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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
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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
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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.
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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
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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
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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.
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equine cervical articular process joint injection. Vet Radiol
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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
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