Chapter 20 Ultrasound-Guided Lumbar Spine Injections

Manfred Greher

Chapter Overview

Chapter Synopsis: This chapter focuses on the use of ultrasound imaging for guidance during many different types of injection procedures for back pain. The benefits of using ultrasonography include its economy, portability, and safety. Any spinal injection procedure requires an intimate knowledge of the underlying anatomy, and use of ultrasound guidance requires a similar familiarity with the intricacies of sonographic data. Ultrasound needle guidance has recently supplanted some more traditionally used imaging techniques, including computed tomography and fluoroscopy. Future development of the technique may include the use of three-dimensional sonographic imaging. The techniques guided by ultrasonography described in the chapter include injections for lumbar medial branch or facet nerve block, facet joint injections, lumbar periradicular injections, and intramuscular trigger point injections. Practitioners should take advantage of hands-on learning opportunities, and novices should focus on intramuscular injections to develop expertise in ultrasound-guided injection techniques.

Important Points:

Ultrasonography is an emerging technique to guide lumbar spine injections.

Basic sonoanatomic knowledge and needle guidance skills are necessary for good-quality blocks with exact target control.

Textbooks, Internet resources, cadaver courses, workshops, and hands-on teaching are excellent ways to increase the individual training level.

For novices, it is best to start with easy blocks such as intramuscular or trigger point injections.

Whenever vascular uptake could be devastating and cannot be ruled out reliably with ultrasonography, ultrasound-guided techniques should not be performed alone (i.e., selective lumbar nerve root injections).

Clinical Pearls:

For a medial branch block, reaching the cranial part of the transverse process with the needle tip immediately at the first puncture attempt can be accomplished as follows: With a paramedian short-axis view between two transverse processes and a transducer movement from cranial to caudal, the first bony line encountered is the cranial edge of the transverse process.

In difficult cases, the practitioner may choose to perform the puncture in a paramedian long-axis view above the transverse processes with an out-of-plane technique and verify the position in the short-axis view afterward.

Clinical Pitfalls:

The L5 dorsal ramus block has not been described and validated methodologically so far.

Sacralization or lumbarization can lead to wrong assignment of the segments; the practitioner should always check the radiographs before, if they are available.

Introduction

This chapter summarizes today’s knowledge and evidence about ultrasound-guided lumbar spinal injections with a focus on sonoanatomy and clinical practice.

Today low back pain is a big medical and economical challenge not only for the physician and the individual patient but also for the community. Although nonspecific low back pain, in which invasive interventions should be reduced to a minimum if not avoided at all, seems to be the predominant entity, in many cases, specific causes and confined anatomical sources are the reason for pain or have to be ruled out. Traditionally, fluoroscopy or even computed tomography (CT) has been used in these cases as guidance devices, first to increase specificity and second to avoid complications arising from improper needle placement. In the past years, ultrasonography moved into the focus of interest not only in regional anesthesia but also for interventions in pain medicine. Ultrasound-guided injection techniques are interesting alternatives to fluoroscopy- and CT-guided methods. Today, portable ultrasound machines offer high quality together with a relatively moderate price. Advantages include no exposure to ionizing radiation for both the patient and the physician, availability as a bedside method, and use in remote locations such as developing countries because there is no restriction to specially equipped radiological facilities. As opposed to radiography, there is no contraindication for ultrasonography during pregnancy, which is another great advantage, when treatment of severe low back pain is especially challenging and injections are unavoidable.

Lumbar medial branch or facet nerve blocks, facet joint injections, intramuscular trigger point injections, and lumbar periradicular injections have become technically possible with ultrasound guidance or assistance. A concise presentation and validation of the methods follows.

Basic Principles of Ultrasound-Guided Injections

Ultrasound Machines, Transducers, and Knobology

Today a huge variety of ultrasound machines in different sizes from different companies is available. Portable machines have reached quality levels comparable to larger scale gear. For applications in regional anesthesia and pain therapy, high-resolution technology combined with excellent musculoskeletal imaging properties is of great help to the practitioner. Linear broadband transducers with high frequencies up to 15 MHz are preferred when small structures close to the surface have to be targeted. Curved-array broadband probes with lower frequencies around 5 MHz are used for deeper targets. At least one of each of these two basic types of transducers should be available to physicians routinely performing ultrasound-guided interventions in pain management. Fig. 20-1 shows a typical linear probe on the left side of the image and a curved-array probe on the right with a schematic shape of the resulting sonographic images. Please note that the side of the mark on the transducer (arrow) is corresponding to the mark on the image (star). This is important for correct image orientation. Color-flow Doppler ultrasonography helps to identify vessels and is part of the basic machine equipment today. Finally, the operator has to be familiar with basic machine settings such as depth, gain, and focus.

Fig. 20-1 Linear transducer (left) and curved array transducer (right). The side of the mark on the transducer (arrow) is corresponding to the mark on the image (star).

Needles, Techniques, and Sterility

Needle choice depends on both target depth and operator preference. Better visualization is possible with larger diameter needles and shallow insertion angles; however, patient comfort is often associated with the contrary. Good choices are needles with facet tips and diameters between 20 and 25 gauges. Recently, higher reflective ultrasound needles have been developed and are the subject of evaluation at the moment. Image orientation can be short or cross axis (SAX; i.e., transverse plane) or long axis (LAX; i.e., longitudinal plane relative to the target nerve or the spinal column). Needle insertion can be out of plane or in plane relative to the LAX of the transducer’s footprint. Whereas out-of-plane techniques offer shorter access but only visualization of the needle tip, in-plane techniques are associated with a longer path to the target but visualization of the entire needle (Fig. 20-2). The needle insertion point for the out-of-plane technique is close to the longer side; for the in-plane technique, it is close to the shorter side of the transducer’s footprint (Fig. 20-3). Sometimes the transducer has to be turned 90 degrees after needle insertion to ensure proper positioning in a second plane. Sterile working conditions are mandatory for invasive procedures, including covering of the probe and use of sterile ultrasound gel. Special covers designed for this purpose are available today; the image shows how to cover a probe with such a shield (Fig. 20-4).

Fig. 20-2 Scheme of transducer relative to the needle and the nerve. IP, in plane; LAX, long-axis view; OOP, out of plane; SAX, short-axis view.

Fig. 20-3 Needle insertion points for out-of-plane (OOP) and in-plane (IP) injections.

Fig. 20-4 Sterile covering of a probe: A, start; B, covering; C, securing; D, ready to use.

Knowledge of Sonoanatomy, Artifacts, and Training

Knowledge of the relevant paravertebral sonoanatomy, including landmark structures, and a basic idea of possible variability is paramount for excellent performance. Moreover, the operator has to be familiar with ultrasound artifacts such as shadowing, reverberations, and mirror imaging to not misinterpret examinations. Continuous training in scanning and needle guidance is necessary to maintain high quality. For the beginner, ultrasound phantoms can be helpful. Workshops and hands-on training are most valuable to accelerate the learning process.

Sonography of the Lumbar Spine—Basic Scanning Sequence

With a curved array probe, first a basic scanning sequence of standard planes should be performed to ensure total anatomical and segmental orientation of the region. Depending on the age and body mass index (BMI) of the patient, frequency ranges between 2 and 7 MHz are applied. For slimmer and younger people, higher frequencies are useful because of better detail resolution in small distances. On the contrary, if the target is deeper, lower frequencies are necessary to provide enough tissue penetration, although this means worse image resolution. Normally, 3 to 5 MHz is a good choice.

The basic scanning sequence can be done before skin disinfection and sterile draping with nonsterile gel and no probe cover or after the preparation but then necessarily with sterile gel and a probe cover on. The patient is in prone position with a pillow under the stomach to compensate for lumbar lordosis. The sonographer sits on the patient’s left side facing the ultrasound machine next to the head of the patient. The basic scanning sequence consists of five standard planes and starts in the midline above the spinous processes of the lower lumbar spine (Fig. 20-5).

Fig. 20-5 Medial longitudinal scan.

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