique requires estimate needle angulation to reach the level. HRUS allows to see the needle trajectory and appreciate thoracolumbar fasciae and muscular layers: latissimus dorsi, erector spinae, quadrats lumborum, psoas. Each of the fasciae or muscles can be a target for intervention if required.
Sacroiliac Joint block and denervation Sacroiliac joint (SI) is the largest synovial joint in human body and often overlooked source of pain. Blind technique achieves intraarticular location in only 20% of cases. 68% are within 1 cm of the joint, epidural and sacral foramina flow appear in 24% and 44% respectively.6 Therefore, image guidance is recommended. Fluoroscopy guidance requires alignment of anterior and posterior part of the joint and does not appreciate iliac bone overlapping and obscuring access to the joint. It has been confirmed by feasibility study that around 60 ultrasound guided injection are required to achieve proficiency.7 Lower part of the joint is usually accessible at the level of S2 foramen. Needle direction from medial to lateral. With progressing age, I synovial cleft become narrower making intraarticular injection very difficult or even impossible forcing needle to be withdrawn. Periarticular injection is acceptable. Fluoroscopy with oblique angulation aiming at ‘tunnel vision’ of the needle completes the procedure.
HRUS may be also used to assist SI joint denervation with Simplicity probe as described by Krol et al.8 Entry point, advancing the probe close to the bone surface, alignment lateral to the line of foramina and medial to the SI reduces the risk of visceral damage or entering the spinal canal. Reduced radiological exposure time is highlight of the procedure.
Figure 7 shows ultrasound and fluoroscopy imaging of the procedure
Caudal epidural Caudal epidurals in chronic pain management are not used for they efficacy but potential safety by entering the epidural space away from spinal stenosis level or postoperative changes. Catheter can be inserted and advanced cranially if desired. Fluoroscopy guided caudal epidural can be surprisingly challenging especially in patient with increased body habitus. HRUS allows to identify sacral cornua in transverse projection and after 90 degrees probe turn, in plane needle trajectory leads to the epidural space. Radiological contrast injection confirms the tip position, visualise epidurogram and excludes intravascular spread.
Hip articular branches Clinical need refreshed anatomical knowledge of the articular, sensory branches innervating the hip joint. It has sparked interest amongst regional anaesthetist, pain physicians and orthopaedic surgeons. The main indication being palliative treatment of inoperable hip fracture and patients with hip OA who are on waiting list for THA for whom simple intraarticular injections stopped being effective, patients for whom operation risk outweigh the benefits, or simply do not have access to such treatment.
Femoral articular branches (FAB), accessory obturator nerve (AON) and obturator articular branch (OAB)are the targets. There are only case reports and case series describing the approach under fluoroscopy guidance, ultrasound guidance or combination of both. Hybrid technique provides the safest approach with ultrasound not only visualising targets but also neurovascular structures to be avoided on the needle trajectory. The inferiomedial acetabulum (radiological teardrop), target for OAB might be difficult to visualize by ultrasound alone. Based on fluoroscopy and US imaging the needle path is chosen on case-to-case bases. Local anaesthetics (LA), radiofrequency ablation and small volume of neurolytic agents 0.5-1.0ml can be used.
Figure 9 shows both imaging modalities.
Knee articular branches- Genicular nerves Publication by Choi et al.9 demonstrating long term benefit after ablation of sensory branches innervating anterior knee joint drawn international attention. Initial description of targeting superiolateral, superiomedial and inferiomedial branches under fluoroscopy guidance has been translated to ultrasound guided technique described also by the author group.10 Both techniques stand and complement each other eg. Fluoroscopy may help in defining inflexion point of diaphysis and epiphysis easily lost with ultrasound when 90 degrees probe adjustment is exercise for in plane needle introduction. Beside precise position, many new anatomical studies described large variety of genicular nerves numbers, their course and origin explaining not consistent outcome after intervention. There are various ways to increase the lesion size not to be discussed in this manuscript.
One of the ways to improve the outcome could be adding inferolateral branches from inferolateral genicular nerve and recurrent articular branch which has become author routine practice. Common peroneal nerve is traced from popliteal area until division to deep and superficial branch and recurrent articular branch along with artery traced cranially to the level of Gerdy’s tubercle.
Figure 10 Ultrasound and fluoroscopy approach with needles inserted at 4 points including inferolateral as described.
Summary Hybrid imaging with combination of ultrasound and fluoroscopy has been increasingly used providing safer approach, precise position on target resulting in better outcome for both patient and provider satisfaction. Author institution St George’s University Hospital Anaesthetic Department and Chronic Pain Service has been recognized ESRA training centre offering hands on experience for those holding GMC registration.
References
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