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THERIOGENOLOGY AND LAMENESS How to Perform Ultrasound Guided Intra-Articular Analgesia of the Cervical Articular Facets Myra F. Barrett, DVM, MS, DACVR*; Kurt T. Selberg, DVM, MS, DACVR; Melinda Story, DVM, DACVS, DACVSMR; Laurie R. Goodrich, DVM, PhD, DACVS; Valerie J. Moorman, DVM, PhD, DACVS; Melissa R. King, DVM, PhD, DACVSMR; and Christopher E. Kawcak, DVM, PhD, DACVS, DACVSMR Authors’ addresses: Department of Environmental and Radiological Health Sciences (Barrett) and Department of Clinical Sciences (Story, Goodrich, Moorman, King, Kawcak), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; Department of Veterinary Bioscience and Diagnostic Imaging, University of Georgia, Athens, GA 30602 (Selberg), e-mail: [email protected]. *Corresponding and presenting author. © 2016 AAEP. 1. Introduction Osteoarthritis of the equine cervical facets can be associated with stiffness, a reluctance to bend or collect, pain on palpation, and forelimb lameness.1 In cases of forelimb lameness, the cervical region may become an area of suspicion as the source of lameness if the patient fails to respond to regional and intra-articular diagnostic analgesia of the affected limb, and/or the patient exhibits other clinical signs of neck pain. At this point, the patient will often undergo further diagnostic imaging, including nuclear scintigraphy, cervical radiography, and cervical ultrasound. Even with an abnormal diagnostic imaging finding in the cervical region, the clinical significance is often unknown, and this does not necessarily indicate a source of pain. Although it is commonplace to correlate diagnostic imaging findings in the limb with results of regional and/or intra-articular analgesia to assess clinical significance, this combination of diagnostics is less routinely performed in the axial skeleton. In many cases, empiric treatment is used based on the results from imaging modalities, and response to treatment is used to confirm or deny the source of pain. Although less commonly performed, ultrasound-guided intra-articular analgesia can be used to more accurately identify the source of a forelimb lameness associated with the cervical spine. 2. Anatomy The articular facets are composed of the caudal articular process of the more cranially located cervical vertebra and the cranial articular process of the caudally located vertebra (Fig 1). The facets vary somewhat in size and shape, depending on anatomic location. The caudal articular processes of C6 are NOTES AAEP PROCEEDINGS Ⲑ Vol. 62 Ⲑ 2016 357 THERIOGENOLOGY AND LAMENESS Fig. 1. Transverse gross section of the articular facet of C4 – C5. The caudal articular process of C4 is located dorsally and the cranial articular process of C5 is located ventrally. The yellow box represents the ultrasound beam. shorter and thicker compared with the same processes on the more cranial vertebrae. The cranial articular processes of C7 are also wider and longer than its caudal articular processes. This gives C6 –C7 a characteristic more rounded, prominent appearance than the adjacent articular facets. Ultrasonographically, C6 –C7 is usually located just cranial to the slope of the shoulder. The ability to visualize C7–T1 varies, and in horses with longer, thinner necks, it may be readily visualized; whereas in horses with shorter necks, C7–T1 may not be visible beyond the shoulder. The ventral branches of the last three cervical nerves and the first two thoracic nerves contribute to the brachial plexus, with the primary component coming from cervical nerves seven and eight and thoracic nerve one. The sixth cervical nerve exits the foramen at C5–C6, the seventh cervical nerve at C6 –C7, and the eighth at C7–T1.2 Thus, nerve root compression would most likely contribute to forelimb lameness from these locations. However, lesions more cranial in the cervical spine have also been associated with forelimb lameness, and site selection need not be limited to these more caudal facets.1 3. Materials and Methods Step 1: Identify the Site for Diagnostic Analgesia Diagnostic imaging findings and the clinical examination should be correlated in selecting the site(s) for diagnostic analgesia. In cases that have undergone scintigraphy, increased radiopharmaeutical uptake of one or more cervical facets may help in site 358 2016 Ⲑ Vol. 62 Ⲑ AAEP PROCEEDINGS selection. Radiographic abnormalities associated with abnormal cervical facets include osteoarthritis, enlargement and modeling, narrowing of the intervertebral foramina, fracture, and osteochondrosis.3 Ultrasound evaluation of the cervical spine is also recommended in most cases. Ideally the ultrasound evaluation should be performed subsequent to radiography, given that radiography can improve lesion identification on ultrasound. Many times when intra-articular medication of facet joints is used, more than one articular facet is treated. Although this may be helpful from a therapeutic standpoint, it limits the specific diagnostic value of assessing response to treatment. For this reason, performing a single site at a time is recommended for diagnostic intra-articular analgesia of the cervical facets. If the patient does not respond to diagnostic blocking at that site, the process can be repeated at the next location of greatest suspicion. Doing a single site at a time also minimizes any potential risk of paresis if the block affects the nerves that contribute to the brachial plexus. When the articular facet has been selected via the diagnostic imaging findings and clinical examination, it should be definitively identified via ultrasound prior to injection. To ensure the proper location, the scan should begin from C2, counting caudally to locate the facet of choice. The site can then be marked with white tape or white correction fluid.a If clipping is permitted, a small square can be clipped at the site of needle placement to further localize the site. Step 2: Preparation Preparation is the same as for ultrasound-guided medication of the cervical articular facets and has been previously described in detail.4,5 If the patient has a sleek haircoat, clipping is not necessary. Otherwise, a small section should be clipped for the site of needle placement, and, if necessary for image quality, a larger section for better contact of the ultrasound probe. Because the site of needle placement will vary depending on the horse’s head position, a generous area should be prepared with aseptic technique. Prior to aseptically preparing the area of injection, the ultrasound machine settings should be arranged for maximum image quality, minimizing the need for image manipulation at the time of the injection. We prefer to use a linear probe to maximize image resolution, but a micro or macro convex probe can be used, if necessary (Fig 2). The depth should be set so that the facet is centered in the image, and the gain and frequency should be at a level that maximizes image quality. After the machine is set, the skin can be prepared routinely for injection. The ultrasound probe should be covered with a sterile glove or sterile probe cover with gel placed inside. For intra-articular analgesia of the cervical facets, we limit the volume of mepivicaine to 2–3 mL. Although the cervical facet joints can reportedly THERIOGENOLOGY AND LAMENESS Fig. 2. Transverse ultrasound images of a cervical articular facet. Dorsal is to the left. The image resolution is superior using the linear ultrasound probe (A) when compared with the macroconvex ultrasound probe (B) at the same depth. The joint space is denoted by the arrows. be distended with up to 20 mL of fluid,6 there is increased risk of extravasation with increasing volume. In an unpublished cadaver study of ultrasound-guided intra-articular contrast evaluated with computed tomography, we found increased risk of extravasation of volumes greater than 6 mL. However, it should be acknowledged that volume of 2–3 mL is an empirically selected dose and has not directly been compared with other amounts. A larger volume of 8 –10 mL has also been used by another experienced clinician with no reported complications.b Because the lameness examination will continue after analgesia, no sedation is used. A nose twitch is applied for restraint. Often, horses will raise their heads with the application of the twitch. It is important to keep in mind that this change in head height will alter the position of the cervical facets and injection site, further emphasizing the importance of a large prep area for injection. We do not routinely use local anesthetic of the skin prior to injection because the location for needle placement can change depending on head position and also because most horses do not significantly object to needle placement. Step 3: Injection Although both longitudinal7 and transverse4,8 approaches to cervical facet injections have been described, we prefer the transverse approach. The injection technique is the same as intra-articular medication of the cervical facets. The transducer is placed in a transverse plane to the long axis of the cervical facet, with the probe marker oriented at approximately 11 o’clock. The handle of the transducer can be kept in a neutral position or lowered slightly ventrally, which helps align the joint space and the trajectory of the needle (Fig 3). An 18-g or 20-g, 3.5-inch spinal needle is used for the injection. The needle is placed at the dorsal aspect of the probe and should be angled toward the joint space, which is centered in the image. The exact angle will vary depending on how the facet is positioned in the image but typically ranges from 30 to 45 degrees from the horizontal plane. A common error is to Fig. 3. Transverse ultrasound images of a cervical articular facet. Dorsal is to the left. Image A is obtained in neutral position. In image B, the handle of the probe is lowered slightly ventrally, displacing the joint space dorsally on the ultrasound image. This dorsal position can facilitate aligning the needle trajectory with the joint space in some cases. The joint space in denoted by the blue arrows. AAEP PROCEEDINGS Ⲑ Vol. 62 Ⲑ 2016 359 THERIOGENOLOGY AND LAMENESS Fig. 4. Angle of the needle for alignment with the joint space. Image A shows the needle positioning on the horse, with the dotted lines representing the trajectory of the needle deep to the skin. Image B is the corresponding transverse ultrasound image. Dorsal is to the left. The dotted white line indicates the correct needle trajectory. The dotted yellow line is the needle placed at too flat of an angle relative to the horizontal plane. The dotted red line is the needle placed at too steep of an angle relative to the horizontal plane. insert the needle at too steep or too flat of an angle and pass the joint space (Fig 4). Once the needle is placed at the margin of the joint space, the stylet is removed and the syringe applied. It is important that the ultrasound probe be kept in place during the entire process to ensure that the needle placement is not altered. The needle should not move deep to the peri-articular margin. Ideally, a second person will attach the syringe while the other person holds the needle and ultrasound probe in place; although, if necessary, a single operator can perform the entire procedure. We do not routinely aspirate joint fluid; to confirm needle placement, a small test injection should be performed and observed on the ultrasound screen to ensure that the fluid is entering the joint and that there is no evidence of peri-articular injection or extravasation. When needle placement is confirmed, the remainder of the mepivicaine can be injected, with the entire process being evaluated on the ultrasound image to ensure that the fluid is within the joint recess. As the fluid enters the joint, the joint capsule should be seen expanding away from the bone margins. Step 4: Evaluation After the injection, we prefer that the horse be walked to a well-bedded or padded stall. Although we consider the risk of paresis to be quite low if only one facet is blocked at a time, we operate with an 360 2016 Ⲑ Vol. 62 Ⲑ AAEP PROCEEDINGS abundance of caution. After 10 minutes, the horse is usually evaluated at a walk and a trot. A repeat evaluation can be performed at 20 minutes. If the lameness is not alleviated or resolved with the intraarticular analgesia, the process can be repeated if there is another site of clinical suspicion. 4. Results Since we began performing this procedure in 2013, we have used this technique in six horses. All horses were Warmblood breeds and ages ranged from 5 to 17 years of age. We have experienced no significant complications, including no evidence of weakness or paresis. Four of the horses exhibited unilateral forelimb lameness, one had a history of stumbling and falling under saddle, and the sixth horse exhibited a stiff neck and decreased performance prior to the procedure. The four horses with forelimb lameness underwent extensive diagnostic blocking of the affected forelimb prior to electing to perform intra-articular analgesia of the cervical facets. All horses had some degree of modeling or osteoarthritic changes of at least one articular facet on diagnostic imaging evaluation, although, in no cases were the changes found to be severe. Two horses had only one location blocked, two horses had two locations blocked at two different time points, and one horse (history of stumbling) had four locations blocked at different time points. THERIOGENOLOGY AND LAMENESS The four horses with forelimb lameness as the primary complaint responded to blocks as follows: Horse 1 exhibited 75% improvement within 15 minutes following block of the second site (no response to the first site). Horse 2 improved 60% after the first block. Horse 3 improved 40% with further improvement to 80% of the lameness with an abaxial nerve block (although previously the horse had not improved with an abaxial block prior to the cervical facet block). Horse 4 had an unusual stride characteristic that improved after diagnostic analgesia of the cervical facet, but the lameness persisted. The horse with a history of neck stiffness and poor performance had improved movement after diagnostic analgesia. No improvement was noted in the horse with a history of stumbling. 5. Discussion Diagnostic analgesia of the cervical facets should be considered in cases of forelimb lameness that cannot be attributed to other locations in the limb. In addition, it can be used in cases of neck stiffness or poor performance, although change may be more difficult to assess in horses with subtle clinical signs. Although medical therapy can be used as both a diagnostic and therapeutic procedure, diagnostic blocking may identify a more specific source of the lameness and may also eliminate unnecessary treatment in horses that are unresponsive to diagnostic blocking. Although it is possible for a horse to have pain originating from locations in the neck, such as from the vertebral body, that would not likely respond to analgesia of the articular facet, the screening performed by the diagnostic imaging can help target which horses have pathologic changes associated with the articular facet rather than elsewhere in the cervical region. The injection technique is quite similar to intraarticular medication of the cervical facets, with the primary complicating factor that the patient is not sedated. Watching the injections in real time on the ultrasound screen minimizes the risk of improper needle placement and the low volume of fluid leads to a low risk of extravasation. Performed in this manner, we believe this of similar safety as intra-articular diagnostic analgesia of other joints. In summary, we have had successful outcomes using ultrasound guided intra-articular diagnostic analgesia of the cervical articular facets for identifying the source of forelimb lameness. This technique is an additional tool that can be used in the workup of forelimb lameness or other abnormalities associated with neck pain. For practitioners already experienced in performing therapeutic ultrasound guided intra-articular injections of the cervical articular facets, the technique is easily applied and can be performed safely. Acknowledgments Declaration of Ethics The Authors have adhered to the Principles of the Veterinary Medical Ethics of the AVMA. Conflict of Interest The Authors declare no conflicts of interest. References and Footnotes 1. Ricardi G, Dyson SJ. Forelimb lameness associated with radiographic abnormalities of the cervical vertebrae. Equine Vet J 1993;25(5):422– 426. 2. Ghoshal NG. Equine nervous system. In: Getty R, ed. Sisson and Grossman’s. Vol 1. The anatomy of the domestic animals. Philadelphia, PA: W B Saunders Co; 1975;665– 671. 3. Dyson SJ. Lesions of the equine neck resulting in lameness or poor performance. Veterinary Clinics of NA. Equine Pract 2011;27(3):417– 437. 4. Chope K. How to perform sonographic examination and ultrasound-guided injection of the cervical vertebral facet joints in horses, in Proceedings. Am Assoc Equine Pract 2008;54: 186 –189. 5. Vaughan B, Whitcomb B, Maher O. How to improve accuracy of ultrasound-guided procedures, in Proceedings. Am Assoc Equine Pract 2009;55:438 – 448. 6. Pepe M, Angelone M, Gialletti R, et al. Arthroscopic anatomy of the equine cervical articular process joints. Equine Vet J 2013;46(3):345–351. 7. Mattoon JS, Drost WT, Grguric MR, et al. Technique for equine cervical articular process joint injection. Vet Radiol Ultrasound 2004;45(3):238 –240. 8. Nielsen JV, Berg LC, Thoefner MB. Accuracy of ultrasoundguided intra-articular injection of cervical facet joints in horses: A cadaveric study. Equine Vet J 2003;35(7):657– 661. a Wite-Out, BIC Corporation, 1 BIC Way #1, Shelton, CT 06484. Dyson, S. Newmarket, Suffolk, 2016 (personal communication). b AAEP PROCEEDINGS Ⲑ Vol. 62 Ⲑ 2016 361