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REGIONAL ANESTHESIA

Ultrasound Guidance for Facet Joint Injections in the Lumbar Spine: A Computed Tomography-Controlled Feasibility Study

Klaus Galiano, MD^*, Alois Albert Obwegeser, MD, MS^*, Gerd Bodner, MD, Martin Freund, MD, Herbert Maurer, MD, Florian Stefan Kamelger, MD, Reinhold Schatzer, MS^||, and Franz Ploner, MD

*Clinic of Neurosurgery, Clinic of Radiology, Institute of Anatomy and Histology, Leopold-Franzens-University, Innsbruck, Austria; Department of Anesthesiology and Pain Care, Hospital of Vipiteno, Vipiteno, Italy; ||RTI International, Durham, NC

Address correspondence and reprint requests to Alois Albert Obwegeser, MD, MS Clinic of Neurosurgery University of Innsbruck Anichstraße 35 A-6020 Innsbruck, Austria. Address e-mail to alois.obwegeser{at}uibk.ac.at.

	Abstract

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We conducted this study to develop an ultrasound-guided approach for facet joint injections of the lumbar spine. Five zygapophyseal joints (L1-S1) on each side of 5 embalmed cadavers were examined by ultrasound for a total of 50 examinations. The joint space was demonstrated under ultrasound guidance. The midpoint of the joint space, defined as the middle of its cranio-caudal extension on its dorsal surface, was taken as a reference point, and its position was computed from its depth and lateral distance from the spinous process. Forty-two of 50 approaches could be clearly visualized. Subsequently, these distances were compared to those obtained by computed tomography (CT). To assess the efficacy of ultrasound in the needle placement, all lumbar facet joints were approached in one embalmed cadaver. The exact placement of the needle tips was again evaluated by CT. Ultrasound and CT measurements showed the same mean depth and lateral distance to the reference point, 3.15 ± 0.5 cm and 1.9 ± 0.6 cm, respectively. Pearson’s coefficient of correlation was 0.86 (P < 0.0001) between ultrasound and CT. All 10 needle tips were within the joint space during simulated facet joint injections. We conclude that ultrasound guidance might be a useful adjunct for facet joint injections in the lumbar spine.

	Introduction

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Facet joint-mediated pain has been identified as a frequent cause of low back pain (1). Injections for facet syndrome are preferentially performed as computed tomography (CT) or fluoroscopically controlled interventions (2,3). Ultrasound is reliable and accurate in visualizing the lumbar paravertebral anatomy (4). The benefits of applying it in real time for different injection therapies have been demonstrated in several studies (5–10).

This study was designed to assess the feasibility and accuracy of an ultrasound-guided approach for facet joint injections of the lumbar spine.

	Methods

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This study was conducted in two steps. The first part included an imaging study to identify and depict the joint space of the lumbar facet joints by using ultrasound. In step two, an experimental study was conducted to evaluate the efficacy of ultrasound in facilitating facet joint needle placements.

Imaging Study
After obtaining institutional approval, one radiologist experienced in musculoskeletal ultrasound performed ultrasound-guided posterior approaches to the facet joints in the lumbar spine on five prepared cadavers that had been donated to the institute of anatomy. To achieve a reasonable similarity to live patients, the cadavers were embalmed following a special procedure (ethyl alcohol/glycerin conservation). However, on 2 cadavers (3 levels on one cadaver, 5 levels on the other) limitations were encountered in the ultrasound imaging process because of entrapped air.

Ultrasound examinations were performed with a standard ultrasound device (Philips, HDI 5000), using a broadband curved array transducer working at 2–5 MHz and a broadband linear array working at 4–7 MHz. Imaging errors can be kept at a minimum by taking the linear array for measurements. However, the curved array provides a better penetration depth.

The cadavers were seated prone and bilateral ultrasound-guided approaches were performed at levels L1-S1. To identify the different spinal levels, posterior paravertebral parasagittal sonograms were obtained (Fig. 1). The spinous process and adjacent structures (lamina of the vertebral arch, facet joint, accessory process, and mamillary process) were delineated by means of transverse sonograms at each level and the midpoint of the joint space of the facet joint was established as the reference point. The midpoint was defined at the center of the cranio-caudal extension of the lumbar facet joint space of its dorsal surface (Fig. 2).

View larger version (28K): [in this window] [in a new window]   Figure 1. Spinous processes of L1-5 demonstrated in a posterior paravertebral parasagittal sonogram using the panoramic view technique of ultrasound.

View larger version (89K): [in this window] [in a new window]   Figure 2. Definition of the reference-point (needle tip) as the midpoint of the lumbar facet joint in its cranio-caudal extension on its dorsal surface in a lumbar model. cp = costal process, sp = spinal process, mf = medial facet, lf = lateral facet.

Each sonogram was frozen and measurements computed by using the measuring functions of the ultrasound device. Two distances (A and B, Fig. 3) were established to assess the position of the joint space relative to the spinous process on the transverse sonograms on all five cadavers. Depth (A) indicates the distance from the middle of the tip of the spinous process to the reference point, whereas the lateral distance (B) was defined as the horizontal distance from the middle of the tip of the spinous process to the reference point (perpendicular to the spinous process) (Fig. 3).

View larger version (54K): [in this window] [in a new window]   Figure 3. Axial transverse anatomical, ultrasound and computed tomography image of the facet joint at level L4-5. Depth (A) indicates the distance from the middle of the tip of the spinous process to the reference point, lateral distance (B) was defined as the horizontal distance from the middle of the tip of the spinous process to the reference point (perpendicular to the spinous process). sp = spinal process, closed arrow = joint space, open arrow = bone fragment with lateral facet.

All ultrasound measurements were made in the center of the sonograms parallel to the axis of the ultrasound beam to achieve the best results (11).

Subsequently, distances A and B were evaluated by using a spiral CT (Synergy; GE Medical Systems, Milwaukee, WI), reformatted to 1-mm axial slices. The distances A and B were measured as described above (Fig. 3). Pearson’s coefficient of correlation was calculated to compare ultrasound and CT measurements. All values are presented as mean ± sd.

Experimental Study
To simulate joint infiltration, on one embalmed cadaver a spinal needle (20-gauge, 90 mm, Yale Spinal, Spain) was advanced under ultrasound guidance into the joint space of each lumbar facet joint. The needles were inserted 3–4 cm laterally from the midline on the lateral end of the transducer and precisely positioned in the ultrasound plane at an angle of approximately 45° with respect to the axial plane. This enabled visualization of the entire needle, which appeared as a bright line-shaped echo pattern in the transverse sonogram (Fig. 4). If a needle deviated from its intended direction during the approach, the inline technique allowed for accurate repositioning under ultrasound guidance. The placement of the needle tips was also identified by CT (Fig. 4).

View larger version (33K): [in this window] [in a new window]   Figure 4. Axial transverse computed tomography and corresponding ultrasound image demonstrating the needle placement within the facet joint. sp = spinal process, mf = medial facet, lf = lateral facet, big open arrow = needle, small open arrow = joint space, small closed arrow = capsule of facet joint.

	Results

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Imaging Study
Fifty ultrasound-guided approaches on 5 embalmed cadavers were performed. Eight of 50 positioning attempts were not feasible because of reduced imaging conditions in 2 embalmed cadavers (trapped air) as a result of cadaver conservation. Two facet joints could not be identified and were incorrectly assessed too lateral and cranial. When transmitting these failed measurements on the corresponding CT scans, the reference points were located between the mamillary process and the accessory process.

Ultrasound and CT provided the same mean measurements for distance A (US, 3.15 ± 0.51 cm; CT, 3.15 ± 0.50 cm) and distance B (US, 1.93 ± 0.60 cm; CT, 1.86 ± 0.56 cm).

The individual differences of ultrasound and CT distances were 0.3 ± 0.2 cm for distance A and 0.3 ± 0.3 cm for distance B. The comparison of ultrasound and CT position revealed a correlation coefficient of 0.86 (P < 0.001), including the 2 failed measurements.

Experimental Study
The experimental study confirmed that all 10 needle tips for facet joint infiltrations were placed into the joint space (Fig. 4).

	Discussion

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Facet joint injections are preferentially performed as CT-controlled or fluoroscopy-controlled interventions (2,3). Greher et al. (5) recently described the ultrasound approach for the lumbar facet nerve block. Facet joint injections and facet nerve blocks have been shown to be of equal value in the management of facet syndrome (12). In contrast to their methodology to the facet nerve, which was only possible at levels L3-5, we could demonstrate the accuracy of ultrasound guided facet joint injections at all lumbar levels. This is particularly relevant because the L5-S1 facet joint is frequently affected (13). Furthermore, the facet injection technique has recently been shown to be beneficial for segmental rigidity (14).

We performed an ultrasound inline approach, in which the needles were strictly advanced in parallel to the long axis of the transducer to keep them in the echo plane. This technique provides real-time monitoring of the inserted needle along its entire length.

Of 42 approaches, 2 missed the joint space articulation. In these cases, the reference point was placed into the fissure between the mamillary process and the accessory process (Fig. 5). It should be noted that the mamillary process is more pronounced in the upper lumbar spine (L1-3). Furthermore, the lamina of the vertebral arch in the upper lumbar spine becomes narrower (15), so that the lumbar facet joint, the mamillary process, and the accessory process are more adjacent and the interjacent cavities can appear like a joint space.

View larger version (37K): [in this window] [in a new window]   Figure 5. Axial transverse anatomical, computed tomography, and corresponding ultrasound image cranial of the facet joint at level L2-3. Cavity (*) between the mamillary process (mp) and the accessory process (ap), costal process (cp), and spinous process (sp).

The lesson learned from these false measurements is that it is important to respect a systematic proceeding in depicting the joint space. First, the spinal level should be determined. This is not shown in this study but is very easily obtained through sagittal ultrasound images of the spinous processes (Fig. 1). Subsequently, the transducer can be rotated and the corresponding spinous process can be traced until the lamina can be delineated. The lamina should be shown in their entire length to assess their lower margin. Proceeding along this margin of the lamina to the lateral and caudal aspect, the inferior articular process of the zygapophyseal articulation with its medial facet can be demonstrated, and the next occurring slit has to be to the joint space. Starting from this imaging, by adjusting and swaying the transducer to a cranial orientation, all subsequently appearing cavities or spaces are established by the lateral aspect of the joint space, the located mamillary process, the accessory process, and the costal process, which cause a typical shadow signal lateral to these structures (Figs. 4 and 5). This systematic technique avoids confounding the facet joints and mamillary or accessory process, as had happened at the beginning of our study.

The comparison of ultrasound and CT measurements demonstrated a good correlation. Thus, ultrasound imaging proved to be reliable and accurate in delineating the needle tips in the facet joints as compared to data obtained by means of CT. This should be emphasized for two reasons: a free-hand technique was performed and no specially designed and hence more expensive needles (as available for interventional ultrasound) were used.

In summary, the described technique of an ultrasound-guided approach to the joint space of the lumbar facet joint articulation proved to be feasible and accurate. However, a systematic proceeding, knowledge in ultrasound imaging of the lumbar paravertebral region and practice in handling a transducer in combination with a needle are required. Apart from these necessary skills, the described technique is simple to perform.

We have not performed a clinical trial of our technique. We first wanted to evaluate its efficacy and accuracy in an experimental setting. However, online guidance of the needle, less expensive equipment, and less patient and operator exposure to radiation are likely advantages of this technique.

	Footnotes

 
Accepted for publication January 18, 2005.

	References

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Galiano, K. Articles by Ploner, F. Search for Related Content PubMed PubMed Citation Articles by Galiano, K. Articles by Ploner, F. Related Collections Anesthetic Techniques